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

Abstract

• Short carbon chain-incorporated g-C 3 N 4 are prepared by carbon atom-self doping route. • Visible-light harvesting ability and charge transfer dynamics of g-C 3 N 4 are promoted. • As-prepared HCN-C x show C doping level-dependent photocatalytic oxidation activity. • Abundant ROS such as •O 2 − , 1 O 2 and •OH are generated in HCN-C x photocatalytic system. • •OH and 1 O 2 are particularly important to elevated photocatalytic oxidation activity. To improve the photocatalytic oxidation performance of graphitic carbon nitride (g-C 3 N 4 ) towards organic pollutants, the present work develops a homogeneous carbon atom-self doping strategy to prepare porous carbon-rich g-C 3 N 4 nanosheets (HCN-C x ). The preparation process of HCN-C x 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 C C C skeleton from L-cysteine are introduced into the heptazine framework of g-C 3 N 4 by the replacement of some C N C units; additionally, the introduction of C C C skeleton can generate defect-induced midgap states in the band structure of g-C 3 N 4 . The HCN-C x 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-C 0.5 performs the best. After visible-light irradiation of the HCN-C 0.5 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-C x 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 •O 2 − , 1 O 2 and •OH are generated, and they are responsible for the elevated photocatalytic oxidation performance of HCN-C x .