Catalytic Properties Of Cu@SiO₂Nanocomposites

Metal nano-materials have unique chemical, optical, magnetic, and electrical properties due to their size and structure. Now, nano-materials technology has gained a tremendous attraction due to their use in catalysis, environment protection, electromagnetic and energy applications. Among them, copper nano-materials have the special catalytic properties and sterilization ability like the other precious metal (such as Au, Ag) nano-materials. Copper nano-materials have attracted wide public concern, because the copper raw material is inexpensive. We demonstrated that Cu@SiO2can be a good catalyst in the hydroxylation of phenol and reduction of p-nitrophenol.First, we use the bifunctional ligand to stabilize Cu2+in the Brij(?)58/cyclohexane reverse micelles microemulsion. Cu@SiO2were prepared by reducing Cu2+to Cu by strong reducing agent NaBH4, and then in situ encapsulated by silica. The different bifunctional ligands can affect morphology of the particles.Next, the Cu@SiO2was used as catalyst in hydroxylation of phenol. Reversed-phase high performance liquid chromatography (HPLC) was used for trace detection in this study. Hydrogen peroxide was used as the oxidant. Reaction temperature, reaction time, amount of catalyst, phenol and hydrogen peroxide molar ratio, and reaction solvent were found to affect the catalytic performance of Cu@SiO2. The optimal conditions were obtained, that is T=75℃, t=3.5h, n(phenol):n(hydrogen peroxide)=1:1, m(Cu@SiO2):m(phenol)=3.0wt%. Under the optimum conditions, the conversion of phenol was39.8%, the selectivity of benzodiazepines was72.5%, and the catalyst showed a good reusability.Finally, the catalytic activity of Cu@SiO2was studied in the catalytic reduction of p-nitrophenol into p-aminophenol with the help of UV-Vis spectroscopy. The results showed that Cu@SiO2displayed the highly catalytic activity with p-nitrophenol conversion of98.0%by the1.0mol%at25℃. Moreover, it showed excellent catalytic activity even after it was reused six times. When the reducing agent NaBH4, was used in excess of p-nitrophenol, the reaction followed pseudo-first-order kinetics. The apparent rate constant was0.159min-1at298K, and the activation energy was51.6kJ/mol.