Precise carbon doping regulation of porous graphitic carbon nitride nanosheets enables elevated photocatalytic oxidation performance towards emerging organic pollutants

To improve the photocatalytic oxidation performance of graphitic carbon nitride (g-C3N4) towards organic pollutants, the present work develops a homogeneous carbon atom-self doping strategy to prepare porous carbon-rich g-C3N4 nanosheets (HCN-Cx). The preparation process of HCN-Cx includes preorganization of L-cysteine and urea under hydrothermal environment followed by thermal copolymerization, and carbon doping level can be precisely adjusted by changing initial urea/L-cysteine molar ratio from 5000, 1667, 1000 to 500. The characteristic results combined with theory calculations confirm that CCC skeleton from L-cysteine are introduced into the heptazine framework of g-C3N4 by the replacement of some CNC units; additionally, the introduction of CCC skeleton can generate defect-induced midgap states in the band structure of g-C3N4. The HCN-Cx nanosheets exhibit carbon doping level-dependent and notably elevated photocatalytic oxidation activity to three emerging organic pollutants including acetaminophen (APAP), levofloxacin (LEV) and methylparaben (MPB), in which the HCN-C0.5 performs the best. After visible-light irradiation of the HCN-C0.5 for 10, 8 and 90 min, the removal efficiency of APAP, LEV and MPB reaches up to nearly 100%. The excellent photocatalytic oxidation performance of HCN-Cx is dominated by carbon atom-self doping, which can not only enhance the visible-light harvesting efficiency but also boost photoexcited charge carrier transfer dynamics. Consequently, abundant reactive oxygen species including •O2−, 1O2 and •OH are generated, and they are responsible for the elevated photocatalytic oxidation performance of HCN-Cx.