Mesoporous Silica Of SBA-15 Type Research Articles

Application of microwave radiation in the grafting of acidic sites on SBA-15 type material

Mesoporous silica of SBA-15 type was modified for the first time with 3-(trihydroxysiyl)-1-propanesulfonic acid (TPS) by post-synthesis modification involving microwave or conventional heating in order to generate the Brønsted acidic centers on the material surface. The samples structure and composition were examined by low temperature N2 adsorption/desorption, XRD, HRTEM, elemental and thermal analyses. The surface properties were evaluated by esterification of acetic acid with n-hexanol used as the test reaction. A much higher efficiency of TPS species incorporation was reached with the application of microwave radiation for 1 h than conventional modification for 24 h. It was found that the structure of mesoporous support was preserved after modification using both methods applied in this study. Materials obtained with the use of microwave radiation showed a superior catalytic activity and high stability.

An efficient synthesis of acidic mesoporous materials

Abstract Ordered mesoporous silica of SBA-15 type was modified with 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS) in order to obtain a solid acid catalyst. The structure and surface properties of the materials obtained were compared with those of SBA-15 silica modified with (3-mercaptopropyl)trimethoxysilane (MPTMS). For this purpose the samples were examined by low temperature N2 adsorption/desorption, XRD, TEM, FTIR, XPS and elemental analysis. Successful incorporation of TPS species on the silica surface was proved. The catalytic activity of the materials obtained was investigated in acetic acid esterification with n-butanol and n-hexanol. Despite a lower concentration of acidic sites, TPS-modified materials showed a superior catalytic behavior over MPTMS modified sample. Moreover, the TPS containing catalysts showed a stable catalytic activity after drying and application in subsequent process.

Studies of the mechanical and extreme hydrothermal properties of periodic mesoporous silica and aluminosilica materials

In order to assess the suitability of mesoporous materials for applications in energy harvesting/storage processes occurring under extreme conditions, their mechanical, thermal and hydrothermal properties need to be fully investigated. In this study, the bulk mechanical and extreme hydrothermal properties of periodic mesoporous SBA-15 type silica and SBA-15 type aluminosilica (Al-SBA-15) were investigated using in situ small angle x-ray scattering (SAXS). In situ SAXS measurements were made on dry mesoporous SBA-15 silica and Al-SBA-15 aluminosilica samples as a function of pressure (at room temperature) to ∼ 12 GPa and on the same mesoporous materials under extreme hydrothermal conditions (to 255 °C and ∼114 MPa) using the diamond anvil cell (DAC). The analyses of the high-pressure SAXS data indicate that the mesoporous Al-SBA-15 aluminosilica has substantially greater bulk mechanical stability (isothermal bulk modulus κ = 34.7(4.5) GPa) than the mesoporous SBA-15 silica (κ = 12.0(3.0) GPa). Our molecular dynamics (MD) simulations are able to accurately model the bulk mechanical stability properties of mesoporous SBA-15 silica but underestimate the same properties of Al-SBA-15 aluminosilica. Analysis of the in situ SAXS data measured under extreme hydrothermal conditions indicates swelling of the pore walls due to water incorporation that is more significant in mesoporous Al-SBA-15 aluminosilica (∼2x) than in SBA-15 silica. In addition, the Al-SBA-15 aluminosilica clearly exhibits superior hydrothermal stability compared to SBA-15 silica under the extreme experimental temperature and pressure conditions.

Evolution of block copolymer template structure during the synthesis of ordered mesoporous silica

The popular belief is that synthesis of mesoporous silica of SBA-15 type proceeds through the phase transformation of block copolymer template which consists in the association of initial spherical micelles into rods or/and cylinders that self-assemble then into hexagonal mesophase. Herein, we showed based on transmission electron microscope observations and mesoporosity characterization by nitrogen adsorption that admixing of silica precursor into a solution of block copolymer triggers a set of transformations first of which is self-organization of initial spherical micelles into the hexagonal mesophase in which their subsequent unidirectional merging results in parallel alignment of cylindrical aggregates that determines the final regular mesoporous structure of silica.

Fermentative production of hydrogen in presence of modified mesoporous silica SBA-15

Hydrogen production was studied in the series of batch tests at 310 K in the presence of digested sludge free from methanogenic bacteria, glucose as the source of organic carbon and mesoporous silica of SBA-15 type as the adhesion-like material. Although mesopores of SBA-15 are too small for accommodation of bacteria (in this study mainly Clostridium and Enterobacter) within the porous system of SBA-15, the obtained results showed that process efficiency and reaction rate were significantly improved in presence of modified SBA-15 in comparison with those results obtained in their absence. The amount of produced hydrogen in presence of small amounts of non-modified and surface modified (NH2, Al3+) SBA-15 was apparently higher of about 50% (20% for non-modified SBA-15) than in suspensions without silica. Experiments with SBA-15 modified with SO3H groups showed negative influence of acidic surface properties on hydrogen production. Appropriate surface properties (mainly basic) of silica are probably responsible for better adhesion and propagation of bacteria properties, biofilm formation and in consequence higher activity. Moreover, systems containing SBA-15 are more resistant to temperature changes of medium. Sequential adjustment of reaction pH with stabilization at 5.5 improved the efficiency of hydrogen production.

Cobalt- and iron-based nanoparticles hosted in SBA-15 mesoporous silica and activated carbon from biomass: Effect of modification procedure

Ordered mesoporous silica of SBA-15 type and activated carbon, prepared from waste biomass (peach stones), are used as host matrix of nanosized iron and cobalt particles. The effect of preparation procedure on the state of loaded nanoparticles is in the focus of investigation. The obtained materials are characterized by Boehm method, low temperature physisorption of nitrogen, XRD, UV–Vis, FTIR, Mossbauer spectroscopy and temperature programmed reduction with hydrogen. The catalytic behaviour of the samples is tested in methanol decomposition. The dispersion, oxidative state and catalytic behaviour of loaded cobalt and iron nanoparticles are successfully tuned both by the nature of porous support and the metal precursor used during the samples preparation. Facile effect of active phase deposition from aqueous solution of nitrate precursors is assumed for activated carbon support. For the silica based materials the catalytic activity could be significantly improved when cobalt acetylacetonate is used during the modification. The complex effect of pore topology and surface functionality of different supports on the active phase formation is discussed.

Pd-loaded mesoporous silica as a robust adsorbent in adsorption/desorption desulfurization cycles

Desulfurization of benzothiophene/isooctane mixtures and gasoline (42.5 and 1000ppmwS) was studied by batch and fixed bed experiments using PdCl2 supported on mesoporous silica of SBA-15 type (PdCl2/SBA-15). The Pd-loaded silica was prepared by solid-phase impregnation of the metal halide on the mesoporous siliceous matrix (SBA-15). SBA-15 and PdCl2/SBA-15 were characterized with N2 adsorption/desorption isotherms, small angle X-ray diffraction and transmission electron microscopy (TEM). Then desulfurization of benzothiophene/isooctane mixtures and gasoline (42.5ppmwS) with these sorbents was investigated by batch and fixed bed experiments. PdCl2/SBA-15 showed much higher capacity for sulfur adsorption than both the starting material and PdCl2 itself. A mathematical model was used to represent the breakthrough curves for adsorption and desorption runs in fixed bed, providing very good agreement between numerical simulations and adsorption data. The spent PdCl2/SBA-15 was regenerated using isooctane as eluent, and the regenerated PdCl2/SBA-15 was tested again for the desulfurization of 1000ppm S gasoline (down to 50ppm). The results showed that the sulfur adsorption capacity at the break point (C=50ppm) remained nearly unchanged for three cycles, even though XPS elemental analysis for the fresh and spent adsorbent revealed some degree of leaching of the metal from the external surface, particularly as Pd(II). In conclusion, PdCl2/SBA-15 appears to be a robust adsorbent for desulfurization of liquid fuels and the model proposed herein was able to predict deep desulfurization of gasoline in cyclic mode.

Free amino and imino-bridged centres attached to organic chains bonded to structurally ordered silica for dye removal from aqueous solution

Ordered mesoporous SBA-15 type silica was synthesized by sol gel polymerization and reacted with 3-aminopropyltriethoxysilane (AP) or triethylenetetramine (TE), to attach pendant chains or bridging molecules, with basic centres. The materials were characterized by elemental analysis, infrared spectroscopy, and nuclear magnetic resonance in the solid state, X-ray diffractometry, scanning and transmission electron microscopy. The nitrogen sorption/desorption data for SBA-15 and the organofunctionalized SBA-15AP and SBA-15TE silicas resulted in IV type isotherms with hysteresis loops of the H1 type, surface areas of 800; 213 and 457 m2 g−1 and average pore diameters of 8.0; 3.2 and 6.8 nm, respectively. The ordered structural features of the mesoporous silica remained preserved after post-functionalization with pendant and bridged organic chains. Sorption data for organofunctionalized silicas gave highly selective sorption capacities for anionic water soluble Reactive Blue dye, with 0.064 and 0.072 mmol g−1. Negligible sorption was observed with the unmodified mesoporous silica. The results suggest that organofunctionalized silica can be a simple, efficient, inexpensive and suitable method for the effective and selective removal of anionic organic dye pollutants from aqueous solutions.

Synthesis and characterization of catalytic metal semiconductor-doped siliceous materials with ordered structure for chemical sensoring

Sensing materials based on doped mesoporous silica of SBA-15 type were obtained by repeated wet impregnation of the solid with semiconductive oxides (Sn and In) and noble metal (Pt). The mesoporous ...

Mesoporous silica containing [tbnd]Si(CH2)3NHC(S)NHC2H5 functional groups in the surface layer

One-step synthesis technique of mesoporous SBA-15 type silica with thiourea Si(CH2)3NHC(S)NHC2H5 groups in the surface layer was developed. According to elemental analysis, the content of surface groups is 1.25mmol/g, which is consistent with TGA data. FT-IR spectra of the obtained sample contain characteristic absorption bands of thiourea groups (NHC(S)NH), as well as polysiloxane network (SiOSi). The synthesized sample was studied by XRD, TEM, SEM, and adsorption method. It was demonstrated that the sample features porous microspheres ∼0.5μm with well-ordered internal spatial structure of the hexagonal lattice type due to the usage of template P123 during synthesis. According to XRD and TEM, the diameter of pores is 4.2–5nm and the wall thickness between them is 2.6nm. These data are consistent with the structural-adsorption characteristics calculated from nitrogen adsorption–desorption isotherms: Ssp.=510m2/g, Vs=0.47cm3/g, and d=4.3nm. Equilibrium is established within 60min during sorption of silver(І) and mercury(ІІ) ions from acidified aqueous solutions for this sample, and with the complexes are formed 1.1/1 for Ag+ and 0.8/1 for Hg2+ at metal/ligand ratio.

Influence of synthesis parameters on the physico-chemical characteristics of SBA-15 type ordered mesoporous silica

The identification of parameters governing structural, textural properties and hydrophilic/hydrophobic balance of SBA-15 type ordered mesoporous silica (OMS) has been investigated by the study of the influence of the temperature and the stirring at the ripening step (first synthesis step), the duration of the two principal synthesis steps (ripening and aging), and the heating process at the aging step.The synthesis medium has been analyzed by dynamic light scattering (DLS), both the as-synthesized and calcined SBA-15 ordered mesoporous solids have been characterized by small angle X-ray diffraction (SAXRD), nitrogen sorption experiments, scanning and transmission electron microscopy (SEM/TEM) and 29Si magic-angle spinning (MAS) NMR spectroscopy.The results show that, the morphology of elementary particles and aggregates is designed during the ripening step and is governed by the temperature and the stirring conditions. The elementary particles were formed exclusively at the early stage of the ripening step, while the morphology of the aggregates results from the assembling of elementary particles that is a slower process occurring during the ripening step. Furthermore, the silanol content changes a little with the ripening temperature but strongly increases with the aging duration. However, calcination seems to suppress any differences between the as-synthesized samples. If only porous characteristics and mesostructure are concern, a mesoporous SBA-15 type silica can be prepared from a freshly precipitated solution (i.e. 0.5h of ripening) followed by a 24h aging step at 90°C. The influence of the heating process during the aging step has been also investigated. Compared to conventional oven, microwave oven allows an increase of the specific surface area, pore diameter, total pore volume and unit cell parameter, whatever the duration of the ripening. However, a minimum ripening duration of 2h is required before aging in microwave oven to obtain a well ordered material with high textural characteristics.