Alkali-assisted fabrication of holey carbon nitride nanosheet with tunable conjugated system for efficient visible-light-driven water splitting

Abstract Graphitic carbon nitride (CN) nanosheets have aroused a great deal of interest due to their capability to utilize visible light to split water into its constituent molecules of hydrogen and oxygen (H 2 and O 2 ). However, the photocatalytic capacity of conventional bulk g-C 3 N 4 , with its large π-π conjugated electronic system, is still constrained by the π-π stacking interaction and small number of active sites. Hence, an uncomplicated post-processing method to construct a different π-π conjugated electronic system of holey CN nanosheets using alkali etching of bulk CN (CN (B)) at 300 °C for 1 h has been developed. Among such compounds, the optimal alkali treatment bulk CN (CN 3(2)) exhibits a suitable conjugated system and copious in-plane holes, and it retains the ability to absorb sunlight during alkali depolymerization. Compared to CN (B), the resultant CN 3(2) has a distensible bandgap of 2.66 eV associated with a much larger specific surface area of 265.2 m 2  g −1 . However, excessive alkali treatment significantly decrease the visible light absorbance and the photocatalytic properties of the CN nanosheet, which demonstrated that a suitable π-π conjugated electronic system is very important in allowing the process to proceed. As such, the photocatalytic H 2 and O 2 production rate of CN 3(2) was nearly 24.6 times that of CN (B) with the addition of carbon quantum dots (CQDs) and Pt.