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 (H2 and O2). However, the photocatalytic capacity of conventional bulk g-C3N4, 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 1h 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 2.66eV associated with a much larger specific surface area of 265.2m2g−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 H2 and O2 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.