Synthesis Of Mesoporous Organosilicas Research Articles

Organosiloxane tunability in mesoporous organosilica and punctuated Pd nanoparticles growth; theory and experiment

Abstract The synthesis of mesoporous organosilicas (MOs) using co-condensation for a high ratio of a long and flexible chained organosiloxane bridge with silica precursor (e.g. tetraethylorthosilicate (TEOS)) is a complex and challenging task. By complementing the experimental characterisations with density functional calculations, The critical ratio of the urea-based organosiloxane bridge (BTPU) to tetraethyl orthosilicate of 1:8 was identified to delivers reliably stable urea bridged MO (MO-urea) with relatively large surface area and mesoporosity. Moreover, the Pd nanoparticles supported on the pore channels of MO-urea achieve a narrow distribution size averaging at a diameter of ~2 nm. This fine distribution is driven by the Pd nanoparticles nucleating only on the exposed SiO2 section of MO-urea while the BTPU bridges punctuate the growth of the Pd nanoparticles limiting their size. As a result, the obtained Pd@MO-urea exhibits excellent multifunctional catalytic activity for hydrogen production from formic acid and p-nitrophenol (PN) reduction in aqueous media with four folds increase in yield compared to the non-punctuated Pd nanoparticles.

Direct Synthesis and Solid-State NMR Characterization of Cubic Mesoporous Silica SBA-1 Functionalized with Phenyl Groups

Well-ordered mesoporous silicas SBA-1 (cubic Pm3n symmetry) functionalized with phenyl groups have been synthesized via co-condensation of tetraethoxysilane (TEOS) and phenyltriethoxysilane (PhTES) under acidic conditions. The synthesis parameters such as temperature, type of surfactant, and synthesis composition have been systematically investigated as a function of PhTES contents. The phenyl-containing units are incorporated quantitatively and reach a maximum PhTES loading up to 33 mol % (based on silicon) without a significant degradation of the structural ordering of the Pm3n mesophase. A combination of multinuclear (1H, 13C, 29Si) solid-state NMR and two-dimensional (2D) solid-state NMR correlation techniques such as 13C{1H} and 29Si{1H} HETCOR (heteronuclear correlation) and 1H-1H exchange NMR has been used to establish framework locations of phenyl functional groups that are incorporated in the mesoporous structure and their interactions with the surfactant molecules. 2D 13C{1H} HETCOR NMR experiments reveal that the phenyl moieties are in close spatial proximity to the trimethylammonium headgroups of the cationic surfactant species in the as-synthesized materials, suggesting that there are some specific interactions between them to maintain the surfactant packing parameter (g) smaller than 1/3 necessary for the formation of the cubic mesophase. The detection of couplings between the protons associated with various 29Si species via 29Si{1H} HETCOR NMR established that the T silicon species due to the phenyl groups incorporated are in closer proximity to the Q4 silicon species than to the Q3 silicon species. This observation also provides direct molecular-level evidence for the co-condensation of PhTES and TEOS in the synthesis of mesoporous organosilicas.

Direct synthesis, characterization and solid-state NMR spectroscopy of large-pore vinyl-functionalized cubic mesoporous silica FDU-12

Large-pore vinyl-functionalized cubic mesoporous silica FDU-12 materials have been synthesized through the room temperature co-condensation of tetraethoxysilane (TEOS) and trimethoxyvinylsilane (TMVS) under acidic conditions templated with triblock copolymer Pluronic F127. The materials thus obtained were characterized by a variety of techniques including powder X-ray diffraction, multinuclear ( 1H, 13C, 29Si) solid-state NMR, two-dimensional (2D) 13C{ 1H} and 29Si{ 1H} HETCOR NMR, IR, thermogravimetric analysis, and nitrogen sorption measurements. Direct evidence of the presence of chemically attached vinyl moieties was provided by solid-state 1H, 29Si, and 13C NMR. The 2D 13C{ 1H} and 29Si{ 1H} HETCOR NMR experiments correlated the well-known vinyl 13C and 29Si T group resonances with their corresponding 1H NMR peak at 5.8 ppm, respectively. In particular, 29Si{ 1H} HETCOR NMR established that the vinyl groups were cross-linked to the mesoporous silica framework, instead of forming a separate phase. This provides direct molecular-level evidence for the co-condensation of TMVS and TEOS in the synthesis of mesoporous organosilicas. The vinyl functional groups were stable to at least up to 300 °C. The accessibility and the reactivity of the vinyl groups in the mesopores were demonstrated by the formation of a polymer/silica composite through in situ polymerization of vinyl groups with adsorbed methyl methacrylate monomer.

Direct Synthesis of Mesoporous Organosilica from Sodium Silicate and Organotrialkoxysilane

Using sodium silicate and organotrialkoxysilane as the silica source and nonionic polyethylene oxide C(11)similar to(15)-H(23)similar to(31) (CH2CH2O)(9)H (AEO(9)) as the structure-directing agent, MSU-type mesoporous organosilica materials that include methyl, 3-aminopropyl group were synthesized. The obtained materials were characterized by XRD, FT-IR, SEM, HRTEM, Si-29 CP MAS NMR, N-2-physisorption and bulk elemental analysis. The effects of synthetic temperature, organotrialkoxysilane content in the precursor and Si/surfactant molar composition in CH3-MSU system were investigated carefully.