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 mu m in length. The formation of plugged SBA-15 materials was confirmed by X-ray diffraction and N-2 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 N-2 adsorption. The window sizes were approximately 2.3, 2.6 and 3.0 nm for plugged SBA-15 synthesized at 70, 80, or 90 degrees C for 1 day, respectively and those were 3.1 and 3.9 nm for plugged SBA-15 synthesized at 70 and 80 degrees 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. (C) 2013 Elsevier Inc. All rights reserved.