Coupling In-plane π-Electrons with Oxygen-Heteroatom in Ultrathin g-C₃N₄Nanosheets for Markedly Improved Photodegradation Activity

Low-dimensional g-C3N4 nanosheets have presented tremendous potential in eliminating water pollution, but the enlarged band gap and limited in-plane charge transmission efficiency partially offset its overall photocatalytic performance. Here, the inplane π-electrons conjugated system and oxygen heteroatoms were simultaneously introduced into ultrathin g-C3N4 nanosheets by a developed gas-shocking exfoliation strategy. Experimental results revealed that sample Cbelt-O-U-CNS possesses porous ultrathin nanosheets morphology (average 3-4 nm thickness), a larger surface area (112 m2 g-1), and a huge pore volume (0.32 cm3 g-1). Meanwhile, some beltlike graphitic carbon sections (Cbelt) have been in-plane stitched into Cbelt-O-U-CNS framework, and partial two-coordinated N atoms have been replaced by O heteroatoms. This unique plane heterostructure in Cbelt-O-U-CNS could expand its local in-plane π-conjugated electric field and stimulate the n → π∗ electronic transition, leading to faster separation of the hole-electron pair and enhanced visible-light absorption. More strikingly, the valence band (VB) of Cbelt-O-U-CNS can be shifted to a positive energy level, thus contributing to directly producing •OH. As expected, Cbelt-O-U-CNS exhibited superior photodegradation activity in various dyes involving wastewater treatment (RhB, MB, MO, AO7) and strong adaptability for wide pH variations, various coexisting ions, and high pollutant concentration. This work provides a perspective for simultaneously regulating the π-electron and oxygen heteroatom in ultrathin g-C3N4 nanosheets.