Preparation, characterization and lysozyme immobilization studies on siliceous mesocellular foams: Effect of precursor chemistry on pore size, wall thickness and interpore spacing

Abstract

Three homologous series of siliceous meso-cellular foams (MCFs) were synthesized using microemulsion templating by incremental variation of ratio of organic pore expander, trimethyl benzene (TMB), and silica precursor (TEOS) concentrations using Pluronic™ block co-polymer (P123) as the surfactant. The calcined materials were tested for lysozyme immobilization to relate the adsorption capacities to meso-structure. Small angle X-ray scattering (SAXS) shows a short range ordering of pores. The pore size and wall thickness were determined from Porod analysis of the SAXS data combined with gas adsorption data. The pore size and lysozyme loading both increase systematically with TMB/P123 ratio, and decrease with increasing TEOS/P123 ratio. By comparing gas adsorption and SAXS data, we show that the BET method overestimates the mesopore specific surface area and therefore leads to an underestimate of the pore size. The effective pore size determined by the BdB-FHH method on the other hand is consistent with that determined by SAXS surface area analysis. The wall thickness (4.4±0.5nm), interpore distance (23.9±1.5nm) and meso-pore volume fraction (0.82±0.04) are independent of synthesis conditions. The mean pore size (33±8nm, spherical equivalent) is generally larger than the interpore distance, which forces the system to adopt a more cylindrical pore morphology at large pore and window sizes, which is confirmed by SAXS and TEM. TEM shows worm-like pores intermixed along with the familiar cellular foam phase.