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Flowerlike copper-doped g-C3N4 is synthesized via a novel molten salt-assisted microwave process in this work. X-ray diffraction, N2 adsorption, UV–vis spectroscopy, scanning electron microscopy, photoluminescence, temperature-programmed desorption, X-ray photoelectron spectroscopy, and electrochemical impedance spectra were used to characterize the prepared catalysts. The results show that Cu+ is not present as oxide but inserts at the interstitial position through the coordinative Cu­(I)–N bonds. These Cu­(I)–N active sites can act as chemical adsorption sites to activate N2 molecules. Moreover, as an “electron transfer bridge”, Cu­(I)–N active sites promote electron transfer from the catalyst to the adsorbed N2 molecules. The as-prepared copper-doped g-C3N4 displays a much higher NH4 + generation rate than neat g-C3N4 prepared by calcination, as well as excellent catalytic and structural stability. Density functional theory simulations prove that Cu­(I)–N active sites can adsorb the N2 molecule with high adsorption energy and elongate the NN bond. Charge density difference result confirms the electrons transfer from the Cu+ doping sites to the N2 molecule. Density of states results indicate that the σg2p orbital in nitrogen atom is delocalized significantly when N2 is adsorbed on Cu+ doping sites; also, the πg*2p orbital is transferred to the vicinity of the Fermi level. These make the nitrogen molecules more efficient to activate.

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Photocatalytic oxidation technology for the anoxic removal of organic pollutants that exist under some oxygen-free conditions is attractive but challenging.