Optimizing organic functionality in mesostructured silica: direct assembly of mercaptopropyl groups in wormhole framework structures

A series of mercaptopropyl-functionalized wormhole mesostructures, denoted MP-HMS, have been prepared through the (SI0)-I-0 assembly of alkylamine surfactants (SO) and mixtures of 3-mercaptopropyltrimethoxysilane and tetraethyl orthosilicate as framework precursors (IO). Unprecedented levels of organo functionalization, corresponding to at least 50% of the silicon sites, were achieved while retaining well-expressed mesostructures with pore sizes, pore volumes, and surface areas as high as 2.8 nm, 0.69 cm(3)/g, and 1225 m(2)/g, respectively. Also, up to similar to 90% of the framework silicon sites could be fully cross-linked, lending exceptional hydrothermal stability to the mesostructures, The key to highly functionalized MP-HMS derivatives lies in the use of long-chain alkylamine surfactants as structure directors (e.g., octadecylamine) in combination with a relatively high assembly temperature (e.g., 65 degreesC) and a high-polarity water-ethanol solvent. Increasing the assembly temperature increased both the framework pore size and the degree of framework cross-linking, whereas increasing the MP content lowered the pore size while improving the framework cross-linking. The effects of assembly temperature and MP loading were attributable to changes in hydration at the H;bonded (SI0)-I-0 interface and concomitant changes in the surfactant packing parameter. Highly functionalized MP-HMS derivatives are promising materials for use as heavy-metal ion-trapping agents and as precursors for sulfonic-acid-functionalized mesostructured catalysts.