Silica Gel Materials Research Articles

Diffusion Mechanism and Quantitative Measurement of Moisture Transport in Porous Silica Gel Filter Using Dynamic Neutron Radiography Technique

Neutron radiography (NR) can investigate the diffusion mechanisms of moisture transport within the silica gel material. Dynamic neutron radiography (DNR) possesses the possibility to investigate the moisture profile inside the silica gel filter. The technique explained the relationship between moisture movement and time. This study investigated the diffusion mechanisms (absorption and infiltration) of moisture in the silica gel filter by state-of-the-art dynamic neutron radiography (DNR) technique and advanced software. This study also measured the ability of the DNR technique to find out the diffusion coefficients of a silica gel filter material as a function of temperature and time.

Porous filtering media comparison through wet and dry sampling of fixed bed gasification products

The syngas produced by fixed bed gasifiers contains high quantities of particulate and tars. This issue, together with its high temperature, avoids its direct exploitation without a proper cleaning and cooling process. In fact, when the syngas produced by gasification is used in an Internal Combustion engine (IC), the higher the content of tars and particulate, the higher the risk to damage the engine is. If these compounds are not properly removed, the engine may fail to run. A way to avoid engine fails is to intensify the maintenance schedule, but these stops will reduce the system profitability. From a clean syngas does not only follow higher performance of the generator, but also less pollutants in the atmosphere. When is not possible to work on the gasification reactions, the filter plays the most important role in the engine safeguard process. This work is aimed at developing and comparing different porous filters for biomass gasifiers power plants. A drum filter was developed and tested filling it with different filtering media available on the market. As a starting point, the filter was implemented in a Power Pallet 10 kW gasifier produced by the California-based company "ALL Power Labs". The original filter was replaced with different porous biomasses, such as woodchips and corn cobs. Finally, a synthetic zeolites medium was tested and compared with the biological media previously used. The Tar Sampling Protocol (TSP) and a modified "dry" method using the Silica Gel material were applied to evaluate the tars, particulate and water amount in the syngas after the filtration process. Advantages and disadvantages of every filtering media chosen were reported and discussed.

Synthesis of 1-(furan-2-yl) imine Functionalized Silica as a Chelating Sorbent and its Preliminary Use in Metal Ion Adsorption

A new silica gel material covalently bonded with 1-(furan-2-yl) imine (SiNFn) was synthesized and well characterized by elemental analysis, FT-IR, 13C NMR of the solid state, nitrogen adsorption-desorption isotherm, BET surface area, B.J.H. pore sizes, thermogravimetry analyzer (TGA) curves, and scanning electron microscope (SEM). The new chelating surface exhibits good chemical and thermal stability. The synthesized SiNFn was investigated as an adsorbent for the removal of Cu(II), Zn(II), Cd(II), and Pb(II) from aqueous solution. The determination of metal ions was carried out on FAAS using batch method. The adsorption capacity was investigated using kinetics and pH effects. The preliminary results show that the new material presents high adsorption toward copper compared to other described sorbents.

Preparation of perfluoro-1,3-propanedisulfonic acid/Nafion/silica hybrid nanoparticles-thermally stable Nafion in these silica hybrid nanoparticles even after calcination at 800 °C

Perfluoro-1,3-propanedisulfonic acid (PFPS)/Nafion/silica hybrid particles were prepared by the sol–gel reactions of PFPS with tetraethoxysilane and silica nanoparticles in the presence of Nafion under alkaline conditions. These obtained composites exhibited a good dispersibility and stability in not only water but also traditional organic media such as methanol, ethanol, 1,2-dichloroethane, tetrahydrofuran, and dimethyl sulfoxide. Dynamic light scattering measurements and field-emission scanning electron microscopy show that these hybrid particles are nanometer size-controlled fine particles before and even after calcination at 800 °C. Nafion/silica hybrid nanoparticles were also prepared in the absence of PFPS under similar conditions. The weight of original Nafion markedly dropped around 350 °C and decomposed gradually, reaching 0% around 450 °C, and Nafion in the Nafion/silica nanocomposites exhibited a similar weight loss behavior to that of the original one. However, Nafion/PFPS/silica hybrid nanoparticles were found to exhibit no weight loss corresponding to the contents of Nafion and PFPS in the silica gel matrices even after calcination at 800 °C. It was demonstrated that the pH value (3.77 at 25 °C) of Nafion/PFPS/silica hybrid nanoparticles after calcination is smaller than that (5.66 at 25 °C) before calcination, and this hybrid nanoparticles exhibited a higher proton conductivity (5.8 × 10−3 S/cm at 85 °C) than that (4.1 × 10−3 S/cm at 85 °C) before calcination. In addition, Nafion/PFPS/silica hybrid nanoparticles after calcination at 800 °C were applied to the Friedel-Crafts acylation of thiophene with acetic anhydride to give the expected 2-acetylthiophene, of whose yield was similar to that before calcination under similar conditions. These findings suggest that Nafion in PFPS/silica hybrid nanoparticle cores should exhibit a nonflammable characteristic even after calcination at 800 °C to act as an effective acid catalyst. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1869–1877

Preparation and characterisation of ionic liquid confined hybrid porous silica derived from ultrasonic assisted non-hydrolytic sol–gel process

A series of porous silica matrices have been synthesized using ionic liquid (IL) 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) by nonhydrolytic sol–gel method with and without ultrasonic irradiation during gelation. The properties of IL confined silica gel matrices so prepared have been studied using N2-sorption measurement (BET characterisation for determining pore parameters), pulse echo technique (for sound velocity and hence elastic modulus determination), DSC, TGA, FTIR, TEM, SEM and fluorescence techniques. From the N2-sorption measurement, it has been found that BET surface area increased (due to creation of pits on the surface caused by ultrasonic irradiation) while pore volume, average pore size and porosity for ultrasonicated samples decreased. Elastic modulus of the samples containing IL in silica matrices have been found to change with IL content. Glass transition temperature and thermal stability of the IL have been found to increase upon confinement in silica gel matrices. FTIR spectra (experimental as well as computed) show changes in vibrational bands of IL on confinement in pores of silica matrices. Particularly, for ultrasonic assisted samples, the bands related to the imidazolium ring, aliphatic chain and anion SCN of the IL are found to shift upon confinement. Optimised geometry of the IL in porous matrix shows interaction of these groups with the oxygen present on silica pore wall. Fluorescence spectra of samples containing IL shows a shift compared to the bulk IL.

Synthesis and spectroscopic characterization of coumarin 440 dye doped silica gel rods

We have studied silica gel by sol–gel technique for the preparation of new dye-laser materials. Silica gel rods with dimension 50×10mm2 have been prepared successfully without breaking. It shows high transparency and good mechanical strength. Tetraethylorthosilicate (TEOS), formamide in molar ratio (0.25:0.70), 80ml ethanol, 20ml dimethylformamide (DMF), 10ml water, hydrochloric acid as a catalyst (at pH 6), and 0.5ml silicone defoaming agent/surfactant have been used. The synthesis has been carried out in a beaker and the reaction mixture is caste in to the flat bottom glass tubes at 40°C after thoroughly mixing of all the ingredients. These complex reactions, that carried out by hydrolysis and condensation in the silica gel formation show less gel time ∼8–10h at 40°C. Coumarin. 440 dye was doped during the preparation of all the ingredients solution mixture. It has been observed that that the compatibility of Nile blue dyes with silica-gel promise good homogeneity with transparency.In the present study, synthesis, dye doping, FTIR, UV–vis/NIR, and fluorescence have been studied. We have observed that coumarin doped silica gel rods give good fluorescence showing sharp peaks in the visible range. UV–vis spectra of prepared silica gel also indicate the absorption in visible range. Thermal stability of rods were studied by DSC/TGA methods. Eventually it is found that these dye doped silica gel materials explore the possibility for new solid-state dye laser materials.

Chemical constituents of Osmanthus fragrans fruits

By Silica gel, Sephadex LH-20 and other materials for isolation and purification and by physicochemical methods and spectral analysis for structural identification, 23 compounds were isolated and identified from ethyl acetate portion of alcohol extract solution of Osmanthus fragrans fruits. Their structures were identified as nicotinamide (1), D-allitol (2), 5-hydroxymethyl-2-furancarboxaldehyde (3), acetyloleanolic acid (4), benzoic acid (5), ergosta-7,22-dien-3-one (6), beta-sitosterol (7), borreriagenin (8), cerevistero (9), c-veratroylglycol (10), methyl-2-O-beta-glucopyranosylbenzoate (11), 3', 7-dihydroxy-4'-methoxyisoflavon (12), umbelliferone (13), caffeic acid methyl ester (14), oleanolic acid (15), (-) -chicanine (16), dillapiol (17), 3beta,5alpha, 9alpha-trihydroxyergosta-7-22-dien-6-one (18), 2alpha-hydroxy-oleanolic acid (19), betulinic acid (20), betulin (21), 3, 3'-bisdemethylpinoresinol (22), and lupeol (23). All compounds were isolated from the osmanthus fruit for the first time. Except for compounds 4, 7, 15, 19, 23, the rest ones were isolated from the this plant for the first time.

1-(Pyridin-2-yl) Imine Functionalized Silica Gel: Synthesis, Characterization, and Preliminary Use in Metal Ion Extraction

A new silica gel material covalently bonded with 1-(pyridin-2-yl) imine (SiNPn) was synthesized and well characterized by elemental analysis, FT–IR, 13C NMR of the solid state, nitrogen adsorption-desorption isotherm, BET surface area, B.J.H. Pore sizes, thermogravimetry curves (TGA), and scanning electron microscope (SEM). The new chelating surface exhibits good chemical and thermal stability. The adsorption capabilities of this new system towards toxic metal ions (Hg2+, Cd2+, Pb2+, and Zn2+) were investigated using the batch method. The percentage limits of extraction were determined by atomic absorption measurements.

Synthesis and spectroscopic characterization of Nile Blue doped silica gel rods

We have studied silica-gel by sol–gel technique for the preparation of new dye-laser materials. Silica gel rods with dimension 50mm×10mm have been prepared successfully without breaking. It shows high transparency and good mechanical strength. Tetraethylorthosilicate (TEOS), formamide in molar ratio (0.25:0.70), 80ml ethanol, 20ml dimethylformamide (DMF), 10ml water, hydrochloric acid as a catalyst (at pH 6) and 0.5ml silicone defoaming agent/surfactant have been used. The synthesis has been carried out in a beaker and the reaction mixture is caste in to the flat bottom glass tubes at 40°C after thoroughly mixing of all the ingredients. These complex reactions, that carried out by hydrolysis and condensation in the silica gel formation show less gel time ∼8–10h at 40°C. The doping of dye (Nile Blue 690) has been taken during the preparation of all the ingredients solution mixture. It has been observed that the compatibility of Nile Blue dye with silica-gel promise good homogeneity with transparency.In the present study, synthesis, dye doping, FTIR, UV/vis–NIR and fluorescence spectroscopy have been studied. We have observed that Nile Blue doped silica gel rods material give good fluorescence showing sharp peaks in the visible range. UV–vis spectra of prepared silica gel material also indicate the absorption in visible range. Thermal stability of rods was studied by DSC/TGA methods. Eventually it is found that these dye doped silica gel materials explore the possibility for new solid-state dye laser materials.

Synthesis and characterization of bimodal mesoporous silica

Mesoporous silica with controllable bimodal pore size distribution was synthesized with cetyltrimethylammonium bromide (CTAB) as chemical template for small mesopores and silica gel as physical template for large mesopores. The structure of synthesized samples were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption-desorption measurements. The experimental results show that bimodal mesoporous silica consists of small mesopores of about 3 nm and large mesopores of about 45 nm. The small mesopores which were formed on the external surface and pore walls of the silica gel had similar characters with those of MCM-41, while large mesopores were inherited from parent silica gel material. The pore size distribution of the synthesized silica can be adjusted by changing the relative content of TEOS and silica gel or the feeding sequence of silica gel and NH4OH.

Synthesis and Adsorption Behavior of Surface Cu(II) Ion-Imprinted Poly(allylamine)-Silica Gel Material

The Cu(II) ion-imprinted poly(allylamine)-silica material (IIP-PAA/SiO2) was synthesized by surface ion imprinting technique. The effects of main imprinting conditions on its adsorption properties were examined. The results showed that there were a large number of cavities distributed in the thin imprinted PAA layers of IIP-PAA/SiO2, which contributed to improving the affinity and selectivity of the imprinted material. Scatchard analysis showed that there were two kinds of binding sites on its surface and the dissociation constants were 0.056 mmol · L−1 and 0.84 mmol · L−1, respectively. The adsorption results showed that IIP-PAA/SiO2 had excellent recognition ability for Cu(II). Additionally, it had also excellent reusability.

Influence of the use of Aliquat 336 in the immobilization procedure in sol–gel of lipase from Bacillus sp. ITP-001

Aliquat 336, a liquid hydrophobic material, was used at different concentrations (0.5–3.0%, w/v) as an additive in the preparation of encapsulated lipase from Bacillus sp. ITP-001 on sol–gel silica matrices using tetraethoxysilane (TEOS) as the precursor. The resulting hydrophobic matrices and immobilized lipases were characterized with regard to specific surface area (BET method), adsorption–desorption isotherms, pore volume (Vp) and size (dp) by nitrogen adsorption (BJH method) and scanning electron microscopy (SEM). The catalytic activities and the corresponding coupling yields were assayed in the hydrolysis of olive oil. In comparison with pure silica matrices, the immobilization process in the presence of Aliquat 336 decreased the values for specific surface area and increased the values for pore specific volume (Vp) and mean pore diameter (dp). This behavior may be related to the partial adsorption of the enzyme on the external surface of the hydrophobic matrix as indicated by scanning electron microscopy. Aliquat 336 concentrations in the range from 0.5 to 1.5% (w/v) provided immobilized derivatives with higher coupling yields and better substrate affinity. The highest coupling yield (YA = 71%) was obtained for the immobilized enzyme prepared in the presence of 1.5% Aliquat which gave the following morphological properties: specific surface area = 183 m2/g, pore specific volume (Vp) = 0.36 cc/g and mean pore diameter (dp) = 91 Å.

Effect of Ultrasonic Irradiation on Preparation and Properties of Ionogels

Silica‐gel matrices containing ionic liquid (IL) 1‐butyl‐3‐methylimidazolium hexafluorophosphate viz. ionogels have been synthesized using one‐pot nonhydrolytic sol‐gel method and taking tetraethyl orthosilicate (TEOS) as starting precursor. Effect of ultrasonic irradiation on pore parameters of ionogels and vibrational properties of the IL upon confinement in the porous matrix has been investigated. The synthesized gels have been characterized by BET, DSC, TGA, and FTIR. BET analysis shows some changes in the pore parameters due to ultrasonic irradiation. DSC results indicate shift in glass transition temperature upon confinement of the IL. The FTIR spectra show changes in vibrational bands on confinement, particularly, the bands related to the imidazolium ring; aliphatic chain and anion PF6 − of the IL are found to shift upon confinement in porous silica matrix obtained due to ultrasonic irradiation. Ultrasonic irradiation has been found to affect the gelation dynamics and kinetics and pore parameters.

Sol–gel immobilized ovarian follicles: collaboration between two different cell types in hormone production and secretion

The immobilization of mammalian cells within semipermeable matrices which allow retention of viability and functionality has recently attracted research interest. In this study, rat mature ovarian follicles were encapsulated in sol–gel silica matrices for the evaluation of in vitro steroid hormones production. Tetraethoxysilane (TEOS) and tetrakis(2-hydroxyethyl)orthosilicate (THEOS) were evaluated for cell viability, progesterone and estradiol secretion and cell structure conservation. Significant differences were observed between TEOS and THEOS, which allowed encapsulation of follicles for 9 days. Although encapsulated follicles showed lower viability and proliferation rates than control follicles, they were able to secrete estradiol to the same extent as control follicles. This study demonstrated an effective collaboration between two different mammalian cell types in hormone production and secretion when encapsulated in silica matrices. These results could lead to the development of ovarian cell-based hormone delivery systems for the treatment of the symptoms of menopause and the Turner syndrome minimizing adverse effects.

Effect of trimethylsilane pre-capping on monomeric C18 stationary phases made from high-purity type-B silica substrates: Efficiency, retention, and stability

Silica-based monomeric C18 stationary phases are the most widely used in reversed-phase liquid chromatography (RPLC), and methods to improve the efficiency and chemical stability of such phases are always being investigated. Previous work showed that stationary phases made by pre-treating the silica surface with small amounts of trimethylsilane (TMS) reagents prior to C18 silanization showed vast improvements in the chromatographic efficiencies of both polar and non-polar analytes. It was concluded that this "pre-capping" step improved efficiency by selectively neutralizing the most reactive highly acidic silanol sites, producing a more energetically homogenous surface prior to exhaustive derivatization that subsequently yielded a more evenly distributed alkyl bonding arrangement. These previous studies were performed on Type-A silica, an older variety of silica gel material that contains higher levels of metal impurities than the Type-B silica used today. The purpose of the work presented here is to investigate the effects of trimethylsilane pre-capping on monomeric C18 stationary phases made from high-purity Type-B silica substrates. The results show little or no efficiency improvements for non-polar compounds, but a more noticeable improvement was observed for some drug compounds and bases under buffered conditions, with the magnitude of the improved efficiencies correlating with metal impurity content and physical parameters of the silica substrate. The results lend supporting evidence that metal impurities are the primary source of highly acidic silanols, but they also suggest a means to improve efficiencies for compounds of interest. Pre-capping also resulted in a decreased retention due to a decrease in carbon loading. In addition, hydrolytic stability of the stationary phases was investigated at high pH and elevated temperature, with results indicating a slight decrease in hydrolytic stability with increased pre-capping.

A Transparent Sand for Geotechnical Laboratory Modeling

AbstractThe paper describes a new transparent granular soil that can be used for laboratory geotechnical modeling purposes. The transparent soil consists of fused quartz particles in combination with a mixture of two mineral oils as pore fluid. The solid particles and the matching liquid have the same refractive index. The soil has important advantages with respect to transparency, stability, health safety, and utility over glass and silica gel materials. The transparent soil is also inexpensive compared to silica gel-fluid materials that have been used in the past. Conventional laboratory shear box, triaxial compression, and permeability tests were carried out to demonstrate that the mechanical properties and hydraulic permeability of the transparent soil are typical of granular soils with angular particles.

Biphenylene units possessing flammable and nonflammable characteristics in fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica gel matrices after calcination at 800 °C

Two kinds of fluoroalkyl end-capped vinyltrimethoxysilane oligomer [RF-(VM)n-RF] silica nanocomposites containing biphenylene units were prepared by the sol-gel reactions of the corresponding oligomer with biphenylene-bridged ethoxysilanes or 4,4′-biphenol under alkaline conditions, respectively. One is the fluorinated oligomer/silica nanocomposites containing biphenylene units [RF-(VM-SiO2)n–RF/Ar-SiO2], of whose biphenylene units were incorporated into nanocomposite cores through the siloxane bondings, and the other is the fluorinated oligomer/silica nanocomposites containing biphenylene units [RF-(VM-SiO2)n–RF/Biphenol], of whose biphenylene units were directly encapsulated into nanocomposite cores through the sol–gel process. Interestingly, the shape of RF-(VM-SiO2)n–RF/Ar-SiO2 nanocomposites is morphologically controlled cubic particles; although the shape of RF-(VM-SiO2)n–RF/Biphenol nanocomposites is spherically fine particles. Thermogravimetric analyses 2H magic-angle spinning nuclear magnetic resonance, Ultraviolet visible, and fluorescent spectra showed that biphenylene units in RF-(VM-SiO2)n–RF/Ar-SiO2 nanocomposites have a flammable characteristic after calcinations at 800 °C; in contrast, biphenylene units in RF-(VM-SiO2)n–RF/Biphenol nanocomposites have a nonflammable characteristic even after calcination at 800 °C. X-ray photoelectron spectroscopy analyses of these two kinds of fluorinated nanocomposites showed that nonflammable characteristic toward biphenylene units in the silica gel matrices is due to the formation of ammonium hexafluorosilicate during the sol–gel process.

Synthesis and spectroscopic characterization of Kiton Red-620 dye doped silica gel rods

The work was carried out to achieve two different but interdependent objectives; one to synthesis a transparent silica matrix with enough strength and thermal stability, by sol–gel technique, to host an organic dye molecule without quenching its fluorescence and two to find the probability if the said material is suitable for the construction of solid state dye lasers. Crack-free transparent silica gel rods with good mechanical strength, thermal stability and dimensions were successfully synthesized by sol–gel techniques. The rods were doped with Kiton Red-620 dye in different concentration separately. Effect of various synthesis parameters like time, temperature and aging condition was extensively studied to obtain crack-free silica rods doped with dye. Optical properties of prepared rods were studied by FTIR, UV/VIS–NIR and fluorescence spectroscopy. It is observed that Kiton Red-620 dye doped silica gel rods show good fluorescence with sharp peaks in the visible range. Their UV–VIS spectrum indicates the absorption in visible range. Thermal stability of rods were studied by DSC/TGA methods. Eventually it is found that these dye doped silica gel materials explore the possibility for new solid-state dye laser materials.

β-Galactosidase entrapment in silica gel matrices for a more effective treatment of lactose intolerance

► A new pharmaceutical formulation for the treatment of lactose intolerance. ► A reliable and reproducible procedure for the immobilization of β-galactosidase. ► A one-pot entrapment of β-galactosidase in a silica network was optimized. ► The entrapment in a silica matrix can prolong the therapeutic action of lactase. ► The sol–gel technique preserves the stability of the enzyme. In this work we present a preliminary study directed to the realization of a new pharmaceutical formulation for the treatment of lactose intolerance. The main aim of the work is to increase the stability of β-galactosidase in order to prolong its activity in the course of time, thus improving its performance as dietary supplement in the digestion of lactose. We describe a reliable and effective procedure for the immobilization of β-galactosidase in a three-dimensional silica network. A one-step approach was optimized by using the sol–gel method to obtain homogeneous and stable β-galactosidase/silica gel composites; the textural properties of the porous surface were characterized by N 2 physisorption analyses. The activity of β-galactosidase was evaluated in vitro in the hydrolysis of o-nitrophenyl-β- d -galactopyranoside (used instead of lactose) at pH 7.4 and 37 °C, thus reproducing the conditions of the human intestine.

Production of monoclonal antibodies from hybridoma cells immobilized in 3D sol–gel silica matrices

The immobilization of mammalian cells in suitable matrices that can retain their viability and capability to produce certain metabolites has gained attention in recent years. In this work, hybridoma cells were immobilized in sol–gel silica matrices for in vitro production of monoclonal antibodies. For that purpose, different matrices were evaluated in terms of cell viability, antibody diffusion to surrounding media and physicochemical properties of the polymeric material. Tetrakis (2-ethoxyethyl) orthosilicate (THEOS) matrices were found to be the best option for hybridoma immobilization. The concentrations of the silica precursor as well as the number of immobilized cells were also optimized. Three hundred mM of THEOS precursor and 5 × 105 hybridoma cells appear to be the most suitable alternative. Hybridoma cells immobilized in THEOS matrices were able to produce monoclonal antibodies to the same extent as free cells, thus introducing the possibility of using them in the design of bioreactors for large-scale production.