Defect engineering of water-dispersible g-C3N4 photocatalysts by chemical oxidative etching of bulk g-C3N4 prepared in different calcination atmospheres

•Water-dispersible g-C3N4 is prepared by chemically oxidative etching of bulk g-C3N4.•Bulk g-C3N4 is polymerized in different calcination atmospheres of air, CO2, or N2.•Water-dispersible g-C3N4 from the N2 (NTw) shows the highest photodegradation rate.•NTw contains abundant O- and S- functional groups and N-deficiency on the g-C3N4.•The best photocatalytic performance of NTw is ascribed to the slowest recombination.