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PhotocatalysisPhotocatalysis
Fundamental and Applications
Environmental PollutionEnvironmental Pollution
Atmosphere pollution Green house effect (CO2) Acid rain
Water pollution Soil pollution
Air PollutionAir PollutionSmog
Acid rain
Burning of fossil fuelsBurning of fossil fuels
Water PollutionWater Pollution
Waste water from textile industry
Soil PollutionSoil Pollution
Contaminated soil
Pesticides buried with strong odor
Advanced Oxidation TechnologyAdvanced 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)••OHOH
Nature’s CleanerNature’s Cleaner ::•• OHOH
In Atmosphere:1) O3+ h(λ < 320 nm) →O2(1∆g) + O (1D)O (1D) + H2O →2•OH2) HONO + h(λ < 400 nm) →NO + •OH [•OH]avg 10∼ 6radicals cm-3 (< 0.1 ppt!!)
In Water:1) FeIII(OH)2+ (aq) + h(λ< 400 nm) →Fe2+ (aq) + •OH
2) NO3-(aq) + h →NO2+ O-
O-+ H2O →OH-+ •OH
Oxidation Potentials of Common Oxidation Potentials of Common Chemical OxidantsChemical Oxidants
Oxidation Potentials (V vs NHE)
HO• 2.80O3 2.07H2O2 1.78HO2• 1.70ClO2 1.57HOCl 1.49Cl2 1.36
What is Photocatalysis?What is Photocatalysis?
The definition of photocatalysis is basically the acceleration of a photoreaction in the presence of a catalyst.
Principle of TiOPrinciple of TiO22 Photocatalysis Photocatalysis
1) Hoffmann, M. S.; Martin, T.; Choi, W.; Bahnemann, D. W. Chem. Rev. 1995, 95, 69-96.
OH
OH
CB
VB
-0.5V
+2.7V
TiO2
e- / H+
H2O2
O2
OH-OH./OH-
O2-
UV light (< 387.5nm)
3.2eV
O2-/O2
e-
h+
Important Reactions during Important Reactions during PhotocatalysisPhotocatalysis
TiO2UV h+ + e-
e- + O2 O2-
O2- + 2H+ + e- H2O2
H2O2 + O2- •OH + OH- + O2
h+ + H2O •OH + H+
Three Parameters Affecting Three Parameters Affecting Photocatalytic ActivityPhotocatalytic Activity
Light absorption Property Light absorption spectrum and coefficient
Rate of reduction and oxidation of reaction substrate by e- and h+, respectively
Rate of e- and h+ recombination
Enhancement of Photocatalytic Enhancement of Photocatalytic ActivityActivity
Enhancing interfacial charge-transfer Improving charge separation Inhibiting charge carrier recombination
Common Semiconductor Common Semiconductor PhotocatalystPhotocatalyst
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 TiOCrystal Structure of TiO22
Anatase Rutile Brookite
Anatase is the most active one!
Approaches to Improve the Approaches to Improve the Activity of TiOActivity of TiO22
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 Hot Research Topics of PhotocatalysisPhotocatalysis
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 PhotocatalystsNanostructured Photocatalysts
Nanocrystals Nanoporous materials
Preparation Methods of Preparation Methods of Nanostructured TiONanostructured TiO22
Thermal decomposition method Sol-gel method Microemulsion method Hydrothermal (or solvothermal) method Combustion method Other methods
microwave nonhydrolytic sonochemical
Approaches to Improve Approaches to Improve the Activity of TiOthe Activity of TiO22
Photocatalytic Activity Photocatalytic Activity Enhancement by Noble Metal Enhancement by Noble Metal DepositionDeposition
OH
CB
VB
-0.5V
+2.7V
TiO2
e- / H+
H2O2
O2
OH-OH./OH-
O2-
UV light (< 387.5nm)
3.2eV
O2-/O2
e-
h+
Au
Inhibition of the recombination of h+ and e-!
OH
Photocatalytic Activity Photocatalytic Activity Enhancement by Semiconductor Enhancement by Semiconductor CouplesCouples
CB
VB
-0.5V
+2.7V
TiO2
CB
VB
e-
h+
Inhibition of the recombination of h+ and e-!
TiOTiO22-based Photocatalysts -based Photocatalysts
Responding to Visible LightResponding 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 TiOSensitization of TiO22-Dye-Dye
CB
VB+2.7V
TiO2
Dye
Dye*
Dye+•
O2
O2-
e-
Visible light
OH
e- / H+
H2O2
This is also the fundamental of dye-sensitized solar cell!
CB
VB
-0.5V
+2.7V
TiO2
O2-/O2
Sensitization of TiOSensitization of TiO22-Narrow Band--Narrow Band-
Gap SemiconductorGap Semiconductor
CB
VB
CdS band-gap:2.4eV
h+
e-
OH
H2O2 O2-
e- / H+
O2
e-
Visible light
Environmental ApplicationsEnvironmental Applications
Water PurificationWater Purification
Water purification (Purifics environmental technologies)
Air CleanerAir Cleaner
Self-Cleaning GlassSelf-Cleaning Glass
Photo-Induced Superhydrophilicity Photo-Induced Superhydrophilicity of TiOof TiO22 Coating Coating
UV
Anti-Bacterial MaterialsAnti-Bacterial Materials
0 min
30 min
60 min
Photo-Electricity Conversion
Strategies of Solar Energy Strategies of Solar Energy ConversionsConversions
LightFuel
Electricity
Electricity
Photovoltaics
sc
e
M
Photosynthesis
Fuels
CO
Sugar
H O
O
2
2
2
H O
O H
2
22
sc M
e
Semiconductor/LiquidJunctions
Traditional Silicon Solar CellTraditional Silicon Solar Cell
GratzelGratzel CellCell
Dye Sensitized Solar Cell
Gratzel, Nature 414, 338 (2001)
Characteristics ofCharacteristics of GratzelGratzel CellCell
Inexpensive 1/10 of amorphous silicon
Flexible Efficiency not high enough Solid electrolyte
20001950 1960 1970 1980 1990
5
10
15
20
25
Effi
cie
ncy
(%
)
Year
crystalline Siamorphous Sinano TiO2
CIS/CIGSCdTe
Efficiency of Photovoltaic Efficiency of Photovoltaic DevicesDevices
Water Splitting Utilizing Solar Energy
-Hydrogen Production-Hydrogen Production
Water Splitting Utilizing Solar Water Splitting Utilizing Solar EnergyEnergy
H2
anodecathode
O2
membrane
MOxMSxe-
H+
4H+ + 4e- 2H2
2H2O O2 + 4H+ + 4e-
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.