Photocatalyzed destruction of chlorinated hydrocarbons

Semiconductor photocatalysis with a primary focus on TiO{dollar}sb2{dollar} 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 TiO{dollar}sb2{dollar}/UV process are investigated.; Time-resolved microwave conductivity experiments provide the recombination lifetimes and interfacial charge transfer rate constants of eight different TiO{dollar}sb2{dollar} 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 surface recombination rates with increasing pH.; Vanadium doped into TiO{dollar}sb2{dollar} affects the quantum efficiency. Depending on the preparation method, vanadium plays three distinct roles. First, vanadium is present as surficial {dollar}>{dollar}VO{dollar}sb2sp+{dollar} and promotes charge-carrier recombination through electron-trapping followed by hole elimination. Second, V(scIV) impurities in surficial V{dollar}rmsb2Osb5{dollar} islands result in enhanced charge-carrier recombination through hole-trapping followed by electron elimination. Third, V(scIV) is substitutional in the TiO{dollar}sb2{dollar} lattice in the form of a solid solution, V{dollar}rmsb{lcub}x{rcub}Tisb{lcub}1-x{rcub}Osb2.{dollar} The V(scIV) centers trap both electrons and holes and thus yield enhanced charge-carrier recombination.; The addition of inorganic oxidants such as HSO{dollar}sb5sp-{dollar}, ClO{dollar}sb3sp-{dollar}, IO{dollar}sb4sp-{dollar}, and BrO{dollar}sb3sp-{dollar} increases the quantum efficiency. BrO{dollar}sb3sp-{dollar} acts by scavenging conduction-band electrons and reducing charge-carrier recombination. When ClO{dollar}sb3sp-{dollar} is present, however, competitive adsorption for the TiO{dollar}sb2{dollar} surface occurs among 4-CP, ClO{dollar}sb3sp-{dollar}, and O{dollar}sb2{dollar}, and the heterogeneous photodegradation of 4-chlorophenol follows three parallel pathways. ClO{dollar}sb3sp-{dollar} favors a reaction pathway involving the thermal oxidation of the reactive intermediates.