L. S. Molochnikov

Spin probe study of acidity of inorganic materials

Acidic characteristics of various inorganic materials, such as silica gel, aluminum, and titanium(IV) oxides, original and modified with F− and SO42− ions, in the form of hydrogels and nanostructured powders doped by copper(II) ions, are studied. It is shown that pH values inside pores of the studied sorbents (pHintr) differ from the pH of external solutions by 0.5–1.1 units. In the pores of original γ-Al2O3, the pHintr values are higher, while, in pores of γ-Al2O3 samples modified with F− и SO42−, as well as nonmodified α-Al2O3, SiO2 gel, and TiO2 hydrogels, pHintr are lower compared to the pH of the external solution. It is found that pHintr decreases, as the content of Cu2+ ions in the TiO2 phase grows, and, beginning with a certain moment, it coincides with pH of an equilibrium solution. The pKa values of functional group dissociation in some materials are determined. It is shown that, using spin probes, that is, pH-sensitive nitroxyl radicals, the electrostatic potential of the surface of nanostructured TiO2 can be estimated.

Synthesis of poly[N-(2,3-dihydroxypropyl)aminostyrene], a new sorbent for boron(III) ions

A procedure was developed for preparation of poly[N-(2,3-dihydroxypropyl)aminostyrene] via successive stages of nitration, reduction, and glycidol treatment of polystyrene, which gives the polymer with a maximal degree of functionalization. The composition and structure of the intermediates and end products of the polymer-analogous reactions were characterized by elemental analysis, IR spectroscopy, and solid-state 13C NMR spectroscopy. The sorption characteristics of poly[N-(2,3-dihydroxypropyl)aminostyrene] toward boroncontaining ions were assessed.

Structure and characteristics of chitosan cobalt-containing hybrid systems, the catalysts of olefine oxidation

Cobalt-containing hybrid organo-inorganic materials based on the chitosan-SiO2, chitosan-Al2O3, and chitosan-cellulose systems were obtained. The surface structure and processes that occur during the formation of metal-containing materials, the catalytic properties of which were studied in the oxidation reactions of alkene, were investigated by EPR spectroscopy using a stable pH-sensitive nitroxyl radical, 4-dimethylamino-2-ethyl-5,5-dimethyl-2-(pyridin-4-yl)-2,5-dihydro-1H-imidazole-1-oxyl, as the adsorbed probe molecules.

Medium acidity and catalytic properties of composite materials based on silica and titania and powder cellulose in the presence of Cu2+ ions

Composite materials (CMs) were synthesized from silica and titania xerogels. The influence of the charged state of the CM surface on complexation with Cu2+ ions and the catalytic activity of the obtained samples in model oxidative dehydrogenation of trimethylhydroquinone with air oxygen was analyzed. Using powder cellulose in the synthesis of CMs increased the specific surface of inorganic dioxides and lowered the negative electric potential of the CM surface. This caused a redistribution of the ratio between different types of copper structures formed in the samples during the copper sorption and led to the catalytic activity of the CMs.

Novel methods for synthesis and sorption properties of N,O -(2,3-dihydroxy)propylchitosan

The direct addition of glycidol to chitosan in a gel medium under exposure to ultrasound afforded the chelating aminopolymer N,O-(2,3-dihydroxy)propylchitosan with a degree of substitution up to 2.3. The sorption characteristics of the crosslinked aminopolymers with respect to boron-containing ions were estimated.

Synthesis of TiO2-SiO2 and TiO2-SiO2-Cu(II) xerogels by cohydrolysis of precursors in the absence of a solvent and redox catalysts

Cohydrolysis of tetrabutoxytitanium and tetraethoxysilane in a desiccator in the presence of water vapor produced a TiO2-SiO2 binary xerogel and its Cu(II)-containing analog. The hydrolysis was performed without using either a solvent, or redox catalysts. The effect of the synthesis conditions on the physicochemical properties of the obtained material was studied.

Investigation of the structure of chitosan hybrid systems by pH-sensitive nitroxyl radical

Hybrid organo-inorganic materials based on the chitosan-SiO2, chitosan-Al2O3, and chitosancellulose systems are prepared. The structure of the surface is studied by means of EPR spectroscopy using the stable pH-sensitive nitroxyl radical, 4-dimethylamino-2-ethyl-5,5-dimethyl-2-pyridine-4-yl-2,5-dihydro-1H-imidazole-1-oxyl as adsorbed probe molecules, and the processes that occur during the formation of hybrid materials are considered.

Effect of the surface charge on the complexing and catalytic properties of Cu2+-containing composite materials based on zirconia and powdered cellulose

Composite materials (CMs) based on zirconia xerogels and powdered cellulose (PC) were synthesized. The effect of the CM surface charge on their complexing properties with respect to Cu2+ ions and on the catalytic activity of the samples in model reactions of the decomposition of H2O2 and the oxidative dehydrogenation of trimethylhydroquinone with atmospheric oxygen was analyzed. It was experimentally proved that the use of PC for the synthesis of ZrO2-based CMs, as in the case of previously studied CMs based on SiO2 and TiO2, leads to an increase in the specific surface area Ssp and a decrease in the negative electric potential of their surface. The surface charge, sorption method, and the composition of the buffer solution used for sorption have a significant effect on the copper(II) content in the CM phase, the distribution pattern, and the composition of the sorbed copper(II) compounds and on the catalytic activity of the synthesized Cu2+-containing CMs.

Crystal structure of N-(3-hydroxypropyl)-β-alanine and Bis(N-(3-hydroxypropyl)-β-alaninato)dicopper(II) [Cu2 (Pro-ala)2]

N-(3-Hydroxypropyl)-β-alanine was synthesized by the reacti on of 3-aminopropanol with acrylic acid. From this ligand and basic copper carbonate, bis(N-(3-hydroxypropyl)-β-alaninato)dicopper(II) [Cu2 (C6H11NO3)2] was obtained. The structures of the chelating agent and the copper complex were studied by X-ray diffraction. The Cu(II) coordination polyhedron is a distorted square pyramid. Each ligand forms six-membered β-alaninate and propanolamine chelate rings. The propoxy group functions as a bridge. In the crystal structure, the molecules form intermolecular coordination bonds C=O→Cu, which are perpendicular to the layers. The EPR signal typical of dimeric copper complexes is not observed due to low occupancy of the excited paramagnetic triplet state. The weak paramagnetic signal from monomeric copper complex allowed recording of the 1H NMR spectrum of [Cu2 (Pro-ala) 2] with characteristic line broadening and contact shift. It follows from the obtained data that on dissolution, the complex dissociates by 40% to give monomeric copper complexes.

Characterization of chitin and its complexes extracted from natural raw sources

It is known that the main source of chitin and chitosan are shells of shrimp and other sea crustaceans. Alternative row sources of chitin, chitosan and its complexes are the lowest plants – mushrooms and insects. Also industrial wastes, especially from brewing of beer and manufacture of wine and ethanol can be used for extracting chitosan-containing products. The present research is aimed to the extraction of chitin and its complexes from alternative row sources, such as insects (cockroaches Pariplaneta Americana linnaeus and bees Apis mellifera lineaus), mushrooms (Amanita phalloides and Lactarius subdulius), waste banana wine (Kovibar and Urwibutso Inc.) and beer products (Bralirwa Inc., traditional sorghum) characteristic for Rwanda and their characterization using FTIR spectroscopy and elementary analysis. In chitin and its complexes extraction from all used raw sources, conditions for deproteinization were: 8% NaOH at 95 °C for 1 h and demineralization involved treatment with 6.7 % HCl at room temper...