Controllable Approach to Carbon-Deficient and Oxygen-Doped Graphitic Carbon Nitride: Robust Photocatalyst Against Recalcitrant Organic Pollutants and the Mechanism Insight

Polymeric g-C3N4 is a promising visible-light-responsive photocatalyst; however, the fast recombination of charge carriers and moderate oxidation ability remarkably restrict its photocatalytic oxidation efficiency towards organic pollutants. To overcome these drawbacks, a self-modification strategy of one-step formaldehyde-assisted thermal polycondensation of molten urea to prepare carbon-deficient and oxygen-doped g-C3N4 (V-C-OCN) is developed, and the carbon vacancy concentration is well-controlled by changing formaldehyde dosage. The V-C-OCN catalysts exhibit interesting carbon vacancy concentration-dependent photocatalytic removal efficiency to p-nitrophenol (PNP) and atrazine (ATN), in which V-C-OCN15 with appropriate carbon vacancy concentration displays significantly higher pollutant removal efficiency than bulk g-C3N4. The apparent first-order rate constant of V-C-OCN15 for PNP and ATN removal is 4.4 and 5.2 times higher than that of bulk g-C3N4. A combination of the experimental results and theoretic calculations confirm that the synergetic effect of carbon vacancies and oxygen doping sites can not only delay the recombination of charge carriers but also facilitate adsorption of oxygen molecules on the carbon vacancies, which leads to the generation of plentiful active oxygen species including not only superoxide anion radicals but also indirectly formed hydroxyl radicals and singlet oxygen. These active oxygen species play a dominant role in the removal of target pollutants.

Automated summary

This study developed a self-modification strategy to prepare carbon-deficient and oxygen-doped g-C3N4 catalyst, which showed high efficiency in photocatalytic removal of p-nitrophenol and atrazine. The mechanism behind this efficiency is the synergistic effect of carbon vacancies and oxygen doping sites in generating abundant active oxygen species.