Scalable and clean exfoliation of graphitic carbon nitride in NaClO solution: enriched surface active sites for enhanced photocatalytic H2 evolution

Abstract

Graphitic carbon nitride (g-C₃N₄) has attracted wide attention as a promising visible-light-driven metal-free semiconductor photocatalyst. The transportation and transformation of photogenerated carriers during the photocatalytic process of g-C₃N₄ are restricted by the insufficient surface active sites and low charge separation efficiency. As a top-down strategy, the exfoliation of layer-stacked bulk g-C₃N₄ into nanosheets is widely recognized as an applicable route, yet still challenging in terms of scalable and clean synthesis. Herein, this challenge was tackled via a simple hydrothermal method in NaClO solution, in which the synergetic effect of alkaline metal ion intercalation and the oxidative exfoliation of bulk g-C₃N₄ was involved. Highly active g-C₃N₄ nanosheets were easily made in the laboratory in tens of grams and this simple process could readily be extended to the scale of kilograms. The hydrothermal treatment created vertical channels for directional electron transfer and obtained ultrathin holey g-C₃N₄ nanosheets with remarkable hierarchical porosity and good hydrophilicity. The holey g-C₃N₄ nanosheets exhibit a high specific surface area (170.7 m² g⁻¹), a narrow band gap (2.55 eV), a large number of exposed edges, and superior electron transport ability. These holey g-C₃N₄ nanosheets have an average H₂ evolution rate 9 times that of bulk g-C₃N₄. This green, facile and scalable method to synthesize few-layer g-C₃N₄ nanosheets affords a new strategy to design and fabricate other functional 2D materials.