Internal and external surface characterisation of templating processes for ordered mesoporous silicas and carbons

Abstract

Characterisation of the multiple pore sizes, or heirarchical porosity, within periodic mesoporous silicas, carbons and carbon silica composites using a combination of standard analysis techniques and also positron annihilation lifetime spectroscopy is reported. The PALS technique was found to complement more standard methods of porous materials characterisation such as nitrogen sorption, small angle X-ray diffraction (SAXRD), and thermogravimetric analysis (TGA). Additional information, particularly on the location of polymer within silica materials, and also on internal surfaces, regardless of surface connectivity or long range order was revealed. The templating process was investigated for the widely employed materials SBA-15, KIT-6 and MCF-2.5. Samples were taken at various times throughout the nanotemplating process. Using commonly reported procedures parent templated silicas, ordered mesoporous carbons, their carbon-silica composite materials and second generation silicas were obtained and have been characterised using the suite of techniques. As a result, new information on the development of pore structure derived from the effectiveness of the templating process is reported. The results obtained highlight the factors that influence the process of pore filling. The new details uncovered regarding the porosity of many materials should be useful in the development of further applications with the characterisation serving as a ready reference for future materials development in this field.