Green synthesis of Bio-CuS quantum dots by sulfate reducing bacteria for solid-phase photocatalytic degradation of polyethylene film

Abstract

In this study, CuS quantum dots (QDs) synthesized through biological method were used as photocatalysts for the photocatalytic degradation of polyethylene (PE) plastics. Bio-CuS QDs were synthesized through a green process using sulfate reducing bacteria, while Che-CuS QDs were prepared by chemical precipitation for comparison. The crystal structure, surface morphology, microstructure and optical properties of the samples were detected by XRD, SEM, TEM and UV–Vis DRS. The green synthesis mechanism of Bio-CuS was inferred by analyzing changes in amino acid concentration and the three-dimensional fluorescence spectra of extracellular polymeric substances before and after synthesis. The photocatalytic degradation of PE films by Che-CuS and Bio-CuS was investigated. The weight loss rates of PE+Che-CuS and PE+Bio-CuS were 9.1 % and 12.8 % after 14 d irradiation, respectively, while pure PE was only 1.7 %. Furthermore, SEM, UV–Vis DRS, contact angle, TGA, GPC and FTIR were adopted to characterize the PE film. The results revealed that PE+Che-CuS and PE+Bio-CuS underwent major changes in morphology, transparency, hydrophilicity, thermal stability, molecular weight and functional groups compared with PE, with more pronounced changes observed for PE+Bio-CuS. The quenching experiments of active species showed that h+ and·OH were critical to the PE degradation. The intermediate products of PE degradation were analyzed by GC–MS, and a possible degradation pathway was proposed. In addition, the possible mechanism of photocatalytic degradation of PE films by CuS QDs was proposed. This work provides a green remediation approach to addressing the growing plastic pollution in the environment.