Sterilization mechanism and nanotoxicity of visible light-driven defective carbon nitride and UV-excited TiO2

The sterilization effect of photocatalysis and biotoxicity of nanomaterial catalysts have attracted high attention. In this study, the novel visible-driven defective carbon nitride (VL/DCN) system exhibits non-photoreactivation, non-toxic superior performance compared with traditional ultraviolet radiation (UV) and UV/titanium dioxide (UV/TiO2). The inactivation of antibiotic-resistant bacteria (ARB) by novel VL/DCN still reached 7 log within 4 h, and the reduction rates of aminoglycoside gene strB and tetracycline gene tetA exceeded 0.8 log and 1.2 log, respectively. Further, the sterilization mechanism and nanotoxicity were contrastively and systematically analyzed among above three systems as following. Firstly, in the VL/DCN system, reactive oxygen species (ROSs) generated from photocatalytic process leads to the destruction of cell membranes, resulting in dissolving out of potassium ion (K+), protein and cell membrane ATP content. Thus, resistant bacteria were completely inactivated and photoreactivation disappears. In contrast, the UV only acted on bacterial DNA and existed the light resurrection. The UV/TiO2 strictly dependent on ultraviolet light and can be used in limited scenarios. Secondly, in cell viability analysis by human lung cell line BEAS-2B experiments, the 10% inhibition of cell growth when DCN was 600 mg/L much lower than 28% inhibition of cell growth when TiO2 was only 200 mg/L. The expression of pro-inflammatory cytokines ((Interleukin, IL) -6), IL-8, IL-1 beta) under the effect of DCN was 1.5-fold, 5.7-fold and 3.7-fold lower than TiO2, respectively. Meanwhile, DCN induced cells to produce less ROSs, malondialdehyde (MDA), and more superoxide dismutase (SOD). Above results demonstrated that DCN has far lower cytotoxicity than TiO2. This study provides theoretical support for the application of photocatalytic sterilization technology and the exploration of the toxicity of nanomaterials.