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

Hollow silica (SiO 2 ) 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 (NH 4 OH) and prepared by dispersion of the PAA-NH 4 OH mixture in ethanol. Upon the addition of silica precursor, tetraethoxysilane (TEOS), into the PAA-NH 4 OH/ethanol suspension, a certain thickness of SiO 2 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 NH 4 ions suspended on the surface of the template. By varying the NH 4 OH amount in reaction solution, it was found that the hollow SiO 2 nanoparticles could be obtained only in the case of NH 4 OH 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 SiO 2 . 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 SiO 2 nanoparticles by optimizing the NH 4 OH and water amount in reaction solution.