Xerogel Samples Research Articles

Selective Catalytic Reduction of CuO/SiO2 Nano-composites towards NO Reduction in Gas-phase

The xerogel samples were prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) by the sol-gel method. In this investigation, a new molar ratio of H2O/TEOS was determined to be 11.7. Also, the necessary amounts of tri-hydrated copper nitrate and penta-hydrated copper sulfate were added to the solution in such a manner that the concentration of the copper oxide in final solution reach to 10-12 wt %. After ambient drying, the xerogel samples were heated at 400, 600, and 800˚C at a slow heating rate (50°C/h). The structural properties were characterized by Transmission Electron Microscopy (TEM), Brunauer, Emmett and Teller theory for specific surface area determination (BET) and Thermal Program Reduction (TPR) methods at different temperatures. Finally, characterization of nano-composites was studied for NH3 selective catalytic reduction (NH3-SCR) of NO in gas phase. The results were presented the systematic reactivity study of NO reduction by NH3 on dispersed copper oxide nano-composites over silica supports, in order to determine the ability of these materials to convert into harmless species at different temperatures.

Electrochemical behavior of platinum nanoparticles on a carbon xerogel support modified with a [(trifluoromethyl)-benzenesulfonyl]imide electrolyte.

A monoprotic [(trifluoromethyl)benzenesulfonyl]imide (SI) superacid electrolyte was used to covalently modify a mesoporous carbon xerogel (CX) support via reaction of the corresponding trifluoromethyl aryl sulfonimide diazonium zwitterion with the carbon surface. Electrolyte attachment was demonstrated by elemental analysis, acid-base titration, and thermogravimetric analysis. The ion-exchange capacity of the fluoroalkyl-aryl-sulfonimide-grafted carbon xerogel (SI-CX) was ∼0.18 mequiv g(-1), as indicated by acid-base titration. Platinum nanoparticles were deposited onto the SI-grafted carbon xerogel samples by the impregnation and reduction method, and these materials were employed to fabricate polyelectrolyte membrane fuel-cell (PEMFC) electrodes by the decal transfer method. The SI-grafted carbon-xerogel-supported platinum (Pt/SI-CX) was characterized by X-ray diffraction and transmission electron microscopy to determine platinum nanoparticle size and distribution, and the findings are compared with CX-supported platinum catalyst without the grafted SI electrolyte (Pt/CX). Platinum nanoparticle sizes are consistently larger on Pt/SI-CX than on Pt/CX. The electrochemically active surface area (ESA) of platinum catalyst on the Pt/SI-CX and Pt/CX samples was measured with ex situ cyclic voltammetry (CV) using both hydrogen adsorption/desorption and carbon monoxide stripping methods and by in situ CV within membrane electrode assemblies (MEAs). The ESA values for Pt/SI-CX are consistently lower than those for Pt/CX. Some possible reasons for the behavior of samples with and without grafted SI layers and implications for the possible use of SI-grafted carbon layers in PEMFC devices are discussed.

Two-component self-assembly with solvent leading to “wet” and microcrystalline organogel fibers

HypothesisThe microcrystalline fibers of N-(2-aminoethyl)-3α-hydroxy-5β-cholan-24-amide 1 provided a useful model system for studying the complex relationship between morphology, experimental parameters, solvent, and the phenomenon of organogelation. The presence of solvents in the solid forms of 1 along with crystallization behavior suggested solvate formation and polymorphic behavior. ExperimentsForty solid state- and xerogel samples of 1 formed in organic solvents and in three categories of experimental conditions were analyzed with single crystal X-ray diffraction (XRD), powder X-ray diffraction (PXRD), Raman microscopy, and attenuated total reflection Fourier-transform infrared spectroscopy (ATR FTIR). FindingsTwo polymorphs and four isostructural aromatic solvates of 1 were found among some unknown forms in the samples. Single crystal X-ray structures of one polymorph and bromobenzene solvate were obtained, the latter from a xerogel. Multiple crystal forms could be present in a sample, and their contributions to gelation were estimated taking the experimental conditions into account. Gelator 1 could act as a variable component gelator, either alone or in combination with an aromatic solvent. The research brings new insight into the structures of microcrystalline organogel fibers, linking solvate/inclusion crystal formation with microcrystalline fibers of an organogelator for the first time.

Characterization of sol–gel derived CuO/SiO2 nanostructure on temperature

Various concentrations of copper are embedded into silica matrix to xerogels form using copper source—Cu(NO3)2·3H2O. The xerogel samples are prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) with determination of new molar ratio of components by the sol–gel method. CuO/SiO2 nanocomposite is prepared with mixture of components with new molar ratio of H2O/TEOS to be 6.2. In this investigation, the necessary amount of trihydrated copper nitrate is added to the solution in such a manner that the concentration of the copper oxide in final solution reaches 1, 2 and 5 wt% (samples A, B and C, respectively). After ambient drying, the gel samples are heated from 60 to 1,000 °C at a slow heating rate (50 °C/h). Thermal treatment effect is characterized by Fourier transmission infrared, thermal gravimetric analysis, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, surface analysis and thermal program reduction methods at different temperatures.

TiO2 xerogels prepared by modified sol–gel method with ethylenediamine are photoactive for the 4-nitrophenol photoreduction

Amorphous and nanocrystalline TiO2 xerogel semiconductors were synthesized by sol–gel using different hydrolysis pH conditions with and without ethylenediamine as structural modifier. Blue-shift of the optical-electronic properties was observed for the amorphous TiO2 xerogel samples obtained in an alkaline hydrolysis medium. Different textural properties (specific surface area, N2 adsorption–desorption isotherm and pore size distribution) were promoted by the use of ethylenediamine for the amorphous TiO2 xerogel semiconductors, as well as high photocatalytic activity for the reduction of 4-nitrophenol. These results are discussed as function of the textural properties of the samples.

Organic xerogels based on condensation of different m-substituted phenols with formaldehyde

Four samples of organic xerogels have been prepared by polycondensation of different m-substituted phenols (3-aminophenol, m-cresol, phenol and resorcinol) with formaldehyde and subsequent drying. From the set of tested solvents, n-butanol has been chosen as the most suitable one. The reactivity of the m-substituted phenols was ascertained in the order phenol < m-cresol < resorcinol < 3-aminophenol. Phenol and m-cresol did not completely react with formaldehyde during polycondensation reactions. The used type of m-substituted phenol strongly influenced the properties of the final material (the appearance of the organic xerogels, the values of densities and shrinkage after drying, the amount of humidity released during drying and the carbon yield after pyrolysis). The pyrolytic process has been evaluated by TG–MS as three-step process. The first step was characterised as volatile substances loss (n-butanol and water) and mostly CO2 evolution, the second step as evolution of the rest volatiles and the beginning of the carbonisation processes, whilst during the third step merely carbonisation reactions occurred. On the basis of all considered results, 3-aminophenol has been evaluated as the most appropriate precursor for carbon xerogel preparation. It is cheap and the most reactive; it exhibited the lowest values of density, shrinkage and humidity content as well as relatively high carbon yield.

Sol-Gel Synthesis of Novel Silica Hybrid Xerogels: Porous Studies

Hybrid silica xerogel mesoporous composite was synthesized by a low temperature acid catalysed sol-gel route where a natural copolymer; sodium alginate (Na-COOH) together with calcium oxide (CaO) powder were incorporated into silica sol precursor prior to gel formation. For this study, bulk xerogels samples were prepared with the amount of silica precursor and the natural copolymer was fixed meanwhile the loading of calcium oxide was varied at 10 and 20 wt%. The porous properties were studied and the comparison between the hybrid silica and monolith was made. The calcium oxide powder used in this study was prepared from calcium hydroxide, CaOH compound, which been calcined at 1000°C for 3 hours in normal air. Mesoporous structure with small particle size and glassy phase of matrixes are the main features of the prepared xerogels. The presence of sodium alginate and calcium oxide in silica matrixes produces a significant decrease especially in total surface area and porosity volume of the xerogel samples. Monolith silica xerogels exhibits a very large surface area approximately at 600 m2/g compared to the hybrid xerogels which showed 120m2/g and 25m2/g for the respective 10 and 20 wt.% of calcium oxide loading. Nevertheless, only a slight increased in pore size has been observed due to the increased amount of calcium oxide loading.

Bioactivity of xerogels as modulators of osteoclastogenesis mediated by connexin 43

In order to investigate the effects of different degrees of bioactivity of xerogels on connexin 43 (cx43) signaling of osteoclasts a cell culture approach was developed. Cells isolated from peripheral blood mononuclear cells were cultured in combination with the xerogels and were harvested for further investigations on day 1, day 5, and day 10. By means of quantitative PCR increased cx43 mRNA levels and coincident decreasing mRNA levels of the calcium sensing receptor, TRAP, and Cathepsin K were detected with increasing bioactivity of the xerogel samples. Additionally, osteoclasts cultured on tissue culture plates were used to perform principle investigations on cell differentiation by means of transmission electron microscopy, life cell imaging, and immunofluorescence, and the results demonstrated that cx43-signaling could be attributed to migration and fusion of osteoclast precursors. Therefore, the positive correlation of cx43 expression with high xerogel bioactivity was caused by proceeding differentiation of the osteoclasts. Finally, the presently observed pattern of cx43 signaling refers to strong effects regarding bioactivity on cx43-associated cell differentiation of osteoclasts influenced by extracellular calcium ions.

Infrared absorption by molecular gases as a probe of nanoporous silica xerogel and molecule-surface collisions: Low-pressure results

Transmission spectra of gases confined (but not adsorbed) within the pores of a 1.4-cm-thick silica xerogel sample have been recorded between 2.5 and 5 \ensuremath{\mu}m using a high-resolution Fourier transform spectrometer. This was done for pure CO, CO${}_{2}$, N${}_{2}$O, H${}_{2}$O, and CH${}_{4}$ at room temperature and pressures of a few hectopascals. Least-squares fits of measured absorption lines provide the optical-path lengths within the confined (${L}^{C}$) and free (${L}^{F}$) gas inside the absorption cell and the half width at half maximum ${\ensuremath{\Gamma}}^{C}$ of the lines of the confined gases. The values of ${L}^{C}$ and ${L}^{F}$ retrieved using numerous transitions of all studied species are very consistent. Furthermore, ${L}^{C}$ is in satisfactory agreement with values obtained from independent measurements, thus showing that reliable information on the open porosity volume can be retrieved from an optical experiment. The values of ${\ensuremath{\Gamma}}^{C}$, here resulting from collisions of the molecules with the inner surfaces of the xerogel pores, are practically independent of the line for each gas and inversely proportional to the square root of the probed-molecule molar mass. This is a strong indication that, for the studied transitions, a single collision of a molecule with a pore surface is sufficient to change its rotational state. A previously proposed simple model, used for the prediction of the line shape, leads to satisfactory agreement with the observations. It also enables a determination of the average pore size, bringing information complementary to that obtained from nitrogen adsorption porosimetry.

Dependence Properties of Sol-Gel Derived CuO@SiO2 Nanostructure to Diverse Concentrations of Copper Oxide

Various concentrations of copper oxide were embedded into silica matrix of xerogel forms using copper source Cu(NO3)2·3H2O. The xerogel samples were prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) with determination of new molar ratios of the components by the sol-gel method. In this paper, three samples of copper oxide were doped into silica matrices using different concentrations. We obtained 10, 20, and 30 wt.% of copper oxide in silica matrices labeled as A, B, and C, respectively. The absorption and transmittance spectra of the gel matrices were treated at different concentrations by Uv-vis spectrophotometer. Quantities of water and transparency in the silica network change the spectral characteristics of Cu2+ ions in the host silica. Absorption spectra of the samples heated to higher concentration complete the conversion of Cu2+ ions to Cu+ ions. The effects of concentration of copper oxide were characterized by X-ray diffraction (XRD) patterns, and the transmission electron microscope (TEM) micrographs. Also, textural properties of samples were studied by surface area analysis (BET method) at different concentrations.

Characterization of Sol-Gel Derived CuO@SiO2 Nano Catalysts towards Gas Phase Reactions

One distinct concentration of copper ions was embedded into the silica matrix to xerogel form using copper source Cu(NO 3)2�3H2O. The xerogel samples were prepared with using hydrolysis and condensation reactions of TetraEthyl Ortho-Silicate (TEOS) by the sol-gel method. In this investigation, new molar ratio of H 2O/TEOS was determined to be 11.7. Also, the necessary amount of tri-hydrated copper nitrate was added to the solution in such a manner that the concentration of the copper oxide in final solution reach to 10 wt. %. The prepared samples were characterized by Thermal Gravimetric Analysis (TGA), Transmission Electron Microscopy (TEM), surface area measurement (using BET method) and Thermal Program Reduction (TPR) methods. Finally, catalytic behavior of nano-composites was studied towards carbon monoxide (CO), nitrogen monoxide (NO) oxidation and di-nitrogen oxide (N 2O) decomposition reactions. The results were presented the systematic reactivity study of CO, NO oxidation and N 2O decomposition on dispersed copper oxide nano-catalysts over silica supports, in order to determine the ability of these materials to convert carbon monoxide, nitrogen monoxide and di-nitrogen oxide to harmless species by different reaction paths at different temperatures.

Nanoparticle characterization of Er-doped SnO2 pellets obtained with different pH of colloidal suspension

SnO2:2 at. %Er xerogel samples were obtained by sol-gel technique from colloidal suspensions with distinct pHs. The evaluation of critical regions inside the nanocrystallite is fundamental for the interpretation of the influence of pH on the emission data. In this way, the nanocrystal depletion layer thickness was obtained with the help of photoluminescence, Raman, X-ray diffraction, and field-emission gun scanning electron microscopy measurements. It was observed that acid suspensions (pH &amp;lt; 7) lead to high surface disorder in which a larger number of cross-linked bonds Sn-O-Sn among nanoparticles are present. For these samples, the nanoparticle depletion layer is larger as compared to samples obtained from other pH. Photoluminescence measurement in the near infrared region indicates that the emission intensity of the transition 4I13/2 → 4I15/2 is also influenced by the pH of the starting colloidal suspension, generating peaks more or less broadened, depending on location of Er3+ ions in the SnO2 lattice (high or low symmetry sites).

Spin crossover polysaccharide nanocomposites

We report in this paper the synthesis, characterisation and spin-crossover (SCO) properties of a series of nanocomposite materials containing very small (∼3 nm) Hofmann clathrate [Fe(pz){M(CN)4}] (M = Ni2+, Pt2+, Pd2+) nanoparticles embedded into different biopolymer polysaccharide matrices: chitosan and alginate. With the objective to understand the influence of the matrix on the SCO properties in these systems, we have modified the internal structure of the matrix, leading to aerogel, xerogel, beads or thin film samples. We show that the cooperativity associated with the spin crossover behaviour depends not only on the cyanometallate bivalent metal, but also on the nature and morphology of the polysaccharide matrix. Moreover, we confirm that for a specific morphology of the matrix, the bistability is maintained in such 3 nm nanoparticles.

Sol–gel synthesis of zinc ferrite-based xerogel monoliths with well-defined macropores

Starting from an aqueous solution, porous zinc ferrite-based xerogel monoliths have been prepared via a sol–gel route accompanied by phase separation mediated by propylene oxide in the presence of poly(acrylamide). The xerogels possess well-defined macropores, and the macroporous morphologies could be easily controlled (macropore size ranges from 0.55 to 1.29 μm) by simply changing the starting composition. As-dried xerogel samples were amorphous under X-ray diffraction, while heat-treatment in air brought about the formation of spinel type ferrite phase, ZnFe2O4. Calcination under Ar atmosphere allowed the crystallization of various iron-based phases/carbon composites (Fe3O4, Fe1-δO, Fe3N, Fe4N, Fe3C, and Fe). Samples heated under Ar flow exhibited hierarchical pore structures, including continuous macropores, in addition to mesopores and micropores embedded in the carbon-containing composite matrices.

Synthesis and properties of magnesium carbonate xerogels and aerogels

A magnesium carbonate sol was synthesised by controlled hydrolysis of methoxymagnesium methyl carbonate and then converted into an alcogel. From this, magnesium carbonate xerogels and aerogels were produced. SEM imaging, XRD and IR spectroscopy revealed that both xerogel and aerogel samples are composed of amorphous magnesium carbonate nanoparticles. Supercritical drying of the alcogel yields an opaque aerogel with high surface area (~400m2/g) and pores in the low nanometer range which makes this aerogel interesting for e.g. insulating applications.

Partial crystallization in exotic phase stishovite of amorphous silica xerogels induced by incorporation of chlorophyll species

Using the Rietveld refinement, we analyze the structural evolution under thermal treatment of silica xerogel samples with incorporation of extract from frozen spinach leaves, prepared by sol–gel method with low molar ratio (R) of water to TEOS of R = 1, and R = 5. Partial crystallization of silica xerogel in the form of stishovite has been obtained at atmospheric pressure conditions and temperatures of 200 °C, they both, very lower than those specified by the phase diagram, in samples containing chlorophyll aggregates dispersed in amorphous silica. The results show that the incorporation of spinach extracts leave together with low water contents induce devitrification of the silica matrix in exotic phase stishovite.

Calcium phosphate phases integrated in silica/collagen nanocomposite xerogels enhance the bioactivity and ultimately manipulate the osteoblast/osteoclast ratio in a human co-culture model

A human co-culture model of osteoblasts and osteoclasts, derived from bone marrow stromal cells and monocytes respectively, was used to characterize the influence of biomaterial modification on the bioactivity and ultimately the ratio of bone-forming to bone-resorbing cells cultivated directly on the surface. Nanocomposites of silica and collagen have been shown to function as skeletal structures in nature and were reproduced in vitro by using a sol–gel approach. The resulting xerogels exhibit a number of features that make it a valuable system for the development of innovative materials for bone substitution applications. In the present study, the incorporation of different calcium phosphate phases in silica/collagen-based gels was demonstrated to enhance the bioactivity of these samples. This ability of the biomaterial to precipitate calcium phosphate on the surface when incubated in simulated body fluids or cell culture medium is generally considered to an advantageous property for bone substitution materials. By co-cultivating human osteoblasts and osteoclasts up to 42days on the xerogels, we demonstrate that the long-term ratio of these cell types depends on the level of bioactivity of the substrate samples. Biphasic silica/collagen xerogels exhibited comparably low bioactivity but encouraged proliferation of osteoblasts in comparison to osteoclast formation. A balanced ratio of both cell types was detected for moderately bioactive triphasic xerogels with 5% calcium phosphate. However, enhancing the bioactivity of the xerogel samples by increasing the calcium phosphate phase percentage to 20% resulted in a diminished number of osteoblasts in favor of osteoclast formation. Quantitative evaluation was carried out by biochemical methods (calcium, DNA, ALP, TRAP 5b) as well as RT-PCR (ALP, BSP II, OC, RANKL, TRAP, CALCR, VTNR, CTSK), and was supported by confocal laser scanning microscopy (cell nuclei, actin, CD68, TRAP) as well as scanning electron microscopy.

Characterization and catalytic behavior of CuO@SiO2 nanocomposites towards NO oxidation and N2O decomposition

Abstract A distinct concentration of copper was embedded into silica matrix to form xerogel using Cu(NO3)2 · 3H2O as the copper source. The xerogel samples were prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) by the sol–gel method. The new molar ratio of H2O/TEOS was determined to be 11.67. Also the necessary amount of trihydrated copper nitrate was added into the solution such that the concentration of the copper oxide in the final solution reached 10 wt.%. After ambient drying, the xerogel samples were heated to 100, 400, 600, 800, and 1000°C at a slow heating rate (50 K h−1). The structural properties were characterized by means of transmission electron microscopy, surface analysis and thermal program reduction methods at different temperatures. Finally, the catalytic behavior of nanocomposites was studied for nitrogen oxide (NO) oxidation and di-nitrogen oxide (N2O) decomposition reactions. The results present a systematic reactivity study of NO oxidation and N2O decomposition on the dispersed copper oxide nanocatalysts over silica supports in order to determine the ability of these materials to convert nitrogen oxide and di-nitrogen oxide into harmless species at different temperatures.

Impact of synthesis conditions on meso- and macropore structures of resorcinol–formaldehyde xerogels

Xerogels were prepared by the sol–gel polymerization of resorcinol with formaldehyde at different conditions. The effects of different synthesis factors (namely, resorcinol-to-formaldehyde ratio, resorcinol-to-water ratio, resorcinol-to-catalyst ratio, and initial solution pH) on the surface areas, pore volumes, pore size distributions, and adsorption capacity of liquid nitrogen were studied. Factorial design was also used to investigate the relative significance of these factors on the resulting xerogels properties, and the possible interactions between them. The mean effects of the most significant factors and factor interactions on determining the pore structures and adsorption capacities were evaluated. The synthesized xerogels were characterized by Fourier transmission infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, and surface area analyzer. The results showed that surface areas, pore size distributions, and nitrogen adsorption capacity are dependent completely on the recipes used to prepare the xerogels. Pore structure results put xerogel samples as candidates for adsorption technology, ultra-filtration, and nano-filtration fields based on pore sizes and pore volume scales.

K +-doped poly(ε-caprolactone)/siloxane biohybrid electrolytes for electrochromic devices

Sol–gel derived KCF 3SO 3-doped di-urethane cross-linked poly(ε-caprolactone) (PCL(530))/siloxane ormolytes with ∞ > n ≥ 0.5 (n indicates the number of (C(= O)(CH 2) 5O) repeat units per K + ion) have been studied. Xerogel samples with n ≥ 1 are thermally stable up to 235 °C. A small amount of PCL crystallites are formed in some dilute-to-concentrated samples. At n ≤ 4 a crystalline PCL(530)/siloxane–KCF 3SO 3 complex with unknown stoichiometry emerges. At n ≤ 2 this complex coexists with pure salt. At temperatures greater than 40 °C the composition which exhibits the highest ionic conductivity is n = 21. “Free” anions, coordinated CF 3SO 3 − ions, contact ion pairs and several higher ionic aggregates are present in all the samples. The K + ions bond to the oxygen atoms of the carbonyl groups of the urethane and ester groups, of the PCL (530) ether chain and of the triflate ions, at all salt concentrations. The ormolytes were successfully used in the assembly of prototype electrochromic devices (ECDs) that exhibit fast switching time and good open circuit memory. The ECD incorporating the ormolyte with n = 21 displays an average transmittance in the visible region of ca. 55% in the colored state and 76% in the bleached state.