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Alkaline fading of bromophenol blue was chosen for the investigation of the effect of heating rate on the activation energies derived from the dynamic kinetic method. Freeman and Carroll's treatment was adopted to compute the activation energies from experimental data taken with three heating rates: namely 1°, 0.5° and 0.25°/min. It was found that the activation energy increases as the heating rate decreases. This is attributed to the non-equilibrium conditions. By extrapolating to zero heating rate, the activation energy obtained is comparable to that obtained via classical isothermal kinetics.

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Abstract  

The extraction of Tc(VII) by the mixture of tri-n-butyl phosphate (TBP) and 2-nitrophenyl octyl ether (NPOE) has been studied. 0.2M NPOE-TBP can extract Tc(VII) effectively from 1M HNO3 and 1M NaOH solutions with distribution ratios of 57.1 and 12.3, respectively. The distribution ratio of Tc(VII) decreases with increasing (>0.5M) HNO3 concentration but increases with the increase of NaOH concentration. A pH 9 NaOH solution has proven to be suitable for Tc(VII) stripping. A simple extraction-stripping cycle can remove Tc(VII) from a sodium hydroxide solution. A more sophisticated extraction process is proposed to remove Tc(VII) from nitric acid solution because the co-extracted HNO3 prevents the direct stripping of Tc(VII) by NaOH solution of pH 9.

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The relationship between plant communities and elevation in the Guandi mountainous area was studied. Data from 89 sampling units, each of 10 m x 20 m size, taken along an elevation gradient were analyzed by TWINSPAN, DECORANA and diversity and evenness indices. The samples were clustered into 23 groups by TWINSPAN, representing 23 vegetation types. The composition and distribution of communities varied greatly along the altitude gradient, suggesting that community diversity is closely related to elevation in the Guandi Mountains. This is due to the change of temperature and water-conditions along the elevation gradient. Species heterogeneity and evenness were significantly correlated with elevation along the entire gradient, but showing first a trend of increases and then decreases, corresponding to the hypothesis of maximum diversity at medium elevation. Species richness varied greatly in the study area, and was not significantly correlated with elevation.

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Testing of some dynamic kinetic equations

Part III. Zero-order reaction

Journal of Thermal Analysis and Calorimetry
Authors: P. H. Fong and D. T. Y. Chen

The acid-catalysed iodination of acetone in aqueous solution was used to test three dynamic kinetic equations. The Freeman and Carroll treatment yields the most satisfactory results.

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Testing of some dynamic kinetic equations

Part II. Second-order reaction

Journal of Thermal Analysis and Calorimetry
Authors: D. T. Y. Chen and P. H. Fong

The conversion of ammonium cyanate into urea in aqueous solution was used to test three dynamic kinetic methods. It is concluded that the Freeman and Carroll method is the most satisfactory.

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A technique has been proposed to promote hydrogen production from water by increasing the energy deposition in water through the conversion of γ-ray to low-energy electrons, which is achieved by putting solid materials into water. Simulation studies by the MCNP code indicate that the average deposited energy in water can be increased by optimizing geometry of the materials. In the present experiments using Al2O3 particles of various average diameters, the maximum amount of hydrogen produced is 3.48 μmol/cm3 for the water containing Al2O3 particles of 3 μm diameter, which is more than two order of magnitude larger of the H2 produced in water-only configuration.

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The degradation and mineralization of dibutyl phthalate (DBP), one of endocrine disruptors, by g-ray irradiation were demonstrated. The degradation was enhanced by the effective energy conversion of g-rays to low-energy electrons and photons with the assistance of the interactions between g-rays and metals, which is especially in the case of high Z materials effective. Numerical simulations using EGS code supported the experimental results. Improvements of the energy conversion process are also suggested by controlling the shape of the metal and its spatial configuration in the DBP solution.

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A series of anion-cation surfactants modified organoclays are prepared by incorporating both cationic surfactant, hexadecyltrimethylammonium bromide (HDTMAB), and anionic surfactant, sodiumdodecyl sulfonate (SDS), to montmorillonite. The added amounts of surfactant varied from 0.2 to 4.0 CEC of the used montmorillonite, similar to those reported in literature. A combination of elemental analysis, X-ray diffraction and thermogravimetric analysis is used in the characterization of the resulting organoclays. The experimental results show that anionic surfactants can not be intercalated into the montmorillonite whereas they can be loaded onto cationic modified montmorillonite, resulting in a further increase of organic carbon content of the resulting organoclays. This study demonstrates that SDS can be intercalated into montmorillonite interlayer space through the interaction with HDTMAB rather than by ion exchange. The intercalation of SDS results in an increase of the basal spacing of the resulting organoclays when comparing with HDTMAB modified montmorillonite and higher decomposition temperature of the intercalated surfactants when comparing with them in bulk state. These new insights are of high importance in the application of organoclays in the fields of remediation of polluted water and synthesis of clay based nanocomposites.

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Sorption of Th(IV) on Na-rectorite as a function of pH, ionic strength, soil humic acid (HA) and fulvic acid (FA) are studied under ambient conditions by using a batch technique. The results indicate that the sorption of Th(IV) on Na-rectorite is not only dependent on medium pH values, but also dependent on medium ionic strength and humic substances. Surface complexation and cation competition exchange account for Th(IV) sorption on Na-rectorite. The sorption of Th(IV) on Na-rectorite decreases with the increase on the concentration of NaNO3, Mg(NO3)2 and Ca(NO3)2, and increases with the increasing amount of HA/FA in the suspension/adsorbed on rectorite. Soil HA/FA enhances the sorption of Th(IV) on rectorite at medium pH<4 drastically, but the presence of FA reduces the sorption of Th(IV) at medium pH>6, and HA has no effect on Th(IV) sorption at medium pH>6. An interpretation for the results is attempted, considering the occurrence of different sorption mechanisms.

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A TiO2/monazite photocatalyst was prepared by embedding TiO2 nanoparticles into a monazite substrate surface. TiCl4 hydrolysis/citric acid chelating procedure under acidic conditions were used to synthesize the nanophase TiO2 particles. The anatase TiO2/monazite photocatalyst surface area, morphology, crystalline and elemental concentrations were characterized using Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM), X-ray diffraction (XRD), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Monazite contains a large amount of Ce-, La-, Nd- and Th-PO4 compounds; it has been known as a natural mineral material with minor radioactivity. TiO2-CeO2 composite is a kind of radiation sensitive photocatalyst in which the radiations of thorium nuclides give energy to trigger TiO2 and cerium ions which play an energy absorber with charge separator. The result showed that methylene blue and phenol were spontaneously photocatalytic decomposed by TiO2/monazite composite even in a dark environment. A synergistic effect was also examined with applied exterior UV or 60Co irradiation. A hybrid mechanism is proposed; according by the radioluminescence (RL) from excited Ce ion by γ-radiation soliciting CeO2/TiO2 heterojunction (HJ). This seems to be a possible mechanism to explain this self-activated photo-catalytic behavior.

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