Mesoporous Silicate−Surfactant Composites with Hydrophobic Surfaces and Tailored Pore Sizes

Mesoporous silicate−surfactant composites were prepared via washing of as-synthesized silicate−surfactant−expander materials in appropriate solvents. The expander can be generated in situ from the surfactant decomposition under high-temperature conditions, or supplied externally at the stage of the synthesis or postsynthesis hydrothermal treatment. The washing removed the expander as well as a minor part of the surfactant ions present and thus opened the mesopores whose walls were covered by a relatively dense layer of surfactant ions. Depending on the synthesis method for silicate−surfactant−expander composites, both ordered and disordered mesoporous silicate−surfactant composites were obtained with narrow pore size distributions and a wide range of adjustable pore sizes (4−12 nm). Despite the fact that these materials contained 25−35 wt % of surfactant, they exhibited large BET specific surface areas (360−550 m² g^-1) and total pore volumes (from 0.4 to as large as 1.8 cm³ g^-1). It is postulated that the surfactant retained in the silicate−surfactant composites is bonded to the silicate walls via electrostatic interactions, which are originally responsible for the formation of silicate−surfactant or silicate−surfactant−expander mesophases. The mesoporosity of the composites is mostly constituted by the space initially occupied by expander, which was later removed upon washing. The synthesis approach described herein is the first successful method for synthesis of ordered and disordered mesoporous silicate−surfactant composites with hydrophobic surfaces, the latter being predominantly formed by long alkyl chains of surfactant ions.