Three-Dimensional Low Symmetry Mesoporous Silica Structures Templated from Tetra-Headgroup Rigid Bolaform Quaternary Ammonium Surfactant

Abstract

Two kinds of highly ordered mesoporous silica materials (FDU-11, FDU-13) with novel three-dimensional (3-D) tetragonal and orthorhombic structures were synthesized by using tetra-headgroup rigid bolaform quaternary ammonium surfactant [(CH(3))(3)NCH(2)CH(2)CH(2)N(CH(3))(2)CH(2)(CH(2))(11)OC(6)H(4)C(6)H(4)O(CH(2))(11)CH(2)N(CH(3))(2)CH(2)CH(2)CH(2)N(CH(3))(3).4Br] (C(3-12-12)(-)(3)) as a template under alkaline conditions. High-resolution transmission electron microscopy (HRTEM), small-angle X-ray scattering (SAXS), and X-ray diffraction (XRD) show that mesoporous silica FDU-11 has primitive tetragonal P4/mmm structure with cell parameters a = b = 8.46 nm, c = 5.22 nm, and c/a ratio = 0.617. N(2) sorption isotherms show that calcined FDU-11 has a high BET surface area of approximately 1490 m(2)/g, a uniform pore size of approximately 2.72 nm, and a pore volume of approximately 1.88 cm(3)/g. Mesoporous silica FDU-13 has primitive orthorhombic Pmmm structure. The cell parameters are a = 9.81, b = 5.67, and c = 3.66 nm. N(2) sorption isotherms show that calcined FDU-13 has a high BET surface area of 1210 m(2)/g, a uniform mesopore size of approximately 1.76 nm, and a large pore volume of approximately 1.83 cm(3)/g. Such low symmetries for 3-D mesostructures (tetragonal and orthorhombic system) have not been observed before even in amphiphilic liquid crystals, which maybe resulted from an oblate aggregation of the bolaform surfactant and its strong electrostatic interaction with inorganic precursor. A probable mechanism has been proposed for the formation of such a 3-D low symmetrical mesostructure. These results will further extend the synthesis of mesoporous materials and may open up new opportunities for their new applications in catalysis, separation, and nanoscience.

The formation of host–guest complexes between surfactants and cyclodextrins

“…Bolaform surfactants are also used in template synthesis for the production of micro-and meso-porous silica [314,315], and hydrophobic nanocalcium carbonate [316].…”

General Synthesis of Ordered Nonsiliceous Mesoporous Materials

“…Designed multihead quaternary ammonium surfactants like bolaform surfactants with different chain lengths and rigid benzene ring groups as structure-directing agents (SDAs), 3D cubic (Pm 3 ri) and face-centered cubic (Fd 3 m) mesoporous silicates were synthesized (19). Lately, the low symmetrical mesostructures with tetragonal and orthorhombic pores were also obtained (20). It has been clearly demonstrated that the derived mesostructures are remarkably influenced by the rational control of inorganic-organic interactions and cooperative assembly of the silica species and the surfactants.…”

Mesostructured Zeolites: Bridging the Gap Between Zeolites and MCM-41

“…Many procedures in which cationic surfactants were used as templates for the preparation of mesostructured silica materials have been reported. As the isoelectric point of silica lies at a pH value of B2, 42 silicon species in alkaline solutions are negatively charged which can be linked and stabilized by cationic surfactants (S + ) through strong electrostatic Coulomb forces in the S + I À pathway, leading to the formation of ordered mesostructured silica materials such as M41S, 36,37 FDU-2, 43 FDU-11 and FDU-13, 44 SBA-2, 45 SBA-6 46 and SBA-8, 47 etc. Likewise, cationic surfactants can also be used as templates to prepare silica mesostructures in strong acidic solutions (pH o 2) where the silicon species are positively charged.…”