Carbon defective carbon nitride with large specific surface area by hot oxygen etching for promoting photocatalytic performance

Defect engineering is an extremely powerful strategy for carbon nitride materials. In our paper, carbon defective-carbon nitride (V-g-C3N4) with a large specific surface area (555.3 m2 g−1) was prepared by multiple thermal and oxygen etching using urea as a precursor. The photocatalytic performance of the materials was evaluated by synthetic ammonia under visible light and full spectrum. Under visible light, V-g-C3N4 can produce 3.60 mmol/h/g of NH3, which is approximately ~ 3.24 times higher than that of g-C3N4. Under the sunlight, V-g-C3N4 can produce 21.35 mmol/h/g of NH3. Particularly, positron annihilation lifetime spectroscopy (PALS) was used to confirm the type of vacancies. The experimental results show that the method of multiple calcinations not only can successfully introduce the carbon vacancy into the polymerization network structure of carbon nitride, resulting in a large number of active sites are added for the reaction of ammonia synthesis, but also can expand the bandgap from 2.82 eV to 3.03 eV. In addition, After g-C3N4 was exposed to high temperature and weak oxygen three times, its structure became loose and porous, which also provides more active sites for the reaction. Herein, these findings provide a novel concept of introducing carbon vacancies to promote the efficiency of photocatalytic ammonia synthesis.