Synthesis Mechanism of Cationic Surfactant Templating Mesoporous Silica under an Acidic Synthesis Process

Abstract

The presence of various counteranions in the interfacial region of the silicate−surfactant mesophase introduces opportunities for manipulation of the phase structure. Well-ordered three-dimensional hexagonal P63/mmc, cubic Pm3̄n, two-dimensional hexagonal p6mm, and cubic Ia3̄d mesoporous materials have been synthesized with the same surfactant (cetyltriethylammonium bromide), depending on the kind of acids. The counteranions of acidic media have resulted in increasing surfactant packing parameter g in the order SO4 2- < Cl- < Br- < NO3 -, which leads to different formation routes to the mesostructures. It has been found that the mesophases are always transformed from the lower curvature one into the higher curvature one in the acidic synthesis gel. The combination of X-ray diffraction patterns, scanning electron microscope images, and high-resolution transmission electron microscope images presented visible evidence for the mesostructural constructions. In particular, the synthesis of a cubic Pm3̄n mesoporous molecular sieve was studied in the presence of trimethylbenzene (TMB) isomers. The rate of transformation is greatly affected by the structure of the TMB isomers and their content; 1,2,3-TMB was the most favorable to the stabilization of the p6mm hexagonal mesophase, 1,3,5-TMB was the least favorable, and 1,2,4-TMB showed intermediate behavior.

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.…”

Organically Functionalized Mesoporous Silica by Co‐structure‐Directing Route

“…As is widely recognized, the salting-in and saltingout properties of a counterion following the Hofmeister series play an important role in this process. [67][68][69][70][71] Carboxylate is a salting-out anion (relative to Cl − ) and is well hydrated. Counterions that have an intense electrostatic fi eld interact strongly with the carboxylate surfactant, thereby weakening the repulsions between the headgroups of the surfactant and inducing a decrease in the organic/inorganic interface curvature.…”

Fabrication of Metal Oxides Occluded in Ordered Mesoporous Hosts via a Solid‐State Grinding Route: The Influence of Host–Guest Interactions

“…[24,25] Secondly, silica species are less-condensed, linear oligomers in acidic conditions (M1 synthesis), while in alkaline solution (M2 synthesis), they contain more crosslinked clusters. [26] The 29 Si MAS-NMR (MAS: magic-angle-spinning) spectra of the samples synthesized in acidic conditions have a Q 3 /Q 4 ratio above unity accompanied with clear Q 2 peaks, [27] implying incomplete polymerization and condensation of the silanol groups. However, the Q 2 peaks disappeared in the spectra of the analogue sample synthesized under basic conditions and the Q 3 and Q 4 peak areas seemed very similar, which indicates the relative complete condensation between the silanol groups.…”