Textile and leather review 3 2020

TEXTILE & REVIEW LEATHER

3/2020 Volume 3 Issue 3 2020 textile-leather.com ISSN 2623-6257 (Print) ISSN 2623-6281 (Online)

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TEXTILE & LEATHER REVIEW ISSN 2623-6257 (Print)

ISSN 2623-6281 (Online) CROATIA

VOLUME 3

ISSUE 3

2020

p. 113-180

CONTENT ORIGINAL SCIENTIFIC ARTICLE 118-134

Chromium Adsorption on Banana Rachis Adsorbent from Tannery Wastewater: Optimization, Isotherm, Kinetics and Desorption Studies Sofia Payel, Md. Abul Hashem, Mrinmoyee Sarker, Md. Shahruk Nur-A-Tomal

135-145

Evaluating Suitability of Glutaraldehyde Tanning in Conformity with Physical Properties of Conventional Chrome-Tanned Leather Md. Minhaz Uddin, Md. Jawad Hasan, Yead Mahmud, Fatema-Tuj-Zohra, Sobur Ahmed

146-157

Synthesis and Application of Graphene Oxide (GO) for Removal of Cationic Dyes from Tannery Effluents Md. Israil Hossain, Amal Kanti Deb, Md. Zakir Sultan, A. A. Shaikh, Manjushree Chowdhury, Md. Rayhan Sarker

SCIENTIFIC REVIEW 158-173

Clothing and Textile Sustainability: Current State of Environmental Challenges and the Ways Forward Sarif Patwary

Ferenc Vasadi ¡ + 36 (0)30 94 69 123 ferenc.vasadi@soliver-shoes.com shoe.com GmbH & Co. KG ¡ soliver-shoes.com Member of the Wortmann Group

PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery‌ TLR 3 (3) 2020 118-134.

Chromium Adsorption on Banana Rachis Adsorbent from Tannery Wastewater: Optimization, Isotherm, Kinetics and Desorption Studies Sofia PAYEL, Md. Abul HASHEM*, Mrinmoyee SARKER, Md. Shahruk NUR-A-TOMAL Department of Leather Engineering, Khulna University Engineering & Technology, Khulna-9203, Bangladesh * hashem_518@yahoo.com, mahashem@le.kuet.ac.bd Original scientific article UDC 675.024.43:628.31:634.773 DOI: 10.31881/TLR.2020.11 Received 21 Jun 2020; Accepted 9 Aug 2020; Published Online 17 Aug 2020; Published 11 Sep 2020

ABSTRACT This study investigates the banana rachis adsorbent for adsorption characterization, removal, and recovery of the chromium ion from the chrome tanning wastewater. The batch analysis was conducted to find out an adsorbent dose, contact time, relative pH of the aqueous solution, and initial and final chromium value in the filtrate. The equipped adsorbent was studied by the Fourier transform infrared spectroscopy (FT-IR) analysis to reveal the associated functional groups during adsorption. Batch adsorption examination reveals the optimum conditions of 3 g adsorbent input for 75 mL wastewater at 15 min contact time. The adsorption mechanism showed chromium removal 99.64% with the obtained reduction of biochemical oxygen demand (BOD), chemical oxygen demand (COD), and chloride (Cl-) 96.65%, 93.18%, and 59.62%, respectively. The adopted method followed the pseudo-second-order kinetics and Freundlich isotherm for physical adsorption. Primary desorption studies exhibit a scope for the reuse of chromium from the adsorbed adsorbent. Moreover, in comparison with other studies, the study discloses that banana rachis might be utilized as a feasible adsorbent to be adopted in industrial wastewater treatment, especially chrome tanning wastewater in the tannery.

KEYWORDS Environment, pollution load, wastewater treatment, chrome tanning, chromium

INTRODUCTION The non-degradable and persistent nature of heavy metals-polluted waste streams, controversial side effects of industrialization and modernization, causes devastating and permanent contamination of the environment [1]. Most of the common heavy metals found, like chromium (Cr), lead (Pb), arsenic (As), nickel (Ni), cadmium (Cd), and zinc (Zn) are posing great threats to the environment because of their harmful effects.

Chromium (Cr) may form in several oxidation states, mainly trivalent and hexavalent forms [2]. Hexavalent chromium, Cr(VI) is 100 times more toxic than trivalent Cr(III), since it is highly soluble in water, mobile, and easily reduced [3]. Trivalent chromium, Cr(III) is essential for human nutrition since it controls sugar level in mammal bloodstream in trace amounts, but noxious to fish at a concentration greater than 5.0 mg/L [4].

The Cr(VI) has been classified as belonging to group 1, which is carcinogenic to humans, whereas metallic chromium and Cr(III) are in group 3 (not classifiable as to their carcinogenicity to humans) [5].

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PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery… TLR 3 (3) 2020 118-134.

Despite all the concerns, Cr has been widely used in different industries (leather tanning, textile, metal, power plant, etc.) [6]. It is reported that about 15×103 tons of chromium salt (basic chromium sulphate) [7] is used globally for the production of 18 billion sq. ft. of tanned leather [8].

It has been assessed that around 22×103 m3 of wastewater, including chromium, is discharged daily into the Buriganga River of Bangladesh without any treatment [9]. Studies found that every day 1.25 tons of chromium is discharged into the river as waste liquor at a peak level of 21,000 m3 per day [10].

Researchers all over the world have been developing numerous methods and techniques to make diminution in Cr exposure to the environment. Different methods like chemical precipitation [11], ion-exchange resins [12], membrane separation [13], solvent extraction [14], and so on, have been tried for chromium removal from aqueous solutions.

In the chrome tanning process, the wastewater contains not only the chromium ion but also other biological and chemical substances that are separated from the pelt during operation. As a result, the already developed techniques for chromium separation from aqueous solutions might not be as efficient in the case of the tannery wastewater. This urges for the specific operational method developed for the chrome-tanning wastewater.

Some researchers have been trying to develop treatment process particularly for the tannery wastewater, e. g. membrane separation [15] or membrane electroflotation [16]; however, high energy and process cost, disposal of toxic precipitates or other sludge that requires further treatment process restrains its appeal in the application.

These problems force the researchers to move towards the adsorption method which overcomes most of the previously mentioned side effects. Different adsorption studies using Brazilian sawdust [17], biological activated carbon [18] or Galactomyces geotrichum fungi [19] have been tried for tannery wastewater treatment, but these are either based on Cr(VI) removal, or do not provide a high removal efficiency. Promising results are reported in removing Cr(III) ions from the tannery effluent by using Syzygium cumini bark [20].

However, in terms of abundant sources, the study showed a deficient supply of the adsorbent.

In this contribution, the adsorbent prepared from the waste banana rachis was used to adsorb Cr from the tannery wastewater. According to the FAO [21] report, world’s total gross export and import for bananas in 2017 was 18.08×106 tons and 17.75×106 tons, respectively. The estimated amount of the banana rachis waste in Costa Rica (one of the biggest banana producers in the world) is 797,000 metric tons per year [22].

In Bangladesh, 800,840 metric tons of banana were produced in 2010-2011 on about 130,589 acres of the cultivated area [23]. In Bangladesh, there is no systematic way to use this waste; generally, it is dumped at the roadside without any purposeful use. This satisfies as a potential opportunity to reuse the rachis waste and makes this technique twice as efficient and attractive.

The goal of this investigation was to develop an industrial-friendly adsorbent from the banana rachis waste to adsorb chromium from the tannery wastewater. The mechanism of chromium removal was analyzed through parameters like the adsorbent input, contact time, and a relative pH impact. Moreover, the kinetics and the reaction mechanism were also evaluated, and FTIR spectroscopy was used to find out different functional groups responsible for the adsorption.

MATERIALS AND METHODS Adsorbent Preparation Banana rachis waste was collected from a nearby banana market at Khulna, Bangladesh, free of cost, since they are generally dumped at the roadside. The rachis was washed with water, chopped, sun-dried and www.textile-leather.com 119

PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery… TLR 3 (3) 2020 118-134.

then burnt at 640-650°C in a muffle furnace (Thermo Scientific) for 3 (three) hours, cooled, made into a fine powder with a laboratory mortar (Pulverisette), and kept preserved in a double stoppered polyethylene bottle, in a dry and cool state, for further experiment.

Collection of Wastewater The tannery wastewater containing Cr, referred to as a sample, was collected just after the chrome tanning process from a tannery at Khulna, Bangladesh. The sample was collected in a plastic container that was pre-washed with diluted nitric acid and rinsed with distilled water. Immediately, it was transported to the laboratory for the experiment.

Reagents Nitric acid (Merck KGaA, Germany), sulphuric acid (Merck KGaA, Germany), perchloric acid (Merck, India), N-phenyl anthranilic acid (Merck, India), ammonium iron(II) sulphate hexahydrate (Merck, India), filter paper (Whatman No. 1) and anti-bumping agent glass beads (Loba Chemie, India) were purchased from a local scientific store, Khulna, Bangladesh.

Analytical Techniques The physicochemical properties of the wastewater were analyzed in terms of Cr, pH, total dissolved solids (TDS), electrical conductivity (EC), salinity, biochemical oxygen demand for 5 days (BOD5) and chemical oxygen demand (COD). The pH of the wastewater was measured by using the pH meter (UPH-314, UNILAB, USA) and the electrical conductivity (EC) was measured by using the conductivity meter (CT-676, BOECO, Germany).

Total solids (TS), total suspended solids (TSS), and total dissolved solids (TDS) of the spent chrome liquor and the treated liquor were determined by the APHA-2540 D method. The biochemical oxygen demand (BOD), chemical oxygen demand (COD) and the chloride content of the spent chrome liquor and the treated liquor were determined by following the APHA-5210 B, APHA-5220 C and APHA-4500 B method, respectively. The Cr content in the untreated wastewater and the filtrate after the treatment was measured by the titrimetric method, following the official method of analysis of the Society of Leather Technologist and Chemists [24], the SLC 208 (SLT6/4) method.

Batch Adsorption Test Batch-wise Cr removal from the wastewater using the prepared adsorbent was performed under different parameters, such as adsorbent dose and contact time. Firstly, the physicochemical parameters of the untreated wastewater containing Cr were analyzed and filtered through a 0.45 µm pore size filter. Secondly, 75 mL of the filtrate wastewater was mixed with the prepared adsorbent and then stirred over a fixed period at a speed of 150 rpm using an orbital shaker (GFL- Model No. 3017) and the mixture was then allowed to settle for a fixed time. After settling, the mixture was filtered through a 0.45 µm pore size filter, and the Cr content measurement was performed, following the SLC 208 (SLT6/4) method.

Method and Adsorbent Selection From an industrial perspective, wastewater treatment is an unprofitable process. Due to the environmental acts and regulations, the wastewater generated in an industry is treated within the standard limit before the discharge. According to ECR 1997 [25], the tanning industry is classified as the “RED” category which is the 120 www.textile-leather.com

PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery‌ TLR 3 (3) 2020 118-134.

PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery‌ TLR 0 (0) 2020 00-00.

highest pollution-generating group. Thus, treatment is obligatory for the tannery wastewater. The proposed method prefers theinadsorption process which can economically meet today’s higher effluent standards and amounts Bangladesh without any defined treatment process.

The proposed method PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery‌ TLR 0 (0) 2020 00-00. water reuse requirements [26]. The adsorption process can be adopted in-situ and can consistently produce with the recommended adsorbent could utilize the banana rachis waste as well as mitigate the high levels of treatment and have a high degree of stability and reliability. In 2017, Bangladesh produced amounts in Bangladesh without any defined treatment process. The proposed method tannery wastewater problem.

16592.1 kg bananas per hectare [21]. The selected adsorbent, prepared from the banana rachis is a waste recommended adsorbent could banana process. rachis waste as well as mitigate the generated inwith largethe amounts in Bangladesh without any utilize definedthe treatment The proposed method Cr Adsorption with the recommended adsorbent could utilize the banana rachis waste as well as mitigate the tannery tannery wastewater problem. wastewater problem.

The quantity of the chromium uptake by the adsorbent was calculated by following Eq. 1, Cr Adsorption

Cr Adsorption

(đ??śđ??ś0 −đ??śđ??śthe The quantity of the chromium đ?‘žđ?‘župtake đ?‘Ąđ?‘Ą )Ă—đ?‘‰đ?‘‰adsorbent was calculated by following Eq. 1, = by đ?‘šđ?‘š was calculated by following Eq. 1, The quantity of the chromium uptake by theđ?‘Ąđ?‘Ą adsorbent

(1)

(đ??śđ??ś −đ??śđ??ś )Ă—đ?‘‰đ?‘‰

(1)C are(1) = 0 đ?‘Ąđ?‘Ąexpressed in mg per g of the adsorbent, C and where qt is the amount of chromiumđ?‘žđ?‘žđ?‘Ąđ?‘Ąadsorbed đ?‘šđ?‘š o t

the initial concentration (mg/L) and concentration at time t (mg/L), respectively. The V indicates the where qt is the amount of chromium adsorbed expressed in mg per g of the adsorbent, Co and Ct are the whereofqsolutions is the amount adsorbed expressed in mg The per Vg indicates of the adsorbent, Co and t(mg/L) volume (L) concentration andofmchromium is the weight oft the adsorbent (g). initial concentration and at time (mg/L), respectively. the volume of Ct are solutionsThe (L)the and m is the weight of the adsorbent (g). initial concentration (mg/L) and timethe t (mg/L), respectively.

The V indicates the chromium removal percentage wasconcentration determined byatusing following Eq. 2.

The chromium removal percentage wasmdetermined by of using following volume of solutions (L) and is the weight thethe adsorbent (g).Eq. 2. (đ??śđ??ś0 −đ??śđ??śđ?‘Ąđ?‘Ą ) Ă— 100 by using the following Eq. 2.

The chromium removal percentage was determined đ?‘…đ?‘… (%) = đ??śđ??ś0

(2) (2)

(đ??śđ??ś −đ??śđ??ś ) Ă— 100 Fourier Transform Infrared Spectroscopy (FT-IR) Fourier Transform Infrared Spectroscopy (%)(FT-IR)0 đ?‘Ąđ?‘Ą

đ?‘…đ?‘…

=

(2)

đ??śđ??ś0

Infrared spectra of the pure adsorbent and after chromium adsorption was acquired by a Fourier transInfrared spectra of the pure adsorbent and after chromium adsorption was acquired by a Fourier form infrared spectrometer (FT-IR 1600,Spectroscopy PerkinElmer).(FT-IR) The pure and the chromium-loaded adsorbent was Fourier Transform Infrared transform infrared spectrometer (FT-IR 1600, PerkinElmer). The pure and the chromium-loaded collected from the same batch adsorption studies at optimized conditions after adsorption. The FT-IR spectra Infrared spectra of the from pureofthe adsorbent andcm after adsorption was acquired by a after Fourier −1 adsorbent batch adsorption studies at optimized conditions were recorded withinwas thecollected wavenumber 650 same and 4000 . chromium transformThe infrared spectrometer (FT-IR 1600, Theofpure and 4000 the chromium-loaded adsorption.

FT-IR spectra were recorded within PerkinElmer). the wavenumber 650 and cm−1.

Adsorption Isotherm Studies

adsorbent was collected from the same batch adsorption studies at optimized conditions after Adsorption Isotherm Studies Adsorption equilibrium were studied using adsorbent the dosages of 1, 2, 4, and g percm 75−1mL adsorption. isotherms The FT-IR spectra were recorded within the wavenumber of3,650 and54000 . of the tannery wastewater with the initial concentration and the pH of 3373.5 mg/L and 4.5, respectively.

Adsorption equilibrium isotherms were studied using adsorbent the dosages of 1, 2, 3, 4, and 5 g per Each batch was carried out at optimum Adsorption Isotherm Studiesconditions: stirred for 15 min at a speed of 150 rpm and then left 75 mL of the tannery wastewater with the initial concentration and the pH of 3373.5 mg/L and 4.5, to settle for 10 min at the room temperature (25¹2°C). The filtration of the mixture was completed by using Adsorption equilibrium isotherms were using adsorbent the dosages of 1, 4,with and g per Each batch carried outand atstudied optimum conditions: for 15 min at2,a 3, speed of 5150 Whatmanrespectively. no.

1 filter paper (porewas size 0.45 Âľm) the filtrate was used stirred for the isotherm analysis two popular models, viz.,wastewater the Langmuir isotherm and the Freundlich isotherm.

The mass of the 75isotherm mLthen of the the initial concentration and the of 3373.5 mg/L and 4.5, rpm and lefttannery to settle for 10 min with at the room temperature (25¹2°C).

ThepH filtration of the mixture adsorbent, the adsorbate,Each the value of thecarried equilibrium and so on, are collected from this batch was atconstant, optimum conditions: 15filtrate min atsection. a speed wasrespectively. completed by using Whatman no. 1out filter paper (pore size 0.45 stirred Âľm) andforthe was usedof for150

rpm and then left to settle for 10 min at the room temperature The filtration of the theAdsorption isotherm analysis with two popular isotherm models, viz.,(25¹2°C). the Langmuir isotherm andmixture the Theory of Kinetics

was completed by using no. 1adsorbent, filter paperthe (pore size 0.45 the Âľm) value and the was used for Freundlich isotherm.

The Whatman mass of the adsorbate, offiltrate the equilibrium In this experiment, the investigation of adsorption kinetics was continued with 30 g of the adsorbent in 750 the isotherm analysis with popular isotherm models, theAtLangmuir isotherm75and the and so 3on, aremL collected from this section. mL (as perconstant, optimum dose g/75 of thetwo wastewater) of the spent chromeviz., liquor. constant stirring, Freundlich The mass of the adsorbent, the20,adsorbate, value of minutes. the equilibrium mL of treated liquor wasisotherm. taken carefully as possible after 1, 5, 10, 15, 25, 30, 35, the 40, 50 and 60 Then, the liquor was filtered thecollected chromiumfrom content was measured for further kinetics analysis. constant, and so and on, are this section.

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PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery… TLR 3 (3) 2020 118-134.

Desorption Study To investigate the desorption of the used adsorbent to recover chromium from the wastewater, 1 g of the used adsorbent was mixed in distilled water of different pH, i. e. 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0. Each batch was stirred for 5 min and then left to settle for 24 hrs. The appearance of the distinct color of the basic chromium sulphate powder shows the possibility of chromium recovery for further application.

RESULTS AND DISCUSSION Characterization of Wastewater The spent chrome liquor of the raw sample was characterized for the physicochemical parameters, like the chromium content, the pH, the BOD, the COD, TDS, the EC, and the chloride content which is shown in Table 1.

Table 1. Tannery wastewater characterization Parameters

Unit

Methodology/ Device

Result

Cr

mg/L

SLC 208 (SLT6/4)

3373.5

pH

-

UPH-314, UNILAB

4.5

BOD

mg/L

APHA-5210 B

3197

COD

mg/L

APHA-5220 C

4297

TDS

g/L

APHA-2540 D

29.83

EC

mS

CT-676, BOECO

66.9

Chloride

mg/L

APHA-4500 B

17021

Table 1 indicates that the wastewater content was high in Cr, the BOD, the COD, and that it was acidic in nature (pH 4.5). These high pollution loads in the wastewater are a threat to the environment if discharged without treatment. The same parameters for the treated samples show that, after treatment, the pH, the BOD and the COD were within the discharge limit. The chloride (Cl-) reduction was noticeable, but it was still higher than the discharge limit. The soluble minerals, namely potassium (K), silicon (Si), phosphorous (P), calcium (Ca) and magnesium (Mg), found in banana rachis adsorbent [27], might raise TDS of the treated sample. The presence of the hydroxyl (–OH) functional group in the adsorbent found in the FTIR data possibly added to the EC value.

During treatment, the banana rachis charcoal acts as an adsorbent and the inorganic and organic pollutants are adsorbed by the charcoal surface. Thus, after filtration, the pollutants are removed with the adsorbent from the wastewater, which reduces Cr, the BOD, and the COD.

Chemical Composition of Raw Banana Rachis The chemical composition (% w/w dry weight matter) of the raw banana rachis of the common Asian banana plant from the Cavendish subgroup of the AAA genetic group [27] is included in Table 2. Lignocellulosic fraction refers to the carbohydrate polymers (the cellulose, the hemicellulose) and an aromatic polymer (lignin) of the plant dry matter (the biomass). Here, the cellulose and the hemicellulose cover the maximum percentage.

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PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery… TLR 3 (3) 2020 118-134.

Table 2. Global chemical composition (%w/w of dry matter) [27] Non-lignocellulosic fraction

Lignocellulosic fraction

Relative composition (%) of neutral sugars

Total ash

30.16±0.10

Cellulose

36.28±0.45

Glucose

71.86±0.97

Water extractives

13.01±1.90

Hemicellulose

17.78±2.97

Xylose

15.76±0.63

Ethanol extractives

0.63±0.20

Acid insoluble lignins

6.58±0.03

Arabinose

6.84±0.17

Proteins

4.88±0.05

Acid soluble lignins

2.06±0.01

Galactose

2.52±0.07

In the case of a non-lignocellulosic fraction, the percentage of total ash content is 30.16±0.10%. Different neutral sugars are also present in a natural banana rachis, e.g. glucose, xylose, arabinose, and so on, where glucose is found in abundance compared to the other sugars.

FT-IR Analysis of Banana Rachis Adsorbent Fig. 1 depicts the FT-IR spectrum of the adsorbent before and after the adsorption of chromium. The figure reveals the changes in peak intensity. In the case of before the chromium load, peak intensity around 3200-1 indicates a strong,Adsorption broad -OH functional Moreover, the presence of C=C, 3600 cmPAYEL S, et al. Chromium on Banana Rachisgroup.

Adsorbent from Tannery…

TLR 0 (0) 2020 00-00.N-H, and =C-H -1 functional group is observed around the 1619, 1387, and 988 cm regions, respectively. These functional groups are vital sites for ion adsorption [28].

100 1630

Transmittance (%)

80

1237

60 40 20 0 4000

873

1058

1619 2997

Before chromium load After chromium load

988 1337

3600

3200

2800

2400

2000

1600

1200

800

-1

Wavenumber (cm ) Figure 1. FTIR spectra of banana rachis adsorbent before treatment and after treatment Figure 1. FTIR spectra of banana rachis adsorbent before treatment and after treatment

However, the peak changes for a noticeable portion after the chromium loading. Here, the most consider-1 wavelength areHere, C=C, the C-O,most and =C-H, able functional present at the 1058 and 675-1000 cmchromium However,groups the peak changes for a1630, noticeable portion after the loading.

-1 respectively.

A shift in 1377, 1043 and 965 cm wavelengths before the adsorption further indicated that considerable functional groups present at the 1630, 1058 and 675-1000 cm-1 wavelength are C=C, Cthe banana rachis was an important component in the adsorption process of Cr [1]. The absence of the O, and =C-H, respectively. A shift in 1377, 1043 and 965 cm-1 wavelengths before the adsorption previous functional group after the chromium loading implies that the hydroxyl and other groups of the further indicated that the banana rachis was an important component in the adsorption process of Cr pure adsorbent were involved in the adsorption process.

[1]. The absence of the previous functional group after the chromium loading implies that the hydroxyl and other groups of the pure adsorbent were involved in the adsorption process.

Adsorbent Intake Analysis The effect of the adsorbent dose on chromium removal was investigated through a batch analysis process where 5 samples of 75 mL of wastewater were taken in varying doses - 1, 2, 3, 4, and 5 g,

www.textile-leather.com respectively. The solutions were shaken for 10 min with a 10-minute settling time. The corresponding pH of each batch was measured after settling.

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Chromium re

40

PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery‌ TLR 3 (3) 2020 118-134.

Adsorbent Intake Analysis

20 0

1 2 3 4 5 The effect of the adsorbent dose on chromium removal was investigated through a batch analysis process Charcoal dose (g / 75 mL) where 5 samples of 75 mL of wastewater were taken in varying doses - 1, 2, 3, 4, and 5 g, respectively. The Figure 2(a). Chromium removal efficiency on adsorbent doses solutions were shaken for 10 min with a 10-minute settling time. The corresponding pH of each batch was PAYEL S, et al. Chromium on Banana Rachis Adsorbent from Tannery‌ TLR 0 (0) 2020 00-00. measured afterAdsorption settling.

10 2 (a)

80 60 40 20 0

2 (b)

8 Relative pH

Chromium removal (%)

100

6 4 2

1

2 3 4 Charcoal dose (g / 75 mL)

5

Figure 2(a). Chromium removal efficiency on adsorbent doses

Figure 2(a). Chromium removal efficiency on adsorbent doses

0

1

2

3

4

5

Charcoal dose (g/ 75 mL) Figure 2(b). removal relative FigureChromium 2(b). Chromium removalefficiency efficiency onon relative pH pH

Relative pH

Fig. 2 showsshown the increase in 2(a), removal

by Fig. 2(a), as in the pH, shown by Fig. 2 shows the increase in removal efficiency,

by Fig. as efficiency, well as inshown the pH, shown bywell Fig.as2(b), 10 2 (b) 2(b),The withincrease the increase adsorbent dose.

The increase of might the pH with the adsorbent dose mi with the increase of the adsorbent dose. of of thethepH with the adsorbent dose be elucibeFT-IR. elucidated from thethe datapresence obtained from the -OH FT-IR.group It ensures the presence of the -OH group in dated from8 the data obtained from the It ensures of the in the adsorbent adsorbentofwhich could be responsible for the escalation of the pH. which could6 be responsible for the escalation the pH. It should also adsorbent be noted thatdose the increment adsorbent dose boosted the removal efficien It should also be noted that the increment in the boosted in thetheremoval efficiency.

Metal 4 adsorption is well dependent on the pHMetal due to the protonation of metalon(chromium) binding sites. At of a lower adsorption is well dependent the pH due to the protonation metal (chromium) bind + 3+ + 3+ pH (2 to 3) 2the H ion competes with the Cr Ation for the metal-binding whichwith reduces sites. a lower pH (2 to 3) the H ionsite, competes the Cr the ionadsorption. for the metal-binding site, wh + As the pH rises, the abundance of the H ion lowers, whereas the amount of the OH ion increases. This 0 3 5 gives the dual 1effect of2 weakening the4competitiveness of the H+ against the Cr3+ ion, and the adsorption of (g/ 75 mL) of metals as colloidal insoluble hydroxides, Cr(OH) [29]. hydrolysis products Charcoal and thedose precipitation 3 Figure 2(b).

Chromium removal efficiency on relative pH At an adsorbent dose of 3 g per 75 mL of wastewater, the process reaches an equilibrium with a 99.64% removal efficiency. Therefore, it was projected that the maximum chromium removal occurred with 3 g Fig. 2 showsadsorbent the increase in removal shown 2(a), as well as the 6.7. pH, shown by Fig. dose forefficiency, every 75 mL by ofFig. wastewater atinpH 2(b), with the increase of the adsorbent dose. The increase of the pH with the adsorbent dose might be elucidated from the data obtained from the FT-IR. It ensures the presence of the -OH group in the Contact Time Analysis adsorbent which could be responsible for the escalation of the pH.

Fig.be3noted shows the chromium removaldose efficiency wasremoval increased with the increase of contact time between It should also thatthat the increment in the adsorbent boosted the efficiency.

the chromium ionsonand binding sites. Forofthe first two batches, Metal adsorption is well dependent the the pH due to the protonation metal (chromium) binding

the adsorption rate increases rapidly as more iscompetes allowedwith to the adsorb onforthe sites with sites. At a lower pH (2 chromium to 3) the H+ ion Cr3+ ion the binding metal-binding site, whichthe increased time. After that, the reaction becomes weaker, because the remaining active sites are less available and the equilibrium phase was reached. The optimized removal efficiency was 99.64% at 15 minutes.

124 www.textile-leather.com

increases rapidly as more chromium is allowed to adsorb on the binding sites with the increased time. After that, the reaction becomes weaker, because the remaining active sites are less available

PAYEL S,the et equilibrium al. Chromium Banana Rachis Adsorbent Tannery‌ TLR 3 (3) 2020 118-134. and phaseAdsorption was reached.on The optimized removal efficiency from was 99.64% at 15 minutes.

Chromium removal (%)

100 98 96 94 92 90

5

10

15

20

25

Contact time (min) Figure 3. Chromium removalefficiency efficiency based on contact time Figure 3. Chromium removal based on contact time

Adsorption Isotherm Studies

Adsorption Isotherm Studies

Adsorption isotherms are used to understand the relation between the adsorbate and the adsorbent.

Adsorption isotherms used toAdsorption understand the relation thefrom adsorbate and adsorbent.

The PAYEL etcapacity al.are Chromium onBanana Banana Rachis Adsorbent Tannery‌ TLRthe (0) 202000-00.

00-00.

The of the adsorbent, the on optimization of the between adsorbent use, surface characteristics PAYEL S,S,et al.

Chromium Adsorption Rachis Adsorbent from Tannery‌ TLR 00and (0) 2020 capacity of the affinity adsorbent, the optimization of the adsorbent use, surface characteristics are evaluated from the equilibrium studies of the adsorption isotherms.

In this study, theand affinity are evaluated frommost the equilibrium studies of the adsorption isotherms. In this study, the most common two LangmuirIsotherm Isothermcommon two isotherm models, the Langmuir isotherm and the Freundlich isotherm are Langmuir isotherm models, the Langmuir isotherm and the Freundlich isotherm are investigated [30]. investigated [30].

Langmuir Isotherm According to Langmuir's Langmuir's theory, the adsorption adsorption takes place atdefinite definite homogeneous siteswithin withinthe the PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery‌ TLR 0 (0) 2020 00-00.

According to theory, the takes place at homogeneous sites According to [31,32].

Langmuir’s theory, themodel adsorption place isotherm at definite[33] homogeneous sitesbelow withininthe adsorbent TheIsotherm standard ofthe thetakes Langmuir represented Eq.adsor3, adsorbent [31,32].

The standard model of Langmuir isotherm [33] isisrepresented below in Eq. 3, Langmuir bent [31,32]. The standard model of the Langmuir isotherm [33] is represented below in Eq. 3, According to Langmuir's theory, the adsorption takes place at definite homogeneous sites within the

1 [33] is represented below in Eq. 3, adsorbent [31,32]. The standard model the1Langmuir isotherm đ??śđ??śđ??śđ??śđ?‘’đ?‘’đ?‘’đ?‘’ of = 1 đ??śđ??śđ??śđ??śđ?‘’đ?‘’ + + 1 = đ?‘’đ?‘’ đ?‘„đ?‘„đ?‘„đ?‘„đ?‘’đ?‘’đ?‘’đ?‘’ đ?‘„đ?‘„đ?‘„đ?‘„đ?‘šđ?‘šđ?‘šđ?‘š đ?‘„đ?‘„đ?‘„đ?‘„đ?‘šđ?‘šđ?‘šđ?‘šđ??žđ??žđ??žđ??žđ?‘Žđ?‘Žđ?‘Žđ?‘Ž 1 1 đ??śđ??śđ?‘’đ?‘’ = or đ??śđ??śđ?‘’đ?‘’ + đ?‘„đ?‘„đ?‘’đ?‘’ đ?‘„đ?‘„or đ?‘„đ?‘„đ?‘šđ?‘š đ??žđ??žđ?‘Žđ?‘Ž đ?‘šđ?‘š

11 = 11 +or11 Ă— 11 = đ?‘šđ?‘š1+ đ??śđ??ś1đ?‘’đ?‘’Ă— đ?‘„đ?‘„1đ?‘šđ?‘šđ??žđ??žđ??žđ??žđ?‘Žđ?‘Ž đ?‘„đ?‘„đ?‘„đ?‘„đ?‘’đ?‘’đ?‘’đ?‘’ 1 đ?‘„đ?‘„đ?‘„đ?‘„ đ?‘Žđ?‘Ž =đ?‘šđ?‘š +đ??śđ??śđ?‘’đ?‘’ Ă— đ?‘„đ?‘„đ?‘šđ?‘š (3) đ??žđ??ž đ?‘„đ?‘„đ?‘’đ?‘’

đ?‘„đ?‘„đ?‘šđ?‘š

đ??śđ??śđ?‘’đ?‘’

(3)(3) (3)

đ?‘„đ?‘„đ?‘šđ?‘š đ?‘Žđ?‘Ž

the equilibrium (mg/L), QQ is the amount ion adsorbed and where CeCCiseisis where the equilibrium concentration (mg/L), is the amount of ion adsorbed (mg/g); eQ mQ(mg/g) where Ce is the concentration equilibrium concentration (mg/L), Qeeis is the the amount of of ion adsorbed (mg/g); Q(mg/g); (mg/g) QQ m (mg/g) m(mg/g); where the equilibrium concentration (mg/L), amount of ion adsorbed e e m (mg/g) Ka (L/mg) are theand empirical denoting monolayer capacity or limiting adsorption, signifying the (L/mg) constants are the empirical constants denoting monolayer capacity or limiting and KKa (L/mg) (L/mg) are areKa the the empirical empirical constants denoting monolayer capacity oradsorption, limiting adsorption, adsorption, and constants denoting monolayer capacity or limiting a signifying the solid-phase can the be charted slope and the intercept the solid-phase concentration, and can concentration, be chartedand from slopefrom andthethe intercept of theoflinear plot of 1/Qe signifying the the solid-phase solid-phase concentration, and can be charted from the slope and the intercept of the the signifying concentration, and can be charted from the slope and the intercept of linear plot of 1/Q in Fig. 4.e versus 1/Ce as shown in Fig. 4. versus 1/Ce as shown linearplot plotof of1/Q 1/Qeversus versus1/C 1/Ceas asshown shownin inFig. Fig.4.

4. linear e

e

0.0014

0.0016 0.0016

0.0010

1/Qe

1/Q 1/Qe e

0.0010 0.0010 0.0008 0.0008

y=0.0049x+0.0004 R2=0.9476

0.0012

0.0014 0.0014 0.0012 0.0012

0.0016

y=0.0049x+0.0004 y=0.0049x+0.0004 =0.9476 R22=0.9476 R

0.0008 0.0006 0.0004 0.0002

0.00

0.05

0.10

0.15

0.20

1/Ce

0.0006 0.0006

Figure 4. Langmuir isotherm plot banana adsorbent Figure 4. Langmuir isotherm plot for for banana rachisrachis adsorbent

0.0004 0.0004 The quality of the Langmuir isotherm can be determined by the magnitude of a dimensionless

0.0002

0.0002 constant Ra known as the separation0.05 factor expressed in Eq. 4 [34], 0.00 0.10 0.00

0.05

0.10 1/Ce 1/C

0.15 0.15

www.textile-leather.com 125 0.20 0.20

Figure 4. Langmuir isotherm plot for banana rachis adsorbent

PAYEL S, et al. Chromium Banana Rachis Adsorbent from TLR Tannery‌ TLR 118-134.

0 (0) 2020 00-00.

PAYEL S, et al. Chromium AdsorptionAdsorption on Bananaon Rachis Adsorbent from Tannery‌ 3 (3) 2020

The quality of the Langmuir isotherm can be determined by the magnitude of a dimensionless where is the initial concentration of the Cr ions mg/L Langmuir constant described The quality of the Langmuir isotherm can be determined byin the magnitude a dimensionless constant Ra constant RCaoknown as the separation factor expressed in Eq. 4 and [34],Ka isofthe known asearlier. the separation factor expressed Eq. 4 [34],within the range 0 < R < 1, unfavorable when R > 1, The adsorption process isinfavorable a

a

1 becomes linear when Ra = 1, and the process đ?&#x2018;&#x2026;đ?&#x2018;&#x2026;đ?&#x2018;&#x17D;đ?&#x2018;&#x17D; = is irreversible when Ra = 0.

1+đ??žđ??žđ?&#x2018;&#x17D;đ?&#x2018;&#x17D; đ??śđ??śđ?&#x2018;&#x153;đ?&#x2018;&#x153;

(4) (4)

Table 3. in Adsorption isotherm parameters ions mg/L and Ka is the Langmuir constant described earlier. where Co is the initial concentration of the Cr Ra > 1, becomes linear The adsorption process is favorable within the range 0Parameters < Ra < 1, unfavorable whenValue Isotherm Models when Ra = 1, and the process is irreversible when Ra = 0. Qm 2500 Ka (L/mg) Langmuir model Table 3. Adsorption isotherm parameters Ra Isotherm Models Parameters R2

0.0816 0.004 Value

Qm

1/n Ka (L/mg) Kf (mg.g-1)(L.g-1)1/n Ra 2 R R2

Langmuir model model Freundlich

Freundlich model

2500 0.0816 0.004 0.9476

1/n

0.3255

Kf (mg.g-1)(L.g-1)1/n

476.372

R

0.9985

0.9476 0.3255 476.372 0.9985

The data of the adsorption isotherm parameters is presented in Table 3. The correlation coefficient 2 of the Langmuir model is found to be 0.9476, which is close to 1. The maximum monolayer The dataadsorption of the adsorption isotherm parameters presented obtained in Table 3.isThe correlation coefficient of the capacity for banana rachis isadsorbent 2500 mg/g and the value of the Langmuirseparation model is found 0.9476, which is close to 1. The maximum monolayer adsorption capacity factor,toRbe a = 0.004 indicates that the process is favorable. The Ra value of this study is for banana rachis adsorbent obtained is 2500 mg/g and the value of the separation factor, Ra = 0.004 indisignificantly low, suggesting a strong interaction between the Cr molecules and the adsorbents [35]. cates that the process is favorable. The Ra value of this study is significantly low, suggesting a strong interaction between the Cr molecules and the adsorbents [35].

Freundlich Isotherm

Freundlich TheIsotherm Freundlich isotherm is derived assuming a non-uniform heterogeneous surface for adsorption.

The Freundlich isotherm is this derived a non-uniform heterogeneous The model used in studyassuming can be represented as below in Eq. 5, surface for adsorption. The model used in this study can be represented as below in Eq. 5, 1

(5) (5)

đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x201E;đ?&#x2018;&#x201E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; = đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ??žđ??žđ?&#x2018;&#x201C;đ?&#x2018;&#x201C; + đ?&#x2018;&#x203A;đ?&#x2018;&#x203A; đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ??śđ??śđ?&#x2018;&#x2019;đ?&#x2018;&#x2019;

where Kf is the Freundlich characteristic constant [(mg.g-1) (L.g-1)1/n] -1and 1/n is the heterogeneity factor of -1 1/n where Kf is the Freundlich characteristic constant [(mg.g ) (L.g ) ] andTLR 1/n is2020 the heterogeneity S, et al. Chromium Adsorption Adsorbent Tanneryâ&#x20AC;Śin 0 (0) 5.

00-00. versus lnCe from as shown Fig. adsorption, obtained from thePAYEL intercept and the slopeonofBanana lnQeRachis factor of adsorption, obtained from the intercept and the slope of lnQe versus lnCe as shown in Fig. 5.

8.2 8.0

y=0.3256x+6.1662 R2=0.9985

7.8

lnQe

7.6 7.4 7.2 7.0 6.8 6.6

1

2

3

lnCe

4

5

6

Figure 5. FreundlichFigure isotherm plotisotherm for banana rachisrachis adsorbent 5. Freundlich plot for banana adsorbent The numerical value of 1/n tabulated in Table 3 is less than 1 but positive, indicating an approvable 126 www.textile-leather.com adsorption process [36]. The correlation coefficient obtained for the Freundlich model is 0.9985, which is closer to 1 than it was in the Langmuir model (R2=0.9476). This implies that adsorption will

The numerical value of 1/n tabulated in Table 3 is less than 1 but positive, indicating an approvable adsorption process [36]. The correlation coefficient obtained for the Freundlich model is 0.9985, PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tanneryâ&#x20AC;Ś TLR 3 (3) 2020 118-134.

which is closer to 1 than it was in the Langmuir model (R2=0.9476). This implies that adsorption will be a multilayer adsorption on a heterogeneous surface following the Freundlich isotherm.

The numerical value of 1/n tabulated in Table 3 is less than 1 but positive, indicating an approvable adsorption process [36]. The correlation Kinetics coefficient obtained for the Freundlich model is 0.9985, which is closer to Theory of Adsorption 1 than it was in the Langmuir model (R2 =0.9476). This implies that adsorption will be a multilayer adsorpThe adsorption ratesfollowing as well the as Freundlich suitable rate expressions, characteristic of possible reaction tion on a heterogeneous surface isotherm. mechanisms of chromium by the banana rachis adsorbent, were estimated by using the kinetic

Theory of Adsorption Kinetics

modeling. In this regard, two well-established kinetic models, pseudo-first-order, and pseudoThe adsorpti on rates as well suitableThe ratevalue expressions, characteristi c of possible mechanisms second-order wereasstudied. of the correlation coefficient (R2)reacti was on studied to ensure the of chromium by the banana rachis adsorbent, were estimated by using the kinetic modeling. In this regard, effectiveness of the experiment. two well-established kinetic models, pseudo-first-order, and pseudo-second-order were studied. The value of the correlation coefficient (R2) was studied to ensure the effectiveness of the experiment.

The pseudo-first-order model

The pseudo-first-order model

The Lagergrenâ&#x20AC;&#x2122;s model [37] was followed for the pseudo-first-order kinetics analysis.

The Lagergrenâ&#x20AC;&#x2122;s model [37] was followed the pseudo-fi kineti cs 6, analysis.

The pseudo-first-order reactionfor is expressed by rst-order the following Eq. The pseudo-first-order reaction is expressed by the following Eq. 6, đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą

= đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC; (đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; â&#x2C6;&#x2019; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą ) from Tanneryâ&#x20AC;Ś TLR 0 (0) 2020 00-00.

PAYEL S, et al. Chromium Adsorption on Banana đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;Ąđ?&#x2018;ĄRachis1 Adsorbent

(6)

(6)

PAYEL S, etqal.

Chromium Adsorption on Banana Rachis Adsorbent from Tanneryâ&#x20AC;Ś TLR 0 (0) 2020 00-00. where qe (mg/g) and t (mg/g) denote the adsorption capacity at equilibrium and at time t (min) respectively, where qe (mg/g) and qt (mg/g) denote the adsorption capacity at equilibrium and at time t (min) and k1 (L/min) is the constant theby pseudo-fi rst-order adsorpti on reacti Using the integrated linear of form applying boundary conditions, viz.on. that the initial conditions are respectively, and k (L/min) is the constant of the pseudo-first-order adsorption reaction.

1 Using integrated linear form byform applying boundary conditi ons, viz. viz.that thatthethe initi al conditi Using the integrated linear by applying boundary conditions, initial conditions areons are qe - qt qe - qthe t = 0 at t = 0, Eq. 6 can be expressed as follows: = 0 at t = 0, Eq. asexpressed follows:as follows: qe -6qtcan = 0 atbe t =expressed 0, Eq. 6 can be

ln(đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; â&#x2C6;&#x2019; đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC; đ?&#x2018;Ąđ?&#x2018;Ą đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; â&#x2C6;&#x2019;â&#x2C6;&#x2019;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą )) = ln(đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; = đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;â&#x2C6;&#x2019; đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC; đ?&#x2018;Ąđ?&#x2018;Ą 1 đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;

đ?&#x2018;Ąđ?&#x2018;Ą

or, or,

đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;

1

đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; â&#x2C6;&#x2019;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą)) (đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;(đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;â&#x2C6;&#x2019;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;

(7)

1 đ?&#x2018;Ąđ?&#x2018;Ą đ?&#x2018;Ąđ?&#x2018;Ą đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122;đ?&#x2018;&#x2122; đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; đ?&#x2018;Ąđ?&#x2018;Ą = =â&#x2C6;&#x2019;đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC; â&#x2C6;&#x2019;đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC; 1

(7)

(7)

A plot of ln(qe â&#x2C6;&#x2019;qt)/qe versus time, t following Eq. 7 is used to describe the suitability of this kinetic

A plot of ln(q e â&#x2C6;&#x2019;qt)/qe versus time, t following Eq. 7 is used to describe the suitability of this kinetic model as 7 is used to describe theslope suitability of this kinetic A plot of ln(q e â&#x2C6;&#x2019;q e versus model ast)/q done in Fig. time, 6. The tqefollowing and k1 are Eq. detected from the intercept and of the plot, done in Fig. 6. The qe and k1 are detected from the intercept and slope of the plot, respectively, and taburespectively, and 6. tabulated model as done in Fig. The qine Table and 4.k1 are detected from the intercept and slope of the plot, lated in Table 4. respectively, and tabulated in Table 4.

6. Pseudo-first-orderplot plot for rachis adsorbent Figure 6.Figure Pseudo-first-order forbanana banana rachis adsorbent

The nonlinear form of Eq. 7 can be written as: đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą = đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; (1 â&#x2C6;&#x2019; đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; â&#x2C6;&#x2019;đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;1 đ?&#x2018;Ąđ?&#x2018;Ą ).

www.textile-leather.com 127

Figure 6. Pseudo-first-order plot for banana rachis adsorbent

Figure 6. Pseudo-first-order plot for banana rachis adsorbent

PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tanneryâ&#x20AC;Ś TLR 3 (3) 2020 118-134.

The nonlinear form of Eq. 7 can be written as: The nonlinear form of Eq. 7 can be written as: PAYEL S, et al. Chromium Adsorption on Banana Rachis â&#x2C6;&#x2019;đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;1 đ?&#x2018;Ąđ?&#x2018;ĄAdsorbent from Tanneryâ&#x20AC;Ś TLR 0 (0) 2020 00-00.

đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą = đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; (1 â&#x2C6;&#x2019; đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;

).

The correlation coefficient obtained for pseudo-fi rst-order kinetics is 0.8987 and the values of qe and k1 are đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą 2 = đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC; (đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; â&#x2C6;&#x2019; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; ) (8) 2 đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; đ?&#x2018;Ąđ?&#x2018;Ą đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;Ąđ?&#x2018;Ą 0.0355 and 0.0434coefficient respectively.

The correlation obtained for pseudo-first-order kinetics is 0.8987 and the values of qe and PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tanneryâ&#x20AC;Ś TLR 0 (0) 2020 00-00.

k1 are 0.0355 and 0.0434 respectively.

The pseudo-second-order model PAYEL is S, etthe al. Chromium Adsorption on Banana Rachis Adsorbent from TLR 0 (0) 2020q00-00. where k2 (g/mg.min) pseudo-second-order adsorption rateTanneryâ&#x20AC;Ś constant, and e (mg/g) and qt

đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tanneryâ&#x20AC;Ś TLR 0 (0) 2020 00-00.

PAYEL

đ?&#x2018;Ąđ?&#x2018;Ą = đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;2 (đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; â&#x2C6;&#x2019;beđ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ąexpressed )2 The pseudo-second-order model The pseudo-second-order model can 8: t (min) respectively. (8) đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;equilibrium (mg/g) are the adsorption capacity at andas at Eq. time đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;Ąđ?&#x2018;Ą [38] đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą 2 đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;Ąđ?&#x2018;Ą

(8)

= đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;2 (đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; â&#x2C6;&#x2019; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą )

For the boundary conditions t = 0[38] to t can = t đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; and qt= 0 to qtas = qEq. , the t2 The pseudo-second-order model beđ?&#x2018;Ąđ?&#x2018;Ą = expressed 8: integrated form of Eq. 8 becomes: đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC; (đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; â&#x2C6;&#x2019; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; ) (8) (8) 2 đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; đ?&#x2018;Ąđ?&#x2018;Ą đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ?&#x2018;Ąđ?&#x2018;Ą where k2 (g/mg.min) is the ispseudo-second-order adsorption constant, and qand (mg/g) and qt where k2 (g/mg.min) the pseudo-second-order adsorption raterate constant, and qe (mg/g) q e t

(mg/g) are the adsorption capacity at equilibrium and1atattime t (min) respectively.

1 adsorpti (mg/g) the adsorption capacity at equilibrium and t constant, (min) respectively. where k2 are (g/mg.min) is the pseudo-second-order ontime rate and qe (mg/g) and qt (mg/g) are = â&#x2C6;&#x2019; đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC; đ?&#x2018;Ąđ?&#x2018;Ą 2 integrated Forwhere the boundary conditions t = 0isto the t đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; = t and q = 0 to q = q , the form of Eq. 8rate becomes: k2 (g/mg.min) pseudo-second-order adsorption constant, and qe (mg/g) and qt t t t â&#x2C6;&#x2019; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; đ?&#x2018;Ąđ?&#x2018;Ą đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; the adsorpti on capacity at equilibrium time For the boundary conditions t = 0 to tand = t at and qt= t0(min) to qt respecti = qt, thevely. integrated form of Eq. 8 becomes: capacity and at time t (min) respectively.

For the boundary(mg/g) conditiare onsthe t = adsorption 0 to t = t and qt= 0 toatqequilibrium t = qt, the integrated form of Eq. 8 becomes: 1

1

2 đ?&#x2018;Ąđ?&#x2018;Ą q = 0 to q = q , the integrated form of Eq. 8 becomes: For the boundary conditions đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;tđ?&#x2018;&#x2019;đ?&#x2018;&#x2019;=â&#x2C6;&#x2019;0đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ąto= tđ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;=â&#x2C6;&#x2019;t đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;and t t t 1 1 = â&#x2C6;&#x2019; đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;2 đ?&#x2018;Ąđ?&#x2018;Ą This stands for the integrated rate law for a đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;pseudo-second-order reaction. The linear form of this đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; â&#x2C6;&#x2019; đ?&#x2018;Ąđ?&#x2018;Ą

1 1 equation is:stands for the integrated for a pseudo-second-order = reaction.

The linearlinear form of this of this equaThis stands [39] forThis the integrated rate lawrate forlaw a pseudo-second-order reactiâ&#x2C6;&#x2019;on. form đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;2 đ?&#x2018;Ąđ?&#x2018;ĄThe đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; â&#x2C6;&#x2019; đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; tion [39] is: equation [39] is:

1 a pseudo-second-order 1 1 1 This stands for the integrated rate law for reaction. The linear form of this = â&#x2C6;&#x2019;ďż˝ ďż˝ (9) đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą 1 =đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;1 â&#x2C6;&#x2019; ďż˝ đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;12 đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;ďż˝21 đ?&#x2018;Ąđ?&#x2018;Ą (9) (9) đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;2 đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; 2 đ?&#x2018;Ąđ?&#x2018;Ą equation [39] is: This stands for the integrated rate law for a pseudo-second-order reaction. The linear form of this 2 2 from the )(R gathered from the the plotplot of 1/ The relevance of this model canmodel be ensured by by the correlati on coeffi cient gathered plot The relevance of this can be ensured bythe the correlation coefficient (R2)(R ) gathered from The relevance of this model correlation coefficient equation [39] can is: be ensured 1 1 1 1 as expressed inexpressed Fig. 7. in = qt versus 1/t ofofEq. 1/q9versus 1/t of Eq. 9 as Fig. 7. â&#x2C6;&#x2019; ďż˝ (9) 2ďż˝ of 1/q versus 1/tt of Eq. 9 as expressed in Fig. 7. t

đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą

đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;

đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;2 đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;&#x2019;đ?&#x2018;&#x2019;

1 đ?&#x2018;&#x17E;đ?&#x2018;&#x17E;đ?&#x2018;Ąđ?&#x2018;Ą

đ?&#x2018;Ąđ?&#x2018;Ą

1

1

1

= â&#x2C6;&#x2019; ďż˝ đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; 2 ďż˝ đ?&#x2018;&#x17E;đ?&#x2018;&#x17E; đ?&#x2018;&#x2DC;đ?&#x2018;&#x2DC;2 đ?&#x2018;&#x2019;đ?&#x2018;&#x2019; đ?&#x2018;Ąđ?&#x2018;Ą 2 The relevance of this model can be ensured by the correlationđ?&#x2018;&#x2019;đ?&#x2018;&#x2019;coefficient (R ) gathered from the plot

(9)

of 1/qt versus 1/t of Eq. 9 as expressed in Fig. 7.

The relevance of this model can be ensured by the correlation coefficient (R2) gathered from the plot of 1/qt versus 1/t of Eq. 9 as expressed in Fig. 7.

Figure 7. Pseudo-second-order plot for banana rachis adsorbent

Figure 7. Pseudo-second-order plot for banana rachis adsorbent values of qe and k2 can be determined from the slope and the intercept of the plot respectively, The values of qThe e and k2 can be determined from the slope and the intercept of the plot respectively, which tabulated in Table 4. Fig. 7 shows that the value of the correlation coefficient is 0.9996. The is tabulated inwhich Tableis 4.

Fig. 7 shows that the value of the correlation coefficient is 0.9996. The poor linepoor linearity of the Lagergren pseudo-first-order plots observed in the present study indicated that arity of the Lagergren pseudo-fi plots observed in the present indicated that the adsorption Figurerst-order 7. Pseudo-second-order plot for banana rachis study adsorbent process did not follow the first-order kinetics, but rather adhered more to the pseudo-second-order kinetics as confirmed by the correlation coefficient. According to the pseudo-second-order model, two reactions The values of qe and k2 can be determined from the slope and the intercept of the plot respectively,

Figure Pseudo-second-order plot for banana adsorbentcoefficient is 0.9996. The which is tabulated in Table 4. 7.

Fig. 7 shows that the value of therachis correlation 128 www.textile-leather.com poor linearity of the Lagergren pseudo-first-order plots observed in the present study indicated that Figure 7. Pseudo-second-order plot for banana rachis adsorbent

The values of qe and k2 can be determined from the slope and the intercept of the plot respectively,

PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tanneryâ&#x20AC;Ś TLR 3 (3) 2020 118-134.

occur, the first one is fast and reaches equilibrium quickly, and the second is slow and can continue for a long time [40].

Table 4. Adsorption kinetics parameters Kinetics Models

Pseudo-first order

Pseudo-second order

Parameters

Value

qe (mg/g)

0.0355

k1 (min )

0.0434

R2

0.8987

qe (mg/g)

2.8827

k2 (g/mg.min)

0.0077

R

0.9996

-1

2

Comparison with Previous Studies The adsorption capacities of some previously used adsorbents are compared with the adsorbent of this study in the case of contact time and chrome removal efficiency and the findings are charted in Table 5.

Table 5. Data comparison of different adsorbents for contact time and chrome removal efficiency Adsorbents

Initial Cr Conc. (mg/L)

Dose (g/L)

Contact time (min)

Cr removal (%)

Ref.

Activated carbon

48.874

24

15000

46

[18]

Eggshell

3210

20

840

25

[41]

Powdered marble

3210

12

30

40

[41]

Bittern

154.95

5 mL/L

21

32

[42]

Banana rachis

3373.5

40

15

99.64

This study

It is clear that among these adsorbents, the banana rachis adsorbent gives higher removal efficiency without any additional chemicals and with minimum contact time. This result indicates that the banana rachis adsorbent can be used as a better alternative for an adsorbent for tannery wastewater effluent treatment in the case of chromium removal.

The proposed adsorbent follows the Freundlich isotherm and the pseudo-second-order kinetics in chromium removal from the tannery wastewater. Table 6 compiles a data comparison for the Freundlich isotherm and the pseudo-second-order kinetics with some previously tried adsorbents in the tannery wastewater.

The value of the Freundlich constant, Kf, represents the adsorption capacity, which is higher for this study compared to the eggshell and the powered marble adsorbent [41]. The higher R2 value of the experiment ensures the consistency of the experiment. The adsorption capacity at equilibrium, qe, for the pseudosecond-order kinetics also indicates a higher capacity for the banana rachis. The correlation coefficient, R2, is also coherent with the found value.

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PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tanneryâ&#x20AC;Ś TLR 3 (3) 2020 118-134.

Table 6. Data comparison for Freundlich isotherm and pseudo-second-order kinetics Parameters

Kf (mg.g-1)(L.g-1)1/n

N

R2

Eggshell [41]

3.45

2.57

0.722

Powdered marble [41]

5.86

2.99

0.945

Banana rachis

476.37

3.07

0.9985

qe (mg/g)

k2 (g/mg.min)

R2

Activated carbon [18]

1.03

0.8333

0.9446

Biological activated carbon [18]

0.13

0.0519

0.8608

Banana rachis

2.88

0.0077

0.9996

Pseudo-second order

Freundlich isotherm

Adsorbent

Treatment Process Efficiency The results of the treatment process at optimum conditions are presented in Table 7. It shows that after treatment the pH, the BOD and the COD were within the discharge limit. Other parameters, e.g. TDS, the EC and chloride (Cl-) were higher than the discharge limit, although, after treatment, they were noticeably reduced.

Table 7. Data inspection with standard Parameters

Raw sample

Treated sample

Removal efficiency(%)

ECR [25]

ISI [43]

Cr (mg/L)

3373.5

12.1

99.64

2.0

0.05

pH

4.5

6.7

-

6-9

6-9

BOD (mg/L)

3197

107

96.65

250

30

COD (mg/L)

4297

293

93.18

400

250

TDS (g/L)

29.83

36.3

21.69

2.1

-

EC (mS)

66.9

81.2

21.38

1.20

0.85

Chloride (mg/L)

17021

6872

59.62

600

600

During the treatment process, the banana rachis adsorbent acts as an adsorbent for the chromium ion, and the chloride ion possibly co-precipitates with it, which might be the reason for chloride reduction. The adsorption of organic and inorganic pollutants at the adsorbent surface is responsible for the BOD and COD reduction. From Table 2 it is clear that the soluble mineral contents might be responsible for the increase in TDS. The rise in the EC might be due to the addition of the -OH group from the adsorbent.

Desorption and Reuse The chromium-loaded used adsorbent was tried to be used for desorption as an effort to recover and reuse the chromium. A qualitative analysis was performed to ascertain the possibility of chromium recovery. In this case, 1.0 g of chromium-loaded adsorbent was mixed with 50 mL of distilled water at different pH of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 and then left to settle for 24 hours after 5 minutes of stirring.

130 www.textile-leather.com

recovery. In this case, 1.0 g of chromium-loaded adsorbent was mixed with 50 mL of distilled water at different pH of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 and then left to settle for 24 hours after 5 PAYEL S, et al. Chromium Adsorption on Banana Rachis Adsorbent from Tannery… TLR 3 (3) 2020 118-134. minutes of stirring.

Figure 8. Desorption of chromium-loaded adsorbent at different pH

The result indicates that the lower the pH is, the more chromium is recovered.

Figure Desorptionofofchromium-loaded chromium-loaded adsorbent adsorbent at Figure 8. 8.

Desorption at different differentpH pH

The chromium ions exist as hydrated [Cr(H2O)6]3+ in a solution. As the pH changes, the water The result indicates the lower the hydroxyl pH is, theions. moreThe chromium molecules can bethat replaced by the numberisofrecovered. hydroxyls exchanged relies on the The result indicates that the lower the pH is, 3+the more chromium is recovered.

The chromium ions exist as hydrated [Cr(H2O)6] in a solution. As the pH changes, the water molecules can pH of the solution [44]: 3+ chromium ions existions. as The hydrated [Cr(H in exchanged a solution.relies As the pHpH changes, the water beThe replaced by the hydroxyl number of hydroxyls on the of the solution [44]: 2O)6]

molecules can be replaced by the hydroxyl ions. The number of hydroxyls exchanged relies on the pH3−4 pH6−7 pH8 →[Cr(H2O)5 ]2+ ← →[Cr(H2O)4 ]1+ ← →[Cr(H2O)2 (OH)4 ]−1 [Cr(H O) ]3+ ←

2 6 pH of the solution [44]:

It shows that a change in the pH can cause changes in the charge on the Cr-ion. Fig. 8 reveals the condiIt of shows that a change in −the pH canofcause in the charge on the chromium Cr-ion. Fig.sulphate.

8 reveals the a −7 a unique pH3 424 hours pH6 pH8 −1 3+ after 2+ changes 1+ of tion the filtered water settling with shade basic Since

→[Cr(H2O)2 (OH)4 ] [Cr(H2O)6 ] ←→[Cr(H2O)5 ] ←→[Cr(H2O)4 ] ←

quantitative was notwater performed, it requires further studies efficiency of the process. condition analysis of the filtered after 24 hours of settling with to a ensure unique the shade of basic chromium

sulphate. Since a quantitative analysis was not performed, it requires further studies to ensure the

It shows that a change in the pH can cause changes in the charge on the Cr-ion. Fig. 8 reveals the CONCLUSION

efficiency of the process. condition of the filtered the water after 24 hours of wastewater settling with a treated unique for shade of basicofchromium In the batch-wise technique, chromium-containing was the removal chromium Since a rachis quantitative analysis not performed, requires further studies tocondition ensure the by sulphate. using the banana adsorbent.

The was removal efficiency ofitchromium at the optimized was 99.64% at 3 gofper mL for 15 min at a relative pH of 6.7. The reduction of the BOD, the COD, and chloride efficiency the75process. was 96.65%, 93.18%, and 59.62%, respectively. The study indicates that the adsorption process follows the Freundlich isotherm for the multi-layer adsorption and the pseudo-second-order kinetics for reaction rate.

The FTIR study reveals the associated functional groups for the adsorption process. Several comparisons with other studies in terms of contact time, removal efficiency, isotherm, and kinetic parameters, reveal that it was an effective technique to minimize the pollution load from the spent chrome liquor as well as an efficient approach towards the banana rachis waste management. The desorption study reveals the reappearance of chromium in a solution. Conclusively, the investigation could be helpful to effectively establish the treatment process of the spent chrome liquor in a tannery reservoir before the discharge.

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UDDIN MMd, et al. Evaluating Suitability of Glutaraldehyde Tanning in Conformity… TLR 3 (3) 2020 135-145.

Evaluating Suitability of Glutaraldehyde Tanning in Conformity with Physical Properties of Conventional Chrome-Tanned Leather Md. Minhaz UDDIN, Md. Jawad HASAN, Yead MAHMUD, Fatema-Tuj-ZOHRA, Sobur AHMED* Institute of Leather Engineering and Technology, University of Dhaka, 44-50, Hazaribagh, Dhaka-1209, Bangladesh *soburahmed@du.ac.bd; soburahmed2001@yahoo.com Original scientific article UDC 675.017:675.024.43 DOI: 10.31881/TLR.2020.09 Received 5 Jun 2020; Accepted 3 Aug 2020; Published Online 20 Aug 2020; Published 11 Sep 2020

ABSTRACT Leather manufacturing involves a number of unit processes, out of which tanning is the most important in so far as it converts the putrescible hides/skins into non-putrescible leather. In this study, glutaraldehyde has been exploited as a means to reduce the use of basic chromium sulfate for the production of quality shoe upper crust leather. The paper consists in studying the physical properties of aldehyde-tanned leather and chrometanned leather. The aim is to find out the possibility of replacing the wet-blue leather, containing Cr(III) salts, with the glutaraldehyde-tanned wet-white leather. The physical properties of the aldehyde-tanned leather were evaluated, analyzed and compared with the conventional chrome-tanned shoe upper crust leather. Statistical analysis illustrated that the tensile strength, the percentage of elongation, stitch tear strength, Baumann tear strength and grain crack strength of the leather was 211±1 kg/cm2, 38±0.5 %, 89±0.11 kg/cm, 63±0.4 kg/cm and 23±0.4 kg respectively. It was observed that the property of the experimental leather was quite comparable with the conventional chrome-tanned leather and able to meet the requirements of the shoe upper crust leather after re-tanning. The shrinkage temperature of the experimental tanned leather was found to be 87 °C, lower than that of corresponding control, which indicates lesser tanning power of aldehyde. However, the morphology of the aldehyde-tanned leather was quite akin with the conventional leather. This study suggests that using glutaraldehyde in the tanning process in order to minimize the chromium load in the tanning and the re-tanning process during the production of shoe upper crust leather reduces the generation of toxic waste and its impact on the environment.

KEYWORDS Glutaraldehyde, tanning, wet-white leather, physical properties

INTRODUCTION In regard to export earnings in Bangladesh, leather comes in second, after readymade garments. It is one of the oldest and fastest growing industries in South and Southeast Asia. Tanning is the process of converting putrescible hide or skin into leather, which is durable and less prone to deterioration [1]. This process in the leather industry is a critical step towards protecting leather from microbial decay, heat, sweat and humidity [2]. During leather manufacturing, raw hides/skins undergo several chemical and mechanical operations.

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Among all these operations, tanning is the most important one [3]. Tanning agents are considered as the most significant material in the leather making process. About 90% of the tanning industries use basic chromium sulfate (BCS) during tanning [4]. At present, basic chromium sulfate is the most popular of among all tanning agents, as it provides unique properties and good hydrothermal stability to tanned leather [5].

Chrome tanning was first introduced in the 19th century [6]. At that time, tanning processes were based on salts of different metals e.g. aluminium [7], sodium [8], titanium [9], iron [10] etc. It has been reported that only 60-70% of chromium used in tanning is consumed by the pelt in the traditional chrome tanning process and the rest is discharged into spent chrome tan liquor, causing severe environmental pollution and a great waste of chrome as well [11, 12]. Nowadays, high exhaust chrome tanning procedure has been developed; though that is not practiced widely yet [13]. The ultimate fate of this waste chromium is to be deposited in soil or water and to accumulate in various plant parts, e.g. leaves, roots, stems and fruits, and finally introduced to the food chain through their consumption [14]. Therefore, it has become essential to introduce an alternative to the chrome tanning agent for the minimization of environmental pollution and health hazards. Many alternative processes, like vegetable tanning, aluminum tanning, aldehyde tanning, etc., have been taken into consideration to produce chromium-free leather for some ecological benefits, however could not achieve the characteristics of the chrome-tanned leather [15]. Due to stricter requirements for leather production and leather waste recycling, the production of chromium-free or, more specifically, inorganic salt-free leather becomes essential. Thatâ&#x20AC;&#x2122;s why demand for metal-free leather is being increased and promoted [16]. Different organic compounds are being considered as tanning agents. Among them, aldehyde alone or in combination with other tanning agents has been found to produce considerably good properties of leather [17]. The use of aldehyde in combination with chromium as a less-chrome approach has been shown to exhibit better leather characteristics. Aldehyde is rarely used as a tanning agent alone.

However, aldehydes have been used in the pre-tanning and the re-tanning process. The use of formaldehyde as a tanning agent is rare as it had been included in the group of hazardous materials due to its toxic, mutant and carcinogenic nature [18]. Glutaraldehyde and some of its modifications have proved to be more competent tanning agents than others [19]. Using optically active unnatural D-Lysine (diamino compound) with Glutaraldehyde (GTA) for tanning is an effective method of eco-friendly processing [20]. Chromium can form certain compounds, which are toxic to humans, animals, and plants [21]. Glutaraldehyde is extensively used as crosslinking agent for the preparation of collagenous biomaterials [22]. It reacts with the alpha amino group of collagens and creates stable pyridinium-ring crosslinks rather than unstable double-Schiff base like other aldehydes [23]. Exposure to glutaraldehyde may lead to irritation in the skin, eyes and the nose among the workers. It may also cause coughing, nausea, headaches, dizziness and problems in the respiratory tract. The toxicity level of glutaraldehyde is not widely known [24]. Toxicity level of glutaraldehyde should be investigated in comparison with chromium before it to be used in the leather making process. In this work, glutaraldehyde was used in tanning for the reduction of chromium content and the physical properties of glutaraldehyde-tanned leather have been compared with the conventional chrometanned leather with a view to stimulate further studies.

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EXPERIMENT Materials and Methods Twenty pieces of wet salted goat skins, 5 sq. ft. in size on average (weight of each being 1 kg), were collected from the hide market in Posta, Lalbagh, Dhaka, Bangladesh. Glutaraldehyde and basic chromium sulfate powder, along with other chemicals for leather processing, were obtained from local chemical dealers at Hazaribagh, Dhaka, Bangladesh. All the chemicals used in leather processing were of commercial grade.

Method of leather processing Leather processing consisted of three stages. The skins were processed in the conventional way from soaking to pickling, stated in Table 1. The pickled pelts were processed through trials for the optimization of tanning, shown in Figure 1, and then the final tanning experiment with glutaraldehyde and basic chromium sulfate is cited in Table 2 and Table 3, respectively. Both the experimental and the control tanned leather were processed into shoe upper crust leather, following the same post-tanning method mentioned in Table 4.

Table 1. Process for pickled pelt production from wet salted goat skins Process

Chemicals

% Offera

Time

Remarks

Desalting was carried out by a nylon brush and trimming was done by a hand knife. Then, salt weight was noted.

Pre-soaking

Main Soaking

Liming

Chemical wash Deliming

Water

500

Soda ash

0.2

Wetting agent

0.2

30 min

Water

500

Soda Ash

0.4

Wetting Agent

0.3

Run 30 min, rest 60 min and then run 5 min per hour for 10 hours

Preservative

0.2

Water

300

Liming auxiliary

1.0

Sodium sulfide

2.0

Lime

2.0

+ Sodium sulfide

1.0

+ Lime

2.0

Run 30 min, rest 60 min

pH adjusted to 12.5-13.0

+ Wetting agent

0.2

Run 5 min/hr. for 12 hours

Drained, unhaired, fleshed and took pelt weight.

Water

200

20 min

Drained

Sodium-meta-bi-sulfite

0.25

Water

80

60 min

pH adjusted to 8.3-8.4 pH checked with phenolphthalein indicator and drained.

Ammonium sulfate

2.0

Sodium-meta-bi-sulfite

0.5

Drained

pH adjusted to 8.5-9.5 and then washed for 10 min and drained.

Run 30 min, rest 60 min

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Bating

Pickling

a

Water at 37 °C

100

90 min

pH adjusted to 8.0-8.2. Checked by thumb test. Scudded and cleaned the pelt.

Bating agent

2.0

Wetting agent

0.5

Water

80

Salt

8.0

Imprapell CO

0.2

Run-15 min

Formic acid (1:10 dilution)

0.5

Run-30 min

Sulfuric acid (1:20 dilution)

+1.0

Run 3 x 10 min

pH was checked 2.8 with bromocresol green.

Left overnight.

Sodium hypochlorite

0.5

Run-30 min

After that, half of the pickled bath was drained.

Note: All percentage of chemicals were calculated based on pelt weight.

Table 2. Recipe for glutaraldehyde tanning

b

Process

Chemicals

% Offerb

Time

Tanning

+ Sodium thio-sulfate

0.5

20 min

+ Glutaraldehyde

3.0

30 min

Phenolic syntan

4.0

Sodium formate

1.0

Fatliquor

1.0

180 min

Remarks

At morning drained, piled up and aged for 2 weeks.

Note: All percentage of chemicals were calculated based on pelt weight.

Table 3. Recipe for chrome tanning Process

Chemicals

% Offerc

Time

Tanning

+ Basic chromium sulfate

4.0

30 min

+ Basic chromium sulfate

4.0

Sodium formate

1.0

Chrome stable fatliquor

0.5

+ Water

50

+ Sodium bi carbonate

1.2

90 min

+ Preservative

0.2

60 min

Basification

c

60 min

Note: All percentage of chemicals were calculated based on pelt weight.

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Remarks

Penetration of chromium sulfate was checked ok.

pH adjusted to 3.7-3.8. Drained, piled up and aged for 2 weeks.

UDDIN MMd, et al. Evaluating Suitability of Glutaraldehyde Tanning in Conformity… TLR 3 (3) 2020 135-145.

Table 4. Recipe for post tanning Process

Chemicals

% Offerd

Acid wash

Water

200

Oxalic acid

0.3

Wetting agent

0.3

Water at 45 °C

100

Neutralizing syntan

2.0

Sodium formate

1.0

Sodium bi carbonate

0.8

Water at 50 °C

100

Resin syntan

2.0

Fat liquoring agent

4.0

Dye

3.0

Dye leveler

1.0

Mimosa

8.0

Quebracho

8.0

Replacement syntan

3.0

60 min

Formic acid

2.0

2 x 20 min

Water at 55 °C

100

Synthetic oil

2.0

Semi-synthetic oil

2.0

Raw oil

0.5

Fungicide

0.2

Formic acid

1.5

Water at 55 °C

200

Dye

1.0

Formic acid

1.0

Resin syntan

1.0

Raw oil

0.5

Cationic fat

0.5

Neutralization

Re-tanning and dyeing

Fatliquoring

Top dyeing and fatliquoring

Time

Remarks

30 min Washed and drained, 30 min

pH adjusted to 4.0-4.5 and checked with BCG indicator.

30 min

Drained and washed.

20 min

20 min

Checked dye penetration.

30 min

Washed and drained.

60 min

30 min

Washed and drained.

30 min 30 min

30 min Washed, drained and horsed up for overnight.

Note: All percentage of chemicals was calculated based on shaved weight. Next day, after setting out and the vacuum-drying operation, leather was hung for natural drying. After a proper drying and conditioning, the vibrating, staking, toggling, trimming and plating/ironing were carried out for completion of the crust leather production.

d

Preliminary experiment for tanning agent optimization Four goat skin samples were collected for the experiments and various percentages of glutaraldehyde (1%, 2%, 3% and 4%) were prepared to optimize the amount of glutaraldehyde requirement. The efficacy of the tanning method was assessed by determining the shrinkage temperature of the produced leather after tanning.

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Organoleptic assessment of crust leather Glutaraldehyde-tanned (experimental) and chrome-tanned (control) crust leather were assessed by fullness, grain tightness, softness, grain smoothness and dye uniformity through visual examination. Three experienced tanners rated the leather on a scale of 0-10 points for each functional property, where higher points indicated better result.

Determination of shrinkage temperature The SATRA STD 114 apparatus for leather shrinkage temperature determination was used to measure the shrinkage temperature by following the standard operating procedure [25]. The samples were taken according to the sampling location of leather. All the experiments were performed in triplicate and reported the average value.

Analysis of discharged liquor The discharged liquor both from the experiment and the control tanning process were collected, filtered and analyzed for the pH, total solids (TS), total dissolved solids (TDS) and chromium content in accordance with the standard procedures [26].

Physical tests The produced leather was conditioned at 20±1 °C and 65±3 % relative humidity over a period of 48 h; the samples were taken from the specified sampling location. The physical properties of produced leather, e.g. tensile strength, the percentage of elongation at break, stitch tear strength, Baumann tear strength and grain crack strength were determined following standard methods set up by IULTCS allowing the assessment of the capacity of the leather to withhold the wear and tear properties [26-29].

RESULTS AND DISCUSSION Hydrothermal stability analysis of produced leather It has been reported that the addition of glutaraldehyde in increased amount considerably increases the shrinkage temperature [30-32]. In this study, it was found that the shrinkage temperature of leather increases gradually up to a certain level with the increase of glutaraldehyde percentage and after that it becomes unchanged with the increasing percentage of doses (Figure 1).

At 3 %, the shrinkage temperature of wet white leather was found 87 °C after aldehyde tanning and there was no increase of shrinkage temperature, although the percentage was increased to 4 %. After observation, the wet white leather tanned with a 3 %-glutaraldehyde dose was taken as experiment and made ready for final post-tanning operations along with the chrome-tanned (wet blue) leather as control.

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experiment and made ready for final post-tanning operations along with the chrome-tanned (wet blue) leather as control.

UDDIN MMd, et al. Evaluating Suitability of Glutaraldehyde Tanning in Conformity… TLR 3 (3) 2020 135-145.

Figure1. Shrinkage temperature of wet white leather with different percentage of glutaraldehyde Figure1. Shrinkage temperature of wet white leather with different percentage of glutaraldehyde

The shrinkage temperature of the glutaraldehyde-tanned (wet white) leather (87 °C) was observed to be Thethan shrinkage of the glutaraldehyde-tanned white) °C) was observed to lower that of temperature the conventional chrome-tanned (wet blue)(wet leather (104leather °C). This(87 is because of weak and lessbe number cross-linkages formation in the case of aldehyde lower of than that of the conventional chrome-tanned (wet tanning. blue) leather (104 °C). This is because of

weak and less number of cross-linkages formation in the case of aldehyde tanning.

Table 5. Resultant shrinkage temperature of produced leather (experiment vs. control) Type of leather Shrinkage temperature (Ts) Table 5. Resultant shrinkage temperature of produced leather (experiment vs. control) Glutaraldehyde (experiment) 87 °C Type of leather Shrinkage temperature (Ts) Chrome tanned leather (control) 104 °C Glutaraldehyde (experiment) 87 °C

SEM analysis

Chrome tanned leather (control)

104 °C

The Scanning Electron Microscopic (SEM) images of the conventional chrome-tanned leather and glutaraldehyde-tanned leather were investigated to assess the effect of tanning on the fiber structure of leather.

SEM analysis The images (Figure 2 and 3) were captured at magnification of x200 and x500.

The Scanning Electron Microscopic (SEM) images of the conventional chrome-tanned leather and glutaraldehyde-tanned leather were investigated to assess the effect of tanning on the fiber structure of leather. The images (Figure 2 and 3) were captured at magnification of x200 and x500.

Figure 2. Cross section (a) (X200) and (b) (X500) of glutaraldehyde-tanned leather (experiment)

It was observed from the images that the fiber structure of glutaraldehyde tanned leather is comparable with that of the conventionally processed chrome-tanned leather.

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Figure 3. Cross section (a) (X200) and (b) (X500) of chrome-tanned leather (control)

Organoleptic analysis The produced crust leather from the experimental and control method have been evaluated for various properties by both tactile and visual evaluation. The average rating for the leather has been calculated for each property and is presented in Figure 4. Higher number denotes better property. The figure shows that the organoleptic properties of the glutaraldehyde-tanned crust leather are comparable to those of the conventional chrome-tanned leather. The glutaraldehyde-tanned (experimental) crust leather exhibited good fullness, grain tightness and grain smoothness compared to the leather produced from the conventional chrome tanning.

Figure 4. Graphical representation of organoleptic properties of produced leather

Physical properties analysis The results of physical properties analysis of produced leather have shown that despite having lower shrinkage temperature, the glutaraldehyde-tanned leather had high tensile strength, stitch tear strength, Baumann tear strength, grain crack strength and elongation at break compared to that of the chrometanned leather (Table 6). The data indicated that the physical properties of the experimental leather were quite comparable with that of the corresponding control samples. It was found that almost all properties were above the minimum requirements of shoe upper crust leather standard [31-32].

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Table 6. Physical properties of control and experimental crust leather Parameter

Glutaraldehydetanned (Experiment)

Chrome-tanned (Control)

Minimum requirements for shoe upper crust leather [7, 30]

Tensile strength (Kg/cm2)

211±1

243±1

200

Elongation at break (%)

38±0.5

43±0.8

40-65

Grain crack strength (Kg)

23±0.4

27±0.4

20

Stitch tear strength (Kg/cm)

89±0.11

98±0.67

80

Baumann tear strength (Kg/cm)

63±0.4

68±0.25

30

Tanning discharge liquor analysis The discharged liquor from chrome tanning and glutaraldehyde tanning was analyzed for the parameters which are listed in Table 7. The table shows that total solids and total dissolved solids are lower in the discharged liquor of experimental tanning than control tanning. However, the pH of the glutaraldehyde tanning effluent was slightly lower than that of the conventional chrome-tanning effluents.

Table 7. Characteristics of tanning discharged liquor

e

Parameter

Glutaraldehyde-tanned (Experimental)

Chrome-tanned (Control)

pH

3.5

3.8

Total solids (TS)

43990

57550

Total dissolved solids (TDS)

39500

51130

Chromium content

0

4330

Note: All the values except the pH are expressed in mg/L

Besides lesser TS and TDS, no chromium is present in the discharged liquor of glutaraldehyde tanning. Hence, glutaraldehyde tanning is better in view of environmental aspects.

CONCLUSION The environmentally compatible tanning method is a dire need for the sustainable development of leather industries throughout the world. This investigation explored the potential of glutaraldehyde as a pre-tanning and re-tanning agent for the production of various types of leather. The reported data i.e. different strength properties, leather morphology, etc. have indicated the eligibility of glutaraldehyde to be used as a pretanning and post-tanning agent. However, gluteraldehyde alone cannot be a suitable tanning agent for the shoe upper crust leather production since the shrinkage temperature was lower than the boiling point of water.

The lower shrinkage temperature of upper leather may require different machineries for shoe manufacturing. The conventional shoe manufacturing process requires steaming at 100 °C which is not possible with the usual glutaraldehyde-tanned leather. Although the strength properties were found comparable with those of the chrome-tanned leather, that may be attributed to the use of syntan and other post-tanning chemicals. Gluteraldehyde could be used in combination tanning to produce quality leather with a reduction in the chromium load both in leather and effluents, which in turn contribute to reduction in the environmental impact.

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HOSSAIN I M, et al. Synthesis and Application of Graphene Oxide (GO) forâ&#x20AC;Ś TLR 3 (3) 2020 146-157.

Synthesis and Application of Graphene Oxide (GO) for Removal of Cationic Dyes from Tannery Effluents Md. Israil HOSSAIN1, Amal Kanti DEB1, Md. Zakir SULTAN2*, A. A. SHAIKH1, Manjushree CHOWDHURY1*, Md. Rayhan SARKER1 Institute of Leather Engineering and Technology, University of Dhaka, Dhaka-1209, Bangladesh Centre for Advanced Research in Sciences (CARS), University of Dhaka, Dhaka-1000, Bangladesh * zakir.sultan@du.ac.bd; israil.rafi.du@gmail.com

1 2

Original scientific article UDC 675.088:628.31 DOI: 10.31881/TLR.2020.12 Received 10 Jul 2020; Accepted 26 Aug 2020; Published Online 30 Aug 2020; Published 11 Sep 2020

ABSTRACT The increasing demands for dye in tanning industries have resulted in unconstrained throwing away of dyes into water bodies causing enormous environmental pollution. The removal of these dyes from effluents is mandatory and needs the recommendation of the latest technology and less expensive processes in this regard.

Graphene oxide (GO) was prepared, characterized, and applied in the process of removal of cationic dye. GO was characterized by FTIR, X-RD, SEM, and TGA and the following functional groups were found: â&#x20AC;&#x201C;COOH, OH, -C=O, and C-O-C. Basic Blue 3 (BB 3) was used as a model synthetic cationic dye. The dye adsorption studies were carried out in terms of the adsorbent dose, the pH, initial dye concentrations, and contact time.

The removal efficiency for BB 3 was found to be 100% dye concentration up to 600 ppm at pH 7 with 10 mg (0.1g/L) of the adsorbent, GO, within 6 minutes. In the case of real tannery effluents, the eradication efficiency was found to be 91.2%. The results revealed that GO was a suitable adsorbent for the removal of cationic dyes from tannery effluents.

KEYWORDS Graphene oxide, adsorption, effluent, tannery, environment

INTRODUCTION With the speedy progress of various industries like leather, textiles, paper, and printing the consumption of dyes has increased and at the same time effluents containing industrial dyes discharged into the water environment were increasing day by day. These discharged effluents are causing serious water pollution and posing a dramatically life-threatening complication for the environment. Due to their strong colour and visual pollution, dyes have the potency to tone down the environment. Many dyes used in leather-dyeing processes can biologically transform into toxic species and cause interference in the natural photosynthesis process [1-2]. It is quantified that more than 10,000 tons of dyes are utilized in different industries and around 100 tons is relieved into water reservoirs annually. Their concentration in effluents usually varies from 10 to 200 mg L-1 [5]. The untreated dye effluents are the key sources of poor surface-water quality and this creates new forms of diseases because of the ecological imbalance. Wastewater treatment is the key 146 www.textile-leather.com

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global environmental concern because water problems are becoming increasingly significant worldwide.

Different types of synthetic dyes have been used in various industries which leads to the contamination of the environment due to harmfulness to the human body, toxicity, and non-biodegradability [2-4]. Leather dyes are considered the most dangerous hazard for the water environment among various types of water pollution. Dyes are a common waste of leather processing, even a low concentration (1 ppm) of dye in water bodies is visible and makes it awful for use. The photosynthetic activities in the ecosystem cannot perform smoothly because of colouring agents in the water surface; these dyes have complex aromatic formations that make them fatal, carcinogenic, and non-biodegradable. There are many treatment processes, including adsorption [6-7] physical and chemical coagulation [8], photocatalytic degradation [9], advanced oxidation processes [10] and biodegradation [11], which are applied for the removal of colour dyes from industrial wastewater. Among them, adsorption is the most widely used, suitable, and inexpensive method to remove heavy metals and organic pollutants including dyes. Moreover, it is cost-effective and has high efficiency.

Graphene oxide (GO) is the most known graphene composite material which is an oxidized product of graphite. It is a highly oxidized form of graphite which consists of different types of oxygen functionalities. GO is a compound which has a hexagonal carbon lattice bonded to oxygen-containing groups such as carboxyl (-COOH), carbonyl (-C=O), epoxy (C-O-C) and hydroxyl (-OH). Graphene oxide (GO) has been considered widely as a prominent precursor and a starting material for the synthesis of different processable materials [12-13]. In the treatment of the dye laden wastewater the chemical groups containing oxygen play a significant role as they have large surface area. Many researchers have proclaimed that graphene oxide (GO) can be utilized as an adsorbent for the decontamination of dye molecules, and heavy metal ions [14-15]. Li et al. have established that fluoride can be eliminated by using graphene oxide [16] and graphene sponges have been tested by the hydrothermal analysis of graphene [17]. Graphene-based composites as nano-adsorbents have tendered prospective advantages for the treatment of various pollutants; for example, the adsorption capacity of graphene sponges was found to be 184 mg g-1, 72.5 mg g-1, and 11.5 mg g-1 for methylene blue, rhodamine B, and methyl orange respectively [18-19]. Basic Blue is a cationic dye, green and light blue in colour with the molecular formula C20H26ClN3O, M.W: 359.89 g, and CAS Number 4444-00-3.

Figure 1. Molecular structure of cationic dye, Basic Blue 3 [20]

In this study, we have prepared graphene oxide (GO) and it was synthesized from graphite powder by the oxidation method. Graphene oxide was characterized by FTIR, SEM, X-RD, UV-visible spectroscopy, and TGA analysis. The adsorption capability of synthesized GO was assessed in the degradation of a synthetic model of the cationic dye Basic Blue 3 (BB 3) and also real tannery effluents. The adsorption processes were investigated in terms of the adsorbent dose, the pH, initial dye concentrations, and contact time.

MATERIALS AND METHODS Chemicals and reagents Analytical grade chemicals and reagents were used for all experimental purposes and without any further purification. The principal raw materials were graphite powder (98% extra pure) which was bought from Loba Chemie Pvt Ltd. and the cationic dye (Basic Blue 3, CAS number 4444-00-3, linear formula C20H26ClN3O, www.textile-leather.com 147

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M.W.: 359.89 g) was collected from Stahl India Pvt Ltd. The other important chemicals and reagents for the production of graphene oxide are sodium nitrite (NaNO3), potassium permanganate (KMnO4), sulfuric acid 98% (H2SO4), hydrochloric acid (HCl) and hydrogen peroxide (H2O2).

Instruments and accessories Graphene oxide was synthesized and analysed using the following instruments and accessories: a digital scale (XB 220A, Precisa), a hotplate with magnetic digital stirrer ( PA 1180, LK LAB Korea), a pH meter, (HANNA instruments), a Fourier transform infrared spectrophotometer (FTIR) (Model IRPrestige21, Shimadzu Corporation, Kyoto Japan), a thermogravimetric analyser (TGA-50, Shimadzu), a UV-visible spectrophotometer (Model Spectro UV-Vis duel beam, uvs-2700, Labomed, Inc.), X-ray diffraction (Ultima IV, X-ray Diffractometer), scanning electron microscopy (SEM, JSM-6490LA, JEOL). A filter paper (102 qualitative, medium speed, pore 20-30µm) and a petri dish were used to prepare graphene oxide.

Synthesis of graphene oxide (GO) Graphene oxide was synthesized from natural raw materials - graphite fine powder (98% extra pure) - by following the Hummer’s method [21]. In detail, 3 g of graphite powder and 2 g of NaNO3 were added in 100 ml of sulfuric acid (H2SO4). The mixture was continuously stirred (60 rpm) for 2 hours. Then the mixture was cooled in an ice bath (below 20 °C) and an oxidizing agent, KMnO4, was slowly added (6 g) while stirring for 1.3 hours. After the reaction was completed, 100 ml of distilled water was added to the above mixture with continuous stirring and the temperature around 98 °C for 1.3 hours. After that the heater was turned off and 200 ml of distilled water was added and stirred for an hour. 10 ml of hydrogen peroxide (H2O2) (30%) was added to the mixture to remove the extra potassium per magnetite. In the end, the mixture was cleaned with HCl (5%) to diverge metal ions and rinsed with distilled water many times. The obtained solid composites were dried in a vacuum oven at 70 °C. Finally, the powder form of graphene oxide (GO) samples were used for the experimental purpose. The physical appearance of the synthesized graphene oxide is shown in fig. 2.

Figure 2. Optical image of prepared graphene oxide (GO)

Adsorption studies of cationic dye Preparation of stock solution Basic Blue 3 (molecular formula: C20H26ClN3O; molecular weight: 359.89g; CAS: 4444-00-3; Stahl India Private Limited) was used to prepare a stock solution of analytical grade. 1 g of BB 3 was dissolved in 1000 ml of 148 www.textile-leather.com

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distilled water to make 1000 mg L-1 / 1000 ppm stock solution. Various concentrations of dyes were prepared by diluting the appropriate amount of the stock solution using the formula V1S1= V2S2, where S1 is the stock solution’s concentration, V1 is the volume of stock solution being diluted, S2 is the dilute solution’s concentration, and V2 is the volume of the dilute solution. Millimetres (ml) is the unit of volume and milligrams per litre (mg/L) or ppm is the unit of concentration.

Calibration curve for Basic Blue 3 (BB 3)

HOSSAIN IMd, et al. Synthesis and Application of Graphene Oxide (GO

Calibration curve for Basic Blue 3 (BB 3)

The molar absorption coefficient of the BB 3 dye solutions was determined from the calibration curve The molar absorption coefficient of the BB 3 dye solutions was determined (absorbance vs. concentration) by using Beer-Lambert law. Seven different concentrations of 20, 50, 80, (absorbance vs. concentration) by using Beer-Lambert law. Seven different 110, 140, 170, and 200 ppm BB 3 solutions were prepared and their absorbance values were determined.

80, 110, 140, 170, and 200 ppm BB 3 solutions were prepared and their UV-vis spectrophotometer (Model Spectro UV-Vis duel beam, UVS-2700, Labomed, Inc.) was used for the determined. UV-vis spectrophotometer (Model Spectro UV-Vis duel beam, spectrophotometric determination. It gives distinct characteristics spectra for BB 3 at 654 nm (Fig. 3)

was used for the spectrophotometric determination. It gives distinct chara at 654 nm (Fig. 3)

Figure 3. Absorbance spectrum of Basic Blue 3 at 654 nm for seven different

Figure 3. Absorbance spectrum of Basic Blue 3 at 654 nm for seven different concentrations

Adsorption studies of BB 3

Adsorption studies of BB 3

The adsorption of dye (BB 3) onto the synthesized GO was studied at ro -1

volume (100 mL) of 200 ppm (200 mg L )volume of dye was taken in a beaker to The adsorption of dye (BB 3) onto the synthesized GO was studied at room temperature.

A fixed (100 studies.the The experimental following four parameters: the adsorbent dose, the initial ads mL) of 200 ppm (200 mg L-1) of dye was taken in a beaker to perform studies. The following pH, and contact time in order to explore the adsorp four parameters: the adsorbent dose, the initial adsorbate concentration, thehave pH,been andinvestigated contact time have graphene oxide. 0.1M NaOH or 0.1M HCl solutions were been investigated in order to explore the adsorption capacitythe of synthesized dye onto the synthesized graphene oxide.

The percentages of removal efficiency of BB 3 dye solutions were calculat 0.1M NaOH or 0.1M HCl solutions were used to calibrate the pH. The percentages of removal efficiency of

A − At BB 3 dye solutions were calculated by using the following equation: whereA0 Ais0 the is the equation: % R = 0 initial × 100% , where A0

initial absorbance (at λmax) and At is the final absorbance at time t in theatdye [2]. [2]. absorbance time solution t in the dyerespectively solution respectively

RESULTS AND DISCUSSION Characterization of synthesis graphene oxide (GO) FTIR analysis The FTIR spectra were applied to measure wavelength and intensity which are characteristic for specific types of molecular vibration and stretching that are used to identify functional groups of GO. The FTIR spectrum of GO is illustrated in fig. 4.

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absorbance (at

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Figure 4. FTIR spectrum of GO

The FTIR spectra of GO indicated the presence of various oxygen-containing functional groups on its surface, assuring its formation. The strong broad peak centred at 3442 cm-1 of stretching vibration of O–H bond referred to alcohol and carboxylic acid groups as well as adsorbed water molecules [22]. The functional groups such as hydroxyl, epoxy group, and carboxyl are introduced as characteristic for GO. The peak at 1714 cm-1 confirmed the carbonyl group (C=O) present in GO. The peak centred at 1625 cm-1 is mainly from stretching vibration of C=C bond indicating the presence of sp2 hybridized carbon along with a contribution from bending vibration of O-H bond resulting in higher intensity [23]. The peak found at 1000 to 1300 cm-1 of stretching vibration of the C-O bond referred to the presence of the epoxy group [24]. Therefore, all the peaks shown in the above figure satisfied the theoretical characteristic peak values of graphene oxide.

XRD analysis X-ray diffraction (XRD) is the most useful technique for the characterization of general crystalline materials. The XRD pattern of the synthesized graphene oxide (GO) is shown in fig. 5. The figure exhibits three major 2θ at 26.52, 43.58, and 54.84 angles. The characteristic peak at 26.52 is the major peak. The diffraction peak at around 2θ=260 confirmed the modification of graphite to graphene oxide [25]. Moreover, the characteristic of the XRD pattern also confirms that the synthesized GO is in crystalline form.

Figure 5. XRD pattern of GO

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SEM analysis The surface of the graphene oxide was investigated by scanning electron microscopy. SEM was used to examine the morphological structures and surface of the analysed samples. Fig. 6 depicts the SEM image of at low (left) and high magnification (right) of the GO sample. At low magnification, as shown in the first picture, the surface appeared agglomerate. Additionally, the sample was taken at high magnification to observe the surface and the observed particles appeared to have clear edges.

Figure 6. SEM images of graphene oxide (GO)

TGA analysis The percentages of weight loss with the increase in the temperature of GO has been investigated by thermal gravity analysis. The graph shows 18.27% weight loss within 24 to 483 °C due to the removal of surface moisture and the interlayer of absorbed water. By increasing the temperature, a large amount of weight loss occurred and it’s about 74.93% weight loss within 483 to 726 °C due to the decomposition of O2, CO, carboxylic, and CO2 gas. Eventually, it reaches 99.19 % weight at 800 0C.

Figure 7. TGA diagram of GO

UV- visible absorption analysis The UV-visible spectroscopy of graphene oxide (GO) is given in fig. 8. From the figure, it is noticed that the absorption peak of GO appeared near 280 nm, which represents the π-π* transition in the aromatic C-C bonds. Moreover, another significant peak was near 320 nm which is assigned to the transitions n-π* [26] of C=O bonds.

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Figure 8. UV-visible absorption spectroscopy for GO

Adsorption study of Basic Blue 3 (BB 3) on GO Molar absorption coefficient The molar absorption coefficient was determined by using the Beer-Lambert law from the slope of the plot of absorbance vs. concentration for Basic Blue 3 (BB 3) solutions at seven different concentrations: 20, 50, 80, 110, 140, 170 and 200 ppm. According to the Beer-Lambert law (A=εcl), it was found that the molar absorption coefficient of BB 3, ε=2.072×103 L mol-1cm-1.

Figure 9. Absorbance of BB 3 solution’s at different concentrations

Effect of adsorbents dose The effect of dissimilar adsorbent doses on the adsorption of BB 3 in aqueous solution was carried out by varying the adsorbent dose from 5 to 12 mg as shown in fig. 10. The doses are added to a series of 100 mL BB 3 dye solution of 200 ppm concentration at pH 7 and room temperature and stirred for 10 minutes at 120 rpm to get the optimum dose of the adsorbent. From the graph, it is visible that the adsorption efficiency increases with the increase in the adsorbent dose due to the higher number of available active binding sites for cations in the dye solution. In the beginning, the adsorption efficiency is 68.1% for a very low amount of the adsorbent dose (5 mg) and 88.58% for 9 mg of the adsorbent dose and then it increases up to 100% for the adsorbent dose of 10 mg. Therefore, the optimum dose for the removal of BB 3 was considered to be 10 mg of GO and used for further adsorption studies.

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Figure 10a. Absorption spectrum of six different adsorbent doses of GO for BB 3

Figure 10b. The effect of adsorbent doses vs. removal efficiency (%) of BB 3 on GO with an initial dye concentration of 200 ppm at room temperature and pH7

Effect of pH The effect of pH on adsorption was studied at room temperature by varying the pH from 2 to 12 to get both acidic and basic conditions in the initial BB 3 dye solution concentration of 200 ppm and the 10 mg adsorbent dose. The pH plays an important role in a solution containing ions as it affects the electrostatic interaction between the adsorbent and the adsorbate. From fig. 11, it is noticeable that the increase in the pH leads to the increase in removal efficiency. It is also manifested that cationic dyes completely were removed at the pH range 6 to 12 but at pH 2 the removal was only up to 75.83% and at pH 4 it was up to 86.44%. The lower pH values lead to protonation of the adsorbent surface; therefore, adsorption efficiency is low due to the electrostatic repulsion of the cationic dye molecules with the adsorbent surface [27]. The negative charges escalated when the pH raised and slowly de-protonation occurred in the surface of GO; therefore, the electrostatic correspondence increases with the cationic dye. The optimum pH value for the adsorption of BB 3 was found at pH 6 to 12; therefore, we considered pH 7 for adsorption studies.

Figure 11a. Absorption spectrum of different pH ranges of GO for the removal of BB 3

Figure 11b. The effect of pH vs removal efficiency (%) of BB 3 on GO with an initial dye concentration of 200 ppm and 10 mg adsorbent dose (0.1 g/l) at room temperature

Effect of contact time The effect of contact time on the removal of BB 3 with GO was observed by using 100 mL of 200 ppm dye solution, 10 mg adsorbent dose at pH 7 and at room temperature by varying the contact times. Firstly, the mixture was stirred for 5 minutes at 120 rpm and then the supernatant was collected in one-minute intervals. Fig. 12 shows that the removal efficiency increased rapidly with contact time for cationic dye BB 3 and it was found that after 5 minutes of stirring it removed almost 91% of impurities. It was discovered that, www.textile-leather.com 153

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initially, the rate of binding is high because of a higher number of open active sites which get saturated with the increase in the stirring time. After 6 minutes, the removal efficiency reached 100%.

Figure 12a. Absorption spectrum of different time intervals (0-6 minutes) of GO for BB 3

Figure 12b. The effect of contact time vs. removal efficiency (%) of BB 3 on GO with an initial dye concentration of 200 ppm, adsorbent dose 10 mg (0.1 g/l) at room temperature and neutral pH; under 5 minutes stirring

Effect of initial dye concentration The experiments were performed to manifest the effect of initial BB 3 dye concentration on adsorption onto adsorbent GO. For this experiment, the initial concentration of dye was varied from 200 ppm to 1000 ppm with optimum adsorption dose, time, and pH. It is noticeable from the result that the adsorption efficiency of BB 3 remained constant up to 600 ppm of dye concentration. Therefore, from fig. 13, it is observed that the removal efficiency decreased from 100% to 62.02%; this is due to the lack of receivable active binding sites needed for the high concentration of BB 3 dye solutions. The results also indicated that the higher uptake of dye at a low concentration of adsorbent may be attributed to the presence of more active binding sites on the surface of adsorbent GO for a small number of adsorbate species.

Figure 13a. Absorption spectrum of varying concentration (200-1000 ppm) of BB 3 adsorbed

by GO

Figure 13b. The effect of initial concentrations of BB 3 vs. removal efficiency (%) by GO with an adsorbent dose 10 mg (0.1 g/l) at room temperature, neutral pH and time 6 minutes after 5 minutes stirring

Adsorption studies of GO for real tannery effluents containing dyes The real tannery effluents containing dyes were collected in October 2018 from a tannery estate located in Savar, Bangladesh. The adsorption tests of tannery effluents were carried out before and after treatment.

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50 mL of tannery effluent was taken in a beaker and 10 mg of GO was added. Then the sample was stirred for 20 minutes at 300 rpm. The visible colours of the effluent were reduced and the adsorption test was carried out using a UV-visible spectrometer. It was found that the removal efficiency was 91.2%.

Mella et al. (2018) [28] found that in the treatment of leather-dyeing effluents with the associated process of coagulation-flocculation/adsorption/ozonation, the removal efficiency of colour was only 61.13%. Harrelkas et al. (2009) [29] studied the treatment of textile effluents by various combinations of physicochemical methods by adjoining coagulation/flocculation (CF) with adsorption on activated carbon (AC), and found that colour reduction was only 50%. These results indicate that the treatment of real tannery dye effluents by using GO as the adsorbent may be a feasible alternative and even applicable on a large scale.

CONCLUSION The studies exhibited that GO can be utilized as an efficient adsorbent for the removal of cationic dyes from tannery effluents. The adsorption performance of GO on the cationic dye BB 3 was found to be 100% by using only a 10 mg adsorbent dose (0.1g/l) at pH 7, within 6 minutes, with the dye concentration up to 600 ppm.

In the case of real tannery effluents, the removal efficiency was found to be 91.2%. The adsorption result was showed very fast and this may be due to the electrostatic interaction of oppositely charged molecules of the cationic dye and GO as the adsorbent along with their π-π interaction and the available binding sites on the surface of the adsorbent. The results from the experiments specified that GO as an adsorbent might be the best alternative when it comes to removing the cationic dyes from tannery effluents.

Acknowledgement The authors wish to acknowledge the Ministry of Science and Technology (MOST) the government of Bangladesh for financial support through M.S. NST Fellowship Program 2018-2019, ID: 795 and government order no: 3900.0000.012.002.03.18.22

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PATWARY S, Clothing and Textile Sustainability: Current State of Environmental... TLR 3 (3) 2020 158-173.

Clothing and Textile Sustainability: Current State of Environmental Challenges and the Ways Forward Sarif PATWARY Kansas State University, Manhattan, Kansas, USA patwary@ksu.edu Scientific review UDC 687:677:502.131.1 DOI: 10.31881/TLR.2020.16 Received 30 Jul 2020; Accepted 07 Sep 2020; Published 11 Sep 2020

ABSTRACT The global clothing and textile industry is facing immense criticism due to its enormous environmental pollution.

While demonstrating a slow adoption, brands, retailers, and manufacturers are recognizing the unsustainable nature of the industry. Consumers, too, are also becoming more aware of the environmental issues of the industry. Policymakers are coming up with relevant regulations to set the industry into a sustainable direction.

However, the plethora of information, ideas, suggestions, and strategies make it difficult to get a holistic idea of the environmental sustainability challenges that the industry is facing and the necessary actions it should take. This paper reviews the current state of environmental challenges, and the required actions articulated in the literature as related to the clothing and textile industry. Based on this review, suggestions are made for the key stakeholders of the clothing supply chain, and the profile of an environmentally sustainable clothing item is examined. The review revisits the complexity of the clothing supply chain and stresses the urgency of expediting actions.

KEYWORDS clothing, textile, apparel, garment, sustainability

INTRODUCTION The clothing and textile (CT) industry is one of the most polluting industries in the world. From raw materials extraction to the final disposal of garments, every stage of the clothing life cycle has a negative impact on the environment to some degree. Although many innovative ideas, thoughts, technologies, actions, solutions, and policies are available to minimize the negative impact of the industry, the industry is nowhere near to achieve a satisfactory environmental profile. The current sustainability score of the fashion industry is only 32 out of 100 [1]. If business-as-usual prevails, the fashion industry will use up 26 percent of the global carbon budget associated with 2 °C ceiling of global temperature by 2050, as targeted by the United Nations [2]. The fashion industry is responsible for 3-10 percent of global carbon emission annually [3-5].

Therefore, the industry must come up with green production strategies and innovative business models that can reduce its environmental burden and help achieve the desired climate target.

Today, many clothing brands are adopting various green production strategies, such as eco-friendly fiber (i.e., ogranic cotton, lyocell, etc.), sustainable yarn (produced from recycled fiber or consuming renewable 158 www.textile-leather.com

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energy), waterless dyeing (requiring no/little water), and sustainable packaging (made from recycled materials), etc. Similarly, many innovative business models are achieving popularity among consumer groups, such as circular fashion, subscription-based clothing (clothing rental), secondhand clothing, etc. However, these strategies and models are very inconsequential comparing to the scale and velocity of fast-fashion consumption (characterized by cheap price, shorter lead-time). This study investigates the environmental challenges of the CT industry and explores pathways towards a more sustainable production and consumption. In reviewing the literature, the following questions guided the researcher to synthesize the relevant information: What are the environmental challenges of the CT supply chain?

What suggestions are articulated for creating a more sustainable CT industry?

What makes a truly environmentally sustainable clothing product?

The review first outlines the CT supply chain and its environmental hotspots and then summarizes the key challenges in themes. Afterward, the required actions are discussed in light of those challenges and the recommendations are made for key stakeholders. Based on this discussion, the profile of a hypothetical sustainable clothing product is examined.

METHOD In this study, a non-systematic literature review approach was applied, using searches in Google, and Google Scholar. The search terms included ‘fashion sustainability’, ‘textile sustainability’, and ‘clothing sustainability’. The author made a conscious, joint, and iterative decision to consider an article as relevant. A nonsystematic review often skips an organized method of identifying, compiling, and synthesizing the body of literature on a particular issue [6, 7]. Rather, the approach focuses on some key studies to summarize a particular issue and present the description of the findings from the studies reviewed. It is “largely based on a knowledgeable selection of current, high-quality articles on the topic of interest” [7, p. 2].

FASHION SUPPLY CHAIN The fashion supply chain is globally stretched, complex, and fragmented [8]. Brands and retailers started exploring offshore production from the early ’80s to take benefit of cheap labor cost and lax environmental regulations of the developing countries. Searching for new cheap manufacturing locations and “race to the bottom” (i.e., profit maximization and cost minimization) brought the businesses to the Far East, with China, Bangladesh, India, Vietnam, Cambodia, Myanmar, etc. being the leading suppliers currently. By implementing different trade policies, for example, Multi-Fiber Arrangement (MFA), North American Free Trade Agreement (NAFTA), and Generalized System of Preferences (GSP), the United States, and European Union (EU) regulated the industry for a while. However, once China joined the World Trade Organization (WTO) in 2001, global brands and retailers flocked en masse to China, gradually leading to the state of affairs today.

In turn, developed countries like U.S., EU, Japan, etc. became the consumers (i.e., demand-side) and developing countries like China, Bangladesh, Vietnam, etc. became the suppliers (i.e., supply-side). For example, the U.S., EU (EU28), and Japan consumed 58.1 % of world apparel, whereas China, Bangladesh, and Vietnam together exported 43.8% of world apparel in 2019 [9]. From an environmental viewpoint, transportation, consumer use phase and the post-consumer waste-related negative impact became the burden of developed countries, whereas fiber production, materials processing, garment production, wastewater, solid waste and the related negative impact etc. became the burden of the developing countries. Although developed countries are managing negative impacts much better than the developing nations, the overall impact of the www.textile-leather.com 159

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fashion industry only grew bigger. For instance, the impact of the global apparel industry on climate change increased by 35 percent between 2005 and 2016 and projected to increase by 49 percent between 2016 and 2030 if business-as-usual prevails [4]. Each stage of the clothing and textile supply chain, as shown in Figure 1, either deteriorates or depletes natural resources in order to prepare the input for the next stage.

Only the end-of-life can potentially produce raw materials (from recycling) and energy (from incineration) to be used further in the value chain.

Figure 1. Resource and burden of clothing and textile supply chain

It should be noted that the different stages of textile and clothing lifecycles have a different level of environmental impact (Table 1). For example, the cultivation of natural fibers consumes a large amount of freshwater, whereas yarn and fabric manufacturing consumes a vast amount of energy. Similarly, not all textile fibers have a similar level of life cycle impact. For instance, a cotton fiber consumes a vast amount of water to grow and be processed, whereas a polyester fiber consumes a significant amount of energy during its production. As a result, considering water issues, cotton is worse than polyester; however, polyester would be worse when considering energy issues. Considering all the life cycle stages, a polyester-made product 160 www.textile-leather.com

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has about double the carbon footprint of that of a cotton-made product [10]. However, there are other impact categories besides carbon footprint for example, acidification, eutrophication, ozone layer depletion, toxicity to humans etc. Therefore, it is difficult to compare between different fibers and different stages without assessing their whole life cycle impact in a comparable system boundary, unit, and impact category.

Table 1. Environmental hotspots of various life cycle stages of clothing and textile supply chain

Fiber

Life Cycle Stage

Environmental Hotspots

Source

Natural fibers (such as cotton, wool, etc.)

Water, land, and chemicals (such as pesticides, insecticides, fertilizers, etc.)

[11,12]

Synthetic fibers (Such as nylon, polyester, etc.)

Petrochemicals (non-renewable) and energy

[13-15]

Yarn manufacturing

Energy

[14-16]

Fabric manufacturing

Energy and chemicals

[4, 17]

Dyeing and finishing

Water, chemicals, energy, and wastewater

[14, 18]

Assembly

Energy

[19, 20]

Primary use

Energy and microplastics

[21-23]

Extended use (Such as reuse, reselling, upcycling, downcycling, donation, sharing, renting, take-back etc.)

Energy and microplastics

[24,25]

End of life (either landfill or incineration)

Emission and groundwater pollution

[26]

Textile

Clothing

Consumer use phase

Although the CT industry pollution is not obvious like mining, oil, or the automotive industry, the environmental impact of its value chain is massive. It is argumentatively the second largest polluting industry in the world [27]. However, the global share of the greenhouse gas emissions of the industry is yet to be confidently established, ranging between 3 and 10 percent with a high degree of uncertainty [5]. Figure 2 presents a profile of the CT industry that gives a gloomy picture of its supply chain. As seen in Figure 2, the industry is characterized by global diffusion and race to the bottom state, with the production and consumption side predominantly divided by the global East and West. In addition, the CT industry is one of the massive polluters in multiple areas, such as freshwater consumption, carbon emission, water pollution, microplastic release etc. Moreover, clothing consumers are fast fashion-oriented (i.e., driven by cheap clothing items and the throwaway culture) and often involved in overconsumption. Between 2000 and 2015, global clothing sales have been doubled [2] and it is estimated that global apparel consumption will increase by 63 percent by 2030 [1]. If this profile of the industry does not change and current practices go on, the industry will have 1.5 times more impact on climate change than what its impact was in 2005 [4].

CHALLENGES OF THE CT INDUSTRY Lack of Transparency The further away the brand headquarter is from the supplier, the less controllable (i.e. less transparent) it becomes. In absence of a fully transparent supply chain, suppliers can cut corners through subcontracts, creating pretty much an unmanageable supply chain. As long as there is leeway for suppliers to cut corners, brands and retailers continue enjoying reduced prices, engendering many environmental issues along the way. That is exactly what happened in the fashion business over the last few decades. www.textile-leather.com 161

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Figure 2. Profile of clothing and textile industry

The price of clothing dropped 53 percent in the UK market and 3 percent in the U.S. market between 1995 and 2014 [43]. This unrealistic push for cheap production with shorter lead-time from retailers led suppliers to press on employee wages and poor factory conditions in developing countries, culminating in a massive disaster like the Rana Plaza collapse in Bangladesh [36]. Yet, brands and retailers are still competing for cheaper products from developing countries, both in the existing and emerging markets, rather than offering suppliers a reasonable price and collaborating with them to build a sustainable infrastructure. For instance, between 2013 and 2018, five years period since the Rana Plaza collapse, lead retailer firms paid 13 percent less to Bangladeshi suppliers [44].

The CT industry is cost-driven where the whole industry is competing to reduce the price. Any adoption of sustainable materials, processes, or technology immediately hits the economic bottom line of the brands.

Although a narrow segment of consumers is willing to pay extra money for sustainable products, general consumers are not even aware of fashion sustainability [39, 45], let alone paying extra money. In addition, a holistic understanding and implementation of sector-wise sustainable practices are yet to be achieved because of the confusion, competition, resistance to change and complexity. On a local level, small-scale artisanal businesses, which are underpinned by craft skill, are thriving. These businesses use biomaterials, for example, natural dyes, and utilize local artisanal skills and are more transparent. Small groups of educated consumers wear their products to oppose the current trend of the unsustainable fast-fashion industry [46].

On a global level, due to the disjointed supply chain, most brands and retailers do not fully know who makes their products and in what condition. Many suppliers in developing countries execute orders with the help of subcontractors, making it difficult for the brands to ensure supply chain transparency [47].

Inadequate Collaboration Since the CT supply chain is globally stretched and complex, the responsibility of taking sustainable action is also complex and requires global collaboration. Both the supply and the demand-side actors of the clothing chain need to take responsibility. Neither is it possible to bring the desired change by the consumers alone,

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nor is it possible by the brands and retailers alone. A combined effort from all parties is necessary with firm global and local public and private initiatives inspired by pro-sustainability ethics [8]. Without changing the current norm of production processes and patterns of consumption, the environmental cost of the industry will continue to increase [3].

Working towards a sustainable clothing supply chain needs massive collaboration of all parties involved.

On one hand, brands and retailers need to push the suppliers to carry operations sustainably. On the other hand, suppliers need to be pushed by the local governments to conduct business within an acceptable sustainability guideline. In the same way, the local government needs to be guided by international bodies to align environmental regulations with global science-based targets (SBT). However, if the sustainability ethos is present at the individual level and sustainability is ingrained in supplier's business strategy, they do not need to wait for the buyer to tell them what to do and how to do it. Therefore, businesses need to be proactive in doing business sustainably. They should seek after and adopt the best sustainable strategies on their own, rather than have outside bodies telling them what to adopt.

Although various institutions, organizations, centers, and non-profits are working on an individual level or with some collaboration, a global-level industry-wide collaboration is missing. For instance, the Center for Sustainable Fashion based at London College of Fashion identified eight key issues to deal with as related to fashion sustainability. Ellen MacArthur Foundation (https://www.ellenmacarthurfoundation.org/) is working towards a circular fashion. UN Alliance for Sustainable Fashion (https://unfashionalliance.org/) commits to ensuring sustainable development through â&#x20AC;&#x2DC;coordinated action in the fashion sectorâ&#x20AC;&#x2122;. Fashion Revolutionâ&#x20AC;&#x2122;s, a non-profit entity (https://www.fashionrevolution.org/), campaign, #whomademyclohtes, has brought transparency to the forefront of discussion. Yet, a global-level industry-wide central monitoring and governing body is imperative to drive the industry to hit the desired target.

Need for Conscious Consumption The consumer has a major role to play in making the fashion industry sustainable. They need to consume reasonably (i.e. avoid overconsumption), prefer durable apparels (i.e. avoid fast fashion), care for the apparels consciously (i.e. washing and drying properly) and dispose of in an appropriate way (i.e. reusing and recycling).

Knowledge of the impact of their actions is the key to the consumers taking proper action [48]. However, due to the attitude-behavior gap in consumer behavior [45], providing them with increased knowledge of sustainability issues might not drastically change consumer purchasing behavior. Rather, brands and retailers can influence change in consumer purchasing behavior by offering different value propositions, changing the pace of product offerings, and utilizing their marketing expertise [2]. Besides, local governments, media (both traditional and social media), NGOs and non-profit and international organizations should disseminate relevant information in an accessible way to the consumers. There need to be appropriate measures to make conscious clothing consumers who will take responsibility of their actions as related to clothing consumption.

Responsible consumers need support from their cultural mechanisms as well, in order to act. In that sense, the ways to reduce consumer demand on fast fashion are debatable. There needs to be a cultural and behavioral shift. There also needs to be a paradigm shift. A circular production and economic system are needed in place of today's linear system (i.e., take-make-waste). Technological innovation, supply chain transparency, and other such initiatives will not work if the industry produces more and more clothes in a linear system of business. Simply put, shifting towards sustainability is not a one-man task; it requires a concerted effort.

Society needs to reevaluate the way economic growth happens and the natural resources consumed in the

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process of that growth. Natural resources are limited, whereas economic growth is not. Does it mean we will continue enjoying economic growth until all the natural resources are gone? Then what?

Lack of Designer Engagement About 80 percent of environmental impact and costs are the outcome of the decisions made in the design phase [49]. Increasing garment longevity lies in designers’ hands. They decide on how emotionally attached consumers will be with apparel, what material to use, and how long the product lasts in terms of its appeal.

The designer’s knowledge of sustainability and a pro-environmental mindset is the key to this. However, working in a competitive market where designers follow the command of high-ups restricts them to follow their sustainable agenda.

In today’s fast fashion culture, propelled by cheap price and shorter lead-time, designers are busy with making low priced trendy designs. Not all designers have sufficient knowledge and resources to design for the environment. Since the average number of fashion collections for European brands has doubled in the last decade [43], designers’ productivity is presumably measured primarily by the ability to design intended products fast, not by how much environmental consideration is spent in designing. As a result, designer engagement in making sustainable fashion products seems to be enormously lacking.

WAY FORWARD Renewable Energy and Energy Efficiency Most of the environmental impact of the clothing supply chain comes from non-renewable energy-related greenhouse gas (GHG) emission. Fiber production, including polymer extrusion for synthetic fibers and agriculture for natural fibers, is the largest contributor to the clothing carbon footprint [15]. Textile production generates 1.2 billion tons of carbon dioxide equivalent (CO2e) annually, more than international flights and maritime shipping combined [2]. Considering the full life cycle, the annual carbon footprint of the fashion industry is 3.3 billion tons of CO2e [44]. The textile industry depletes 98 million tons of non-renewable resources each year, including oil, in the production of synthetic fibers, fertilizers for growing natural fibers and chemicals for producing, dyeing, and finishing purposes [2], in order to produce about 80-100 billion pieces of clothing annually [50]. The impact of the global apparel industry on climate change is projected to increase by 49 percent between 2016 and 2030 if business-as-usual prevails [4]. Therefore, it is very urgent to identify energy-intensive hotspots in different stages of the clothing supply chain and make a transition to renewable energy. Especially, current oil-based synthetic fibers (i.e., polyester, nylon, etc.) need to be replaced by alternative sustainable fibers offering similar properties. Similarly, energy-intensive stages, for instance, the spinning and weaving sector should reduce their dependency on non-renewable energy and make a hasty transition to renewable energy. However, it is worth noting that this transition is not going to be easy considering the limitations of energy alternatives in various geographical locations.

Eco-friendly Raw Materials As stated above, using eco-friendly raw materials can reduce a good share of negative impact along the supply chain. Oil-based synthetic fibers should be replaced by plant-based materials because of their comparatively low carbon footprint. For instance, the projected demand for polyester fiber by 2030 is about 70 million tons [51] and polyester has double the carbon footprint of that of a cotton shirt [10]. In the case of other innovative sustainable fibers, this number might go lower. Therefore, plant-based alternative fibers need to 164 www.textile-leather.com

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be explored more. Anyway, the cultivation and processing of those natural fibers should also include ecofriendly strategies in order to reduce the overall environmental footprint. For instance, cotton cultivation consumes 11% of all pesticides and 24% of all insecticides produced globally [52]. There are about 3,600 different types of textile dyes in the market and the textile industry uses 8,000 different chemicals in the dyeing and finishing activities [18]. Most of these dyes and chemicals are harmful and have a tremendous environmental cost. Therefore, plant-based fibers might not be the best case if agriculture and processing are not managed well. Sometimes, the majority of the negative impact happens in later life-cycle stages of certain fiber types [21]. As a result, life-cycle impact assessment is important to understand the holistic impact of each fiber type, take the right action, and chose among alternative material options.

Circular Fashion There is an ongoing movement to make the fashion value chain circular. Circular fashion is based on the ‘closed-loop’ or ‘cradle-to-cradle design’ principle, which requires a complete overhaul of the current linear (i.e. take-make-waste) system. In order to make fashion circular, the major contribution needs to come from the designers. Most of the environmental impact and costs are the outcome of the decision made in the design phase [49]. Therefore, designers need to be circular fashion-minded. In addition, purchasing and consumption patterns of consumers need to be changed to make circular fashion succeed. This could be achieved through education, such as including curriculum on circular fashion in academic programs offering fashion studies or instilling a sustainability mindset early in the age. For instance, the Amsterdam Fashion Institute, the largest fashion institute in the Netherlands, collaborated with Circle Economy (https://www. circle-economy.com/) and Fashion for Good (https://fashionforgood.com/) to offer the world’s first master’s program in circular fashion [53]. Likewise, the University of Arts in London created the Center for Circular Design in order to accelerate circular technologies, economies, and communities worldwide [54]. Many other programs incorporated circular design in the curriculum, such as the MA Fashion Futures course at London College of Fashion, Sustainable Fashion Academy’s online course on The Sustainability Fundamentals, etc. Apart from educational programs, there are other initiatives, such as Redress Design Award (https:// www.redressdesignaward.com/), a sustainable design competition, which educates emerging designers to drive a global circular fashion system. Similarly, Friday’s for Future campaign (https://fridaysforfuture. org/) encourages school students to take time off on Friday to participate in a demonstration, demanding action from policymakers to fight climate change. Apart from educational program, a robust infrastructure is needed in order to close the loop of fashion. However, if the CT industry does not switch to renewable energy and the consumption pattern of consumers does not change, circular fashion alone will not bring a tangible outcome [4]. Therefore, the CT supply chain needs to become circular as well as shift to renewable energy consumption.

Product longevity Product longevity and a longer use of fashion clothing items can reduce environmental impact significantly.

Allwood et al. [21, p. 40] reported, “Extending the life of clothing so that demand for new products is reduced by 20% leads to a reduction of about 20% in all measures in the producing country”. Other studies also reported the benefit of a direct reuse of clothing [55, 56]. Using second-hand clothing that can reduce the need of 1 kg of virgin cotton fibers might save 65 kWh and up to 90 kWh for polyester [57]. However, a longer use of quality products is in direct conflict with fast fashion, which promotes throwaway culture.

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habitual, behavioral and economic shift. In order to extend the garmentâ&#x20AC;&#x2122;s useful life, the physical durability of the products might not be the only solution. There needs to be some type of consumer attachment to the product. Designers might approach two strategies: emotional durability and co-creation. Emotional durability can be achieved by offering the right fit, transparency of production, brand loyalty etc., while co-creation is the strategy of involving consumers in the designing of their own clothes [58]. Co-creation provides a consumer with a unique opportunity to make the products they will keep longer by collaborating with brands through some kind of a platform.

Supply Chain Transparency Supply chain transparency is crucial for multiple reasons. It gives brands and retailers good control over supply chain optimization, helps improve brand loyalty of consumers, and identifies risks, to name a few.

The most important aspect of supply chain transparency of the CT industry is that it will drastically reduce the undocumented subcontracting, and thereby those less visible social and environmental costs of the business. In many of the developing countries, subcontracting is prevalent among suppliers. There should be a proper guideline for subcontracting and transparent disclosure of it. Apart from subcontracting, supply chain transparency is needed to ensure proper identification of what materials are being used and who is making the products. Ensuring these two aspects is the key to take care of many social and environmental issues.

Conscious Consumer Above all, there is no better way than consumers being conscious of their purchasing, care, and disposal behavior. A popular approach to making conscious decisions in clothing consumption is Slow Fashion. The movement focuses on informed and careful consumption by consumers [59]. In a slow fashion mindset, consumers value the quality over quantity, tradition over speed, and ecological well-being over resourcedepleting growth. The consumer purchasing decision is the biggest driver of product demand. In todayâ&#x20AC;&#x2122;s social media era, electronic word of mouth (eWOM) goes viral in no time. Therefore, by creating market demand for sustainable fashion through objective communication and spreading knowledge in social media, consumers can drive the brands towards sustainable fashion [60]. Various social media platforms, like Facebook, Twitter, Blogs etc. can make a great impact in this regard. Especially, bloggers and other opinion leaders can disseminate relevant information over these media [61].

The use phase (washing, drying, and ironing) is an important stage of the clothing life cycle. For certain fabric, for example, cotton, the use phase contributes most of the carbon footprint [21]. Therefore, consumers need to be educated regarding the proper care of the garments. In addition, a more sustainable washing machine needs to be promoted. Another great problem associated with the clothing use phase is microplastic pollution. Each year half a million ton of plastic microfibers, equivalent to 50 billion plastic bottles, are released into the ocean from textile washing activities [3]. About 20-30% of the primary source of microplastic pollution is synthetic clothing [25]. One washing of 6 kg load might release about 700,000 fibers [22]. Three interventions were suggested by the House of Commons Environmental Audit Committee [44] to reduce microplastic release from apparel washing: a) Change in the yarn and clothing design/construction b) Modification in the washing technology, for example, improved filtering system and c) An improved filtration system in the wastewater treatment process.

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SUGGESTIONS FOR KEY STAKEHOLDERS One can easily understand that making fashion sustainable requires a massive level of global collaboration, as well as a cultural and economic shift. A plethora of information and strategies is available, which makes it even more confusing to come up with a unified goal for both the supply and the demand-side stakeholders.

There is an urgent need for a central governing body, which would set up global guidelines, frameworks, and targets, as well as hold accountable different supply chain players. As such, the following suggestions can be made for various authorities: International bodies • Impose a tax on natural capital usage through a standardized framework. This way, brands and retailers as well as manufacturers will be careful in using natural capital.

• Impose carbon tax on the emission of GHG gases. This way, manufacturers would be careful about their emissions.

• Accelerate the circularity of the business, because a 1% increase in the market of the circular model has the potential to reduce GHG emissions by about 13 million tons [5].

• Set up a framework on social media marketing strategies centering on fashion advertisements. Nowadays, social media is playing a big role in accelerating fast fashion, thereby overconsumption and waste [44].

• Ensure responsible consumption and production.

• Ban burning of unsold stocks of textile and clothing goods.

Buyer countries • When imposing taxes, make a clear distinction between the brands and retailers who do the business sustainably and those who do not.

• Hold brands and retailers responsible to take care of the clothing waste they generate. Retailers should have a transparent account of the afterlife of the garments they are selling. The government should impose a tax on them in order to manage textile waste in a better way. For example, a charge of one penny to producers can generate a huge amount of money to take care of textile waste responsibly [44].

• Make it mandatory for brands and retailers to make their supply chain transparent. Brands and retailers must know which factory is making garments for them.

• Make it mandatory to publish corporate sustainability reports annually.

• Ensure an air-dry facility for the consumers on a community basis.

• Implement a door-to-door garment collection system on a community basis.

Supplier countries • Ensure that factories are operating in a standard environmental and social framework.

• Discharge wastewater after treating it well (as per set standard).

• Offer solid waste treatment comparable to international standards.

• Ensure that factories are safe and the employees work in a safe condition.

• Ensure that factories are offering the employees a minimum wage set by the local laws.

Consumers • Avoid overconsumption.

• Understand how overconsumption affects the environment and the society.

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• Wear items for longer. If consumers do not want to use items that still have their useful life left, they should donate or sell them to their family, friends, and community through different channels, such as social media groups, thrift stores, secondhand stores, by swapping etc. Clothing reuse substitutes new purchases, leading to the reduced need for virgin material consumption and thereby potentially saving the environment [62].

• Care for the garments sustainably. In other words, they should follow the following steps during the care phase [23, 63]: • Wash less if you can • Utilize the full load of the machine • Use cold setting (30 degrees or less) • Use liquid detergent (because it is less abrasive) • Use softener (because it reduces friction) • Reduce spin speed (it provides less agitation) • Dump lint fibers into the bin, not in the sink

WHAT MAKES A TRULY ENVIRONMENTALLY SUSTAINABLE CLOTHING PRODUCT? Although the industry can follow many different strategies to do things in the right way, the question becomes what a truly sustainable clothing product is. It is almost impossible to produce a clothing item that is a hundred percent clean and green. A truly sustainable item does not exist in the market. What exists today are partially sustainable products. For instance, a clothing item might be made of organic cotton, but did not take care of the harmful production processes involved. Similarly, an item might be produced with zero-waste in mind, but with the usage of harmful chemicals in the dyeing stage. Therefore, it is important to look at the key steps that need to be in place to make a product fully sustainable. Looking at these steps again demonstrates how complex the supply chain is and how challenging it is to make sustainable clothing. Although it is not an exhaustive list, the key steps for producing a fully sustainable clothing item are the following: • Made of 100% natural fibers, grown organically with the best available water and land management, locally produced and sourced if possible.

• The major stages (i.e. spinning, weaving, dyeing, and cut-and-sew process) are 100% renewable energybased and efficiently managed water, chemical and solid waste resources; carried out in a LEED-certified facility.

• Utilizing bio-based chemicals and dyes in dyeing, printing, and finishing operations. If synthetic dyes are used, only certified chemicals are used and managed properly. The wastewater is treated well before discharging.

• During the assembly process, zero-waste fabric cutting is adopted. Solid waste is managed properly.

• All the accessories’ materials (i.e. buttons, threads, zippers, lace etc.) are sustainable.

• Utilizing a cradle-to-cradle design approach. The durable and emotional element is incorporated within the product by properly researching consumer data.

• The most sustainable shipping route is used (for exporting items). For instance, maritime shipping instead of airfreight.

• The final price of the product is calculated based on materials’ cost, manufacturing cost, cost of natural capital, a penalty for resource depletion, and margin. The final price does not disregard the cost of externalities. A proportionate share of the profit made is spent in recompensing depleted natural resources.

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CONCLUSION This study conducted a review of the main body of literature concerning the current state of the CT environmental sustainability and the recommended ways forward. Through a non-systematic review, the study made a synthesis of the key studies and offered an insightful discussion regarding the CT environmental sustainability. The study also summarized the initiatives that various stakeholders may take and offered an ideal profile of a truly environmentally sustainable clothing item. The discussion revisited the complexity of the CT supply chain and stressed the need for an industry-wide collaboration as well as a central monitoring authority.

Understanding the environmental impact of the clothing life cycle and the associated processes is important to take corrective actions. The current understanding is very limited, as we do not have a comparative understanding of different textile materials. Only cotton and polyester fiber-related life- cycle studies are abundant, whereas other fiber-related studies are not comprehensive. With COVID-19 disrupting all aspects of life in 2020, there is no better time to take stern climate actions than now. This pandemic should make the world conscious about the impact of climate change. While in the case of COVID-19, society can continue to function to some extents, there would be a complete standstill in case of a climate-related disaster. Therefore, it is high time both the supply and the demand-side actors became conscious of the impact of their actions on the environment and the society. Brands and retailers should reduce the environmental burden from the top impactful areas, such as fiber production, spinning, dyeing and finishing, fabric preparation, and assembly [4]. In order to align with the industry-wide 1.5-degree climate target, the industry needs to cut its current level of emission in half [4, 5]. One of the potential pathways is to switch to either 78 %-renewable energy or 72 % energy efficiency to achieve the emission reduction target by 2030 [4]. Hence, there should be a coordinated effort to set industry-wide global targets and hold stakeholders accountable to align with that target.

Overall, the CT industry needs to resort to renewable energy, minimum use of fossil fuel, energy efficiency, and circular economy. Consumers need to consume consciously. Businesses need to value labor forces and should treat them fairly. Designers need to emphasize the durability of the product and map the possible materials required to make the product. They should have enough knowledge to choose from sustainable materials. In order to extend the garmentâ&#x20AC;&#x2122;s useful life, the physical durability of the products might not be the solution. Designers need to incorporate some types of consumer attachment to the product. Two strategies might be emotional durability and co-creation. Emotional durability can be achieved by offering the right fit, transparency of the production, brand loyalty, transparency of the place and the people making the products etc. Co-creation can be achieved by customers designing their products through some kind of a platform, adding their valuable input into the product so that they celebrate the product for a long time. However, any solution that compromises with the hedonistic and psychogenic pleasure consumers derive from clothing will not be viable. Potential solutions should be able to offer these opportunities to consumers as well as tackle the environmental impact. At the same time, any quick fix of the problem will create a problem shift, meaning somebody somewhere along the supply chain will pay the price. A new economic model needs to be in place, one that will support both sustainability and growth.

This study offers insight into crucial research directions. For instance, future studies should focus more on identifying the evidence of the environmental benefit of various strategies discussed in this study, such as the impact of different pathways of circularities on climate target, potential scenarios of modified consumer clothing-care behavior etc. Studies should also emphasize understanding the challenges and opportunities of supplier countries in coping with the accelerated climate targets. Furthermore, future studies should inves-

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tigate how the social and economic dimension of sustainability evolves with different routes of achieving climate targets. Only a comprehensive benchmarking of the GHG emission of the CT industry, backed by scientific evidence, and coordinated actions will be able to put the industry on the right track.

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INSTRUCTIONS FOR AUTHORS EDITING YOUR MANUSCRIPT Please use our template to edit your article before submitting for review.

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The received manuscripts are categorized into: Original scientific papers means it is the first publication of original research. It must be presented so that the research can be repeated giving results with equal precision within the limits of the trial error, which means that the correctness of analyses and conclusions can be checked.

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Conference paper is the work presented at a professional conference organized on local, regional or state level. It will be published if it has not been published in full in Proceedings, as a report, a study etc.

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In-text citation examples The in-text citation is placed immediately after the text which refers to the source being cited: ...and are generally utilized as industrial textile composites.[1] Including page numbers with in-text citations: Page numbers are not usually included with the citation number. However should you wish to specify the page number of the source the page/s should be included in the following format: …and are generally utilized as industrial textile composites.[1 p23] Hearle [1 p16-18] has argued that...

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Electronic journal article – Niculescu O, Deselnicu DC, Georgescu M, Nituica M. Finishing product for improving antifugal properties of leather. Leather and Footwear Journal [Internet]. 2017 [cited 2017 Apr 22];17(1):31-38. Available from: http://revistapielarieincaltaminte.ro/revistapielarieincaltaminteresurse/en/ fisiere/full/vol17 -nr1/article4_vol17_issue1.pdf ▪ Author AA, Author BB. Title of article. Title of Journal [Internet]. Date of publication YYYY MM [cited YYYY Mon DD];volume number(issue number):page numbers. Available from: URL Book – Hu J. Structure and mechanics of woven fabrics. Cambridge: Woodhead Publishing Ltd; 2004. 61 p.

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[90-114].

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Thesis/dissertation – Sujeevini J. Studies on the hydro-thermal and viscoelastic properties of leather [dissertation]. Leicester: University of Leicester; 2004. 144 p.

▪ Author AA. Title of thesis [dissertation]. Place of publication: Publisher; Year. Number of pages Electronic thesis/dissertation – Covington AD. Studies in leather science [dissertation on the internet].

Northampton: University of Northampton; 2010. [cited 2017 Jan 09]. Available from: http://ethos.bl.uk/ OrderDetails.do?uin=uk.bl.ethos.579666 ▪ Author AA. Title of thesis [dissertation on the Internet]. Place of publication: Publisher; Year. [cited YYYY abb. month DD]. Available from: URL This quick reference guide is based on Citing Medicine: The NLM Style Guide for Authors, Editors, and Publishers (2nd edition). Please consult this source directly for additional information or examples.

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Notes

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