Probing the microporous nature of hierarchically templated mesoporous silica via positron annihilation spectroscopy

Abstract

The technique of positron annihilation lifetime spectroscopy (PALS) in conjunction with standard nitrogen sorption techniques is used to probe the micropores present in microemulsion templated mesocellular foam (MCF) silica materials and hybrid MCF silica materials formed via a post synthesis functionalisation with (3-aminopropyl)triethoxysilane (APTES). For the MCF silica materials, the PALS results show that the number of micropores present decreases as the synthesis aging temperature is increased, which follows the trend seen in the micropore volumes determined from nitrogen sorption t-plot analysis. The presence of the micropores and the trend seen in the micropore volumes with increasing temperature was attributed to the level of hydration of the poly(ethylene oxide) components in the amphiphilic block copolymer/trimethylbenzene microemulsion from which the materials are templated. For the hybrid APTES functionalised MCF silica, analysis via PALS completed in both nitrogen and air environments, indicates that the micropores are blocked and replaced by a closed microporosity associated with the APTES layer formed within the mesopores.