Facile in-situ fabrication of ZnO2/CQD composites with promoted visible-light photocatalytic activities for organic degradation and bacterial inactivation

Herein, the novel zinc peroxide/carbon quantum dots (ZnO2/CQD) composites were synthesized by an in-situ composite process for visible-light photocatalytic tetracycline (TC) degradation and Escherichia coli (E. coli) inactivation. It was found that 0.1 g/L ZnO2/CQD composite could degrade over 80 % of 50 mg/L TC and inactivate around 7-log E. coli cells after 2 h and 50 min of irradiation, respectively. The as-obtained ZnO2/CQD composites exhibited superior visible-light photocatalytic performance to individual ZnO2, and superoxide radical (O-center dot(2)-) and singlet oxygen (O-1(2)) were identified to be the main reactive oxygen species (ROSs) for TC degradation and E. coli inactivation. The introduction of CQD reduced the particle size and increased specific surface area, benefiting for adsorption. Meanwhile, it promoted visible-light absorption and accelerated the separation of photogenerated electron-hole pairs with a 3-fold increase in photocurrent, thus producing more ROSs under visible-light irradiation. Moreover, the ZnO2/CQD composites exhibited a high adaptability towards initial solution pH, common coexisting anions, oxygen-deficient environment, diverse water sources and organic pollutants. This study not only provided highly adaptable visible-light-driven photocatalysts for organic degradation and bacterial inactivation, but also shed light on the multifunctional roles of CQD in boosting visible-light photocatalytic performance.