Mikhail Chislov

Photocatalytic properties and hydration of perovskite-type layered titanates A2Ln2Ti3O10 (A = Li, Na, K; Ln = La, Nd)

Layered perovskite-type oxides A2Ln2Ti3O10 (A = Li, Na, K; Ln = La, Nd) prepared by solid-phase synthesis and their hydrated forms were characterized by the methods of TGA, XRD, and by UV-Vis spectroscopy. Photocatalytic activity of A2Ln2Ti3O10 oxides in reaction of hydrogen evolution from aqueous alcoholic suspensions irradiated by UV-light was studied. It was shown that the ability to intercalation of water into interlayer space essentially affects the rate of photoinduced hydrogen evolution and is a determining factor leading to a high photocatalytic activity.

Ion-Exchange Reactions in the Structure of Perovskite-like Layered Oxides: I. Protonation of NaNdTiO 4 Complex Oxide

The behavior of perovskite-like NaNdTiO4 complex oxide in acid aqueous solutions was studied. By the X-ray and thermogravimetry analyses the instability of NaNdTiO4 in aqueous solutions was found, which is determined by the sodium cation exchange for protons and by water molecules intercalation into the interlayer space of the crystal structure. The proton-containing layered oxides HNdTiO4 and HxNa1−xNdTiO4·yH2O were obtained (1 < x < 0.64, 0 < y < 0.47). The structure of the H0.73Na0.27NdTiO4·0.3H2O compound was refined.

Polar Nature of (CH3NH3)3Bi2I9 Perovskite-Like Hybrids

High-quality single crystals of perovskite-like (CH3NH3)3Bi2I9 hybrids have been synthesized, using a layered-solution crystal-growth technique. The large dielectric constant is strongly affected by the polar ordering of its constituents. Progressive dipolar ordering of the methylammonium cation upon cooling below 300 K gradually converts the hexagonal structure (space group P63/mmc) into a monoclinic phase (C2/c) at 160 K. A well-pronounced, ferrielectric phase transition at 143 K is governed by in-plane ordering of the bismuth lone pair that breaks inversion symmetry and results in a polar phase (space group P21). The dielectric constant is markedly higher in the C2/c phase above this transition. Here, the bismuth lone pair is disordered in-plane, allowing the polarizability to be substantially enhanced. Density functional theory calculations estimate a large ferroelectric polarization of 7.94 μC/cm2 along the polar axis in the P21 phase. The calculated polarization has almost equal contributions of the methylammonium and Bi3+ lone pair, which are fairly decoupled.

Sorption and transport of aqueous isopropanol solutions in polyimide-poly(aniline-co-anthranilic acid) composites

Separation of aqueous isopropanol solutions by pervaporation using membranes based on composites of a polyimide with an aniline-anthranilic acid copolymer was studied.

Photocatalytic activity and intercalation of layered perovskite-like tantalates ANdTa2O7 (A = H, Li, Na, K, Rb, Cs)

Layered perovskite-like oxides ANdTa2O7 (A = H, Li, Na, K, Rb, Cs) were synthesized and characterized by means of diffuse reflection spectroscopy, thermogravimetry, and simultaneous thermal and X-ray phase analysis. Comparative analysis of the photocatalytic activity of ANdTa2O7 in the UV-induced hydrogen evolution from an aqueous isopropanol solution was performed. NaNdTa2O7 and HNdTa2O7 are able to intercalate water to the interlayer space. The compositions and thermal stability ranges of intercalates were determined. No explicit correlation between the photocatalytic activity of layered oxides and their ability to intercalate water to the interlayer space was found.

Relative Reactivity of Benzothiophene-Fused Enediynes in the Bergman Cyclization

To find promising analogues of naturally occurring enediyne antibiotics with a sufficient reactivity in the Bergman cyclization and moderately stable under isolation and storage, a scale of relative enediynes reactivity was created on the basis of calculated free activation energies for the Bergman cyclization within 12 known and new benozothiophene, benzene, and cinnoline annulated 9- and 10-membered enediynes. To verify the predicted reactivity/stability balance, three new carbocyclic enediynes fused to a benzothiophene core bearing 3,4,5-trimethoxybenzene, fluoroisopropyl, and isopropenyl substituents were synthesized using the Nicholas-type macrocyclization. It was confirmed that annulation of a 3,4,5-trimethoxybenzene moiety to a 10-membered enediyne macrocycle imparts high reactivity to an enediyne while also conferring instability under ambient temperature. Fluoroisopropyl-substituted 10-membered enediyne from the opposite end of the scale was found to be stable while moderately reactive in the Bergman cyclization. Along with the experimentally confirmed moderate reactivity (DSC kinetic studies), (fluoroisopropyl)enediyne showed a significant DNA damaging activity in plasmid cleavage assays comparable with the known anticancer drug Zeocin.

Similar nature leads to improved properties: cyclic organosilicon triperoxides as promising curing agents for liquid polysiloxanes

Cyclic organosilicon triperoxides were found to be vinyl-selective free-radical initiators for thermal curing at 100–180 °C of vinyl-terminated polydimethylsiloxane and trimethylsilyl-terminated polymethylhydrosiloxane producing homogeneous transparent silicone rubbers with antibacterial properties. The usage of the cyclic organosilicon triperoxides as the curing agents does not require free radical inhibitors in comparison with diacyl- and dialkyl peroxides. Among the tested compounds, the peroxide with the Me–Si–Me fragment and two cyclohexane rings is a much more active curing agent (180 °C, c = 0.22 M, τcuring = 45 min) than other organosilicon peroxides. Cured silicone samples from mixtures with vinyl-terminated polysiloxane and silicone hydride have improved mechanical properties: peroxides provide more than 200% elongation, and compression sets of the samples are less than 1%. The prepared silicone rubbers showed pronounced antibacterial activity.

Thermal transformations of gamma alumina with phosphorus oxide surface nanostructures

Differential scanning calorimetry, thermogravimetry, and X-ray diffraction analysis were used to study the fundamental aspects of structural-chemical transformations occurring under the action of temperature in the range 50–1530°C in the system constituted by alumina core and phosphorus oxide shell synthesized by the molecular-layering method. It was shown that, as the P/Al molar ratio in the system increases from 0.05 to 0.14, the stability range of low-temperature forms of alumina extends to higher temperatures because crystalline aluminum phosphate is formed on the surface. It was demonstrated that using an inorganic binder based on a silicate binding agent and alumina modified with an aluminum phosphate layer provides a ~3.5-fold increase in the mechanical strength of the material at a ~5-fold decrease in the internal stress as compared with the composition with the unmodified oxide.