High-yield hydrothermal synthesis of mesoporous silica hollow capsules

• Mesoporous silica hollow capsules can be obtained via hydrothermal treatment.
• The 1st hydrothermal treatment promotes gelation to form rigid silica frameworks.
• The 2nd hydrothermal treatment decomposes the organic templates via oxidation.
• Yield = (Number of obtained capsules)/(Number of template particles used).
• The yield of the proposed method > twice that obtained for the calcination method.

An improved method for the preparation of mesoporous silica hollow capsules (MSHCs) is reported. In the previous method, polystyrene (PS) particles and cylindrical assemblies of surfactants served as the templates for the hollow parts and mesopores of the capsules, respectively, which were thermally decomposed via calcination in ambient air at 550 °C. However, during calcination, the MSHCs aggregated and a considerable loss of the monodispersed capsules occurred. To reduce this loss, hydrothermal treatment was employed instead of calcination. As a result, the yield of the capsules (defined as the ratio of the numbers of the obtained capsules and PS particles) was increased from 35% for the calcination process to approximately 85% for the present method. Optimization of the conditions for hydrothermal synthesis of MSHCs to maximize the yield and minimize the fraction of unwanted products is also discussed in detail.

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