1. Photocatalytic and catalytic routes for removal of pollutants present in water and air
G. Magesh
CY04D012

2. Contents of the thesis Chapter 1: Introduction
Chapter 2: Materials and methods
Chapter 3: Characterization and photocatalytic activity of Ce modified TiO2
Chapter 4: Characterization and photocatalytic studies of carbon-TiO2 composites
Chapter 5: Characterization, photocatalytic and electrochemical studies of CdSnO3 and Cd2SnO4
Chapter 6: Characterization and CO oxidation activity of Au/TiO2

3. Environmental pollution
Environmental pollution is having a deadly effect on humans and ecosystems
Water pollution is mostly due to pesticides, oil, sewage, dyes, and heavy metals
Air pollution is mostly due to automobile and industrial exhaust
Photocatalysis
Photocatalysis - reaction assisted by photons in the presence of a catalyst
In photo catalysis - simultaneous oxidation and reduction
Light excites electrons from valence to conduction band - electrons and holes
Light induced excitation processes in a photo catalyst 3 3

4. Factors to be considered in a photocatalyst
Recombination of electrons and holes
Amount of visible light utilized (Bandgap)
Stability against photo-corrosion
Position of VB and CB
Objectives
To use heterogeneous photocatalysts for degrading/oxidizing organic pollutants in water effectively.
To expand the range of radiation required in TiO2 for the photocatalytic redox process to visible region.
To increase adsorption capacity of photocatalyst towards organic pollutants.
To investigate new materials with suitable properties for their photocatalytic activity in visible light.
To study new support materials for Au as catalyts for oxidation of CO. 4

5. Chapter - 3
Preparation, characterization and photocatalytic activity of Ce modified TiO2

6. Cerium modified TiO2
TiO2 is a widely studied and applied photocatalyst because of its favorable properties
Solar radiation contains only 7 % UV light & pure TiO2 inactive in sunlight
Various methods have been attempted to improve the visible light absorption
- dye sensitization, doping of metal/non-metallic ions
- coupling of two semiconductors
CeO2 having a bandgap of 2.8 eV will increase visible light activity by coupled semiconductor mechanism
The Ce3+\Ce4+ redox couple is expected to increase charge transfer. This will lead to reduction in recombination 6

7. Preparation of cerium modified TiO2
Aq. NH3 (pH 12.7)
Titanium(IV) isopropoxide in
CH2Cl2 at 1.5 ml/min
Ammonium ceric nitrate in water at 0.5 ml/min
Sol
Stirred 12 h
Washed, centrifuged
Dried
Calcined 600 oC, air 6 h
0.25 %, 0.5 %, 1 %, 2 %, 3 %, 5 % and 9 % CeO2 modified TiO2, pure TiO2 and pure CeO2 were prepared

8. XRD patterns
XRD patterns of the samples
X-ray diffraction patterns of CeO2-TiO2 samples (a) CeO2
(b) 9% CeO2-TiO2 (c) 5% CeO2-TiO2 (d) 3% CeO2-TiO2
(e) 2% CeO2-TiO2 (f) 1% CeO2-TiO2 (g) 0.5% CeO2-TiO2
(h) 0.25% CeO2-TiO2 (i) TiO2
Peaks corresponding to CeO2 start to appear at 2.0 % CeO2 loading

9. TEM images of 3 % CeO2-TiO2 Particle size ranges from 10 – 50 nm
Maximum no. of particles are around 25 nm in size

10. SEM image of 3 % CeO2-TiO2
Agglomerates of particles were observed in SEM
EDAX confirms presence of Cerium

11. Diffuse reflectance UV-Visible spectra
Red shift observed with CeO2-modified samples
Increase in red shift with increase in % of CeO2

12. Reaction conditions for irradiation and dark studies
Photocatalytic reaction conditions
Amount of catalyst : 100 mg
Duration : 90 minutes
Methylene blue : 80 ml of 20 ppm solution
Visible light source : 400 W high pressure Hg lamp ( > 420 nm using filter)
UV light used : Eight 8 W Hg lamps ( = 365 nm)
Analysis : Measuring max of methylene blue at 662 nm by UV-visible spectrophotometry
Adsorption studies were carried out for the same duration without irradiation

13. Amount of MB adsorbed in dark
Amount of MB adsorbed in dark after 90 minutes of stirring
Catalyst
Amt adsorbed (× 10-7 mol / 0.1 g catalyst)
TiO2
9.10
0.25 % CeO2-TiO2
8.34
0.50 % CeO2-TiO2
7.27
1.00 % CeO2-TiO2
6.53
2.00 % CeO2-TiO2
5.78
3.00 % CeO2-TiO2
5.46
5.00 % CeO2-TiO2
4.60
9.00 % CeO2-TiO2
4.18
CeO2
3.42
Adsorption of MB decreases with increase in CeO2 loading
Pure CeO2 shows about 1/3 adsorption of TiO2

14. Amount degraded ( x 10-7 mol / 0.1 g catalyst)
Overall and photocatalytic decrease in MB under UV and visible irradiation
Catalyst
Amount degraded ( x 10-7 mol / 0.1 g catalyst)
Visible UV
Overall
Photocatalytic
(Overall-Dark)
TiO2
9.63
0.53
32.40
23.30
0.25 % CeO2-TiO2
14.65
6.31
34.56
26.22
0.50 % CeO2-TiO2
17.01
9.74
37.28
30.01
1.00 % CeO2-TiO2
16.80
10.27
40.45
33.92
2.00 % CeO2-TiO2
8.87
39.22
33.44
3.00 % CeO2-TiO2
14.12
8.66
31.61
26.18
5.00 % CeO2-TiO2
11.34
6.74
28.17
23.57
9.00 % CeO2-TiO2
9.73
5.55
26.83
22.65
CeO2
5.24
5.18
1.76
UV light

15. Calculation of band position
No considerable change in d-value for CeO2-TiO2 compared to pure TiO2
Electronegativity of TiO2, (TiO2) = [(Ti) 2(O)]1/3
where (TiO2), (Ti), and (O) are the electronegativities of TiO2, titanium, and oxygen respectively
VB energy = Ionisation energy, IE(TiO2) = EVB(TiO2) = (TiO2) + ½ Eg
CB energy = Electron affinity, EA(TiO2) = ECB(TiO2) = (TiO2) – ½ Eg
ECB(TiO2) (in NHE) = ECB(TiO2) – 4.5 eV (in Absolute vacuum scale)
Band positions of TiO2, CeO2 and Ce2O3 were calculated
Y. Xu, M.A.A. Schoonen, Am. Mineral., 85 (2000) 543

16. Mechanism in visible light
Bandgap, conduction and valence band energy positions of the various oxides
Semiconductor
Bandgap
(in eV)
ECB in NHE
EVB in NHE
TiO2
3.20
-0.29
2.91
CeO2
2.76
-0.32
2.44
Ce2O3
2.40
-0.47
1.93
G. Magesh, B. Viswanathan, R.P. Viswanath, T.K. Varadarajan, Ind. J. Chem. A, 48A (2009) 480

17. Summary CeO2-TiO2 prepared by co-precipitation method
No new phase observed due to CeO2 loading
On loading CeO2 red shift of upto 75 nm was observed in UV-visible spectrum compared to TiO2
CeO2-TiO2 composite shows higher activity in visible light and UV light
CeO2 has conduction band position more negative than that of TiO2
CeO2-TiO2- works in visible and UV light by coupled semiconductor mechanism

18. Chapter - 4
Preparation, characterization and photocatalytic studies of carbon-TiO2 composites

19. Carbon-TiO2 Adsorption: Adsorption - important step in photocatalysis
TiO2 has less adsorption capacity
Improving adsorption leads to
Electron and hole transferred quickly to adsorbed compounds
Leads to reduction in recombination
Improving adsorption:
One way of improving adsorption is carbon- TiO2 catalysts
Carbon is a good adsorbent
Carbon - conducting and improves charge transfer
Preparing carbon-TiO2
Literature shows carbon prepared over TiO2 and TiO2 prepared over carbon
Preparing TiO2 and carbon together is expected to have better activity 19

20. Preparation of carbon-TiO2 Sucrose + Titanium trichloride solution
Dissolved in water
Kept in oven at 150 °C for 15 h
Calcined at 300 °C for 4 h in air
Calcined at 300, 400, 500, and 600 °C in N2 for 6 h to vary the amount of carbon
XRD patterns
XRD pattern of C-TiO2 calcined at 300 oC in air; at various temperatures in N2

21. C-TiO2 calcined at 300 oC air ; 600 oC N2
SEM images
TEM images
C-TiO2 calcined at 300 oC air ; 600 oC N2

22. Raman spectra Diffuse reflectance UV visible spectra
C-TiO2 calcined at 300 oC in air- at 600 oC in N2
Prepared carbon graphitic in nature
Diffuse reflectance UV visible spectra
C-TiO2 calcined in air 300 oC ; in N2 different temperatures
Carbon-TiO2 shows no absorbance in visible region
No doping of carbon is taking place 22

23. Photocatalytic activity of C-TiO2 from TiCl3 and sucrose
Source : 400 W Hg lamp Pollutant : 80ml 50ppm methylene blue
Irradiation : 90 min Catalyst : 0.1 g
Absorbance at 662 nm was monitored by UV-visible spectroscopy
Catalyst
% C
% MB conc. decrease under irradiation
% MB conc. decrease in dark
% Photocatalytic (Irradiation – Dark)
TiO2
600 oC NA
34.0
13.0
21.0
C-TiO2 300 oC
5.4
88.0
41.3
46.7
C-TiO2 400 oC
3.0
87.7
31.8
55.9
C-TiO2 500 oC
2.1
74.5
26.8
47.7
C-TiO2 600 oC
1.4
72.7
23.8
48.9
All C-TiO2 samples showed at least 25 % increase in activity than TiO2

24. Preparation of carbon-P25 TiO2
Sucrose + P25 TiO2
Dispersed in water
Kept in oven at 150 °C for 15h
Calcined at 360, 365, 370, 375 and 400 °C for 4 h in air
XRD pattern

25. TEM images Diffuse reflectance UV-visible spectra
Carbon – P25 TiO2 calcined at 370 oC
Diffuse reflectance UV-visible spectra
C-P25 TiO2 from sucrose calcined at different temps in air with varying amounts of carbon
No shift in UV-visible absorption was observed
This shows absence of C doping

26. Photocatalytic activity of C-TiO2 from sucrose and P25 TiO2
Source : 400W Hg lamp Pollutant : 80ml 50ppm Methylene blue
Irradiation : 90 min Catalyst : 0.1 g
Catalyst
% C
% MB conc. decrease under irradiation
% MB conc. decrease in dark
% Photocatalytic (Irradiation – Dark)
P oC air NA
55.2
9.4
45.8
C-P oC
2.3
95.4
38.8
56.6
C-P oC
0.5
90.5
25.5
65.0
C-P oC
0.2
59.5
12.2
47.3
Carbon-P25 TiO2 showed higher activity than P25 treated under similar conditions
Up to 20 % improvement in activity observed

27. Summary Carbon and TiO2 were prepared together using sucrose and TiCl3
Carbon was prepared over commercial P25 TiO2
SEM and TEM images confirmed the existence of carbon and TiO2 together
Amount of carbon was varied by changing the calcination temperatures
Photocatalytic studies for the degradation of methylene blue showed that carbon and TiO2 prepared together showed better activity than carbon prepared over commercial TiO2

28. Chapter - 5
Preparation, characterization, photocatalytic and electrochemical studies of CdSnO3 and Cd2SnO4 28

29. Choice of materials for new visible light photocatalysts
Semiconductor valence band are composed of d-orbitals and p-orbitals
Conduction band is composed of s-orbitals and p-orbitals
Materials containing elements with completely filled d-orbitals (d10) have VB edge at higher energy and hence small bandgap 13 Al 14 Si 15 P 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi
Elements whose compounds show small bandgap

30. Preparation of CdSnO3 Aqueous SnCl4.5H2O solution
Aq. 3CdSO4. 8H2O solution
Added simultaneously
Aq. NaOH solution
Stirred overnight
Washed, dried, calcined 850 oC air 6 h
CdSnO3 30

31. Rhombohedral (JCPDS no. 880287)
XRD pattern of CdSnO3
Rhombohedral (JCPDS no )
SEM images 31

32. Diffuse reflectance UV-visible spectrum
Absorbance starts 415 nm
Bandgap 3.0 eV
Photocatalytic decontamination of water
Catalyst : 50 mg Light source : 480 W Hg lamp
Irradiation time : 90 min Model pollutant : 50 ml 25 ppm p-chlorophenol
Visible light :  > 420 nm (HOYA L-42 filter)
Catalyst
% Degradation
UV-Visible
Visible
CdSnO3
94.47
0.00 32

33. Precipitated with NaOH
Preparation of Cd2SnO4
Aq. SnCl4.5H2O solution
Aq. NaOH solution
Mixed together
Sn(OH)4 precipitate
Washed till absence of Cl-
Dissolved in con. H2SO4
Mixed with aq. 3CdSO4 . 8H2O solution
Precipitated with NaOH
Precipitate washed till absence of SO42-
Dried calcined air 900 oC
Cd2SnO4 33

34. XRD pattern SEM images of Cd2SnO4
Orthorhombic (JCPDS no )
SEM images of Cd2SnO4 34

35. Diffuse reflectance UV-visible spectrum
Absorbance starts at 532 nm
Bandgap : 2.3 eV
Photocatalytic decontamination of p-chlorophenol
Catalyst : 50 mg Light source : 480 W Hg lamp
Irradiation time : 90 min Model pollutant : 50 ml 25 ppm p-chlorophenol
Visible light :  > 420 nm (HOYA L-42 filter)
Catalyst
% Degradation
UV-Visible
Visible
Cd2SnO4
75.81
24.94 35

36. Types of semiconductors suitable for water splitting
For H2 evolution
Conduction band potential - more negative than 0.00 V vs NHE
For O2 evolution
Valence band potential - more positive than V vs NHE
-ve
Potential
Reduction (H+ /H2) 0.00 V
Energy
Oxidation (HO-/O2) V
+ve
Band positions of various types of semiconductors 36

37. Determination of band potential by Mott-Schottky plot
Impedance measurements
Coated on Ti plates using PVDF as binder
Frequency : – Hz Reference electrode : Ag/AgCl
Counter electrode : Pt Amplitude : V
Electrolyte : 0.5 M Na2SO4 Potential range : 0 V to 0.9 V
MS plot of CdSnO3
MS plot of Cd2SnO4
Flat band potential : 0.23 V vs Ag/AgCl V vs NHE
Cannot evolve H2 and only O2 evolution possible
Flat band potential : 0.15 V vs Ag/AgCl V vs NHE
Cannot evolve H2 and only O2 evolution possible 37

38. Photocatalytic water splitting studies
Hydrogen evolution reaction using CdSnO3 and Cd2SnO4
Medium : 35 ml Water-methanol (5:1 ratio)
Catalyst : 50 mg
Light source : 480 W Hg lamp
No hydrogen evolution occurred in UV-visible and visible irradiation 38

39. Summary
Rhombhohedral CdSnO3 and orthorhombic Cd2SnO4 were prepared by co-precipitation method
Diffuse reflectance measurements showed bandgaps of 3.0 and 2.3 eV for CdSnO3 and Cd2SnO4 respectively
Photocatalytic p-chlorophenol degradation measurements showed both catalyst were effective in UV-visible radiation
Only Cd2SnO4 was found to be photoactive in visible radiation ( > 420 nm)
Mott-schottky plots showed flat band potentials of 0.35 and 0.43 V (vs NHE) for CdSnO3 and Cd2SnO4 respectively
Water splitting studies showed no H2 evolution in accordance with measured flat band potentials 39

40. Preparation, characterization and CO oxidation activity of Au/TiO2
Chapter - 6
Preparation, characterization and CO oxidation activity of Au/TiO2

41. Carbon monoxide oxidation
CO is a toxic gas from the partial combustion of fuel from Internal Combustion Engines
Oxidation to CO2 is one of the ways of removing CO
Gold nanoparticles supported on TiO2 is a suitable catalyst
TiO2 exists in different crystalline forms
Mostly anatase and rutile were studied as supports
Report shows brookite phase of TiO2 gives a higher activity than anatase and rutile 41
W. Yan, B. Chen, S.M. Mahurin, S. Dai and S.H. Overbury, Chem. Commun., (2004) 1918.

42. Preparation of TiO2 Preparation of Au/TiO2 – sol deposition
TiO2 was prepared from TiCl4 and TiCl3 and were labeled as BRT4 and BRT3 respectively
Preparation of Au/TiO2 – sol deposition
32 ml 1 % sodium citrate + 8 ml 1 % tannin ml water. pH adjusted to 8 using 4 % Na2CO3
40 ml HAuCl4 (5 millimoles) in 600 ml water
Heat 60 oC
Heat 60 oC
Both solutions mixed, stirred maintained at 60 oC for 30 mins
Pink colored gold sol
Gold sol was deposited with the help of poly(diallyldimethylammonium chloride) (PDDA)
Calculated amount of gold loading – 2 wt %
Gold loaded on BRT4, BRT3 and Degussa P25 TiO2 42

43. XRD analysis and surface area % Au loading based on ICP
Catalyst
XRD
Surface area (m2/g)
% Anatase
% Rutile
% Brookite
BRT4
100
114
BRT3 55 45
197
P25 75 25 50
Gold estimation by ICP
Catalyst
% Au loading based on ICP
Au/BRT4-Sol
2.22
Au/P25-Sol
2.15
Au/BRT3-Sol
Catalyst
Average size in nm
(No. of particles)
Au/BRT4-asprep
15.2 (56)
Au/BRT4-used
17.0 (167)
Au/P25-asprep
15.1 (59)
Au/P25-used
15.0 (149)
Particle size from TEM

44. TEM images of Au/TiO2 prepared by sol method
Au particles on Au/BRT4 were agglomerated after reaction
No change in size observed in Au particles on Au/P25 after reaction
TEM images of Au/TiO2 samples prepared by sol method (A) Au/BRT4-sol-asprepared (B) Au/BRT4-sol-after reaction (C) Au/P25-sol-asprepared and (D) Au/P25-sol-after reaction

45. CO oxidation activity results CO oxidation activity of catalysts
Reaction mixture 35 ml/min of gas flow (0.5 vol. % CO, 9.4 % O2, 51.9 % He and 38.2 % Ar) and at a ramp rate of 4 oC/min
Reaction performed before and after calcination in O2
60 mg of catalyst calcined at 400 oC in 20 % O2 in Ar for 1 h (10 oC /min heating rate, 30 ml/min gas flow)
Products monitored online by mass spectrometer
CO oxidation activity of catalysts
100 % conversion is achieved at 100 oC, 200 oC and 220 oC for Au/P25, Au/BRT3 (anatase + brookite) and Au/BRT4 (brookite) respectively
Activity of Au/P25 is retained after calcination whereas considerable decrease observed in Au/BRT4 and a slight decrease in Au/BRT3 45

46. Preparation of Au/TiO2 by deposition-precipitation method
15 ml of M HAuCl4.3 H2O soln ml water in a beaker
pH adjusted to 8 using 1 M KOH
Heated up to 60 oC with stirring
500 mg TiO2 added
Stirred at 60 oC for 2 h
Centrifuged 5000 RPM 10 mins
Washed & centrifuged 3 times in water and once in ethanol
Dried 60 oC for 12 h
Au/TiO2
Calculated gold loading – 2.2 wt %
Gold loaded on P25 and BRT4
W. Yan, B. Chen, S.M. Mahurin, S. Dai and S.H. Overbury, Chem. Commun., (2004) 1918.

47. CO oxidation activity of samples from DP method Important observations
Temperature programmed reaction was performed with 27.5 ml/min of gas flow (0.5 vol. % CO, 9.4 % O2, 51.9 % He and 38.2 % Ar) and at a ramp rate of 5 oC/min
30 mg of catalyst calcined at 400 oC in 20 % O2 in Ar for 1 h (10 oC/min heating rate, 12.5 ml/min gas flow)
Important observations
Au/Brookite shows higher activity in DP method
Au/P25 shows higher activity in sol method
Brookite shows considerable decrease in activity after calcination in both cases 47

48. XRD pattern of Au/BRT4 and Au/P25 prepared by sol method
Peaks corresponding to Au were observed
Au (200) peak showed an increase in intensity after reaction
Other phases of TiO2 not observed after reaction
No peaks corresponding to Au were observed 48

49. Summary
Au supported on brookite and P25 TiO2 were prepared by deposition-precipitation and sol deposition methods
CO oxidation studies were carried out with the catalysts
Au/P25 more active in sol deposition method
Au/Brookite showed better activity in deposition-precipitation method
Au/Brookite prepared by both methods showed decrease in activity after calcination 49

50. Conclusions
CeO2-TiO2 showed redshift up to 75 nm and higher activity than TiO2 in visible light and UV light. CeO2 has a conduction band position more negative than that of TiO2 and CeO2-TiO2 works in visible and UV light by coupled semiconductor mechanism.
Carbon-TiO2 composites were prepared by two different methods namely preparation of carbon and TiO2 together and preparation of carbon over commercial P25 TiO2. Photocatalytic degradation of methylene blue experiments showed that carbon and TiO2 prepared together showed better activity than carbon prepared over commercial TiO2.
Photocatalytic p-chlorophenol degradation studies showed that both Cd2SnO4 and CdSnO3 were active in UV-visible radiation whereas, Cd2SnO4 alone was active in visible radiation. Mott-Schottky plots showed that both CdSnO3 and Cd2SnO4 have flat band potentials lower in energy than the H2 evolution potential. Photocatalytic water splitting experiments showed no H2 evolution.
Au supported on brookite and P25 TiO2 (Anatase+Rutile) were prepared by deposition precipitation and sol deposition methods. Au/P25 was found to be more active in sol deposition method whereas Au/brookite showed better activity in deposition-precipitation method. Au/brookite prepared by both the methods showed decrease in activity after calcination at higher temperature.

51. Thank you Acknowledgements Grateful thanks are due to
(Late) Prof. R.P. Viswanath
Prof. T.K. Varadarajan
Prof. B. Viswanathan
The current and past Heads of Department of Chemistry
The Doctoral committee members and faculty of the Department of Chemistry
The supporting staff
Colleagues and friends
DST and CSIR for fellowships
Thank you

52. LIST OF PUBLICATIONS
REFEREED JOURNALS
Magesh, G., B. Viswanathan, R.P. Viswanath and T.K. Varadarajan (2009) Photocatalytic behavior of CeO2-TiO2 system for the degradation of methylene blue. Indian J. Chem., Sec A, 48A,
OTHER PUBLICATIONS
Magesh, G., B. Viswanathan, R.P. Viswanath and T.K. Varadarajan (2007) Photocatalytic routes for chemicals. Photo/Electrochemistry & Photobiology in the Environment, Energy and Fuel,
PRESENTATIONS IN SYMPOSIUM/CONFERENCE
Magesh, G., B. Viswanathan, R. P. Viswanath and T. K. Varadarajan, ‘Visible light photocatalytic activity of Ce modified TiO2 nanoparticles for methylene blue decomposition’, International Conference on Nanomaterials and its Applications (Poster presentation), February 4-6th 2007, NIT, Trichy, India.
Magesh, G., B. Viswanathan, T.K. Varadarajan and R.P. Viswanath, ‘CeO2-TiO2 system as visible light photocatalyst for the degradation 4-chlorophenol’, Catworkshop-2008 (Poster Presentation), February 18-20, 2008, IMMT, Bhubaneswar, India.
Magesh, G., T.K. Varadarajan and R.P. Viswanath, ‘Enhanced photocatalytic activity of carbon-TiO2 composites towards pollutant removal’, CATSYMP-19, (Poster presentation) January 18-21, 2009, National Chemical Laboratory, Pune, India.
Magesh, G., B. Viswanathan, T.K. Varadarajan and R.P. Viswanath, ‘Cadmium stannates as photocatalysts for decontamination of water’, Indo-Hungarian workshop on future frontiers in catalysis (poster presentation) February 16-18, 2010, IIT Madras, Chennai, India.