Synthesis and characterization of ceria-coated silica nanospheres: their application in heterogeneous catalysis of organic pollutants

Τhe present work investigates the parameters for the successful coating of silicon oxide nanoparticles surface with a homogeneous cerium oxide shell in an effort to develop core–shell nanostructures. For this, spherical silica nanoparticles (~ 300 nm) were developed by a biomimetic approach and their coating with ceria was performed through a precipitation method. Several processing conditions, such as the precipitation pH, the cerium precursor concentration and the treatment of silica cores (i.e., their use either as-received after their biomimetic formation, or after their calcination followed by surface modification), were examined and optimized. The as-obtained powder material was characterized by scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction analysis, N2 adsorption and UV–Vis reflectance spectroscopy. The analysis revealed the formation of spherical core–shell nanostructures bearing a uniform shell layer of crystalline cerium oxide around each silica core which after calcination at 600 °C was comprised of cubic CeO2 nanocrystals with sizes ranging between 2 and 6 nm. The material with the optimum core–shell structure and pure cerium dioxide were studied in terms of their catalytic reduction activity over 4-nitrophenol to 4-aminophenol.