From Hollow Nanosphere to Hollow Microsphere: Mild Buffer Provides Easy Access to Tunable Silica Structure

Abstract

A facile synthesis method for producing silica hollow spheres from nano- to microsize level is realized by adjusting the hydrolysis and condensation kinetics of silane precursors in a mild buffer solution (NaH2PO4−Na2HPO4, pH ≈ 7.0) in the presence of F127 (EO106PO70EO106) surfactant. Characterization using transmission electron microscopy, field-emission scanning electron microscopy, and nitrogen sorption techniques reveals that the silica hollow nanospheres with outer diameter of about 12 nm can be obtained with tetramethoxysilane as silane precursor. Silica hollow nanospheres (∼20 nm) can also be prepared using tetraethoxysilane (TEOS) as silane precursor with the addition of hydrolysis and condensation catalyst NH4F. Using TEOS as the silane precursor without F−, the formation of silica hollow microspheres (0.5∼8 μm) was observed. Time-resolved in situ UV-Raman results show that TEOS does not hydrolyze at room temperature, and the hydrolysis of TEOS occurs immediately at room temperature when NH4F was...