Preparation of silica particles doped with uniformly dispersed copper oxide nano-clusters

Nano-spherical silica particles with high framework copper species content have been synthesized in an aqueous reaction mixture consisting of tetraethyl orthosilicate (TEOS), copper salt and ammonia hydroxide by using copper cations as the nucleator to carry out the nucleation and growth of the composite particle. Ammonia hydroxide is used to catalyze the hydrolysis and condensation of TEOS, and allows the product derived from the hydrolysis of TEOS to carry negative charges. The higher amount of copper species incorporated in the silica matrix can be attributed to basic reaction conditions (pH 12.3) and the high dielectric constant of the solvent. The physiochemical properties of all resultant particles are individually characterized by energy dispersive X-ray spectroscopy (EDS), atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The XPS results reveal that the chemical states of incorporated copper ions are the mixture of Cu(0), Cu(I) and Cu(II). SEM results show that the particle size distribution and particle configuration are associated with the concentration of copper ions present in the reaction mixture, while EDS and AAS results indicate that the amount of copper species incorporated in the silica matrix is tunable. The distribution of incorporated copper species is interpreted by the TEM images taken from the synthesized particle, the images of which show that the incorporated copper species are well dispersed in the silica matrix. Heat-treating the resultant particles at different temperatures in air enables doped copper ions to migrate in the silica matrix and causes oxidation of the doped copper species. This results in the formation of CuO clusters being distributed in the particle, the crystal size of which depends on pre-treating temperature.