Mesoporous System Research Articles

Synthesis of hexagonal aluminosilicate from liquid-crystalline mesophase using zeolitic nanoclusters: bottom-up versus top-down approach

An amorphous porous hexagonal aluminosilicate Al-ZAT was prepared using liquid crystal phase of Brij-56 and preformed MFI zeolite nanoclusters solution through bottom-up approach. The HCl concentration (0.5–2.0 M), HCl to Brij-56 ratio and zeolitic seed solution wss varied for the mesoporous system at ambient synthesis condition. The optimum Brij-56 to HCl ratio was found to be 1 Brij 56: 9–19 HCl (0.5 M) by mass. The addition of preformed zeolite seed (7–14 ml) as precursor solution instead of conventional silica source tetramethyl orthosilicate (TMOS) generate uniform mesophase and subsequently avoids formation of methanol (from TMOS hydrolysis) that affects liquid crystalline mesophase. MCM-41 (ZMCM-41) and SBA-15 (ZSBA-15) derived from similar zeolite precursor solution was synthesized for comparative study. The porous textural characteristics, and type of surface acidity were studied. The analysis showed a highly porous hexagonal structure of Al-ZAT. ZMCM-41 prepared through top-down approach, showed formation of ordered nanostructured mesoporous (disordered hexagonal). Al-ZAT and ZSBA-15 shows weaker Bronsted acid sites compared to ZMCM-41.

PH-dependent release of environmentally friendly corrosion inhibitor from mesoporous silica nanoreservoirs

Coatings for corrosion protection usually contain pigments that constantly release substances actively inhibiting corrosion. However, this constant leaching places an important limitation on the protection lifetime of the coating. An intelligent release system may improve the long-term function of a coating, as uncontrolled loss by leaching is inhibited. This ensures that high amounts of inhibitors are still present when needed. Furthermore, this is also favourable for the environment, as no inhibitor is unnecessarily released into it. In this sense, smart mesoporous systems are excellent candidates thanks to their ability to provide more efficient and longer lasting anticorrosive protection by responding quickly to external stimuli such as local environmental changes (temperature, pH, local defects, humidity, etc.). A change in pH is a particularly interesting stimulus since, as is well known, corrosion activity leads to local pH changes in cathodic and anodic areas.In the present paper an environmentally friendly corrosion inhibitor, sodium phosphomolybdate, has been loaded into mesoporous silica nanoparticles. One of the main goals has been to study whether this corrosion inhibitor compound can offer controlled release as a function of pH, even in the absence of encapsulation. The results have shown that the polymerisation processes experienced by molybdenum species, as well as the different phosphate ions present as a function of pH, prevent their release into the environment in the absence of an outer capsule within the pH 3–9 range, thus avoiding the need to carry out an encapsulation stage.

A Review of Recent Developments of Mesoporous Materials

This personal account concerns novel recent discoveries in the area of mesoporous materials. Most of the papers discussed have been published within the last two to three years. A major emphasis of most of these papers is the synthesis of unique mesoporous materials by a variety of synthetic methods. Many of these articles focus on the control of the pore sizes and shapes of mesoporous materials. Synthetic methods of various types have been used for such control of porosity including soft templating, hard templating, nano-casting, electrochemical methods, surface functionalization, and trapping of species in pores. The types of mesoporous materials range from carbon materials, metal oxides, metal sulfides, metal nitrides, carbonitriles, metal organic frameworks (MOFs), and composite materials. The vast majority of recent publications have centered around biological applications with a majority dealing with drug delivery systems. Several other bio-based articles on mesoporous systems concern biomass conversion and biofuels, magnetic resonance imaging (MRI) studies, ultrasound therapy, enzyme immobilization, antigen targeting, biodegradation of inorganic materials, applications for improved digestion, and antitumor activity. Numerous nonbiological applications of mesoporous materials have been pursued recently. Some specific examples are photocatalysis, photo-electrocatalysis, lithium ion batteries, heterogeneous catalysis, extraction of metals, extraction of lanthanide and actinide species, chiral separations and catalysis, capturing and the mode of binding of carbon dioxide (CO2 ), optical devices, and magneto-optical devices. Of this latter class of applications, heterogeneous catalysis is predominant. Some of the types of catalytic reactions being pursued include hydrogen generation, selective oxidations, aminolysis, Suzuki coupling and other coupling reactions, oxygen reduction reactions (ORR), oxygen evolution reactions (OER), and bifunctional catalysis. For perspective, there have been over 40,000 articles on mesoporous materials published in the last 4 years and about 1388 reviews. By no means is this personal account thorough or all inclusive. One objective has been to choose a variety of articles of different types to obtain a flavor of the breadth of diversity involved in the area of mesoporous materials.

Preparation of mesoporous silica-LDHs system and its coordinated flame-retardant effect on EVA

This paper mainly studies synergistic flame-retardant effects and smoke suppression properties of mesoporous silica-LDHs system on the ethylene-vinyl acetate copolymer (EVA). The mesoporous silica-LDHs/EVA composites were prepared based on EVA as resin matrix, mesoporous silica-LDHs as flame-retardant composites. The flame-retardant and thermal degradation properties of the composites were characterized by limiting oxygen index (LOI), cone calorimeter test, scanning smoke density test (SDT), electronic microscopy (SEM) and thermogravimetry–Fourier transform infrared spectrometry (TG-IR) analysis. Remarkably, addition of certain amount of mesoporous silica-LDHs could evidently increase LOI values. The heat release rate and the total heat release of the composites were much lower than of pure EVA. The SDT results showed that the composites containing mesoporous silica-LDHs produced less smoke than pure EVA for a period of time. The morphologies and structures of the residues, revealed by SEM, ascertained that the formed char layers on the composites were denser than that of the LDHs/EVA composites. Mesoporous silica in the material can help smoke suppression. TG-IR data reveal that the incorporation of mesoporous silica-LDHs promoted the release of H2O, and CO2, meanwhile reduced harmful gases release.

Acid-programmed control of dual-mesoporous carbon nanospheres with predictable diameter

To date, the pursuit of dual-meospores while maintaining definite dispersity and small particle size of mesoporous carbon nanospheres (MCN) still remains a great challenge, due to the aggregation tendency of small particles (especially below 200nm) and the destruction of nanospherical structure after excessively creating mesopores. Herein, we report a high acid induced heterogeneous nucleation and growth approach to synthesize dual-mesoporous carbon nanospheres (DMCN) with well-controlled small diameters. This highly acidic driven method has effectively balanced the organic-organic, organic-inorganic and inorganic-inorganic assembly to control the polymerization kinetics, thus forming dispersed nanospheres. The surface incompatibility issues between silica nanoparticle (SN, the inorganics) and resorcinol/formaldehyde (RF, the organisms) were addressed through the employment of inorganic/ionic/organic interaction to synthesize DMCN under highly acidic condition. An extended I+X−S+ mechanism is proposed to interpret this formation process. By precisely controlling the processes of growth and cooperation-assembly, the diameter can be easily manipulated over a wide range (130–60nm), which is a facile route for preparing dispersed small-size DMCN. Meanwhile, a linear function model is established to quantitatively control and predict the particle size. Since the DMCN integrated both the advantages of small diameter (nanosize effect) and bimodal mesopore system (reduction of transport limitation) in one single unit, it exhibits an excellent performance in the release of poorly water-soluble drug and the adsorption of dye molecules.

Low-cost disordered carbons for Li/S batteries: A high-performance carbon with dual porosity derived from cherry pits

A micro- and mesoporous carbon obtained from cherry pit waste and activated with H3PO4 acid has been studied as the sulfur host for Li/S batteries. The carbon has a high specific surface area of 1,662 m2·g–1 (SBET) and micropore and mesopore volumes of 0.57 and 0.40 cm3·g–1, respectively. The S/C composite, with a sulfur content of 57% deposited by the disproportionate reaction of a S2O3 2− solution in an acid medium without an additional heating step above the S melting point, delivers an initial specific capacity of 1,148 mAh·g–1 at a current of C/16. It also has a high capacity retention of 915 mAh·g–1 after 100 cycles and a Coulombic efficiency close to 100%. The good performance of the composite was also observed under higher current rates and long-term cycling tests. The capacities delivered by the cell after 200 cycles were 707 and 410 mAh·g–1 at C/2 and 1C (1C = 1,675 mA·g–1), respectively, maintaining the high Coulombic efficiency. The overall electrochemical response of this carbon as the sulfur matrix is among the best reported so far among the other biomass-derived carbons, probably because of the micro- and mesopore system formed upon activation.

Preparation, characterization, and cytotoxicity studies of niclosamide loaded mesoporous drug delivery systems

Recent reports on the anticancer potential of niclosamide have opened new avenues for anticancer treatment. Niclosamide belongs to the BCS class II, which is indicative of poor solubility and dissolution rate limited absorption. The aim of this study was to improve the dissolution rate of the drug by mesoporous drug delivery system. Porous silica grades (ordered and nonordered) with different pore size, pore volume and surface area were used in the study. The drug was loaded on silica carriers by the solvent evaporation method and characterized by BET surface area analysis, SEM, P-XRD, DSC, and FTIR. A discriminatory dissolution medium was developed for performing the in vitro dissolution of niclosamide. In comparison to the plain drug, all silica based formulations showed improvement in the dissolution rate. Maximum enhancement in the dissolution rate was observed in 1:2 drug:carrier loading ratio when compared to 1:1 ratio. Different properties of mesoporous silica like structural geometry, pore size and microenvironment pH demonstrated a significant impact on drug release from the formulations. Cytotoxicity of the optimized mesoporous formulations of niclosamide was explored in HCT-116, HCT-15, NCI, MDA-MB-231 and A549 cancer cell lines. Nearly 3 fold and 2 fold increase in% cytotoxicity of drug loaded Syloid-244 and Sylysia 350 at 1:2 ratio respectively, were observed when compared to the plain drug.

Synthesis of metallic silver nanoparticles decorated mesoporous SnO 2 for removal of methylene blue dye by coupling adsorption and photocatalytic processes

Abstract Herein, we report a successful route for synthesis SnO2 and SnO2 decorated with 5 wt% metallic silver nanoparticles by sol-gel route using PVP as structure and pore directing agent. X-ray diffraction [XRD], N2-adsorption-desorption isotherm, diffuse reflectance spectra [DRS], Photoluminescence [PL] and high resolution transmission electron microscope [HRTEM] were selected to give a clear clue on the physicochemical features of the prepared nanoparticles. Homogeneous dispersion of metallic silver nanoparticles on the surface and the pore wall of SnO2 are accompanied by creation of various types of pores ranging from supermicropores to wide mesoporous system that results in remarkable increase in surface area, pore volume and C-BET constant by about 50%. This situation can explain the exceptional increase in the amount of dye adsorbed under dark conditions. Both adsorption and photocatalytic reactivity of silver decorated SnO2 are responsible by nearly the same extent for removal of methylene blue dye. COD experimental result confirms the degradation of the majority of methylene blue dye. The scavenger study indicates that all charge carrier and reactive radicals contribute by the same extent in case of pure SnO2. However, the positive holes and hydroxyl radicals are the predominant reactive species on Ag/SnO2. This result confirms the electron transfer from SnO2 conduction band to Ag Fermi level, so, the positive holes and the hydroxyl radical are more available to oxidize the organic pollutants. A new photocatalyst can be developed as an economically feasible and environmentally friendly method to mineralize wastewater from organic pollutants.

Positronium lifetime measurements in micro- and mesoporous ferrisilicates

Positron annihilation lifetime, Doppler broadening measurements have been used to study microporous FER and MFI structures containing framework subtituted iron in different amounts. Mesoporous SBA-15 samples without and with iron introduced to the pore walls were also investigated by these methods. Mössbauer measurements have been accompanied to prove the extent of isomorphous incorporation of iron into the different structures. The results reveal a certain dependence of lifetimes on the various pore and channel sizes. Addition of iron does not influence significantly the observed lifetimes in FER microporous systems. However a slight decrease of lifetimes can be observed in the MFI samples. The effect of addition of iron in mesoporous SBA-15 system is more expressed. Supplement of iron also has an influence on the S parameter of Doppler broadening spectra.

Sodium NMR relaxation in mesoporous systems

We explore the NMR relaxation of 23Na nuclei in brine confined in mesoporous controlled porous glass. Bi-exponential decays characteristic of the relaxation of the quadrupole sodium nuclei under confinements can be clearly identified and contrasted with the mono-exponential decays observed for motional narrowed bulk brine solutions. The concentration dependence of either of the bi-exponential relaxation times of confined 23Na nuclei, shows a trend opposite to that in bulk solutions. The understanding of this behavior could be fundamental for inferring sodium dynamics in bound water for oilfield formation evaluation and other applications such as monitoring the quality of building materials.

Enhanced osteogenesis and angiogenesis by mesoporous hydroxyapatite microspheres-derived simvastatin sustained release system for superior bone regeneration

Biomaterials with both excellent osteogenic and angiogenic activities are desirable to repair massive bone defects. In this study, simvastatin with both osteogenic and angiogenic activities was incorporated into the mesoporous hydroxyapatite microspheres (MHMs) synthesized through a microwave-assisted hydrothermal method using fructose 1,6-bisphosphate trisodium salt (FBP) as an organic phosphorous source. The effects of the simvastatin-loaded MHMs (S-MHMs) on the osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) and angiogenesis in EA.hy926 cells were investigated. The results showed that the S-MHMs not only enhanced the expression of osteogenic markers in rBMSCs but also promoted the migration and tube formation of EA.hy926 cells. Furthermore, the S-MHMs were incorporated into collagen matrix to construct a novel S-MHMs/collagen composite scaffold. With the aid of MHMs, the water-insoluble simvastatin was homogenously incorporated into the hydrophilic collagen matrix and presented a sustained release profile. In vivo experiments showed that the S-MHMs/collagen scaffolds enhanced the bone regeneration and neovascularization simultaneously. These results demonstrated that the water-insoluble simvastatin could be incorporated into the MHMs and maintained its biological activities, more importantly, the S-MHMs/collagen scaffolds fabricated in this study are of immense potential in bone defect repair by enhancing osteogenesis and angiogenesis simultaneously.

Simple and Facile Approach To Create Charge Reversible Pores via Hydrophobic Anchoring of Ionic Amphiphiles.

Mesoporous silica-based charge reversal systems have gained significant attention in recent years due to a variety of applications such as drug delivery, dye adsorption, catalysis, chromatography, etc. Such systems often use covalent strategies to immobilize functional groups on the silica scaffold. However, lack of dynamism, modularity, and postsynthetic flexibility associated with covalent routes limit their wider applicability. Alternatively, supramolecular routes are gaining increased attention owing to their ability to overcome these limitations. Here, we introduce a simple and facile noncovalent design for a highly reversible assembly of charged amphiphiles within mesopores. Hexyl pendant groups were covalently attached to the surface to provide hydrophobic anchoring for charged amphiphiles to enable facile switching of surface charge of the mesoporous silica. These charge-switchable surfaces were used for fast and selective adsorption of dyes from aqueous solutions.

Hexagonal Mesoporous Silica-Supported Copper Oxide (CuO/HMS) Catalyst: Synthesis of Primary Amides from Aldehydes in Aqueous Medium.

Hexagonal mesoporous silica (HMS)-supported copper oxides (CuO/HMS) have been prepared by a sol-gel method and characterized by X-ray diffraction, FTIR spectroscopy, transmission electron microscopy, N2 sorption, inductively coupled plasma (ICP), X-ray photoelectron spectroscopy (XPS), H2 temperature-programed reduction (TPR), NH3 temperature-programed desorption (TPD), and high-resolution (HR)-TEM techniques. An analysis of these results revealed a mesoporous material system with a high surface area (974 m2 g-1 ) and uniform pore-size distribution. The catalytic efficacy of CuO on the HMS support with varying Cu loadings (1, 3, 5, 10, and 15 wt %) was investigated for the transformation of aldehydes to primary amides; 3 wt % CuO/HMS exhibited good catalytic performance with good to excellent yields of amides (60-92 %) in benign aqueous medium. The intrinsically heterogeneous catalyst could be recovered after the reaction and reused without any noticeable loss in activity.

Structural and magnetic properties of the nanocomposite materials based on a mesoporous silicon dioxide matrix

The structural and magnetic properties of the mesoporous systems based on silicon dioxide with a regular hexagonal arrangement of pores several microns in length and several nanometers in diameter, which are filled with iron compound nanofilaments in various chemical states, are studied in detail. The studies are performed using the following mutually complementary methods: transmission electron microscopy, SQUID magnetometry, electron spin resonance, Mossbauer spectroscopy, polarized neutron small-angle diffraction, and synchrotron radiation diffraction. It is shown that the iron nanoparticles in pores are mainly in the γ phase of Fe2O3 with a small addition of the α phase and atomic iron clusters. The effective magnetic field acting on a nanofilament from other nanofilaments is 11 mT and has a dipole nature, the ferromagnetic–paramagnetic transition temperature is in the range 76–94 K depending on the annealing temperature of the samples, and the temperature that corresponds to the change in the magnetic state of the iron oxide nanofilaments is T ≈ 50–60 K at H = 0 and T ≈ 80 K at H = 300 mT. It is also shown that the magnetization reversal of an array of nanofilaments is caused by the magnetostatic interaction between nanofilaments at the fields that are lower than the saturation field.

Mesoporous Silica Molecular Sieve based Nanocarriers: Transpiring Drug Dissolution Research.

Improvement of oral bioavailability through enhancement of dissolution for poorly soluble drugs has been a very promising approach. Recently, mesoporous silica based molecular sieves have demonstrated excellent properties to enhance the dissolution velocity of poorly water-soluble drugs. Current research in this area is focused on investigating the factors influencing the drug release from these carriers, the kinetics of drug release and manufacturing approaches to scale-up production for commercial manufacture. This comprehensive review provides an overview of different methods adopted for synthesis of mesoporous materials, influence of processing factors on properties of these materials and drug loading methods. The drug release kinetics from mesoporous silica systems, the manufacturability and stability of these formulations are reviewed. Finally, the safety and biocompatibility issues related to these silica based materials are discussed.

Investigating the Effects of Loading Factors on the In Vitro Pharmaceutical Performance of Mesoporous Materials as Drug Carriers for Ibuprofen.

The aim of the study was to investigate the effects of the loading factors, i.e., the initial drug loading concentration and the ratio of the drug to carriers, on the in vitro pharmaceutical performance of drug-loaded mesoporous systems. Ibuprofen (IBU) was used as a model drug, and two non-ordered mesoporous materials of commercial silica Syloid® 244FP (S244FP) and Neusilin® US2 (NS2) were selected in the study. The IBU-loaded mesoporous samples were prepared by a solvent immersion method with a rotary evaporation drying technique and characterized by polarized light microscopy (PLM), Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC). Dissolution experiments were performed in simulated gastric media at 37 °C under non-sink conditions. The concentration of IBU in solution was determined by HPLC. The study showed that the dissolution rate of IBU can be improved significantly using the mesoporous S224FP carriers due to the conversion of crystalline IBU into the amorphous form. Both of the loading factors affected the IBU dissolution kinetics. Due to the molecular interaction between the IBU and NS2 carriers, the loading factors had little effects on the drug release kinetics with incomplete drug desorption recovery and insignificant dissolution enhancement. Care and extensive evaluation must therefore be taken when mesoporous materials are chosen as carrier delivery systems.

Peculiarities of vanillin release from amino-functionalized mesoporous silica embedded into biodegradable composites

Mesoporous silica nanoparticles are among the most promising nanovectors for controlled release of active compounds. In this work we design a mesoporous silica-based delivery system in which the release of the active compound is controlled by specific pore/wall interactions and can also be triggered by an external stimulus, such as the simple addition of water into the surrounding releasing medium. Due to its reversibility in presence of water, imine bond formation between amino groups and aldehydes has been proposed as a valuable approach to reach this scope. The amino-group is provided by the amino-functionalized mesoporous silica which has been obtained through the functionalization of Santa Barbara Amorphous (SBA)-15 with aminopropyltrietoxysilane. Whereas the aldehyde is represented by the active compound itself: the natural antimicrobial vanillin. The obtained particles have been embedded into PCL-based films. The amino-functionalization of mesoporous silica has been confirmed through NMR analysis and X-ray diffraction. Imine bond formation and evolution has been followed by 13C NMR before and after the contact of mesoporous silicas with water. Release kinetics of vanillin show that the diffusion of vanillin from films containing the functionalized mesoporous silica is delayed by about 20% and 75% with respect to films containing free vanillin, in water and in ethanol respectively. The most significant feature of the system is the stepwise behavior which shows that the release of the amount of vanillin bound to the NH2 groups of functionalized SBA is triggered only after the addition of water to the surrounding ethanolic solution. These findings give an important insight into the use of pristine and functionalized mesoporous silicas for the development of polymer films for active responsive packaging materials.

In vitro dissolution models for the prediction of in vivo performance of an oral mesoporous silica formulation

Drug release from mesoporous silica systems has been widely investigated in vitro using USP Type II (paddle) dissolution apparatus. However, it is not clear if the observed enhanced in vitro dissolution can forecast drug bioavailability in vivo. In this study, the ability of different in vitro dissolution models to predict in vivo oral bioavailability in a pig model was examined. The fenofibrate-loaded mesoporous silica formulation was compared directly to a commercial reference product, Lipantil Supra®. Three in vitro dissolution methods were considered; USP Type II (paddle) apparatus, USP Type IV (flow-through cell) apparatus and a USP IV Transfer model (incorporating a SGF to FaSSIF-V2 media transfer). In silico modelling, using a physiologically based pharmacokinetic modelling and simulation software package (Gastroplus™), to generate in vitro/in vivo relationships, was also investigated. The study demonstrates that the in vitro dissolution performance of a mesoporous silica formulation varies depending on the dissolution apparatus utilised and experimental design. The findings show that the USP IV transfer model was the best predictor of in vivo bioavailability. The USP Type II (paddle) apparatus was not effective at forecasting in vivo behaviour. This observation is likely due to hydrodynamic differences between the two apparatus and the ability of the transfer model to better simulate gastrointestinal transit. The transfer model is advantageous in forecasting in vivo behaviour for formulations which promote drug supersaturation and as a result are prone to precipitation to a more energetically favourable, less soluble form. The USP IV transfer model could prove useful in future mesoporous silica formulation development. In silico modelling has the potential to assist in this process. However, further investigation is required to overcome the limitations of the model for solubility enhancing formulations.

Sol-gel synthesis of less expensive mesoporous titania-tin dioxide systems: Investigation of the influence of tin dioxide on the phase structure, morphology and optical properties

Herein the influence of SnO2 on the optical, morphology and phase structure of mesoporous TiO2-SnO2 composites was examined. Composites with Sn/Ti ratio ranging from 0.1 to 5 were synthesized using less expensive sources in the absence of additives. The obtained samples were examined by XRD, HRTEM, SEM-EDAX, XPS, UV–vis DRS, XRF, TGA and nitrogen gas physisorption studies analyses. The physicochemical properties of the TiO2-SnO2 systems depended mainly on the Sn-to-Ti ratio, calcination temperature and the interaction between Sn4+and Ti4+. XRD results depicted that samples with Sn/Ti=0.1 calcined at ≤600°C exhibited pure anatase TiO2 crystals and the tendency of increasing Sn4+ content facilitated a phase transformation to attain rutile structure. Optical analyses of the samples showed that the absorption of the samples can be extended into the visible region. This study provides a systematic and economical method for large-scale production of TiO2 based composites with desirable properties for various applications.

Talented Mesoporous Silica Nanoparticles

The structure and functionality of mesoporous silica nanoparticles can be tuned by means of numerous and diverse synthetic strategies. Focusing on experimental methods, we describe how pore size and pore topology of the mesopore system can be modified through templating and pore-swelling agents, as well as different synthesis conditions. Moreover, we show how the mesoporous nanoparticles can be functionalized through co-condensation methods with silane coupling agents, with specific emphasis on the spatially selective anchoring of different molecular functionalities within the nanoparticles. We discuss methods for changing the composition of the pore walls of the mesoporous particles, for example by including redox-sensitive sulfide bonds or by creating autofluorescent curcumin-containing mesoporous organosilica. The efficiency of targeted drug delivery applications strongly depends on morphological parameters such as size and shape of the mesoporous nanoparticles. It is demonstrated how the particle size of the mesoporous nanoparticles can be modified over a wide range from about 30 nm to several hundred nanometers. Developing this context further, we consider several examples of triggered molecular mechanisms intended for the controlled intracellular release of bioactive substances from the pore system of mesoporous nanoparticles.