Photocatalytic degradation of some organic sulfides as environmental pollutants using titanium dioxide suspension

The photocatalytic degradation of four organic sulfide compounds containing different functionalities; methyl phenyl sulfide (MPS), methyl benzimidazoyl sulfide (MBS), propyl benzimidazoyl sulfide (PBS) and 3-propenyl benzimidazoyl sulfide (3-PBS) as environmental pollutants using TiO2 photocatalyst suspension under UV-light irradiation in aqueous and organic (ethanol, methanol, acetonitrile, CCl4 and n-hexane) solvents was studied. The effect of important operational parameters such as solvent, catalyst loading, oxygen flow, irradiation time, pH, and comparison of photocatalytic activity with different commercial ZnO and TiO2 (rutile and anatase) catalysts were also studied. The photodegradation rate was determined for each experiment and the following trend viz. TiO2 (rutile) > ZnO > TiO2 (anatase) was observed, suggesting that ZnO absorbs a large fraction of the UV-light and absorbs more light quanta than TiO2 (anatase). The effectiveness of large particles in this reaction is understandable from the properties of TiO2 particles, which indicate that band bending is necessary to oxidize sulfide compounds. To develop the band bending in particles, their size and donor density are important. Usually, rutile powders have larger particle sizes than the anatase powders, because they are produced at higher temperature, and thus are advantageous for band bending. Results show that the photocatalytic degradation is well progressed in the aqueous solution and in the presence of oxygen. Optimum value of TiO2 (rutile) photocatalyst was obtained 30 mg per 20 ml of solution. The best UV-light irradiation time for MPS was 100 min and for the other sulfide compounds was 3 h. Further studies showed that the optimum values of solution pH were observed 8 and 6 for MPS and for the others, respectively. The complete mineralization was confirmed by total organic carbon (TOC) analysis and estimation of the formation of inorganic ions such as NH4+, CO2 and SO42−.