The radioactivity and the chemical nature of additives as factors determining the photocatalytic activity of TiO2

Microcomposites consisting of TiO₂ and ThF₄ or UO₃ (0.5?C2% of the TiO₂ mass) are produced by sol-gel synthesis of TiO₂ in presence of the respective additives. X-ray diffraction study reveals small effect of the latter on TiO₂ phase composition and cell parameters and significant influence on the crystallite size and UV/Vis reflectance spectra. The photocatalytic tests in presence of TiO₂-ThF₄ microcomposites under UV and solar irradiation show a non-monotonic increase of the Malachite Green degradation rate constant with the increase of ThF₄-content. No changes in the photocatalytic activity are observed in the presence of UO₃ but the latter composites exhibit activity in darkness. The results are compared with previously reported data on the performance of TiO₂-ThO₂ photocatalyst with the same radioactivity and suggest that both radioactivity and the chemical nature of the dopants are responsible for the photocatalytic performance of TiO₂-based composites containing radioactive substances.      

Physicochemical fractionation of americium, thorium, and uranium in Chernozem soil after sharp temperature change and soil drought

A sequential extraction procedure was used to study the changes in the physicochemical forms of americium (Am), thorium (Th), and uranium (U) in laboratory-contaminated Chernozem soil as a result of sharp variations of the environmental temperature and soil moisture. The influence of freezing and soil drought on the radio-ecological hazard was evaluated three months after radioactive contamination with aqueous solutions of ²⁴¹Am, ²³⁴Th, and U. The subsequent changes in the physicochemical forms of the actinides, caused by sharp increases in the environmental temperature and soil moisture, were examined for one month. The data showed that continuous freezing increased the potentially mobile forms of Am and Th but had the opposite effect on U. Prolonged soil drought did not influence the fractionation of Am and Th but led to the redistribution of U between the carbonates and organic matter and caused its immobilisation. The sharp increase in the temperature of the frozen soil caused the immobilisation of Am and Th and increased the potential mobility of U. The warming and enhanced humidity of the dry soil led to the immobilisation of Am and redistribution of U between the soil phases.     

An analogue of Montel's theorem for some classes of rational functions

For sequences of rational functions, analytic in some domain, a theorem of Montel's type is proved. As an application, sequences of rational functions of the best L _p -approximation with an unbounded number of finite poles are considered.     

Rational functions of best uniform approximation and holomorphic continuation of functions

Let f be a function, continuous and real valued on the segment Δ, Δ ⊂ (−∞, ∞) and {R_n} be the sequence of the rational functions of best uniform approximation to f on Δ of order (n, n). In the present work, the convergence of {R_n} in the complex plane is considered for the special caseswhen the poles (or the zeros, respectively) of {R_n} accumulate in the terms of weak convergence of measures to acompact set of zero capacity. As a consequence, sufficient conditions for the holomorphic and the meromorphic continuability of f are given. The work is supported by Project 69 with Ministry of Science and Education, Bulgaria.     

Synthesis and characterization of Al-and Y-Al-citrates as potential precursors for YAlO3

Al-and Y-Al-citric complexes have been synthesized in ethylene glycol medium at conditions close to the ones used in polymerized complex method and their composition and spectral characteristics have been studied. Proofs have been found for the formation in the bimetallic system of a mixed-metal Al-Y-complex. Doubly ionized and esterified ligands take place in the Al-complex. All of the ligands forming Y-Al-complex are mono-or doubly esterified. Deprotonation of the alcoholic group takes place in the formation of the mixed-metal complex. Both complexes contain adduct-bonded ethylene glycol. Heating of the bimetallic complex or of the polyester resin formed leads to not phase-homogeneous YAlO₃-along with cubic YAlO₃, its orthorhombic modification as well as Y₄Al _l2O₉ are found by X-ray diffractometry.     

Effect of structural analogy between ZSM-5 and silicalite catalysts on the oxidative methylation of toluene with methane

Summary With ZSM-5 and silicalite (both initial and BaO modified) the yield of styrene, the most desirable reaction product, was highly represented when BaO modified silicalite was used as catalyst for the reaction. The catalytic results fitted the basicity, surface area and structural crystallinity.     

Mechanochemical effects in U3O8

The effect of the mechanical treatment of U₃O₈ in a planetary ball mill in air or as a suspension in benzene solution of thyolilthreefluoroacetone (TTA) on the nature of the oxide and on the leaching of U and ²³⁴Th into diluted aqueous solutions of HCl, Na₂EDTA and NaCl has been studied. Transformation of U₃O₈ to UO₂, is much stronger expressed when the mechanoactivation is performed in air is established. The leaching behavior of U and Th depends significantly on the activation mode and on the leaching reagent nature. The role of mechanochemically enhanced UO₂-ThO₂ solid solution formation for the observed effects is discussed.     

Organic/Inorganic bioactive materials Part III: in vitro bioactivity of gelatin/silicocarnotite hybrids

In this work we present our experimental results on synthesis, structure evolution and in vitro bioactivity assessment of new gelatin/silicocarnotite hybrid materials. The hybrids were obtained by diluting gelatin (G) and silicocarnotite (S) ceramic powder with G:S ratios of 75:25 and 25:75 wt.% in hot (40°C) water. The hybrids were characterized using XRD, FTIR, SEM/EDS and XPS. FTIR depicts that the “red shift” of amide I and COO⁻ could be attributed to the fact that the gelatin prefers to chelate Ca²⁺ from S. The growth of calcium phosphates on the surface of the hybrids synthesized and then immersed in 1.5 SBF for 3 days was studied by using of FTIR, XRD and SEM/EDS. According to FTIR results, after an immersion of 3 days, A and B-type CO₃HA can be observed on the surface. XRD results indicate the presence of hydroxyapatite with well defined crystallinity. SEM/EDS of the precipitated layers show the presence of CO₃HA and amorphous calcium phosphate on the surface of samples with different G/S content when immersed in 1.5 SBF. XPS of the G/S hybrid with 25:75 wt.% proved the presence of Ca-deficient hydroxyapatite after an in vitro test for 3 days.