Photocatalytic degradation of dye sulforhodamine B: a comparative study of photocatalysis with photosensitization

The direct photocatalytic degradation of dye pollutant sulforhodamine B (SRB) in aqueous TiO2 dispersions has been examined and compared to the photosensitization process. The mineralization extent of SRB degradation, the formation of intermediates and final products were monitored to assess the degradation pathways caused by direct photocatalysis. In the initial stage of the direct photocatalysis, SRB is mainly oxidized by a positive hole upon band-gap excitation of TiO2 by UV light (330 nm < lambda < 380 nm) and subsequently undergoes the similar degradation pathways as occur in the photosensitization under visible irradiation (lambda > 420 nm). Diethylamine, N,N-diethylacetamide, N-ethylformamide, N,N-diethylformamide, formic acid and acetic acid were identified as intermediate species; SO42-, NH4+, CO2 and H2O are final mineralized products produced in the direct photocatalytic process.