Synthesis and shell structure design of hollow silica nanoparticles using polyelectrolyte as template

Hollow silica (SiO2) nanoparticles with tunable shell microstructures were synthesized in ethanol solvent by using a polyelectrolyte as template. The polyelectrolyte template was composed of poly (acrylic acid) (PAA) with small amount of ammonia solution (NH4OH) and prepared by dispersion of the PAA-NH4OH mixture in ethanol. Upon the addition of silica precursor, tetraethoxysilane (TEOS), into the PAA-NH4OH/ethanol suspension, a certain thickness of SiO2 shell could be gradually formed outside the template through+the sol-gel reaction of TEOS, which was supposed to be driven by the catalytic effect of NH4 ions suspended on the surface of the template. By varying the NH4OH amount in reaction solution, it was found that the hollow SiO2 nanoparticles could be obtained only in the case of NH4OH amount below a critical value. Furthermore, it was found that the water amount in reaction solution had a significant influence on the shell microstructure of hollow SiO2. The shells formed in water-free solution were thick, rough and rich of mesopores, which became relatively thinner, smoother and richer of micropores if the water amount was gradually increased within a limited range. Therefore, it was thought to be possible for the controllable synthesis and shell structure design of hollow SiO2 nanoparticles by optimizing the NH4OH and water amount in reaction solution.