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