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. 2
The pathway of pharmaceutical pollutants entry in aquatic environment
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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). 7
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. 9
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. 10
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 L1)
Overall Oxidant degradation (4× 104 M) k × 104 (s1)
k × 104 (s1) (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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