B and cyano groups co-doped g-C3N4 with multiple defects for photocatalytic nitrogen fixation in ultrapure water without hole scavengers

B atoms and cyano groups co-doped graphite carbon nitride with nitrogen vacancies (VN-BC-CN) was explored via one-step in-situ route. A series of comprehensive experiments confirmed that B atoms and cyano groups had been doped into the framework of graphite carbon nitride, forming VN-BC-CN catalyst sample with a large number of nitrogen-vacancy defects. As electron acceptors, B and cyano groups could be used as active sites for nitrogen conversion. The defect level caused by nitrogen vacancy led to red shift of the light absorption edge, which resulted in higher separation efficiency of photo-induced carriers and faster transfer rate of photo-induced electrons for the VN-BC-CN catalyst. This VN-BC-CN catalyst had good photocatalytic nitrogen fixation performance in the ultrapure water without any hole-scavengers. The nitrogen photofixation rate of VN-BC-CN (115.53 μmol g−1 h−1) was 25.5 times that of pure carbon nitride (GCN, 4.53 μmol g−1 h−1). Moreover, NH4+ generation rate hardly decreased after 10 h reaction, and the NH4+ generation rate could reach 79.56 μmol g−1 h−1 in the fifth cycle, showing the good photocatalytic stability of the VN-BC-CN catalyst.