Facile Mesophase Control of Periodic Mesoporous Organosilicas under Basic Conditions

Abstract

The mesophase structure of ordered periodic mesoporous organosilicas (PMOs) can be easily adjusted under basic conditions by variation of the sodium hydroxide concentration. PMOs with hexagonal (p6mm, two-dimensional pore system), cubic (Pm3n or Fm3m, three-dimensional cagelike pore system), and disordered hexagonal (MSU-type) symmetry were obtained from 1,2-bis(triethoxysilyl)ethane (BTEE)-derived synthesis gels in the presence of binary surfactant mixtures, [CH 3 (CH 2 ) 15 NMe 3 ] + Br -(C 16 TABr) and [CH 3 (CH 2 ) n NMe 2 (CH 2 ) 3 NMe 3 ] 2+ 2Br -(n ) 15, 17), as structure-directing agents. With an increasing amount of NaOH, mesophase-mesophase transitions from p6mm f Pm3n f Fm3m f distorted cubic f MSU-type (3D-network of "wormholelike" mesopores) were evidenced by powder X-ray diffraction analysis and transmission electron microscopy. Slight variations of the NaOH concentration not only affected the PMO mesophase structure via the charge matching principle but also the PMO morphology. Among others, hexagons with smooth faces, regular decaoctahedrons, and spherical particles were found from scanning electron microscopy. The PMO mesophase was further found to be dependent on the carbon chain length of the surfactant. 13 C and 29 Si magic-angle-spinning NMR spectroscopy revealed that intact ethylene moieties were incorporated uniformly into the framework. According to N 2 physisorption measurements, the PMOs display Brunauer-Emmett-Teller surface areas as high as 870 m 2 /g and cage diameters in the [55,63] Å size range. Finally, the hydrothermal stability of three representative PMOs with cubic Pm3n, cubic Fm3m, and hexagonal p6mm symmetry was investigated in detail.

Mesoporous organosilicas with ultra-large pores: Mesophase transformation and bioadsorption properties

“…The H2 hysteresis loop found for OMOs-13 is the characteristic of the cage-like mesopores. The total pore volume of OMOs-13 is 0.73 cm 3 /g, only half of that of OMOs-20 (Table 1), confirming the presence of a large domain of cubic mesostructure according to the previous report that the pore volume of a 2D hexagonal mesophase is twice more than that of a cubic mesophase [35]. Expectably, OMOs-10 and OMOs-8 also display H2 hysteresis loops, implying a cage-like pore structure connected by small windows.…”

“…doi:10.1016/j.jcis.2010.02.020 lamellar, bicontinuous cubic Ia3d, 2D hexagonal p6mm, 3D hexagonal p6 3 /mmc, and cubic Pm3m symmetry using different gemini surfactants as structure-directing agents under basic conditions [34]. Liang et al synthesized a series mesoporous organosilicas with cubic and hexagonal symmetry under basic condition and revealed the effect of sodium hydroxide on the mesoporous organosilicas mesophase structure based on the charge-matching mechanism [35][36][37][38]. Kipkemboi et al found that the length of the EO blocks of polymer templates is essential for establishing a mesoporous structure and only long EO chains can lead to a cubic structure [39].…”

Hierarchical Mesoporous Organosilica–Silica Core–Shell Nanoparticles Capable of Controlled Fungicide Release

“…The PXRD pattern of Me‐HSMSCSNs shows a series of well‐resolved diffraction peaks in the 2 θ range of 1.4–4.5°, which can be indexed as the (210), (211), (321), (400), (420), and (422) reflections of the cubic Pm n space group, arising from the PMO core structure (cf. Me‐PMO, Figure S18 of the Supporting Information) . The (100) plane indicated by the peak/shoulder at 2 θ =1.495° may represent a distorted hexagonal p 6 mm symmetry of the shell layer with large pore size (Figure c).…”

A new application of mesoporous carbon microparticles to nucleic acid detection

“…Fig. 9 The mesoporous structure of MC is also evidenced by the nitrogen adsorption-desorption isotherm, as shown in Fig. It is clearly seen that the MC products consist of a large amount of NPs.…”