Preparation Of Au/SiO₂Nanoparticles In Room Temperature Ionic Liquid

Room temperature ionic liquids, as ionic liquids, are salts composed of bigorganic cations and small inorganic anions. Different from other ionic compounds,melting points of ionic liquids are close to the room temperature. They have uniqueproperties: nonvolatile, nonflammable; good solvents for a wide range of organic,inorganic materials and polymer; high thermal stability and chemical stability, widerange of liquids temperatures, good ionic conductivity and large electrochemicalwindow. Up to now, as a new type of green environment-friendly solvent, ionicliquids have attracted much interest of the researchers. As a green environmentfriendly solvent, ionic liquids are used for organic synthesis，multiphase catalysis andseparation. Now it is very significant for using ionic liquids in nanoparticles synthesisBecause of the expensive of the gold, as the same character of the gold and the silver,the silve is a example synthesized in ionic liquids. In this paper, ionic liquids synthesizedby two-step method, were used for synthesizing the Ag nanoparticles and the nanoAu/SiO₂catalyst. The effect of ionic liquids on synthesizing the Ag nanoparticles andthe nano Au/SiO₂catalyst was discussed. The composite particles were characterizedand investigated by FT-IR spectra, X-ray power diffraction, UV-Visible absorptionspectra, scanning electron microscopy SEM, transmission electron microscopy （TEM）.The results showed that the mean diameter of the Ag nanoparticles is about17nm andthe surface of the Ag nanoparticles was modified with room temperature ionic liquids[hmim] PF₆. So the room temperature ionic liquids were used as stabilizing agent toprevent the silver nanoparticles aggregating. The gold in the nano Au/SiO₂catalystsynthesized with the ionic liquids has nano character, the nano Au/SiO₂catalystpreserve the near-infrared absorbance of gold nanoparticles, ionic liquids [hmim] PF₆can prevent the gold nanoparticles aggregating. Epoxidation of styrene for preparingstyrene oxide was used the nano Au/SiO₂as catalysts （80℃,3h）.The nano Au/SiO₂catalyst synthesized with the ionic liquids [hmim] PF₆can effectively catalyzeepoxidation of styrene, the conversion rate of styrene can achieve6.5%, theselectivity of styrene oxide is66.3%. The baking temperature of500℃was best respectively, synthesized the nano Au/SiO₂catalyst with6mL reducing agent was bestfor epoxidation of styrene reaction..