Search

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.

The aim of the present study was to prepare nanocomposites with different CoCr2O4 content (20%, 50%, and 80% CoCr2O4/SiO2 mass%) starting from Co(II) carboxylate and ammonium dichromate using a modified sol–gel method and to evaluate the final product (nature, size and shape) based on the different precursor amount. Thermal analysis was used in order to reveal the formation and decomposition of Co(II) carboxylate to CoO and (NH4)2Cr2O7 to Cr2O3+x, inside the silica gel pores. The oxide mixture interacts at temperatures of ~ 400 °C when Cr2O3+x turn to α-Cr2O3 which leads together with CoO to the formation of CoCr2O4 inside the SiO2 matrix. XRD and FTIR analyses revealed the formation of the single spinel structure in all synthesized samples. The results show that a higher cobalt chromite content inside the silica matrix leads to higher crystallinity. The particle sizes were in nanometer range, and the size variation was small from a sample to another, independent on the concentration (3.9–12.4 nm). [ABSTRACT FROM AUTHOR]

Copyright of Romanian Journal of Civil Engineering / Revista Română de Inginerie Civilă is the property of Matrix Rom and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A polyvinyl chloride membrane chromium(III)-selective electrode based on a synthesized A3B free base porphyrin, namely 5-(4-pyridyl)-10,15, 20-tris(phenoxy-phenyl)porphyrin, as membrane carrier was formulated and evaluated. The electrode exhibits a near-Nernstian response over the chromium(III) concentration range of 3x10-5 ÷ 1x10-1 M and shows good selectivity with respect to a wide range of cations. The aggregation behavior of the porphyrin macrocycle was investigated using TEM and STEM analytic techniques and revealed the formation of different shapes of nanostructures. Electron tomography was also employed in the study of the porphyrin aggregates. [ABSTRACT FROM AUTHOR]

Previous studies have shown that pyrazine-2,3-dicarboxylic acid (PDCA) can be obtained through quinoxaline (Q) oxidation with electrochemically regenerated KMnO4 using Pt, Ni, stainless steel, Cu, brass and bronze electrodes. This corresponds to a smaller oxidant consumption as compared to the chemical oxidation reaction, a smaller energy consumption, an increase in the PDCA manufacturing efficiency and a significantly smaller impact on the environment due to secondary products removal (both from Q oxidation as well as from KMnO4 production). This paper presents the analysis methods used for the quantitative determination of PDCA obtained through Q oxidation (such as conductometric titration, UV-VIS and IR spectrophotometry) as well as those used for monitoring Mn7+ and Mn6+ concentrations (UV-VIS spectrophotometry and the visual method). The right conditions for applying these methods were established in order to properly evaluate the electrochemical process. [ABSTRACT FROM AUTHOR]

In order to improve current knowledge and to expand the variety of electrodes used for the pyrazine-2,3-dicarboxylic acid (PDCA) production process, we investigated the behaviour of the copper anode. A laboratory electrolyser for PDCA synthesis with copper anode using electrochemically regenerated KMNO4 as chemical reagent was manufactured based on results from cyclic voltammetry studies performed on copper electrode. The best performances of this electrolyser are current efficiencies of ~55% and substance efficiencies up to 72% - achieved at a current density of 3,5 A/dm2. Maximum conversion was 90%. [ABSTRACT FROM AUTHOR]

Zn(Ta1-xNbx)2O6 pseudo-binary oxide nanocrystalline materials (where x = 1; 0.5; 0.1; 0.05 and 0) were obtained through the solid-state method and characterized by X-ray diffraction, Fourier Transform Infrared Spectroscopy and Ultraviolet-visible spectroscopy. In addition, their morphology and topography have been determined by field emission-scanning electron microscopy (SEM) and atomic force microscopy (AFM). There is a significant dependence between the rugosity and the uniformity of crystals. The evenly crystals organized in multilayers have the lowest value of rugosity and the non uniform fractal type architectures have the highest value of rugosity. The compounds’ anti-corrosion features were evaluated after deposition on carbon steel (OL) in 0.1 M Na2SO4 media by open circuit potential measurement and potentiodynamic polarization technique with Tafel representation. The inhibition efficiency of pseudo-binary oxides deposited on carbon steel electrode was in the range 42.3-52.7 % promising for their further multiple layer deposition with porphyrins in order to improve anticorrosion properties. Due to the high band gap (3.80 - 4.30 eV) provided by increasing the tantalum content, four of these pseudo-binary oxides might find applications in photovoltaic cells.

Corrosion prediction of galvanized steel ground electrodes in the soil of Timisoara represents an area of interest for ensuring the good functioning of the earth electrodes , the safety of the electrical installation, and of the lightning rodes. Taking in the account that the soil is exposed to different kind of pollutants which have an effect on the ground electrodes we consider that a research is needed in this area.

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]

The studies were focused on the relationship between morphology features and synthesis variables, looking for their implications in the drug loading and release capacities. Increasing the amount of methylated tri-alcoxide toward the tetra-alcoxide precursor caused shrinkage of the hexagonally ordered mesoporous structure and also the reduction of the pore diameters, while the total pore volumes and surface areas remain high and suitable for drug loading. In drug release profiles: silica prepared with the largest amount of hydrophobic precursor retained about twice as much of drug, compared with the sample obtained of pure TEOS.The studies were focused on the relationship between morphology features and synthesis variables, looking for their implications in the drug loading and release capacities. Increasing the amount of methylated tri-alcoxide toward the tetra-alcoxide precursor caused shrinkage of the hexagonally ordered mesoporous structure and also the reduction of the pore diameters, while the total pore volumes and surface areas remain high and suitable for drug loading. In drug release profiles: silica prepared with the largest amount of hydrophobic precursor retained about twice as much of drug, compared with the sample obtained of pure TEOS. [ABSTRACT FROM AUTHOR]