Tuning the visible-light photocatalytic degradation activity of thin nanosheets constructed porous g-C3N4 microspheres by decorating ionic liquid modified carbon dots: roles of heterojunctions and surface charges

Abstract

Ionic liquid modified CDs and novel thin nanosheets constructed graphitic carbon nitride (g-C₃N₄) microspheres were synthesized by the template method and by calcination of a supramolecular precursor, respectively. The CDs were decorated onto the surface of g-C₃N₄ by solvothermal treatment to tune the visible-light photocatalytic degradation performance of g-C₃N₄. The CDs could not only form heterojunctions with g-C₃N₄ by chemical bonding, π–π stacking and electronic attraction interactions, but also change the surface charges of g-C₃N₄ from negative to positive. The roles played by heterojunctions and surface charges in the photocatalytic performance of CDs (1.6 wt%)/g-C₃N₄ composites were explored by photocatalytic degradation of anionic (methyl orange, MO), nonionic (p-nitrophenol, p-NP) and cationic (methylene blue/rhodamine B, MB/RhB) pollutants. Compared with g-C₃N₄, the composite showed obviously higher and lower photocatalytic activity for MO/p-NP and MB/RhB degradation, respectively. These results demonstrated that the surface charges might play a positive or negative but dominant role by enhancing or inhibiting the absorption of pollutant molecules despite the fact that heterojunctions always played a positive role by promoting the light-harvesting ability and separation efficiency of photo-generated electron–hole pairs of g-C₃N₄.