Post-synthesis Grafting Method Research Articles

A nanocomposite structure based on modified MCM-48 and polystyrene

A highly ordered vinyl-functionalized MCM-48 material has been synthesized through both co-condensation and post-synthesis grafting methods. The co-condensation method gives samples with larger pore sizes and higher thermal stability than the post-synthesis grafting method. But the sample resulting from post-synthesis grafting is much more ordered. A nanocomposite structure based on vinyl-functionalized MCM-48 and polystyrene (PS) was prepared through in situ polymerization. Characterization by FT-IR, Raman, XRD and N 2 adsorption–desorption techniques indicates that inorganic/organic nanocomposites coupled at the nanometer level have been prepared by efficient polymerization of styrene monomers with the intrapore grafted vinyl groups. Bulk composites were produced by addition of the PS/post-synthesis vinyl grafted MCM-48 particles to a PS matrix. The stress–strain measurements demonstrate considerable improvement in Young’s modulus and tensile strength, when compared with the pure PS or with composites derived from PS and precipitated SiO 2 or vinyl-functionalized MCM-48 particles without polymer pre-incorporated in the pores.

Trans-(1 R,2 R)-Diaminocyclohexane-functionalized mesoporous organosilica spheres as chiral stationary phase

The bifunctionalized mesoporous organosilica spheres with trans-(1 R,2 R)-diaminocyclohexane (DACH) in the pore were synthesized and their application as chiral stationary phase in high-performance liquid chromatography (HPLC) was demonstrated. Bifunctionalized mesoporous organosilica spheres with narrow particle size distribution of 5–7 μm were prepared by the co-condensation of N-[3-(triethoxysilyl)propyl]- trans-(1 R,2 R)-diaminocyclohexane (M propyl) with 1,2-bis(trimethoxysilyl)ethane (BTME) in basic medium using octadecyltrimethylammonium chloride (C 18TACl) as structural directing agent and ethanol as co-solvent. The morphologies of the bifunctionalized mesoporous organosilicas were sensitive to the molar fraction of M propyl. At higher M propyl/BTME molar ratio, the bifunctionalized organosilica spheres with ordered mesoporous structure can be formed in a wide range of synthetic conditions. When the molar percent of M propyl/(M propyl + BTME) is less than 20, the formation of spheres could be hardly observed. The structural order of the materials mainly depends on the base concentration and M propyl/BTME molar ratio in the initial sol mixture. A column packed with the bifunctionalized mesoporous organosilica spheres exhibits higher selectivity and resolution for racemic amino acids than that packed with DACH-SiO 2 prepared by conventional post-synthesis grafting method.

Adsorption of phosphate and nitrate anions on ammonium-functionnalized mesoporous silicas

Surface modified mesostructured silica materials represent potential adsorbents offering an opportunity to remediate several important water pollutants. In the present work, ammonium-functionnalized MCM-41, MCM-48 and SBA-15 mesoporous silica materials were synthesized via post-synthesis grafting and co-condensation. Their efficiency to remove nitrate and phosphate anions in aqueous solutions was investigated. The adsorbent materials showed high adsorption capacities reaching 46.5 mg NO 3 − /g and 55.9 mg H2PO 4 − /g under the operating conditions explored. The mesoporous silica materials functionalized via post-synthesis grafting method exhibited higher performances in terms of percentage pollutant removal and adsorption capacities if compared to their analogs synthesized according to the co-condensation strategy.

Novel ways of Mn-Salen complex immobilization on modified silica support and their catalytic activity in cyclooctene epoxidation

The covalent immobilization of Mn(III)-Salen complexes on an amorphous mesoporous silica support is reported. Both (3-aminopropyl)trimethoxysilane (APTMS) and (3-iodopropyl)trimethoxysilane (IPTMS) were used in a post-synthesis grafting method to prepare organosilane-modified porous materials. Peptide and ester interactions were employed to anchor the Salen complex to the silica framework. The catalytic activity of the immobilized Salen catalyst was studied by epoxidation of cyclooctene. The comparison of the homogeneous and the immobilized catalyst shows that there was no significant loss of catalytic activity for epoxidation by immobilization. In the current study, the effects of reaction temperatures, solvents, and amount of catalyst on the catalytic activity were investigated. The optimal yield of cyclooctene oxide was obtained at 45°C using toluene as the solvent.

Heterogenized vanadyl cations over modified silica surfaces: A comprehensive understanding toward the structural property and catalytic activity difference over mesoporous and amorphous silica supports

Using a postsynthesis grafting method, 3-aminopropyltriethoxysilane (3-APTS) was functionalized over silica gel and mesoporous silica materials like SBA-15 and MCM-41. Vanadyl cations were then immobilized over the functionalized amino groups of the silica samples and used as a catalyst in the liquid-phase oxidation reaction of cyclohexane. Elemental analysis, PXRD, TEM, N 2 adsorption–desorption isotherms, FTIR, C 13 and Si 29 MAS NMR, UV–vis, and EPR techniques were used to characterize the developed materials. Characterization results suggest that the percentage of 3-APTS grafting depends on the number of isolated and geminal silanol sites of the support material, the solvents used during the grafting reactions, and the sample pretreatment conditions. We found that using toluene as the dispersing medium and Si-MCM-41 as a support provides the maximum amount of amine functionalization, and thereby the highest percentage of vanadium immobilization. Catalytic activity and metal leaching studies show that vanadium-immobilized mesoporous solids are more active and stable than the silica gel-functionalized vanadium catalyst and a framework-substituted V-MCM-41 catalyst. The enhanced activity and stability of the immobilized vanadium catalysts compared with the V-MCM-41 and silica gel samples are attributed to the active metal site isolations, as well as to the spatial restrictions imparted from the concave silica surfaces of the mesoporous solids rather than the convex silica surfaces of the silica gel sample.

Design of multifunctionalized mesoporous silicas for esterification of fatty acid

Organosulfonic acid mesoporous silicas further functionalized with hydrophobic organic groups were synthesized via postsynthesis grafting and one-step co-condensation methods. The resulting materials were tested in the esterification of fatty acid with methanol to produce methyl esters as a pretreatment step in the production of biodiesel. Incorporation of the hydrophobic group into the organic–inorganic hybrid acid catalyst was found to improve the performance of the resulting catalyst. However, the performance of the multifunctionalized mesoporous materials demonstrated a strong dependence on the incorporation method and on the size of the hydrophobic organic groups. Solution effects within the reaction mixture appeared to influence the catalytic activity of the catalysts. The results indicate the potential for intentional design of the catalytic environment at a molecular level with the use of organic–inorganic mesoporous materials.

Aluminum-grafted MCM-41 molecular sieve: an active catalyst for bisphenol F synthesis process

Liquid-phase bisphenol F synthesis from phenol and formaldehyde condensation reaction in the presence of water has been investigated over mesoporous Al:MCM-41 catalysts, with different Si/Al ratios, prepared by a post-synthesis grafting method. The catalysts have been characterized for their phase purity, surface area, average pore diameter and acidity. Introduction of Al into the framework of MCM-41 increased the acidity; however, the increase in the acidity only up to a certain level increased the acid-catalyzed phenol and formaldehyde condensation activity. Among the different Al-grafted MCM-41 molecular sieves (having Si/Al ratios from 15 to 200 mol mol −1 ), Al:MCM-41 having a Si/Al ratio of 70 mol mol −1 shows the best catalytic performance in the bisphenol F synthesis process.

Aluminum-grafted MCM-41 molecular sieve: an active catalyst for bisphenol F synthesis process

Liquid-phase bisphenol F synthesis from phenol and formaldehyde condensation reaction in the presence of water has been investigated over mesoporous Al:MCM-41 catalysts, with different Si/Al ratios, prepared by a post-synthesis grafting method. The catalysts have been characterized for their phase purity, surface area, average pore diameter and acidity. Introduction of Al into the framework of MCM-41 increased the acidity; however, the increase in the acidity only up to a certain level increased the acid-catalyzed phenol and formaldehyde condensation activity. Among the different Al-grafted MCM-41 molecular sieves (having Si/Al ratios from 15 to 200 mol mol −1), Al:MCM-41 having a Si/Al ratio of 70 mol mol −1 shows the best catalytic performance in the bisphenol F synthesis process.

Synthesis of amino-functionalized MCM-41 via direct co-condensation and post-synthesis grafting methods using mono-, di- and tri-amino-organoalkoxysilanesElectronic supplementary information (ESI) available: XRD patterns of (A) x-dNN-MCM-41 and (B) x-dNNN-MCM-41 after the extraction of the surfactant, 29Si MAS NMR spectra of MCM-41 samples prepared by (A) direct co-condensation and (B) post-synthesis grafting methods. See http://www.rsc.org/suppdata/jm/b3/b310576h/

Amino-functionalized mesoporous MCM-41 materials were synthesized directly by co-condensation of 3-aminopropyltrimethoxysilane (N silane), [1-(2-aminoethyl)-3-aminopropyl]trimethoxysilane (NN silane) or 1-[3-(trimethoxysilyl)propyl]diethylenetriamine (NNN silane) with tetraethyl orthosilicate. The maximum proportions of N, NN and NNN silanes in the Si sources for obtaining the hexagonally structured functionalized silica were 0.5, 0.4 and 0.4, respectively. The 29Si MAS NMR measurements of the materials thus obtained indicate that the Si atoms containing Si–C bonds accounted for 26.0, 17.0 and 7.8 Si mol% of the total silicons, respectively. By comparing with the results from the elemental analyses and the argentometric titrations of the surfactant-extracted samples, it was revealed that all the amino moieties incorporated were not present on the surface, but some of them were in the wall of the hexagonal channels. Amino-functionalized MCM-41 samples were also synthesized via a post-synthesis grafting on dehydrated MCM-41. At the maximum level of silylation with N, NN and NNN silanes, Si atoms containing Si–C bonds of about 20.6, 19.2 and 17.9 Si mol%, respectively, were obtained, indicating that the surface coverage of amino-organoalkoxysilanes anchored to silanol groups on the surface of MCM-41 were almost the same, irrespective of the size of the amino-organoalkoxysilanes. The adsorption experiments of Co2+ and Fe3+ were conducted in order to comparatively investigate the activity and the location of the amino-organic moieties introduced via the two methods, and some differences in the activity of amino groups derived from N, NN and NNN silanes were found. The cations adsorbed on the amino-functionalized samples via the co-condensation method were increased with an increase in the surface density of amino groups regardless of the amino-organoalkoxysilanes. When N and NN silanes were grafted onto the surface of MCM-41, the adsorption capacity was increased with an increase in the surface density of amino groups. However, when NNN silane was anchored to the surface, the adsorption capacity was decreased with an increase in the surface density of the amino groups. These results imply that the locations of the amino groups introduced to the silica via the direct co-condensation and the post-synthesis grafting methods are clearly different.

Ti-containing MCM-41 catalysts for liquid phase oxidation of cyclohexene with aqueous H2O2 and tert-butyl hydroperoxide

Framework Ti-substituted and Ti-grafted MCM-41 mesoporous material has been prepared by direct hydrothermal synthesis and a post-synthesis grafting method. The materials have been tested as catalysts for cyclohexene oxidation with aqueous H2O2 and tert-butyl hydroperoxide (TBHP). With aqueous H2O2 in methanol, the major products were cyclohexene diol and its methyl ethers. No cyclohexene oxide was produced. Titanium leaching was a serious problem, and the catalyst lost its activity irreversibly after only one cycle of reaction. With TBHP, the selectivity for cyclohexene oxide was near 100%, titanium leaching was negligible, and the catalyst could be repeatedly used after regeneration without suffering significant activity loss. However, the reaction rate was lower than when H2O2 was used. Framework substituted material and catalysts prepared by Ti-grafting onto a MCM-41 support behaved similar, but the Ti-grafted MCM-41 is somewhat more active. The turnover frequency (TOF) per mole of Ti decreases with an increase of Ti content in the catalyst. This is caused by a reduced Ti dispersion within the silica matrix.