Intra-layer Na and inter-layer K doping synergistically enhance photocatalytic activity of g-C₃N₄

Graphitic carbon nitride (g-C₃N₄) has garnered significant interest in photocatalytic technology for addressing energy crisis and environmental pollution, owing to its remarkable structural stability and photocatalytic properties. Nevertheless, the photocatalytic performance of g-C₃N₄ is limited by its low efficiency in carrier separation. This study synthesizes Na and K co-doped g-C₃N₄ hollow spheres (NaK₂₀-CN) with an ultra-thin shell through high-temperature calcination, substantially improving its photocatalytic activity in hydrogen production from water splitting. The photocatalytic hydrogen production efficiency of NaK₂₀-CN reaches 4502 μmol h^-1 g^-1, which is five times that of the original g-C₃N₄ hollow sphere. This significant improvement is attributed to the formation of intralayer NaN and interlayer KN bonds, which enhances carrier separation and transfer within and between the layers, as evidenced by DFT calculations and ultrafast transient absorption (TA) spectroscopy. The results demonstrate that the creation of a 3D carrier transport network by Na and K doping at different crystallographic sites significantly improves the photocatalytic activity of C₃N₄ and introduces a novel strategy for developing highly efficient photocatalysts.