Water Treatment Using Iron Nanoparticles

1 Synthesis, Characterization, and Biomedical Application of Nanostructured Materials: Water Treatment Using Iron Nanoparticles Abstract The world is experiencing a significant rise in the number of ground sites contaminated with organic and inorganic materials. These contaminants reach the ground water making it unsafe for human and animal consumption. Contamination of water affects its supply to the people, besides increasing the health risks among those who drink such water. Conventional water treatment technologies have not sufficiently addressed human water needs. The use of nanomaterials in water treatment holds the promise of resolving all human water needs. This paper explores the possibility of using iron nanoparticle sin treatment of water.

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2 Synthesis, Characterization, and Biomedical Application of Nanostructured Materials: Water Treatment Using Iron Nanoparticles The world has experienced an unprecedented increase in populations over the last few decades. The increase in global populations has subsequently elevated the pressure on water supplies. This implies that the number of people in need of a constant supply of safe, clean water has been increasing day by day. Further, the rise in global population has led to an increment in waste production. Gutierrez, Dziubla, and Hilt (2017) noted that the quantity of domestic and industrial waste produced globally has almost tripled over the last two decades.

Over the years, different measures have been put in place to minimize the risk of water pollution. The development of efficient waste management facilities is, nonetheless, a costly affair that many nations are still struggling to accomplish. Consequently, waste materials end up being dumped in areas where they easily mix with groundwater leading to pollution. Pasinszki and Krebsz (2020) noted that present and past pollution have been a huge safety and environmental concern around the world.

Protection and remediation of the environment comprise the biggest challenges in modern-day life. These challenges are contributed largely by the exhaustion of water resources, excessive has of the environment, uncontrolled developments that utilize groundwater, climate change, and global warming (Guerra, Attia, Whitehead & Alexis, 2018). Industrial advancements have been blamed for rampant environmental pollution. Industrial sectors, doubtlessly, produce large quantities of wastewater containing inorganic and organic compounds (Santhosh, Malathi, Dhaneshvar, Bhatnagar, Grace & Madhavan, 2019). Due to the non-biodegradable nature of most of these compounds, they exert toxic effects on marine life and other animals that depend

3 on sea animals. Other than industrial plants, pollution is also contributed by abandoned mining sites and domestic activities among other sources.

Problem Statement Water contamination and limited access to clean water continue to be huge environmental problems facing the people globally. The United Nations, as reported by Gutierrez, Dziubla, and Hilt (2020), estimates that over 3.1% of global deaths are associated with unsafe and inadequate access to water. Access to clean safe water has been acknowledged not only as a human right but a critical factor for social sustenance, technological development, and economic productivity.

Thus, there is an ever-growing need for people to develop effective and affordable technologies to enhance water quality to satisfy human and environmental needs. Unfortunately, despite water pollution is a huge problem that decreases the already little amount of clean water supplied to the people, the existing water treatment technologies are not able to meet the growing demands for the constant supply of clean, safe water. People in some settings have been forced to use water from unconventional sources to replenish the dwindling conventional sources. The use of polluted water, as well as water from unconventional sources, predisposes people to the risk of numerous water-borne diseases including cholera, and dysentery among others.

Current Status Contamination emanating from organic pollutants remains to be a huge health risk to human beings and aquatic environments. Pharmaceutical and personal care products (PPCPs), pesticides, polychlorinated biphenyls (PCBs), industrial wastes, polycyclic aromatic hydrocarbons (PAHs), and other Persistent organic pollutants (POPs) are found in almost all environments (Santhosh, Malathi, Dhaneshvar, Bhatnagar, Grace & Madhavan, 2019). These organic pollutants have consistently been found in drinking water, ground and seawater, as well

4 as domestic and industrial wastes, thus, increasing their risk of entering the food chain subsequently causing devastating health effects on those who consume contaminated substances (Hao, Liu, Wang & Li, 2018).

Gutierrez, Dziubla, and Hilt (2020) noted that in a study to evaluate the level of organic pollutants in European marine animals, the findings revealed that PCB levels were dangerously high in crustaceans. This implies that the crustaceans were living in environments that were heavily polluted with inorganic substances. In other studies, researchers have shown extremely high levels of bioaccumulation of PCBs in fish, birds’ eggs, and human beings (Gutierrez, Dziubla & Hilt, 2020). This is an indication that organic pollutants pose a ubiquitous threat to the health of people and animals.

Currently, numerous strategies have been employed to improve the quantity and safety of water supplied to the people. People across all settings have been made aware of the impact of water pollution on their health besides being sensitized on the best ways to avoid pollution.

Unfortunately, water pollution is still rampant (Gutierrez, Dziubla & Hilt). To ensure the water being supplied to the people is clean and safe, local authorities have invested heavily in water treatment plants. Large quantities of chemicals such as chlorine are utilized in these plants to improve the safety of the water. Further, various physical and chemical treatment strategies have been developed to enhance the treatment of wastewater as well as water obtained from unconventional sources. These treatment tactics include photocatalytic degradation, ion exchange, adsorption, electrochemical methods, and membrane filtration among others.

Adsorption and photocatalytic degradation have particularly gained popularity due to their ability to eliminate organic and inorganic pollutants (Santhosh, Malathi, Dhaneshvar, Bhatnagar, Grace & Madhavan, 2019). These interventions are eco-friendly and have low operating costs. Local

5 governments prefer to use these interventions due to their effectiveness in eliminating toxic pollutants. Nonetheless, the people’s demand for clean water surpasses the rate at which water is being treated and supplied.

Main Issues Facing the Field Current remediation technologies have proven insufficient in achieving 100% improvement in water quality and access to clean water. Water treatment plants are currently facing huge problems. For instance, huge operation and maintenance costs are threatening to cripple the current remediation interventions. These facilities consume huge quantities of electricity to filter wastewater (Russell, 2019). Although some facilities have shifted to green energy, the cost of installing solar equipment is still enormous. Another issue facing water treatment and wastewater management is the lack of skilled staff. Effective treatment of water requires efficient and productive workers. Unfortunately, only a few skilled employees are available to conduct water treatment duties. Environmental footprint has also been a huge problem. The treatment of wastewater and water from unconventional sources is intended to make it eco-friendly (Ghernaout, Alshammari & Alghamdi, 2018). Challenges arise because the organic matter has to be properly disposed of to prevent recontamination of water sources. It is therefore, essential to design and develop equipment that utilizes highly catalytic materials to address the challenges associated with the creation of a pollutant-free environment.

Proposed Solution Regrettably, even the treatment of all wastewater and unconventional water sources cannot achieve the global demand for clean safe water. The rampant problem of water pollution indicates that there is a need to establish cost-effective technologies for waste management and water treatment. This paper proposes the use of nanomaterials-based technology in water

6 treatment activities to meet global environmental and human water needs. Zero-Valent Iron Nanoparticles (nZVI) and Iron oxide magnetic nanoparticles (IONPs) are some of the nanomaterials applicable in water treatment technologies. These nanomaterials possess highquality properties such as magnetism, efficient adsorption capacity, high surface area to volume ratio, high reactivity and fast kinetics that are suitable for the separation of pollutants from water (Gutierrez, Dziubla & Hilt). The hypothesis for this project is that Zero-Valent Iron Nanoparticles have the potential to improve the water quality to achieve the set standards while maximizing efficiency in the removal of pollutants. Researchers and health professionals consider nanotechnology as a potential alternative to increase the quantity of water supplied to the local people through remediation of already contaminated water in addition to providing access to unconventional sources. In this technology, the Iron Nanoparticles are used as nano adsorbents thus enhancing the magnetic separation of pollutants during water treatment.

Research Questions The main research question for this project is whether the use of Zero-Valent Iron Nanoparticles in water treatment has the potential to improve the quality, safety, and amount of water supplied to the people. Another research question that will guide his project is whether nZVI is safe. The project will also explore the main properties that make nZVI effective and safe for use in water treatment.

RESULTS Studies have confirmed that groundwater has a higher risk of contamination from organic micro-pollutants, metallic substances and inorganic elements. Wang et al., (2018) for instance, revealed that organic micro-pollutants are being detected in surface and groundwater at an alarming rate. Regions surrounding industrial plants, major cities, and other commercial centers

7 have a high level of ground pollution than other regions across the world (Phenrat, Skácelová, Petala, Velosa & Filip, 2020). The presence of contaminants in groundwater and soil is a great danger to the health of people and animals. Contamination of groundwater has been acknowledged as a huge problem in Europe and the United States. The figure below shows the percentage of groundwater and soil pollution in Europe.

Fig 1: Soil and groundwater pollutants in Europe (Phenrat et al. 2020).

Pasinszki and Krebsz (2020) recommended the use of effective ways to remove toxic elements from water to make it safe for human consumption. One of the proposed strategies was Nanosized zero-valent iron particles. The use of these nanomaterials has also been supported by Pasinszki and Krebsz (2020) and other researchers. To determine its effectiveness and safety of zero-valent iron nanoparticles, these materials have been subjected to comprehensive analysis.

Studies show that nanoscale particles with oxide outer surfaces and metallic cores demonstrate broad applicability for the treatment of water containing heavy metallic substances and toxic organic compounds.

How iron Nanomaterials could resolve the identified problems Findings from different studies on Nanosized zero-valent iron show that these nanomaterials can be effectively utilized in the removal of toxic compounds from water.

Industries produce huge quantities of organic and inorganic compounds. These compounds are not only biodegradable, but also persistent and toxic (Pasinszki, & Krebsz, 2020). The removal

8 of these toxic compounds from groundwater is extremely challenging without effective technology. nZVI provides a combination of magnetic, adsorption, and reduction functions appropriate for the removal of contaminants from water (Guerra, Attia, Whitehead & Alexis, 2018). Iron has a remarkable reduction potential as compared to other metals. The table below shows the negative reduction potential of iron, aluminum, nickel and zinc.

Fig 2: Standard reduction potentials of metals (Liu et al. 2018). nZVI is usually covered with capping materials aimed at reducing reactivity while enhancing the nanoparticle properties. Notably, however, a balance must be sought between improved properties and reduced reactivity. Guerra, Attia, Whitehead and Alexis (2018) pointed out that the enhanced properties together with the efficiency of nZVI make them particularly beneficial in water remediation processes due to their high surface area to volume ratio. The figure below highlights some of the capping materials used on nZVI and the respective pollutants removed from water and soil.

9 Fig 3: Organic compounds removed from the water and soil (Pasinszki, & Krebsz, 2020).

The strong reducing power of nZVI, as highlighted by Abd El-Lateef, Ali, and Saleh (2018), makes these particles suitable for use as a reductant in water purification processes. This nanomaterial can also be used as an adsorbent. The figure below shows some of the mechanisms through which toxic metallic materials and chlorinated compounds are removed from water by nZVI.

Fig 4: Mechanisms of removal of toxic components from water (Pasinszki, & Krebsz, 2020) Appropriate concentrations of nZVI have to be used to ensure the anticipated reduction effects are achieved. Contamination of soil almost always results in the contamination of groundwater. Pasinszki and Krebsz (2020) noted that this contamination can be reduced through the creation of reactive zones containing either immobile nanoparticles or nanoparticles that migrates to contaminated areas. nZVI can be applied and distributed on topsoil using simple agricultural practices as illustrated in the figure below.

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Fig 5: Treatment of contaminated groundwater (Pasinszki, & Krebsz, 2020) Synthesis and Characterization of Iron Nanoparticles Nanosized zero-valent iron materials are usually produced through chemical or physical methods (Pasinszki, & Krebsz, 2020). These processes may involve the reduction of the size of larger iron materials to nanoscale parameters or the buildup from atoms produced from ions and iron-containing molecules. In the top-down synthesis of nZVI, iron microparticles are milled to fine nanosized particles. A capping layer is added to the nanoparticles during synthesis to reduce reactivity before the particles are used in water treatment. The figure below highlights the topdown synthesis of nZVI.

Fig 6: Top-down synthesis of nZVI (Pasinszki, & Krebsz, 2020). nZVI can also be synthesized through laser ablation (Pasinszki, & Krebsz, 2020). This process involves the irradiation of a larger iron material with a laser beam to melt and vaporize

11 the metal. Iron nanoparticles are formed once the hot metal atoms are cooled by the surrounding medium.

Progress in Nano applications Although the use of nZVI in the treatment of water is a potentially beneficial exercise, it has several disadvantages. For instance, these nanomaterials can undergo extensive oxidation and aggregation, thus making them hard to separate from solutions (Liu, Chen, Guan & Xu, 2018). Various procedures have been proposed to solve these problems. The proposed approaches include surface coating, encapsulation in a matrix, doping the nanomaterials with other metals, emulsification, and conjugation with supports (Liu, Chen, Guan & Xu, 2018).

These procedures help to reduce the reactivity of the nanomaterials when not in use. Further research is being conducted to determine if nZVI can be used in soil remediation. Findings from these studies are expected to guide the full-scale application of the nanomaterials in polluted soil and real water contaminated sites. The fig below shows some of the areas where nZVI can be applied for treatment and remediation purposes.

Fig 7: Application areas for zero-valent iron nanoparticle (Pasinszki & Krebsz, 2020) DISCUSSION The use of iron has a history dating back many years. This natural resource has numerous benefits for human beings. Over the years, people have been carrying out extensive studies to determine the best ways to utilize iron components to improve their health and quality of life.

12 Analysis of iron over the years led to research on how it can be utilized in the purification of polluted water and contaminated soil (Liu, Chen, Guan & Xu, 2018). Further research has been conducted to determine the best form in which to use iron components for environmental protection and remediation practices. Research on the application of iron has been boosted by the advancement in nanotechnology. The introduction of nanotechnology in water treatment, doubtlessly, represents important technological advancement. Nanoscale iron particles, as highlighted by Ebrahiminezhad et al. (2018), have attracted huge interest as potential water purification materials due to their distinct chemical and physical properties. Complex physical and chemical strategies have been developed to facilitate the production of nZVI. Structural and chemical aspects of nZVI The applicability of iron nanoparticles is based on their properties including reactivity and mobility. These properties are influenced by the size of the nanoparticles, the modifying capping material, the surface, the support material, and the oxide layer (Pasinszki, & Krebsz, 2020). The manufacturing process also influences the properties of the nanoparticles. The synthesis of iron nanoparticles is guided by the proposed use of the nanoparticles. For instance, some applications require bare nZVI that are more reactive than granular nZVI (Lei et a., 2018). nZVI constitutes a thin layer of surface oxide and a metallic iron core which form a core-shell structure (Wang et al., 2019). The thin oxide layer is usually formed when nZVI is immersed in water. In water treatment activities, nZVI with proper oxide shell thickness is used to ensure that the transfer of electrons is not blocked. These nanoparticles are also preferred since they are more stable than pyrophoric iron nanoparticles (Kašlík et al., 2018). The images below show Atomic Force Microscopy of zero-valent iron nanoparticles.

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Fig 8: nZVI particles (Hassan, Hassan, Hamad & Shther, 2019)

Fig 9: nZVI particlesat (Hassan, Hassan, Hamad & Shther, 2019) The use of nZVI has received support from researchers across the board. Liu, Chen, Guan, and Xu (2018) for instance, noted that even though these nanoparticles are highly reactive and thermodynamically unstable in the presence of water, the oxides formed do not completely block the transfer of electrons to the contaminants. The nZVI is thus better purifiers than other nanomaterials. nZVI is a better reducing agent since it allows electrons to flow from the surface of the metal to the contaminated solution. Notably, iron can undergo oxidation in the presence of H+ or H2O to produce the potential reducing agents Fe2+ and H2 (Liu, Chen, Guan and Xu 2018).

In the redox reaction between nZVI and contaminants, Fe2+ undergoes oxidation to Fe3+. Fe3+ forms Fe(OH)3 that increases the pH of the solution. In the presence of dissolved oxygen, nZVI can oxidize and degrade numerous organic compounds. This process leads to the formation of H2O2 which is a potent reducing agent.

Future expectations Extensive studies focusing on nanomaterials and applicability in water treatment is anticipated to generate data to guide large scale use of these materials. Although research findings have demonstrated that iron nanoparticles possess properties essential for use in water treatment, these nanomaterials have to be subjected to a range of modifications to improve

14 efficiency and safety. In the future, iron nanoparticles will undergo major modifications to improve their adsorbent and reduction properties. Since research has shown that nZVI can potentially remove organic compounds from water, it is expected that these nanomaterials will be used in industrial and domestic water purification exercises. It is also likely that in the future a combination of iron nanoparticles and other nanomaterials will be used for greater water treatment results.

Recommendations Despite iron nanoparticles have proven effective in the separation of toxic metals and organic compounds from water, the application of this technology in water treatment is still contentious. Issues of safety have hindered the largescale application of this technology. This paper recommends that further studies are needed to generate reliable data regarding transport properties, oxide-fluid interactions, and eco-toxicity of iron nanoparticles. The development of nanocomposites containing iron nanoparticles can be explored as the best next step in the development of nanomaterials that are best suited for large-scale applications in the water industry.

Conclusion Over the years, research on the prevention of water contamination has led to the use of nanomaterials to enhance the separation of pollutants from water. Iron is one of the components that have long been used for this purpose. Unfortunately, large iron particles cannot purify water.

Researchers have thus turned to the use of Nanosized zero-valent iron (nZVI) in the treatment of contaminated water. For nanomaterials to be considered potentially effective in the purification of contaminated water, they must possess reduction, adsorbent, and magnetic properties. nZVI

15 has most of these properties hence it is capable of purifying water contaminated with organic compounds and other toxic pollutants. nZVI has particularly attracted attention due to its lowcost production, non-toxicity, high efficiency, eco-friendliness and high photo-stability. The physical properties of nZVI can be modified to several morphologies, heterostructures and particle dimensions to enhance reactivity and safety. Various environmental cleanup technologies in water treatment that utilize iron nanoparticles as photocatalysts and Nanosorbents have been developed. The nZVI properties of precipitation, adsorption, oxidation and reduction in the presence of dissolved oxygen have been utilized successfully in the removal of a wide range of contaminants including organic and inorganic compounds from water.

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