Study of reaction dynamics of photocatalytic degradation of 4-chlorophenol using SrTiO3, sulfur doped SrTiO3, silver metallized SrTiO3 and silver metallized sulfur doped SrTiO3 catalysts: Detailed analysis of kinetic results

This research work was carried out with the objective of understanding the reaction kinetics involving different catalysts like SrTiO3 (STO), sulfur doped SrTiO3 (S-STO), Ag metalized SrTiO3 (Ag-STO) and Ag metalized sulfur doped SrTiO3 (Ag-S-STO) which possess unique surface and bulk characteristics. Each catalyst was modified and improved by either bulk lattice modification or surface modification by metallization or by both the above process and the obtained results were compared with pristine SrTiO3. Though the nature of each catalyst was different, the photocatalytic degradation reaction taking place on their surface was found to fit for first order reaction only by 50% whereas, the reaction fitted well with the zero order reaction process. Ag-S-STO sample shows excellent photocatalytic activity under the illumination of solar light compared to the other catalysts. This activity can be correlated to the bulk / surface lattice modification by sulfur and also to the SPR effect of metallized silver particles. The photocatalytic degradation reaction rate was further enhanced in the presence of H2O2 as an oxidizing agent due to the formation of highly reactive species like hydroxyl free radicals and peroxy radicals. The reaction was found to follow bimolecular Langmuir Hinshelwood mechanism. The degradation reaction mechanism was proposed based on the intermediates detected by HPLC technique during the reaction process.