Microstructure of carbon nitride affecting synergetic photocatalytic activity: Hydrogen bonds vs. structural defects

Carbon nitride has emerged as one of the most attractive materials for developing photocatalysts with low cost, high efficiency and structural stability. However, fast charge recombination caused intrinsically by the π–π conjugated electronic system severely limits its photocatalytic performance. Constructing carbon nitride photocatalysts with modulated electronic structures is thus a promising but challenging task. In this paper, carbon nitride with different microstructural features, such as degree of polymerization, hydrogen bonds, bandgap, structural defects and ratio of C/N, were synthesized by polymerization of different types of nitrogen-rich precursors. Synergetic reactions were rationally designed for hydrogen production and the efficient and simultaneous removal of multiple contaminants, using carbon nitrides as metal-free photocatalysts. The significant impact of hydrogen bonds on synergetic photocatalysis was comprehensively demonstrated. With the smallest amount of hydrogen bonds, carbon nitride derived from urea exhibited fast charge transfer between interlayers, which is a prerequisite for superior photoactivity. By contrast, the polymerization of melamine and cyanamide was favorable for the formation of abundant hydrogen bonds and intrinsic vacancy defects. It was found that the coexistence of nitrogen deficiency and oxygen-doped microstructures could facilitate the activation of oxygen molecules, and thereby contributed to their moderate photoactivity. This research provides fundamental insights into the microstructural engineering of carbon nitride for high-performance synergetic applications.