P15-36

High surface area Ag-TiO2 nanotubes for photocatalytic application

Dr. N. Pugazhenthiran

School of Chemistry Madurai Kamaraj University Madurai-625 021 E-mail: npugazhmku@gmail.com 1

Why do we need water treatment ?

POLLUTION

Fig. 1. Industrialization and their impact on the environments.

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The pathway of pharmaceutical pollutants entry in aquatic environment

3

Types of waste water treatment

Why TiO2 ?

Photoactive.

Able to utilize visible and/or near-UV light.

Biologically and chemically inert.

Photostable.

Inexpensive.

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Synthesis of Ag-TiO2 NTs 10M NaOH TiCl4 + NH4OH

HCl

AgNO3 hď Ž (365 nm) N2

Ag-TiO2 NTs

TiO2 NTs

Fig. 2. Schematic representation for the synthesis of Ag-TiO2 NTs 5

Characterization of catalysts

Fig. 4. XRD patterns of TiO2 NTs and Ag-TiO2 NTs.

Fig. 3. TEM images of TiO2 NTs (A & B), Ag-TiO2 NTs (C & D) and EDX spectrum of Ag-TiO2 NTs (E).

Insets are their corresponding SAED patterns.

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Fig. 5. BET of TiO2 NTs and Ag-TiO2 NTs. Inset: Corresponding pore size distribution curves.

Catalyst

BET surface area (m2/g)

BJH pore volume (cm3/g)

BJH pore size (nm)

TiO2 NTs

469

0.896

9

Ag-TiO2 NTs

448

0.791

7

Fig. 6. DRS of TiO2 NTs and Ag-TiO2 NTs and their corresponding Tauc plots (Inset).

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Model pollutant – ceftiofur sodium (CFS)

Fig. 7. UV-vis spectrum of ceftiofur sodium. Inset: corresponding molecular structure.

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Photocatalytic degradation of CFS

Fig. 8. Photocatalytic degradation of CFS at various amount of Ag-TiO2 NTs.

Fig. 9. Photocatalytic degradation of CFS in the presence of various catalysts under UVvisible and visible-light (ď Ź > 395 nm) irradiation.

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Fig. 10. PL spectra of TA in the presence of different catalysts under UV-visible light irradiation (at 60 min). Inset: PL spectra of TA (at various irradiation times) in the presence of Ag-TiO2 NTs.

Fig. 11. HPLC chromatographs of CFS solution at different light irradiation periods in the presence of Ag-TiO2 NTs. The major intermediate peak observed at tR of 3.0 min is desfuroyl ceftiofur.

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Table 1. Summary of results obtained from the photocatalytic degradation of CFS in the presence of Ag-TiO2 NTs and oxidants.

Catalyst (1.0 g L1)

Overall Oxidant degradation (4× 104 M) k × 104 (s1)

k × 104 (s1) (with added TB-OH)

% k reduced

by TB-OH addition

Major oxidizing species

---

PMS

0.12  0.005

0.11  0.006

8

SO4

---

PDS

0.082  0.006

0.08  0.007

2

SO4

---

H2O2

0.064  0.005

0.001  0.001

98

TiO2 NTs

---

0.96  0.07

0.002  0.001

99

TiO2 NTs

PMS

2.1  0.11

1.37  0.07

34

TiO2 NTs

PDS

1.31  0.07

0.56  0.04

57



OH

TiO2 NTs

H2O2

1.03  0.07

0.01  0.001

99



OH

Ag-TiO2 NTs

---

4.9  0.18

0.03  0.003

99



OH

Ag-TiO2 NTs

PMS

12.8  0.35

7.7  0.29

40

Ag-TiO2 NTs

PDS

7.8  0.32

2.7  0.15

65



OH

Ag-TiO2 NTs

H2O2

7.0  0.31

0.12  0.007

98



OH





OH

OH

SO4

SO4

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Fig. 12. Schematic representation of the electron transfer events and activation of PMS occur in the Ag-TiO2 NTs catalytic system upon bandgap irradiation during CFS degradation.

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Fig. 13. Photocatalytic mineralization of CFS in the presence of Ag-TiO2 NTs with and without oxidants.

Fig. 14. Reusability of Ag-TiO2 NTs catalyst towards the photocatalytic degradation of CFS. 13

Conclusions 

Titanium dioxide nanotubes (TiO2 NTs) with very high surface area (469 m2/g) were synthesized, modified with Ag NPs.



The TiO2 NTs exhibited better photocatalytic activity than TiO2 NPs, due to their very high specific surface area and good crystallinity.



As high as 87 % of CFS was mineralized within 6 h using Ag-TiO2 NTs photocatalyst system in combination with PMS.



The current plasmonic catalyst, Ag-TiO2 NTs, is highly stable during photocatalytic reactions and it is reusable up to 4 cycles without significant loss in activity.

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