Search results for "RAV"
showing 10 items of 5866 documents
Complex formation of hypoxanthine and 6-mercaptopurine with Cd(II) ion
1984
Reaction of Cd(II) ion with hypoxanthine (H2 Y) and with 6-mercaptopurine (H2 MP) in dioxane-water (50%) leads to the formation of CdY·2H2O and Cd(HMP)2·2H2O, respectively. In methanolic medium Cd(II) and H2 MP give Cd(MP)·H2O. These compounds have been characterized by chemical analysis, IR spectra and thermogravimetric analysis. The stability constant of CdY complex at 25±0.1 °C and 1M ionic strength with NaClO4 in dioxane-water medium is log β=10.25±0.05.
Synthesis and thermal behavior of Janus dendrimers, part 1
2010
Abstract Eight Janus-type dendrimers up to the second generation were synthesized, and their thermal properties were evaluated. Compounds consist of the dendritic bisMPA based polyester moieties, and either 3,4-dihexyloxybenzoic acid or 3,4-dihexadecyloxybenzoic acid moieties, attached to opposite sides of the pentaerythritol core. The structures of the molecules were verified with 1 H NMR, 13 C NMR, ESI TOF mass spectrometry and elemental analysis. The thermal stability was evaluated by thermogravimetric analysis, displaying onset decomposition temperatures ( T d ) ranging from 241 to 308 °C. Phase transitions were studied by differential scanning calorimetry. Based on the performed studie…
Preparation and characterization of gels with garnet structure: A3B2C3O12, using ‘non-classical’ solvents
1992
Abstract Synthesis and characterization of some crystalline garnets by sol-gel techniques is described. The effects of emthanol, dimethyl sulfoxide (DMSO), CH2Cl2 and toluene solvents on gelation of TEOS are considered. Multicomponent gel formation in systems with stoichiometries 3CaO·Cr2O3·3SiO2 and 3CaO·Al2O2 was studied using DMSO, a polar solvent, and toluene, an apolar solvent. The dried gel was thermally treated and the powder was characterized by X-ray diffraction, differential thermal analysis/thermogravimetric analysis and scanning electron microscopy.
Influence of crystallinity and OH surface density on the photocatalytic activity of TiO2 powders
2014
Abstract The aim of the work was to study the influence of crystallinity and OH surface density on the photocatalytic activity of two commercial and two home-prepared TiO 2 powders. The samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG) and electron paramagnetic resonance (EPR) measurements. The photoactivity of the powders was tested employing the photodegradation of 4-nitrophenol (4-NP) and the selective oxidation of 4-methoxybenzyl alcohol (4-MBA) to 4-methoxybenzaldehyde ( p -anisaldehyde) under UV irradiation. An anti-correlation between oxidant power and selectivity of the various samples was found. A higher rate of 4-NP degradation was exhibited by…
Covalent and Ionic Functionalization of HLN Layered Perovskite by Sonochemical Methods
2017
We describe the functionalization of the layered perovskite HLaNb2O7 with n-propanol, n-decanol, 3-mercaptopropyl-trimethoxysilane, imidazole, n-decylamine, and histamine. The use of sonication is found to significantly improve the reaction yield and to reduce the reaction time, compared to conventional thermal treatment under reflux. The obtained intercalates are thoroughly characterized through the use of several complementary experimental techniques (scanning electron microscopy, IR spectroscopy, X-ray diffraction, thermogravimetric analysis, magic-angle spinning NMR), clarifying their structure and chemical bonding. The implications for the design of inorganic–organic composite material…
Surface and bulk changes of a Pt 1%/Ce0.6Zr0.4O2 catalyst during CO oxidation in the absence of O2
2004
The reduction of a Pt 1%/Ce0.6Zr0.4O2 catalyst by CO in the absence of gaseous oxygen was studied by transient reactivity tests, temperature programmed surface reaction with CO, flow thermogravimetric tests and DRIFTS experiments, in order to obtain information generally on the OSC properties and, specifically, on the mechanism of CO oxidation over both, Pt catalyst and support-only sample (Ce0.6Zr0.4O2). The results of thermogravimetric experiments showed the presence of an induction time in the weight change % of the catalyst, depending on the CO concentration in the gas flow. This induction time could be related to the presence of two oxygen reactive sites. The first one leads to strongl…
Kinetics of thiophene reactive adsorption on Ni/SiO2 and Ni/ZnO.
2008
Abstract Kinetics of thiophene reactive adsorption on Ni/SiO2 and Ni/ZnO was studied by thermal gravimetric analysis at 280–360 °C under 5–40 mbar of thiophene in H2. In the case of Ni/SiO2 the interaction proceeds in two steps: a rapid surface reaction is followed by a slower bulk transformation into Ni3S2. Maximum Ni conversion depends on reaction conditions and observed conversion profiles can be described by an exponential equation corresponding to a reaction of first order relatively to both sulfidable Ni amount and thiophene. The interaction between Ni/ZnO and thiophene proceeds in a rather different manner. A rapid increase of weight, similar to the first stage observed on Ni/SiO2, i…
Copper-, cobalt-, and manganese-containing 17-tungsto-2-germanates.
2009
The sandwich-type tungstogermanates [Cu(3)(H(2)O)(B-beta-GeW(9)O(33)(OH))(B-beta-GeW(8)O(30)(OH))](12-) (1), [Co(H(2)O)(2){Co(3)(B-beta-GeW(9)O(33)(OH))(B-beta-GeW(8)O(30)(OH))}(2)](22-) (2), and [Mn(H(2)O)(2){Mn(3)(H(2)O)(B-beta-GeW(9)O(33)(OH))(B-beta-GeW(8)O(30)(OH))}(2)](22-) (3) were synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, and infrared spectroscopy. Polyanion 1 is composed of two nonequivalent Keggin units, (B-beta-GeW(8)O(31)) and (B-beta-GeW(9)O(34)), linked to each other via three copper(II) ions in such a way that there is a plane of symmetry passing through both Ge atoms and the unique Cu atom, resulting in…
An efficient acetylation of dextran using in situ activated acetic anhydride with iodine
2010
A facile, efficient, cost-effective and solvent-free acetylation method has been developed for the acetylation of dextran. Dextran acetates were successfully synthesized using different molar ratios of acetic anhydride in the presence of iodine as a catalyst without the use of any solvent. The reactions were realized at 50?C for 3 h under stirring and nitrogen. This efficient method yielded highly pure and organosoluble dextran esters. The reaction appears highly effective for obtaining higher degrees of substitution (DS) with great efficiency. Under solvent-free conditions, dextran triacetates were efficiently synthesized. It was also observed that the molar ratio can easily control the DS…
Hydrogen Adsorption in Zeolite Studied with Sievert and Thermogravimetric Methods
2012
Natural clinoptilolite (mixture from clinoptilolite, quartz and muscovite) is activated with palladium and tested for hydrogen adsorption capability at temperatures RT - 200 o C. Thermogravimetric and volumetric methods showed that zeolite activated with palladium (1.25%wt) shows markedly high hydrogen adsorption capacity - up to 3 wt%. Lower amount of adsorbed hydrogen (~1.5 wt%) was found for raw zeolite and activated with higher amount of palladium sample. Hypothesis is proposed that the heating of zeolite in argon atmosphere forms and activates the pore structure in zeolite material, where hydrogen encapsulation (trapping) is believed to occur when cooling down to room temperature. An e…