摘要：

The ZnO-SiO₂ nanocomposite was obtained using the sol-gel method^[1] and the sample of ZnO/SiO₂ was prepared by conventional impregnation way. A narrow size distributed ZnO nanoparticles had been observed on silica matrix through both methods by TEM. The particle size increased slightly with zinc oxide content and treatment temperature from the particles of an average value of ca. 3-5 nm for Zn₁₀-T₄₀₀ (the treatment 400℃ and the zinc oxide content 10 wt%) sample to an average value of ca. 6-8 nm in Zn₁₀-T₇₀₀ sample. Furthermore, the ZnO crystalline transition from monocrystal to polycrystalline phase had been observed with treatment from 400℃ to 700℃ in ZnO-SiO₂ from the selected area diffraction patterns. XPS investigation indicated that the Zn 2p binding energy in samples of ZnO/SiO₂ and ZnO-SiO₂ increased greatly compared with zinc oxide, which suggested that strong interactions between nanometer-size ZnO and silica support were established. And it also suggested that the Si-O-H groups present in the surface of silica may be partially or totally substituted by Si-O-Zn bonds. Comparison of the ZnO-SiO₂,the Zn 2p binding energy in the ZnO/SiO₂ is lower, which implied that more Si-O-Zn groups existed on the former than the latter. The ESR results showed an interesting phenomena that a first-order standard differential ESR spectra (g_e=2.062) appeared in all ZnO-SiO₂ samples and no any signals in other samples. The ESR signal obtained may be due to O^-, O^2-, Zn⁺ or other ions. But the O^- ion vacancy is unstable, and if the Zn⁺ and the O^2- ions are the paramagnetic centers the g-factor should be equal to 2.0021^[2] or 2.109^[3], so the ESR signal from ZnO-SiO₂ sample does not arise from the ions above. Perhaps it comes from Zn³⁺, because the g-factor is close to d⁹ and Zn 2p binding energy in ZnO-SiO₂ is much higher than ZnO. The results showed that the interaction between microcrystlline ZnO and silica support in ZnO-SiO₂ is stronger than in the ZnO/SiO₂.

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