Surfactant Mediated Control of Pore Size and Morphology for Molecularly Ordered Ethylene-Bridged Periodic Mesoporous Organosilica

Abstract

A series of ethylene-containing mesoporous organosilica materials were fabricated via surfactant-mediated assembly of 1,2-bis(triethoxysilyl)ethylene (BTEE) organosilica precursor using alkyltrimethylammonium bromide (CnTAB) surfactants with different alkyl chain length (n=12, 14, 16, 18) as supramolecular templates. The presence of molecularly ordered ethylene groups in the resulting periodic mesoporous organosilica (PMO) materials was confirmed by XRD data along with 29Si and 13C MAS NMR analysis. Additional characterization techniques, namely nitrogen sorption, TEM, and TGA, confirmed the structural ordering and thermal stability of the molecularly ordered ethylene-bridged PMOs. The PMOs exhibit molecular-scale ordering (with a periodicity of 5.6 A) within the organosilica framework and tunable pore size, which depending on the alkyl chain length of the surfactant templates, varied in the range 23-41 A. Furthermore, depending on the alkyl chain length of the templates, the particle morphology of the PMOs gradually changed from monodisperse spheres (for C12TAB) to rod or cakelike particles (for C14TAB) and elongated ropelike particles for longer chain surfactants. Variations in the surfactant chain length therefore allowed control of both the pore size and particle morphology without compromising molecular-scale or structural ordering. The reactivity of ethylene groups was probed by bromination, which demonstrated the potential for further functionalization of the PMOs.

Grafting of Molecularly Ordered Mesoporous Phenylene‐Silica with Molybdenum Carbonyl Complexes: Efficient Heterogeneous Catalysts for the Epoxidation of Olefins

“…[4][5][6] Most of these materials have amorphous pore wall structures, that is, the organic groups are randomly arranged within the framework. In a few selected cases [R = C 6 H 4 , [7][8][9][10] (C 6 H 4 ) 2 , [11,12] CH=CH, [7,13,14] CH=CH À C 6 H 4 À CH= CH, [15,16] and 2,6-naphthylene [17] ), the self-organization of bis-silylated organic precursors has been exploited to prepare PMOs with molecular scale ordering of the organic groups within the pore walls. [18,19] The first report of an ordered mesoporous material possessing a crystal-like periodic pore wall structure came from Inagaki et al, who used 1,4-bis(triethoxysilyl)benzene (BTEB) as the precursor to a phenylene-silica hybrid mesoporous material.…”

“…Bromination experiments performed for vinylene-and phenylenedivinylene-bridged PMOs showed that up to 35% of the organic groups were accessible for functionalization. [14,16] Crystal-like mesoporous phenylene-silica can be sulfonated in one step (by treatment with fuming sulfuric acid or chlorosulfonic acid) or aminated in two steps (by nitration with HNO 3 -H 2 SO 4 followed by treatment with SnCl 2 -HCl). [7,22,23] The amino-functionalized material was found to be a reusable base catalyst for the Knçevenagel condensation reaction.…”

Periodic Mesoporous Organosilicas

“…80 In an NaOH aqueous solution instead of a dilute ammonia solution in ethanol, Kim et al 81 synthesized ordered ethane-bridged PMO spheres with diameters of 1.5 and 2.5 µm by a microwave heating treatment at different temperatures • C). Depending on the alkyl-chain length of the used templates (C n TAB), Mokaya and coworkers 57 found that the morphologies of the ethylene-bridged PMOs gradually changed from monodisperse spheres to rod or cakelike particles and elongated ropelike particles. They also reported that hierarchical superstructures of ethylene-bridged PMOs could be prepared by simply varying the degree of agitation.…”

Organic Functionalized Porous Silica Nanoparticles for Adsorption of Cd (II) Ions from Aqueous Solutions

“…At present, to obtain diversified functional porous silica materials, three general methods (postgrafting, co-condensation, and PMOs (periodic mesoporous organosilicas)) were developed [6][7][8][9][10][11]. The post-grafting refers to the subsequent modification of the inner surfaces of mesostructured silica phases with organic groups, nevertheless, this may lead to pore blocking.…”