Enhanced photodegradation of toxic organic pollutants using dual-oxygen-doped porous g-C3N4: Mechanism exploration from both experimental and DFT studies

Abstract

Novel visible-light-driven dual-oxygen-doped porous g-C3N4 (OPCN) photocatalysts were synthesized by a facile thermal copolymerization of urea and ammonium oxalate. The introduced O atoms were preferable to synchronously substitute for two sp2-hybridized N atoms in the para-positions (i.e., N1′ and N4′ sites) of the melem unit by forming dual-O-doped g-C3N4. Together with porous structures, OPCN exhibited enlarged specific surface area, narrowed band gap and expanded visible light response. The photocatalytic activity of the optimal OPCN was approximately 9 times higher than that of pure g-C3N4 for bisphenol A (BPA) removal under visible light irradiation, and efficient removal rates for various chlorophenols, phenols and dyes were also observed. Combined with experiments and DFT calculations, this dual-O-doped structure resulted in effective charge transfer and separation of OPCN under visible light irradiation by forming e− and h+-related conjugated delocalized systems on the surface, which contributed to its interfacial contact with organic pollutants and adsorbed O2. As a result, the degradation of BPA was readily induced by photoinduced h+ and then thoroughly mineralized by O2−. On the other hand, more O2− radicals were generated, which could also oxidize BPA directly due to their strong oxidation power. The superior stability and reusability of OPCN catalysts were also revealed during photoreaction. This work provides a novel viewpoint to fabricate high-performance nonmetal photocatalysts for wastewater treatment.