Application of Zirconium Dioxide as a New Photocatalyst

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Application of Zirconium Dioxide as a New
Photocatalyst

• By Christopher Ciptadjaya
• CHEM 6100

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Overview

• Photocatalyst (Advantages, Applications)
• Properties of Zirconium Dioxide
• Comparison of Zirconium Dioxide and Titanium
  Dioxide Band Gap Energy
• A New Photocatalyst Zirconium Dioxide
• Photoreduction of CO2 (selected paper)
• Summary

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Photocatalyst

• A catalyst that accelerates photoreaction
• Does not change in itself or being consumed in
  the chemical reaction
• Since its property was discovered in 1968,
  titanium dioxide (TiO2) has been the primary
  photocatalyst used in various applications in
  industry
• It has strong oxidation and decomposition
  strength
• Photocatalytic activity (PCA) is the ability of a
  material to create an electron hole pair as a
  result of exposure to ultraviolet radiation

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Photosynthesis and Photocatalysis
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How Does Photocatalyst Work?
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Advantages of Using Photocatalyst

• Degradation of pollutants at ambient air and
  temperature
• Adapted for a large range of pollutant
• Build with easily available materials and by mean
  of well-known techniques
• Economical, cheap and low energy consumption
• Excellent transparent and strength, possible for
  coating

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Application of Photocatalyst

• Photocatalytic superhydrophilicity technology,
  e.g.. anti-fogging and self-cleaning properties
• Oil on the super-hydrophilic surface is easily
  removed by soaking the material in water
• Hydroxyl radicals kills bacteria and breaks down
  odor-causing organic compounds

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Properties of ZrO2

• Stable chemical properties
• Low thermal conductivity
• Large band gap semiconductor properties
• Can be recovered easily
• Ampotheric property
• High activity for heterogeneous photochemical
  process
• High adsorption to wide range of pollutants

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Energy Band Gap of Materials
ZrO2 wide band gap semiconductor or low end
insulator (Eg5.0 eV)
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Band Gap and Charge Distribution of ZrO2 vs TiO2
CB
CB
Vs.
5.0 eV
3.2 eV
e-
h
VB
h
e-
e-
e-
VB
h
h
e-
e-
TiO2
ZrO2
? 378 nm
? 250 nm
Fermi Level
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Electron Trapping and Storage in ZrO2 Conduction
Band
e-
e-
e-
e-
e-
CB
CB
hn
5.0 eV
5.0 eV
e-
e-
e-
VB
h
h
VB
h
e-
e-
h
Fermi Level (EF)
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A New Photocatalyst Application of Zirconium
Dioxide

• Water splitting (H2 fuel)
• Photooxidation of organic molecules, eg. Aniline
  to azobenzene
• Degradation of 2,4-dichlorophenoxiacetic acid and
  2,4,6-trichlorophenol
• Photocatalytic Degradation of Trichloroethylene
• Photoreduction of CO2

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Photocatalytic Water Splitting

• Hydrogen is an important chemical feed and
  non-polluting renewable fuel
• ZrO2 photocatalyzes the decomposition of water
  into H2 and O2
• ZrO2 prepared by precipitation method of
  zirconium oxychloride with various hydrolyzing
  agents was studied for photocatalytic water
  splitting reaction under UV irradiation

Reykjavik, Iceland

• Korean J. Chem. Eng, 2003, 20, 1026

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Paper of interest

• A New Type Of Photocatalysis Initiated By
  Photoexcitation
• Of Adsorbed CO2 On ZrO2
• Satohiro Yoshida and Yoshiumi Kohno, Catalysis
  Survey, 2000, 4,107

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Carbon Dioxide (CO2)

• A very stable and inert compound
• Biomass respiration
• Generated from electricity, steam
• Potent greenhouse gas
• Causes global warming

www.rst.gsfc.nasa.gov
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Why Worried About Excessive CO2 Emission?

• Trap re-radiated energy
• Causes greenhouse effect
• Affects climate change
• Elevated temperature

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Synthesis and Photochemistry of Zirconium Dioxide

• Hydrolysis zirconium oxychloride by NH3
• Dry at 373 K overnight
• Calcinate at 773 K for 5 hours in a dry air steam
• Photoreaction was done using 500 W Mercury lamp
  as UV light source
• Mixture of CO2 with H2 or CH4 was injected to the
  system

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Time Dependence Plot of Amount of CO Formation
and H2 Consumption
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Effect of Reaction Temperature on Photoreaction
of CO2 H2
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Surface Intermediates

• Introduction of CO2 causes the appearance of 6
  bands corresponding to surface carbonates and
  bicarbonates
• Second surface species was formed during
  photoirradiation of ZrO2 by the reaction between
  hydrogen and adsorbed carbon dioxide
• These species are surface formate ion

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What is the Role of Surface Formate?

• Involves in reaction pathway or spectator?
• Investigation Formic acid was used as substrate
• Observation of evolution of CO using formic acid
  as a reactant
• 13CO2 was used and the evolution of CO was
  observed
• Formate acts as a reductant of CO2

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Formation of CO2- Radicals

• CO2 is adsorbed as carbonates on the surface
• Photoexcitation of molecules causes activation of
  CO2
• Activated species are radicals
• Recorded with EPR (Electro Paramagnetic
  Resonance)
• Results from EPR spectra suggest CO2- radicals
  formed
• Precursor of CO2- radicals formation is carbonate
  formation on the surface

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Summary of Reaction Mechanism for Photoreduction
of CO2 by H2 over Irradiatied ZrO2

• CO2- radicals is formed by photoactivation of
  adsorbed CO2
• CO2- radicals reacts with H2 to form surface
  formate
• Surface formate works as a reductant of CO2 to CO
  under irradiation
• Surface formate is being reoxidized to become
  adsorbed CO2 species again

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Summary of reaction mechanism for photoreduction
of CO2 by methane over irradiated ZrO2

• CO2- radicals reacts with CH4 producing surface
  acetate and surface formate
• Surface acetate does not react
• Surface formate works as a reductant of CO2 to CO
  under irradiation
• Surface formate is being reoxidized to become
  adsorbed CO2 species again

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Conclusion

• ZrO2 is an active photocatalyst for
  photoreduction of CO2 by hydrogen and methane
• Role of photoirradiation are as follows
• To convert adsorbed carbonates to CO2- radicals
• To assist reaction of CO2 and formate derived
  from CO2- and hydrogen or methane
• ZrO2 photocatalyst promises an alternative
  solution for the reduction of CO2 emission

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Acknowledgement

• Dr. Sherine Obare
• Lab research group
• CHEM 6100 colleagues

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Thank you!!
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Semi-conductor materials are doped with
impurities chosen to give the material special
characteristics. One may want to add extra
electrons or remove electrons N- type
semiconductor current is carried by a (-)
electron P- type semiconductor current is
carried by a () hole
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