Mesoporous Silica Material SBA-15 Research Articles

Radical-Facilitated Green Synthesis of Highly Ordered Mesoporous Silica Materials.

In the hydrothermal synthesis of highly ordered mesoporous silica material SBA-15, strong acid is typically required to catalyze the hydrolysis and condensation of silica species. Meanwhile, under strongly acidic conditions, the transition metal ions, e.g., iron ions, are difficult to incorporate into SBA-15 because of the facile dissociation of Fe-O-Si bonds. Here, we demonstrate an acid-free green synthetic strategy for the synthesis of highly ordered mesoporous SBA-15 and Fe-SBA-15 with the assistance of hydroxyl free radicals that are generated by physical or chemical methods. The prepared materials exhibit a large specific surface area compared to the counterparts prepared by conventional method under acidic conditions. Moreover, Fe-SBA-15 shows high metal loading efficiency as over 50%. Density functional theory calculations suggest that the hydroxyl free radicals exhibit higher catalytic activity than H+ ions for the hydrolysis of tetraethyl orthosilicate. This radical-facilitated synthesis approach overcomes the challenge to the direct synthesis of highly ordered SBA-15 and Fe-SBA-15 without adding any acid, providing a facile and environmentally friendly route for future large-scale production of ordered mesoporous materials.

N-α-acylation of lysine catalyzed by immobilized aminoacylases from Streptomyces ambofaciens in aqueous medium

Aminoacylases (EC 3.5.1.1.4) of Streptomyces ambofaciens ATCC 23877 were immobilized by chemical and physical adsorption onto SBA-15 mesoporous silica materials. The activity of the immobilized aminoacylases was firstly evaluated by considering the hydrolysis reactions of N-α-acetyl-lysine, used as rapid method of screening. After chemical adsorption, a significant loss of activity was observed probably due to a conformational change of the aminoacylases structures upon immobilization. When the immobilization was performed by physisorption a higher amount of enzyme (0.20 against 0.05 mg per mg of support) can be adsorbed onto the mesoporous silica material. The physisorbed biocatalyst also presented a higher hydrolytic activity than the chemisorbed enzyme. Recycling of the supported biocatalysts was performed three times with no loss of the specific activity. Furthermore, a better thermostability was also noted in comparison with free enzyme upon aminoacylases physisorption.Finally, lauroyl-lysine synthesis was catalyzed for the first time by immobilized aminoacylases. The crude extract from S. ambofaciens exhibited the rare ability to catalyze the N-acylation on amino group in the α-position of the lysine whereas the lipase B of Candida antarctica catalyzed the acylation of lysine on its amino group in ε-position. This particular and original regioselectivity was maintained with immobilized enzymes.

Adsorption of Th(IV) and U(VI) on functionalized SBA-15 mesoporous silica materials using fixed bed column method; breakthrough curves prediction and modeling

ABSTRACTRemoval–separation of Th(IV)/U(VI) by Schiff base functionalized SBA-15 materials SBA/SA and SBA/EnSA using fixed bed column method was investigated. The effects of flow rate and bed height were studied and the experimental breakthrough curves were obtained. The analysis of experimental data showed that the breakthrough time and exhaustion time, metal uptake capacity and total metal removal increased with reducing the flow rate, and with increasing the bed height. Thomas and Yan models were applied to the experimental data for evaluating the dynamic behavior and the characteristic parameters of the column for the process design.

Influence of synthesis conditions on morphological features of the SBA-15 containing only elongated and rounded/spherical grains

Mesoporous silica SBA-15 materials of high specific surface area (~700 m2 g?1) were synthesized by using block copolymer Pluronic P123 as template and tetraethoxysilane as silica source. The obtained materials were characterized by XRD, nitrogen adsorption - desorption measurements, SEM, EDS and AFM analysis. It was found that small modifications of synthesis conditions influenced the morphological features of the synthesized SBA-15 samples. The SEM analysis had shown that the SBA-15 synthesized at lower temperature and longer time of reaction (80?C, 48 h) provided elongated rod-shaped grains about 1?m long. The other sample synthesized at higher temperature and shorter time of reaction (100 ?C, 24 h) had rounded grains and grains of regular spherical shape with diameters ranging from 0.5 to 2 ?m. The EDS analysis confirmed that the particles of both synthesized samples were of the SiO2 content. In addition, the AFM analysis had shown different surface morphologies of the materials synthesized under various conditions.

Mesoporous SBA-15 modified with titanocene complexes and ionic liquids: interactions with DNA and other molecules of biological interest studied by solid state electrochemical techniques.

The immobilization of two titanocene complexes on SBA-15 has been accomplished following post-synthetic procedures. The ionic liquid, 1-methyl-3-[(triethoxysilyl)propyl]imidazolium chloride, has also been incorporated into the titanium containing materials to determine its influence on the interaction with molecules of biological interest. Cyclic voltammetry has been used to study the influence of the ionic liquid on the mechanism of reduction of titanocene derivatives. The interaction of titanocene and titanocene/ionic liquid-containing mesoporous silica SBA-15 materials, with molecules of biological interest associated with important processes of metallodrug action against cancer cells, has been studied. Thus, we have carried out hydrolysis experiments on the materials functionalized with titanocene derivatives in physiological media to determine their stability and the interaction with serum/transport proteins such as transferrin and BSA and with target molecules such as guanosine, single-stranded DNA and double-stranded DNA by means of solid state voltammetry techniques. A qualitative analysis of the data based on peak current and reduction potential value changes of the couple Ti(iv)/Ti(iii) in the presence of biomolecules at physiological pH, has revealed that grafted titanocene complexes show higher affinity for serum/transport proteins than for nucleic acids, indicating that the transport steps to the cells may be easier than the subsequent attack on DNA.

Fabrication of chitosan-mesoporous silica SBA-15 nanocomposites via functional ionic liquid as the bridging agent for PPL immobilization

A nanocomposite (SBA-CIL-CS) which was combined mesoporous silica SBA-15 material with chitosan via ionic liquid as the bridging agent was successfully fabricated. The morphology and structure of the nanocomposite were characterized in detail with transmission electron microscope, fourier transform infrared spectroscopy, thermogravimetric analysis and nitrogen adsorption–desorption techniques. SBA-CIL-CS was investigated as an efficient support for immobilization of porcine pancreas lipase (PPL) and possessed high immobilization efficiency. The properties of immobilized enzyme (SBA-CIL-CS-PPL) such as activity, stability and reusability have been significantly improved, and a preferable pH and temperature tolerance were obtained as well. Results demonstrated the inorganic-organic nanocomposite could be used as an ideal support for enzyme immobilization.

Synthesis and Structural Characterization of G-SBA-IDA, G-SBA-EDTA and G-SBA-DTPA Modified Mesoporous SBA-15 Silica and Their Application for Removal of Toxic Metal Ions Pollutants

Modified mesoporous SBA-15 silica materials (G-SBA-IDA, G-SBA-EDTA and G-SBA-DTPA) (where IDA, EDTA and DTPA represent iminodiacetic acid, ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid, respectively) were prepared by treatment of grafted monoamine or diamine or triamine mesoporous SBA-15 silica (G-SBA-N, G-SBA-NN , G-SBA-NNN) nanomaterials with ethylchloroacetate, followed by acid hydrolysis of ester groups. These materials were characterized by several techniques including transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS), thermal analysis (TGA) and X-ray photoelectron spectroscopy (XPS). TEM and BET analysis revealed that the IDA functionalized amine mesoporous SBA-15 silica materials have maintained their mesostructure after modification of the amine mesoporous silica with ethylchloroacetate. Thermal analysis (TGA-DTA) and FTIR confirmed that ethylchloroacetate groups are covalently bound to the amine groups. The acid forms of IDA functionalized materials showed high potential for extraction and removal of heavy pollutant metal ions (Co2+, Ni2+, Cu2+and Pb2+) from aqueous solutions.

Al-Rich Ordered Mesoporous Silica SBA-15 Materials: Synthesis, Surface Characterization and Acid Properties

Al–SBA-15 is an interesting mesoporous material having highly ordered nanopores and a large surface area, which is widely employed as catalysts and adsorbents, but relatively few studies on the surfaces properties of this type of materials have been carried out. The purpose of the present work was to advance knowledge on the textural properties of Al–SBA-15 by applying the accurate NLDFT method as well as to gain insight into the surface characterisation and acidic trend of this material. Mesoporous Al–SBA-15 molecular sieves, in three SiO2/Al2O3 ratios: 50, 75 and 100 were accomplished by post-synthesis alumination in aqueous solution of a purely siliceous SBA-15 material. The obtained solids were characterized using powder X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption–desorption (BET/DFT), transmission electron microscopy (TEM), water adsorption and zeta potential measurements. The results indicate that Al atoms have been successfully incorporated into the framework of the hexagonal mesoporous SBA-15. The aluminum introduced amount has remarkably affected the surface properties of the SBA-15 solid, indeed microporosity decreased. Furthermore, the esterification test showed that the Al–SBA-15 material exhibit Bronsted acid properties with an interesting activity leading to yields of ~90% of biodiesel.

A chromotropic acid modified SBA-15 as a highly sensitive fluorescent probe for determination of Fe3+ and I− ions in water

A novel organic–inorganic hybrid nanomaterial (SBA-15-CA) was prepared by covalent immobilization of chromotropic acid onto the surface of mesoporous silica material SBA-15. Different techniques such as XRD, TEM, FT-IR, N2 adsorption–desorption and TGA analyses were employed to characterize the grafting process. The data showed that the organic moiety (0.41 mmol g−1) was successfully grafted to the SBA-15 and the primary hexagonally ordered mesoporous structure of SBA-15 was preserved after the grafting procedure. SBA-15-CA has been realized as a highly sensitive and selective fluorescent probe towards Fe3+ and I− ions in aqueous media. SBA-15-CA exhibited a remarkable fluorescent quenching in the presence of Fe3+ ion over other competitive cations including Na+, Mg2+, Al3+, K+, Ca2+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, and Pb2+ as well as I− ion among a series of anions including F−, Cl−, Br−, CO32−, HCO3−, CN−, NO3−, NO2−, SCN−, SO42−, H2PO4−, HPO42−, and CH3COO−. A good linear response was observed between the concentration of the quenchers (Fe3+ and I− ions) and fluorescence intensity of SBA-15-CA with detection limits of 1.5 × 10−7 M for Fe3+ and 0.2 × 10−7 M for I−. Moreover, the effects of various pH values on the sensing ability of SBA-15-CA were investigated. Finally, the proposed method was successfully utilized for the determination of Fe3+ and I− ions in river water, well water and tap water samples.

Isatin functionalized nanoporous SBA-15 as a selective fluorescent probe for the detection of Hg(II) in water.

A highly ordered mesoporous silica material functionalized with isatin (SBA-Pr-IS) was designed and synthesized. Characterization techniques including XRD, TGA, BET, SEM, and FT-IR were employed to characterize the pore structure, textural properties, microscopic morphology, and molecular composition of grafted organic moieties of SBA-Pr-IS. The successful attachment of the organic moiety (0.34mmolg-1) without the SBA-15 structure collapsing after the modification steps was confirmed. Fluorescence characterization of SBA-Pr-IS was examined upon addition of a wide variety of cations in aqueous medium and it showed high sensitivity toward Hg2+ ions. During testing in an ion competition experiment, it was observed that the fluorescence changes of the probe were remarkably specific for Hg2+ ions. Furthermore, a good linearity between the fluorescence intensity of this material and the concentration of Hg2+ ions was constructed with a suitable detection limit of 3.7 × 10-6M. Finally, the applicability of the proposed method was successfully evaluated for the determination of Hg2+ ions in real samples. Therefore, SBA-Pr-IS can be used as an efficient fluorescence probe for Hg2+ ions. Graphical Abstract A novel organic-inorganic hybrid material was designed and synthesized by functionalization of SBA-15 mesoporous silica material with isatin. The evaluation of the sensing ability of SBA-Pr-IS using fluorescence spectroscopy revealed that the SBA-Pr-IS was a selective fluorescent probe for Hg2+ ion in water in the presence of a wide range of metal cations.

Freezing-point Depression of Benzene Confined in Mesoporous Silica SBA-15 on Doping with a Slight Amount of Toluene: Ideal Behavior in a Nanometer-sized Space

We introduced benzene–toluene solution into the pores of the mesoporous silica material SBA-15 and investigated its fusion behavior using differential scanning calorimetry. On introduction into the...

A novel functionalized nanoporous SBA-15 as a selective fluorescent sensor for the detection of multianalytes (Fe3+ and Cr2O72−) in water

A novel silica-based chemosensor (SBA-Is-INH) was prepared through the functionalization of mesoporous silica SBA-15 material with a fluorescent chromophore, (Z)-N'-(2-oxoindolin-3-ylidene)isonicotinohydrazide. The synthesized materials were characterized by different techniques such as low angle XRD, N2 adsorption-desorption, TGA, TEM and FT-IR spectroscopy. The data showed that the organic moiety (0.41mmolg−1) was successfully grafted to the SBA-15 and the primary hexagonally ordered mesoporous structure of SBA-15 was preserved after the grafting procedure. Photoluminescence spectroscopy has been used to investigate the sensing behavior of this material. SBA-Is-INH showed high selectivity for Fe3+ and Cr2O72− in water over a wide range of tested ions. Upon introducing trace amounts of Fe3+ and Cr2O72− ions into aqueous solution, remarkable quenching in the fluorescence was observed. Furthermore, a good linearity was observed between the fluorescence intensity of SBA-Is-INH and the concentration of Fe3+ and Cr2O72− with satisfactory detection limits of 6.04×10−7M and 5.09×10−7M, respectively. Finally, the proposed method was successfully utilized for the determination of Fe3+ and Cr2O72− in river water, well water and tap water samples.

Fixed-bed column dynamic studies and breakthrough curve analysis of Eu(III) ion adsorption onto chemically modified SBA-15 silica materials

ABSTRACTA continuous fixed bed study was carried out by using two SBA-15 mesoporous silica materials decorated with Schiff base ligands for the removal of Eu(III) from aqueous solutions. The impact of flow rates of the sample and eluent, column bed height, sample, and eluent volumes was investigated. The analysis of the breakthrough investigations showed the exhaustion time, exhaustion volume, and metal uptake capacities accrued with a decrease in the flow rate and with an increase in the bed height. Thomas and Yan models were fitted to the experimental data to work out the characteristic parameters of the column for process design.

Surface-functionalization of mesoporous SBA-15 silica materials for controlled release of methylprednisolone sodium hemisuccinate: Influence of functionality type and strategies of incorporation

Mesoporous SBA-15 silica materials functionalized with several organic moieties, that include different polarities and hydrophobicities, were investigated as matrices for controlled drug delivery. The functionalities were incorporated into SBA-15 using two methods: direct synthesis or co-condensation route and post-synthesis grafting. Methylprednisolone sodium hemisuccinate, a synthetic pharmaceutical compound used as anti-inflammatory and immunosuppressant, was loaded onto the pristine and functionalized mesoporous SBA-15 silica materials. The influence of the type of organic moieties as well as their incorporation method onto the inorganic silica framework has been evaluated. The results show that SBA-15 functionalized with aminopropyl trimethoxysilane groups has the largest capacity of drug adsorption, clearly higher than the provided by materials functionalized with other groups, independently of the synthesis route. Additionally, materials synthesized by the co-condensation approach show a lower degree of drug retention than the same material synthesized by grafting technique. This fact is attributed to the distinct localization of the functionality, more accessible in the case of the grafting procedure, and hence suggesting that stronger interactions among the SBA-15 functionalized surfaces and the model drug are established. To ascertain whether other organosilanes containing amino groups can provide more effective loading and controlled drug delivery, at neutral and acidic conditions (pH of 7.4 and 4.6, respectively), it was also investigated the incorporation by grafting of several amino organic moieties onto the SBA-15 silica materials. It was concluded that as the number of amino groups incorporated into SBA-15 material increased, not only the drug loading capacity was higher, but the functionalized silica material vehicles slowed down the drug delivery. Finally, it was confirmed that cell viability was largely unaffected by amino-functionalized mesoporous SBA-15 silica materials after 72 h of incubation time.

FDU-12 Mesoporous Materials Detection Hg (II) Ions by QCM

Thiol-functionalized three-dimensional (3D) mesoporous silica FDU-12 and SBA-15 with ordered pore were prepared. All the obtained materials were characterized by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Mesoporous silica FDU-12 (Fm3m) materials with various unit cell sizes, multifaceted pore were convenient for the interaction of subject and object; the 2D SBA-15 mesoporous silica materials with short and order pore channel were better than the traditional SBA-15 mesoporous silica, in which the pore channel can be used fully. 3D mesoporous silica FDU-12 is used as a sensing material to reconstruct QCM sensors to enhance the stability and this material is an ideal material to deal with heavy metal ions in water.

Correlating Surface-Functionalization of Mesoporous Silica with Adsorption and Release of Pharmaceutical Guest Species

We present here a detailed molecular-level understanding of the interactions among surface-functionalized mesoporous SBA-15 silica and pharmaceutical guests that influence macroscopic adsorption and release behaviors. A model drug species, methylprednisolone sodium succinate, was adsorbed on the surfaces of functionalized mesoporous SBA-15 silica materials with different aminoalkyl species and without or with C60 fullerene moieties. Zeta potential measurements show that the electrostatic interactions among methylprednisolone species and modified silica surfaces are important for the adsorption and release of the methylprednisolone molecules. Complementary one and two-dimensional (2D) solid-state 13C{1H} NMR measurements provide evidence for specific intermolecular interactions between adsorbed methylprednisolone species and different types of functionalized silica surfaces. In particular, correlated 13C and 1H signal intensities from the methylprednisolone alkyl moieties and the aminoalkyl groups of the f...

AC Humidity Sensing Properties of Mesoporous K2CO3-SiO2Composite Materials

The mesoporous silica SBA-15 and mesoporous K2CO3-SiO2composite material were synthesized. Characterization of microstructure and morphology of materials indicated that the composite material had saved the porous framework of mesoporous silica SBA-15. Humidity sensing properties of different inverse proportion K2CO3-SiO2composite material were studied and we found that the sample with 0.16 g/g K2CO3exhibited excellent linearity in the wide humidity range. The complex impedance changed five orders of magnitude from 11% RH to 95% RH. The rapid response and recovery time were 10 s and 38 s, respectively. Finally a feasible ion transfer mechanism was brought forward to explain the sensing mechanism.

Magnetic nanocomposites based on mesoporous silica for biomedical applications

In the present work we report the synthesis procedure of magnetic mesoporous SBA-15 silica materials with controlled morphology as potential composites for biomedical applications, mainly as scaffolds for bone tissue engineering. Different procedures and synthetic parameters are varied to control the physico-chemical, textural and magnetic properties of these materials. Our results show that magnetic mesoporous silica presents two-dimensional hexagonal symmetry with the presence of mesoporous cylindrical geometries, open at both ends, with magnetite nanoparticles in the channels as shown by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) micrographs. Determined by the Brunauer-Emmett-Teller (BET) method, these materials show a surface area above 150 m2/g, which assures a loading capacity higher than conventional ceramics. The presence of crystalline magnetite is corroborated by X-ray diffraction (XRD). The magnetisation cycles show no hysteresis or coercive forces, evidencing their superparamagnetic (SPM) behaviour, which is highly desirable for biomedical applications to avoid magnetic agglomeration of particles.

Adsorption characteristics of Eu(III) and Th(IV) ions onto modified mesoporous silica SBA-15 materials

SBA-15 mesoporous silicas functionalized with N-propyl salicylaldimine(SBA/SA) and ethylenediaminepropylesalicylaldimine (SBA/EnSA) were prepared, characterized and employed as efficient adsorbents for solid phase extraction (adsorption) of europium(III) and thorium(IV) ions from water solutions. The effect of pH, adsorbent dosage, contact time, initial concentration, solution volume and competitive ions were investigated and discussed. Extraction process of europium and thorium ions by both of the adsorbents was shown to be pH dependent, whereas it was independent on ionic strength of the aqueous. This study revealed high performance of SBA/EnSA and SBA/SA with relatively rapid kinetics in the removal and preconcentration of europium and thorium ions from aqueous solutions. Although SBA/EnSA showed higher affinity towards the studied ions with respect to SBA/SA, both of the adsorbents showed more selective characteristics towards thorium ions. The isotherms and kinetics of the processes were well described by Langmuir and pseudo second order models, respectively. The evaluated thermodynamic parameters showed the extraction process of both of the studied metal ions by SBA/EnSA and SBA/SA was spontaneous and was controlled by positive entropy changes. The adsorbents were used for decontamination of real water samples from europium and thorium ions.

Catalytic oxidation of toluene over Au–Co supported on SBA-15

Au–Co supported on mesoporous silica materials SBA-15 was prepared with about 15wt.% cobalt then deposition-precipitation with 2wt.% Au. The results showed that while SBA-15 provided the long ordered arrangement of the channels for support, mixtures of cobalt oxides and gold nanoparticles are dispersed in the mesoporous channels. The sample exhibited excellent catalytic activity for toluene combustion, a complete decomposition (about 100%) of toluene had been achieved at the reaction temperature over 573K and space velocity 30,000h−1. The kinetics showed that the activation energy of the sample was 96.06kJ/mol (22.96kcal/mol) and frequency factor was 1.05×1010s−1, respectively. All these results indicate that while mesoporous materials give a high surface area support for metals, cobalt offers active supports for gold particles, which might be a combined way to overcome the shortcomings of low specific area for reducible transition metal oxides and low activity for inert oxides.