Solar-Driven Photocatalysis for Wastewater Treatment Promoted by Sulfite Addition

Solar-driven heterogeneous photocatalysis is considered a promising technique for degradation of organic pollutants in wastewater. Visible light from the solar spectrum is however not efficiently utilized in photocatalysis. In this work, we have developed a sulfite-enhanced visible-light-driven photocatalysis process using BiOBr as the model photocatalyst and methyl orange (MO) as the model organic pollutant. We found that the degradation rate of MO was improved by 29 times in the presence of 20 mM sulfite, and the enhancement increased with the concentration of sulfite. Studies using hole scavengers suggest that sulfite radicals generated by the reactions of sulfite (sulfite anions or bisulfite anions) with holes or hydroxyl radicals are the active species for MO photodegradation using BiOBr under visible light. In addition to the BiOBr/MO system, the sulfite-assisted photocatalysis approach has been successfully demonstrated in a variety of photocatalysis systems including BiOBr/rhodamine B (RhB), BiOBr/phenol, BiOI/MO, and Bi 2 O 3 /MO systems under visible light irradiation, as well as in TiO 2 /MO system under simulated sunlight irradiation. The developed method implies the potential of introducing external active species to improve photocatalytic degradation of organic pollutants.