G. Magesh

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

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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

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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.

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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

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Preparation of cerium modified TiO2
Aq. NH3 (pH 12.7)
Ammonium ceric nitrate in water at 0.5 ml/min
Titanium(IV) isopropoxide in CH2Cl2 at 1.5 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

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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

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TEM images of 3 CeO2-TiO2

• Particle size ranges from 10 50 nm
• Maximum no. of particles are around 25 nm in size

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SEM image of 3 CeO2-TiO2

• Agglomerates of particles were observed in SEM
• EDAX confirms presence of Cerium

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Diffuse reflectance UV-Visible spectra

• Red shift observed with CeO2-modified samples
• Increase in red shift with increase in of CeO2

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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 (? gt 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

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Amount of MB adsorbed in dark
Amount of MB adsorbed in dark after 90 minutes of
stirring

• Adsorption of MB decreases with increase in CeO2
  loading
• Pure CeO2 shows about 1/3 adsorption of TiO2

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Overall and photocatalytic decrease in MB under
UV and visible irradiation
UV light
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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
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Mechanism in visible light
Bandgap, conduction and valence band energy
positions of the various oxides
G. Magesh, B. Viswanathan, R.P. Viswanath, T.K.
Varadarajan, Ind. J. Chem. A, 48A (2009) 480
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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

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

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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
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SEM images
TEM images
C-TiO2 calcined at 300 oC air 600 oC N2
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Raman 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

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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

• All C-TiO2 samples showed at least 25 increase
  in activity than TiO2

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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
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TEM images
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

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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

• Carbon-P25 TiO2 showed higher activity than P25
  treated under similar conditions
• Up to 20 improvement in activity observed

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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

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

Elements whose compounds show small bandgap
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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
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XRD pattern of CdSnO3
Rhombohedral (JCPDS no. 880287)
SEM images
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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 ? gt
420 nm (HOYA L-42 filter)
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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
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XRD pattern
Orthorhombic (JCPDS no. 801467)
SEM images of Cd2SnO4
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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 ? gt
420 nm (HOYA L-42 filter)
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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
1.23 V vs NHE
-ve
Potential
Reduction (H /H2) 0.00 V
Energy
Oxidation (HO-/O2) 1.23 V
ve
Band positions of various types of semiconductors
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Determination of band potential by Mott-Schottky
plot
Impedance measurements
Coated on Ti plates using PVDF as
binder Frequency 0.01 10000 Hz
Reference electrode Ag/AgCl Counter
electrode Pt Amplitude 0.005
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
  0.43 V vs NHE
• Cannot evolve H2 and only O2 evolution possible

• Flat band potential 0.15 V vs Ag/AgCl
  0.35 V vs NHE
• Cannot evolve H2 and only O2 evolution possible

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Photocatalytic water splitting studies

• Hydrogen evolution reaction using CdSnO3 and
  Cd2SnO4
• Medium 35 ml Water-methanol (51 ratio)
• Catalyst 50 mg
• Light source 480 W Hg lamp
• No hydrogen evolution occurred in UV-visible and
  visible irradiation

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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 (? gt 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

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

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W. Yan, B. Chen, S.M. Mahurin, S. Dai and S.H.
Overbury, Chem. Commun., (2004) 1918.
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Preparation of TiO2
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 120
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

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XRD analysis and surface area
Gold estimation by ICP
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-asprepar
ed and (D) Au/P25-sol-after reaction

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CO oxidation activity results

• 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

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Preparation of Au/TiO2 by deposition-precipitation
method
15 ml of 0.0254 M HAuCl4.3 H2O soln. 10 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

• 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

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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

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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

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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
  (AnataseRutile) 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.

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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,
480-488. 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, 321-357. PRESENTAT
IONS 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.