ROLE OF OXYGEN AT THE TIO2 INTERFACE DURING PHOTODEGRADATION OF BIOLOGICALLY DIFFICULT-TO-DEGRADE ANTHRAQUINONE-SULFONATE DYES

Heterogeneous photocatalysis via TiO2 suspensions is effective in anthraquinone-2-sulfonic acid sodium salt (ASS) degradation. The presence of oxygen promotes the observed semiconductor powder oxidation of the substrate. Degradation of ASS in aerated dispersions of TiO2 needed about 24 h at 60 degrees C. Added H2O2 enhances the degradation rate considerably. As the pH increases, the H2O2 produced also increases. Also, peroxide production was observed as the concentration of TiO2 is increased owing to the availability of more surface states for the reaction. The Langmuir adsorption isotherm of ASS on TiO2 Degussa P-25 shows that ASS adsorbs readily on the TiO2 particles. The observed rate for H2O2 production decreased as the concentration of isopropanol (hole scavenger) is increased, suggesting an oxidative pathway as the main reaction responsible for H2O2 photoproduction. The degradation of ASS is a result of indirect action due to light mainly absorbed by TiO2. The experiments described here demonstrate the feasibility of dyestuff decomposition via semiconductor powders.