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Photocatalytic Degradation of Organics. Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor: Mike Schmotzer Faculty Advisor: Dr. Farhang Shadman. Overview. Goals and objectives Introduction/ background

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photocatalytic degradation of organics

Photocatalytic Degradation of Organics

Elizabeth Buitrago

University of Arizona

Department of Chemical and Environmental Engineering

Grad Student Mentor: Mike Schmotzer

Faculty Advisor: Dr. Farhang Shadman

overview
Overview
  • Goals and objectives
  • Introduction/ background
    • TiO2 as a photocatalyst/photocatalytic process
    • Role of promoters in catalytic oxidation (Ag)
    • Effects of nitrogen doping in TiO2
  • Experimental
  • Results/Highlights
  • Future goals
goals and objectives
Goals and Objectives
  • Develop new method for photocatalytic oxidation of organics:
    • Lower the energy use through catalytic oxidation (UV 185nm used last year--> UV 254 nm used this year)
    • Reduce the use of chemicals
    • Remove total organic carbon (TOC) produced by process operations of semiconductor manufacturing
introduction photocatalytic process
Introduction: Photocatalytic Process

Photo-generation

electron/hole pairs

Formation of radicals

Radical oxidation of organic

compound.

role of promoters in photocatalytic process
Role of Promoters in Photocatalytic Process

Photo-generation electron/hole

pairs

Formation of radicals (Ox- radical)

Radical oxidation of organic

compound.

Recombination of electron/hole pair

Metal attracts free electron

slows recombination and

promotes radical formation

role of promoters in tio 2 photocatalytic process
Role of Promoters in TiO2 Photocatalytic process

Conduction Band

e- e- e- e- e- e- e- e- e- e- e- e-

e-(M) <-- M+e-

Electron/hole pair

recombination

Electron/hole pair

generation

Eg

Valence Band

h+ h+ h+ h+ h+ h+ h+ h+ h+ h+

Metallic promoter attracts electrons from TiO2 conduction

band and slows recombination reaction

slide7

Effects of Nitrogen Doping in TiO2

Energy

TiO2 Bond

TiO

N

Bond

2-x

x

Orbitals

Orbitals

Conduction Band

Ti d +

Ti d + (O2p)

O2p +N2p)

Ti d

Ti d

Eg = 3.2 eV

Eg = 2.5 eV

N2p

O2p

O2p

N2p + O2p

O2P + (

Ti d)

+ (

Ti d)

Valence Band

Addition of nitrogen increases the size of the bond

orbitals, decreasing the energy bandgap

experimental
Experimental

-Ethylene glycol

-urea

-Triton X-100 surfactant

contaminants

-Sol-gel method #1

3-TiO2 layers

3-bakes

-Sol-gel method #2

3-TiO2 layers

2-extra TiO2 coats Ag doped

before 3rth bake

-CVD method N2 doped

preparation of supported catalyst by chemical vapor deposition method cvd experimental setup
Preparation of Supported Catalyst by ChemicalVapor Deposition Method (CVD)Experimental Setup

1

4

TiCl4 reservoir

Stripper

HP nitrogen cylinder

3

2

Impregnation chamber

slide10

Experimental Setup for Batch Reactivity Testing

UV lamp 254 nm

Water bath/

shaker/

lamp holder

Coated screens

batch experiments
Batch Experiments

#1 (ethylene glycol)

#2 (ethylene glycol)

#3 (ethylene glycol)

-TiO2 sol gel method

-TiO2 method #2

-TiO2 method #1

#1

-Ag/TiO2 method #2

-CVD method

-Control

-control

-Control

#4 (Urea)

#5 (Triton X-100)

#6 (ethylene glycol)

-TiO2 method #2

-TiO2 method #2

-CVD/N2

-Ag/TiO2

-Ag/TiO2 method #2

-Control

results and highlights13
Results and Highlights

Sol-gel method #2 used

results and highlights14
Results and Highlights

Sol-gel method#2 used

slide16

Model for Photocatalytic Reaction

1. Electron/hole formation

2. Electron/hole recombination

3. Radical formation

4. Oxidation of organics

5. Radical combining with X (anything other than TOC)

6. Metal attracts electron = 0 not metal

present.

photocatalytic model
Photocatalytic Model

TiO2#1 S = 3.5 CVD S = 10 TiO2 #2 S = 14 cm2

S = active surface area

photocatalytic model18
Photocatalytic Model

k

·

+

¾

¾

®

+

3

OH

TOC

CO

H

O

2

2

Triton X100 k3 = 0.6

ethylene glycol k3 = 0.4

Urea k3 = 0.05

future goals
Future Goals
  • Find new substrates for better deposition of TiO2.
  • Investigate new ways that would improve our TiO2 loading method.
  • Improve CVD method.
  • Improve nitridation method.
acknowledgments

Acknowledgments

Mike Schmotzer, Dr. Shadman, Sally Clement

NSF/SRC for their funding