Pore Size Of Mesoporous Silica Research Articles

COMPARATIVE STUDY OF THE LOADING AMOUNT OF DRUG WITHIN MESOPOROUS SILICA WITH VARIOUS PORE SIZE

Objective: The loading of drugs into mesoporous silica (MS) is an effective strategy to improve the solubility of poorly water-soluble drugs. Previous reports have stated that the surface area and pore volume of MS can affect drug loading and its crystallization in MS. Therefore, this study aims to elucidate the effect of MS pore size on the maximum drug loading and its dissolution profile. Methods: The ritonavir (RTV) and itraconazole (ITZ) were encapsulated-MS using the solvent evaporation method. The RTV and ITZ loaded-MS were characterized using differential scanning calorimetry (DSC) and PXRD measurement. Results: The amorphization of RTV loaded-MPS and ITZ loaded-MPS were confirmed as a halo pattern in the powder X-ray diffraction pattern. The melting peak and the glass transition of RTV and ITZ were not discovered in MS with the pore size of 80 Å (weight ratio of 3:7), while in the RTV and ITZ loaded-MS with the pore size of 45 Å, the melting peak and the glass transition were observed. This indicated that the loading amount of RTV and ITZ with larger pore sizes is higher than the lower sizes. Conclusion: This study demonstrated that the pore size of MS has a significant effect on the loading amount of drugs in MS.

Effects of morphology and pore size of mesoporous silicas on the efficiency of an immobilized enzyme.

An investigation is performed into the efficiency of the Streptomyces griseus HUT 6037 enzyme immobilized in three different mesoporous silicas, namely mesoporous silica film, mesocellular foam, and rod-like SBA-15. It is shown that for all three supports, the pH value changes the surface charge and charge density and hence determines the maximum loading capacity of the enzyme. The products of the enzyme hydrolytic reaction are analyzed by 1H-NMR. The results show that among the three silica supports, the mesoporous silica film (with a channel length in the range of 60–100 nm) maximizes the accessibility of the immobilized enzyme. The loading capacity of the enzyme is up to 95% at pH 7 and the activity of the immobilized enzyme is maintained for more than 15 days when using a silica film support. The order of the activity of the enzyme immobilized in different mesoporous silica supports is: mesoporous silica film > mesocellular foam > rod-like SBA-15. Furthermore, the immobilized enzyme can be easily separated from the reaction solution via simple filtration or centrifugation methods and re-used for hydrolytic reaction as required.

Differential Scanning Calorimetry Study on the Adsorption of Myoglobin at Mesoporous Silicas: Effects of Solution pH and Pore Size.

In the present study, pore adsorption behavior of globular myoglobin (Mb) at mesoporous silicas was examined utilizing the low-temperature differential scanning calorimetry (DSC) method. The DSC method relies on a decrease in heat of fusion for the pore water upon adsorption of Mb. The amount and structure of Mb adsorbed into the mesoporous silica were examined by DSC and optical absorption spectroscopy. The results indicated that the pore adsorption behavior of Mb strongly depended on the solution pH and pore size of mesoporous silica. For the adsorption of Mb (diameter = 3.5 nm) into mesoporous silica with narrow pores (pore diameter = 3.3 nm) at a pH ranging from 7.0 to 3.7, the penetration of both folded and denatured Mb molecules was confirmed. The folded Mb could penetrate into large mesoporous silica pores (pore diameter = 5.3 and 7.9 nm), whereas the penetration of the denatured Mb molecules was completely inhibited. The distribution of folded Mb at mesoporous silica depended on the pore size; almost all folded Mb molecules located inside mesoporous silica pores of diameters 3.3 and 5.3 nm, whereas the Mb molecules distributed at bot internal and external pore surfaces of mesoporous silica with 7.9 nm in pore diameter. These pore adsorption behaviors suggest that aggregation or stacking of the Mb molecules at the pore entrance regions of the large pores affected the pore adsorption behavior.

An intelligent nanoplatform for imaging-guided photodynamic/photothermal/chemo-therapy based on upconversion nanoparticles and CuS integrated black phosphorus

The strategy of combining imaging and treatment has been shown as a widely studied and promising approach. In this work, we first integrated copper sulfide (CuS) nanoparticles and black phosphorus (BP) nanosheets with strong negative charges via mesoporous silica-coated upconversion nanoparticles (UCNPs). Synergistic treatment of photothermal, photodynamic and chemotherapy can be achieved after loading doxorubicin (DOX). The nanocomposites perform excellent antitumor efficiency under 808 nm near-infrared (NIR) light, and avoid the slightly lower efficiency and limited penetration depth of conventional ultraviolet and visible (UV–vis) light. In this system, the pore size of mesoporous silica and the large specific surface area of BP are advantageous for achieving high DOX loading capacity. Furthermore, the reduction in the red/green (R/G) ratio elicited by DOX release can be employed to determine the extent of DOX release by the fluorescence resonance energy transfer (FRET) process. CT/MR imaging induced by doping of rare earth ions imparts multimode imaging capabilities to nanosystem under 808 nm light irradiation, thereby enabling imaging-guided cancer treatment.

A biomimetic mesoporous silica–polymer composite scaffold for bone tissue engineering

A biomimetic organic–inorganic composite system comprising of microspheres fabricated from combination of a biodegradable polymer poly(lactide-co-glycolide) (PLGA) and bioactive mesoporous silica (SBA-15) has been developed through sintering technique for bone regeneration applications. The morphological and structural properties of the SBA-15/PLGA composite scaffold were evaluated using electron microscopy and fourier transform infrared spectroscopy and the results showed spherical morphology and composite nature. The presence of mesopores in the silica was confirmed through nitrogen adsorption–desorption isotherms. The surface area and pore size of mesoporous silica were found to be 792 m2 g−1 and 3.7 nm, respectively. The thermal characteristics of the SBA-15/PLGA composites studied using thermogravimetry analysis shows a weight loss of around 80% with the degradation occurring at 324 °C. The prepared scaffold is also found to support the adhesion and proliferation of osteoblast cells. The expression of specific bone markers is significantly enhanced in the SBA-15/PLGA composite scaffold when compared with the pristine polymeric scaffold indicating the positive effect of mesoporous silica. Hence, these SBA-15/PLGA composite scaffolds can be explored further for bone regeneration applications.

Effect of pore size, aminosilane density and aminosilane molecular length on CO2 adsorption performance in aminosilane modified mesoporous silica

Mesoporous silicas with different pore size were modified by aminosilanes with different molecular length. CO2 adsorption capacity was improved by all aminosilane modification, and the CO2 adsorption capacity was further improved with increasing the aminosilane density. However, CO2 adsorption capacity and the amine efficiency of (3-trimethoxysilylpropyl)diethylentriamine (TA) modified mesoporous silicas with small pores such as MCM-41(2.9 or 3.1 nm) and SBA-15(6.2 or 7.1 nm) were significantly decreased at high aminosilane density. In contrast, TA modified SBA-15 with a large pore (10.6 nm) exhibited further improvement of CO2 adsorption capacity and amine efficiency. N2 adsorption desorption measurements suggested that the pore plugging occurred at high aminosilane density in TA modified mesoporous silicas with small pores. In situ FT-IR spectra and the half-value period of CO2 equilibrium adsorption capacity clearly shows the CO2 adsorption kinetics in these adsorbents with small pores were significantly lower than that in the adsorbent with large pores. To develop the CO2 adsorbents with high adsorption performance, the correlation between aminosilane molecular length, pore size of mesoporous silica and aminosilane density should be considered.

Effect of the Pore Diameters and Amino-Organo Functional Structures on Mesoporous Silicas for DNA Adsorption

Deoxyribonucleic acid (DNA) adsorption onto particles has applications in biosensors, separation methods, and gene delivery. Mesoporous silica (MPS), which exhibits a high surface area and large pore volume, is used in these applications because its pore size is easily controlled and its surface functional groups are easily exchanged. In this study, three types of MPSs with different pore sizes (2.4, 5.6, and 11.8 nm) were functionalized with different aminosilane coupling reagents and the effects of the MPS pore size and surface functional groups on DNA adsorption were evaluated. As the pore size of MPS increased, MPSs with diethylenetriamine (–3NH2) adsorbed higher amounts of DNA, whereas MPSs with hexylenediamine groups (–2HNH2) adsorbed lower amounts of DNA. Moreover, the fitting of DNA adsorption equilibrium data to Langmuir and Freundlich isotherm models was investigated.

Effect of salts on synthesis of mesoporous materials with mixed cationic and anionic surfactants as templates

Mesoporous silica materials were synthesized using tetraеthoxysilane as precursor and liquid crystals formed in aqueous mixtures of cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) as templates, without and with the addition of NaBr or Na2SO4. For this purpose, the formation of liquid crystals as a function of the ratio of CTAB and SDS under different conditions was studied. It was found that liquid crystals formed in the mixed system of CTAB and SDS at certain mixing ratios are well-structured templates for the synthesis of mesoporous silicas. The synthesized silica materials were characterized by transmission electron microscope and nitrogen adsorption/desorption analysis. The pore size of mesoporous silicas could be controlled between 3 to 6 nm by simply changing the concentration of NaBr in solution. The mesoporous silicas exhibited lamellar structure and the order of structural arrangement was promoted with addition of NaBr. However, addition of Na2SO4 led to ink-bottle type pores of mesoporous silica with a narrow pore size distribution of around 2 nm and a higher specific surface area of 610 m2 g–1.

Enhanced visible photoluminescent and structural properties of ZnO/KIT-6 nanoporous materials for white light emitting diode (w-LED) application

Mesoporous metal oxides ZnO are prepared by wet impregnation via hard templating synthesis method using KIT-6 mesoporous silica. The pore size of mesoporous silica with the symmetry of bicontinuous cubic Ia3d have been controlled in the range of 3.4–4.9 nm, indicating the existence of ordered within the silica walls respectively, by choosing surfactants and adjusting the temperature. The pore size of the silica template has been considered to be an important factor that determines the mesostructure of the resulting metal oxides. The prepared ZnO/KIT-6 samples have been studied by XRD, transmission electron microscope (TEM), BET surface area, and photoluminescence (PL) spectroscopy. The ZnO/KIT-6 nanocomposite has the ordered mesostructure of KIT-6 can be used as a white light emitting diode (w-LED) and ultraviolet nanolasers.

Amine-modified ordered mesoporous silica: The effect of pore size on CO2 capture performance

The objective of current research is to investigate the effect of pore size of mesoporous silica supports on the CO2 capture performance of solid amine sorbents. Two ordered mesoporous silicas (OMS) with different pore sizes (5.6nm and 7.6nm) were synthesized as tetraethylenepentamine (TEPA) supports. A serious of techniques, such as physical adsorption, infrared spectroscopy and thermal gravimetric analysis were used to characterize the solid amine sorbents. The CO2 capture performances of the sorbents were evaluated using breakthrough method with a fixed-bed reactor equipped with an online mass spectrometer. The experimental results indicate that the pore size has significant influence on CO2 capture performance. Larger pore size could decrease the mass transfer resistance and increase the interaction between CO2 and TEPA. Therefore, OMS-7.6 is better than OMS-5.6 as amine support. The highest CO2 sorption capacities achieved with OMS-7.6 with 50wt% TEPA loading (OMS-7.6-50) in the absence and presence of moisture are 3.45mmol/g and 4.28mmol/g, respectively, under the conditions of 10.0% CO2/N2 mixture at 75°C. Cyclic CO2 adsorption–desorption experiments indicate that the solid amine sorbents are fairly stable and regenerable.

High drug load, stable, manufacturable and bioavailable fenofibrate formulations in mesoporous silica: a comparison of spray drying versus solvent impregnation methods

Encapsulation of drugs in mesoporous silica using co-spray drying process has been recently explored as potential industrial method. However, the impact of spray drying on manufacturability, physiochemical stability and bioavailability in relation to conventional drug load processes are yet to be fully investigated. Using a 23 factorial design, this study aims to investigate the effect of drug-loading process (co-spray drying and solvent impregnation), mesoporous silica pore size (SBA-15, 6.5 nm and MCM-41, 2.5 nm) and percentage drug load (30% w/w and 50% w/w) on material properties, crystallinity, physicochemical stability, release profiles and bioavailability of fenofibrate (FEN) loaded into mesoporous silica. From the scanning electronic microscopy (SEM) images, powder X-ray diffraction and Differential scanning calorimetry measurements, it is indicated that the co-spray drying process was able to load up to 50% (w/w) FEN in amorphous form onto the mesoporous silica as compared to the 30% (w/w) for solvent impregnation. The in vitro dissolution rate of the co-spray dried formulations was also significantly (p = 0.044) better than solvent impregnated formulations at the same drug loading. Six-month accelerated stability test at 40 °C/75% RH in open dish indicated excellent physical and chemical stability of formulations prepared by both methods. The amorphous state of FEN and the enhanced dissolution profiles were well preserved, and very low levels of degradation were detected after storage. The dog data for the three selected co-spray-dried formulations revealed multiple fold increment in FEN bioavailability compared to the reference crystalline FEN. These results validate the viability of co-spray-dried mesoporous silica formulations with high amorphous drug load as potential drug delivery systems for poorly water soluble drugs.

Investigation of the stability of Platinum nanoparticles incorporated in mesoporous silica with different pore sizes

The effect of the pore size of mesoporous silica on the stability of Pt nanoparticles (NPs) has been investigated. TEM observation and XRD measurement were conducted in situ for Pt loaded mesoporous silica with different mesopore sizes. It turns out that smaller pores are more effective to stabilize Pt NPs below 600°C. However, aggregation of Pt NPs on the surface of particles is not fully suppressed more than 1000°C in ambient atmosphere even though smaller mesopore size is applied. The type of precursor does not affect the stability of Pt NPs.

Synthesis of Mesoporous Silica from Poly(ethylene oxide)/Polystyrene Copolymers: Influence of Block Architecture and Each Copolymer Block on Porous Size

Several well defined block copolymers PEO-b-PS and PS-b-PEO-b-PS were synthesized by atom transfer radical polymerization using PEO-Br and Br-PEO-Br as macroinitiators. These copolymers were characterized by GPC and 1H NMR. Mesoporous silicas with large and tunable accessible pores were successfully synthesized by evaporation-induced self-assembly using block copolymers as templates. The structures of these materials were characterized by BET and TEM. When block copolymers possess similar hydrophobic block length but different block architecture, the pore size of mesoporous silica templated by triblock copolymers is larger than that templated by diblock copolymers. For diblock copolymers, with the increasing of PEO block, the mesoporous size decreases; and with the increasing of PS block, the mesoporous size increases. The increase in the degree of polymerization of the PS block leads to a loss of pore organization. When PS block reaches long enough, the product was not mesoporous silica but silica nanowire. In addition, a method of a preparation of block copolymers vesicles by EISA approach was accidentally found.

A Novel Way to Synthesize Mesoporous Silica Coated on the CNTs with Larger Holes Based on “MCM-41” CNTs@SiO<sub>2</sub>

We present a novel method to synthesize mesoporous nickel siliceous coated on CNTs with larger hole based on the mesoporous silica coated on CNTs, the pore size of mesoporous silica coated on CNTs was enlarged to 7.8 nm from 2.72 nm. Compared to others’ work, our method is low cost, simple and high efficiency. And more importantly, this method shows great potential in applying other type of mesoporous materials such as SBA-15 etc.

On Defining a Simple Empirical Relationship to Predict the Pore Size of Mesoporous Silicas Prepared from PEO-b-PS Diblock Copolymers

Mesoporous silicas with large and accessible pores have been successfully synthesized using laboratory-made poly(ethylene oxide)-b-polystyrene (PEO-b-PS) copolymers as templates. The PEO-b-PS copolymers were synthesized using living/controlled radical polymerization. The porous structure (mesopore size, size distribution, and microporous volume) was characterized using small-angle X-ray scattering, electron transmission microscopy, and nitrogen sorption measurements. In this study, we have investigated the dependence of the mesoporosity on both the PS and PEO blocks length using two series of PEO-b-PS copolymers with a constant degree of polymerization of the PEO block for each series (NPEO = 114 and NPEO = 232). It was found that the mesopore size increases and the microporous volume decreases as the PS block length (NPS) increases. The PEO block participates to both the micropore and mesopore formation. By fitting these experimental data, a simple empirical relationship between the pore radius and the length of the both PS block (NPS) and PEO block (NPEO) is found RP (nm) = 0.36.NPEO0.19NPS0.5. This relationship is in agreement for both low- and high-molecular-weight copolymers and can be easily be used to fine-tune the mesopore size of silica materials, in a large range (from 4 to 22 nm), when using PEO-b-PS copolymers as templates. Furthermore, the influence of the synthesis temperature (between 25 and 60 °C) on the porous structure was also investigated and it was found that by increasing the synthesis temperature, the mesopore diameters remain relatively constant; however, the pore entrances increase in size, leading to more open pore structures.

Control of pore size in mesoporous silica templated by a multiarm hyperbranched copolyether in water and cosolvent

Worm-like mesoporous silica with various pore sizes has been prepared successfully templated by a multiarm hyperbranched copolyether (PEHO- star-PPO). The pore size of the resultant mesoporous materials can be controlled easily through adjusting the ratio of water to cosolvent. As the molar ratio of water to ethanol changes from 0.02 to 0.73, the pore size of the calcined materials can be enlarged from 32 to 94 Å, attributing to the aggregation behavior of the multiarm hyperbranched polymer in different systems. Moreover, the pore size of the obtained mesoporous silica can be also adjusted by selecting different kinds of cosolvent. The polarity and solubility of cosolvents are believed to be two important factors in affecting the pore size. Thus, a facile and efficient method for controlling the pore size of mesoporous silica has been developed by using hyperbranched polymers as templates.

Improvement in Photocyclization Efficiency of Diaryl Ethenes by Adjusting the Pore Size of Mesoporous Silica

Photochromie im Nanoraum: Diarylethene (DE) gehen in den Poren von MCM-41-Materialien, die mit organischen Gruppen modifiziert wurden, reversible photochrome Reaktionen ein. Die Effizienz der Photocyclisierung steigt um das Vierfache, wenn der Porendurchmesser soweit verkleinert wird, dass er ungefähr der Molekülgröße entspricht. Demnach verändert der Einschluss in der Pore die Konformation des offenen Isomers (siehe Bild).

Improvement in Photocyclization Efficiency of Diaryl Ethenes by Adjusting the Pore Size of Mesoporous Silica

Photochromism in nanospace: Reversible photochromic reaction of a diaryl ethene (DE) takes place in the pores of MCM-41s modified with organic groups. The efficiency of the photocyclization reaction increases fourfold when the diameter of the pore is decreased to approximately the same size of the DE, which indicates that the conformation of the open-ring isomer is regulated in the confines of the pore (see picture).

Drug Loaded Porous Hydroxyapatite and Its In Vitro Release

Porous hydroxyapatite coated with mesoporous silica has been utilized as the matrix for controlled drug delivery. TEM observation confirms the pore size of mesoporous silica scatters about 50 Å. Porous hydroxyapatite was coated with mesoporous silica via sol-gel process. Ibuprofen and was loaded into the pores of mesoporous silica, and controlled release profiles were studied by soaking the samples in a simulated body fluid using a UV-VIS spectrophotometer.

Control of Pore Size in Mesoporous Silica by Incremental Surface Modification Using Tetramethyl Orthosilicate

Abstract The pore size of mesoporous silica is precisely controlled by repeated surface treatment with tetramethyl orthosilicate (TMOS) and water. This surface treatment produces a silica monolayer by reaction between surface hydroxy groups and TMOS, and successive water treatment regenerates the surface silanol groups ready for further TMOS modification. This treatment method reduces the pore size of SBA-15 mesoporous silica incrementally by ca. 0.5 nm per treatment step, while preserving the original hexagonal pore structure.