Novel ZnO nanoparticles modified WO3 nanosheet arrays for enhanced photocatalytic properties under solar light illumination

ZnO nanoparticles deposited on WO3 nanosheet arrays (NSAs) were prepared by hydrothermal process and impregnation method followed by thermal treatment for photocatalytic degradation of nonbiodegradable azo dyes methylene blue (MB) under solar light irradiation. The uniform WO3 NSAs grew on the 316L stainless steel substrate and ZnO nanoparticles immobilized on the surface of WO3 NSAs. The morphology and structure of WO3/ZnO NSAs can be well tailored by adjusting the preparative factors (e.g., hydrothermal time and the concentration of precursor solution). The detailed characterizations of the WO3/ZnO NSAs such as morphology, crystal structure and light absorption were examined. The X-ray diffraction and X-ray photoelectron spectroscopy results showed that the as-prepared samples were two-phase photocatalysts including WO3 NSAs and ZnO nanoparticles. The UV-Vis diffuse reflectance spectroscopy results indicated that the introdution of ZnO altered the optical properties of the photocatalysts. After ZnO loading at the optimum amount, the WO3/ZnO heterojunction with good stability displayed superior photocatalytic activities compared with WO3 NSAs in the degradation of MB. The enhanced photocatalytic performance should be attributed to favorable band structures, strong light-absorption ability and fast separation of photogenerated electron-hole pairs. Particularly, the 30-WZ nanocomposite exhibited the highest photocurrent density of about 1.275 mA/cm2 at 0.8 V versus Ag/AgCl under solar light illumination. In addition, the photogenerated reactive species were identified through free radicals trapping experiments, which revealed that the photodegradation of MB over WO3/ZnO NSAs was dominated by hydroxyl radical rather than the hole and superoxide radical. The mechanism for photocatalytic degradation reaction over the WO3/ZnO heterojunction was also investigated.