Mesoporous Silica Xerogel Research Articles

Transforming volcanic mud into mesoporous silica xerogel and its performance for efficient humidity adsorption

A high humidity level in the environment leads to the development of desiccants as hygroscopic material for adsorbing water vapor. Mesoporous silica xerogel, one of the solid adsorbents used for humidity adsorption, was synthesized from hazardous waste of volcanic mud via sol–gel methods by controlling the pH of the solution. The disordered amorphous silica was obtained, with the properties varied depending on the pH of the solution. Silica xerogel obtained at pH 8 exhibits the highest specific surface area of 576.527 m2g−1 and mesoporous surface area of 527.842 m2g−1. It also has the highest adsorption capacity of 18.90% gw/gads determined from the conventional method and 22.14% gw/gads from TG analysis. The performance for humidity adsorption exceeds the commercial silica with an efficiency of 0.9–7% gw/gads. This result indicates that the potential SiO2 extracted from volcanic mud can be commercialized as desiccants for humidity adsorption.

Biomimetic aminoated mesoporous silica xerogel exhibiting chiral surface topology for delivery insoluble drug with multiple-controlled manners and improved oral adsorption

Driven by the clinical demand on improving the oral bioavailability and reducing the side effects of insoluble drug, aminoated mesoporous silica xerogel (named L/d-BPEIN-MSX) with chiral surface topology was constructed through a facile, economical, and biomimetic strategy within 2 min, and served as the carrier of indomethacin (IMC). In the synthetic process, L/d-tartaric acid (L/d-TA) self-assembled with branched polyethyleneimine (BPEI) to endow chirality and synergistic promoted silica deposition, while 3-aminopropyl triethoxysilane (APTES) polycondensated with the silica source to form aminoated mesostructure. By premixed strategy, IMC can be in situ loaded into L/d-BPEIN-MSX with high efficiency, which then became active in circular dichroism (CD) spectra owing to induced chirality. Noteworthy, IMC-L/d-BPEIN-MSX significantly improved the release rate of IMC with multiple controlled release manners. That is, d-BPEIN-MSX had favorable drug release behavior which could respond to the chiral stimuli, whereas l-BPEIN-MSX exhibited advantageous chiral surface topology that was beneficial for bio-processes related to oral adsorption. Undoubtedly, they increased the bioavailability of IMC to 8–9 times, displayed good anti-inflammatory effect, and reduced the gastrointestinal irritation of IMC. In addition, L/d-BPEIN-MSX had low toxicity and irritation, and was proven to be biodegradable and biocompatible, which could meet the requirement for biomedical applications.

Synthesis of Mesoporous Silica Xerogel from Geothermal Sludge using Sulfuric Acid as Gelation Agent

A large amount of sludge is produced by the geothermal brine at the Dieng Geothermal power plant, exceeding 165 tons per month. This sludge is generally not utilized, except for use in landfills. The precipitate (sludge) is primarily composed of silica. The aim of this research is to synthesis mesoporous silica (SiO2) xerogel from geothermal sludge (GS) and to investigate the effects of pH as an effort to elevate the economic value of sludge through alkaline extraction followed by acidification. SiO2 xerogel was prepared by extracting the GS to become sodium silicate (Na2SiO3) assisted by a base NaOH and precipitated using H2SO4 as a gelation agent. The FTIR analysis of the SiO2 xerogel showed a group of silanol (Si-OH) and siloxane (Si-O-Si). The XRD analysis indicated that SiO2 xerogel was amorphous. Furthermore, it was observed from nitrogen absorption-desorption using BET (Breneur-Emmet-Teller) method test that decreased pH tends to the specific surface area increase, and the pore size becomes decrease. The largest specific surface area observed at SiO2 xerogel prepared at pH of 5.5 reached 400.10 m2/g with a pore size of 4.5 nm. The pore sized for all cases was in the range of 4 ~12 nm, indicating that the SiO2 xerogels were mesoporous. Pore size of the as-prepared silica affected the thermal stability property of the sample.

Biomimetic micellar mesoporous silica xerogel performs superior nitrendipine dissolution, systemic stability and cellular transmembrane transport.

To combine the advantages of micelles and biomimetic silica materials, biomimetic micellar mesoporous silica xerogel (BM-SX) was initially established, biomimetic silica xerogel (B-SX) was also studied as control and nitrendipine (NDP) was taken as model drug. The content mainly focused on drug dissolution, systemic stability and cellular transmembrane transport of NDP loaded B-SX and NDP loaded BM-SX. With extra mesopores formed due to HPMC E50 micelles, the mean pore diameter, surface area and pore volume of BM-SX were all larger than B-SX. After loading NDP into the two carriers, crystal NDP changed to amorphous phase, leading to enhanced NDP dissolution. BM-SX presented superior abilities not only for its higher drug dissolution compared to B-SX but also for its capacity in remaining high amorphous drug phase and therefore no drug dissolution reduction can be observed. The dynamic contact angle result confirmed the strong power of HPMC E50 micelles in maintaining amorphous NDP in the carrier to improve high systemic stability. Both B-SX and BM-SX could increase drug absorption permeability and exert function as drug efflux inhibitor to inhibit the efflux effect of p-gp drug pump and promote NDP absorption and transport, and BM-SX was superior owing to micelles in the system.

Strategy to isolate ionic gold sites on silica surface: Increasing their efficiency as catalyst for the formation of 1,3-diynes

A new strategy is presented to obtain an efficient heterogeneous gold catalyst constituted by isolated ionic gold sites, which is known to be effective in alkyne coupling reaction. The procedure is based on a significant difference between offered gold amount and available adsorbent sites on the support, ensuring the formation of very active isolated gold ion sites. In order to achieve this purpose, mesoporous silica xerogel was grafted with an ionic silsesquioxane containing charged ammonium quaternary group. The modified silica showed 0.25 mmol of cationic sites per gram of material and presented thermal stability up to 200 °C. This material was applied as support for immobilization of Au(III) ions as square planar AuCl4− complex. The gold amount offered was just 12 % of the exchangeable capacity. The catalyst was efficiently applied in the cross coupling reactions, in which only 0.22 mol% was applied to obtain symmetric and non-symmetric 1,3-diynes.

How biomimetic amino modified mesoporous silica xerogel regulates loading and in vitro sustained delivery of levorotary ofloxacin.

The purpose of this study was to facilely develop biomimetic amino modified mesoporous silica xerogel (AMSX) and study how AMSX regulated loading and in vitro sustained delivery of carboxyl-containing drug levorotary ofloxacin (LOFL). Characteristics of AMSX, including morphology, porous structure, elements and crystalline state were investigated and pharmaceutical performance of AMSX for the delivery of LOFL was studied. The result showed that AMSX was accumulational spherical nanoparticles with mesoporous structure. Hydrogen bonding force was formed between carboxylic groups of LOFL and amino groups grafted on the surface of AMSX. Furthermore, a three-level three-factorial Box-Behnken experimental design was applied to optimize the amount of major agent for synthesizing AMSX with expected drug loading capacity and also to figure out how AMSX regulated in vitro delivery of LOFL. It is believed that the present work will provide novel insights for designing mesoporous silica as drug carrier and favored the development of sustained release system.

A novel silica xerogel synthesized from volcanic tuff as an adsorbent for high‐efficient removal of methylene blue: parameter optimization using Taguchi experimental design

AbstractBACKGROUNDIn this study, silica xerogel was synthesized using volcanic tuff instead of expensive silica precursors at ambient pressure drying. The mesoporous silica xerogel with unique structural and textural properties was evaluated as an adsorbent for methylene blue (MB) removal from aqueous solution. Taguchi method was applied to optimize controllable factors (contact time, initial MB concentration, silica xerogel dose, temperature and pH) for MB removal.RESULTSThe temperature was determined as the most significant factor with percentage contribution of 54.50%. MB removal efficiency was 96.18% at optimum conditions (contact time: 60 min, initial MB concentration: 20 ppm, silica xerogel dose: 0.0016 g mL−1, temperature: 40 °C, pH: 5). The experimental data fitted with the Langmuir isotherm, yielding a maximum adsorption capacity of 51.967 mg g−1. MB desorption process was performed depending on eluent concentration and contact time. Maximum desorption efficiency was specified as 88% using 1 M hydrochloric acid for 4 h. The silica xerogel was easily recycled with retaining approximately 70% of adsorption efficiency after five cycles.CONCLUSIONIn the light of the promising results, the silica xerogel can be used as an effective adsorbent in many environmental applications. © 2019 Society of Chemical Industry

Amine activated diatom xerogel hybrid material for efficient removal of hazardous dye

The effective removal of organic pollutants from aqueous media is still an eminent challenge. In the present work, naturally available diatomaceous earth (DE) particles was surface modified with mesoporous silica xerogel denotes as diatom xerogel material. Subsequently amine functionality has been successfully introduced on diatom xerogel (DXEA) for the efficient removal of hazardous dye, Eriochrome Black T (EBT). The adsorbents before and after EBT adsorption were characterized using various techniques such as XRD, FE-SEM, FTIR and BET. The adsorption process was conducted by varying many parameters such as pH, dosage, initial concentration of dye and time. The designed adsorbent, DXEA showed increased removal efficiency (∼99 %) in comparison with neat DE (∼58 %) due to the presence of amine functional group, which favours the rapid adsorption of EBT. This study showed that adsorbent DXEA was adequate to remove 50 mg/L and 100 mg/L of aqueous EBT in 5 and 60 min of contact time respectively. The maximum dye adsorption capacity of DXEA was found to be ∼62 mg/g whereas, for DE it was ∼56 mg/g. The dye adsorption kinetics of EBT onto both the DXEA and the DE follow the pseudo-second-order model. Also, DXEA was used for selective removal of EBT in the presence of other dyes and recycle studies were discussed. These studies showed that DXEA is a promising material for EBT removal by adsorption in real sample.

Comparison of bare and amino modified mesoporous silica@poly(ethyleneimine)s xerogel as indomethacin carrier: Superiority of amino modification

The purpose of this study was to facilely develop amino modified mesoporous silica xerogel synthesized using biomimetic method (B-AMSX) and to investigate its potential ability to be a drug carrier for loading poorly water-soluble drug indomethacin (IMC). For comparison, mesoporous silica xerogel without amino modification (B-MSX) was also synthesized using the same method. The changes of characteristics before and after IMC loading were systemically studied using fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS) and nitrogen adsorption/desorption analysis. The results showed that B-MSX and B-AMSX were spherical nanoparticles with mesoporous structure. Compared with B-MSX, IMC loading capacity of B-AMSX was higher because more drug molecules can be loaded through stronger hydrogen bonding force. DSC and SAXS analysis confirmed the amorphous state of IMC after being loaded into B-MSX and B-AMSX. The in vitro drug release study revealed that B-MSX and B-AMSX improved IMC release significantly, and B-AMSX released IMC a little faster than B-MSX because of larger pore diameter of IMC-AMSX. B-MSX and B-AMSX degraded gradually in dissolution medium evidenced by color reaction and absorbance value, and B-AMSX degraded slower than B-MSX due to amino modification. In conclusion, B-AMSX with superiority of higher loading capacity and enhanced dissolution release can be considered to be a good candidate as drug carrier for IMC.

Mesoporous silica xerogel modified with bridged ionic silsesquioxane used to immobilize copper tetrasulfonated phthalocyanine applied to electrochemical determination of dopamine

Silica xerogel was modified with an ionic silsesquioxane containing the cationic 1,4-diazoniabicyclo[2.2.2]octane bridged group and it was used as matrix for immobilization of copper tetrasulfonated phthalocyanine, resulting in Si/Db/CuTsPc material. This material was characterized by ultraviolet-visible and infrared spectroscopy, elemental and thermogravimetric analyses, nitrogen adsorption-desorption isotherms, and scanning electron microscopy. The Si/Db/CuTsPc material was used to develop a carbon paste electrode for dopamine determination. The electrochemical behavior of dopamine was evaluated by cyclic voltammetry and chronoamperometry. The optimal experimental conditions were determined (pH = 4.5 and oxygen atmosphere) using a 0.1 mol L−1 phosphate buffer solution. The carbon paste electrode modified with the Si/Db/CuTsPc material shows a linear response for current intensity with the dopamine concentration in the range of 0.010 to 0.107 mmol L−1. The detection limit was 0.42 μmol L−1, and the sensitivity was 7.15 μA (mmol L−1)−1, making the system promising to be applied as electrochemical sensor for dopamine.

High Fluorescence of Thioflavin T Confined in Mesoporous Silica Xerogels

Trapping of organic molecules and dyes within nanoporous matrices is of great interest for the potential creation of new materials with tailored features and, thus, different possible applications ranging from nanomedicine to material science. The understanding of the physical basis of entrapment and the spectral properties of the guest molecules within the host matrix is an essential prerequisite for the design and control of the properties of these materials. In this work, we show that a mesoporous silica xerogel can efficiently trap the dye thioflavin T (ThT, a molecule used as a marker of amyloid fibrils and with potential drug benefits), sequestering it from an aqueous solution and producing a highly fluorescent material with a ThT quantum yield 1500 times greater than that of the free molecule. The study of spectroscopical properties of this system and the comparison with fluorescence of an uncharged analogue of ThT give indications about the mechanism responsible for the fluorescence switching-on of ThT molecules during their uptaking into the glass. Diffusion and nanocapillarity are responsible for ThT absorption, whereas electrostatic interaction between positive ThT molecules and negative dangling ≡SiO groups covering the pore surfaces causes the immobilization of ThT molecules inside the pores and the enhancement of its fluorescence, in line with the molecular rotor model proposed for this dye. We also show that entrapment efficiency and kinetics can be tuned by varying the electrostatic properties of the dye and/or the matrix.

The Degradation and BMP Release Dynamics of Silica-Based Xerogels Modified by Adding Calcium and Magnesium or Sintering Process

A new mesoporous silica xerogel used as biodegradable material was synthesized by improved sol-gel methods. The xerogel’s degradation character and property of releasing character for bone morphological protein (BMP)were modified by adding calcium (Ca) and phosphor (P) elements into pure silica xerogel, and uesing sintering processes, as well as adding magnesium (Mg) into silica xerogel. The differential thermal and thermogravimetric analysis (DTA-TG), X-Ray diffraction analysis(XRD), Fourier infrared spectrum analysis (FITR), N2 adsorption-desorption analysis, Scanning electron microscope(SEM) and Transmitting electron microscope (TEM) observation were used to measure the thermal effects, crystalline state, pore diameter and specific surface area, surface morphology and inner structure of the xerogels. The xerogel’s degradability and BMP release were studied by simulated body fluid (SBF) immersion. The results indicated that the synthesized xerogels were mesoporous structure with pore diameter around 3 nm and the big specific surface area about 1000 m2/g.They were non crystall with hydroxyl and micro-molecular silica-oxygen groups. Xerogels dried at low sintering temperature degraded completely in 42 days in bursting manner and degraded in linear curves with sintering temperature increased as well as adding calcium and magnesium into xerogels. The BMP release behaviour from the Mg-xerogel dried naturally was in controlled manner.

PALM OIL BASED FATTY ALCOHOLS TEMPLATED MESOPOROUS SILICA AND SILICA SPHERES

Mesoporous silica xerogels with wormhole-like pore structure were successfully synthesized using a series of surfactantless oil-in-water emulsion at room temperature. The surfactantless emulsion systems consisted of palm-oil derived fatty alcohols having several carbon chain lengths to act as mesoporous templates in place of commercial surfactants in a direct base–acid catalyzed sol–gel method. This method allowed direct decomposition of fatty alcohols in situ during calcination process to create mesoporosity in the materials. The mesoporous silica xerogels exhibited relatively high surface area at ca. 505 m2/g and pore sizes at ca. 8 nm to 13 nm as the carbon chain lengths were varied. The pore size obtained in this study was larger than the conventional MCM-41 materials (at ca. 2 nm). The mesopores were generated from the interstices of the primary particles (framework-confined porosity) and secondary particles (textural porosity). Furthermore, by changing the co-solvent amount and oil/water ratio, surfactantless oil-in-water microemulsions were obtained. These microemulsions were useful in the synthesis of monodispersed silica spheres. The size of the silica spheres could be controlled at two different size clusters, ca. 50–200 nm and at ca. 500 nm.

Stimulated osteoblastic proliferation by mesoporous silica xerogel with high specific surface area

Specific surface area is a critical parameter of mesoporous silica-based biomaterials, however, little is known about its effects on osteoblast responses in vitro. In the present study, mesoporous silica xerogels (MSXs) with different surface area (401, 647 and 810 m(2)/g, respectively) were synthesized by a sol-gel process. Surface silanol contents decreased with the increase of surface area with which protein adsorption capability positively correlated. And the apatite-like surface seemed to form faster on MSXs with higher surface area determined by XRD analysis. Using MG63 osteoblast-like cells as models, it was found that cell proliferations were promoted on MSXs with higher surface area, based on the premise that the effects of Si released from materials on osteoblast viability were excluded by real-time Transwell(®) assay. RT-PCR results indicated cell adhesion-related integrin subunits α5 were up-regulated by higher surface area at day 1, which was further confirmed by flow cytometry analysis. The data suggest that increasing SSA of MSXs could promote surface cellular affinity by adsorbing serum proteins and accelerating apatite-like layer formation, which results in promoted osteoblastic proliferation via integrin subunit α5 at initial adhesion stage. Regulating SSA, an effective approach in designing mesoporous silica-based materials, provides an alternative method to obtain desirable tissue-response in bone regeneration and drug-delivery system.

Molecular imprinted macroporous chitosan coated mesoporous silica xerogels for hemorrhage control

Efficacious hemostatic agents have significant potential for use in rapid exsanguinating hemorrhage control by emergency medical technician or military medic nowadays. Unfortunately, the topical hemostats currently available in market still have various disadvantages. In this study, a series of macroporous chitosan coated mesoporous silica xerogel beads (CSSX) with good biocompatibility were developed. They consisted of mesoporous silica xerogel cores and chitosan layers with macroporous structure by using modified sol-gel process and PEG molecular imprinting technique. The textural properties of the CSSX beads were optimized by in vitro and in vivo evaluation for promoting blood clotting and the results indicated that the prepared CSSX beads can significantly accelerate the contact activation pathway of coagulation cascade and produce desirable hemostasis, with the best efficiency from the CSSX prepared with 2% chitosan and 5% PEG. Furthermore, these CSSX beads were observed to create no exothermic reaction and the subsequential tissue thermal injury by histological examination, and exhibited no obvious cytotoxicity even after 7 days. The results of the present study forward CSSX bead as a safe hemostatic system and present a platform for further optimization studies of materials with enhanced hemostatic capabilities for specific injury types.

Chemical characteristics and hemostatic performances of ordered mesoporous calcium-doped silica xerogels

A well-ordered mesoporous silicon dioxide calcium-doped xerogel (m-SXC) was synthesized by a sol–gel process. The in vitro bioactivity of the m-SXC was investigated by analyzing the apatite-forming ability in simulated body fluid (SBF) and MC3T3-E1 cell culture with materials, and the hemostatic activity of the m-SXC was determined by measuring the activated partial thromboplastin time (APTT) and prothrombin time (PT) in vitro. The results suggested that the m-SXC exhibited excellent in vitro bioactivity, with surface apatite formation for the m-SXC containing 10 w% Ca (m-SXC10) exceeding that containing 5 w% Ca (n-SXC5) and 0% Ca (m-SXC0) at 7 days, and the cell response test (MTT assay) and cell morphology observation demonstrated that these materials were biocompatible with no obvious negative effects on cellular viability. Moreover, the m-SXC with a high surface area (m-SXC0: 489.9 m2 g−1, m-SXC5: 466.5 m2 g−1, m-SXC10: 438.1 m2 g−1) possessed good hemostatic property because it could absorb a large amount of water from the blood, which could concentrate the components of blood and reduce the clotting time. Furthermore, the addition of calcium in the m-SXC had significant effects on the clotting time, in which the APTT (m-SXC0: 8 s, m-SXC5: 7 s, m-SXC10: 6 s, respectively) and PT (m-SXC0: 16 s, m-SXC5: 11 s, m-SXC10: 10 s, respectively) were shortened with the increase of Ca amounts in the m-SXC, indicating that incorporation of Ca in the m-SXC could improve its hemostatic activity.

The bio-functional role of calcium in mesoporous silica xerogels on the responses of osteoblasts in vitro

Mesoporous silica xerogels with various amount of calcium (0, 5, 10 and 15%, named m-SXC0, m-SXC5, m-SXC10 and m-SXC15, respectively) were synthesized by template sol-gel methods, and cell responses to m-SXCs were studied using murine pre-osteoblast MC3T3-E1 in vitro. The results showed that cell morphology was not affected by m-SXCs indicating good biocompatibility. Furthermore, cell proliferation ratio on the m-SXCs increased over time, among which m-SXC10 was highest. NO production obviously rose with the increase of Ca content in m-SXCs. ALP activity and PGE(2) level on m-SXC5 significantly improved compared with m-SXC0 while decreased with the increase of Ca content for m-SXC10 and m-SXC15. No obvious discrepancy on osteopontin mRNA expressions was observed among m-SXCs. The collagen I and osteocalcin mRNA expression on m-SXC5 were up-regulated, while decreased on m-SXC15 evidently. The phosphorylation level of ERK 1/2 for the m-SXC10 was highest after 7 days. In conclusion, calcium in m-SXCs plays an important role in osteoblast activity, which indicates mesoporous silica xerogel containing appropriate calcium could stimulate osteoblast proliferation, differentiation, gene expression via the activation of ERK 1/2 signaling pathway, and shows great prospects in bone regeneration field using as a drug controlled release filler.

Antibacterial properties of mesoporous copper-doped silica xerogels

Mesoporous copper-doped silica xerogels (m-SXCu) with antibacterial properties were synthesized by a sol–gel process, and the morphology, structure and composition of m-SXCu were characterized. The results show that m-SXCu5 with a high surface area of 463.1 m2 g−1 have a mesoporous structure with a pore size of about 2 nm. The addition of Cu from 1 to 5 wt% to m-SXCu had a slight effect on the surface area and a not-so-obvious effect on the mesoporous size of m-SXCu. Cu ions can be released from m-SXCu into the simulated body fluid, and the release rate depends significantly on their number. The m-SXCu possessed good antibacterial activity against both E. coli and S. aureus, in which the antibacterial rate reached 99% for m-SXCu5 at 1 h while reaching 99% for all m-SXCu at 24 h. The antibacterial rate was improved with the increase of the amount of Cu, indicating that addition of Cu ions to m-SX enhanced its antibacterial activity.

A facile method for production of high-purity silica xerogels from bagasse ash

In this paper, we systematically report the synthesis of mesoporous silica xerogels in high purity from bagasse ash. The bagasse ash was chosen as the raw material due to its availability and low-price, and environmental considerations also were important. Silica was extracted as sodium silicate from bagasse ash using NaOH solution. The sodium silicate was then reacted with HCl to produce silica gel. To produce high-purity silica xerogels, three different purification methods were investigated, i.e., acid treatment, ion exchange treatment, and washing with de-mineralized water. We were able to produce high-purity silica (>99wt.%) by washing the produced gels with either de-mineralized water or with ion exchange resin. The specific surface area of the prepared silica xerogels ranged from 69 to 152m2g−1 and the pore volume ranged from 0.059 to 0.137cm3g−1. The pore radii were 3.2–3.4nm, which indicated that the silica xerogels was mesoporous. From the adsorption characterization, it was obvious that adsorptive capacity was better for high-purity silica xerogels compared with low-purity. The maximum adsorption capacity by high-purity silica xerogel was 0.18g-H2O/g-SiO2. Finally, we demonstrate the potential of bagasse ash for mesoporous silica production with its excellent adsorptive capacity that makes it beneficial as an environmental solution.

Engineering Silica Particles as Oral Drug Delivery Vehicles

Porous silica particles are emerging as complementary systems to polyester microspheres for the encapsulation and controlled delivery of small-organic drugs. Their recent application in pharmaceutics is strengthened by well-established characterization and synthetic routes from the chemical engineering sciences. Silica is an interesting scaffold material for the encapsulation of organic molecules. It can be formed into hierarchical structures over a wide range of length scales and interconnectivities. Encapsulation can therefore be tailored not only to the drug but the desired release properties. In addition to surfactant-templating of hierarchical silica structures, polypeptides from marine organisms may offer biological routes to novel silica materials. Silica sol-gels have also been evaluated as delivery vehicles, particularly with regard to generating hybrid systems with mesoporous silica or composite xerogels. This review will first focus on the detailed characterisation of pore size and structure of mesoporous silica with regards water penetration and drug diffusion. We then describe the pharmaceutical applications of silica materials with regard to improving oral bioavailability, multiparticulate systems for gastroretention or sustained release, composite xerogels and in vivo biocompatibility.