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 Na[sbnd]N and interlayer K[sbnd]N 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.