Effects of Impurity Ions on the Synthesis of Hollow Silica

Abstract

In this study, we aimed to synthesize plate shaped hollow silica powder using Mg(OH)2 as an inorganic core particle that can be removed conveniently through an acid-based process without using any additional organic solvents or heat treatment. We also elucidated the effects of the impurity ions formed during the synthesis process on the properties of the hollow silica. Plate type hollow silica could be synthesized successfully from sodium silicate by the precipitation method while using Mg(OH)2 as the template. A silica shell was formed on the Mg(OH)2 particles, and a sulfuric acid treatment was performed to remove the template, yielding hollow silica. The impurity ions generated during the synthesis process resulted in undesirable spherical silica particles, as they acted as additional silica formation sites. The number of silica particles formed reduced with a decrease in the number of impurity ions in the reaction solution; this, in turn, increased the thickness of the silica shell. This result indicated that, as the amount of impurity ions in the reaction solution is reduced, silica reaction sites other than the inorganic Mg(OH)2 particles are also minimized. As a result, the added silica precursors will not be consumed for the formation of the silica particles and will react completely on the Mg(OH)2 core particles to form shells with increased thickness. Finally, we also believe that NH4OH, which contains the OH group, would be a suitable another silica formation site.