To stir or not to stir: formation of hierarchical superstructures of molecularly ordered ethylene-bridged periodic mesoporous organosilicas

Abstract

The effect of stirring during the synthesis of mesoporous organosilica materials prepared via surfactant (cetyltrimethylammonium bromide, CTAB) mediated assembly of distilled 1,2bis(triethoxysilyl)ethylene (BTEE) under basic conditions has been probed. A variety of hierarchical superstructures of periodic mesoporous organosilicas that contain molecularly ordered ethylene groups were obtained by simply varying the extent of stirring (i.e., agitation of the synthesis gels). Under static conditions, large (>10 mm in diameter) hierarchical cake-like particles made up of loosely or closely aggregated rods were obtained as the predominant particle morphology; virtually no other particle morphology was observed. Fast stirring conditions generated spongy flower-like particles that extended for up to 160 mm. Intermediate stirring conditions resulted in a mixture of smaller cake-like particles and elongated rope-like particles that are made up of closely aggregated rods. Despite remarkable differences in the morphology of the hierarchical periodic mesoporous organosilicas, their structural ordering, textural properties and the molecular ordering of ethylene groups were comparable. The formation of hierarchical superstructures did not affect the accessibility and reactivity of the ethylene groups as demonstrated by their successful bromination.

Periodic Mesoporous Organosilica Materials: Self‐Assembly of Carbamothioic Acid‐Bridged Organosilane Precursors

“…This phenomenon means that the organic groups in all the samples of the PMOs are stable up to 250 8C. [40,41] A second weight loss is observed in the MI10 and MI30 samples near 500 8C (see Figure 7 b and Figure S3 in the Supporting Information), which is associated with thermal degradation of the cross-linked organosilicate framework in these materials. A gradual increase in the weight loss in the range 250-600 8C was proportional to the amount of the organic bridges incorporated into the hybrid materials (Figure 7 a).…”

How nucleation affects the aggregation of nanoparticles

“…Interestingly, other groups have also recently demonstrated that stirring in the reaction process also has a dramatic effect on the morphology of mesoporous silica particles. For example, Xia and Mokaya 19 have shown that during the surfactant-mediated synthesis of mesoporous organosilica materials, monodispersed particles of y10 mm in diameter are obtained as the predominant particle morphology if the reaction is carried out under static conditions. In contrast, fast stirring conditions generate spongy flower-like particles that extend for up to 160 mm.…”

Periodic Mesoporous Organosilicas: from simple to complex bridges; a comprehensive overview of functions, morphologies and applications

“…The addition of bromine is already elaborately described by different research groups such as Stein et al, 22 Ozin et al, 70 Sayari et al, 73 Mokaya et al, [79][80][81] Yoshitake et al 212 and Van Der Voort et al 213 The reaction is very straightforward and easy to perform with gaseous bromine or bromine dissolved in a chlorinated solvent. Bromination of the ethenylene bond of the PMO material slightly decreases the specific surface area, pore volume and pore diameter because of the modification of the pore walls.…”

“…80 Different types of particles were also prepared depending on the agitation conditions. 81 Tatsumi et al 82 synthesized hexagonal (P6mm) ethenyleneand phenylene-bridged PMOs with helical mesostructures from BTEENE and BTEB, respectively, in the presence of the cationic fluorinated surfactant CF 3 (CF 2 ) 3 SO 2 NH(CH 2 ) 3 N + (CH 3 ) 3 I À (FC-4911) and CTAB as templates. A TEM image of the phenylene-bridged PMO with helical channels is shown in Fig.…”