Various titania samples of industrial origin (Degussa and Tioxide)
have been characterized by electrical
photoconductance measurements and tested as photocatalysts in various
liquid media (either pure organic
liquids or aqueous solutions) as a function of their structure (anatase
versus rutile). Anatase was constantly
found more active than rutile, whatever the reaction chosen (mild
oxidation of pure cyclohexane and 2-propanol;
total degradation of phenol and nitrophenol isomers in water). In
identical conditions, Degussa was found
more active, but the intrinsic activity, expressed in moles converted
per hour and per square meter of active
surface, was found slightly higher for anatase Tioxide. The higher
activity of anatase with respect to that of
rutile could be explained by the interpretation of the photoconductance
measurements, which evidence the
higher aptitude of anatase (i) to photoadsorb oxygen, in
O2
- and O- forms; (ii) to
photodesorb it; and (iii) to
have a lower relative electron−hole recombination rate. The
origin of the differences in the photocatalytic
behavior of titania leading to mild oxidation in pure liquid organic
phase and total oxidative degradation in
aqueous medium is also analyzed.
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