Synthesis Of Silica Xerogel Research Articles

Penentuan Kondisi Optimum Waktu Aging dan Temperatur Pengeringan Pada Sintesis Silika Xerogel dengan Bahan Dasar Natrium Silikat dari Silika Alam

Abstract — Silica is one kind of porous material that is suited to adsorben. In the synthesis process, silica gel can be produced using a sol-gel method based on the sodium silicate (Na2SiO3), which is prepared by an acid. The project of this research is to establish optimum conditions in aging time and gel-drying temperatures to produce a broad surface and pore size for silica xerogel. Based on the iod's absorption of variations in aging time (14, 16, 18, 20 and 24 hours) and drying temperatures (60, 70, 80, 90 and 100°C) give the most absorption to optimum conditions of aging time at 18 hours and drying temperatures of 70°C. The presence of XRD pattern leads to amorphous nature structures that dilate at one peak in 2θ = 22.545°, which indicates synthesis of silica xerogel with a basic sodium silicate obtained from natural silica was successfully made and highly pure. Keywords — Silica, Sodium Silicate, Silica xerogel

Imidazolium-based ionic liquid silica xerogel as catalyst to transform CO2 into cyclic carbonate

In this work silica xerogel samples containing different imidazolium ILs (EMIM-CF3SO3, EMIM-MSO3, BMIM-Cl, MBMIM-TF2N, BMIM-TF2N and EMIM-TF2N) were synthesized, characterized and used as catalyst in cyclic carbonate synthesis. ILs mass percentage was varied from 5% to 25%. The effect fostered by the ILs mass variation in the synthesis of silica xerogel was observed both in the materials characterization as well as in the performance of these materials as solid catalysts in the cyclic carbonate synthesis from the cycloaddition reaction of CO2 with propylene epoxide. The obtained silica xerogel samples (SXs) were characterized by FTIR, RAMAN, TGA, SEM and TEM. The selectivity of the cycloaddition reaction was analyzed by GC and 1H and 13C NMR. The best results were obtained for SX-EMIM MSO3 (20% of IL) and SX-BMIM Cl (15% of IL) with propylene carbonate yields of 91.4% and 83.4% and selectivities >99% and 97.4% respectively.

Hybrid Ionic Liquid–Silica Xerogels Applied in CO2 Capture

The imidazolium-based ionic liquids (ILs) are solvents known for selectively solubilizing CO2 from a gas CH4/CO2 mixture, hence we have produced new hybrid adsorbents by immobilizing two ILs on xerogel silica to obtain a solid–gas system that benefits the ILs’ properties and can be industrially applied in CO2 capture. In this work, the ILs (MeO)3Sipmim.Cl and (MeO)3Sipmim.Tf2N were used at different loadings via the sol–gel process employing a based 1-methyl-3-(3-trimethoxysylilpropyl) imidazolium IL associated to the anion Cl− or Tf2N− as a reactant in the synthesis of silica xerogel. The CO2 adsorption measurements were conducted through pressure and temperature gravimetric analysis (PTGA) using a microbalance. SEM microscopies images have shown that there is an IL limit concentration that can be immobilized (ca. 20%) and that the xerogel particles have a spherical shape with an average size of 20 µm. The adsorbent with 20% IL (MeO)3Sipmim.Cl, SILCLX20, shows greater capacity to absorb CO2, reaching a value of 0.35 g CO2 / g adsorbent at 0.1 MPa (298 K). Surprisingly, the result for xerogel with IL (MeO)3Sipmim.Tf2N shows poor performance, with only 0.05 g CO2 / g absorbed, even having a hydrophobic character which would benefit their interaction with CO2. However, this hydrophobicity could interfere negatively in the xerogel synthesis process. The immobilization of ionic liquids in silica xerogel is an advantageous technique that reduces costs in the use of ILs as they can be used in smaller quantities and can be recycled after CO2 desorption.

Sustainable nanocomposites of epoxy and silica xerogel synthesized from corn stalk ash: Enhanced thermal and acoustic insulation performance

Abstract The synthesis of silica xerogel from corn stalk ash in ambient pressure drying was carried out by sol-gel method. With the usage of silica xerogel (0.5, 1.0 and 1.5 wt%) in epoxy resin (ER), silica xerogel/epoxy nanocomposites were successfully prepared. The uniform dispersion of silica xerogel in neat ER was observed except nanocomposite including 1.5 wt% silica xerogel. The low density nanocomposites showed high thermal stability and low thermal conductivity. The char residue at 600 °C and thermal conductivity of nanocomposite including 1.5 wt% silica xerogel were specified as 20.30% and 0.220 W/mK, respectively. The acoustic velocity of the nanocomposites was decreased with increasing amount of silica xerogel. The water sorption of the nanocomposites was slightly higher than neat ER. The water contact angle of the nanocomposites were between 75° and 70°. The study provided a new thermal and acoustic insulation material instead of expensive and health risk traditional materials.

Synthesis of silica xerogel–poly(styrene sulphonic acid) nanocomposites as acid catalysts: effects of temperature and polymer concentration on their textural and chemical properties

A series of silica–poly(styrene sulphonic acid) (SiO2–PSSA) nanocomposites were prepared using the sol–gel route. Tetraethoxysilane and (3-aminopropyl)-triethoxysilane (APTES) were used as the SiO2 xerogel sources. The latter was used to provide anchoring sites for retaining the PSSA polymer via acid–base reactions between the amino groups and sulphonic acid sites (electrostatic interactions). During the synthesis, the Si/N atomic ratio was maintained constant (close to 11), whereas the temperature and the PSSA concentration (PSSA/APTES mol ratio, that is, the S/N at. ratio) were varied. The prepared organic–inorganic nanohybrids were characterised by chemical analysis, thermogravimetric analysis, N2 adsorption isotherms and DRIFT and 29Si and 13C MAS-NMR spectroscopic analyses. These materials were applied as catalysts in the dehydration of xylose to furfural and compared with a conventional sulphonic resin, with specific attention to the reusability properties of the catalysts. A synthesis temperature of 348 K and an initial S/N at. ratio between 4 and 8 provided the best balance between the textural, chemical and reutilisation properties of the nanocomposite. Regardless of the temperature and S/N at. ratio initially used for the synthesis, the catalysts deactivated during the first reuse cycle but reached a stable state in successive runs. In contrast, the sulphonic resin continuously and progressively deactivates.

Synthesis of silica xerogels with highly distinct morphologies in the presence of imidazolium ionic liquids

This article describes the preparation of silica xerogels by the sol–gel technique, using tetraethoxysilane as precursor and hydrofluoric acid as catalyst, in the presence of imidazolium ionic liquids (ILs). The applied ILs 1–3 contained the 1-monoethylene glycol monomethyl ether-3-methylimidazolium cation in combination with the methanesulfonate (1), tetrafluoroborate (2) and hexafluorophosphate (3) anions, respectively. Characterization of these materials was performed by photography, scanning electron microscopy, atomic force microscopy, X-ray diffraction, thermogravimetric analysis and nitrogen adsorption-desorption isotherms. The IL anion was identified as a powerful morphology controller. The methanesulfonate anion of IL 1 induced the formation of a compact lamellar monolith with an interlamellar distance of 1.5 nm and a flat surface. A free flowing powder of aggregated spherical particles was obtained in the presence of tetrafluoroborate IL 2, and the hexafluorophosphate anion of IL 3 induced the formation of porcelain like aggregates with honeycomb shapes.

Synthesis of silica xerogels with high surface area using acetic acid as catalyst

The influence of acetic acid on the pore structure and surface area of silica prepared by the sol-gel method was investigated. Experimental conditions of synthesis, such as gelation temperature and solvents, were also studied. N2 adsorption isotherms of the samples were type 1, typical of microporous materials, explaining the high surface area values (BET) observed. The simultaneous addition of acetic and hydrochloric acids as catalysts and of acetone as solvent, together with the use of a gelation temperature of 20 ºC, made it possible to prepare amorphous silica materials with surface area values up to 850 m² g-1. The high surface area value of these samples could be explained by the microporosity and the nanometric size of the particles.

Nanocomposites Containing Nanoclusters of Metals or Semiconductors

ABSTRACTNeutral, low-valent complexes of transition metals or an organometallic compound of Ge are prepared containing ancillary ligands which bear silicate ester or (alkoxy)silicon functional groups. Inclusion of these molecules as dopant species in a conventional sol-gel synthesis of silica xerogels affords silica xerogels in which dopant molecules have presumably been covalently incorporated into the xerogel matrix with uniform and high dispersion. Subsequent thermal treatment of these molecularly doped xerogels under reducing or oxidizing/reducing conditions gives nanocomposites containing nanoclusters of metals or semiconductor substances. By this procedure, nanocomposites containing nanoclusters of Ag, Cu, Pt, Os, CCo3, Fe2P, Ni2P, or Ge have been prepared. Preliminary evidence for the formation of a nanocomposite containing Pt-Sn nanoclusters derived from a bimetallic molecular precursor is also presented. Characterization data for the nanocomposite materials include TEM, electron diffraction, EDS, XRD, and selected use of micro-Raman spectroscopy. These results support the hypothesis that covalent incorporation of molecular precursors containing low-valent metals into a silica xerogel can afford nanocluster phases with high dispersion, relatively small particle size, and unusual elemental composition.