Solar photocatalytic generation of hydrogen from hydrogen sulfide in an alkaline solution using CdS-ZnS/TiO2 nanocomposites

Abstract

Hydrogen sulfide (H2S) is a toxic gas and it is generated due to various industrial activities and sewage treatment plants (STPs). Sulfide wastewater generated from anaerobic digestion of sewage sludge in STPs, tanning of hides, pulp and paper industries and caustic scrubbing of H2S. It may lead to SO2 emission and cause corrosion of pipelines. Hence the removal of sulfide ion from the wastewater is necessary. In this research study, five types of novel solar UV-visible light responsive nanophotocatalysts viz., CdS NPs, ZnS NPs, TiO2 NTs, CdS-ZnS NCs and CdS-ZnS/TiO2 NCs were synthesized for the photocatalytic generation of H2 from H2S in an alkaline solution. The outdoor solar feasibility studies were conducted for evaluating the activity of the nanophotocatalysts. The H2 generation rate over CdS NPs, ZnS NPs, TiO2 NTs, CdS-ZnS NCs and CdS-ZnS/TiO2 NCs were observed to be 419, 157, 209, 838 and 1100 and#956;mol/h, respectively. From the results, it was concluded that CdS-ZnS/TiO2 NCs was better than other nanophotocatalysts. In order to study the applicability of the process, sulfide wastewater was collected from the sewage treatment plant for the photocatalytic generation of H2. Kinetic analysis of the experimental data was done for finding rate constants (k obs and kc). This reaction followed the first order reaction. Based on the performance of the photocatalytic reactors, continuous mode was selected and the pilot-plant reactor was designed for treating 1m3 of sulfide wastewater from the sewage treatment plant. The calculated length of the reactor for treating of 1m3 of sulfide wastewater was 55 m. The cost for treating 1m3 of sulfide wastewater was Rs. 284/m3. From this study, it is concluded that the solar photocatalytic generation of H2 from H2S in an alkaline solution is feasible and quite suitable for solar belt areas.