Photocatalytic H2O-to-H2O2 synchronized oxidation of an organic pollutant by carbon dot/g-C3N4 composites

Photocatalytic oxidation of organic pollutants using the solar energy is environmentally and economically attractive for developing an energy sustainable organic wastewater treatment process. Here, we employed the impregnation-thermal method to prepare novel carbon dot (CD) dispersed graphitic carbon nitride (g-C3N4) (GCN)/pyromellitic dianhydride (PDI) (CD/GCN/PDI) composites for photocatalytic H2O-to-H2O2 and on-site oxidation of organic pollutants in contaminated or waste water. After a 5-h visible-light irradiation, 252 μM of H2O2 can be yielded by the CD/GCN/PDI composites. The CD, serving as an electron reservoir, dispersed on the GCN/PDI composite (i.e., CD0.003/GCN/PDI) facilitates the separation of photo-excited electrons to promote the two-electron reduction O2-to-H2O2 (O2→˙O2−→H2O2). Most importantly, it also on-site activates H2O2 to form ·OH radicals (H2O2→·OH) to enhance oxidation of organic pollutants (e.g., methylene blue and bisphenol A). The ·OH, ∙O2−, and photogenerated h+ account for 4–5%, 14–18%, and 20–25% oxidation of organic pollutants under visible-light irradiation for 3 h, respectively. The CD0.003/GCN/PDI composite was also tested for photocatalytic oxidation of the organic pollutant under visible-light irradiation for at least 12 h to demonstrate its photostability and reusability. This visible-light photocatalytic H2O-to-H2O2 for the enhanced oxidation of organic pollutants by the low-cost and metal-free CD/GCN/PDI composites using solar energy was developed to demonstrate the feasibility of an energy self-sufficient organic wastewater treatment process.