Solid-state structure of copper complexes of N-(2-carboxyethyl)chitosan

The sorptivity for ions of the Irving-Williams series (Zn2+, Cu2+, Co2+, Ni2+) was estimated for the chelate sorbent N-(2-carboxyethyl)chitosan cross-linked by nanosecond electron-beam irradiation. The maximum capacity reaches 3.7 mmol/g using a mixture of the appropriate sulfates at pH 4.5. The selectivity of copper sorption is 80%. The structure of the coordination sphere of the copper complexes with N-(2-carboxyethyl)chitosan was investigated by ESR spectroscopy

Coordination of Cu(II) and Ni(II) in polymers imprinted so as to optimize amine chelate formation

Molecular imprinting has become an established technique. However, little was done on direct investigation of the sorbents produced. In the present work, en ESR method was used for the investigation of the complex formation processes within the sorbents imprinted with copper(II) and nickel(II). The sorbents were synthesized from a mixture of linear low molecular weight polyethyleneimine oligomers. The composition, structure and distribution of complexes in the resin phase were investigated. The effects of the synthesis conditions, loading degree and water content were examined. The presence of certain copper complexes was found to be a convenient characteristic of the imprinting efficiency. The optimum synthesis conditions for obtaining sorbents imprinted with copper(II) or nickel(II) were identified. The imprinting results in the improvement of the stability of the complexes and the selectivity and working capacity of the sorbents. The imprinted samples are also characterized by a more even distribution of chelating sites. The synthesis conditions and loading by ions allow for the regulation of the ratio between individual complexes and magnetic associates in the resin phase. This is a critical point on the future use of the metal containing imprinted sorbents as catalysts. (C) 2003 Published by Elsevier Science Ltd

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 temperature. Chitin and its complexes in the extracted samples were identified by FTIR spectroscopy using reference sample of Aspegillus Niger mushrooms. The presence of chitin parts causes the absorption band at 1650, 1552 and 1376 cm-1, which correspond to vibrations of amide groups amide I amide II and amide III, respectively. Using elemental analysis, the ratios of chitin and glucan parts were estimated and the percentage of chitin composition of all species was determined. For most of raw sources a fraction of chitin part was greater than that of glucan part. The chitin content of the samples studied ranged between 0.7-0.8 % of DM (dried mass) for wine (beer) waste products and 38% of dried mass (DM) for cockroaches. © 2016 Author(s).2014/239, 4.1626.2014/KRussian Foundation for Basic Research, RFBR: 14-03-00898Government Council on Grants, Russian FederationThis work was supported by the Russian Foundation for Basic Research (Grant 14-03-00898), the Program 211 of the Government of the Russian Federation No 02.A03.21.0006 and the State Tasks of the Ministry of Education (Russian Federation) No. 4.1626.2014/K and No. 2014/239 and the local Grant of University of Rwanda "Chitosancontaining materials of multifunctional application for needs of Rwanda". The authors are thankful to J.P. Intwali (Rwanda), E.V. Habumugisha (Rwanda), Ch. Ukundineza (Rwanda) and D. Niyoyita (Rwanda) for capturing insects and gathering mushrooms and their initial preparation for chitin extraction

Oxidative dehydrogenation of 2,3,5-trimethyl-1,4-hydroquinone in the presence of titanium dioxide hydrogel

Liquid-phase oxidative dehydrogenation of 2,3,5-trimethyl-1,4-hydroquinone in the presence of titanium dioxide hydrogel was studied by a kinetic method. Associative interactions between the substrate, oxidant, and gel were detected by voltammetry and ESR and IR spectroscopy.Russian Foundation for Basic Researc

Dynamics of pH-sensitive nitroxide radicals in water adsorbed in ordered mesoporous molecular sieves by EPR Spectroscopy

A spin pH probe technique was used to study the influence of the channel diameter on the EPR spectra of pH-sensitive nitroxide radicals (NR) located in the channels of the mesoporous molecular sieves MCM-41 and SBA-15 with diameters ranging from 2.3 to 8.1 nm. From EPR spectra analysis and the results of the NR retention by the mesoporous molecular sieves upon washing with an aqueous KCl solution, the regularities of NR molecular location inside the channels were studied. The obtained dependence of the fraction of the radical molecules in the fast motional regime (with the rotational correlation times, τc = 2 × 10-11 s-9 × 10-11s) in the channels of the mesoporous molecular sieves as a function of pH indicates that both NR in the fast and slow motional regime (with τc = 8 × 10 -9s-7 × 10-10s) may be used for estimation of the solution acidity inside the channels and of the near-surface electrical potential. © 2013 Elsevier Inc. All rights reserved

Surface electrical potential of ZrO2-SiO2 binary xerogels by EPR pH-sensitive spin probes

In this paper, we performed a qualitative assessment of the surface electrical potential for individual and binary xerogels based on silica and zirconia which were synthesized by hydrolysis in aqua ammonia medium. The effect of surface charge on near surface local acidity of solid-phase compositions was studied. © 2019 Author(s)

Surface Electrical Potential of ZrO2–SiO2 Binary Xerogels by EPR pH-Sensitive Spin Probes

We acknowledge the financial support of the Program 211 of the Government of the Russian Federation № 02.A03.21.0006, RFBR grants № 17-03-00641 and 18-29-12129mk, the State Task from the Ministry of the Education and Science of the Russian Federation № 4.9514.2017/8.9

Synthesis of Cu(II)-containing TiO2-SiO2 binary xerogels by hydrolysis of a mixture of tetrabutoxytitanium, tetraethoxysilane, and copper(II) chloride in a water-ammonia atmosphere

A Cu(II)-containing binary xerogel TiO2-SiO2 was synthesized by joint hydrolysis of tetrabutoxytitanium, teraethoxysilane and copper(II) chloride dissolved in their mixture. The synthesis was performed in a vapor of 10% aqueous ammonia under static conditions. EPR spectroscopy was used to examine the state of Cu(II) in the xerogel matrix. Data on specific features of the behavior of saccharose within xerogel pores under heating were obtained. The catalytic activity of the xerogel was tested by the kinetic method on model reactions of hydrogen peroxide decomposition and oxidative dehydrogenation of trimethylhydroquinone. © 2013 Pleiades Publishing, Ltd

Dimerization and low-dimensional magnetism in nanocrystalline TiO2 semiconductors doped by Fe and Co

The report is devoted to an analysis of the structural and magnetic state of the nanocrystalline diluted magnetic semiconductors based on TiO2 doped with Fe and Co atoms. Structural and magnetic characterization of samples was carried out using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR) spectroscopy, SQUID magnetometry, and the density functional theory (DFT) calculations. Analysis of the experimental data suggests the presence of non-interacting paramagnetic Fe3+ and Co2+ ions in the high-spin state and negative exchange interactions between them. The important conclusions is that the distribution of dopants in the TiO2 matrix, even at low concentrations of 3d-metal dopant (less than one percent), is not random, but the 3d ions localization and dimerization is observed both on the surface and in the nanoparticles core. Thus, in the paper the quantum mechanical model for describing the magnetic properties of TiO2:(Fe, Co) was suggested. The model operates only with two parameters: paramagnetic contribution of non-interacting 3d-ions and dimers having different exchange interactions between 3d magnetic carriers. © Published under licence by IOP Publishing Ltd

Unconventional magnetism of non-uniform distribution of Co in TiO2 nanoparticles

High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), magnetic methods, and density-functional theory (DFT) calculations were applied for the investigations of Co-doped anatase TiO2 nanoparticles (∼20 nm). It was found that high-spin Co2+ ions prefer to occupy the interstitial positions in the TiO2 lattice which are the most energetically favourable in compare to the substitutional those. A quantum mechanical model which operates mainly on two types of Co2+ – Co2+ dimers with different negative exchange interactions and the non-interacting paramagnetic Co2+ ions provides a satisfactorily description of magnetic properties for the TiO2:Co system. © 2020 Elsevier B.V.Russian Foundation for Basic Research. Ministry of Science and Higher Education of the Russian Federatio