Preparation of Cu2O@SiO2 particles and their evolution to hollow SiO2 particles

This study demonstrates an environment-friendly process to synthesize hollow SiO2 particles. The preparation of Cu2O@SiO2 particles via the sol–gel process is presented for the first time. Silica coating on the Cu2O particles has been considered not possible due to the easy etching of Cu2O in an NH4OH solution. We found that diluted NH4OH solution delayed the etching of the Cu2O particles in the sol–gel process and allowed thick coating of silica. The time-dependent etching of the Cu2O core in the Cu2O@SiO2 particles generated yolk/shell particles and finally produced the hollow SiO2 particles. The etched Cu solution could be recycled to produce Cu2O particles again.