Biogenic ZnS quantum dots for efficient photocatalytic degradation of polyethylene microplastics in water

Microplastic pollution in aquatic environments has become an emerging environmental challenge due to the persistent and inert nature of polymeric materials. Developing efficient and sustainable photocatalytic systems for microplastics (MPs) degradation remains highly desirable. In this study, biogenic ZnS (Bio-ZnS) quantum dots (QDs) were successfully synthesized by sulfate reducing bacteria (SRB) and pioneer employed for the photocatalytic degradation of polyethylene (PE) MPs in water. Among the Bio-ZnS catalysts prepared at different SRB growth stages, Bio-ZnS-7d exhibited optimized photocatalytic properties with enhanced light response, efficient charge separation, and accelerated interfacial charge transfer. Under xenon lamp irradiation, the Light + Bio-ZnS-7d system achieved a PE MPs weight loss of 28.38% within 48 h, which was approximately 2.9 times higher than that of direct light irradiation alone. Comprehensive characterization analyses demonstrated that Bio-ZnS-induced photocatalytic oxidation resulted in severe surface cracking, reduced crystallinity, decreased particle size, and the generation of oxygen-containing functional groups. Furthermore, the free radical trapping experiments and electron paramagnetic resonance tests implied that ·O₂^- and HO^• played a key role in the photocatalytic degradation of PE. And the density functional theory calculations revealed the preferential reactive sites of PE molecules during photocatalytic oxidation. Degradation intermediates were further identified by GC-MS, and possible degradation pathways were proposed. Finally, the mechanism of Bio-ZnS QDs photocatalytic degradation of PE MPs was elucidated. This study demonstrates a green biological strategy for synthesizing highly active ZnS QDs and provides a sustainable photocatalytic approach for mitigating persistent microplastic contamination in aquatic systems.