Rapid and high yield synthesis of hollow silica nanoparticles using an NH4F catalyst

The rapid synthesis of hollow silica nanoparticles based on the CaCO3 template method is proposed. Typically, it contains two steps for the silica coating on a CaCO3 template by a sol–gel reaction and template removal by a dilute acid solution. To promote the conversion of tetraethoxysilane (TEOS) to a silica shell on the CaCO3 template, the effects of fluoride catalysts on the TEOS consumption rate during the silica coating were investigated using energy dispersive spectroscopy (EDS). The TEOS consumption rate of the NH4F-catalyzed system reached 100% within 15 min while the conventional NH4OH system took 120 min to consume the TEOS. The obtained samples using the NH4F system for 15 min showed a uniform hollow structure with a thin silica shell. For the KF system as the other fluoride catalyst, the TEOS consumption rate did not reach 100% even after 120 min. When the polystyrene (PS) template was used with the NH4F system, dense silica particles were formed as well as hollow structures. Based on these results, a rapid and high yield of hollow silica nanoparticles can be achieved by not only F−, but also NH4+ using the CaCO3 template method.