Photocatalysis
Fundamental and Applications
Environmental Pollution
 Atmosphere
pollution
 Green
house effect (CO2)
 Acid rain
 Water
pollution
 Soil pollution
Air Pollution
Smog
Acid rain
Burning of fossil fuels
Water Pollution
Waste water from textile industry
Soil Pollution
Contaminated soil
Pesticides buried with strong odor
Advanced Oxidation Technology
O3/H2O2
 O3/UV
 O3/CATALYSTS
 Fenton reaction (H2O2/Fe2+)
 Photo-Fenton reaction (H2O2/Fe2+/UV)
 H2O2/UV
 O3/H2O2/UV
 UV/TiO2 (Photocatalysis)

•OH
Nature’s Cleaner：•OH
In Atmosphere:
1) O3+ h(λ < 320 nm) →O2(1∆g) + O (1D)O
(1D) + H2O →2•OH
2) HONO + h(λ < 400 nm) →NO + •OH
[•OH]avg∼106radicals cm-3 (< 0.1 ppt!!)
In Water:
1) FeIII(OH)2+ (aq) + h(λ< 400 nm) →Fe2+ (aq) + •OH
2) NO3-(aq) + h →NO2+ OO-+ H2O →OH-+ •OH
Oxidation Potentials of Common
Chemical Oxidants
Oxidation Potentials (V vs NHE)
HO•
O3
H2O2
HO2•
ClO2
HOCl
Cl2
2.80
2.07
1.78
1.70
1.57
1.49
1.36
What is Photocatalysis?
 The
definition of photocatalysis is basically
the acceleration of a photoreaction in the
presence of a catalyst.
Principle of TiO2 Photocatalysis
UV light (< 387.5nm)
O2
-0.5V
H2O2
e- / H+
e-
CB
O2 3.2eV

OH
+2.7V
h+
TiO2
1)
O2-/O2
OH-
.
OH /OH-
VB
OH
Hoffmann, M. S.; Martin, T.; Choi, W.; Bahnemann, D. W. Chem. Rev.
1995, 95, 69-96.
Important Reactions during
Photocatalysis
TiO2
e- + O2
O2- + 2H+ + eH2O2 + O2h+
+ H2O
UV
h+ +
e-
O2H2O2
•OH + OH- + O2
•OH + H+
Three Parameters Affecting
Photocatalytic Activity
 Light
absorption Property
 Light
 Rate
absorption spectrum and coefficient
of reduction and oxidation of reaction
substrate by e- and h+, respectively
 Rate of e- and h+ recombination
Enhancement of Photocatalytic
Activity
Enhancing interfacial charge-transfer
 Improving charge separation
 Inhibiting charge carrier recombination

Common Semiconductor
Photocatalyst
TiO2
 Why TiO2?

 Strong
oxidizing power of valance band hole
 Excellent chemical and photochemical stability
 Availability: One of top 50 chemicals

Band gap: 3.2 eV
 Only
active under UV light (4% of the incoming solar
energy)
Crystal Structure of TiO2
Anatase
Rutile
Anatase is the most active one!
Brookite
Approaches to Improve the
Activity of TiO2
To enlarge band gap by reducing crystal sizes
(quantum size effect)
 To increase surface area (mesoporous structure)
 To reduce crystal defects ( high crystallinity )
 To dope metal ions
 To deposit noble metal nanoparticles
 To couple two kinds of semiconductors

Hot Research Topics of
Photocatalysis
How
to enhance the efficiency
Preparation
of nanostructured
photocatalysts
Extension of absorption of TiO2 to the
visible region
Design of novel non-titania based visible
Light photocatalysts
Nanostructured Photocatalysts
 Nanocrystals
 Nanoporous
materials
Preparation Methods of
Nanostructured TiO2






Thermal decomposition method
Sol-gel method
Microemulsion method
Hydrothermal (or solvothermal) method
Combustion method
Other methods



microwave
nonhydrolytic
sonochemical
Approaches to Improve
the Activity of TiO2
Photocatalytic Activity
Enhancement by Noble Metal
Deposition
UV light (< 387.5nm)
O2
H2O2
e- / H+
Au -0.5V
e- CB
O23.2eV

OH
O2-/O2
+2.7V
h+
OH-
VB
TiO2
Inhibition of the recombination of h+ and e-!
OH
.
OH /OH-
Photocatalytic Activity
Enhancement by Semiconductor
Couples
-0.5V
e-
CB
CB
+2.7V
h+
VB
VB
TiO2
Inhibition of the recombination of h+ and e-!
TiO2-based Photocatalysts
Responding to Visible Light
 Sensitization
of TiO2
 Organic
dyes
 Metal complexes
 Narrow band gap semiconductors
 Polymers
 Ion-doped TiO2
 Metal
ions
 Non-metal ions
Sensitization of TiO2-Dye
Dye*
O2
H2O2

e- / H+
e-
Visible light
CB
O2-
Dye
+2.7V
VB
OH
Dye+•
TiO2
This is also the fundamental of dye-sensitized solar cell!
Sensitization of TiO2-Narrow BandGap Semiconductor
O2
Visible light
-0.5V
e- / H+ H2O2
O2
e- CB
e-
CB
h+
VB
OH
+2.7V
VB
TiO2
CdS
band-gap:2.4eV
O2-/O2
Environmental Applications
Water Purification
Water purification (Purifics environmental technologies)
Air Cleaner
Self-Cleaning Glass
Photo-Induced Superhydrophilicity
of TiO2 Coating
UV
Anti-Bacterial Materials
0 min
30 min
60 min
Photo-Electricity Conversion
Strategies of Solar Energy
Conversions
Fuel
Light
Electricity
Fuels
CO
2
Electricity
O2
H
2
e
e
Sugar
sc
H2O
M
sc
M
H 2O
O
2
Photosynthesis
Semiconductor/Liquid
Junctions
Photovoltaics
Traditional Silicon Solar Cell
Gratzel Cell
Dye Sensitized
Solar Cell
Gratzel, Nature 414, 338 (2001)
Characteristics of Gratzel
Cell
 Inexpensive
 1/10
of amorphous silicon
 Flexible
 Efficiency
not high enough
 Solid electrolyte
Efficiency of Photovoltaic
Devices
25
Efficiency (%)
20
15
10
5
1950
crystalline Si
amorphous Si
nano TiO2
CIS/CIGS
CdTe
1960
1980
1970
Year
1990
2000
Water Splitting Utilizing
Solar Energy
-Hydrogen Production
Water Splitting Utilizing Solar
Energy
4H+ + 4e- 2H2
2H2O  O2 + 4H+ + 4e-
H2
O2
MSx
e-
MOx
H+
cathode
membrane
anode
纳米二氧化钛光催化性能研究
实验目的
1. 了解纳米光催化材料的性质；
2. 确定纳米二氧化钛光催化降解罗丹明B水
溶液的反应速率常数；
3. 了解光催化剂催化性能评价的一般方法。
仪器与药品
分光光度计，离心机，电动搅拌器，光催化
反应器(自制)，卤钨灯（220V 500W）
罗丹明B，纳米二氧化钛P25（德国Degussa
公司产品）。
实验步骤
1. 取罗丹明B水溶液100 mL置于光催化反应器(自制)中，加
入0.1 g P25，避光，开启冷凝水，搅拌。
2. 2 h后，取6 mL反应液，离心分离，测上层清液的吸光度
A0 。
3. 0.5 h后，取6 mL反应液，离心分离，测上层清液的吸光
度A0 ，将其与第2步测定的吸光度进行比较，判断罗丹
明B在催化剂上是否达到吸附平衡。
4. 确认罗丹明B在催化剂上是否达到吸附平衡后，打开卤
钨灯，每隔1 h取样6 mL反应液，离心分离，取上层清
液用分光光度法测定其吸光度A。
5. 实验完毕，关闭卤钨灯，停止搅拌，清洗反应器，将仪
器恢复原位，桌面擦拭干净。
注
释
1．数据处理
lnA对t作图，求出k及t1/2 。
2．注意事项
实验前仔细阅读离心机说明书，使用时
一定要遵守操作规程。
思考题
1．如何确定光催化剂的暗态吸附达到稳定时间？
2．简述TiO2做为光催化剂降解有机污染物 的原理。
3．欲提高TiO2的光催化活性，你认为可采取哪些措施？
参考文献
[1] Fujishima A，Honda K. Nature[J]. 1972，37:238~239.
[2] Piscopo A，Robert D，Weber J V. Journal of Photo chemistry
and Photobiology A: Chemistry[J]. 2001，139 (2):253~256.
[3] 李越湘，吕功煊，李树本等. 分子催化[J]. 2002，
16(4):241~246.
[4] 黄东升，陈朝凤，李玉花，曾人杰.无机化学学报[J]. 2007
，4(4):738～742.
[5] 张立德，牟季美. 纳米材料和纳米结构[M]. 北京:科学出版
社，2001.