COMPARISON OF THE PHOTOELECTRONIC AND PHOTOCATALYTIC ACTIVITIES OF VARIOUS ANATASE AND RUTILE FORMS OF TITANIA IN PURE LIQUID ORGANIC PHASES AND IN AQUEOUS-SOLUTIONS

Various titania samples of industrial origin (Degussa and Tioxide) hav e been characterized by electrical photoconductance measurements and t ested as photocatalysts in various liquid media (either pure organic l iquids 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 wat er). In identical conditions, Degussa was found more active, but the i ntrinsic activity, expressed in moles converted per hour and per squar e meter of active surface, was found slightly higher for anatase Tioxi de. The higher activity of anatase with respect to that of rutile coul d be explained by the interpretation of the photoconductance measureme nts, which evidence the higher aptitude of anatase (i) to photoadsorb oxygen, in O-2(-) and O- forms; (ii) to photodesorb it; and (iii) to h ave a lower relative electron-hole recombination rate. The origin of t he differences in the photocatalytic behavior of titania leading to mi ld oxidation in pure liquid organic phase and total oxidative degradat ion in aqueous medium is also analyzed.