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A derivatograph was used for the thermal modification of the surface properties of different silica gels. Analogous investigations were carried out with an isothermal method. The possibility of using the thermal method of temperature programming to modify adsorbents is discussed.

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Fourteen different Achillea species were extracted using the Soxhlet apparatus with dichloromethane and then methanol as solvents. The obtained dichloromethane and methanolic extracts were analyzed using thin-layer chromatography (TLC) and high-performance thin-layer chromatography (HPTLC) to obtain fingerprint profiles. The first chromatographic system consisted of silica gel as adsorbent, a mixture of toluene—ethyl acetate—formic acid (5:4.9:0.1, v/v) as the mobile phase and anisaldehyde as the derivatization reagent. The second adsorbent was cyano (CN) silica gel with non-aqueous (2-propanol and n-heptane [5:5, v/v], both for dichloromethane and methanolic extracts) and aqueous (methanol and water [6:4, v/v] for dichloromethane extracts and methanol and water [4:6, v/v] for methanolic extracts) mobile phases. Anisaldehyde (for dichloromethane extracts) and Naturstoff (for methanolic extracts) derivatization reagents were used. The obtained chromatograms were processed to obtain selected images using the ImageJ program. The similarity between the studied Achillea species was confirmed using the chemometric methods (principal component analysis [PCA], similarity, and distance measures).

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Abstract  

Hypocrellins, natural photosensitizers including hypocrellin A (HA) and hypocrellin B (HB), have been used as a traditional Chinese herbal medicine to cure various skin diseases. Hypocrellins have excellent antiviral activity, which can inhibit the growth of human immunodeficiency virus. They also exhibit significant light-induced antitumor property. In this article, thermal analysis technologies (e.g., differential scanning calorimetry and thermogravimetry) are employed to characterize whether the photosensitive hypocrellin A could be encapsulated with silica nanoparticle (SN) material or not, and evaluate the stability of inclusion complex. The results show that the inclusion complex exhibits improved performance in both stability and hydrophilicity than natural hypocrellin A. Fluorescence spectrophotometry studies have also been performed to verify the thermal analysis results. The results suggest that the thermal analysis technology could be used as an effective and rapid tool to characterize the encapsulation properties of the novel anticancer HA–SN complex.

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Abstract  

The physicochemical properties (crystal structure, surface acidity, surface area, catalytic activity and electrical conductivity) of TiO2-silica gel mixed oxides have been investigated. A series of mixed oxides of various compositions in the range of 0–100% for each component were prepared by calcining the mixed oxides in air at temperatures of 115, 300, 600 and 1000°C. The results obtained have been discussed and correlated.

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Journal of Thermal Analysis and Calorimetry
Authors: Ana Brăileanu, M. Răileanu, M. Crişan, D. Crişan, R. Bîrjega, V. Marinescu, J. Madarász, and G. Pokol

Abstract  

Two series of nanocomposites from the FexOy–SiO2 system, containing 20 mass% iron oxide were prepared by the alkoxide route of the sol–gel method, in the absence and presence of catalyst. The silica gel has been obtained using tetraethoxysilane. The iron(III) nitrate nonahydrate has been used as iron oxides source. The samples have been prepared in identical conditions, differing only by the gelation times, induced by different surface of evaporation/volume (S/V) ratios of sol let to gelify. Thermal analysis data have established the thermal treatments conditions of the prepared samples and were correlated with X-ray diffraction, IR spectroscopy and TEM results, in order to accomplish a complete structural characterization. The correlation between the structural modifications of the FexOy–SiO2 nanocomposites and different conditions of drying has been established.

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The size effect of silica nanoparticles (SiO2) on thermal decomposition of poly(methylmethacrylate) (PMMA) was investigated by the controlled rate thermogravimetry. Thermal degradation temperature of PMMA–SiO2 composites depended on both fraction and size of SiO2, the thermal degradation temperature of 23 nm (diameter) SiO2–PMMA (6.1 wt%) was 13.5 °C higher than that of PMMA. The thermal stabilities of 17 nm SiO2–PMMA (3.2 wt%) and 13 nm SiO2–PMMA (4.8 wt%) were 21 and 23 °C, respectively, higher than that of PMMA without SiO2. The degree of degradation improvement was increased linearly with the surface area of SiO2. The number of surface hydroxyl group in unit volume of SiO2 particle increased with increasing the specific surface area of SiO2, and the interaction between hydroxide group of SiO2 and carbonyl group of PMMA had an important role to improve the thermal stability of PMMA.

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Abstract  

A comparative method based on thermogravimetry is applied in order to characterise chemically functionalised surfaces. The mass loss of silica modified with -aminopropyl-trimethoxysilane (-APS) adsorbed from a range of solvents is interpreted by considering the physically adsorbed water, the silanol groups and the organic solvent. DRIFT spectroscopy is used to analyse the binding structure and adsorption mechanism. The mass loss calculated from thermogravimetric analysis is found to be in agreement with the values obtained by classical elemental analysis. Thermogravimetric analysis is found to be a quick and reproducible method, which only requires a few milligram sample. The amount adsorbed seems to be primarily dependent on the solvation of the -aminopropyl-trimethoxysilane by the solvent. A good solvent prevents adsorption as shown when comparing the magnitude of the mass loss with the difference between the solubility parameters of the -APS and the solvents. Ethanol seems to influence the structure of the adsorbed -aminopropyl-trimethoxysilane film.

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Abstract  

A new ion exchange material prepared by impregnating Aliquat-336 on silica-gel has been investigated for the recovery of plutonium from nitric-oxalic acid solutions. The distribution ratio of Pu(IV) was studied at various concentrations of nitric and oxalic acids. The presence of Al(III) and Fe(III) in the solution, enhances the uptake of Pu(IV). Pu(IV) breakthrough capacities (btc) have been determined using 2.5 ml bed of the ion exchange material column in the absence and the presence of Al(III) and Fe(III) nitrate. The elution behavior of Pu(IV) was also studied using nitric acid solutions containing reducing agents. More than 90% of plutonium could be recovered from nitric-oxalic acid solutions.

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Abstract  

Benzoylthiourea derivatives (N,N-diphenyl-N′-(3-methylbenzoyl)thiourea and diphenyl-N′-(4-methylbenzoyl)thiourea) were impregnated onto silica gel. The preconcentration of uranium(VI) from aqueous solution was investigated. Extraction conditions were optimized in batch method prior to determination by uv–visible absorption spectrometry using arsenazo(III). The optimum pH for quantitative adsorption was found as 3–7. Quantitative recovery of uranium (VI) was achieved by stripping with 0.1 mol L−1 HCl. Equilibration time was determined as 30 min for 99% sorption of U(VI). Under optimal conditions, dynamic linear range of for U(VI) was found as 0.25–10 μg mL−1. The relative standard deviation as percentage and detection limit were 5.0% (n = 10) for 10 μg mL−1 U(VI) solution and 8.7 ng mL−1, respectively. The method was employed to the preconcentration of U(VI) ions in soil and tap water samples.

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Abstract  

Nb2O5 supported on SiO2-Al2O3 were prepared with a wide loading range (2, 5, 10, 15, 20 and 25 mass%) and analyzed by simultaneous thermogravimetric (TG) and differential thermal analysis (DTA). The materials presented a phase transition close to 1364°C. This phase transition was studied by XRD, FTIR and Raman spectroscopy. Amixture of orthorhombic (T) andmonoclinic (H andM) crystalline phases was evidenced in the supported samples, which is coverage dependent, in contrast to the formation of only the monoclinic phase (H and M) when pure Nb2O5 is heated under the same conditions. These results indicate the stabilization of Nb2O5 on silica-alumina surface.

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