Mesoporous Silica Structure Research Articles

Thermoresponsive Coatings on Hollow Particles with Mesoporous Shells Serve as Stimuli-Responsive Gates to Species Encapsulation and Release.

Nanoscale capsule-type particles with stimuli-respondent transport of chemical species into and out of the capsule are of significant technological interest. We describe the facile synthesis, properties, and applications of a temperature-responsive silica-poly( N-isopropylacrylamide) (PNIPAM) composite consisting of hollow silica particles with ordered mesoporous shells and a complete PNIPAM coating layer. These composites start with highly monodisperse, hollow mesoporous silica particles fabricated with precision using a template-driven approach. The particles possess a high specific surface area (1771 m2/g) and large interior voids that are accessible to the exterior environment through pore channels of the silica shell. An exterior PNIPAM coating provides thermoresponsiveness to the composite, acting as a gate to regulate the uptake and release of functional molecules. Uptake and release of a model compound (rhodamine B) occurs at temperatures below the lower critical solution temperature (LCST) of 32 °C, while the dehydrated hydrophobic polymer layer collapses over the particle at temperatures above the LCST, leading to a shutoff of uptake and release. These transitions are also manifest at an oil-water interface, where the polymer-coated hollow particles stabilize oil-in-water emulsions at temperatures below the LCST and destabilize the emulsions at temperatures above the LCST. Cryogenic scanning electron microscopy indicates patchlike particle structures at the oil-water interface of the stabilized emulsions. The silica-PNIPAM composite therefore couples advantages from both the hollow mesoporous silica structure and the thermoresponsive polymer.

Highly productive xylose dehydration using a sulfonic acid functionalized KIT-6 catalyst

A highly efficient and selective dehydration of xylose to furfural was achieved using a sulfonic acid-functionalized, mesoporous silica KIT-6 type catalyst in a water/toluene biphasic system. The catalyst was prepared by co-condensation between tetraethoxysilane and 3-mercaptopropyl(methyl)dimethoxysilane, in the presence of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic, P123, Mw = 5800). The catalytic performance was then investigated with respect to the molar ratio of tetraethoxysilane and 3-mercaptopropyl(methyl)dimethoxysilane, as well as the reaction temperature and reaction time. The optimal catalyst was prepared using tetraethoxysilane and 3-mercaptopropyl(methyl)dimethoxysilane in a molar ratio of 0.8:0.2, giving both high xylose conversion and furfural selectivity (greater than 94%) at 170 °C for 2 h. In addition, the catalyst had a high turnover frequency and could be reused without treatment for up to three cycles. The high turnover frequency in the xylose dehydration reaction was attributed to the three-dimensional structure of the KIT-6 mesoporous silica that facilitates the diffusion of both the reactant and products in the xylose dehydration reaction.

Ultrasensitive immunoassay of tumor protein CA 15.3 in MCF-7 breast cancer cell lysates and unprocessed human plasma using gold nanoparticles doped on the structure of mesoporous silica

Breast cancer is the most common threat in women worldwide. Increasing death rate of diagnosed cases is the main leading cause of designing specific immunoassay for tumor marker in breast cancer. Cancer antigen 15-3 (CA 15-3) is a tumor protein for many types of cancer, most notably breast cancer. Herein, we report a sandwich-type electrochemical immunosensor based on signal amplification strategy of multiple nanocomposites to detection of CA 15-3 biomarker. The proposed immunosensor fabricated by reduced graphene oxide (rGO), poly-dopamine (PDA) and amino functionalized mesoporous silica (MCM-41-NH2) doped by gold nanoparticles composite on the glassy carbon electrode with a large surface area which was prepared a new platform to immobilization of primary antibodies and provide excellent conductivity. To further amplify the electrochemical signal, the trace tag on the foundation of gold nanoparticles (AuNPs) is coated with MCM-41-NH2 nanocomposite through thionine linking, which provides more amino groups to capture more horseradish peroxidase-labeled antibodies (HPR-Ab2) and enhances the conductivity. Under optimal conditions, the developed immunosensor exhibits excellent analytical performance for the determination of CA 15-3 with a wide linear range from 0.002 to 125 U/mL and a low limit of quantification of 0.002 U/mL. Furthermore, satisfactory results are obtained for the determination of CA 15-3 in human plasma samples, indicating the potential of the immunoassay to be applied in clinical analysis.

Tailored synthesis of polymer-brush-grafted mesoporous silicas with N-halamine and quaternary ammonium groups for antimicrobial applications

Antimicrobial mesoporous materials with polymer brushes on the surface were prepared, and their structure and antimicrobial performance investigated. Poly ((3-acrylamidopropyl) trimethylammonium chloride) (PAPTMAC) modified mesoporous silica was prepared by a polymer-brush-grafted method through treatment with the initiator 4,4′-azobis (4-cyanovaleric acid) (ACVA) and polymerized with (3-acrylamidopropyl) trimethylammonium chloride (APTMAC). A covalent bond was formed between mesoporous silica and N-halamine precursor; N-H bonds were successfully transformed to N-Cl bonds after chlorination. Morphology and structure of mesoporous silica were affected to some extent after modification. The surface area of the polymerized sample decreased, but was sufficient for further applications. Compare to the original sample, antimicrobial properties of the polymerized samples with quaternary ammonium groups (QAS) increased slightly. After exposure to dilute household bleach, the chlorinated samples showed excellent antimicrobial properties against 100% of S. aureus (ATCC 6538) (7.63 log) and E. coli O157:H7 (ATCC 43895) (7.52 log) within 10 min. The prepared mesoporous silicas with effective antimicrobial properties could be very useful for potential application in water filtration.

Outside-in synthesis of mesoporous silica/molybdenum disulfide nanoparticles for antitumor application

Very different from traditional inside-out method, which used guest material as the inside core and then surface-coated outer layer, herein, we propose a facile and unique outside-in approach for the synthesis of high dispersive mesoporous silica nanoparticle (MSN)/MoS2-PEG nanoparticles (SMPs) based on the differences of precursor solubility in different solvents, for the first time. The prepared SMPs exhibit both higher drug loading efficiency of 64.7% owing to the pore structure of mesoporous silica, and excellent photothermal performance with photothermal efficiency of 41.5% due to the inside decorated MoS2 nanosheets, which could be used for the combination of tumor hyperthermia and chemotherapy. The in vivo results indicate that SMPs show great synergistic effect, i.e., the heat produced during PTT can increase the chemotherapy sensitivity of DOX and synergistically improve its therapeutic effect. Such a facile strategy provides a new facile way to construct a novel theranostic agent by integrating different functions into one dosage, and shows a promising approach for the construction of nanomaterials using MSN as a template.

The Analysis of Hierarchical Structure of Mesoporous Silica in Nanometer Scale by Small Angle Scattering Method

The analysis of hierarchical structure of mesoporous silica material with template of cetyltrimethylammonium bromide (CTAB) with co-surfactants of tetra-methylammonium hydroxide (TMAOH) and Triton X-100 was conducted by using the technique of s mall a ngle s cattering (SAS) using neutron (SANS) and X-ray (SAXS) . The analysis was supported by the data of n itrogen a bsorption and e lectron m icroscopy. The analysis showed that the concentration of CTAB affected the characteristics and pore structures of particles. The increase of co-surfactant concentration s tended to form particles that were more uniform in size and more regular in the shape of the sphere. The results of SAS analysis showed that the morphology, shape, and size of the large particles were arranged by smaller (primary or secondary) particles that had pores. The variation of surfactant template s had influenced the formation of pore structure. For CTAB-TMAOH, it would had resembled MCM-41 type which has a hexagonal structure, wh ereas for CTAB-Triton X -100, it would have resembled MCM-48 type which has a cubic structure. The particles that have a high surface area which resembled pore structure MCM-41 has been able to set up by using 0.25 M of CTAB with 0.040 M of TMAOH. Moreover , the particles which resembled pore structure MCM-48 were able to set up by using 0.03 M of Triton X-100 with 0.4 M of CTAB. The analysis of SANS data that was supported by electron microscopy results is entirely showing a complete information of the particles formed by each template. Whereas SAXS analysis that supported by nitrogen adsorption method is fully confirming the information of pore characteristics.

Humidity sensing behavior of tin-loaded 3-D cubic mesoporous silica

The present scientific investigation deals with template synthesis of 3D-cubic mesoporous KIT−6 with in-situ loading of SnO2 to obtain a material with enhanced number of surface active sites. The structural insights have been reported through analysis of XRD, TEM, FESEM, N2 sorption and mid-IR absorption data. X-ray diffraction confirmed 3D-cubic mesoporous structure of silica with Ia3¯d symmetry and existence of anatase SnO2 species. A decrease in surface area on loading of SnO2 nanoparticles is revealed via analysis of N2 adsorption-desorption isotherms. Rapid response time of 15 s and super rapid recovery time of 2 s (with response > 100) have been exhibited by sensor based on sample containing 1 wt% of SnO2. Further investigation on sensing performance of nanocomposite with 1 wt% of SnO2 confirmed its ohmic behavior (with negligible V-I hysteresis), excellent cycle stability, outstanding long term stability and very low hysteresis (1.4% at 53% RH).

IR spectroscopy study of SBA-15 silicas functionalized with the ethylthiocarbamidepropyl groups and their interactions with Ag(I) and Hg(II) ions

Mesoporous structure of silica is determined by the type of template, but the introduction of functional groups during the synthesis has additional influence. The structure of SBA-15 may be violated by the introduction of long functions, such as ≡Si(CH2)3NHC(=S)NHC2H5. These ethylthiocarbamidepropyl groups can form complexes with metal ions in thiol or thione tautomeric forms. We determined that the 2D hexagonal p6 mm structure is preserved for SBA-15 with thiourea groups at maximal TEOS:trifunctional silane ratio (mol) = 10:2, which was confirmed by TEM and by the presence of an intense reflex in the small-angle region of diffractograms of the final product. It was shown that the obtained sorbents possess high kinetic characteristics. The experimental data fit pseudo-second-order kinetic equation, but the rate constants depend on the content of functional groups in the surface layer. Template Pluronic P-123 defines the porosity of functional mesoporous silica materials even at increasing content of trifunctional silane in the initial solution. Infrared spectroscopy analysis showed that thione form of thiourea ligand is prevalent on the surface of pores of mesoporous samples. However, during the sorption of silver(I) ions, there are both thione and thiol forms on the surface. Thione form is transformed into thiol with increasing concentration of mercury(II) ions in the sorption solution. Adsorption experiments showed that the SBA-15 silicas functionalized with ethylthiocarbamidepropyl groups had high selectivity for silver(I) ions and could concentrate Ag(I) ions from metal ions mixture at pH ~ 2.

Improved CO2 Sorption in Freeze-Dried Amine Functionalized Mesoporous Silica Sorbent

This work investigates the structural and CO2 sorption properties of amine-functionalized mesoporous silica prepared by a freeze-drying method. It was found that the freeze-dried samples delivered significantly higher CO2 sorption capacities up to a factor of 18 times as compared to samples prepared by the conventional oven-drying evaporation method. The improved performance of the freeze-drying method was attributed to a higher surface area and access to active amine sites for CO2 sorption. The freeze-dried samples also exhibited good stability at a relatively high sorption temperature (90 °C) and flue gas CO2 partial pressure (15 kPa). The freeze-drying method reached the best CO2 sorption capacity of 4.71 mmol g–1 for samples with 70 wt % amine loading. Higher loading (80 and 90 wt %) led to excess amine not being incorporated into the mesoporous silica structure, thus covering active sites and limiting CO2 diffusion.

Pore structure of mesoporous silica (KIT-6) synthesized at different temperatures using positron as a nondestructive probe

Ordered mesoporous SiO2 (KIT-6) was synthesized using triblock copolymer P123 as the structure template and tetraethyl orthosilicate (TEOS, C8H20O4Si) as silica source. Small-angle X-ray scattering and high resolution electron microscope measurements indicate the 3d cubic Ia3d symmetry of the pore structure of KIT-6 synthesized at 30–120 °C. When the synthesis temperature increases to 180 °C, the order of pores was deteriorated. The pore size was estimated by nitrogen adsorption/desorption measurements, which increases from 3.8 nm to 18.5 nm as the synthesis temperature increases from 30 °C to 180 °C. With the increase of mesopore size, the pore wall thickness shows continuous decrease. Positron annihilation lifetime spectra was measured for the synthesized KIT-6. The lifetime spectra can be resolved to two short and two long lifetime components. The two long lifetimes τ3 and τ4 correspond to o-Ps lifetime in micropore and mesopores, respectively. The size of mesopores was estimated from the o-Ps lifetime by using Goworeck’s model for cylindrical pores, which shows continuous increase with synthesis temperature, and is consistent with the N2 adsorption/desorption measurements. The size of micropore has no change with increasing synthesis temperature. However due to the decrease in wall thickness, the number of micropores in the wall shows subsequent decrease. In addition, the second lifetime component τ2 is also found to be a sensitive parameter for the pore size, which shows the same trend as lifetime τ4 with increasing synthesis temperature.

Tailoring Pore Size, Structure, and Morphology of Hierarchical Mesoporous Silica Using Diblock and Pentablock Copolymer Templates

Mesoporous materials of tailored pore size, structure, and morphology are of interests for a wide range of applications. It is important to develop synthetic methods that will allow for easy proces...

Synthesis and structural characterization of ZnO-and CuO-NPs supported mesoporous silica materials (hexagonal SBA-15 and lamellar-SiO2)

Two different mesoporous silica structures (hexagonal and lamellar) were synthesized via sol-gel method using a series of triblock copolymer (Pluronic) surfactants. L81, L61 & L31 surfactants form lamellar structure whereas P123 surfactant forms a hexagonal structure. CuO and ZnO nanoparticles (NPs) supported mesoporous silica were synthesized using impregnation method. The structural properties of these materials were investigated using several characterization techniques such as FTIR, XRD, SAXS, TEM and TGA. SAXS and TEM confirmed that the obtained mesoporous silica is based on the EO/PO ratio of Pluronic surfactants. They proved that the mesoporosity of silica is well maintained even after they loaded with metal oxide nanoparticles.

Microwave-Assisted Controllable Synthesis of Nickel Nanoparticles Embedded in Mesoporous Silica for Catalytic Reduction of 4-Nitrophenol

Nickel nanoparticles embedded in mesoporous silica (Ni/SiO[Formula: see text] were successfully synthesized by microwave-assisted in situ self-assembly method using colloidal silica, urea and nickel nitrate as precursors and glucose as carbon template, which resulted in mesoporous structure of silica through removal of template. Ni nanoparticles were uniformly well-dispersed within mesoporous silica, which were 3.5–4.0[Formula: see text]nm in diameter and had a very narrow particle size distribution. In addition, particle size of Ni nanoparticles can be controllably adjusted by microwave power. As-prepared Ni/SiO2 catalyst exhibited better catalytic activity for reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) than Ni/SiO2-IM catalyst, which was mainly attributed to confinement effect of mesoporous silica support. This simple and versatile method can also be extended to cover many kinds of other supported catalysts for broad applications in many other catalytic reactions in the future.

The effect of structure of mesoporous silica and niobiosilicate on incorporation and stability of modifiers introduced by the click reaction catalyzed by different copper salts

The study was aimed at comparison of the stability and effectiveness of anchoring of the amine and sulfonic groups formed on mesoporous silica by the click reaction. The impact of silica dopant (niobium) and the structure of mesoporous silica (hexagonally ordered SBA-15 vs cellular foam MCF) on the properties and behavior of these surface groups was characterized in details. The modifiers stability was found to have a significant effect on the catalytic reactions in liquid phase. In order to increase the catalysts stability, the mesoporous silica and niobiosilicate were used as supports for ((3-azidopropyl)(triethoxy)silane) – AZPTES followed by the condensation with propargylamine or propargylsulfone by the click reaction performed in the presence of different copper salts used as catalysts of the process. The number of copper ions left in the material after the click reaction was also estimated.

Sustained-release study on Exenatide loaded into mesoporous silica nanoparticles: in vitro characterization and in vivo evaluation

BackgroundExenatide (EXT), the first glucagon-like peptide-1 receptor agonist, has been approved as an adjunctive therapy for patients with type 2 diabetes. Due to EXT’s short half-life, EXT must be administrated by continuous subcutaneous (s.c.) injection twice daily. In previous studies, many studies on EXT loaded into polymer materials carriers for sustained release had been reported. However, these carriers have some defects, such as hydrophobicity, low surface energy, low mechanical strength, and poor chemical stability. Therefore, this study aims to develop a novel drug delivery system, which is EXT loaded into well-ordered hexagonal mesoporous silica structures (EXT-SBA-15), to control the sustainability of EXT.MethodsSBA-15 was prepared by hydrothermal method with uniform size. Morphology of SBA-15 was employed by transmission electron microscopy. The pore size of SBA-15 was characterized by N2 adsorption–desorption isotherms. The in vitro drug release behavior and pharmacokinetics of EXT-SBA-15 were investigated. Furthermore, the blood glucose levels of diabetic mice were monitored after subcutaneous injection of EXT-Sol and EXT-SBA-15 to evaluate further the stable hypoglycemic effect of EXT-SBA-15.ResultsEXT-SBA-15 showed a higher drug loading efficiency (15.2 ± 2.0%) and sustained-release features in vitro. In addition, pharmacokinetic studies revealed that the EXT-SBA-15 treatment group extended the half-life t1/2(β) to 14.53 ± 0.70 h compared with that of the EXT solution (EXT-Sol) treatment group (0.60 ± 0.08 h) in vivo. Results of the pharmacodynamics study show that the EXT-SBA-15 treatment group had inhibited blood glucose levels below 20 mmol/L for 25 days, and the lowest blood glucose level was 13 mmol/L on the 10th day.ConclusionsThis study demonstrates that the EXT-SBA-15 delivery system can control the sustainability of EXT and contribute to improve EXT clinical use.Graphical abstract

The structure of mesoporous silica obtained by pseudomorphic transformation of SBA-15 and SBA-16

Mesoporous silica with bimodal pore size distributions was prepared by pseudomorphic transformation of SBA-15 and SBA-16 in the presence of hexadecyltrimethylammonium ions as a structure-directing agent. The characteristic particle morphology of the starting materials was retained after the transformation. Analysis of the products by gas sorption and small-angle X-ray scattering (SAXS) revealed hybrid pore structures, which featured – depending on the degree of transformation – variable contributions from the original and the newly introduced pore systems. In the case of SBA-15, it was found that a high degree of transformation leads to a seemingly complete conversion of the original pores with a diameter of 7.1 nm to pores with a diameter of 4.0 nm. The SAXS pattern of the product shows additional peaks that can be assigned to the original SBA-15 pore spacing. Similarly, a cubic phase could be observed in the samples prepared by pseudomorphic transformation of SBA-16, despite an almost complete conversion of the SBA-16 cavities. This leads to the conclusion that the pore structure of the starting material significantly affects the outcome of the pseudomorphic transformation, thus opening possibilities for the synthesis of new porous materials with complex pore systems.

WITHDRAWN: Features of the surface layer and structure of SBA-15 type mesoporous silica with thiourea ligands

WITHDRAWN: Features of the surface layer and structure of SBA-15 type mesoporous silica with thiourea ligands

Diffusion NMR Characterization of Catalytic Silica Supports: A Tortuous Path

Mesoporous silicas have found widespread application within the field of heterogeneous catalysis. Acid functionalization of such materials, through one-pot or postsynthetic grafting of sulfonic acid groups, imparts activity for fatty acid esterification, with the studious choice of pore geometry facilitating significant rate enhancements. Diffusion NMR has been utilized for the first time to characterize the structure of mesoporous silicas through the transport behavior of systematically related carboxylic acids confined within their mesopore networks. A reduced diffusion coefficient is obtained for species constrained within the 3-dimensional interconnected pores of KIT-6 relative to the 2-dimensional noninterconnected pore channels of SBA-15. The effective tortuosity of both porous silicas increases with the acid chain length, with the diffusion behavior of long-chain acids dominated by the alkyl chain and silica architecture. Carboxylic acid diffusion within these two pore networks is unlikely to be rate-limiting in catalytic esterification over sulfonic acid silica analogues. Physicochemical insights from diffusion NMR will aid the future design of optimal silica architectures for catalytic applications.

Phase formation, microstructure and setting time of MCM-48 mesoporous silica nanocomposites with hydroxyapatite for dental applications: Effect of the Ca/P ratio

Abstract Nanocomposites of MCM-48 mesoporous silica and hydroxyapatite (HA) are investigated as possible alternatives for the commonly used Mineral Trioxide Aggregate (MTA) dental cement, and the effect of their Ca/P ratio on their structure, properties and setting times is reported. XRD, FTIR and EDS/SEM analysis of the nanocomposites indicate that crystalline HA is formed within the mesoporous silica structure. High Ca/P ratios lead to the formation of free CaO within the nanocomposite, decreasing its setting time; the shortest setting time (~ 40 min), which occurs in the MCM-48/HA nanocomposite with a Ca/P ratio of 5, in physiological saline solution, is considerably shorter than the setting time of MTA (~ 140 min under identical conditions). Thus, the shorter setting time of the MCM-48/HA nanocomposites, coupled with their lack of toxicity, high degree of bioactivity and their stability in tissue fluids, suggest that they could serve as a useful replacement for MTA.

Effects of pore topology and iron oxide core on doxorubicin loading and release from mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNs) have a network of pores that give rise to extremely high specific surface areas, making them attractive materials for applications such as adsorption and drug delivery. The pore topology can be readily tuned to achieve a variety of structures such as the hexagonally ordered Mobil Crystalline Material 41 (MCM-41) and the disordered “wormhole” (WO) mesoporous silica (MS) structure. In this work, the effects of pore topology and iron oxide core on doxorubicin loading and release were investigated using MSNs with pore diameters of approximately 3 nm and sub-100 nm particle diameters. The nanoparticles were loaded with doxorubicin, and the drug release into phosphate-buffered saline (PBS, 10 mM, pH 7.4) at 37 °C was monitored by fluorescence spectroscopy. The release profiles were fit using the Peppas model. The results indicated diffusion-controlled release for all samples. Statistically significant differences were observed in the kinetic host–guest parameters for each sample due to the different pore topologies and the inclusion of an iron oxide core. Applying a static magnetic field to the iron oxide core WO-MS shell materials did not have a significant impact on the doxorubicin release. This is the first time that the effects of pore topology and iron oxide core have been isolated from pore diameter and particle size for these materials.