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![Page 1: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/1.jpg)
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
![Page 2: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/2.jpg)
UPW Use
• Wet standard operations account 1/3 of total processing steps:– Standard cleans.– Wet etch processes. – Chemical mechanical planarization (CMP)
• Wafer is redundantly cleaned to remove contaminants and prepare the surfaces between processes.
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The Concern
• More than 3000 gallons of UPW can be used to process an 8 inch wafer from start to finish.
• Present semiconductor fabrication facilities (FABS) typically use 1-3 million gallons of UPW per day.
• Final UPW quality highest of any industry.
• Contaminants remaining in water end up in wafer surfaces, render a device non-functional.
Water Quality Parameter
Units Typical Municipal Water Supply
Typical Ultrapure Water Product
Resistivity M ohms-cm 0.004 >18
pH Units 8 6
TOC ppb 3500 <10
Ammonium ppb 300 <1
Calcium ppb 22000 <1
Magnesium ppb 4000 <1
Potassium ppb 4500 <10
Silica ppb 4780 <1
Sodium ppb 29000 <1
Chloride ppb 15000 <1
Fluoride ppb 740 <1
Sulfate ppb 42000 <1
![Page 4: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/4.jpg)
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
![Page 5: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/5.jpg)
Goals and Objectives
• Develop new method for photocatalytic oxidation of organics:– Lower the energy use through catalytic oxidation
(UV 185nm used 2003 UV 254 nm used 2004).– Reduce the use of chemicals.
![Page 6: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/6.jpg)
Introduction: Photocatalytic Process
Photo-generation
electron/hole pairs
Formation of radicals
Radical oxidation of
Organic compound.
TiO2 hv
e- + h+
h+ + H2O OH + H+
e- + O2 O2-
O2- + H+ HO2
TOC + Ox(radical) TOC (partially oxidized species) + CO2 + H2O
![Page 7: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/7.jpg)
Role of Promoters in Photocatalytic Process
)M(eeM
(energy)TiOhe 2
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
TiO2 hv
e- + h+
h+ + H2O OH + H+
e- + O2 O2-
O2- + H+ HO2
TOC + Ox TOC(partially oxidized species) + CO2 + H2O
![Page 8: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/8.jpg)
Conduction Bande- e- e- e- e- e- e- e- e- e- e- e-
Role of Promoters in TiO2 Photocatalytic process
Valence Bandh+ h+ h+ h+ h+ h+ h+ h+ h+ h+
Electron/hole pairrecombination
Electron/hole pair generation
Metallic promoter attracts electrons from TiO2 conduction band and slows recombination reaction
e-(M) <-- M+e-
Eg
![Page 9: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/9.jpg)
Effects of Nitrogen Doping in TiO2
TiO2 BondOrbitals
TiO2-xNx BondOrbitals
Conduction Band
Ti d + (O2p) Ti d +O2p +N2p)
Valence Band
N2p + O2p
O2P + (Ti d) + (Ti d)
Energy
Ti d
O2p
Ti dN2pO2p
Addition of nitrogen increases the size of the bondorbitals, decreasing the energy bandgap
Eg = 3.2 eV Eg = 2.5 eV
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Experimental
-Sol-gel method #1 3-TiO2 layers3-bakes
-Sol-gel method #23-TiO2 layers2-extra TiO2 coats Ag dopedbefore 3rth bake
-CVD method N2 doped
-Ethylene glycol-urea-Triton X-100 surfactant contaminants
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Preparation of Supported Catalyst by ChemicalVapor Deposition Method (CVD)
Experimental Setup
14
Impregnation chamber
23HP
nitrogen cylinder
Stripper
TiCl4 reservoir
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Experimental Setup for Batch Reactivity Testing
UV lamp 254 nm
Water bath/shaker/
lamp holder Coated screens
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Ethylene glycol/UV 254 nm
0
100
200
300
400
500
600
700
0 20 40 60 80 100 120 140
time (hrs)
TO
C (ppb)…
TiO2#2
TiO2#1
CVD
Results and Highlights
![Page 14: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/14.jpg)
Ethylene glycol
0
100
200
300
400
500
600
700
0 20 40 60 80 100 120
time(hrs)
TO
C (ppb)... TiO2
TiO2/Ag
Results and Highlights
Sol-gel method #2 used
![Page 15: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/15.jpg)
Triton X-100
0
100
200
300
400
500
600
700
800
900
1000
0 50 100 150 200time (hrs)
TOC
(ppb
)... TiO2
TiO2/Ag
Urea
0
100
200
300
400
500
600
700
800
900
1000
0 20 40 60 80 100 120
time (hrs)TO
C (ppb)...
TiO2TiO2/Ag
Results and Highlights
Sol-gel method#2 used
![Page 16: Photocatalytic Degradation of Organics Elizabeth Buitrago University of Arizona Department of Chemical and Environmental Engineering Grad Student Mentor:](https://reader035.fdocuments.us/reader035/viewer/2022062717/56649e185503460f94b04ce5/html5/thumbnails/16.jpg)
Ethylene glycol/ 254 nm
0
100
200
300
400
500
600
700
800
0 20 40 60 80 100 120time (hrs)
TO
C (ppb)...
CVD/ N2blank
Results and Highlights
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Model for Photocatalytic Reaction
evap
k
2k
22k
k2
2k
k2
r)(TOC)(OHkdt
d(TOC)
)(OHk)(TOC)(OHk)(hkdt
)d(OH
)(ek))(h(ekSkdt
)d(e
)(hk))(h(ekSkdt
)d(h
)M(eeM
OHOH
OHCOTOCOH
HOHOHh
(energy)TiOhe
hehvTiO
3
432
m11
211
m
4
3
2
1
1
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.
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Ethylene glycol/UV 254 nm
0
100
200
300
400
500
600
700
0 20 40 60 80 100 120 140time (hrs)
TO
C (ppb)
TiO2#2
TiO2#1
CVD
model #2
CVD model
model #1
Photocatalytic Model
TiO2#1 S = 3.5 CVD S = 10 TiO2 #2 S = 14 cm2
S = active surface area
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Triton X100/ UV 254 nm
0
200
400
600
800
1000
0 50 100 150 200
time (hrs)
TO
C (ppb) model TiO2/Ag
model TiO2
TiO2
TiO2/Ag
Urea/ UV 254 nm
0
200
400
600
800
1000
0 20 40 60 80 100 120
time (hrs)
TO
C (p
pb)
model TiO2/Ag
model TiO2
TiO2
TiO2/Ag
Ethyl glycol/ UV 254 nm
0
100
200
300
400
500
600
700
0 20 40 60 80 100 120 140
time (hrs)
TO
C (ppb) TiO2/Ag
TiO2
TiO2/Ag model
TiO2 model
Photocatalytic Model
OHCOTOCOH 22k3 +¾ ®¾+·
Triton X100 k3 = 0.6ethylene glycol k3 = 0.4Urea k3 = 0.05
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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.