Bulgarian natural diatomites: modification and characterization

Natural Bulgarian diatomite modified by oxidation with sulfuric acid and H₂O₂ or by coating with manganese oxide was characterized considering its chemical composition, surface area, pore volume, and structure. Modified diatomites displayed larger surface area and pore volumes in comparison with untreated natural diatomite, which favored their sorption behavior. Sorption properties of diatomites towards Fe³⁺, Pb²⁺, Cu²⁺, Cd²⁺, Mn²⁺, Ni²⁺, Co²⁺, Cr³⁺, Pd²⁺, Ca²⁺, and Mg²⁺ were investigated and their sorption capacities were determined. Sorption properties of manganese oxide-modified diatomite were superior to those of diatomite modified by oxidation. Owing to its high sorption capacity towards Co²⁺, Ni²⁺, Pb²⁺, Cr³⁺, Fe²⁺, Cu²⁺, and Cd²⁺, the manganese oxide-modified diatomite is a promising low-cost sorbent for selective removal of milligram amounts of these toxic metal ions from contaminated water.     

Electrolytic Deposition of Cobalt(III) Oxide in the Presence of Nickel(II) and Chromium(III) Ions

Preparation conditions and nature of anodic processes in electrolytic deposition of cobalt(III) oxide in the presence of nickel(II) and chromium(III) ions from mixed aqueous solutions of their sulfates were studied. The deposits obtained are of interest for creating effective cathode materials for lithium batteries.     

Model atom approximation for estimating the localized bond energy based on the Morse potential

A method for solving the vibrational problem by using an effective energy operator containing Morse potentials and new model atom approximations is developed. The approach is explained by reference to the trifluoromethylacetylene molecule where the model atom is a CCC or CC atomic group. Using certain assumptions for parameters in the spectrum, we managed to confirm the known experimental result of bond strengthening of the terminal hydrogen atom when the CC bond order increases and to predict the CH bond energy (462.5±4.6 kJ/mole). This procedure seems to be also effective for more complex adsorption problems where the model atom is a crystal. Given that the surface effect is predicted by the parameters of the method, the corresponding model energy operator is constructed. With appropriate spectral data, the approach guarantees very accurate estimations of adsorption bond energies. Translated from Zhumal Struktumoi Khimii, Vol. 38, No. 2, pp. 263–269, March–April, 1997.     

Temperature dependence of resonance Raman spectra of carotenoids

To understand the mechanism of the photoprotective and antioxidative functions of carotenoids, it is essential to have a profound knowledge of their excited electronic and vibronic states. In the present study we investigate the most powerful antioxidants: β-carotene and lutein by means of resonance Raman spectroscopy. The aim was to study in detail their Raman spectra in solution at room temperature and their changes as a function of temperature. To measure the spectra in their natural environment pyridine has been used as a solvent. It has been chosen because of its polarizability (n=1.5092) which is close to that of membrane lipids and proteins. The temperature dependence of the most intensive ν(1) band in the range from 77 K to 295 K at 514.5 nm excitation has been obtained. It was found that in pyridine the CC stretching frequency, its intensity, line shape, and line width are very sensitive to the temperature (the sensitivity being different for the two studied carotenoids). The observed linear temperature dependence of the CC stretching frequency is explained by a mechanism involving changes of the vibronic coupling and the extent of π-electron delocalization. The different behavior of the temperature-induced broadening of the ν(1) band and its intensity for the two studied carotenoids can be associated with the different nature of their solid matrices: glassy for β-carotene and crystalline-like for lutein, owing to their different chemical structures.     

The maximum value of the size effect and its manifestation in the thermodynamic properties of nanomaterials

We propose a method for estimating the radius of the maximum r _max and significant r _sign for the manifestation of the size effect in nanomaterials. Our method is based on the size dependence of the melting temperature and the concept of limit values for the effect at points where properties vary by factors of e ₂ and e. It was established that an empirical dependence based on the vibrational approach is most advantageous for determining r _max and r _sign. The Kelvin equation allows to estimate the r value and to predict its periodic dependence on the atomic number of individual elements. The range of variation of r for transition metals is ∼1 nm within the limits of 0.62–1.69 nm.     

Electrolytic Sodium-Vanadium Oxide Compounds in Intercalation Cathodes of Lithium Battery

Electrolytic mixtures of vanadium(V) oxide and -Na_xV₂O₅ bronze were synthesized and studied by X-ray diffraction and thermal analyses, step galvanostatic titration, IR absorption spectroscopy, mass spectroscopy, and electrochemical methods.     

钕玻璃的光泵感应热畸变

本文对钕玻璃的光泵感应热畸变作了理论分析,给出了光泵感应热畸变与钕玻璃热光性质的关系,并对高重复率脉冲器件和单次脉冲器件作了热畸变的定量测量,实验结果在一定程度上与理论分析相符。     

微量量热法研究温度对两种石油菌生长的影响

本文采用微量量热法测定了两种石油菌在不同温度下的生长热谱图. 按限制性条件下微生物生长模型 ,用三点法进行了数学处理, 得出了生长速率常数(k) ; 计算机拟合 k-T 非线性方程,得到了石油菌 I,II的最佳生长温度( To pt)分别为 322. 07K 和 322. 85K. 按阿仑尼乌斯公式和过渡态理论计算得到有关热动力学函数, 并根据所得结果对两种石油菌的生长代谢过程进行了热动力学分析.     

Theory of phonon properties in doped and undoped CuO nanoparticles

We have studied the phonon properties of CuO nanoparticles and have shown the importance of the anharmonic spin–phonon interaction. The Raman peaks of CuO nanoparticles shift to lower frequency and become broader as the particle size decreases in comparison with those of bulk CuO crystals owing to size effects. By doping with different ions, in dependence of their radius compared to the host ionic radius the phonon energies ω could be reduced or enhanced. The phonon damping is always enhanced through the ion doping effects.     

Multiferroism in the dielectric function of CuO

The multiferroic properties of bulk CuO are manifested in the dielectric function which can be triggered by an external magnetic field h and by the temperature T. Within a microscopic model and a Green's function technique we have calculated the dielectric function \varepsilon ({\bf k};T,\;h). At the magnetic phase transition temperature T_{{\rm N}2} the dielectric function offers a pronounced anomaly. This kink disappears when the magnetic field is enhanced and \varepsilon ({\bf k};T,\;h) decreases with increasing h ‐field. Both properties are indications for a strong magnetoelectric coupling in this material. The observation of multiferroism in CuO within an analytical approach is achieved by considering frustration and a linear magnetoelectric coupling. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)