Enhanced visible-light photocatalytic degradation and disinfection performance of oxidized nanoporous g-C3N4 via decoration with graphene oxide quantum dots

Abstract Oxidized nanoporous g-C3N4 (PCNO) decorated with graphene oxide quantum dots (ox-GQDs) was successfully prepared by a facile self-assembly method. As co-catalysts, the ultrasmall zero-dimensional (0D) ox-GQDs can achieve uniform dispersion on the surface/inner channels of PCNO, as well as intimate contact with PCNO through hydrogen bonding, π-π, and chemical bonding interactions. In contrast with PCNO, the ox-GQDs/PCNO composite photocatalysts possessed improved light-harvesting ability, higher charge-transfer efficiency, enhanced photooxidation capacity, and increased amounts of reactive species due to the upconversion properties, strong electron capturing ability, and peroxidase-like activity of the ox-GQDs. Therefore, the visible-light photocatalytic degradation and disinfection performances of the ox-GQDs/PCNO composite were significantly enhanced. Remarkably, the composite with a 0.2 wt.% deposited amount of ox-GQDs (ox-GQDs-0.2%/PCNO) exhibited optimum amaranth photodegradation activity, with a corresponding rate about 3.1 times as high as that of PCNO. In addition, ox-GQDs-0.2%/PCNO could inactivate about 99.6% of Escherichia coli (E. coli) cells after 4 h of visible light irradiation, whereas only ˜31.9% of E. coli cells were killed by PCNO. Furthermore, h+, •O2−, and •OH were determined to be the reactive species generated in the photocatalytic process of the ox-GQDs/PCNO system; these species can thoroughly mineralize azo dyes and effectively inactivate pathogenic bacteria.