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Photocatalyzed Destruction of Chlorinated Hydrocarbons


Martin, Scot Turnbull (1996) Photocatalyzed Destruction of Chlorinated Hydrocarbons. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/597h-8896.


Semiconductor photocatalysis with a primary focus on TiO₂ as a durable photocatalyst has been applied as a method for water and air purification. In this thesis, the basic electronic and chemical processes underlying the quantum efficiencies of the TiO₂/UV process are investigated.

Time-resolved microwave conductivity experiments provide the recombination lifetimes and interfacial charge transfer rate constants of eight different TiO₂ catalysts. Their quantum efficiencies towards the photooxidation of chlorinated hydrocarbons vary from 0.04 to 0.44%. A direct correlation between (1) the quantum efficiencies and (2) the recombination lifetimes and the interfacial charge transfer rate constants is observed.

The charge-carrier recombination rate in size-quantized particles ( 1-4 nm) is increased due to the mixing of states that relaxes the selections rules of an indirect bandgap semiconductor.

The effects of protonation (i.e., pH 7-12) of amphoteric ZnO surface states on cross-sections for electron capture at the surface are studied by time-resolved radio frequency conductivity. Electrostatic repulsion due to a negatively-charged ZnO-surface leads to decreasing surf ace recombination rates with increasing pH.

Vanadium doped into TiO₂ affects the quantum efficiency. Depending on the preparation method, vanadium plays three distinct roles. First, vanadium is present as surficial > VO₂⁺ and promotes charge-carrier recombination through electron-trapping followed by hole elimination. Second, V(IV) impurities in surficial V₂O₅ islands result in enhanced charge-carrier recombination through hole-trapping followed by electron elimination. Third, V(IV) is substitutional in the TiO₂ lattice in the form of a solid solution, Vₓ Ti₁₋ₓO₂. The V(IV) centers trap both electrons and holes and thus yield enhanced charge-carrier recombination.

The addition of inorganic oxidants such as HSO₅⁻, ClO₃⁻, IO₄⁻, and BrO₃⁻ increases the quantum efficiency. BrO₃⁻ acts by scavenging conduction-band electrons and reducing charge-carrier recombination. When ClO₃⁻ is present, however, competitive adsorption for the TiO₂ surface occurs among 4-CP, ClO₃⁻, and O₂, and the heterogeneous photodegradation of 4-chlorophenol follows three parallel pathways. ClO₃⁻ favors a reaction pathway involving the thermal oxidation of the reactive intermediates.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Hoffmann, Michael R. (advisor)
  • Dougherty, Dennis A. (advisor)
Thesis Committee:
  • Lewis, Nathan Saul (chair)
  • Hoffmann, Michael R.
  • Dougherty, Dennis A.
  • Gray, Harry B.
  • Marcus, Rudolph A.
Defense Date:6 October 1995
Non-Caltech Author Email:smartin (AT)
Record Number:CaltechTHESIS:12092020-003246663
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Ch. 1 adapted for Ch. 2 adapted for Ch. 3 adapted for Ch. 4 adapted for Ch. 5 adapted for Ch. 6
Martin, Scot Turnbull0000-0002-8996-7554
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14020
Deposited By: Kathy Johnson
Deposited On:09 Dec 2020 01:01
Last Modified:09 Dec 2020 01:16

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