Study On Synthesis And High Photocatalytic Activity Of Hierarchical Zn₂GeO₄Microsphere Photocatalysts

Photocatalysts have been a hot topic in environmental field due to its low energy consumption and no second pollution. The photocatalyst is the key factor of the photocatalytic technology, so the development of new and efficient photocatalyst is the hot topic in the photocatalytic field. Zn2GeO4has the special crystal structure and much dispersed band, thus the photo-generated electrons have high mobility in the CB, and can make full use of the electrons and holes. Besides, the Zn2GeO4photocatalysts is very stable under irradiation of the UV light. So it is a new and excellent photocatalysts. Hierarchical Zn2GeO4microspheres have been successfully synthesized via a simple hydrothermal route, using Zn(NO3)2and GeO2as Zn and Ge sources, respectively. The as-prepared samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherm, UV-vis diffuse reflectance spectrum (UV-vis DRS), and fourier transform infrared (FT-IR) spectroscopy.The temperature experiment results showed that it was better to form well-dispersed hierarchical Zn2GeO4microspheres at the140℃. Moreover, the obtained samples has no impurity and good crystallinity and the crystalline size of Zn2GeO4microsphere was smaller than that of bulk Zn2GeO4. SEM, FESEM and TEM results showed the hierarchical Zn2GeO4microspheres with diameters ranging from5-10μm were found to be constructed of randomly aggregated nanorods which had dimensions of about0.5-1μm in length and200-500nm in width. From the UV-vis DRS analyses, the obvious blue shift of the optical band gap of the hierarchical Zn2GeO4microspheres can been found, compared with the bulk Zn2GeO4. The experiment results showed the dissolution rate of GeO2will increase with the increasing of the urea dosage, which promoted the growth of the Zn2GeO4crystal. Finally, a formation mechanism of the hierarchical Zn2GeO4microspheres was researched by the time-dependent experiments. The results presented the formation of Zn2GeO4microsheets and microspheres constructed of nanorod bundles for30min. With increasing the time, Zn2GeO4solid microspheres were formed by dissolution-recrystallization-self-assembly. Meanwhile, the hollow Zn2GeO4microspheres were formed through the complicated Ostwald ripening process.The Zn2GeO4microspheres exhibited high photocatalytic properties and excellent stability for the degradation of ARG and4-NP as compared to the Zn2GeO4prepared by the solid-state reaction. Besides, the HCHO gas can be effective degradated by the microspheres. The hydroxyl radicals (·OH) were measured by TAPL for the photocatalysis. Based on the experimental results, we have discussed the possible mechanism of the photocatalysis over the Zn2GeO4...