Synthesis of porous organosilicates in the presence of alkytrimethylammonium chlorides: Effect of the alkyl chain length

A series of organosilicates were prepared using 1,2-bis(trimethoxysilyl)ethane (BTME) as silica precursor and alkyltrimethylammonium chloride (C(n)TMACl) surfactants with different chain lengths (n = 8, 10, 12, 14, 16, 18) as supramolecular templating materials. C-13 and Si-29 NMR data showed that after surfactant extraction, all samples consisted of pure organosilicate. Additional characterization techniques, that is, XRD, N-2 adsorption, and SEM, were also used to gain insights into the structure, porosity, and morphology of the materials. These properties were found to be strongly dependent on the surfactant chain length and the preparation conditions. Materials prepared in the presence of surfactants with the shortest carbon chains were microporous akin to amorphous organosilicate xerogels. However, in the presence of long chain surfactants, periodic mesoporous organosilicates with narrow pore size distributions occurred. The pore sizes of such materials were found to increase with the surfactant carbon chain length. With only one exception, these materials exhibited two-dimensional hexagonal symmetry.