Effect of thermal treatment on hydrophilic/hydrophobic structure of hollow silica nanoparticles

Hollow silica nanoparticles (HSNPs) having inner cavity and porous silica shell were prepared using polyacrylic acid/ammonium hydroxide templates, and the effects of thermal treatment on their structural and hydrophilic/hydrophobic properties were investigated. As the temperature of the thermal treatment increased the number of micropores within the silica shell decreased, whereas the inner cavity (mesopores) of the HSNPs remained unchanged up to 900 °C. The change in the microstructure led to a reduction in the specific surface area (SSA) of the HSNPs. At 1100 °C, a sharp decline in SSA was observed, accompanied by partial collapse of the inner cavity and necking between particles, indicating sintering had occurred. The number of surface silanol groups decreased with increasing temperature, forming hydrophobic siloxane bonds because the silanol groups were close enough to react with each other.