Silica Gel Matrix Research Articles

Effects of Carbon Phase Deposition in Silica Gel Pores on NO2 Reactive Adsorption at Ambient Conditions on Carbon/Silica Composites

Silica-carbon composite samples containing various carbon contents deposited within a silica gel matrix were synthesized. The composites were evaluated as nitrogen dioxide adsorbents at ambient conditions in either wet (70% RH) or dry air streams. The surface chemistry and textural features of the initial and exposed samples were characterized using nitrogen adsorption, potentiometric titration, thermal analysis, and FT-IR. The deposition of the carbon phase significantly increased the amount of NO2 adsorbed in comparison with that adsorbed on the silica gel. With an increase in the amount of carbon an increase in the performance was found. The positive effect was especially noticed when water was present in the system. An oxidation of the surface and release of NO was observed. The acidification/oxidation of the surface is more pronounced in moist conditions, and it is linked to the formation of nitric acid adsorbed in the pore system. The carbon phase besides providing some level of hydrophobicity also brings phenolic groups to the system, on which immobilization of NO2 takes place via nitrification reactions.

Silica sol-gel encapsulation of cyanobacteria: lessons for academic and applied research

Cyanobacteria inhabit nearly every ecosystem on earth, play a vital role in nutrient cycling, and are useful as model organisms for fundamental research in photosynthesis and carbon and nitrogen fixation. In addition, they are important for several established biotechnologies for producing food additives, nutritional and pharmaceutical compounds, and pigments, as well as emerging biotechnologies for biofuels and other products. Encapsulation of living cyanobacteria into a porous silica gel matrix is a recent approach that may dramatically improve the efficiency of certain production processes by retaining the biomass within the reactor and modifying cellular metabolism in helpful ways. Although encapsulation has been explored empirically in the last two decades for a variety of cell types, many challenges remain to achieving optimal encapsulation of cyanobacteria in silica gel. Recent evidence with Synechocystis sp. PCC 6803, for example, suggests that several unknown or uncharacterized proteins are dramatically upregulated as a result of encapsulation. Also, additives commonly used to ease stresses of encapsulating living cells, such as glycerol, have detrimental impacts on photosynthesis in cyanobacteria. This mini-review is intended to address the current status of research on silica sol-gel encapsulation of cyanobacteria and research areas that may further the development of this approach for biotechnology applications.

A protected annealing process for the production of high quality colloidal oxidenanoparticles with optimized physical properties

Colloidal synthesis of inorganic materials is usually achieved in solvents under milder conditions of temperature than those usually used for the preparation of bulk compounds. As commonly shown on oxide nanoparticles with sizes of more than typically 20 nm, this leads to particles exhibiting an altered crystallinity with the presence of more or less extended defects that may impact the physical properties of the particles. Considering that post-annealing treatments on powders of nanoparticles inevitably lead to their sintering (i.e. growth and irreversible aggregation), the influence of these defects has rarely been discussed. For a few years, we have been investigating a post-synthesis process of “protected annealing”. The basic principle relies on thermal treatment of preformed particles that have been previously dispersed into a sol–gel silica matrix. After annealing at temperatures up to 1000 °C, the dissolution of the host matrix allows recovery of a suspension of particles with the same size as the pristine particles and an almost perfect crystallinity. Investigation of the physical properties of these particles permitted us to show their optimized properties, thus discriminating the influence of altered crystallinity compared to small size or surface effects and high surface area. Results are presented in the case of oxide phosphors (YVO4:Eu, YAG:Ce), photocatalytic TiO2 and magnetic γ-Fe2O3 particles. Finally, an extension of the process is shown in the case of a reactive protected annealing, when the thermal treatment is associated with a change of chemical composition of the particles, thus allowing the investigation of systems that are difficult to obtain through conventional colloid chemistry. This latter strategy is presented in the cases of Zn2SiO4:Mn nanophosphors, Co-doped γ-Fe2O3 and N-doped TiO2.

Macromolecular Imprinting by sol-gel silica in the presence of polymer grafted carbon black

A novel method of producing macromolecular imprinted silica particles (MIP) in the presence of polymer grafted carbon black is presented. For the silica gel matrix, tetraethyl orthosilicate (TEOS) was used as the backbone monomer and 3-aminopropyl triethoxysilane (APS) as a functional monomer. Carbon black was added to the sol-gel process, yielding black silica particles. A total of 16 MIP's were synthetized in parallel with four variables in order to better understand and evaluate the role of key reactants in the synthesis procedure. Agglomeration tests were performed with all 16 MIP's in the presence of their template, alongside their respective controls using only PBS. Each of the MIPs were evaluated using an in house built device capable of simultaneously measuring up to four samples for near infrared transmission.

Highly efficient up-conversion and bright white light in RE co-doped KYF4 nanocrystals in sol–gel silica matrix

Transparent nano-glass–ceramics comprising Yb3+, Er3+ and Tm3+ co-doped KYF4 nanocrystals have been developed from sol–gel method. A structural analysis by means of X-ray diffraction confirmed the precipitation of cubic KYF4 nanocrystals into a silica matrix. Visible luminescence has been analyzed as function of treatment temperature of precursor sol–gel glasses. Highly efficient up-conversion emissions have been obtained under 980nm excitation and studied by varying the doping level, processing temperature and pump power. Color tuneability has been quantified in terms of CIE diagram and in particular, a white-balanced overall emission has been achieved for a certain doping level and thermal treatment.

Morphology and dispersion control of titania–silica monolith with macro–meso pore system

Macroporous gels with bicontinuous morphology in micrometer range were prepared in a titania–silica system containing 5 and 7.6 mass % titania using tetraethoxysilane and four kinds of Ti precursors, two titanium alkoxides, titanium chloride and titanium sulfate, under coexistence of poly(ethylene glycol) (PEG) with an average molecular weight of 20,000. In all the systems with different Ti precursors, the addition of PEG induced phase separation, and the macroporous morphology was formed when the transitional structure of phase separation was frozen-in by sol–gel transition of inorganic components. However, we can see large differences in phase separation tendency and Ti dispersion in silica network depending on the Ti precursors used. When titanium alkoxides were added into pure silica sol–gel system, phase separation tendency largely decreased, so that low temperature reaction was necessary for macropore formation. When we used titanium salts, on the other hand, phase separation tendency does not change much from pure silica system. The difference has been tentatively attributed to the difference in the mixing level of Ti in silica network. Although titania tended to aggregate when titanium alkoxides were used as precursors, Ti could be well dispersed in silica gel matrix when acetylacetone was added in the alkoxide system or when titanium salts were used as Ti precursors.

Array-Based Disease Diagnostics Using Lipid/Polydiacetylene Vesicles Encapsulated in a Sol–Gel Matrix

We demonstrate a novel array-based diagnostic platform comprising lipid/polydiacetylene (PDA) vesicles embedded within a transparent silica-gel matrix. The diagnostic scheme is based upon the unique chromatic properties of PDA, which undergoes blue-red transformations induced by interactions with amphiphilic or membrane-active analytes. We show that constructing a gel matrix array hosting PDA vesicles with different lipid compositions and applying to blood plasma obtained from healthy individuals and from patients suffering from disease, respectively, allow distinguishing among the disease conditions through application of a simple machine-learning algorithm, using the colorimetric response of the lipid/PDA/gel matrix as the input. Importantly, the new colorimetric diagnostic approach does not require a priori knowledge on the exact metabolite compositions of the blood plasma, since the concept relies only on identifying statistically significant changes in overall disease-induced chromatic response. The chromatic lipid/PDA/gel array-based "fingerprinting" concept is generic, easy to apply, and could be implemented for varied diagnostic and screening applications.

Sorption of Asphaltenes onto Nanoparticles of Nickel Oxide Supported on Nanoparticulated Silica Gel

The aim of this study is to analyze the effect of temperature and NiO content on the asphaltene uptake by a hybrid nanomaterial composed of nickel oxide nanoparticles supported on a nanoparticulated matrix of silica gel. The silica gel nanoparticles were synthesized by sol–gel method. The silica-supported nanomaterial was prepared by an incipient wetness technique. At constant temperature, adsorption of asphaltenes onto the hybrid nanomaterials increased with increasing its nickel oxide content. Regardless of the asphaltene concentration, asphaltene uptake by the hybrid nanomaterials decreased with increasing temperature. Experimental data on asphaltene sorption isotherms were adequately adjusted by the Freundlich model. The calculated thermodynamic properties for the sorption of asphaltenes onto the nanoparticulated-materials confirmed the spontaneity and exothermic nature of this process.

Ni, Co, Cu, Ni-Co, and Ni-Cu nanoparticles in opal matrices and mesoporous silica gels

NiCo solid solutions and Ni-Cu bimetallic particles have been prepared in opal-matrix nanocomposites by reacting Ni, Co, and Cu double salts and oxides with supercritical (SC) isopropanol. According to X-ray diffraction and transmission electron microscopy data, the nanocomposites have an X-ray amorphous opal matrix and contain crystalline nanoparticles of individual metals, solid solutions, or bimetallic materials of various morphologies in the opal pores. Mesoporous silica gel matrix composites remain X-ray amorphous after treatment in SC alcohols because of the small particle size of the metallic phase, or form solid solutions between Ni and Co silicates. The phase composition of the composites can be controlled by varying experimental conditions.

Characterization of silica particles prepared via urease-catalyzed urea hydrolysis and activity of urease in sol–gel silica matrix

Urease templated precipitation of silica synthesized by sol–gel chemistry produces a composite material allowing high urease activity. This study investigates the structural properties of the composite material that allow for the retention of the urease hydrolysis activity. Scanning (SEM) and transmission (TEM) electron microscopy reveal that the composite has a mesoporous structure composed of closely packed spherical structures ∼20–50nm in diameter. Brunauer–Emmett–Teller (BET) analysis revealed that the surface area and pore volume of the composite prepared under the conditions of 50mM urea and 25°C is relatively high (324m2/g and 1.0cm3/g). These values are equivalent to those of usual mesoporous silica materials synthesized from the self-assembly of triblock copolymers as organic templates. In addition, after encapsulating in a sol–gel silica matrix, urease retained high activity (∼90% of the activity compared with native urease). Our results suggest a new method for synthesizing mesoporous silica materials with highly tunable pore sizes and shapes under mild conditions.

Study on Au nanoparticles, TiO2 nanoclusters, and SiO2 nanoshells coated multi-wall carbon nanotubes/silica gel-glass

Multi-wall carbon nanotubes (MWCNTs) coated with crystalline Au nanoparticles, TiO2 nanoclusters, and amorphous SiO2 nanoshells, to represent conductors, semiconductors, and insulators, respectively, were embedded in transparent silica gel-glass. The coated MWCNT/silica gel-glasses were prepared by the sol–gel technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD), UV/Vis spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy and pore structure measurements were used to investigate the morphology, structure, and texture properties of the coated MWCNT/silica gel-glasses. The hardness and elastic modulus of the silica gel-glasses were characterized using a Nanoindenter and found to depend on the coating materials. Coating the MWCNTs with crystalline Au nanoparticles, TiO2 nanoclusters, and amorphous SiO2 nanoshells leads to an increase in the hardness and elastic modulus, despite the higher specific surface area and pore volume of the coated MWCNT/silica gel-glasses. Consequently, we can conclude that the mechanical properties of coated MWCNT/silica gel-glass might be greatly dependent on the guest MWCNTs rather than the silica gel matrix.

Reactivity of the Antitumor Complex (H2trz)[trans-RuCl4(N2-Htrz)2] in the Presence of DNA Purines within a Fluorinated Silica Matrix

The stability of the antitumor Ru(III) complex (H(2)trz)[trans-RuCl(4)(N(2)-Htrz)(2)] within a tailored sol-gel silica matrix was studied, combining the information from UV-vis and infrared spectroscopies. The matrix was synthesized by a one-step sol-gel process catalyzed by hydrofluoric acid, resulting extremely light, hydrophobic and fluorinated. It is shown that upon encapsulation, the complex undergoes a series of processes, starting with the increase in charge density on the metal center, followed by hydrolysis reactions. The modified complex interacts with the matrix through hydrogen bonds between the aquo/hydroxo ligands and the fluorine atoms. Its interactions with DNA purines (guanine and adenine) were probed within the confined medium defined by the same silica matrix. It is found that coencapsulated guanine does not interfere with the complex aquation processes, while coencapsulated adenine has a delaying effect. No covalent bonding between the complex and the purines is detected, but interactions between the triazole ligands and the imidazole ring of guanine and the imidazole and pyrimidine rings of adenine are observed. Hydrogen bonding is established between the carbonyl and the ammine groups of guanine and the aquo/hydroxo ligands of the complex. For adenine, those interactions involve mostly the N9H of the purine and the NH groups of the triazole ligands, in addition to π-π interactions.

Binary ZrO2-SiO2 xerogels: Synthesis and properties

Binary systems of silica and zirconia xerogels have been prepared by hydrolysis of zirconium(IV) oxychloride in the silica gel matrix. Systems of various composition have been studied by 1H NMR, IR spectroscopy, and thermogravimetry and have been tested in a model process of hydrogen peroxide decomposition. It has been shown that the physicochemical properties of binary oxide systems can be tailored by varying the component ratio.

Water-compatible surface imprinting of ‘baclofen’ on silica surface for selective recognition and detection in aqueous solution

One of the challenges being faced by molecular imprinting fraternity is water-incompatibility. We have addressed this problem in this paper by using water soluble functional monomers for preparing an imprinted polymer network. Here, silica gel was used as the supporting matrix and preparation of molecularly imprinted polymers (MIP) for baclofen (4-amino-3-p-chlorophenylbutyric acid), a skeletal muscle relaxant, was carried out on the surfaces of silica gel. An imprinting network of sulfobetaine polyelectrolyte was prepared in aqueous medium only, which was grafted onto the silica gel matrix using (3-aminopropyl) triethoxy silane as a silane coupling agent and Michael addition reaction for further propagating the polymer grafting procedure. Thus prepared MIPs were characterized by FT-IR spectroscopy and thermogravimetric analysis (TGA), providing evidence for the quality and quantity of grafted films. The binding studies showed that the MIP illustrated good recognition for baclofen as compared to non-imprinted polymers (NIPs). Meanwhile, selectivity experiments demonstrated that MIP had a high affinity to baclofen in the presence of close structural analogues (interferrants). Hence, a facile, specific, selective and water-compatible technique to detect baclofen in the presence of various interferrants is presented here and moreover these materials can be applied in HPLC as well as in capillary electrochromatography (CEC) and in addition they can be applied to different template targets.

Osteogenic capacity of nanocrystalline bone cement in a weight-bearing defect at the ovine tibial metaphysis

The synthetic material Nanobone® (hydroxyapatite nanocrystallines embedded in a porous silica gel matrix) was examined in vivo using a standardized bone defect model in the ovine tibial metaphysis. A standardized 6 × 12 × 24-mm bone defect was created below the articular surface of the medial tibia condyles on both hind legs of 18 adult sheep. The defect on the right side was filled with Nanobone®, while the defect on the contralateral side was left empty. The tibial heads of six sheep were analyzed after 6, 12, and 26 weeks each. The histological and radiological analysis of the defect on the control side did not reveal any bone formation after the total of 26 weeks. In contrast, the microcomputed tomography analysis of the defect filled with Nanobone® showed a 55%, 72%, and 74% volume fraction of structures with bone density after 6, 12, and 26 weeks, respectively. Quantitative histomorphological analysis after 6, and 12 weeks revealed an osteoneogenesis of 22%, and 36%, respectively. Hematoxylin and eosin sections demonstrated multinucleated giant cells on the surface of the biomaterial and resorption lacunae, indicating osteoclastic resorptive activity. Nanobone® appears to be a highly potent bone substitute material with osteoconductive properties in a loaded large animal defect model, supporting the potential use of Nanobone® also in humans.

Fluorometric estimation of surface associated microbial abundance

Surface associated microbes have historically been difficult to accurately and effectively enumerate. In the current study, we propose a rapid and simple method for estimating abundance of surface associated microbial cells by fluorescence of SYBRGreen stained bacteria and in vivo chlorophyll a fluorescence of benthic diatoms in 24 and 48-well microtiter plates. The effectiveness of this high-throughput technique is demonstrated by assessing sensitivity of a clinical strain of Vibrio cholerae, a benthic bacterial isolate and the benthic microalgae Cylindrotheca closterium to three antibiotics — tylosin, lincomycin and ciproflaxacin. We report on the significant linear relationships between spectral chl a fluorescence and cell abundance and between microalgal growth rates derived from cell counts and fluorescence. Additionally, we provide a simplified and improved method for preparation of a silica gel matrix (SGM), which is an ideal plating media for fluorescence applications. These findings indicate that spectrofluorometry is an inexpensive tool for rapidly estimating abundance of surface associated microbiota and can be employed for assessing antibiotic sensitivity.

One-step preparation of CdS nanocrystals supported on thiolated silica-gel matrix and evaluation of photocatalytic performance

Here we report the use of a thiol-functionalized silica-gel to prepare supported CdS nanocrystals by a facile one-step procedure. Upon changing the relative proportion of the matrix we obtained nanocrystals with different average sizes and size distributions, as evidenced by spectroscopic measurements as well as TEM images. Photoluminescence spectra also indicated that the main effect of the matrix is related to the size control since the spectral profiles were found to be strongly dependent on the excitation wavelength. The performance of the material in the photocatalytic degradation of two commercial dyes (methylene blue and rhodamine 6G) has been tested under sunlight radiation, showing promising results. Almost complete decolorization has been observed after 80 min of exposure, with no adsorption on the silica surface.

Structure formation of the mixed gels of zirconium oxyhydrate and silicic acid produced with different sequencing of reagents

The physicochemical characteristics of single and mixed zirconia and silica gels produced by the sol-gel technique at different synthesis pH and sequence of introducing the reagents in the mother liquid are presented. As a result of comparing the data obtained by different research methods, it is found that in the mixed gels, irrespective of the synthesis technique, Si-O-Zr bonds are present. The introduction of a zirconium salt in the mother liquid containing a silicate salt leads to the preferred formation of zirconia gel granules of 20–30 nm in diameter enclosed in the matrix of silica gel. The inverse sequence of introducing the gel-forming components in the reaction mixture promotes the formation of large gel aggregates containing the particles of less that 10 nm and having a high degree of polymerization. Mixed gels of zirconium oxyhydrate and silicic acid have an order higher sorptive capacity for yttrium (III) and calcium cations, as compared to single silica gels and zirconia gels.

Nanocrystalline Pentaerythritoltetranitrate using Sol-Gel Process

The secondary explosives developed with reduced particle size tend to be more insensitive for mechanical stimuli and may release energy with faster rate and gaining more importance nowadays. Therefore, aiming to reduce the particle size of one of the popular explosives, viz., pentaerythritoltetranitrate (PETN) to the nanometer range, a method for preparation of nanocrystalline PETN in the silica (SiO2) gel matrix using sol-gel process has been demonstrated. The PETN-SiO2 xerogels were prepared containing PETN content ranging from 50 per cent to 90 per cent (w/w) and the xerogels were characterised using different techniques. An exothermic peak at around 185 oC preceded by an endotherm in thermal analysis accompanied with weight loss in the temperature range from 150 oC to 200 oC for the xerogel confirmed the presence of PETN in xerogel. Infrared spectra of xerogels showed peaks at around 1285 cm-1 and 1700 cm-1 assigned to O-NO2 and C-O bond representing PETN. Small angle x-ray scattering measurements on xerogels indicated that PETN entered in the pores of silica matrix. Transmission electron microscopy revealed that cystalline PETN with particle size of around 15 nm dispersed in silica xerogel. The specific surface area for the PETN-SiO2 (90:10) xerogels was found to be 75 m2/g. Defence Science Journal, 2011, 61(6), pp.534-539 , DOI:http://dx.doi.org/10.14429/dsj.61.594

Synthesis, structural and optical characterization of nanocrystalline ZnS:Cu embedded in silica matrix

The synthesis of Cu doped ZnS nanoparticles inside the pore of an inorganic silica gel matrix is presented. The synthesized nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). X-ray diffraction pattern reveals the crystalline wurtzite phase of ZnS. The existence of silica gel in modeling morphologies of the nanoparticles was characterized using Fourier transform infrared (FTIR) spectrometer. Thickness of the silica shell was also calculated. UV- absorption spectrum shows the appearance of an absorption peak at 273 nm which confirms the blue shift as compared to that of bulk ZnS. The photoluminescence (PL) emission spectrum of the sample showed a broad band in the range 465–510 nm due to the transition from the conduction band edge of ZnS nanocrystals to the acceptor like t2 state of Cu.