Study On Synthesis And Properties Of The Mesoporous SiO₂ Composites And Copper Nanomaterials

Mesoporous solids possess high surface energy and chemical activity, because of the high specific surface area, great porosity rate and a large number of unsaturated bonds existing on their pore walls. Nanoparticles also hold high activity attributed to the size dependent properties and quantum size effect. Mesoporous nanocomposites prepared by nanoparticles incorporated into the pores of the mesoporous solids, not only retain the excellent properties of the dispersed nanoparticles sufficiently, but also will exhibit many new peculiarities resulting from the interactions of the particles and the matrix, which didn't appear as either of them existed lonely. So it is significative to find an operable and easy sample nanoparticles preparation method in investigating the physical properties of the nanoparticles as well as the mesoporous composites. Based on the above, the work from five aspects below has been processed:1. The sol-gel process and theγ-ray irradiation were combined together to develop a new preparation method of mesoporous nanocomposite. We have successfully prepared the mesoporous SiO₂ composites with the small Cu₂O, Cu particles or clusters dispersed in the pores and were examined by x-ray diffraction (XRD), transmission electron microscope (TEM), x-ray photoelectron spectroscopy (XPS), and the optical absorption spectroscopy. The optical absorption of the Cu/SiO₂ mesoporous composite revealed the matrix's effect on the optical properties of the dispersed particles. The optical properties of the nanocomposites were analysed and discussed by combining the classical eletrodynamic theory and the quantum effects, and XPS were used to investigate the interaction between the Cu particles, and finally concluded that the optical properties of the CU/SiO₂ composite are collectively decided by the quantum size effect (QSE) and the effect from the matrix (through the interface interactions).2. Based on the effect of the matrix on the nanoparticles, we introduced the TiO₂ that owns good optical properties to the SiO₂ matrix, and prepared the SiO₂-TiO₂ composite matrix. And then, we have successfully prepared various mesoporous SiO₂-TiO₂ composites with the Cu particles or clusters dispersed in the pores by theγ-ray irradiation and reductive methods. The structures of these composites were examined by x-ray diffraction (XRD), transmission electron microscope (TEM), x-ray photoelectron spectroscopy (XPS), and the optical absorption spectroscopy. The particles prepared byγ-ray irradiation are smaller, more dispersive and more symmetrical than those prepared by reductive methods. And the study of the optical properties told us not only the matrix made an effect on the optical character of the metal nanoparticles, but also metal nanoparticles made an effect on the optical character of the matrix.3. TiO₂/SiO₂ composite were synthesized successfully by two step sol-gel method and its effect on the optical degradation of methyl red under heat treatment at different temperatures was studied. With the temperature of heat treatment increasing, the catalytic capability improved at first and then decreased a little. Compared with the catalytic capability of TiO₂ powder prepared under the same conditions, the catalytic capability of TiO₂/SiO₂ composite with low temperature treatment is a little less than that of TiO₂ powder, but after the high temperature treatment, the catalytic capability of TiO₂/SiO₂ composite is much more than that of TiO₂ powder. So we think that two step sol-gel preparation of TiO₂/SiO₂ composite may have excellent catalytic capability under high temperature.4. With the existence of the PVP as surfactant, porous copper nanorods with rectangular cross sections of column shape have been successfully prepared with the ascorbic acid as ligand and reducer, and the trisodium citrate as the assistant vesicant. The resultant porous copper nanorods may provide interesting possibilities for further applications in catalyzing for the large surface area.5. Well-dispersed cupric oxide (CuO) nanoparticles with the size from 10 nm to 100 nm were successfully synthesized by thermal decomposition of CuC₂O₄ precursor. The electrochemical tests showed an interesting phenomenon that the larger average size and the smaller surface of the particles are, the smaller discharge capacity of the first time is, while that of the second time is larger. However, by the study of the discharged sample with the XRD and SEM, almost all the CuO particles have changed as Cu particles. So, we believe that electrochemical method can synthesize Cu particles with different sizes by using the CuO particles with different sizes as the positive electrode.