SBA-15 Powder Research Articles

Novel techniques for drug loading quantification in mesoporous SBA-15 using chemometric-assisted UV and FT-IR data

Albendazole is a crystalline drug that is poorly soluble in water, thus the dissolution rate in gastrointestinal fluids is limited. Mesoporous materials loaded with poorly water-soluble drugs become an interesting strategy to increase their solubility/dissolution rate as the drug state changes from crystalline to amorphous. In order to determine the drug loading content into mesoporous materials analytical methods such as elemental analysis, UV and HPLC are commonly used. However, elemental analysis and HPLC are destructive and relatively expensive. In addition, UV is time consuming. Moreover, UV and HPLC require the drug release from the mesoporous material before the quantification step. Therefore, the aim of this work was to develop quantifications techniques based on chemometric models combined with UV and FT-IR spectra without needing the drug release from the mesoporous material. Partial least squares regression (PLSR) was used as chemometric regression method. Albendazole content in the SBA-15 powders was first quantified by elemental analysis as reference measurement for multivariate calibration. The excellent drug loading predictions prove that robust calibration models can be obtained from both techniques (i.e., 0.999 and 0.998 adjusted correlation coefficient for UV and FT-IR, respectively). Additionally, the adjusted correlation coefficients determined from the validation models for UV and FT-IR are 0.963 and 0.930, respectively. It is important to highlight that the prediction adjustment of the FT-IR model (root-mean-square error of prediction=2.196%) presented lower error than the UV model (root-mean-square error of prediction=3.553%). Therefore, this development contributes to improve the overall time and cost of drug loading determination into mesoporous materials.

Tunable random lasing in dye-doped mesoporous silica SBA-15

Mesoporous silica, known as SBA-15, possesses a hexagonal pore structure, with 8-nm-diameter pores and high surface area $(\ensuremath{\sim}700\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{2}/\mathrm{g})$. The mesoporosity of SBA-15 is excellent to be filled with luminescent chromophores aiming at optical and photonic applications. SBA-15 powder infiltrated with Rhodamine B (RB) was prepared with different RB loads. Using the second harmonic of a pulsed Nd:yttrium aluminum garnet (YAG) laser (8 ns, 10 Hz) as the excitation source, the light emission spectra of the samples were investigated. Typical incoherent feedback random laser behavior was observed. Tunable random laser emissions from 579 to 585 nm were obtained depending on the excitation laser spot diameter and the RB load. The results indicate that mesoporous SBA-15 infiltrated with RB is a promising material for the development of solid-state random lasers.

Impact of bentonite content on the structural, textural and mechanical properties of SBA-15 mesoporous silica beads

This work aims to evaluate the impact of bentonite content on the structural, textural and mechanical properties of SBA-15 beads prepared by shearing using an Eirich mixer. X-Ray Diffraction analysis (XRD) of conventional and sheared SBA-15 powders and bentonite–containing beads confirms the attainment of hexagonal structure. According to the nitrogen adsorption–desorption isotherms, the bentonite content has a significant impact on mesoporous volume. SBA-15 beads containing 9.1 wt% of bentonite (B-SBA-Be9), 16.7 wt% of bentonite (B-SBA-Be17) and 33.3 wt% of bentonite (B-SBA-Be33) showed an increase in mesoporous volume of 15, 25 and 20%, respectively. Indeed, the presence of the basic bentonite-water solution during the preparation stage of the beads generates a chemical attack of the SBA-15 walls that leads to the increase in the mesopores size. Beads containing 16.7 wt% of bentonite present more promising result in relation to their good balance between textural properties and mechanical strength. Thus, this sample could be used for a future application as a catalyst support for desulfurization process. Therefore, these results confirm that porosity and mechanical resistance are strongly dependent on the bentonite content and beads preparation process, in comparison to literature data.

Mesoporous silica pellets – A promising oral drug delivery system?

In this study we investigated the application potential of ordered mesoporous silica SBA-15 powders as an excipient in development of prolonged release pellets for doxycycline.The doxycycline adsorption onto the SBA-15 powders was performed using adsorption from a concentrated solution. The pellets were obtained via wet granulation, extrusion and spheronization method. The pellets were composed of drug-loaded SBA-15, microcrystalline cellulose (Avicel PH 101), ethylcellulose (22 cP) and magnesium stearate. The 5 wt% polyvinylpyrrolidone (PVP K30) ethanolic solution (96% v/v) was used as a binder. The yield, drug content, size analysis, hardness, friability, disintegration time and pharmaceutical availability tests were carried out. The classic doxycycline pellets based on microcrystalline cellulose were prepared and investigated in the same manner for comparative purposes.The SBA-15 powders were characterized by efficient adsorption of doxycycline (103.5 ± 3.1 mg/g equal to 9.4% drug loading). The SBA-15 pellets were successfully obtained in laboratory scale. The prolonged 12 h drug release in phosphate buffer solution (pH = 6.8) was observed for SBA-15 pellets which was 2 times longer compared to drug release profile of microcrystalline cellulose-based pellets. The obtained mesoporous silica pellets may represent a novel solution in the development of prolonged release formulations for water soluble drugs.

Low-temperature sintering of bismuth-doped glass with high fluorescence properties from mesoporous silica SBA-15

A kind of bismuth-doped silica glasses have been produced successfully by spark plasma sintering at 1070 °C using bismuth-doped SBA-15 powders. The samples were detected by X-ray diffraction, UV–vis–NIR, photoluminescence, fluorescent decay curve and X-ray photoelectron spectroscopy. The results showed that the samples possess favorable near-infrared fluorescence and the 0.9 mol% sample is the best one among these glasses. The emission peaks at ~1180, ~1150 and ~1250 nm can be observed when excited by 500, 700 and 800 nm. The average lifetimes of 0.9 mol% under 500, 700 and 800 nm excitation are 189.87, 311.46 and 132.16 μs. Furthermore, the value of the important optical parameter σemτ is 5.79 × 10−24 cm2s at 800 nm excitations, which is 36.8% and 9.2% larger than bismuth-doped germanate glasses and phosphate glasses that have been reported. These emission peaks could be decomposed into three bands at ~1150, ~1240 and ~1440 nm via Gaussian decomposition. Based on the results of this work, it is concluded that the NIR emission peaks at ~1150, ~1240 and ~1440 nm correspond to Bi0, Bi+ and (Bi2)2-, respectively. This glass with excellent luminescence properties could offer a practical material to improve the performance of broadband fiber amplifiers and tunable lasers.

Templated Growth of Pd Nanoparticles Using Sputtering Deposition Process and Its Catalytic Activities.

A simple method based on sputtering deposition of Pd onto mesoporous SiO2 (SBA-15) was employed to produce supported Pd nanoparticles (NPs) that can be used as hydrogenation catalysts. The use of sputtering deposition eliminates contaminants and avoids additional drawbacks of traditional chemical methods applied to prepare heterogeneous supported metal catalysts. A mechanical resonant stirrer was used to revolve the SBA-15 powder and ensure homogeneous distribution of the Pd NPs over the support. The SBA-15 pores act as templates for Pd NPs and drive nanostructure growth. Consequently, the NPs obtained have the same diameter as that of the SBA-15 channels (~5 nm) and elongated particles are formed as sputtering deposition increases. The SBA-15 supported Pd NPs (Pd NPs/SBA-15) were tested in a probe hydrogenation of cyclohexene reaction to evaluate the catalytic activity of the Pd NPs. Turnover frequency (TOF) of 2000 min-1 were achieved with the lower Pd NPs concentration (0.15 wt%) catalyst.

Solvent-free direct formulation of poorly-soluble drugs to amorphous solid dispersion via melt-absorption

To improve the dissolution properties of poorly water soluble active pharmaceutical ingredients (APIs), a solvent-free melt-absorption process was applied to directly load the APIs into mesoporous SBA-15 silica powder as an amorphous solid dispersion. Two model compounds, poorly aqueous soluble ibuprofen (IBU) and fenofibrate (FEN), were individually mixed with SBA-15 powder and heated above their respective melting points. Upon cooling, the physicochemical and solid-state properties of the solid dispersions were investigated by N2 adsorption, DSC, XRD, SEM and solid-state NMR. The molten API was found to be absorbed into the pores, confined within the nano-channels of SBA-15, and re-solidified to an amorphous solid dispersion. Due to the amorphous properties, the APIs showed a significant enhancement in dissolution rate as compared with the untreated crystalline APIs. Although the amorphous forms were not at thermodynamic equilibrium, the APIs exhibited excellent solid-state physical stability even under accelerated stress conditions. In comparison with APIs loaded using a co-spray drying process (previous work), the melt-absorption process required no organic solvent, produced powders with a coarser size distribution and more desirable flow properties. This solvent-free direct melt-absorption process can be used to formulate a wide range of poorly soluble drugs to be amorphous solid dispersions.

Immobilization of D-Amino Acid Oxidase (DAAO) Enzyme on Hybrid Mesoporous MCF, SBA-15 and MCM-41 Nanomaterial.

Hybrid mesoporous materials as carriers for immobilization of D-amino acid oxidase (DAAO) were prepared via three steps: (i) hydrothermal synthesis of nanoporous MCF, SBA-15 and MCM-41 powders, (ii) functionalization with 3-aminopropyltriethoxysilane (APTES) by post-synthesis grafting; and (iii) activation with glutardialdehyde. The resulting mesostructured solids were characterized by various techniques: XRD, IR, TGA-DTA and N2 adsorption–desorption (BET). The characterization results indicated that these materials still maintained their structure after functionalization. IR data and TGA-DTA analysis demonstrated the existence of amine functional groups on the surface of APTES-functionalized samples. The DAAO immobilized on these materials exhibited higher catalytic activity and stability of enzyme for conversion of cephalosporin C (CPC) as compared to those of the non-functionalized ones. The catalytic activity and stability of enzyme decreased in the order MCF > SBA-15 > MCM-41.

Highly Ordered Mesoporous Si/C Nanocomposite as High Performance Anode Material for Li-ion Batteries

Highly ordered mesoporous Si/C (OMP-Si/C) anode composite for lithium ion battery is fabricated by a moderate magnesiothermic reduction and carbon coating using SBA-15 as a precursor. The synthesized OMP-Si/C composite rods preserve the original nanostructure of ordered honeycomb pore channels in SBA-15 and link one by one to form lotus-root-like chains which tightly agglutinate into bundles with a high packing density. A liquid ambient reaction model is also proposed to describe the reaction mechanism between SBA-15 and magnesium powder and the formation of this unusual highly ordered mesoporous structure at temperature of 660°C. The samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption, and Raman spectroscopy. The highly ordered mesoporous structure provides buffering space to accommodate the large volume expansion/contraction and consequent stress induced inside silicon during Li+ insertion/extraction. Furthermore, this mesoporous structure can also provide transportation routes for electrolyte and shorten the diffusion paths for lithium ions. The carbon coating on mesoporous silicon can provide electronically conductive networks for the electrode. These effectively mitigate silicon pulverization issue and help achieve higher reversible capacity and better capacity retention. The excellent electrochemical performance of this highly ordered mesoporous Si/C shows its promising applications in anode materials for Li-ion batteries.

Ni/SBA-15 Catalysts for combined steam methane reforming and water gas shift—Prepared for use in catalytic membrane reactors

This study focuses on the preparation, characterization and catalytic performance evaluation of Ni/SBA-15 catalysts for the combined steam methane reforming (SMR) and water gas shift (WGS) reaction. Specific efforts have been directed towards the impact of the SBA-15 preparation methods on further incorporating the resultant catalysts into the micro-structured ceramic hollow fibres for the development of more advanced membrane reactors. The effect of Ni loading (5–25wt.%) on the catalytic performance was investigated using the SBA-15 prepared via a sol–gel method. Furthermore, the effect of SBA-15 preparation methods (sol–gel and hydrothermal methods) on the catalyst properties and performance were also systematically investigated in a packed-bed reactor, using a fixed Ni loading of 25wt.%. For the purpose of comparison, a commercially available SBA-15 powder was also employed. Apart from the different distribution and particle size of Ni, the interaction between Ni and SBA-15 is considered as the major reason for the difference in catalytic performance.

Simple thiol-ene click chemistry modification of SBA-15 silica pores with carboxylic acids

A straightforward approach for anchoring tailored carboxylic groups in mesoporous SiO2 colloidal materials is presented. The thiol-ene photochemical reaction between vinyltrimethoxysilane precursors and various thiocarboxylic acids which has, click chemistry features (i.e. high conversion yields, insensitivity to oxygen, mild reaction conditions), results in carboxylated silane precursors that can be readily used as surface modifiers. The carboxylic groups of acetic, undecanoic and succinic acid were immobilized on the silica mesopore walls of SBA-15 powders employing the synthesized silane precursors. Post-grafting has been confirmed through infrared spectrometry (FTIR), energy dispersive X-ray spectroscopy (EDS), elemental analysis (EA) and zeta potential measurements. Detailed field-emission gun scanning electron microscopy (FESEM) images and small angle X-ray scattering (SAXS) data revealed parallel mesopores and ordered mesostructures. It is shown that the immobilized COOH groups are chemically accessible for acid–base reactions as well as copper adsorption. Immobilization of easily synthesized tailored carboxylic modified alkoxide precursors within mesoporous systems provides a unique chemical nanoenvironment within these ordered frameworks.

Sinterability Enhancement by Collapse of Mesoporous Structure of SBA‐15 in Fabrication of Highly Transparent Silica Glass

Highly transparent silica glass was prepared from mesoporous silica SBA‐15 powders at low temperature using Spark Plasma Sintering. It was found that the combined effect of pressure and temperature resulted in collapse of porous structure of SBA‐15 and transformation to transparent glass. A sinterability enhancement mechanism involving generation of incremental surface area from pore collapse during sintering process was proposed to interpret the fully densification at low temperature.

In vitro controlled release of antihypertensive drugs intercalated into unmodified SBA-15 and MgO modified SBA-15 matrices

The use of nanotechnology in medicine and more specifically in drug delivery systems is set to spread rapidly. In order to broaden the range of matrices and implicitly to develop the class of drug delivery systems based on diffusion mechanism, in this study the starting materials, SBA-15 powder matrices, were engineered by MgO modification for antihypertensive drugs intercalation. Captopril and aliskiren were used as drug models. All powders, unmodified and MgO-modified silica matrices, and their corresponding drug-loaded samples were characterized by X-ray diffraction, N(2) adsorption and desorption, FTIR spectroscopy and scanning electron microscopy. The studied drug carriers were tested in the controlled drug release process and the influence of the silica pore morphology and geometry on drug release profiles was extensively studied. In order to analyze the data obtained from the in vitro release studies and to evaluate the kinetic release mechanism, the Korsmeyer and Peppas equation was used. The obtained drug delivery system based on MgO-SBA-15 matrix exhibits exciting structural features and is therefore promising for its use as antihypertensive drug delivery system, having potential therapeutic benefits resulting in safe and effective management of captopril and aliskiren adsorption and in vitro release.

Increasing the oral bioavailability of poorly water-soluble carbamazepine using immediate-release pellets supported on SBA-15 mesoporous silica

Background and methods:The aim of this study was to develop an immediate-release pellet formulation with improved drug dissolution and adsorption. Carbamazepine, a poorly water-soluble drug, was adsorbed into mesoporous silica (SBA-15-CBZ) via a wetness impregnation method and then processed by extrusion/spheronization into pellets. Physicochemical characterization of the preparation was carried out by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption, small-angle and wide-angle x-ray diffraction, and differential scanning calorimetry. Flowability and wettability of the drug-loaded silica powder were evaluated by bulk and tapped density and by the angle of repose and contact angle, respectively. The drug-loaded silica powder was formulated into pellets to improve flowability.Results:With maximum drug loading in SBA-15 matrices determined to be 20% wt, in vitro release studies demonstrated that the carbamazepine dissolution rate was notably improved from both the SBA-15 powder and the corresponding pellets as compared with the bulk drug. Correspondingly, the oral bioavailability of SBA-15-CBZ pellets was increased considerably by 1.57-fold in dogs (P < 0.05) compared with fast-release commercial carbamazepine tablets.Conclusion:Immediate-release carbamazepine pellets prepared from drug-loaded silica provide a feasible approach for development of a rapidly acting oral formulation for this poorly water-soluble drug and with better absorption.

Effects of preparation methods on the property of PMMA/SBA-15 mesoporous silica composites

In the paper, poly(methyl methacrylate)(PMMA)/SBA-15 composite materials were prepared by four different methods, that is, in-situ batch emulsion polymerization in the presence of mesoporous SBA-15, PMMA emulsion mixed with SBA-15 powder or dispersion in water, PMMA powder mixed with SBA-15 powder, and the properties of the composite materials were determined and compared. The composites were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanics analysis (DMA) and scanning electron microscope (SEM). The results showed that the glass transition temperatures (Tg), the storage modulus and tensile strength of the PMMA/SBA-15 composites were all improved obviously, while the thermal decomposition temperature did not influenced apparently. The composite made by in-situ batch polymerization exhibited the most improvement in the mechanical properties and Tg while the composite prepared by mixing PMMA emulsion and SBA-15 dispersion gave rise to the least improvement in the mechanical properties and Tg. These results were contributed to introducing different amount of voids into polymer matrix which were demonstrated by dielectric constant measurement and SEM morphology observation.

Titania-Phosphotungstic Acid Nanocomposites Dispersed Homogeneously in Mesopores as the Recyclable Photocatalyst

Heterogeneous photocatalytic materials, titania–phosphotungstic acid nanocomposites in the mesopores of SBA-15 (TiO2-H4PW12O40/SBA15) were prepared by sol–gel method. Compositions and structures of the nanocomposites were characterized by X-ray diffraction (XRD), UV-visible absorption spectroscopy and transmission electron microscopy (TEM). Uniform mesoporous SBA15 consisting of long-range channels provides the immobilization of titania-phosphotungstic acid nanocomposites. The photocatalytic activity of the prepared TiO2-H4PW12O40/SBA15 powders was evaluated from an analysis of the photocatalytic degradation of methyl orange. The results indicated that photocatalytic activity increased with the amount of H4PW12O40 from 0% to 10% and decreased when the amount of H4PW12O40 was above 10%. It is due to the synergetic reaction of H4PW12O40 and TiO2. However, much more H4PW12O40 can occupy the active center of TiO2. TiO2 can inhibit the decomposition of H4PW12O40 in the TiO2-H4PW12O40/SBA15 composites. On the other hand, H4PW12O40 repressed the TiO2 particle growth during calcination process. The composite catalyst also had the advantage of easily being recovered and reused.

Synthesis and properties of dense bulks for mesoporous silica SBA-15 by a modified hydrothermal method

Dense SBA-15 bulks with mesoporous structure as well as powdered SBA-15 were successfully synthesized by the modified hydrothermal method. These SBA-15 bulks have the higher density of 1.16 to 1.19 g/cm 3, compared to green density of 0.68 g/cm 3 for the pellet from SBA-15 powder. Obtained SBA-15 bulks possessed extremely high BET surface area of 467 m 2/g and mesopore of 4.0 nm in diameter The possibility of densification for SBA-15 bulks using this method was confirmed.

Direct observation of surface structure of mesoporous silica with low acceleration voltage FE-SEM

Recent progress of SEM technology enabled us to observe the ordered structure of mesoporous materials. Direct SEM observation of mesoporous materials can provide detail information on the external and internal structures, though it often faces charging problems of insulating frameworks and the structural collapse due to the electron beam irradiation. Low voltage SEM observation has become common both for top-surface imaging and reducing beam damage. In this work, high-resolution, direct SEM imaging of mesoporous silica powders and films was carried out under the condition of low voltages to characterize the surface structure that cannot be evaluated by TEM, XRD and N 2 adsorption/desorption measurements. We synthesized SBA-15 powders using different aging temperatures, and observed the differences in surface structure. We also observed the surface structure of dip-coated SBA-16 films prepared with different template concentrations. The SBA-15 powder, which was aged at a lower temperature, was extremely beam sensitive, and the SBA-16 films prepared on glass substrates were heavily charging. For the SEM observation, we used beam deceleration and an improved scanning method to reduce the charging phenomenon and beam damage. We achieved this using a Hitachi S-4800 or an SU8000 FE-SEM, which both employ a snorkel type objective lens, a beam deceleration function and newly designed beam scan settings that combine slow and fast scanning techniques.

Physical State of Poorly Water Soluble Therapeutic Molecules Loaded into SBA-15 Ordered Mesoporous Silica Carriers: A Case Study with Itraconazole and Ibuprofen

The ordered mesoporous silica material SBA-15 was loaded with the model drugs itraconazole and ibuprofen using three different procedures: (i) adsorption from solution, (ii) incipient wetness impregnation, and (iii) heating of a mixture of drug and SBA-15 powder. The location of the drug molecules in the SBA-15 particles and molecular interactions were investigated using nitrogen adsorption, TGA, DSC, DRS UV-vis, and XPS. The in vitro release of hydrophobic model drugs was evaluated in an aqueous environment simulating gastric fluid. The effectiveness of the loading method was found to be strongly compound dependent. Incipient wetness impregnation using a concentrated itraconazole solution in dichloromethane followed by solvent evaporation was most efficient for dispersing itraconazole in SBA-15. The itraconazole molecules were located on the mesopore walls and inside micropores of the mesopore walls. When SBA-15 was loaded by slurrying it in a diluted itraconazole solution from which the solvent was evaporated, the itraconazole molecules ended up in the mesopores that they plugged locally. At a loading of 30 wt %, itraconazole exhibited intermolecular interactions inside the mesopores revealed by UV spectroscopy and endothermic events traced with DSC. The physical mixing of itraconazole and SBA-15 powder followed by heating above the itraconazole melting temperature resulted in formulations in which glassy itraconazole particles were deposited externally on the SBA-15 particles. Loading with ibuprofen was successful with each of the three loading procedures. Ibuprofen preferably is positioned inside the micropores. In vitro release experiments showed fast release kinetics provided the drug molecules were evenly deposited over the mesoporous surface.

Formation of Indium Nitride Nanorods within Mesoporous Silica SBA-15

We report the first formation of arrays of InN nanorods inside the nanoscale channels of mesoporous silica SBA-15. In(NO3)3 dissolved in methanol was incorporated into SBA-15 powder without prior pore surface functionalization. Formation of InN nanorod arrays was carried out by ammonolysis at 700 degrees C for 8 h. The final products have been characterized by FT-IR spectra, (29)Si MAS NMR spectra, Raman spectra, XRD patterns, TEM images, nitrogen adsorption-desorption isotherm measurements, and optical spectroscopy. The freestanding InN nanorods observed after silica framework removal with HF solution show diameters of 6-7.5 nm and lengths of 25-50 nm. Formation of a trace amount of In2O3 was also verified. The InN nanorods exhibit a broad band centered at around 550-600 nm, and a band gap energy of 1.5 eV was determined. No light absorption in the near-IR region was measured. The nanorods give a weak emission band centered at around 600 nm. These optical properties are believed to be related to the possible incorporation of oxygen during InN nanorod synthesis.