Synthesis and characterization of CuO containing mesoporous silica spheres

A new series of mesoporous silica spheres containing nanodispersed copper oxides were synthesized in H₂O/EtOH/ammonia solution at room temperature. The mesoporous structures were characterised using X-ray powder diffraction and N₂ adsorption-desorption techniques. Scanning electron micrograph and transmission electron micrograph revealed that the MCM-41 particles have spherical morphologies. The DTA curve of pure MCM-41 exhibited a sharp single exothermic peak between 290°C and 340°C, while a broad peak with several shoulders in the temperature range between 180°C and 380°C was observed for Cu-MCM-41, indicating the possible complexation of Cu²⁺ with surfactants adhering to the inner surfaces of the mesopores. Electron paramagnetic resonance spectra of uncalcined samples revealed that Cu²⁺ ions are in an octahedral or distorted octahedral coordination with nitrogen ligands of the surfactant while in the calcined samples they are coordinated with oxygen of the MCM-41 framework. The redox properties of samples were examined by a temperature-programmed reduction and N₂O passivation method. The results indicate that CuO with increasing particle size could be formed in the mesoporous materials with increasing Cu contents, and this decreased the reducibility of the resulting CuO.