Visible-light-responsive photocatalytic inactivation of ofloxacin-resistant bacteria by rGO modified g-C3N4.

The visible light responsive graphitic nitride (g-C3N4) mediated photocatalysis has drawn extensive attention in water treatment field. Carbon doping could improve the photocatalytic activity of g-C3N4 in promoting charge separation efficiency, visible-light utilization, etc. In this paper, the g-C3N4 (as MC) was modified by barbituric acid (as MCB0.07) and further treated by reduced graphene oxide (rGO) (as n%GCN) and then applied to inactivate ofloxacin-resistant bacteria (OFLA) under light irradiation at UVA-visible wavelength. The results showed that the n%GCN presented strong photocatalytic activity when the GO mass ratio was 7.5% (as 7.5%GCN). The inactivation efficiencies of OFLA by MC, MCB0.07, and 7.5%GCN were 5.77 log, 8.48 log, and 8.25 log, respectively, under UVA-visible wavelength (λ > 305 nm), compared to 4.83 log, 5.56 log, and 6.08 log, respectively, within 16 h under visible wavelength (λ > 400 nm). The rGO-doping obviously improved the inactivation efficiency of MCB0.07 on OFLA under visible wavelength. Furthermore, the photoreactivation and dark repair phenomena of OFLA were examined after MC, MCB0.07, and 7.5%GCN treatment, respectively, and it was found that all approaches led to permanent damage to OFLA of which the regrowth was not observed after 24-48 h. Based on the quenching test, reactive oxygen species of O2-• and hole (h+) exhibited dominant roles in the photocatalytic inactivation of OFLA, which may result in oxidative stress and damage to the cell membrane. This study could shed light on the inactivation of OFLA under visible light radiation by rGO modified g-C3N4.