Photocatalytic degradation of Congo red dye using magnetic silica-coated Ag 2 WO 4 /Ag 2 S as Type I heterojunction photocatalyst: Stability and mechanisms studies

In the present study, magnet silica-coated Ag 2 WO 4 /Ag 2 S nanocomposites (FOSOAWAS) were fabricated via a multistep method to address the drawbacks related to single photocatalysts (pure Ag 2 WO 4 and pure Ag 2 S) and to clarify the significant influence of semiconductor heterojunction on the enhancement of visible-light-driven organic degradation. Different techniques were performed to investigate the elemental composition, morphology, magnetic and photoelectrochemical properties of the fabricated FOSOAWAS photocatalyst. The FOSOAWAS photocatalyst (1 g/L) exhibited excellent photodegradation efficiency (99.5%) against Congo red dye (CR = 20 ppm) after 140 min of visible-light illumination. This result confirmed the ability of the heterojunction between Ag 2 WO 4 and Ag 2 S species to improve the efficiency of the photogenerated electron/hole pair separation and to reduce their recombination. The kinetics studies of CR photoreaction suggested that the photodegradation rate of the FOSOAWAS photocatalyst was 3.26 and 2.94 times higher than that of pure Ag 2 WO 4 and Ag 2 S NPs, respectively. The CR dye was investigated under various operating conditions (FOSOAWAS dosage, CR concentration, and pH of solution). The trapping experiments proved the significant roles of H 2 O 2, • OH, and h + oxidants in the photoreaction of CR dye. The proposed mechanism explains that the Type I heterojunction between Ag 2 WO 4 and Ag 2 S semiconductors was responsible for the improved photocatalytic activity of the FOSOAWAS nanocomposite. Finally, the reusability and stability experiments proved the sufficient stability and facile separation of FOSOAWAS heterojunction, which may be employed in practical applications.