Control and assessment of plugging of mesopores in SBA-15 materials

Plugged SBA-15 materials consist of mesoporous channels constricted along the central axis by windows. Tailoring and measurement of physical properties, particularly the window sizes, of plugged SBA-15 materials are crucial for potential host–guest applications. In this paper we report a synthesis procedure over a wider range of conditions (temperature and time of synthesis) for tailoring the physical properties of plugged SBA-15 materials and then assess the window sizes for the first time. The plugged SBA-15 materials showed rod-like morphology of 1–3 μm in length. The formation of plugged SBA-15 materials was confirmed by X-ray diffraction and N2 physisorption. Each of the plugged SBA-15 materials was modified by a series of alkoxysilanes with increasing alkyl chain length, and the window size was estimated from the shortest alkyl chain length blocking N2 adsorption. The window sizes were approximately 2.3, 2.6 and 3.0 nm for plugged SBA-15 synthesized at 70, 80, or 90 °C for 1 day, respectively and those were 3.1 and 3.9 nm for plugged SBA-15 synthesized at 70 and 80 °C for 3 days. The results showed that increase in the temperature at synthesis time of 1 day enhanced both the pore and window sizes, whereas extended synthesis time enhanced the window sizes predominantly. The found trend is that plugged SBA-15 materials lost plugging at extended synthesis times and higher temperatures. Overall, the procedures described here now make it possible to rationally design and synthesize plugged SBA-15 materials for host–guest applications in different fields. --------------------------------------------------------------------------------