Oxygen-containing groups and P doped porous carbon nitride nanosheets towards enhanced photocatalytic activity

Metal-free polymer graphite carbon nitride (CN) is a promising photocatalyst that has garnered significant research attention. However, unmodified CN possesses several shortcomings such as low specific surface area, poor dispersibility in water, and rapid photogenerated electron-hole recombination, which have severely impacted its mass adoption. Here, this study proposed a two-step heat treatment method to incorporate P dopant and the containing-oxygen groups successively into CN. The final product, denoted as PO-CN, possessed a porous ultrathin nanosheet-like morphology. The introduction of P dopant altered the intrinsic electronic structure of CN. Meanwhile, the presence of oxygen-containing groups improved the dispersibility of PO-CN in water. Also, it led to the formation of a porous ultrathin structure that could provide more active sites. Through the synergistic effects of these two methods, PO-CN demonstrated superior photocatalytic performance compared to the unmodified counterpart. Based on the collective results obtained experimentally and theoretically, PO-CN possessed a porous ultrathin structure, low resistance, and low carrier recombination. The results show an optimal hydrogen evolution rate of PO-CN (997.7 mol h^-1 g^-1), which was 11.2 times and 3.22 times that of the CN (88.89 mol h^-1 g^-1) and PCN (310.3 mol h^-1 g^-1). Moreover, PO-CN was then used in the degradation of Rhodamine B, and a degradation kinetic constant (k) of 0.15009 was calculated, which was 18.42 times and 8.22 times higher as compared to those of CN (0.00815) and PCN (0.01826). Hence, this work provides a new strategy for the alteration of the morphology and electronic structure of CN.