Interlayer Potassium Single-Atom-Coordinated g-C₃N₄ for Significantly Boosted Visible Light Photocatalytic H₂...

In recent years, graphitic carbon nitride (g-C₃N₄) has attracted considerable attention because it includes earth-abundant carbon and nitrogen elements and exhibits good chemical and thermal stability owing to the strong covalent interaction in its conjugated layer structure. However, bulk g-C₃N₄ has some disadvantages of low specific surface area, poor light absorption, rapid recombination of photogenerated charge carriers, and insufficient active sites, which hinder its practical applications. In this study, we design and synthesize potassium single-atom (K SAs)-doped g-C₃N₄ porous nanosheets (CM-K_X, where X represents the mass of KHP added) via supramolecular self-assembling and chemical cross-linking copolymerization strategies. The results show that the utilization of supramolecules as precursors can produce g-C₃N₄ nanosheets with reduced thickness, increased surface area, and abundant mesopores. In addition, the intercalation of K atoms within the g-C₃N₄ nitrogen pots through the formation of K-N bonds results in the reduction of the band gap and expansion of the visible-light absorption range. The optimized K-doped CM-K₁₂ nanosheets achieve a specific surface area of 127 m² g^-1, which is 11.4 times larger than that of the pristine g-C₃N₄ nanosheets. Furthermore, the optimal CM-K₁₂ sample exhibits the maximum H₂ production rate of 127.78 μmol h^-1 under visible light (λ ≥ 420 nm), which is nearly 23 times higher than that of bare g-C₃N₄. This significant improvement of photocatalytic activity is attributed to the synergistic effects of the mesoporous structure and K SAs doping, which effectively increase the specific surface area, improve the visible-light absorption capacity, and facilitate the separation and transfer of photogenerated electron-hole pairs. Besides, the optimal sample shows good chemical stability for 20 h in the recycling experiments. Density functional theory calculations confirm that the introduction of K SAs significantly boosts the adsorption energy for water and decreases the activation energy barrier for the reduction of water to hydrogen.