Selective SnO2 deposition on inner/outer shell surface of hollow SiO2 nanoparticles by control of shell microstructure

A selective SnO2 deposition on the inner or outer shell surface of hollow SiO2 nanoparticles was proposed using the shell microstructure difference and electrostatic interaction between SiO2 and tin precursor. Hollow SiO2 nanoparticles were first prepared via the sol–gel route using a polystyrene template. The obtained hollow particles appeared to have similar morphologies based on microscopic observations, however, different micropore sizes were found; one was above 1 nm (type B) and the other was undetectable (type C) by the gas adsorption analysis. When they were mixed with the tin source, hollow particles were kept in a vacuum to induce the tin source solution to the inside of the hollow interior through the micropores in the shell. The mixed compounds were then filtered to remove any excess tin source. Our strategy is that the shell microstructure induces different tin source retention times in the hollow interior, which results in the selective SnO2 deposition on the intended shell surface. The microscopic results clearly showed that SnO2 depositions were observed on only the outer surface in type B and on the inner surface in type C. The SnO2-deposited type B indicated an electro-conductivity, while the SnO2-deposited type C showed a good optical property compared to commercial SnO2.