Design of SiO2/ZrO2 core–shell particles using the sol–gel process

Core–shell particles of SiO2/ZrO2 were developed using a sol–gel process. Spherical core particles of SiO2, 320 nm in diameter, were initially prepared using tetraethylorthosilicate (TEOS), and then uniformly shelled with ZrO2 nano-particles synthesized with zirconium(IV) butoxide (TBOZ). The deposition of ZrO2 nano-particles on the SiO2 core particles was generally promoted when increasing the H2O and TBOZ concentrations and temperature of the sol–gel process. However, micron-sized homo-aggregates of ZrO2 were formed above certain concentrations of H2O and TBOZ due to self-aggregation of the nano-ZrO2 particles. It was very interesting to discover that a chemical bonding between zirconium and silicon bridged by oxygen (Si–O–Zr bond) was developed during the formation of the ZrO2 shell around the core particles, as the silane groups on the core particles were condensed with zirconium hydroxyl groups during the deposition of ZrO2. XPS and FT-IR confirmed the chemical bonding of Si–O–Zr in the core–shell particles.