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

In this study, water-dispersible graphitic carbon nitride (g-C3N4) photocatalysts were successively prepared through the chemically oxidative etching of bulk g-C3N4 that was polymerized thermally in different calcination atmospheres such as air, CO2, and N2. The different calcination atmospheres directly influenced the physicochemical and optical properties of both bulk and water-dispersible g-C3N4, changing the photocatalytic degradation behavior of methylene blue (MB) and tetracycline hydrochloride (TC-HCl) for water-dispersible g-C3N4. The bubble-burst process in the thermal polymerization of thiourea produced defective edges containing C=O groups that preferred substituting the C-NHx groups over bulk g-C3N4. In the oxygen-free N2 atmosphere among the different calcination atmospheres, more C=O functional groups were generated on the defective edges of bulk g-C3N4, resulting in the highest N vacancy of the tri-s-triazine structure. During the successive chemical oxidation, S- or O-containing functional groups were introduced onto water-dispersible g-C3N4. The water-dispersible g-C3N4 photocatalyst from the oxygen-free N2 atmosphere (NTw) contained the most O- and S- functional groups on the g-C3N4 surface. Consequently, NTw exhibited the highest photocatalytic activity in the MB and TC-HCl photodegradation because of its slowest recombination process, which was ascribed to the unique surface properties of NTw such as abundant functional groups on the defective edges and N-deficient property.