The Effect of the Counteranion on the Formation of Mesoporous Materials under the Acidic Synthesis Process

Abstract

The presence of various counteranions at the interfacial region of the silicate-surfactant mesophase introduces opportunities for manipulation of the phase structure. Well-ordered 3D-hexagonal P63/mmc, cubic Pmn, 2D-hexagonal p6mm, and cubic Iad mesoporous materials have been synthesized with the same surfactant, cetyltriethylammonium bromide, in the presence of various acids. The counteranions of acidic media have resulted in increasing the surfactant packing parameter g in the order SO42- < Cl- < Br- < NO3-, which leads to the different time course of formation of mesostructures. The effect of counteranions on the formation of mesostructures is explained in terms of not only the adsorption strength on the headgroups of the surfactant micelle but also the rate of silica condensation affecting the charge density matching between the surfactant and silica. It has been found that the mesophase is always transformed from the larger g parameter into the smaller one. The distinct morphologies of the 3D-hexagonal P63/mmc mesophases have been rationally explained by supposing this particular mesostructure. The cubic Iad phase has been first synthesized under acidic conditions.

Effect of copolymer and additive concentrations on the behaviors of mesoporous tungsten oxide

“…Under basic condition, the hydrogen bonding between the surfactants may be destroyed and lead to an instability of micellization in the tungstic acid solution. A similar result for the series of triblock copolymer L62 was reported for mesoporous silica material synthesis [22][23][24].…”

Photocatalytic activity of (sulfur, nitrogen)-codoped mesoporous TiO2 thin films

“…Baute and Goldfarb [38] investigated the interaction of NaNO 3 with P123 micelles and their role in the phase formation of the mesoporous SBA-15 through electron-spin echo envelope modulation (ESEEM). The impact of the salts on the mesostructure has been explained through the influence of the anions on the surfactant-packing parameter, which, in turn, changes the micellar curvature and packing [39,40]. In our case, the hydrolysis products of thiourea in the acidic solution decreased the micellar curvature, thus, a larger pore size can be obtained in the codoped mesoporous TiO 2 samples.…”

In Situ Time-Resolved SAXS Study of the Formation of Mesostructured Organically Modified Silica through Modeling of Micelles Evolution during Surfactant-Templated Self-Assembly

“…In this sense, the use of an organically-modified silica precursor also showed to have a very strong influence on the structure of the final mesophase, [4][5][6][17][18][19] thus making practically impossible to predict in any way whatsoever the type of pore organization when the chemical complexity of the system increases. This is clear when phenyl-modified alkoxysilanes are employed using CTAB as porogen.…”