Co-condensation Of Tetraethylorthosilicate Research Articles

Mesoporous silica functionalized with diethylenetriamine moieties for metal removal and thermodynamics of cation–basic center interactions

The inorganic–organic hybrid material was synthesized by co-condensation of tetraethylorthosilicate and the organosilane N-[3-(trimethoxysilyl)propyl]diethylenetriamine. Spectroscopic analysis of the hybrid material by FTIR showed bands at 2937 and 2839 cm −1 related to ν(C H); 29Si NMR spectrum gave signals at −108, −99, −68 and −59 ppm, Q 4, Q 3, T 4 and T 2 species related to the silica backbone structure. The well-defined peaks obtained in the 13C NMR spectrum in the 10–58 ppm region confirmed the attachment of organic functional groups as pendant chains bonded into the porous silica. Particle morphology evaluated by a scanning electron microscopic (SEM) study showed the formation of spherical particles in the nanometer range. The X-ray diffraction pattern showed a peak at a 2 θ of 2.3°, demonstrating the mesoporous characteristic of the synthesized material. Adsorption evaluated by batch equilibrium processes gave the maximum adsorption of 2.2 and 2.8 mmol g −1 for copper and nickel, respectively. From these values a stoichiometry of 2:1 for cation/ligand was established, considering the amount of 1.2 mmol of pendant groups per gram of the hybrid material. Thermodynamic parameters related to the adsorption of metal ions, evaluated using the calorimetric titration technique presented a negative Gibbs free energy value, in agreement with the spontaneity of cation removal on the basic center in the mesoporous silica at the solid/liquid interface.

Bifunctional ordered mesoporous materials: direct synthesis and study of the distribution of two distinct functional groups in the pore channels

In this paper, we report the study of the distribution (regular or irregular distribution or segregation) of two distinct functional groups located within the pore channels of ordered mesoporous organosilicas. For that purpose, we have chosen two probes, both of them depending on the proximity of two organic groups. One was based on the chelating property towards EuCl3 of acetyl acetonate (acac) and carboxylate groups. The other concerns the ion-exchange capability of the sulfonic acid moieties, which depends on the proximity of the acid groups. In the first part, various ordered monofunctional mesoporous organosilicas were prepared by co-condensation of tetraethylorthosilicate (TEOS) and an organotriethoxysilane Σ–(CH2)3–Si(OEt)3 (with Σ = acetylacetonate (acac), CN, SH, Cl, NH2 and H) in the presence of the triblock copolymer P123 as a structure-directing agent at pH = 1.5. Thanks to the probes, we have first showed that all the organic groups (SH, CN, acac) are accessible and regularly distributed within the channel pores of monofunctional mesoporous materials. In the second part, several ordered mesoporous materials containing two distinct functional groups including at least one probe were prepared in one step by co-condensation of TEOS and two organotriethoxysilanes Σ–(CH2)3–Si(OEt)3 and Σ′–(CH2)3–Si(OEt)3, under the same experimental conditions as previously. Taking into account the results obtained with the monofunctional materials as references, the distribution of two distinct functional groups located on the pores surfaces of mesoporous materials was determined and discussed.

Novel Inorganic−Organic Hybrid Fluorescence Chemosensor Derived from SBA-15 for Copper Cation

A novel mesoporous SBA-15 type of hybrid material (3-trimethoxysilylpropyl)[4-(2-hydroxyphenyl)methylene] benzenesulfonamide (Schiff-SBA-15) has been obtained by co-condensation of tetraethyl orthosilicate and the organosilane, and the result of XRD confirms the order hexagonal structure of the composite. This hybrid mesoporous material is fluorescent-active, exhibiting high selectivity for sensing Cu2+ in polar solution. The remarkable fluorescence quenching in emission spectrum upon the addition of Cu2+ is attributed to the intramolecular charge transfer after the formation of a coordinate complex of a large conjugate system and Cu2+ ions.

Polymer-templated organosilicas with hexagonally ordered mesopores: the effect of organosilane addition at different synthesis stages

Two series of ordered mesoporous organosilica (OMO) SBA-15 materials with surface and bridging groups were fabricated by varying the organic precursor addition at different synthesis stages. The consequence of the delayed introduction of organic precursor on the structural and adsorption properties of the resulting OMOs was investigated. The OMOs studied were synthesized via co-condensation of tetraethyl orthosilicate (TEOS) and ureidopropyltrimethoxysilane (UPS) as well as TEOS and bis(triethoxysilylpropyl) disulfide (BTDS) in the presence of poly(ethylene oxide)-poly(propylene oxide)- poly(ethylene oxide) triblock copolymer Pluronic P123 (EO20PO70EO20). The aforementioned OMOs were characterized by nitrogen adsorption-desorption isotherms at −196 °C and powder X-ray diffraction (XRD). Nitrogen adsorption isotherms were used to estimate the pore volume, mesopore diameter and the BET specific surface area, whereas the XRD data provided information about structural ordering and unit cell of the samples studied.

Dual-functionalized large pore mesoporous silica as an efficient catalyst for bisphenol-A synthesis

Mesoporous SBA-15 materials dual-functionalized with arenesulfonic acid and mercapto (or disulfide) groups were synthesized by co-condensation of tetraethylorthosilicate (TEOS) and organosilane precursors in the presence of EO 20PO 70EO 20 (P123) copolymer under acidic condition. The amount of sulfur incorporated in the silica framework increased with the concentrations of the organosilane precursors in the synthesis gel, and sulfur contents up to 3.6 mmol/g silica could be obtained. Based on the sulfur K-edge X-ray absorption spectra, the chlorosulfonyl moieties in 2-(4-chlorosulfonyl-phenyl)ethyltriethoxysilane (CSPETES) precursors were completely in situ hydrolyzed to sulfonic acid, while a large portion of the mercapto groups was oxidized to disulfide under the synthesis condition. The dual-functionalized SBA-15 was much more efficient as catalysts than the single functionalized counterparts in condensation of phenol and acetone to form bisphenol-A. Both mercapto and disulfide groups demonstrated promoter effect in formation of p, p′-bisphenol-A. Moreover, ordered mesopores facilitated the diffusion of reactants and the accessibility of the catalytic and promoting sites.

Octadecylsilane hybrid silicas prepared by the sol–gel method: Morphological and textural aspects

A series of octadecylsilane-modified silicas was prepared by the sol–gel method through the hydrolysis and cocondensation of tetraethylorthosilicate (TEOS) with octadecyltriethoxysilane (ODS). The ODS:TEOS ratio was varied between 0:100 and 100:0. The resulting carbon content was between 2.5 and 53.4%. In the case of pure ODS, the resulting silica presented 68.6% of C. Hybrid silicas were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and 29Si nuclear magnetic resonance spectroscopy. Spheres of ca. 0.5–1.0 μm were obtained in the case of hydrolysis of pure TEOS. The combination of ODS:TEOS ratio yielded systems combining spherical and lamellar patterns zones. Monitoring the particle growth, it seems that spherical particles grow around lamellar zones, these latter concentrating the organosilicon moieties. The degree of cross-linking of ODS moieties was shown to be dependent on the ODS addition time and stirring speed.

Aerobic oxidation of alcohols catalyzed by gold nano-particles confined in the walls of mesoporous silica

Gold nano-particles confined in the walls of mesoporous silica (GMS) catalysts were successfully prepared by a novel and simple technique utilizing thioether functional groups in the walls of mesoporous silica to anchor HAuCl 4. Calcination of the materials removed organic moieties and reduced the gold salt to gold nano-particles. In this procedure, the thioether groups were introduced into the silica wall via a co-condensation of tetraethyl orthosilicate (TEOS) with 1,4-bis(triethoxysily)propane tetrasulfide. These gold containing mesoporous catalysts have unusually high surface area and pore volume. The catalysts were evaluated for the solvent free liquid phase oxidation of benzyl alcohol by molecular oxygen. High selectivity to benzaldehyde was obtained under the reaction conditions of 403 K, 15 atm and 5 h in an autoclave. The 1.5% GMS catalyst was also evaluated for oxidation of alcohols using toluene as solvent under flowing oxygen at atmospheric pressure at 353 K in a two-necked flask. Under these conditions the conversion of benzyl alcohol reached 100% after 2 h and it was demonstrated that the catalyst can be recycled three times without significant loss of activity.

Direct synthesis of ordered mesoporous silica containing iodopropyl groups. A useful function for chemical modifications

In this paper, we report a clever approach permitting, in one step, the synthesis of ordered (hexagonal phase) mesoporous silica functionalized with iodopropyl groups [I(CH2)3] located in the pore channels. This material was obtained by the hydrolysis and co-condensation of tetraethylorthosilicate (TEOS) and iodopropyltriethoxysilane (I(CH2)3Si(OEt)3) in the presence of P123 as a non-ionic structure-directing agent and hydrogen iodide as an acid catalyst. All materials were characterised by X-ray diffraction measurements, transmission electron spectroscopy, nitrogen adsorption analyses, elemental analyses, and solid-state 13C and 29Si NMR spectroscopy. The accessibility and reactivity of this functional group was investigated, showing the advantage of the iodo group for the introduction of bulky or hydrophilic groups.

Homoallylic Alcohol Isomerization in Water over an Immobilized Ru(II) Organometallic Catalyst with Mesoporous Structure

PPh(2)-functionalized SBA-15 was synthesized by co-condensation of tetraethyl orthosilicate and 2-(diphenylphosphino)ethyltriethoxysilane through prehydrolysis. The as-prepared PPh(2)-SBA-15 was used as the support to immobilize the Ru(II) organometallic catalyst through the strong coordination between the Ru(II) and the PPh(2)-ligand (Ru-PPh(2)-SBA-15). During 1-phenyl-3-buten-1-ol isomerization carried out in water as an environmentally friendly medium, the Ru-PPh(2)-SBA-15 catalyst exhibited almost the same activity and selectivity as the corresponding RuCl(2)(PPh(3))(3) homogeneous catalyst and could be used repetitively nearly 7 times. On the basis of various characterizations, the correlation of the catalytic behaviors of the Ru-PPh(2)-SBA-15 to its structural characteristics was discussed briefly. Obviously, the high activity of the Ru-PPh(2)-SBA-15 could be attributed to both the high surface area of the support, which ensured the good dispersion of Ru(II) active sites, and the ordered mesoporous structure, which facilitated the diffusion of organic reactants.

Tetramethylguanidine covalently bonded onto silica gel as catalyst for the addition of nitromethane to cyclopentenone

A catalyst based on silica chemically modified with tetramethylguanidine (TMG) was synthesized by the co-condensation of tetraethylorthosilicate (TEOS) with a new silylant agent derived from the reaction between the TMG molecule and (3-chloropropyl)trimethoxysilane. A neutral n-dodecylamine template was used to organize the polymerization of the inorganic-organic catalyst. Thermogravimetry showed that the number of active pendant groups in the catalyst was 1.35 mmol g-1, with a surface area of 811 ± 75 m² g-1. Infrared spectroscopy and 13C and 29Si nuclear magnetic resonance data are in agreement with the proposed structure. This material has been used to catalyse the addition of nitromethane to cyclopentenone. The catalytic efficiency was followed and the nitromethylcyclopentanone conversion presented a yield of 98% at 3 h of reaction. The catalyst was recovered and reused 14 times, maintaining about 98% of its catalytic efficiency.

New approach to the immobilization of glucose oxidase on non-porous silica microspheres functionalized by (3-aminopropyl)trimethoxysilane (APTMS)

The immobilization and encapsulation of glucose oxidase (GOD) onto the mesoporous and the non-porous silica spheres prepared by co-condensation of tetraethylorthosilicate (TEOS) and (3-aminopropyl)trimethoxysilane (APTMS) in the water-in-oil (W/O) emulsion system were studied. The terminal amine group was used as the important functionality for GOD immobilization on the silica substrate. When only TEOS is used as a silica source, the disordered mesoporous silica microspheres are obtained. As the molar ratio of APTMS to TEOS ( R AT) increases, the surface area and pore volume of the silica particles measured by nitrogen adsorption and desorption method and SEM decrease rapidly. Particularly, the largest change of the surface morphology is observed between R AT = 0.20 and R AT = 0.25. The amount and the adsorption time of immobilized enzyme were measured by UV spectroscopy. About 20 wt% of GOD was immobilized into the silica substrates above R AT = 0.60 and was completely adsorbed into the substrate of R AT = 0.80 with lapse of 4 h after addition. In the measurement of the thermal stability, GOD dissolved in buffer solution loses nearly all of its activity after 30 min at 65 °C. In contrast, GOD immobilized on the surface-modified silica particles still retains about 90% of its activity after the same treatment. At this temperature, the immobilized glucose oxidase retained half of its initial activity after 4 h. It is shown that the suitable usage of functionalizing agent like APTMS as well as the control of surface morphology is very important on the immobilization of enzyme.

Adsorption and structural properties of channel-like and cage-like organosilicas

Channel-like and cage-like mesoporous silicas, SBA-15 (P6mm symmetry group) and SBA-16 (Im3m symmetry group), were modified by introducing single ureidopropyl surface groups, mixed ureidopropyl and mercaptopropyl surface groups, and single bis(propyl)disulfide bridging groups. These hexagonal and cubic organosilicas were prepared under acidic conditions via co-condensation of tetraethyl orthosilicate (TEOS) and proper organosilanes using poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) amphiphilic block copolymer templates, P123 (EO20PO70EO20) and F127 (EO106PO70EO106). The modified SBA-15 and SBA-16 materials were synthesized by varying the molar ratio of organosilane to TEOS in the initial synthesis gel. The removal of polymeric templates, P123 and F127, was performed with ethanol/hydrochloric acid solution. In the case of SBA-15 the P123 template was fully extracted, whereas this extraction process was less efficient for the removal of F127 template from the SBA-16-type organosilicas; in the latter case a small residue of F127 was retained. The adsorption and structural properties of the resulting materials were studied by nitrogen adsorption-desorption isotherms at −196∘C (surface area, pore size distribution, pore volumes), powder X-Ray diffraction, CHNS elemental analysis and high-resolution thermogravimetry. The structural ordering, the BET specific surface area, pore volume and pore size decreased for both channel-like and cage-like mesoporous organosilicas with increasing concentration of incorporated organic groups.

Co-condensation synthesis and adsorption properties of cage-like mesoporous silicas with imidazole groups

Two cubic cage-like mesoporous silicas, SBA-16 (Im3m) and FDU-1 (Fm3m), with different concentrations of imidazole groups were synthesized by co-condensation of tetraethyl orthosilicate and N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole in the presence of poly(ethylene oxide)- block-poly(propylene oxide)- block-poly(ethylene oxide) (EO 106PO 70EO 106) and poly(ethylene oxide)- block-poly(butylene oxide)- block-poly(ethylene oxide) (EO 39BO 47EO 39) triblock copolymers, respectively, under low acidic conditions and with addition of sodium chloride. The polymeric templates used were removed via extraction with acidified ethanolic solution. The organosilicas studied were characterized by nitrogen adsorption, powder X-Ray diffraction, thermogravimetry and elemental analysis. The amount of incorporated imidazole groups gradually increased with increasing concentration of N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole in the synthesis gel. This incorporation was slightly better for FDU-1, which has larger mesopores and mesopore entrances than those in SBA-16. The interplanar d-spacing, total pore volume, pore diameter and specific surface area tended to systematically decrease with increasing loadings of organic ligands. This work reveals that an enlargement of pore openings in the cage-like organosilicas studied can be achieved by controlling time of their hydrothermal treatment. In addition, it was shown that their calcination in air at 550 °C caused a complete removal of organic species but this process did not lead to the disappearance of structural ordering in the resulting silica.

Preparation and characterization of vinyl-functionalized mesoporous SBA-15 silica by a direct synthesis method

Vinyl groups were used to functionalize the pore channels of mesoporous SBA-15 materials by the co-condensation of tetraethyl orthosilicate (TEOS) and triethoxyvinylsilane (TEVS) in the presence of poly(ethylene glycol)–B-poly(propylene glycol)–B-poly(ethylene glycol) (P123) surfactants under acidic conditions. The final materials were investigated in detail by means of FT-IR, XRD, TEM, solid state NMR and N 2 adsorption, in order to study the effect of vinyl concentration on their mesoscopic order and pore structure. The results show that vinyl groups are attached covalently to the pore wall of SBA-15 after modification. The mesoscopic architecture almost remains intact upon functionalization, with only a minor decrease of the intensity of (110) diffractions for the 20 mol% TEVS-functionalized samples, which still preserve a desirable pore structure, with a surface area of 883.7 m 2/g, a pore volume of 0.98 cm 3/g and a mean pore size of 4.4 nm.

Effect of synthesis conditions on the mesoscopical order of mesoporous silica SBA-15 functionalized by amino groups

Mesoporous amine-functionalized SBA-15 silica has been synthesized directly by the co-condensation of tetraethyl orthosilicate (TEOS) and aminopropyl-trimethoxysilane (APTMS) under acidic conditions with an APTMS/(APTMS + TEOS) molar ratio of 10%. The effect of synthesis conditions, including TEOS pre-hydrolysis, as well as the heating temperature and time, on the mesoscopical order and pore structure of the functionalized SBA-15 have been studied in detail by means of powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, infrared spectra and solid state 29Si nuclear magnetic resonance. A functionalized SBA-15 silica with a highly ordered two-dimensional P6 mm hexagonal symmetry and a narrow pore size distribution centered at 6 nm can be obtained if TEOS is allowed to pre-hydrolyze for 2 h. For the sample with TEOS pre-hydrolysis time of 4 h, aging at 50°C or 150°C leads to a more ordered pore arrangement compared to 100°C and also a narrower pore size distribution with larger pore volume. Increasing aging time is in favor of the formation of mesoscopically ordered structure, but fails to obtain a superior pore structure.

Synthesis, characterization and catalytic activity of ordered SBA-15 materials containing high loading of diamine functional groups

Diamine-functionalized mesoporous SBA-15 materials have been synthesized by co-condensation of tetraethylorthosilicate (TEOS) with [3-(2-aminoethyl aminopropyl)]trimethoxysilane (ATMS) using amphiphilic block copolymer P123 as pore-directing agent under the aid of inorganic salt NaCl and with prehydrolysis of TEOS prior to the addition of organosiloxane. The functionalized materials have hexagonal mesostructure ordering, narrow pore-size distribution with diameter around 60 Å, and high loadings of amino groups (up to 3.49 mmol g −1). Prehydrolysis of TEOS was a key step for preparation of well-ordered mesoporous materials with amino functionalities. Inorganic salt had great influence on the ordering of mesostructure and the morphology of the resultant materials. The diamine-functionalized materials showed better catalytic performance than the aminopropyl-functionalized counterpart in the Knoevenagel reaction of benzaldehyde with ethyl cynoacetate to form α,β-unsaturated compound in liquid phase.

A comparative study of solid sulfonic acid catalysts based on various ordered mesoporous silica materials

Acid catalysts based on ordered mesoporous silica materials (MCM-41, HMS, and SBS-15) with covalently anchored propanesulfonic or benzenesulfonic acid groups were synthesized. Six samples were prepared by co-condensation of tetraethylorthosilicate with 3-mercaptopropyltrimethoxysilane or phenyltriethoxysilane in the presence of appropriate templating agents. Six other samples were made by post-synthesis modification of the parent silica materials. Syntheses were followed by oxidation or sulfonation to form surface sulfonic acid groups. Sample characterization was performed by physical (low-angle X-ray powder diffraction, nitrogen adsorption and desorption, diffuse reflectance IR, Raman, NMR, and X-ray photoelectron spectroscopies) and chemical (acid–base titration) methods. Spectroscopic techniques proved successful incorporation of the functional groups. Functionalization of the parent silicas, however, results in changes in structural characteristics (decreasing BET surface areas, changes in pore size distribution, decreasing long range orders). The samples exhibit high activities in various catalytic transformations. Catalysts with anchored benzenesulfonic acid groups of high acid strength and high acid site densities allow the selective synthesis of the cyclic dimer indan product in the dimerization of 2-phenylpropene. 2,3,5-Trimethylhydroquinone diacetate can also be produced in similar high yields in the rearrangement–aromatization of ketoisophorone. Characteristic differences in selectivities are interpreted by taking into account of differences in acid site densities, active site distribution, and the polarity of reactants and catalyst surface. The low activity and selectivity of samples made by grafting in the transformation of ketoisophorone are attributed to the non-random distribution of the acidic functions.

Synthesis and characterization of Co(II) salen functionalized MCM-41-type hybrid mesoporous silicas and their applications in catalysis for styrene oxidation with H 2O 2

Schiff base functionalized MCM-41-type hybrid mesoporous silica (MCM-41-SalenH) was synthesized by co-condensation of tetraethyl orthosilicate (TEOS) and the precursor of salicylaldehyde modified (3-aminopropyl)triethoxysilane (SalenHSi) in the presence of cetyltrimethylammonium bromide (CTAB) followed by surfactant extraction. Imprinting technique was carried out to recover the salicylaldimine groups disrupted during the acid extraction process. The recovery of the Schiff base was confirmed by Fourier transform infrared (FT-IR) spectroscopy. Solid state CP-MAS NMR spectroscopy of 29Si ( 29Si CP-MAS NMR) showed a highly condensed siloxane network. The co-condensation and imprinting technique produced MCM-41-SalenH hybrid mesoporous silica with uniform mesoscale channels, high specific surface areas (>1200 m 2 g −1) and large pore volumes (>1.25 cm 3 g −1). Solid oxidation catalysts can be obtained by introducing Co 2+ into the hybrid materials via a ligand exchange reaction. The solid catalysts showed higher activity for the liquid-phase oxidation of styrene with H 2O 2 under mild condition and stability against leaching of active Co 2+ compared with the corresponding homogeneous catalysts.

Direct synthesis of thiol-ligands-functionalized SBA-15: Effect of 3-mercaptopropyltrimethoxysilane concentration on pore structure

Mesoporous thiol-functionalized SBA-15 silicas have been directly synthesized by co-condensation of tetraethyl orthosilicate and 3-mercaptopropyltrimethoxysilane with triblock copolymer poly(ethylene glycol)-B-poly(propylene glycol)-B-Poly(ethylene glycol) as structure-directing agent under hydrothermal condition. Mesoporous structure was obtained after the surfactant removal by Soxhlet ethanol extraction. These materials have been characterized by means of powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, thermogravimetry analysis, elemental analysis and solid state 29Si nuclear magnetic resonance. The effect of 3-mercaptopropyltrimethoxysilane concentration in the initial mixture on the pore structure of functionalized SBA-15, including pore ordering, surface area, pore size and pore volume, is investigated in detail. In order to functionalize the SBA-15 silicas without a significant change of pore structure, the molar concentration of 3-mercaptopropyltrimethoxysilane should be limited to less than 20%.

Interaction of divalent copper with two diaminealkyl hexagonal mesoporous silicas evaluated by adsorption and thermochemical data

Hexagonal mesoporous silicas chemically modified with ethylenediamine moieties were synthesized through the co-condensation of tetraethylorthosilicate (TEOS) with two different silylating agents: (i) N-[3-(trimethoxysilyl)propyl]-ethylenediamine and (ii) the new agent prepared from the incorporation of the ethylenediamine molecule into the epoxide group of the precursor 3-glycidoxypropyltrimethoxysilane. From these silylating agents under neutral n-octylamine template methodology, the respective MNN and MGNN inorganic–organic hybrids were synthesized. Elemental analysis showed that the number of pendant groups in these hybrids were 1.69 and 1.62 mmol g −1, with pore diameters and surface areas of 1.81 and 1.53 nm and 663 ± 14 and 614 ± 16 m 2 g −1. Infrared spectroscopy, nuclear magnetic resonance for 13C and 29Si nuclei and X-ray diffraction patterns are in agreement with the success of the proposed synthetic methods, as confirmed for the formation of the mesoporous hybrids. Both mesoporous materials have been used for divalent copper adsorption from aqueous solution at 298 ± 1 K. The series of adsorption isotherms were adjusted to a modified Langmuir equation. The maximum number of moles adsorbed gave 1.4 ± 0.1 and 1.4 ± 0.2 mmol g −1 for MNN and MGNN, respectively. The same interactions were calorimetrically followed and gave exothermic enthalpy, negative Gibbs free energy and positive entropy values. These favorable thermodynamic data indicate cation/nitrogen basic center interactions on the new mesoporous materials at the liquid/solid interface for both systems.