Mesoporous Molecular Sieve SBA-15 Research Articles

Synthesis and characteristics of SBA-15 with thick pore wall and high hydrothermal stability

Highly ordered SBA-15 mesoporous molecular sieves with thick pore wall and extremely high hydrothermal stability have been synthesized successfully by a facile procedure which directly added the required amount of PVA powder during preparation. As-synthesized materials were characterized by means of X-ray diffraction, nitrogen adsorption–desorption, scanning electron microscope and transmission electron microscope. Results show that the thickness of pore wall of calcined materials is about 5.3nm, the pore diameter is about 5.6nm, and the materials have highly ordered mesoporous structure and excellent thermal and hydrothermal stability. The basic structure and morphology of as-synthesized samples are nearly unchanged on addition of different amounts of PVA powder, but specific surface areas and pore volume change. It can be expected that these mesoporous materials with highly hydrothermal stability will have a potential application prospect in the fields of multi-disciplinary.

Novel Efficient Synthesis of Glycol Monoethers over Highly Active Tungsten-Containing Mesoporous Molecular Sieve SBA-15

A tungsten-containing mesoporous molecular sieve SBA-15 (W-SBA-15) was synthesized directly by the hydrolysis of tetraethylorthosilicate and ammonium tungstate with triblock copolymer EO20PO70EO20(P123) as template in acidic medium. The W-SBA-15 was characterized by XRD, N2adsorption/desorption, UV-Vis spectroscopy, Raman spectroscopy and ICP-AES spectrometry. The W-SBA-15 exhibited high catalytic activity for the hydroxylation of cyclohexene with hydrogen peroxide (H2O2) as oxidant. The complete conversion of cyclohexene into glycol monoethers with very high selectivity (92.6%) were obtained over the W-SBA-15 catalyst.

Electrical potential near hydrated surface of ordered mesoporous molecular sieves assessed by EPR of molecular pH-probes

Some of the most important parameters of mesoporous materials are Stern potential of double electrical layer (DEL) and surface charge because of the pivotal role they play in the adsorption of charged molecular species. There are not any conventional and easy-to-perform techniques used to measure Stern potential in porous systems. The purpose of this work is to measure Stern potential in a specific case, i.e., practically cylindrical nanosized hydrated channels of the mesoporous molecular sieves (MMS) MCM-41 and SBA-15 with channel diameters ranging from 2.3 to 8.1nm using pH-sensitive nitroxide radicals (NR). A technique for direct measurement of the near-surface (Stern) potential using pH-sensitive NR was developed. Negative and positive values of Stern potential for the positively and negatively charged surface of MMS channels were found. The ranges of pH of external solution for the near-zero charge, boost-charging of the channel surface and for dissociation of functional groups in the MMS studied were found.

Stability, Hydration, and Thermodynamic Properties of RNase A Confined in Surface-Functionalized SBA-15 Mesoporous Molecular Sieves

Mesoporous silicates (MPS) have several advantages for the immobilization of enzymes and large organic molecules. They possess well-defined pores and their surfaces can be functionalized by chemical methods. In this study, the model protein ribonuclease A (RNase A) was encapsulated in unmodified amino- and carboxy-functionalized rodlike SBA-15 with pore widths ranging from 4.0 to 5.8 nm. Differential scanning (DSC) and pressure perturbation (PPC) calorimetric techniques were employed to evaluate the stability, hydration, and volumetric properties of the confined protein. In addition, the influence of the solution pH, the surface functionalization, and cosolvents on the protein immobilization and the thermal stability of the immobilized protein are reported. The extent of stabilization depends strongly on the surface characteristics of the host, such as the charge density, and on geometric parameters, i.e., the pore size and pore volume. The addition of the chaotropic agent urea leads to an increased protein loading. Addition of the kosmotropic agent glycerol has the opposite effect. The stability of the protein RNase A confined in all the mesoporous silicates is drastically enhanced and is of the order of ΔTm ≈ 30 ± 10 °C regarding the increase in temperature stability. The highest immobilization capacity, fastest immobilization rate, and maximum thermal stability was achieved for the surface-functionalized SBA-15-COOH. The increased temperature stability is probably not only due to the entropy-driven excluded volume effect but also due to an increased hydration strength of the protein within the narrow silica pores, similar to the effects compatible osmolytes impose on protein hydration and stability. The absence of an expansivity increase of the confined protein after thermal denaturation indicates that inside the pores complete unfolding of the protein is not feasible anymore.

Rapid Synthesis of Mesoporous Molecular Sieve SBA-15 by Different Techniques with Microwave Assistance

Mesoporous molecular sieves SBA-15 were prepared by using two different procedures taken from the scientific literature. In the first procedure, a hydrogel was prepared with the molar composition: 1.0 TEOS: 0017 P123: 5.7 HCl: 193 H2O with stirring at 35 °C. In the second procedure a hydrogel was prepared with the molar composition: 1.0 TEOS: 0017 P123: 8.14 HCl: 168 H2O with stirring at room temperature. In both procedures the samples were synthesized in a microwave. The samples were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), nitrogen adsorption-desorption analysis, and scanning electron microscopy (SEM). The analysis of XRD and nitrogen adsorption-desorption showed that the samples prepared with stirring at 35°C presented a higher ordering degree, an increase of crystallinity and larger volume of adsorbed nitrogen. The differential thermal analysis reveals that the SBA-15 presented high thermal stability, and the SEM revealed fiber type morphology consistent with this type of material.

Comparative study on the structural and catalytic properties of mesoporous hexagonal silica anchored with H3PW12O40: Green synthesis of benzoic acid from benzaldehyde

Mesoporous silica anchored with 25wt.% 12-tungstophosphoric acid (H3PW12O40, HPW) were comparatively characterized on their structures and catalytic activities for benzaldehyde oxidation with H2O2. The results revealed that the mesoporous materials retained the typical hexagonal mesopores for the supports of HPW. It was found that HPW exhibited higher dispersion within MCM-41 than those within SBA-15 and other mesoporous molecular sieves. Moreover, the as-prepared materials were found to be the efficient catalysts for the green synthesis of benzoic acid. In particular, HPW/MCM-41 exhibited the best catalytic properties due to its suitable textural and structural characteristics.

Metathesis of cardanol over Ru catalysts supported on mesoporous molecular sieve SBA-15

The Hoveyda–Grubbs type Zhan catalysts (ZC) and Grubbs second generation catalyst (GII) were immobilized on SBA-15 mesoporous molecular sieve by non-covalent interactions and phosphine linkers, respectively. Both hybrid catalysts proved to be highly active and selective in cardanol metathesis and cardanol cross-metathesis with ethene and cis-1,4-diacetoxy-2-butene (DAB). GII/SBA-15 was less active than ZC/SBA-15, however, Ru leaching was significantly lower for GII/SBA-15 (0.5%) than for ZC/SBA-15 (2.5%). In ethenolysis of cardanol, 3-(non-8-enyl)phenol was isolated as a major product. In cross-metathesis with DAB 9-(3-hydroxyphenyl)non-2-enyl acetate and non-2-enyl acetate were formed with high selectivity. Easy catalyst–product separation and low Ru leaching provide the products (applicable as detergent precursors and fragrance and flavor agents) free from the catalyst residue.

One-pot hydrothermal preparation of SBA-15 supported Keggin-type 12-tungstophosphoric heteropolyacid mesoporous material and its bifunctional catalytic performance

In this work, a series of 12-tungstophosphoric acid (HPW) catalysts supported on mesoporous molecular sieves SBA-15 were prepared by a one-pot hydrothermal method and their physical and chemical properties were characterized by various techniques such as fourier transform infrared spectroscopy, powder X-ray diffraction, nitrogen adsorption–desorption and transmission electron microscopy. It has been found that all the catalysts retained the mesopore structure of SBA-15 and the primary Keggin-type structure of heteropoly acid. The surface areas and pore volumes of HPW-SBA-15 decreased with the increase of HPW heteropoly acid loadings. HPW units were mostly encapsulated inside the mesopores of SBA-15. The prepared catalysts showed excellent multifunctional catalytic properties. Their bifunctional catalytic performances were examined by photo-catalytic degradation of rhodamine-B dye and microwave-catalytic synthesis of isoamyl acetate. The sample with 20 wt% loading of 12-tungstophosphoric acid was found to be more active than the other catalysts under the photo and microwave-catalytic reaction conditions. Accordingly, reasons for the catalytic activity difference were simply explicated by the effect of HPW concentration on the physicochemical characteristic of HPW-SBA-15 catalysts such as surface areas, porosity, and mesostructure.

Surface and catalytic properties of Ce-, Zr-, Au-, Cu-modified SBA-15

Au- and CeO2-containing catalysts, supported on SBA-15 mesoporous molecular sieves and loaded with additives such as Cu and Zr species, were obtained and characterised. Cerium oxides are preferentially located in the bulk of SBA-15, whereas Zr species on its surface. Gold and copper loaded on supports strongly interact resulting in the electron transfer from Cu+ to metallic gold, thus enhancing redox properties. Moreover, cerium species interact with gold, increasing redox properties of the system. The presence of copper increases the gold dispersion. Ce- and Zr-containing supports contain Lewis acid sites (LAS). The number of LAS is increased by the modification with copper species, whereas gold loading diminishes the LAS content. The presence of Zr species is responsible for Bronsted acidity and directs the oxidation of methanol to dimethyl ether. Copper enhances the selectivity to methyl formate. Gold and cerium are responsible for total oxidation of methanol, which is enhanced by modification with copper. The most attractive catalyst for low temperature total oxidation of methanol is bimetallic AuCu/CeSBA-15.

Immobilization of Cytochrome c on the Cylindrical Mesoporous Silica Extrudates

Siliceous and aluminum containing C12-MCM-41, C16-MCM-41 and SBA-15 mesoporous molecular sieves were synthesized in the powder (P) form by hydrothermal method. These materials were shaped into cylindrical extrudate (Ex) form by compounding with additives such as bentonite (binder), methyl cellulose and water. The adsorption of cytochrome c (cyt c) onto the extrudates of these mesoporous molecular sieves was studied at different solution pH. It was observed that maximum adsorption was found to be near the isoelectric point (pI) of the protein. The extrudates of SBA-15 showed a maximum amount of cyt c adsorption capacity and this may be due to the high pore volume and large pore diameter compared to other C12-MCM-41(Ex) and C16-MCM-41(Ex). Incorporation of aluminium in to the siliceous material showed maximum adsorption of cyt c compared to pure siliceous materials. The observed consequence may be due to the strong electrostatic interaction between the negative charges on the aluminium sites and positively charged amino acid residues of cyt c.

The structure and activity of potassium supported on SBA-15 molecular sieve: Density functional theory study

The geometries, vibrational frequencies, electronic properties and reactivity of potassium supported on SBA-15 have been theoretically investigated by the density functional theory (DFT) method. The structural model of the potassium supported on SBA-15 was constructed based on our previous work [Wang ZX, Wang DX, Zhao Z, Chen Y, Lan J, A DFT study of the structural units in SBA-15 mesoporous molecular sieve, Comput. Theor. Chem.963, 403, 2011]. This paper is the extension of our previous work. The most favored location of potassium atom was obtained by the calculation of substitution energy. The calculated vibrational frequencies of K /SBA-15 are in good agreement with the experimental results. By analyzing the properties of electronic structure, we found that the O atom of Si - O (2)- K group acts as the Lewis base center and the K atom acts as the Lewis acid center. The reactivity of K /SBA-15 was investigated by calculating the activation of oxygen molecule. The oxygen molecule can be activated by K /SBA-15 with an energy barrier of 103.2 kJ/mol. In the final state, the activated oxygen atoms become new Lewis acid centers, which are predicted to act as the active sites in the catalytic reactions. This study provides a deep insight into the properties of supported potassium catalysts and offers fundamental information for further research.

Oxidative degradation of pentabromophenol in the presence of humic substances catalyzed by a SBA-15 supported iron-porphyrin catalyst

Pentabromophenol (PBP), a widely used brominated flame retardant, is found in landfill leachates, and humic substance (HS) is a major concomitant in leachates. To suppress the inhibition of HS for the oxidative degradation of PBP by a heterogeneous catalytic system, a mesoporous molecular sieve SBA-15 supported iron(III)-5,10,15,20-tetrakis(4-pyridyl)-porphyrin (FeTPyP-SBA-15) was synthesized and applied to the degradation of PBP using KHSO5 as an oxygen donor. The prepared FeTPyP-SBA-15 showed a high catalytic activity and 50μM of PBP was efficiently degraded at pH 7 and 8 using 125μM KHSO5 even in the presence of 50mgL−1 HS. SiO2 supported FeTPyP (FeTPyP-SiO2) was synthesized as a control catalyst, and the turnover frequency for the FeTPyP-SiO2 catalyst (16.7h−1) was smaller than that for FeTPyP-SBA-15 (58.3h−1) in the presence of 25mgL−1 of HS. These results show that the FeTPyP-SBA-15 catalyst has a higher catalytic activity for the degradation of PBP in an aqueous solution containing HS. The FeTPyP-SBA-15 had a high selectivity for the catalytic degradation of PBP and the orderly porous structure of FeTPyP played a key role in decreasing the adverse effect of the HSs.

Preparation of NiO Nanoparticles Supported on SBA-15 Mesoporous Molecular Sieve Modified by Schiff Base Monomer

Preparation of NiO Nanoparticles Supported on SBA-15 Mesoporous Molecular Sieve Modified by Schiff Base Monomer

Synthesis, Characterization and Catalytic Performance Toward the Friedel-Crafts Acylation of Tributyltin Functionalized SBA-15

The organotin inorganic complexes(C4H9) 3Sn-O-SBA-15[Bu3SnS]were successfully synthesized by grafting tributyltin on SBA-15 mesoporous molecular sieves in a nitrogen atmosphere.The composition,structure and properties of the samples were characterized by X-ray diffraction(XRD),transmittance electron microscopy(TEM),Hammett indicator method,N2 adsorption-desorption,solid nuclear magnetic resonance(NMR),in-situ pyridine infrared spectroscopy(Py-IR) and so on.The results show that the hexagonal P6mm mesostructure of parent siliceous SBA-15 is maintained in Bu3SnS.The surface areas,proe size and volume of Bu3SnS are all deceased with the increase of acidity,compared to those of SBA-15.Friedel-Crafts acylation of anisole and benzoyl chloride can be efficiently catalyzed in the presence of Bu3SnS.The reaction conversion of anisole and the selectivity of p-benzoylanisole are 76.0% and 97.8%,respectively,when the molar ratio of anisole to benzoyl chloride is 0.5∶ 1.0,the amount of catalyst is 6%,the reaction temperature is 130 ℃ and the reaction time is 5 h.

Synthesis of SBA-15 within Short Reaction Time

Mesoporous molecular sieves SBA-15 was synthesized by using tetraethyl orthosilicate (TEOS) as silica source and pluronic 123 (EO20PO70EO20) as a template within short reaction time (6 hours) in acidic media. The influences of the different synthesis parameters such as crystallized time and crystallized condition was investigated .The resultant samples were characterized through XRD and Nitrogen adsorption. The results showed the well ordering channels SBA-15 can be synthesized under air atmosphere within 6 hours, and the best proportion could be obtained with 1 TEOS: 0.010 P123:2.17 HCl:231 H2O. After heating at 1273K for 2 hours and boiling at 373K for 24 hours, the calcined SBA-15 was proved there is well stability.

Dynamics of pH-sensitive nitroxide radicals in water adsorbed in ordered mesoporous molecular sieves by EPR Spectroscopy

A spin pH probe technique was used to study the influence of the channel diameter on the EPR spectra of pH-sensitive nitroxide radicals (NR) located in the channels of the mesoporous molecular sieves MCM-41 and SBA-15 with diameters ranging from 2.3 to 8.1nm. From EPR spectra analysis and the results of the NR retention by the mesoporous molecular sieves upon washing with an aqueous KCl solution, the regularities of NR molecular location inside the channels were studied. The obtained dependence of the fraction of the radical molecules in the fast motional regime (with the rotational correlation times, τc=2×10−11s–9×10−11s) in the channels of the mesoporous molecular sieves as a function of pH indicates that both NR in the fast and slow motional regime (with τc=8×10−9s–7×10−10s) may be used for estimation of the solution acidity inside the channels and of the near-surface electrical potential.

Synthesis, characterization and catalytic evaluation of SBA-15 supported 12-tungstophosphoric acid mesoporous materials in the oxidation of benzaldehyde to benzoic acid

A series of 12-tungstophosphoric acid catalysts supported on mesoporous molecular sieves SBA-15 were synthesized via wet impregnation method and characterized by various techniques. It has been found that all the catalysts retained the mesopore structure of SBA-15. The surface areas and pore volumes decreased with the increase of HPW loadings, whereas the mean pore diameter exhibited the opposite behavior. In addition, HPW units were highly dispersed on the SBA-15 supports when the 12-tungstophosphoric acid loading was less than 20wt.%. The results of the catalytic oxidation of benzaldehyde to benzoic acid with aqueous hydrogen peroxide, in the absence of any organic solvent and co-catalysts, indicated that SBA-15 supported 12-tungstophosphoric acid was an efficient catalyst. The sample with 20wt.% loading of 12-tungstophosphoric acid was found to be more active than other catalysts under the reaction conditions.

Modification of MCM-41 and SBA-15 mesoporous silicas by imidazolium ionic liquids

MCM-41 and SBA-15 mesoporous molecular sieves are modified with imidazolium ionic liquid (IL) via both physical adsorption and covalent grafting. The considerable effect of IL grafting on the porous structure and the particle morphology of mesoporous supports is shown. The pore size of these supports is found to be a key parameter determining the possibility of loading IL into such support materials.

Synthesis and Characterization of Large Pore Size and Highly Ordered Mesoporous Molecular Sieve SBA-15

In this study, large pore size and highly ordered mesoporous molecular sieve SBA-15 was successfully synthesized in the acidic medium by using n-propanol as the pore-expanding agent, and tetraethyl orthosilicate (TEOS) as silicon source and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock copolymer (P123 triblock copolymer) as a template agent. The samples were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Nitrogen Adsorption-Desorption. It is found that the particles of mesoporous molecular sieve SBA-15 have regular morphology and ordered pore structure, and also have high specific surface area, large pore size and pore volume.

Assembly of Mesoporous SBA-15 with an Asymmetry Copper Porphyrin and Study of Its Luminescent Property

The asymmetry porphyrin incorporates into mesoporous molecular sieves SBA-15 which through the reaction of the OH group of SBA-15 with the fluorine group of the porphyrin. The resultant material was characterized by means of XRD, TEM, solid UV/Vis, FTIR and nitrogen adsorption. Results indicate that the channels of SBA-15 have been filled with porphyrins. Luminescent property was studied by solid fluorescent emission and excitation spectra. Result indicates that the property of SBA-15/porphyrin is better than that of the pure porphyrin. Keywords: Assembly, Asymmetry porphyrin, Characterized, Hydrogen bond, Luminescent property, Mesoporous, Mesoporous material, Metal complex, SBA-15, Synthesis.