Sulfur- and chlorine-co-doped g-C3N4 nanosheets with enhanced active species generation for boosting visible-light photodegradation activity

Abstract

Elemental doping is an important strategy for modifying the electronic properties of graphitic carbon nitride and tuning its visible-light photocatalytic activity. In this study, sulfur- and chlorine-co-doped g-C3N4 (S/Cl-CN) have been synthesized by a thermal condensation method. Among a series of samples, S/Cl-CN exhibited the best photocatalytic activities for the degradation of rhodamine B (RhB) and 4-nitrophenol (4-NP). The as-synthesized S/Cl-CN possessed a modified electronic structure and large specific surface area as well as more active sites. According to diffuse-reflectance spectroscopy (DRS), UPS (ultraviolet photoelectron spectrometer), and valence band (VB)-XPS investigations, S/Cl-CN displayed a narrowed band gap and positively shifted VB edge potential with enhanced oxidation ability. First-principles calculations implied that the narrower band gap and better charge-separation ability may be attributed to the Cl 3p orbital as the doping level. Moreover, the S/Cl-CN with narrowed band-gap and positively shifted VB potential could possess double channels to form OH by direct oxidation of h+ at VB and reduction of O2 at CB. Based on the strong oxidizing ability of the S/Cl-CN, the possible formation of reactive chlorine-based species in the photocatalysis process is proposed. This work provides a new perspective for tuning the band structure of a photocatalyst through a doping strategy and greater insight into the generation paths of active species involved in the photocatalytic process.