Photocatalytic transformation of organic compounds in the presence
of inorganic ions*
Paola Calza and Ezio Pelizzetti
Dipartimento di Chimica Analitica, Università
di Torino, via P. Giuria 5, 10125 Torino, Italy
Abstract: The influence of halide ions on the photocatalytic
process on titanium dioxide has been investigated carefully. Chloride
and bromide ions, acting as hole scavengers, generate active radical
species (e.g., ·Cl and ·Br) that participate in reactions
with the organic compounds and the transient intermediates. Chloride
and bromide ions have shown to deeply inhibit the degradation rate of
chloroform and tetrachloromethane and to modify both the qualitative
and quantitative distribution of their intermediates formed during the
degradation process. In the presence of bromide, CBrCl3 is detected
as intermediate during CCl4 degradation, while in the presence of chloride,
formation of CCl4 is observed in the CHCl3 degradation. Fluoride ions,
differently from the other halides, cannot be oxidized by the valence
hole and may be used as a diagnostic tool in mechanistic studies. The
influence of fluoride on phenol has been investigated, and, by choosing
appropriate experimental conditions, it was possible to evaluate the
role of the different active species in the photocatalytic process.
* An issue of reviews and research papers based on
presentations made at the IUPAC/ICSU Workshop on
Electrochemistry and Interfacial Chemistry in Environmental Clean-up
and Green Chemical Processes, Coimbra, Portugal, 6-7 April, 2001.
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