Visible Light Enhancement of Elemental Sulfur Production from Hydrogen Sulfide by Bacterial Cellulose (BC)-Confined Metalloporphyrin Hydrogel

Abstract

Hydrogen sulfide removal is a crucial environmental and safety issue, but its removal mostly involves high energy consumption or the utilization of toxic chemicals. Photocatalytic oxidation is a green process for sulfide removal, but its efficiency using dispersed catalysts has been restricted by uneven light intensity. In this study, a high efficiency catalytic material was designed and synthesized for the enhanced photooxidation of sulfide to elemental sulfur. 5,10,15,20-Tetrakis(p-carboxylphenyl)porphyrin (4-Car-PP) associated with transition metal ions was confined on bacterial cellulose (BC) as a hydrogel and operated under visible light with microaeration. Nickel was identified as the most efficient catalyst, and BC could significantly improve its photocatalytic process. Compared to Ni-Car-PP alone, sulfur recovery increased from 0.14 to 20.1 mmol dm^-3 h^-1 with the BC-Ni-Car-PP hydrogel. Light also showed a 4.3-fold enhancement in elemental sulfur fixation. Transient adsorption study revealed that the chelation of sulfide on the nickel center facilitated singlet state photoexcited electron transfer, which enhanced electron transfer through the metal-ligand cooperative effect. This limited polyoxosulfur ion formation but facilitated polysulfide formation, leading to an increase in elemental sulfur formation. The combination of the hydrogel catalyst, microaeration, and mild operational requirements implies its potential application in air pollution control, biogas purification, and wastewater management without the need for sophisticated pH control and regulations.