Influence of chemical structure of dyes, of pH and of inorganic salts on their photocatalytic degradation by TiO2 comparison of the efficiency of powder and supported TiO2

Anionic (Alizarin S (AS), azo-Methyl Red (MR), Congo Red (CR), Orange G (OG)) and cationic (Methylene Blue (MB)) dyes were degraded, either individually or in mixtures, by using UV-irradiated TiO2) in suspension or supported on glass and on paper. The influence of the chemical structure of different dyes as well as that of pH and of the presence of inorganic salts on the photocatalytic properties of TiO2, has been discussed. The role of adsorption is suggested, indicating that the reaction occurs at the TiO2 surface and not in the solution. S and N hetero-atoms are respectively mineralized into SO42-, NO3- and NH4+, except azo-groups which mainly formed N-2 which represents an ideal case for a decontamination reaction. The fate of nitrogen strongly depends on its initial oxidation degree. High photocatalytic activities have been found for TiO2 coated on glass by the sol-gel method. Its efficiency was intermediate between those of PC-500 and P-25 powders. The efficiency of PC-500 TiO2 sample, fixed on paper by using a binder, is slightly less important than that of the powder. The presence of a silica-binder with an acidic pzc is suggested to be at the origin of the decrease in efficiency. (C) 2003 Elsevier Science B.V. All rights reserved.