To address the issues of small specific surface area, high recombination rate of photogenerated electron-hole pairs, and low solar light utilization efficiency in pure-phase graphitic carbon nitride (g-C3N4) photocatalysts, at the first time a combined process of hydrothermal and calcination methods was proposed. Semiconductor SnO2 and ZnO materials into the g-C3N4 matrix, constructing a SnO2/ZnO/C3N4 composite photocatalytic system were simultaneously introduced. Techniques such as XRD, SEM, DRS, and photoelectrochemical tests were employed to systematically characterize the crystal structure, microstructure, optical properties, and charge separation characteristics of the composite catalysts. The results indicate that SnO2 and ZnO were successfully loaded onto the surface of the g-C3N4 layered structure, forming a heterojunction. The 5 wt% SnO2/ZnO/C3N4 composite catalyst (labeled 5-SnZnCN) exhibited a complete crystal structure with no impurity phases. Its microstructure featured ZnO micro-blocks embedded within the g-C3N4 layers and SnO2 nanoparticles dispersed on the surface, effectively increasing the specific surface area. DRS analysis revealed that although the absorption threshold of the composite catalyst blue-shifted due to the wide bandgap characteristics of SnO2/ZnO, the construction of the heterojunction significantly enhanced the separation efficiency of photogenerated carriers. In photoelectrochemical tests, the 5-SnZnCN composite demonstrated a photocurrent density significantly higher than those of pure g-C3N4, SnO2, ZnO, and binary ZnO/g-C3N4 catalysts. It also exhibited the smallest EIS Nyquist arc radius and the earliest LSV oxidation peak, confirming its superior charge transfer capability and oxidation activity. An experimental basis or the structural design and optimization of preparation processes for novel, highly efficient composite photocatalysts was provided.
