Morphology Of Mesoporous Silica Research Articles

Quantitative Study of the Enhanced Content and Chemical Stability of Functional Groups in Mesoporous Silica by In-Situ Co-condensation Synthesis

The chemical stability and content of organic functional groups significantly affect the application of materials in the field of adsorption. In this study, we quantitatively studied the effect of in-situ co-condensation and post grafting on the physico-chemical properties and sorption properties of modified mesoporous silica. The results showed that the grafting method changed the morphology of mesoporous silica while the in-situ method kept the spherical morphology well, and the amino groups were both successfully introduced into the materials. Besides, the amino content of the material prepared by in-situ method (ami-MSN) was 2.71 mmol/g, which was significantly higher than the 0.98 mmol/g of the grafting method (ami-g-MS). Moreover, the chemical stability of functional groups in ami-MSN was much better than ami-g-MS. Furthermore, ami-MSN showed better capability in removing toxic metals of Pb, Cd, Ni, and Cu, and the removal efficiency of Pb reached 98.80%. Besides, ami-MSN exhibited higher dynamic CO2 adsorption of 0.78 mmol/g than ami-g-MS of 0.34 mmol/g. This study revealed the relationship between modification methods and the modification efficiency, functional groups stability, and sorption properties through quantitative comparative studies, which provided a reference for preparing modified mesoporous silica materials with high sorption properties.

METHANOL MASS VARIATION OF MESOPOROUS SILICA SYNTHESIS USING RICINOLEIC METHYL ESTER AS A TEMPLATE

This study aims to synthesize mesoporous silica using ricinoleic methyl ester as a template with the variation of methanol mass. Mesoporous silica was synthesized using ricinoleic methyl ester as a template, 3-aminopropyltrimethoxysilane as a structural directing agent, and tetraethyl orthosilicate (TEOS) as a source of silica. The novelty of this study lies in the use of ricinoleic methyl ester as a template. The reaction conditions were varied by varying the amount of methanol without adding hydrochloric acid 0.1M. The yield of mesoporous silica in samples named MSME A, MSME B, and MSME C was 1.63 g, 1.70 g, and 1.80 g. It shows that adding methanol mass affects the yield of mesoporous silica. Fourier-transform infrared spectroscopy (FTIR) analysis revealed that all silica products formed Si-O-Si bonds between 1103 cm-1 and 1111 cm-1 due to asymmetric stretching vibration. All silica products have a diffractogram at 2θ between 10o and 30o, indicating amorphous. The scanning electron microscope (SEM) image demonstrates the mesoporous silica morphology as a mixture of spherical particles and multiple sheets, fused round particles, aggregated particles, and spreading spherical particles. The BET analysis reveals a homogeneous pore size distribution in the third and fourth treatments. Each is dominated by a pore size range of 8.43 nm to 8.50 nm.

ВПЛИВ РОЗМІРУ ПОР ТА МОРФОЛОГІЇ МЕЗОПОРИСТОГО КРЕМНІЮ НА ВИВІЛЬНЕННЯ МЕТОПРОЛОЛУ ТАРТРАТУ

Purpose. Study pore size effect and morphology of mesoporous silica on metoprolol tartrate release.Methodology. A sample of hollow mesoporous silicon dioxide with amino-functional groups containing 12.7 wt. % metoprolol tartrate has been investigated as potential carriers for the controlled release of active substance. Studies of the release profiles of metoprolol tartrate were performed under the following conditions: dissolution medium was buffer solution with a pH of 7.4 (phosphate buffer); sampling time: from 0.5 h before 18 h. The metoprolol concentration in the liquid phase was evaluated by a UV-Vis spectrophotometer (Persee TU-190, Beijing, China) by use of quartz cuvettes with an optical path length of 1 cm at a maximum wavelength of 274 nm.Findings. In this work we have studied mesoporous silica as possible carrier to controlled release of metoprolol tartrate, a drug used in the treatment of some diseases of the cardiovascular system. The material for research was a sample of hollow mesoporous silicon dioxide with amino-functional groups 200–400 nm in size and 20–30 nm in shell thickness. A calibrated curve to determine the amount of metoprolol was constructed by determining the absorption dependence of the concentration of metoprolol in the range from 10 to 300 ppm. The same drug concentration was obtained as calculated from the drug release test formula, which concludes that the release of metoprolol is controlled.Originality. The controlled release of a sample of hollow spheres of mesoporous silicon dioxide filled with metoprolol tartrate was studied, which was synthesized by the School of Chemistry and Chemical Engineering, Qilu University of Technology, using a new technology, where hollow spheres of mesoporous silicon dioxide with amino groups were synthesized using CO2 gas bubbles as templates.Practical value. The metoprolol release amount could achieve a 50% release amounts within 1 hour and 90% within 5 hours, indicating that the synthesized mesoporous hollow sphere could achieve controlled drug release, and shows the potential of carriers with stimulus response and targeted therapy.

Orienting the Pore Morphology of Core-Shell Magnetic Mesoporous Silica with the Sol-Gel Temperature. Influence on MRI and Magnetic Hyperthermia Properties.

The controlled design of robust, well reproducible, and functional nanomaterials made according to simple processes is of key importance to envision future applications. In the field of porous materials, tuning nanoparticle features such as specific area, pore size and morphology by adjusting simple parameters such as pH, temperature or solvent is highly needed. In this work, we address the tunable control of the pore morphology of mesoporous silica (MS) nanoparticles (NPs) with the sol-gel reaction temperature (Tsg). We show that the pore morphology of MS NPs alone or of MS shell covering iron oxide nanoparticles (IO NPs) can be easily tailored with Tsg orienting either towards stellar (ST) morphology (large radial pore of around 10 nm) below 80 °C or towards a worm-like (WL) morphology (small randomly oriented pores channel network, of 3–4 nm pore size) above 80 °C. The relaxometric and magnetothermal features of IO@STMS or IO@WLMS core shell NPs having respectively stellar or worm-like morphologies are compared and discussed to understand the role of the pore structure for MRI and magnetic hyperthermia applications.

Formation of mesoporous silica particles with hierarchical morphology

The transformation of mesoporous silica morphology from monoliths to spherical particles was investigated at room temperature in Pluronic F127/TEOS system as a function of HCl acid catalyst concentration to understand and control the mechanism. It is shown that the specific surface area and the size of mesoporous spherical silica particles can simply be adjusted by the catalyst concentration without using any additives or post-treatment. Above 3 M acid concentration, novel monodisperse micron sized spherical silica with hierarchical order of two levels was obtained. These silica spheres were formed of densely packed distorted hexagonal platelets of 20–30 nm in diameter. Within these platelets mesoporous channels were oriented along a single direction, however the platelets were randomly oriented in the spherical particles. Controlling the agglomeration of mesoporous silica primary particles by the concentration of the acid catalyst to obtain micron-sized spherical particles is novel. This approach allows the synthesis of particles whose sizes can be controlled in the range of ~1–4 μm and specific surface area in the range of ~200–500 m2/g. The morphology of the particles transforms from spherical shape to mesoporous monoliths at acid concentrations below 1 M due to slow hydrolysis and condensation. These results are important in understanding the role of catalyst concentration on the formation mechanism of different morphologies of mesoporous silica.

Controllable silica morphology transition from tremella-like spheres to brush-like fibers induced by β-cyclodextrin

Tremella-like silica spheres (TSSs) and brush-like silica fibers (BSFs) with well-defined structures were synthesized using cetyltrimethylammonium bromide and sodium dodecyl sulfate aggregate as structure-directing agent and β-cyclodextrin (β-CD) as inducing agent. By controlling the amount of β-CD, the morphology of mesoporous silica was changed from TSSs to BSFs and then back to TSSs. The materials were characterized by using several techniques. The extraordinary mesoporous silica with a brush-like shape and measuring 180–220 nm wide and 6–20 μm long were formed as a result of the diameter of the U-shaped silica skeleton. These two kinds of materials can be used as fluorescent hybrid materials by immobilizing Rhodamine B (Rh B). Furthermore, the hybrid materials were well characterized by the fluorescence spectra to prove that BSFs-Rh B has excellent fluorescence property.

Effect of synthesis conditions on the morphology of mesoporous silica from elephant grass and its application in the adsorption of cationic and anionic dyes

In this study, various low cost mesoporous silica (MS) were synthesised from elephant grass (EG) a biowaste material often regarded as a weed, by varying synthesis conditions, such as temperature and surfactant concentration (cetyltrimethyl ammonium bromide (CTAB)), thus revealing the transformation of mesoporous silica from silica nanoparticles to silica nanotubes. MS obtained were extensively characterised. Highly porous silica nanoparticles (SNP) were obtained at 2 wt. percent of surfactant to silica and at 45 wt. silica nanotubes (SNT) were obtained. It was observed that 600 °C was the optimum temperature in MS synthesis as it gave higher surface area and an all-round better textural property in the sorption of methylene blue (cationic dye) and methyl orange (anionic dye) from wastewater. Batch adsorption was carried out to determine the effect of time, temperature, initial concentration, pH and adsorbent dose. SNP had a higher qm value of 123.5 mg/g for MB and 83.3 mg/g for MO which may be attributed to its larger surface area. Adsorption mechanism was through ion exchange and pore filling. Thermodynamic study revealed the adsorption process was exothermic. This study showed the transformation of EG into highly efficient sorbents with desorption studies showing that adsorbents could be reapplied in adsorption.

Growth process and morphology control of SBA-15 particles: synergistic effects of tetraethoxysilane and Pluronic-123 concentrations

The synergistic effects of the template [Pluronic-123 (P123)] and the silica source [tetraethoxysilane (TEOS)] concentrations on the SBA-15 mesoporous silica morphology were investigated through adjusting the system initial solution volume with the same amounts of silica source and template. It found interestingly that the SBA-15 morphology changed from the hexagonal plate-like shape to the gear-like shape with the decrease of the P123 and TEOS concentration. Based on the morphology variations, the growth of the gear-like morphology was speculated to be formed through the preferential growth at the corner and the layer-by-layer growth in the end face of the ordinary hexagonal plate-like particle.

Optimization of pore structure and particle morphology of mesoporous silica for antibody adsorption for use in affinity chromatography

Antibodies have received significant attention for use as antibody drugs, because they bind the objective protein (antigen) via antigen–antibody reactions. Recently, many reports have appeared on various monoclonal antibodies that recognize a single antigen. In this study, monoclonal antibodies are used as adsorbates on mesoporous silica (MPS) for affinity chromatography. MPS has high surface area and large pore volume; moreover, pore diameter, pore structure, and particle morphology are relatively easy to tune by adjusting the conditions of synthesis. The pore structure (two-dimensional (2D) hexagonal and three-dimensional cubic) and particle morphology (spherical and polyhedral) of MPS are optimized for use in a monoclonal antibody/MPS composite. When anti-IgG (one of the monoclonal antibodies) adsorbs on the MPS material and IgG (antigen) binds to anti-IgG/MPS composites, MCM-41p with a 2D-hexagonal pore structure and polyhedral particle morphology has the highest IgG binding efficiency. In addition, the antibody/MPS composites remain stable in chaotropic and low-pH solutions and can be cycled at least five times without decreasing IgG elution. In purification and removal tests, the use of the antibody/MPS composites allows only the objective protein from protein mixtures to be bound and eluted.

Simultaneous control of rod length and pore diameter of SBA-15 for PPL loading

Mesoporous silica materials are attractive materials for immobilizing enzymes because of their well-ordered structures, large surface area are pore volume. Diffusion of large enzyme molecules such as porcine pancreatic lipase (PPL) through the lengthy channels of MPS takes place too slowly. Therefore, the squat of the enzyme at the pore mouth entrance, actually makes the rest of the channel useless. In this study, to overcome this problem, synthesis parameters of SBA-15 were changed, since along with pore diameter increasing, the mesochannel length becomes shorter. The main point to obtain a well-ordered 2D hexagonal pore structure was the pre-hydrolysis of tetraethyl orthosilicate (TEOS) before the addition of 1,3,5-trimethyl benzene as a micelle swelling agent. Due to the strong effect of zirconium in changing the morphology of SBA-15 particles, we modified SBA-15 in the presence of a small amount of ZrOCl2 in the synthesis solution under acidic conditions. As a result, mesochannel length of SBA-15-Zr was shortened from 600 to <200 nm. The morphology of mesoporous silica was also changed from rod-like to platelet, because of the accelerating effect of Zr(IV) on the self-assembly rate of P123 and TEOS condensation. Characteristic results conducted by low angle XRD, high resolution transmission electron microscopy and nitrogen adsorption, confirmed tuning effect of Zr(IV) in SBA-15. Furthermore, it was shown that the number of pore entrances increases with decreasing the length of SBA-15 mesochannels, leading to obvious improvement of enzyme uptake. PPL has been successfully immobilized in the mesoporous channels of SBA-15-Zr. The total amount of lipase adsorbed on the mesoporous SBA-15-Zr was measured by thermal gravimetric analysis. The largest PPL adsorption capacity was 784 mg/g belonging to the SBA-15-Zr with the length of 150 nm and the mean pore size diameter of 9.22 nm.

Diffusion, adsorption and reaction of glucose in glucose oxidase enzyme immobilized mesoporous silica (SBA-15) particles: Experiments and modeling

Glucose oxidase (GOD) enzyme is widely used as a sensing molecule for glucose and is thus immobilized in different porous hosts for sensing applications. We have synthesized different morphologies of mesoporous silica (SBA-15) host particles and impregnated GOD in it. Rod and cuboid shaped SBA-15 particles having internal pore diameters of 6.8 and 11.4nm respectively, were synthesized, in order to measure enzyme activity. The latter primarily determines the performance of a glucose sensor. In this quest, we therefore developed a mathematical model to predict variation of glucose concentration with time, by considering diffusion, adsorption and reaction rates of glucose by immobilized GOD. The model was validated with our own experiments, by fitting diffusion coefficient of glucose inside mesopores and the competitive product inhibition constant of GOD. The validated model indicates that, specific activity of GOD immobilized in SBA-15 is lower at higher GOD loading. Thus, this provides insight into the effect of pore-confinement on diffusion and reaction kinetics of the substrate (glucose) by an immobilized enzyme (GOD). Understanding the interplay of chemical transport and reaction kinetics issues in a porous solid nanoparticle host (SBA-15) can lead to superior detection and measurement of glucose concentration.

Rhizopus oryzae lipase immobilized on hierarchical mesoporous silica supports for transesterification of rice bran oil.

The tunable textural properties of self-oriented mesoporous silica were investigated for their suitability as enzyme immobilization matrices to support transesterification of rice bran oil. Different morphologies of mesoporous silica (rod-like, rice-like, and spherical) were synthesized and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption-desorption isotherms. The surface area, pore size, and ordered arrangement of the pores were found to influence the immobilization and activity of the enzyme in the mesopores. The immobilization in rod-like silica was highest with an immobilization efficiency of 63 % and exhibited minimal activity loss after immobilization. Functionalization of the mesoporous surface with ethyl groups further enhanced the enzyme immobilization. The free enzyme lost most of its activity at 50 °C while the immobilized enzyme showed activity even up to 60 °C. Transesterified product yield of nearly 82 % was obtained for 24 h of reaction with enzyme immobilized on ethyl-functionalized SBA-15 at an oil:methanol ratio of 1:3. Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography-mass spectrometry (GC-MS) were used to characterize the transesterified product obtained. The reusability of the immobilized enzyme was studied for 3 cycles.

Effect of drying technique on the morphological and textural characteristics of mesoporous silica synthesized in the microreactor

The mesoporous silica with high monodisperse inter-particle voids was obtained through different drying methods (oven, freeze, and spray) of wet-gel silica. And the wet-gel silica was prepared in the microreactor system through the precipitation of TEOS. The effects of different drying techniques on the textural properties and morphology of mesoporous silica synthesized in the microreactor were studied. The textural properties of silica were evaluated using nitrogen adsorption/desorption experiments. The morphology of the silica was described using transmission electron microscopy and field-emission scanning electron microscope. It was found that the oven drying (OD) silica exhibited the most uniform pore structures and compact structures. The freeze drying silica maintained the original network of wet-cake silica after drying. Due to the rapid and uniform heating of silica in the spray drying (SD) process, the silica obtained had the more porous structure than that of OD technique. Additionally, the surface tension of solution in the SD process affected the structures of final products. And the ethanol resulted in the more porous structures of silica than that of water.

A facile approach for the tunable wormlike or ordered pore morphology of mesoporous silica: Effect of catalyst types and polyethylene glycol

Two different basic catalysts, NaOH and NH4OH, to the formation of mesoporous silica with completely different pore morphology at the same mole concentration with or without polyethylene glycol (PEG) were investigated. NaOH catalyzed system seemed to have a more ordered structure and larger particle size than NH4OH catalyzed system. The addition of PEG tended to promote the charge matching probability for silicate oligomers and micelles, which resulted in the more ordered pore morphology for NH4OH system. With increased ammonia concentrations, the pore morphology of disordered wormlike structure was transformed into ordered MCM-41 type mesoporous structure with particle dimension in a few tenths of nanometer to hundred nanometer. With the addition of PEG, at low ammonia concentration, the mesoporous pores became more orderly arranged as well. However, the effect of PEG on the pore and particle morphology of the NaOH catalyzed system was less evident than that of the NH4OH system. The catalyst types were also investigated at the same pH to contrast the significance of catalyst effect on the preparation of mesoporous silica, which was often neglected in the literature. NaOH catalyzed system still indicated a more ordered wormlike structure and slightly larger particle size than NH4OH catalyzed system. The XRD (X-ray diffraction) results and N2 adsorption–desorption isotherms were in agreement with the TEM (Transmission electron microscope) morphology. The significance of two different catalysts with the addition of PEG in tuning pore morphology was justified.

Effect of polyvinylpyrrolidone on mesoporous silica morphology and esterification of lauric acid with 1-butanol catalyzed by immobilized enzyme

Mesoporous silica materials with a range of morphology evolution, i.e., from curved rod-shaped mesoporous silica to straight rod-shaped mesoporous silica, were successfully prepared using polyvinylpyrrolidone (PVP) and triblock copolymer as dual template. The effects of PVP molecular weight and concentration on mesoporous silica structure parameters were studied. Results showed that surface area and pore volume continuously decreased with increased PVP molecular weight. Mesoporous silica prepared with PVP K30 also possessed larger pore diameter, interplanar spacing (d100), and cell parameter (a0) than that prepared with PVP K15 and PVP K90. In addition, with increased PVP concentration, d100 and a0 continuously decreased. The mechanism of morphology evolution caused by the change in PVP concentration was investigated. The conversion rate of lauric acid with 1-butanol catalyzed by immobilized Porcine pancreatic lipase (PPL) was also evaluated. Results showed that PPL immobilized on amino-functionalized straight rod-shaped mesoporous silica maintained 50% of its esterification conversion rate even after five cycles of use with a maximum conversion rate was about 90.15%.

Effects of particle morphology, pore size and surface coating of mesoporous silica on Naproxen dissolution rate enhancement

Naproxen (Nap) is a commonly used drug for antiphlogosis and analgesia, but its dissolution rate in water is quite low. In this work, the dissolution behavior of Nap after loading in mesoporous silica materials was investigated in a simulated intestinal fluid (pH=6.8). The results indicated that the pore sizes, morphologies and surface chemical groups of the mesoporous silica were significant factors on the dissolution behavior of Nap. The physical state of encapsulated Nap was affected by the pore sizes of mesoporous silica, which influenced its dissolution rate. Amorphous Nap exhibited a higher dissolution rate than crystallized Nap, even though the larger pore size could facilitate its diffusion from the matrix. The effect of the morphology of mesoporous silicas on the dissolution of Nap can be ascribed to the length of pore channels, that the longer channel showed a longer diffusion pathway of Nap. Moreover, the release rate of Nap from functionalized mesoporous materials was effectively controlled compared with that of unmodified materials.

Effect of morphology of mesoporous silica on characterization of protic ionic liquid-based composite membranes

Effects caused by the morphology of mesoporous silica on the characterization of protic ionic liquid-based composite membranes for anhydrous proton exchange membrane applications are investigated. Two types of SBA15 materials with platelet and fiberlike morphologies are synthesized and incorporated into a mixture of polymerizable monomers together with an ionic liquid (IL) [1-butyl-3-methylimidazolium bis(trifluoromethane sulfone)imide (BMIm-TFSI)] to form new conducting membranes using an in situ photo crosslinking process. Incorporation of a defined amount of fiber-shaped SBA 15 and platelet 15 significantly increases the ionic conductivity to between two and three times that of a plain poly(methyl methacrylate) (PMMA)/IL membrane (2.3 mS cm −1) at 160 °C. The protic ionic liquid (PIL) retention ability of the membranes is increased by the capillary forces introduced by the mesoporous silica materials, while ionic conductivity loss after leaching test is retarded. The highest ionic conductivity (5.3 mS cm −1) is obtained by incorporating 5 wt% of P-SBA 15 in the membrane to about six times that of plain PMMA/IL membrane (0.9 mS cm −1) at 160 °C after leaching test.

Effects of Morphology and Structural Characteristics of Ordered SBA-15 Mesoporous Silica on Release of Ibuprofen

Three kinds of highly ordered SBA-15 mesoporous materials with different pore sizes and morphologies denoted as LPS-SBA-15 (stick-like with pore size 7.28 nm), CPS-SBA-15 (stick-like with pore size 5.96 nm) and T-SBA-15 (tablet-like with pore size 4.64 nm) have been prepared, characterized and employed as carrier materials. The release behaviors of the ibuprofen in a simulated body fluid from these mesoporous silica materials were studied. The influences of pore size and exterior morphologies of mesoporous silica on the release behaviors of ibuprofen have been investigated. It has been found that the release becomes fast with increasing of pore size and slow with extending of transport pathway, and that the release rate of ibuprofen from the three kinds of SBA-15 is LPS-SBA-15 > T-SBA-15 > CPS-SBA-15. The results show that the inner structure as well as the exterior morphologies of SBA-15 mesoporous silica can seriously affect the release behaviors of ibuprofen.

Synthesis of mesoporous silica with cationic-anionic surfactants

Ordered mesoporous silica was successfully synthesized by using mixed surfactants, cetyltrimethylammonium bromide and sodium dodecylsulfate, proceeded with the hydrolysis and condensation of tetraethyl orthosilicate in a mixture of TritonX-100 as a cosolvent. The synthesized products were characterized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen sorption analysis. It was found with increasing the anionic surfactant sodium dodecylsulfate to cetyltrimethylammonium bromide molar ratio, the morphologies of mesoporous silica changed from spherical shape to ellipsoidal shape, at last became rod-like and lamellar shape. Correspondingly the pore diameter and surface area of mesoporous silica all decreased according to nitrogen sorption analysis. The TEM analysis illustrated the product with ordered hexagon mesostructure and homogeneous pore arranged can be obtained, when the molar ratio of cetyltrimethylammonium bromide/sodium dodecylsulfate is 15: 1. It also demonstrated the less the molar ratio of sodium dodecylsulfate was used, the more ordered pore structure the products exhibited. Furthermore, prolonging the crystal time was beneficial to improve the stability of the product.

Tuning the morphology of mesoporous silica by using various template combinations

By using different dual-template combinations, four types of mesoporous silica materials with different morphologies were successfully synthesized. A solid-sphere mesoporous (SSM) silica was obtained using a combination of tri-block copolymer (F127) and 1,12-diaminododecane (DADD), but when F127 was substituted with poly(vinylpyrrolidone) (PVP), a leaf-shaped mesoporous (LSM) silica was obtained. In addition, a hollow-sphere mesoporous (HSM) silica was obtained by using a combination of PVP and dodecylamine (DDA), but a cotton-like mesoporous (CLM) silica was obtained using F127 instead of PVP. All four types of synthesized materials were characterized by SEM, TEM, XRD, and N 2 adsorption–desorption isotherms, and the results showed that all of them exhibited high surface area, large pore volume, worm-like pore structure, and beautiful shapes. The results of storage experiments revealed that the HSM and CLM showed good adsorption and storage properties. The HSM (the largest pore volume) seemed to have the larger storage capacity when compared to the CLM, albeit CLM had the highest surface area among all.