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

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

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,…)

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

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

광촉매 이용 오염물질 제거기술의 장단점 장점 단점 거의 모든 유기오염물질을 완전분해 낮은 광효율 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

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

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

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

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

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

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

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

Migrating Active Photooxidants on TiO2 Reaction medium Reaction medium Organic substrate Organic substrate UV OH= or HO2 = 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. B 2001, 105, 3045. Cho & Choi, J. Photochem. Photobiol. A : Chem. 2001, 143, 221. Kim & Choi, Environ. Sci. Technol. 2002, 36, 2019.