The photocatalytic oxidations of CN" and SO32' were studied at several semiconductor powders including Ti02, ZnO, CdS, Fe203, and W03 using a xenon light source. Ti02, ZnO, and CdS were active photocatalysts for cyanide oxidation, while no oxidation was seen for Fe203 and W03. The catalyzed oxidation of CN" at Ti02 using sunlight was also investigated. The rate constant for CN" oxidation at Ti02 in sunlight was 3.1 X 10"6 mol day"1 cm"2 illuminated surface. The product of the oxidation of CN" at Ti02 was quantitatively determined to be OCN". Ti02, ZnO, CdS, and Fe203 photocatalyzed the oxidation of S032". The order of the catalytic activity was Fe203 ~ZnO ~CdS > Ti02. The rates of the photocatalytic oxidations were greater for S032" than for CN" in the cases of Ti02, ZnO, and CdS. The chemical and photochemical stabilities for the most active catalysis were determined.
Single crystal semiconductors (n‐Si, p‐Si,
normaln‐normalGaAs
,
normalp‐normalGaAs
,
normaln‐normalGaP
,
normaln‐normalInP
, and
normaln‐normalCdS
) were coated with n‐type
TiO2
by a chemical vapor deposition technique, and the electron and hole transfer properties across the heterojunction so produced were investigated. The quality of the deposited
TiO2
film depended upon several factors including temperature and substrate material. When high quality crack‐free
TiO2
coats were obtained on n‐type substrates, the substrate was stabilized with no dissolution during the photo‐oxidation of water. However, the oxidation was due only to the photoexcitation of the
TiO2
, and any holes produced in the substrate were not transferred through the
TiO2
to the solution. The use of p‐type substrates coated with
TiO2
as photocathodes was limited by band‐bending requirements at the p‐n heterojunction and the
TiO2‐normalsolution
interface.
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