‘TiO2’, GREEN CATALYST:
CLEAN ENVIRONMENT
1st National Conference on Biotechnology & Microbiology
Dr. Romana Khan
Department of Environmental Sciences, COMSATS
Institute of Information Technology, Abbottabad
Introduction
Photocatalysis - Need of the day
Photocatalysis
CO2 + H2O
CO2
Chlorophyll
Photocatalyst
Organic
Compound
H2O
Starch + O2
Organic compound
+ H2O + O2
Photocatalytic Applications
Antimicrobial Effect
Antimicrobial Effect
Self-Cleaning Effect
Photocatalysts
TiO2 – an Ideal Photocatalyst
 Cheap and can be reused
 High photo-chemical corrosive resistance
 Strong oxidizing power
 Photocatalysis takes place at ambient temperature
 Atmospheric oxygen is used for the reaction
TiO2 - Photocatalysis
3.12 eV (380 nm)
Redox potential of h+
1.
The redox potential for photogenerated h+ is +2.53 V vs. the SHE
2.
After reaction with water, these h+ can produce •OH
3.
Both h+ and •OH are more positive compare to ozone
Photocatalytic Reactions
TiO2 + h
h+ + H2O
O2 + eO2 - + H+
HO2 + HO2
O2
-
+ HO2
TiO2 (e- + h+)
OH + H+
O2
-
HO2
H2O2 + O2
O2 + HO2-
HO2- + 
H2O2
H2O2 + h
2 OH
H2O2 + O2
-
H2O2 + e-
HO + OH- + O2
HO + OH-
Entail Physicochemical Properties of TiO2
The applications of TiO2 is a function of specific physicochemical properties like:
 High Surface area
 Small Crystalline Size
 Anatase form of TiO2
 High crystallinity
 Porous structure
 Activation light source
An appropriate synthetic procedure can provide TiO2 with promising efficiency
Synthesis of TiO2 Powders
Synthesis of TiO2 powders
Sulfate Method
Chloride Method
Specific Methods
Sol-Gel Method
Hydrolysis and Condensation
Sol-Gel Technology
Visible-Light Active Photocatalyst
TiO2 – efficient photocatalyst under UV light
Yet, need visible-light active photocatalyst for practical purpose
Can be achieved by doping TiO2 with nonmetals, transition metals and dyes
Activity increases by loading a metal oxide
Metal oxide reduces the chance of recombination of electrons & holes
produced during photocatalytic reactions
Modification of TiO2
e-
e-
e-
TM-TiO2
TiO2
NM-TiO2
h+
h+
h+
Coating Techniques
A- Spin Coating Method
B- Dip Coating Method
C-Spray Coating Method
D- Sputtering Method
Setting Substrates
Vacuuming
Coating / Discharging plasma
Collecting Substrates
E- Plate Coating
An Acid-Base Catalyzed Sol-Gel Synthesis of
TiO2 Photocatalysts
Ti(OBu)4 + EtOH
HCl + H2O + EtOH
Stirring (12 h)
Sol (pH 0.8)
Stirring (12 h)
NH4OH
Gel (pH 9.0 )
Drying (1100C, 12 h)
Calcination
Phase Structure and Thermal Stability
(f)
Intensity (a.u.)
(e)
(d)
(c)
(b)
(a)
20
30
40
2
50
60
70
XRD patterns of TiO2 samples; (a) as-dried, and calcined
at (b) 350 oC, (c) 400 oC, (d) 500 oC, (e) 600 oC and (f)
800 oC.
80
Some Selected Properties of TiO2 Powders
Catalyst
Crystal Phasea
Size of A(nm)b
SBET(m2/g) c
V(cm3/g)d
DBJH(nm)e
P-25
A:R (75:25)
25
50
-
-
T-as dried
A
4.3
331
0.21
2.4
T-350
A
9
102
0.18
5.2
T-400
A
11
83
0.16
5.2
T-500
A
18
63
0.12
8.1
T-600
A: R (98: 2)
29.6
27
0.08
12.5
T-800
A: R (5:95)
45.5
1.9
0.007
3.4
Photocatalytic Efficiency
-5
Concentration (6.6 x 10 mole)
7
6
5
4
3
2
1
0
0
30
60
90
120
150
180
Time (min)
Catalytic degradation of toluene by different TiO2 samples;
(a)Blank (■)(b)TiO2 – as-dried (●); (c) P-25 (▲); and TiO2 calcined at
(d) 350 oC (▼); (e) 400 oC () (f) 500 oC (◄ ); (g) 600 oC (►).
Photoreactor
Publications
1.
Romana Khan, S.W. Kim, T.J. Kim, H.S. Lee – A novel acid-base catalyzed sol-gel synthesis of highly active
mesoporous TiO2 photocatalysts, Bulletin of the Korean Chemical Society, 28(11), 1951-1957 (2007).
2.
Romana Khan, S.W. Kim, T.J. Kim – Synthesis and control of physical properties of titania nanoparticles as a
function of synthetic parameters, Journal of Nanoscience and Nanotechnology, 8(9), 4738-4742 (2008).
3.
Romana Khan, S.W. Kim, T.J. Kim, C.M. Nam – Comparative study of the photocatalytic performance of boron–
iron co-doped and boron-doped TiO2 nanoparticles, Materials Chemistry and Physics, 112(1), 167-172 (2008).
4.
Romana Khan, S.W. Kim, T.J. Kim, C.M. Nam – Comparative study of the photocatalytic performance of boron–
iron co-doped and boron-doped TiO2 nanoparticles, Materials Chemistry and Physics, 112(1), 167-172 (2008).
5.
Romana Khan, T.J. Kim – Preparation and application of visible-light responsive Ni-doped and SnO2-coupled TiO2
nanocomposite photocatalysts, Journal of Hazardous Materials, 163(2-3), 1179-1184 (2009).
Thank You