Graphene–CdS nanocomposite inactivation performance toward Escherichia coli in the presence of humic acid under visible light irradiation

Abstract Graphene–CdS (G–CdS) nanocomposite was prepared successfully via a two-step solvothermal process, with CdS uniformly dispersed on the graphene nanosheets. The photocatalytic disinfection activity of G–CdS was evaluated, and the result shows that G–CdS exhibited higher inactivation efficiency toward the gram-negative bacterium, Escherichia coli , than pure CdS nanoparticles under visible light irradiation. Exposure to 10 mg of pure CdS resulted in a 1.1-log inactivation after 60 min, but resulted in 5.3-log reduction of viable bacteria when exposure to 10 mg G–CdS under the same illumination conditions. In addition, the impacts of humic acid (HA), a kind of natural organic matter (NOM), on its bactericidal properties have also been determined. G–CdS in the presence of HA (10 mg/L) significantly decreased its toxicity, causing less than 0.4-log inactivation after 60 min. Lipid peroxidation, intercellular ROS generation and antioxidant enzyme activities assays indicate that excess oxidative stress induced by G–CdS suppressed the antioxidant defense system, subsequently affected the normal function of lipid, protein and nucleic acid, and thus resulted in cell death. However, the decreased toxicity of G–CdS in the presence of HA may be attributed to that (1) HA presents a barrier to prevent the physical contact between bacteria cells and G–CdS, which was the first step of toxicity mechanisms; (2) HA acts as an antioxidant to react with any ROS and reduce the toxicity.