Low-temperature microwave-assisted synthesis of Bi2WO6/Bi2S3 heterojunction for photocatalytic reduction of Cr(VI) in industrial wastewater

Abstract

Cr(VI) pollution has become a worldwide environmental issue due to its toxicity and non-biodegradability in wastewater. Herein, a Bi2S3/Bi2WO6 (BWS) Z-scheme heterojunction was successfully fabricated via a low-temperature in situ sulfurization process assisted by microwave irradiation and applied to the photocatalytic reduction of Cr(VI) in industrial electroplating wastewater. The effects of Bi2S3 loading, catalyst dosage, light source, and synthesis method on the catalytic performance of the heterojunctions were investigated. Remarkably, the optimized BWS-6 heterojunction achieved 100% Cr(VI) removal within 50min under LED light irradiation and 30min under sunlight irradiation, which greatly exceeded the pure Bi2S3 and Bi2WO6. In addition, BWS-6 exhibited high photostability, and it still sustained preferable photocatalytic Cr(VI) reduction activity under sunlight irradiation when the experiment was scaled up 20 times. The high photocatalytic activity of BWS photocatalysts can be ascribed to enlarged surface area, active centers, and intimate interfacial contact of Z-scheme heterojunction, which greatly improve visible-light harvesting, surface adsorption, and the transport efficiency of interfacial charge. Experimental and theoretical calculation results further evidenced a built-in electric field forming at the interface of the Z-scheme heterojunction and unveiled a possible photocatalytic reduction pathway. This work provides valuable information for large-scale applications in the removal of Cr(VI) from industrial wastewater by Z-scheme heterojunctions.