Research progress on g–C3N4–based photocatalysts for organic pollutants degradation in wastewater: From exciton and carrier perspectives

Graphitic carbon nitride (g-C 3 N 4 ) can be used to degrade organic pollutants in wastewater owing to its excellent chemical stability, tunable band structure, and visible light (VL) responsiveness. Nevertheless, the application of pristine g-C 3 N 4 is significantly hindered by its low specific surface area, unsatisfactory VL utilization (<460 nm), high exciton binding energy ( E b ≈ 0.2 eV), and low photoinduced carrier separation. Development of strategies to overcome these limitations and improve the degradation efficiency has attracted considerable attention. Considering the principles of photoexcitation, this paper describes two unique photoexcitation processes, the carrier and exciton processes, of which the strong exciton effect of g-C 3 N 4 has not been extensively discussed in prior reviews. In addition, we comparatively present the latest progress and related mechanisms of the modification strategies such as morphology controlling, elemental doping, defect engineering, and heterojunction building employed in polluted water treatment are compared from the carrier and exciton perspectives. Finally, the unique characteristics, challenges, and future directions are discussed. This review presents research progress on the photoexcitation processes involved in g–C 3 N 4 –based materials, and proposes that the modification based on the exciton effect and direct verification of the transfer mechanism in the heterojunction can be potential areas of future investigations. • Energy band theory and exciton effect related to photoexcitation mechanism were discussed. • Various modification strategies for enhancing the photocatalytic activity of g-C 3 N 4 are reviewed. • Construction of the Z-scheme system can improve photocatalytic activity.