Boosting photocatalytic oxidation on graphitic carbon nitride for efficient photocatalysis by heterojunction with graphitic carbon units

[Display omitted] •Carbon units modified g-C3N4 has been synthesized through m-phenylenediamine doping.•Direct in-plane junction between the carbon units and g-C3N4 was observed.•Band edges of g-C3N4 was downwards shifted by 1 eV via carbon unit doping.•Doped g-C3N4 is more efficient in the generation of OH radicals for oxidation process.•In situ infrared spectra confirmed the OH group adsorbed on surface of doped g-C3N4. Graphitic carbon nitride has been considered as a promising metal-free visible light photocatalyst for air pollutants oxidation due to its suitable band-gap energy and higher conduction band edge. Herein, we have developed a facile approach for dramatically downwards shifting band edge positions of carbon nitride up by about 1 eV via in-plane heterojunction with graphitic carbon units to enhance the oxidation capability of the electron holes generated from the valence band. The graphitic carbon units in junction with tri-s-triazine domains were clearly observed and its in-plane hybridization with carbon nitride was formed during the copolymerization using melamine with a small amount of m-phenylenediamine as the precursors. The direct intralayer junction between the tri-s-triazine and the graphitic carbon domain, essentially different with interlayer junction reported in literature, is able to shift downwards the band edge positions via merging electron density of states of carbon nitride with that of graphitic carbon, and thus would be beneficial for separation of photoexcited charge carriers and generation of hydroxyl radicals for the oxidation of pollutants. The hybrid photocatalyst prepared with a small quantity (less than 1%) of m-phenylenediamine and melamine as precursors has shown much enhanced NO oxidation to final products (NO2− and NO3−) and increased NO removal 10% than the one from melamine only.