ZnO/ZnS photocatalyst from thermal treatment of ZnS: Influence of calcination temperature on development of heterojunction structure and photocatalytic performance

New strategy to create sunlight-active photocatalysts is a vital research topic in photocatalysis. In this work, ZnO/ZnS heterojunctions were fabricated very easily by thermal oxidation of hydrothermally grown ZnS in air. XRD, FT-IR, FESEM, TEM, XPS, XAS and PL results confirmed that ZnS-500 (ZnS calcined at 500 degrees C) contains the ZnO/ZnS heterojunctions. The ZnS-500 exhibited the highest photoactivity toward removal of azo dyes (reactive red 141, Congo red) and antibiotics (ofloxacin, norfloxacin) under natural sunlight. The combination of ZnS and ZnO enhances the photoactivity by suppressing the recombination of electron-hole pairs. The photodegradation of the organic contaminants followed pseudo-first order kinetics. The photocatalyst showed structural stability after five cycles. To understand the photocatalytic degradation mechanism, trapping experiment using various scavengers have been investigated. Photogenerated electrons are the crucial species involved in the degradation of the pollutant. It is also proposed that charge transfer at the ZnO/ZnS heterojunction is the Z-scheme type. This work provides a facile strategy for the interfacial engineering of heterojunctions with enhanced photocatalytic performance for environmental remediation.