postech advanced remediation & treatment lab. 광촉매 반응의 메커니즘 연구 최 원...
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POSTECH Advanced Remediation & Treatment Lab.
광촉매 반응의 메커니즘 연구
최 원 용최 원 용
포 항 공 과 대 학 교포 항 공 과 대 학 교환 경 공 학 부환 경 공 학 부
Photocatalyst
Applications
Photo-functional Coating Material
- Superhydrophilicity
- Anti-fogging
- Self-cleaning
- Sanitary Coating
- UV blocking
Environmental Remediation
- Drinking Water Treatment
- Wastewater Treatment
- Air Purification
- Deodorization
- Sterilization
- Destructing EDCs/POPs
Solar Energy & Chemical Conversion
- Dye-Sensitized Solar Cell
- Water Splitting
- CO2/N2 Conversion
- Selective Synthesis
Various Aspects of Photocatalytic ResearchVarious Aspects of Photocatalytic Research
• Photocatalyst Syntheses and Modifications for Higher Activities
(sol-gel synthesis, thin-film coating, ion doping, metalization, sensitization, visible-lig
ht photocatalyst,…)
• Kinetics and Mechanisms (intermediates and products analysis, identification of
active oxidants, understanding degradation pathways, radical chemistry …)
• Reaction Modeling
• Surface and Photoelectrochemistry (surface & electrochemical characterization)
• Dynamics of Charge Carriers (laser spectroscopic study of recombination and int
erfacial charge transfer,…)
• Reactor Development (catalyst immobilization or recovery, efficient delivery of lig
ht on photocatalyst surface, solar reactor, scaling-up,…)
• Integration with Other Water Treatment Processes (biological processes, AOP
s, adsorption, membranes,…)
O2- + H+ HO2
O2
OH2+O-
OH
Active Redox Species Generated on IlluminatActive Redox Species Generated on Illuminated TiOed TiO22 Particles Particles
>OHs (H2O)
•OH
h
ecb-
hvb+
H2O2
e-/H+
x2
e-
A
A•-
D
D•+
O2
O2
HO 2.80
O3 2.07 H2O2 1.78
HO2 1.70
ClO2 1.57 HOCl 1.49
Cl2 1.36
Oxidation Potentials of Common Chemical Oxidants Used in Water Treatment
Oxidation Potentials (V vs NHE)
거의 모든 유기오염물질을 완전분해
수처리와 가스처리 시스템에 모두 적용 가능
상온 · 상압 조건에서 작동
광촉매 (TIO2) 가 값싸고 공업적으로 대량생산
공정이 안전하고 ( 유독 산화제 불필요 ) 간단
태양광 사용가능 (act < 388 nm)
광촉매 이용 오염물질 제거기술의 장단점
낮은 광효율
가시광 비활성 (TiO2)
대용량 처리시스템에는 부적합
슬러리상 수처리에서는 광촉매 분리 회수 공정∙ 필요
다양한 광촉매 고정화 기술 개발 필요
인공광원 사용시 관리비용 증대
전체 광촉매 표면적에 균등한 빛 조사 어려움
장점 단점
Products and byproducts formation Products and byproducts formation from photocatalytic degradation of from photocatalytic degradation of
N(CHN(CH33))44++
pH 3.4 pH 11.0
(S. Kim and W. Choi, Environ. Sci. Technol. 2002, 36, 2019)
Schematic Pathways of the Photocatalytic Schematic Pathways of the Photocatalytic Degradation of (CHDegradation of (CH
33))nnNHNH4-n4-n
++ (0 (0 ≤≤ n n ≤≤ 4) 4)
NCH3
CH3CH3CH3 N
CH3
CH3CH3H N
H
CH3CH3H N
H
HCH3H N
H
HHH
NCH3
CH3CH3 N
H
CH3CH3 N
H
HCH3 N
H
HH
NCH3
CH3OHN CH3OHH
NOHH
H
NO2- NO3
-
H+ H+ H+ H+
HO2 HO2HO2
OHO2
OHO2
OHO2
OHCH3
OHCH3
O2OH
O2OH
O2OH
Slow
FastOH
CH3
As(V)
H2O2
O2
HA+ + ecb-
O2-
As(III)
As(IV)
O2
HA + TiO2
hv
FeIII(OH)2+ Fe2+ + •OHhv
hvb+
hvb+
TiO2 ecb- + hvb
+ +hv O2
H2O
ecb-
•OH
O22- + 2H+
•OH ecb
-H+O2
-
O2-
+ OH-
Scheme of As(III) Photooxidation
Irradiation Time (min)
-20 0 20 40 60 80 100 120 140
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
NH3NO2
-
NO3-
Total N
Photocatalytic Conversion of NHPhotocatalytic Conversion of NH33 on Naked TiO on Naked TiO22
[NH3] = 100 M
pH = 10
[TiO2] = 0.5 g/L
Air-Saturated
Irradiation Time (min)-20 0 20 40 60 80 100 120 140
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
NH3
NO2-
NO3-
Total Ndark control
Photocatalytic Conversion of NHPhotocatalytic Conversion of NH33 on Pt-TiO on Pt-TiO22
[NH3] = 100 M
pH = 10
[TiO2] = 0.5 g/L
Air-Saturated
Irradiation Time (min)
-20 0 20 40 60 80 100 120 140
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
NH3
NO2-
NO3-
Total Ndark control
Photocatalytic Conversion of NHPhotocatalytic Conversion of NH33 on Pt-TiO on Pt-TiO22
[NH3] = 100 M
pH = 10
[TiO2] = 0.5 g/L
N2O-Saturated
NH3 (aq) NH3,ad
NH3,ad + OH• NH2,ad + H2O
NH2,ad + OH• NHad + H2O
NHad Nad + Had
NH2,ad NHad + Had
Proposed Mechanism for NProposed Mechanism for N22 Production on Pt/TiOProduction on Pt/TiO22
On Pt surface
Nad + Nad N2,ad
Migrating Active Photooxidants on TiO2
Tatsuma et al., J. Phys.Chem. B. 1999, 103, 8033/ 2001, 105, 6987. Haick & Paz, J. Phys. Chem. B 2001, 105, 3045. Cho & Choi, J. Photochem. Photobiol. A : Chem. 2001, 143, 221.Kim & Choi, Environ. Sci. Technol. 2002, 36, 2019.
Illuminated-TiO2
OHor HO2
Organic substrate
UV Dark-TiO2
Organic substrate
Reaction medium
Previous reports on migrating/diffusing OH radicals on TiO2:
Reaction medium