광촉매 반응의 메커니즘 연구

1. 광촉매 반응의 메커니즘 연구 최 원 용 포 항 공 과 대 학 교 환 경 공 학 부 POSTECH Advanced Remediation & Treatment Lab.

2. Photocatalyst Applications Photo-functional Coating Material - Superhydrophilicity - Anti-fogging - Self-cleaning - Sanitary Coating - UV blocking Solar Energy & Chemical Conversion - Dye-Sensitized Solar Cell - Water Splitting - CO2/N2 Conversion - Selective Synthesis Environmental Remediation - Drinking Water Treatment - Wastewater Treatment - Air Purification - Deodorization - Sterilization - Destructing EDCs/POPs

3. Various Aspects of Photocatalytic Research • Photocatalyst Syntheses and Modifications for Higher Activities • (sol-gel synthesis, thin-film coating, ion doping, metalization, sensitization, visible-light 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 interfacial charge transfer,…) • Reactor Development(catalyst immobilization or recovery, efficient delivery of light on photocatalyst surface, solar reactor, scaling-up,…) • Integration with Other Water Treatment Processes(biological processes, AOPs, adsorption, membranes,…)

4. Active Redox Species Generated on Illuminated TiO2 Particles O- OH2+ OH A O2 ecb- O2 A•- O2- + H+ HO2 h e-/H+ x2 D •OH H2O2 e- hvb+ O2 D•+ >OHs (H2O)

5. Oxidation Potentials of Common Chemical Oxidants Used in Water Treatment Oxidation Potentials (V vs NHE)

6. 광촉매 이용 오염물질 제거기술의 장단점 장점 단점 • 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 (lact < 388 nm) • 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

7. Products and byproducts formation from photocatalytic degradation of N(CH3)4+ pH 3.4 pH 11.0 (S. Kim and W. Choi, Environ. Sci. Technol.2002, 36, 2019)

8. Schematic Pathways of the Photocatalytic Degradation of (CH3)nNH4-n+ (0 ≤ n ≤ 4)

9. O2 TiO2 ecb- + hvb+ + O2- •OH H2O ecb- H+ As(III) O22- + 2H+ H2O2 hv FeIII(OH)2+ Fe2++ •OH ecb- hvb+ As(IV) + OH- O2- •OH hvb+ As(V) O2 O2 hv hv HA++ ecb- HA+ TiO2 O2- Scheme of As(III) Photooxidation

10. Photocatalytic Conversion of NH3 on Naked TiO2 [NH3] = 100 M pH = 10 [TiO2] = 0.5 g/L Air-Saturated

11. Photocatalytic Conversion of NH3 on Pt-TiO2 [NH3] = 100 M pH = 10 [TiO2] = 0.5 g/L Air-Saturated

12. Photocatalytic Conversion of NH3 on Pt-TiO2 [NH3] = 100 M pH = 10 [TiO2] = 0.5 g/L N2O-Saturated

13. Proposed Mechanism for N2 Production on Pt/TiO2 On Pt surface NH3 (aq) NH3,ad NH3,ad + OH• NH2,ad + H2O NH2,ad + OH• NHad + H2O NH2,ad NHad + Had NHad Nad + Had Nad + Nad N2,ad

14. Migrating Active Photooxidants on TiO2 Reaction medium Reaction medium Organic substrate Organic substrate OH= or HO2 = UV Dark-TiO2 Illuminated-TiO2 Previous reports on migrating/diffusing OH radicals on TiO2: Tatsuma et al., J. Phys.Chem. B. 1999, 103, 8033/ 2001, 105, 6987. Haick & Paz, J. Phys. Chem. B2001, 105, 3045. Cho & Choi, J. Photochem. Photobiol. A : Chem. 2001, 143, 221. Kim & Choi, Environ. Sci. Technol.2002, 36, 2019.