Antibacterial Activity of Graphene Oxide/g-C3N4 Composite through Photocatalytic Disinfection under Visible Light

Carbon-based nanomaterials have been widely developed into innovative antimicrobial agents due to their advantages of high surface-to-volume ratio, extremely high mechanical strength, and distinct physicochemical properties. Here, the nanocomposite of graphene oxide/graphitic carbon nitride (GO/g-C3N4), a free-metal photocatalyst, was fabricated through sonication at room temperature and its antibacterial activity against Escherichia coli (E. coli) was investigated. The 100 μg/mL GO/g-C3N4 composite was found to kill 97.9% of E. coli after 120 min visible light irradiation, which was further confirmed by fluorescent-based cell membrane integrity assay. Additionally, the holes produced by photocatalysis were confirmed by electron spin resonance (ESR) spectra and trapping experiments to participate in photocatalytic sterilization as principal active species and were further verified by transmission electron microscopy (TEM) and scanning electron microscope (SEM) to lead to the distortion and rupture of cell membrane and finally cell death. Further photoluminescence (PL) spectra, cyclic voltammetry, photocurrent generation, and impedance spectroscopy (EIS) characterization revealed that the introduction of GO contributed to separate photogenerated electrons and prevents the electron–hole pairs of g-C3N4 from recombing to generate more h+, thus directly improving the bactericidal ability of GO/g-C3N4. Reusability assays indicated that the GO/g-C3N4 retained more than 90% of activity after four cycles of use. This study facilitates an in-depth understanding of the mechanism of visible light-driven disinfection and provides an ideal candidate sterilizing agent for treating microbial-contaminated water.