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The mesoporous silica particles were prepared by the sol–gel method in one-step synthesis, in acidic conditions, from tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES), varying the mole ratio of the silica precursors. Nitric acid was used as catalyst at room temperature and hexadecyltrimethyl ammonium bromide (CTAB) as structure directing agent. Optical properties, porosity and microstructure of the materials in function of the MTES/TEOS ratio were evaluated using infrared spectroscopy, nitrogen adsorption and small angle X-ray scattering. All materials showed the ordered pore structure and the high specific surfaces, making them suitable as the drug delivery systems. Drug loading and release tests using ketoprofen were performed to assess their performance for drug delivery applications. The amount of the methylated precursor used in the synthesis had little effect on the drug loading capacity, but had a strong influence on the initial rate of the drug release.

Magnetic iron oxide-silica shell nanocomposites (IONP@SiO2) have been prepared in a two-step procedure. IONPs were obtained by coprecipitation of iron salts, and coated by silica in sol-gel method under sonication. Two IONP/silica ratios and two drying methods, heating in oven and supercritical CO2 drying, were used. The samples were analyzed using X-ray diffraction (XRD), infrared spectroscopy, magnetic measurements, small-angle neutron scattering (SANS), nitrogen sorption, and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray analysis (EDX). The iron oxide silica nanocomposites obtained via supercritical drying exhibited higher values of the specific surface area and of saturation magnetization compared to the samples synthesized with the same iron oxide content but obtained after drying at 60 °C. Pd(II) adsorption experiments were performed on the materials prepared by supercritical drying. The maximum adsorption capacity 6.5 mg/g showed that the materials can be used as good and cheap adsorbent for palladium ions from aquatic environment. [ABSTRACT FROM AUTHOR]

Hematite/silica nanocomposite (α-Fe2O3/SiO2) was synthesized by sol-gel method at room temperature followed by thermal treatment through calcination at the temperature of 500o C selected based on thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) results. The crystalline phases of α-Fe2O3 and SiO2 were characterized by the correlation of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results. The composite average particle size values ranged between 10 and 22 nm were estimated through XRD and transmission electron microscopy (TEM). The composite exhibited a high capacity to remove humic acids (HA) from water, through the sorption and VIS irradiation-assisted photocatalysis processes. The heterogeneous structure of the composite was found by corroborating Brunauer-Emmett-Teller (BET) results with the HA sorption physical mechanism determined by Dubinin-Radushkevich isotherm model. A synergic effect regarding visible irradiation-assisted photocatalysis process using α-Fe2O3/SiO2 was manifested for HA removal by comparison with the sorption and photolysis under VIS irradiation, which suggested a great potential for developing of a new nature-based inspired unitary processes for advanced treatment water for drinking purpose. [ABSTRACT FROM AUTHOR]

Spherical silica xerogels were synthesized by Stöber route using tetra-ethyl-orthosilicate (TEOS) in order to obtain good properties for opto-electronic and catalytic applications. The reactants mole ratio was n TEOS: H2O: ETOH: NH3 (where n = 0.098 - 0.26: 0.45: 0.789: 0.06). To study these properties, we know from literature, that nanoparticles under 100 nm show unique electrical, mechanical and optical properties. We have choosen the optimum sample, with the smaller surface area and particles size of 91 nm. To improve the optical properties, this sample was further doped with 0.1% Ce3+. The obtained xerogel was thermally treated at 300, 600 and 900 °C. The changes in properties were put in evidence by morpho-textural (N2 adsorption-desorption isotherms and SEM images) and optical measurements (FT-IR, Fluorescence and Raman spectra's). [ABSTRACT FROM AUTHOR]

In situ functionalized, with different organically groups, mesoporous matrices were generated, starting from silica tetra-alcoxide and functionalized tri- or di-alkoxides, (triethoxyvinylsilan, diethoxy(methyl)vinylsilane and methyltriethoxysilane) mixtures, via sol-gel synthesis. Mesoporous silica matrices have been prepared with the purpose of tailor and optimize their performances as gas storage materials. In this concern, it was designed different experiments to study how the synthesis variables influence the matrix morpho textural properties, being aware that this kind of properties play an important role in the gas adsorption-desorption processes. In order to prepare spherical particles, ammonia was used as catalyst. Eventually, in order to tailor the pore shape and size and implicitly the specific surface area, hexadecyltrimethyl ammonium bromide as directing agent was added, and the molar ratios of organically functionalized precursors/TEOS, were varied. The H2, CH4 and CO2 adsorption properties of prepared functionalized mesoporous silica with different compositions have been studied. In the used experimental conditions, data analysis permits to conclude that the methyl functionalized sample, according to its structural parameters, at 77 K and elevate pressure it showed the best performances concerning the adsorption capacity toward H2 and CO2. CH4 molecules. Toward CH4 molecules, in particular, the analysis performed at room temperature point out that the vinyl- functionalized samples have an appreciable affinity toward this gas specimen. [ABSTRACT FROM AUTHOR]

Two series of magnetic nanopowders were synthesized at room temperature starting from a mixture of iron II and III precursors, FeSO4 and FeCl3, respectively. Precipitation agents, as KOH and NaOH were used. While the concentration of the added ferrous and ferric solutions ranged between 0.1 M and 0.0125 M, the hydroxide solution concentration was maintained constant (1 M). TEM images of the samples showed that the particles shape changes from quasi spherical to spherical. For both series the crystallite size decreases with iron concentration, from 9 to 2 nm for KOH series and from 10 to 3 nm for NaOH series. Moessbauer Spectroscopy was signaling only Fe3+ in the final spinel product. BET measurements revealed the material mesoporosity and fractal structure of maghemite nanoparticles that explain the unusual high surface area, ~240 m2/g. All the samples actually exhibit superparamagnetic behavior at room temperature with saturation magnetization up to 73 emu/g value closed to those of bulk maghemite. [ABSTRACT FROM AUTHOR]

Template free, base catalysed sol-gel route (Stöber method) and low power sonic-activated sol-gel process (20 kHz ultrasonic bath) were used to obtain two series of samples. The influence of the concentration of the supplying ammonia solution upon the silica sols stability and solid products properties was followed. The reactants molar ratio TEOS: H2O: ETOH: NH3 of 1: 25: 20: 0.2 was rigorously kept constant. We have examined the influence of adding the ammonia solutions of different concentrations, specifically: 25% NH3, 12% NH3, 6% NH3, and 3% NH3. Either relatively stable colloidal suspensions or precipitates were obtained. The silica sols stability was related to the evolution of the turbidity over time. The resulted solid materials, xerogel's and sonogel's texture and morphology have been studied by using BET, SEM techniques. FT-IR was used to exhibit the main silica bonds. It was observed that by supplying base catalyst of variable concentrations, by changing initial pH of the process, it makes a difference concerning silica suspension behaviour and also in silica particle morphology. The used variable produced distinct effects upon both classic process and resulted xerogels, and sonoactivated sol-gel process and resulted sonogels. For all concentrations of ammonia solution, by classic sol-gel process, silica precipitates were obtained, and under ultrasonic field action, relatively stable translucent silica colloids resulted. [ABSTRACT FROM AUTHOR]

The H2 adsorption properties of prepared functionalized porous silica with different compositions have been studied. Mesoporous silica particles were synthesized by using the sol-gel method, with tetradecyltrimethyl ammonium bromide (C14) or dodecyl trimethyl ammonium bromide (C12) as structure directing agents from tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) precursors, by varying the molar ratio of the silica precursors. The porosity and microstructure of the materials in function of the MTES/TEOS ratio were evaluated by using nitrogen adsorption, and the transmission electron microscopy method. The textural characterization was performed in order to connect their properties to possible applications as hydrogen adsorptive materials. The ability of a material to store gas molecular species may not only be governed by on the specific surface area but also by the porosity and to the possibility to form more than one monolayer of adsorbed gas molecules. These are the reasons why the evaluation of the adsorbed hydrogen molecules per nm2 could be useful to indicate the efficacy of the samples to create more than one monolayer [1]. Improving the interaction between adsorbent and adsorbate is the breakthrough for synthesizing an optimum hydrogen storage material [2]. Thus, studies on physisorption materials aim to increase surface area, optimize the pore diameter, and increase the affinity toward incoming hydrogen molecules through the introduction of atoms and/or molecular groups into the porous material. A previous study had been demonstrated that the amorphous structure of the adsorbent and the use of shorter surfactant molecules in the synthesis increased both the storage capacity and the strength of the interaction between the surface and the adsorbate [1]. In our previous study the data analysis shows that the methyl functionalized sample, according to its structural parameters is the best material either from the point of view of maximum adsorption capacity showed for H2 [3]. The higher adsorption capacity of the samples synthesized with no MTES and with C12 directing agent can be debited to a different and stronger sorbent-adsorbent interaction beyond that slightly differences in the textural properties. In the C14 directing agent series of samples, the sample with no MTES and the samples with low amount of MTES, appears the most performing at 77K immediately followed by the samples synthesized with increase amount of MTES. In each series of samples, C12 and respectively C14, the samples show different grade of interaction with the incoming H2 molecules (K) and different values of homogeneity (t). The distance between two pore centers of parallel pore channels was estimated from TEM at: 3.3 nm for all samples from C12 series. Therefore, the inter-pore distanced is almost the same with the addition of small amounts of MTES, in the present synthesis conditions. [ABSTRACT FROM AUTHOR]