Cadmium sulfide inverse opal for photocatalytic hydrogen production

Photocatalysis based on visible light is an efficient and promising strategy to convert solar energy into chemical energy and solve the global issues of environmental pollution and energy shortages. CdS, as a visible light responsive semiconductor material, is widely used in photocatalysis and photoluminescence because of its simple synthesis, abundant raw materials, and appropriate bandgap structure. The inverse opal (IO) structure belonging to photonic crystal structure with unique threedimensionally ordered macro-mesopore, which can tune the propagation direction of incident light and improve photocatalytic performance. Therefore, IO has attracted extensive attention for photocatalysis applications. Herein, CdS IO photonic crystal films were prepared by co-assembly using CdS nanocrystals and poly(styrene-methyl methacrylate-3-sulfopropyl methacrylate, potassium salt) (P(St-MMA-SPMAP)) emulsion. This method is widely used because it is simple and can rapidly prepare large photonic crystal films. The pore size of the IO structure was regulated by changing the diameter of the polymer. The IO structure was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-Vis), and reflectance spectroscopy. The photocatalysis performance of three samples was evaluated via photocatalytic water splitting under visible light irradiation (λ ≥ 420 nm). The photocatalytic hydrogen production rate of the CdS IO film fabricated using a 310 nm P(St-MMA-SPMAP) template (CdS-310) was twice that of CdS nanoparticles (CdS-NPs) under visible light irradiation. This photocatalytic performance enhancement was ascribed to the hierarchically porous structure of the IO photonic crystal. On the one hand, the IO structure increased the propagation of photons in the photocatalytic material and improved sunlight utilization. On the other hand, the structure is conductive to transport and adsorption of molecules. In addition, the IO structure was composed of nanoparticles, providing more active sites for the photocatalytic reaction.