Type Mesoporous Silica Research Articles

BTEX Detection Using Piezoelectric Cantilever with Mesocellular Foam Silica Functionalized with Hexamethyldisilazane Sensitive Coating

Introduction Gas detection with gravimetric sensors such as SAW, MEMS, FBAR or QCM is based on a frequency shift when the target specie is (ad)sorbed on a sensitive layer covering the sensor [1]. Sensor’s sensitivity and reliability depend on transducer type and sensitive coating, while selectivity and reversibility are correlated with the sensitive coating’s nature. Research studies are still active on the development of transducers to reduce their cost and power consumption but sensitive coating optimization remains a hot topic for sensitive and selective sensor achievements. Among attractive sensitive coating for gravimetric sensors, high specific area coatings such as CNTs, graphene oxide, microporous/mesoporous materials or MOFs are nowadays majorly studied one [2-3]. Their performances in gas detection can be modified by tuning of pores or surface functionalization. In this work we are interested in applying mesoporous foam silica (MCF), a type of mesoporous silica, as a base for hydrophobic hexamethy-disilazane (HDMS) functionalization, and tested for BTEX detection. Also, low cost printed piezoelectric MEMS cantilevers are used as gravimetric transducers. Piezoelectric cantilever sensor fabrication and tests One type of inorganic mesoporous silica (MPS), mesocellular foam (MCF), is synthesized by using P123 as a template and 1,3,5-trimethylbenzene (TMB) as a pore expander as described in [4]. After the template removal by ethanol extraction, the template removed MCFs are then functionalized by hexamethyldisilazane (HDMS) following protocol described in [5]. For the piezoelectric PZT based transducer fabrication, the process consists of screen-printing of all the layers before a co-sintering at 900°C allowing releasing of the PZT cantilever with Au electrodes. Details on the process can be found in [6]. Photographs of the fired cantilever (~ 3x2x0.08 mm3) are shown Fig. 1. The HDMS functionalized MCF (F_MCF) powder is dispersed in deionized water with the ratio of 100 mg/1 mL before depositing by drop-coating with 1µl of this suspension, followed by a drying . The cantilever is self-actuated and self-readout thanks to piezoelectric effect. Admittance circle B(G) (Fig.3a and Fig. 3b)) shows the piezoelectric effect for the 31 in-plane longitudinal mode. Conductance (G(f)) curve before and after F_MCF deposit (weight ~0.05mg) shows the damping effect due to the additional mass (Fig.3c). Based on the measured dimensions of the cantilever, its density and its resonance, frequency f0 , a theoretical sensitivity S=-f0/2m of ~23Hz/µg is calculated. Finally, the cantilever is tested under gas. A PULL110 vapor generator controls N2 flow (100ml/min) and toluene concentration sent in a home-made PTFE cell. Temperature is controlled during the measurements, and acquisition data (f0 as a function of time) are extracted from G measurement using a polynomial fit described in [6]. Results and Conclusions After washing and drying of the MCF, interconnected spherical pore structure are observed by TEM analysis even after functionalized by HMDS (Fig.2). The analysis results of the N2 adsorption-desorption isotherms of the MCFs are shown in Table 1. Pore and window sizes are not affected by functionalization whereas BET surface areas and BJH pore volumes decrease with the increasing HMDS ratio. Also, after functionalization, as expected, reduction of water adsorbed on the surface of the MCF has been observed by TGA and FTIR analysis, and the optimum HDMS:SiO2 for VOCs detection has been shown to be 0.15 (for benzene detection in fact) [5]. This composition is selected for further experiment under gas. Tests under toluene with F_MCF show a sensitivity of 241 mHz/ppm at f0 ~ 256kHz (Figs. 4a and 3b). The blank cantilever also demonstrates slight sensitivity to toluene (~6 mHz/ppm) (Fig. 4b), attributed to density/viscosity changes of the surrounding fluid and cantilevers’s stiffness. In previous work using polymer PEUT coating, silicon cantilever (0.15x0.15x0.095mm3 ) showed sensitivity of 125mHz/ppm at 350 kHz (out of plane mode), whereas similar printed PZT cantilever of size 8x2x0.08mm3 gave sensitivity of 15mHz/ppm at 70kHz (in plane vibration mode) [7]. Size reduction leading to higher sensitivity because of the increased f0 and lower m, combined with the F_MCF coating clearly improves the sensor performances. Good reversibility is also observed. The noisy curve is mainly due to temperature fluctuation which is not precisely controlled in the cell (±0.2°C). The sensor is indeed sensitive to temperature as shown Fig. 3c. Tests under humidity and benzene are ongoing and temperature compensation with another dummy cantilever fabricated in the same conditions could be implemented.

Pharmaceutical Characterization and In Vivo Evaluation of Orlistat Formulations Prepared by the Supercritical Melt-Adsorption Method Using Carbon Dioxide: Effects of Mesoporous Silica Type.

Orlistat, an anti-obesity drug, has two critical issues—the first is its low efficacy due to low water solubility and the second is side effects such as oily spotting due to its lipase inhibition. The present study was designed to propose a solution using a formulation with mesoporous silica to simultaneously overcome two issues. Orlistat was loaded onto mesoporous silica by the supercritical melt-adsorption (SCMA) method, using carbon dioxide (CO2). Various types of mesoporous silica were used as adsorbents, and the effects of the pore volume, diameter and particle size of mesoporous silica on the pharmaceutical characteristics were evaluated by various solid-state characterization methods and in vitro and in vivo studies in relation to pharmacological efficacy and the improvement of side effects. The results showed that the pore volume and diameter determine loadable drug amount inside pores and crystallinity. The dissolution was significantly influenced by crystallinity, pore diameter and particle size, and the inhibition of lipase activity was in proportion to the dissolution rate. In vivo studies revealed that the serum triglyceride (TG) concentration was significantly decreased in the group administered amorphous orlistat-loaded Neuisilin®UFL2 with the highest in vitro dissolution rate and lipase activity inhibition in comparison to the commercial product. Furthermore, oily spotting tests in rats revealed that undigested oil was adsorbed onto mesoporous silica after orlistat was released in the gastro-intestinal tract, and it correlated with in vitro result that oil adsorption capacity was dependent on the surface area of empty mesoporous silica. Therefore, it was concluded that mesoporous silica type plays a major role in determining the pharmaceutical characteristics of orlistat formulation prepared using SCMA with CO2 for improving the low solubility and overcoming the side effects.

Engineered pH-Responsive Mesoporous Carbon Nanoparticles for Drug Delivery.

In this work, two types of mesoporous carbon particles with different morphology, size, and pore structure have been functionalized with a self-immolative polymer sensitive to changes in pH and tested as drug nanocarriers. It is shown that their textural properties allow significantly higher loading capacity compared to typical mesoporous silica nanoparticles. In vial release experiments of a model Ru dye at pH 7.4 and 5 confirm the pH-responsiveness of the hybrid systems, showing that only small amounts of the cargo are released at physiological pH, whereas at slightly acidic pH (e.g., that of lysosomes), self-immolation takes place and a significant amount of the cargo is released. Cytotoxicity studies using human osteosarcoma cells show that the hybrid nanocarriers are not cytotoxic by themselves but induce significant cell growth inhibition when loaded with a chemotherapeutic drug such as doxorubicin. In preparation of an in vivo application, in vial responsiveness of the hybrid system to short-term pH-triggering is confirmed. The consecutive in vivo study shows no substantial cargo release over a period of 96 h under physiological pH conditions. Short-term exposure to acidic pH releases an experimental fluorescent cargo during and continuously after the triggering period over 72 h.

Effect of Piperazine Functionalization of Mesoporous Silica Type SBA-15 on the Loading Efficiency of 2-Mercaptobenzothiazole Corrosion Inhibitor

This work intends to study the effect of functionalization of SBA-15 on the loading and release behaviors of 2-mercaptobenzothiazole (MBT). SBA-15 mesoporous silica was first synthesized and functi...

Supercapacitor behaviour of manganese dioxide decorated mesoporous silica synthesized by a rapid sol-gel inverse micelle method.

A new type of mesoporous silica (MS) with high surface area and large pore volume has been synthesised by employing a rapid sol-gel based inverse micelle method and electrochemically active metal center, manganese, has been incorporated into it. The MnO2 decorated silica composites are obtained through the wet impregnation technique using KMnO4 followed by their reduction under neutral conditions. The structure and surface area of the samples have been characterised by powder X-ray diffraction (XRD), BET surface area and pore size analysis, transmission and scanning electron microscopy (TEM and FE-SEM), FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). Electrochemical techniques, i.e. cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS), have been used to evaluate the electrochemical properties of the composites. The resultant composite MS/MnO2-3 with a significantly high surface area (453 m2 g-1) is found to exhibit a superior specific capacitance of 1158.50 F g-1 at a scan rate of 5 mV s-1 which is very close to the theoretical value and retains 87.8% of its capacitance up to 1000 cycles at 1 A g-1 current density. The outstanding electrochemical performance of the composite can be attributed to the high surface area and uniform pore size distribution of the novel silica host which simultaneously increases the electrochemically active centres, promotes electrolyte penetration and enhances electron transport. The simplicity of the synthesis process developed here is interesting for wide-scale production of MnO2-based electro-active materials.

Functionalization of Mesoporous Silica Materials Using Calix[4]arenes

\Six new products were obtained by deposition of para-tert-butylcalix[4]arene (t-Bu-C4OH), calix[4]arene (C4OH) and tetra-methoxy-calix[4]arene (C4OMe) on two types of SBA-15 mesoporous silica. All the products were characterized through thermogravimetric methods and SEM microscopy. The obtained results confirm the functionalization of the silica materials with the calixarene macrocycles. Considering all the obtained products, the thermal analysis suggests the strongest connectivity to form between the C4OMe systems and mesoporous silica substrate.

Influence of mesoporous silica on powder flow and electrostatic properties on short and long term

We study the effect of three types of mesoporous silica (MPS) particles on the flow of three common excipients: microcrystalline cellulose, lactose and maize starch. While MPS are commonly considered as excipient and also as drug delivery carrier, the effects of MPS as flow aid additive and as powder stabilizer are investigated. MPS particles, called additive in the present study, are found to decrease powder cohesiveness, in particular for powders having higher water content and higher initial cohesiveness. According to both particle and pore size of MPS particles, the effect can be immediate (for small MPS particles having small pore size) or on the longer term (for larger MPS particles having higher pore size). Moreover, the electrostatic properties of the blends are modified by the presence of MPS. The quantity of electrostatic charge created in the blends during a flow in contact with stainless steel is decreased by the addition of MPS. We show that this decrease is induced by a modification of electric resistivity.

Caging cells in functional shells

Biomaterials Unprotected cells are sensitive to changes in their environment, including temperature, pH, and osmotic pressure. Zhu et al. have developed a facile route to encapsulating mammalian cells inside functional nanoparticles. A range of nanoparticles, encompassing several types of metal-organic frameworks, mesoporous silica, and iron oxide, were mixed with interparticle ligands to form a shell or exoskeleton around HeLa cells. The rapid complexation of the particles prevented uptake via endocytotic pathways. The cells are then protected from changes in their surrounding conditions, including the presence of toxins and pathogens larger than 5 nanometers, and can be recovered via chelation of the shell. Depending on the choice of nanoparticle, the caged cells can exhibit magnetic, conductive, or fluorescent properties. Adv. Mater. 31 , 1900545 (2019).

Nanosized carriers for hydrophobic compounds based on mesoporous silica: synthesis and adsorption properties

MCM-41 type mesoporous silica particles were obtained using a template method in an alkaline medium and cetyltrimethylammonium bromide as a matrix. The structural and adsorption characteristics of the mesoporous material were studied by dynamic light scattering, scanning electron microscopy, low-temperature adsorption—desorption of nitrogen, IR spectroscopy, and simultaneous thermal analysis. It was shown that the obtained mesoporous material possesses high porosity with the specific pore volume in excess of 1 cm3 g−1. It was established that the size of silica particles does not exceed 200 nm, which is a value acceptable for the penetration of drugs through cell membranes. The optimal compositions of aqueous dispersions of MCM-41 with minimal sedimentation processes were determined. A drug (indomethacin) was encapsulated into the silica pores using the precipitation method at various temperatures (40 and 60 °C), the quantitative parameters of loading efficiency were calculated. The infl uence of temperature on the encapsulation ability was demonstrated.

The utilization of bagasse fly ash for mesoporous silica synthesis

Natural silica sources such as from biomass ashes provide an alternative cheap silica precursor for synthesizing advanced materials. Mostly, the silica content in the biomass is in the form of amorphous structure which is suitable to be used directly into the material formation. Bagasse fly ash (BFA) contains carbon and silica in a significant amount. The silica content can be recovered by a simple NaOH fusion method followed by water dilution to produce sodium silicate solution. Then, the obtained solution can be used for various material preparations such as zeolites and mesoporous silica materials. It was observed that the alkaline dissolution method is not only extracting silica but also other content such as Alumina and trace metals. Two different type of mesoporous silica, MCM-41 and SBA-15, have been synthesized by incorporating suitable template and sol-gel hydrothermal method using extracted silica source. The synthesized materials were characterized using TEM and XRD to confirm the morphology and crystal structure. Gas adsorption experiment of n-hexane has been done to examine the adsorption behaviour of the two prepared mesoporous silica. The results suggest that low cost natural silica sources can be an alternative for advanced material preparation.

Adsorption of norfloxacin on a hexagonal mesoporous silica: isotherms, kinetics and adsorbent reuse

The adsorption of the antibiotic norfloxacin (NFX) on MCM-41 type mesoporous silica has been studied in batch experiments by performing adsorption kinetics and isotherms under different conditions. Regeneration of the adsorbent and reuse studies were also carried out and are discussed. On the one hand, the adsorption is very fast and strongly dependent on pH, increasing from 30.6 µmol g−1 at pH 3.0 to 192.3 µmol g−1 at pH 7.0 and then decreasing up to 29.6 µmol g−1 as pH increases. The adsorption takes place by direct binding of NFX to silica active sites through electrostatic interactions and H-bonds formations, as deduced from adsorption experiments at several ionic strengths and temperatures. The hydrophobic conformation of the antibiotic zwitterion seems to play also a key role on the maximum adsorption at neutral pH. The presence of calcium ions strongly increases the adsorption of NFX at pH > 4.5 due to the formation of ternary NFX-Ca2+-MCM-41 complexes by calcium-bridging. After the first cycle of regeneration through washing using several solvents, the studied solid significantly reduces its removal efficiency—up to 60%—but then it remains constant for another three cycles. The analysis of thermodynamic parameters suggests that the adsorption is exothermic (− 28.8 kJ mol−1) and spontaneous in nature. On the other hand, the capacity of MCM-41 to remove a concentration of the antibiotic commonly-found in water environments is still being too low if it compares with other adsorbents. Improving the silica surface reactivity should be the main goal by the researchers in order to use the material as adsorbent of this kind of molecules in the future.

Fabrication of spherical CNT skeins formed by self-entangled fibers from hollow type mesoporous silica microcapsules

Various type CNT balls were fabricated using porous hollow microcapsules, and they were characterized by XRD, TEM and N2 adsorption/desorption analysis. The CNT Balls tangled together showed extremely improved thermal and electrical properties as compared to the fibrous CNTs. Notably increased strain values, such as more than 30% strains at fixed stress, with high toughness have resulted in for those entangled CNT skeins. Even though the CNT skeins entangled together with fibrous bundles have been fabricated as a multi wall-type, they could be applied successfully as a DNA separator and highly conducting electrochemical/rheological materials.

Amine-modified mesoporous silicas: Morphology-controlled synthesis toward efficient removal of pharmaceuticals

Abstract To investigate the effect of porous structure and surface chemistry on the efficiency of pharmaceuticals removal four different types of pristine and amine-modified mesoporous silicas have been synthesized and characterized: Ordered Mesoporous Silicas (SBA-15), Mesocellular Silica Foams (MCF), Porous Silica Nanotubes (PSN) and Amorphous Silica Xerogels (ASX). Functional alkoxysilanes bearing one, two and three amine groups were co-condensed with tetraethoxysilane to obtain highly functionalized materials. The designed materials were tested as sorbents of several drugs commonly considered priority hazardous pharmaceuticals, including diclofenac, ibuprofen, penicillin G and naproxen. The porous structure turned out to have a minor effect on the sorption capacity but the number of surface amine groups was the crucial parameter. Unprecedented uptakes of drugs sometimes exceeding 0.9 g g−1 testify that the obtained materials can be applied for removal of drugs from water and wastewaters, particularly when high concentrations of pharmaceutical are needed to be removed.

Ice crystallization observed in highly supercooled confined water.

We investigate the state of water confined in the cylindrical pores of MCM-41 type mesoporous silica, with pore diameters of 2.8 nm and 4.5 nm, over the temperature range 160-290 K by combining small angle neutron scattering and wide angle diffraction. This allows us to observe simultaneously the intermolecular correlations in the local water structure (which shows up in a main water peak around Q = 1.7 Å-1), the two-dimensional hexagonal arrangement of water cylinders in the silica matrix (which gives rise to a pronounced Bragg peak around Q = 0.2 Å-1), and the so-called Porod scattering at smaller Q, which arises from larger scale interfacial scattering within the material. In the literature, the temperature evolution of the intensity of the Bragg peak has been interpreted as the signature of a density minimum in confined water at approximately 210 K. Here we show that, under the conditions of our experiment, a fraction of freezable water coexists with a layer of non-freezable water within the pore volume. The overall temperature dependence of our data in the different Q regions, as well as the comparison of the data for the two pore sizes, leads us to conclude that the observed variation in the intensity of the Bragg diffraction peak is actually caused by a liquid to ice transition in the freezable fraction of confined water.

Synthesis and Preparation of Al-MCM-41 Mesoporous Materials Using Oil Shale Residue

An Al-supported cage-like mesoporous silica type MCM-41 has been prepared using a simple one-step synthetic procedure using oil shale residue and CTAB(Hexadecyl trimethyl Ammonium Bromide) as the template. The effects of temperature on the porosity, structure and surface area of Al-MCM-41 mesoporous materials were characterized by X-ray powder diffraction, N2adsorption desorption, scanning electron micrographs (SEM), transmission electron microscopy (TEM) techniques and Fourier transform infrared spectroscopy (FT-IR). The results indicated that temperature was a key to the characteristics of Al-MCM-41 materials, and when the temperature up to 333 K, Al-MCM-41 exhibited excellent characteristics with high degree of order, high surface area and pore volume. The one-step hydrothermal synthesized MCM-41 mesoporous material possessed high BET surface area, high pore size and high pore volume. They are respectively 835.1 m2/g, 32.6 Å and 1.22 cm3/g under the condition of the Si : Al =78:1, pH =10, crystallization temperature was 333K, crystallization time was 48h and calcination at 823 K for 5 h in air. All the results indicated the possibility of using oil shale residue as silicon and aluminum source to produce Al-MCM-41, and gave us a new way to recycle a solid waste. As well as this made it impossible to large-scale production of Al-MCM-41. Keywords: Al-MCM-41 mesoporous materials, oil shale residue, one-step synthesis

Biomimetic Cu, Zn and Cu2 complexes inserted in mesoporous silica as catalysts for superoxide dismutation

Abstract Three CuZn-superoxide dismutase (SOD) functional mimics, [CuZn(dien)2(μ-Im)](ClO4)3 (1), [Cu2(dien)2(μ-Im)](ClO4)3 (2) (Im = imidazole, dien = diethylenetriamine), and [CuZn(salpn)Cl2] (3) (H2salpn = 1,3-bis(salicylideneamino)propane), were successfully inserted into the nanochannels of SBA-15 type mesoporous silica with retention of the silica mesostructure. X-ray absorption spectroscopic studies indicate that the encapsulated complexes keep unchanged the first-shell environment of Cu(II) and Zn(II) ions. Magnetic measurements suggest that the nanochannels constrain the geometry of the μ-imidazolate-Cu(II)2 core modifying the relative orientation of the two copper coordination planes. Confinement imposed by the silica nanochannels upon encapsulation of complexes 1 and 2 leads to stable hybrid materials at physiological pH with enhanced SOD activity relative to the free complexes. Unlike the imidazolato-bridged compounds, insertion of 3 in mesoporous silica leads to a less stable hybrid material exhibiting partial release into the aqueous solution and O2•− dismutation rate slower than the free complex. The covalent binding of a mononuclear Cu(dien)Im+ moiety to the mesoporous silica showed lower SOD activity than encapsulated imidazolato-bridged CuZn and Cu2 complexes. The results emphasize the positive effect of encapsulation on SOD activity of imidazolato-bridged dinuclear complexes.

Catalytic Activity of Tungstophosphorous Acid Supported on Mesoporous Silica for Glycerol Acetalisation to Glycerol Formal

For the acetalization reaction between glycerol and formaldehyde two mesoporous catalyst were prepared, characterized and tested. Mesoporous silicas (MCM-41 and HMS) were synthesized and used as supports for the phosphotungstic acid based catalysts. Glycerol was converted to glycerol formal through a solventless acetalization reaction with formaldehyde catalyzed by tungstophosphorous acid supported on two type of mesoporous silica (30PW/MCM41 and 30PW/HMS). The reaction was carried out in a batch reactor, at 120�C, using 2% catalyst. The highest yield ] 98.5% was achieved over mesoporous 30PW/HMS catalyst. Catalyst characterization was performed by determining the textural characteristics, acid strength and by SEM analyses. The catalytic activity of the catalysts was compared, using the same conditions with two comercial acid catalysts : Amberlyst 15 and p-toluen sulphonic acid on polymer support (PTS/polymer).

Optimization of carboxyl-functionalized mesoporous silica for the selective adsorption of dysprosium

Dysprosium (Dy), one of the rare-earth elements, was adsorbed on the four types of mesoporous silica, having pore size 3–22 nm and functionalized with amino and carboxyl groups on the surface. The influence of the pore size on the selective Dy ion adsorption capacity was examined using a metal ion mixture. The synthesized materials was characterized by field emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller analyzer. In addition, the functionalized materials were characterized by thermogravimetric analyzer, Fourier transform infrared, and zeta-potential. The adsorption amount of Dy ions on the functionalized particles was evaluated by inductively coupled plasma optical emission spectrometry. The material having a large pore size (22 nm) as well as amino and carboxyl chains manifested an excellent adsorption capacity for Dy ions (32.9 μg/mg). The recycling efficiency of adsorption-desorption process retained approximately 100% of the capability at least five cycles. These results suggested that the functionalized material with pore size 22 nm can be used for an adsorbent for the selective and efficient removal of Dy ions from mixtures.

Structural Characterization of Myoglobin Molecules Adsorbed within Mesoporous Silicas

In the present study, we examined the secondary and tertiary structure of myoglobin (Mb) within folded sheets mesoporous material (FSM)- and Santa Barbara amorphous (SBA)-type mesoporous silicas. The Barrett–Joyner–Halenda pore diameters of SBA-type mesoporous silicas were 39, 70, and 75 A, and that of FSM-type mesoporous silica was 40 A. The secondary and tertiary structures of myoglobin were observed by Fourier transform infrared (FTIR) and small-angle neutron scattering (SANS), respectively. The FTIR and SANS results indicated preservation of the secondary and tertiary structures of myoglobin inside the pores of SBA-type mesoporous silicas. Adsorption of myoglobin within FSM-type mesoporous silica, however, resulted in perturbation of the tertiary structure, accompanied by partial unfolding of the secondary structure. Lower structural stability of myoglobin within the FSM-type mesoporous silica was also confirmed. These findings suggest that the Mb structure is more influenced by the inner pore surface...

Mesoporous silica supported samarium as recyclable heterogeneous catalyst for synthesis of 5-substituted tetrazole and 2-substituted benzothiazole

Synthesis of nitrogen-containing heterocycles such as tetrazoles and benzothiazoles gains immense importance as they are omnipresent structural modules often utilized in pharmaceuticals. In the present study, well ordered MCM-41 type mesoporous silica with large pore (l-MSN) was synthesized and impregnated with samarium nitrate (Sm@l-MSN). Due to high abundance of samarium relative to many catalytically active transition metals (e.g. Ru, Ir, Pt), it may offer an opportunity to develop sustainable catalysts for organic conversions. The synthesized materials were characterized using nitrogen sorption, scanning electron microscopy, energy-dispersive X-ray, elemental mapping and transmission electron microscopy. The catalytic efficiency of the materials was explored for the synthesis of tetrazoles and benzothiazoles, two very important heterocyclic moieties in medicinal chemistry and biology. The catalyst was readily recovered and recycled up to five consecutive runs without noteworthy loss of activity or leaching.