Unveiling the enhanced photocatalytic degradation of metronidazole over green-synthesized Ag@ZnCdS QDs Schottky heterojunction: Pathway, toxicity evaluation and mechanistic insights

This study introduces an eco-friendly catalyst ZnCdS QDs/Ag nanocomposites (NCs) through green synthesis by using plant extract from Sansevieria zeylanica. The ZnCdS QDs/Ag-0.5 % demonstrated exceptional efficiency in the visible light photocatalytic degradation of the pharmaceutical pollutant metronidazole (MNZ), achieving a notable 95 % degradation within a short period of 260 min. Rigorous characterization revealed impeccable band alignment, evenly distributed surface area, and reduced charge transfer resistance in the designed NCs. The bandgap energy of ZnCdS QDs was 2.6 eV and decreased to 2.48 eV upon deposition over the Ag surface, facilitating the enhanced sensitivity to visible light. ZnCdS QDs/Ag-0.5 % exhibited outstanding stability and reusability, maintaining 94.5 % degradation efficiency even after six consecutive cycles of MNZ photocatalytic degradation, confirmed by XRD and XPS analysis. Scavenging studies show that the degradation rate was influenced by IPA and p-BZQ confirming the involvement of O2− and OH radicals in MNZ degradation. A comprehensive GC–MS analysis unveiled intermediates and the MNZ degradation pathway was elucidated. Furthermore, the possible toxicity associated with the intermediates was assessed using the ECOSAR program. In conclusion, the ZnCdS QDs/Ag catalyst presents a highly promising and sustainable green route for remediating various environmental pollutants, demonstrating potential advancements in green chemistry applications and paves a way for process innovation.