Precursor-driven defect engineering in CdS photocatalyst: Influence of sulfur sources on structure, charge dynamics, and solar-light-driven photocatalytic performance

Abstract

The application of cadmium sulfide (CdS) photocatalyst for practical wastewater treatment in the photocatalysis field is strictly limited by the main disadvantages of ultrafast charge-carrier recombination rate and extensive photo-corrosion under solar exposure, making the CdS less than ideal for large-scale lifetime potentials and translatability. Although recent literature attempts to remedy such concerns with complicated heterojunction construction or elemental doping, such methods increase synthetic intricacies making real-world implementation impossible. On the other hand, limited focus has been placed on the precursor sulfur source to create the desired defects, crystallite formations, and charge transfer mechanisms despite its fundamental research toward tuning photocatalyst performance. Thus, in the present paper, we explore the precursory sulfur source during the synthetic step to demonstrate a structure-function relationship across two distinct precursors of surfer (S) namely sodium sulfide (CdS-SS) and thiourea (CdS-TU). The finding shows that the CdS-TU photocatalyst boasts superior long-range crystallinity while the CdS-SS photocatalyst provides a mesoporous structure abundant in advantageous sulfur-vacancy defects. Interestingly, the CdS-SS exhibits greatly quenched photoluminescence emission which corelates well with the exceptional solar-driven photocatalytic performance of 99% degradation of azo dyes, Reactive Red 141 (RR141) dye and Congo Red (CR) dye, together with 90% detoxification of ofloxacin (OFL) antibiotic. The prepared CdS-SS photocatalyst provides the enhanced first-order rate constant, about three times higher than that detected from the CdS-TU photocatalyst. Trapping experiment demonstrates that photogenerated holes (h⁺) are the dominant reactive species involved in removal of the pollutant. The prepared CdS-SS retains its promising photoactivity with the original morphology after five cycles of use. This paper demonstrates the precursor-based defect engineering strategy to fabricate a promising solar-driven CdS photocatalyst for environmental application.