Here we report on the method of synthesis in gel of a new heterocyclic aminopolymer-N-2-(4-pyridyl)ethylchitosan (4-PEC) via direct addition of 4-vinylpyridine to chitosan that yields a derivative ...with the substitution degree (DS) up to 0.8. The comparison of reactivity, thermal, spectroscopic, and sorption properties of a new derivative and its isomer N-2-(2-pyridyl)ethylchitosan (2-PEC) is presented. 2-PEC has higher sorption capacity and forms more stable chelates with PdCl42− and PtCl62− ions than 4-PEC, but the latter shows higher selectivity to noble metals ions in the presence of Cl− ions. A gradual increase of the sorption capacities and the affinity coefficient for Cu2+ and Ni2+ in the row chitosan<4-PEC<2-PEC was related to the increase of electron donor nitrogen atoms content and chelating properties of 2-PEC. A nearly negligible increase of the 4-PEC sorption capacity for Ag+, as compared to plain chitosan, was suggested to be dependent on the difference in complexation models for 2-PEC and 4-PEC derivatives. The density functional theory (DFT) calculations have shown that the “pendant” model of the complex with Ag(I) is energetically favorable only for 2-PEC derivative, while in cases of chitosan and 4-PEC only “bridge” complexes can be formed that results in lower sorption capacity.
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•New crystal hydrate of the composition ZnZr2F10∙6H2O has been synthesized.•The crystal structure of the compound was determined by the X-ray method.•The crystal structure is built of ...flat anion layersZrF5∞2−and Zn(H2O)62+ cations.•The complex cations and anions are linked by hydrogen bonds.•The IR, Raman and NMR spectroscopy data for the compound and products of its dehydration were analyzed.
The synthesis and study of the structure and properties (by methods of X-ray structural analysis, DTA, IR, Raman, and 1H, 19F NMR, including 19F MAS NMR) of a new crystal hydrate of the composition ZnZr2F10∙6H2O (1) have been performed.
The compound 1 crystallizes in the monoclinic system with the following unit cell parameters: a = 6.5628(2), b = 10.2031(4), c = 9.0965(4) Å, β = 100.532(1)°, sp.gr. C2/m, Z = 2. The crystal structure is built of flat cross-linked anion layers of the composition Zr2F10∞22−and octahedral Zn(H2O)62+ cations. The complex cations and anions are linked in the structure into a three-dimensional network by OH⋯F and OH⋯O hydrogen bonds.
It has been established that decomposition of 1 in temperature range 50−850 °C in air proceeds stepwise through the following stages: ZnZr2F10∙6H2O → ZnZr2F10∙4H2O → ZnZr2F10∙2H2O → ZnZr2OF8 with formation of the mixture of the final products ZnO and ZrO2. The vibrational and NMR spectroscopy data for the initial compound and intermediate products of its decomposition have been obtained, systematized, and summarized.
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•Ni2+ complexes with chitosan and its N-derivatives were simulated using DFT.•11 model structures of “bridge” and “pendant” complexes were calculated.•N-atoms of chitosan and its ...N-derivatives play a governing role in Ni2+ binding.•Degree of charge transfer from the ligand to Ni2+ correlate with complex stability.
Here we report the results of density functional theory (DFT) investigations of Ni2+ complexes with chitosan and its N-heterocyclic derivatives – N-(2-pyridylethyl) chitosan (2-PEC), N-(4-pyridylethyl)chitosan (4-PEC), and N-(5-methyl-4-imidazolyl)methyl chitosan (IMC). 11 model structures corresponding to ‘bridge’ and ‘pendant’ types of complexes have been calculated. We have shown that in most cases formation of ‘pendant’ complexes is more favorable. It was found that nitrogen atoms of chitosan and its N-heterocyclic derivatives played a governing role in Ni2+ binding and that the degree of charge transfer from the ligand to the central ion in the complexes correlated with the complex stability. A row of complexes stability depending on the type of functional substitute in chitosan macromolecules (IMC≈2-PEC>chitosan>4-PEC) was in a good agreement with experimental data obtained from the nickel ion sorption isotherms on chitosan, 2-PEC, 4-PEC and IMC.
The possibilities of using chitosan and its composites with transition metal oxides for arsenic removal from solutions with low concentrations are discussed. Methods for the formation of composite ...sorbents based on chitosan and molybdenum in a composition with a carbon fiber providing improved physical and chemical properties with respect to the recovered component are considered. The sorption properties of the obtained materials under dynamic conditions for the purification of solutions from arsenic are compared. It is shown that the preliminary modification of the carbon fiber with chitosan by ionic gelation using sulfate ion and then by adsorption with molybdate ion leads to the production of an efficient sorption material that provides the purification of 1600 column volumes of an arsenic solution at an initial concentration of 105 μg L
–1
to a maximum permissible concentration of 50 μg L
–1
. The calculation methods show that the gel ability of sulfate and molybdate ions is approximately the same.
Desorption of hydrogen from the powders of metal hydrides (MH) is affected by several interplaying processes including hydrogen desorption from and recombination on the metal surface, diffusion ...within the bulk metal and different hydride phases, and decomposition of the hydride phase. In present work, possible mechanisms of hydrogen release from the MH are proposed and discussed. Analytical models are developed which cover common distributed and confluent cases. The models adequately fit the experimental data of the thermal desorption spectroscopy and barometric thermocycling studies. Rate constants of the reactions of hydrogen release from the MH are evaluated on the basis of the fitting of the experimental data by the proposed models. These data are of significant importance in the assessments of suitability of the MH in particular applications.
The possibilities of producing low-ash crystalline graphite from high-carbon rocks of the southern Far East have been investigated. Promising setups for purifying the natural graphite from impurities ...using the processes of hydrothermal treatment of flotation concentrates have been developed.
Fluoridezirconate crystallohydrates ZnZrF
6
·
n
H
2
O (
n
= 6–2) and anhydrous ZnZrF
6
are investigated by vibrational spectroscopy and thermography. The influence of the hydrate number on the ...structure of the cationic and anionic sublattices of the crystallohydrates is studied. The changes in the strength of HOH···F and HOH···O hydrogen bonds of coordinated and outer-sphere water molecules occurring with variations in the hydrate number are determined by changes in the IR spectra. The IR spectra of ZnZrF
6
·
n
H
2
O (
n
=6, 4) compounds, which have isolated complex anions ZrF
6
2–
in their structure, revealed a band with two peaks in the range of 3470–3430 cm
–1
, which corresponds to stretching vibrations of coordinated water molecules. The spectra of ZnZrF
6
·
n
H
2
O (
n
= 5, 3, 2, 1) crystallohydrates with a polymeric structure show a high-frequency shift of this band, which corresponds to weakening of hydrogen bonds. The vibrations of crystallization water molecules involved in the network of strong O–H···F and O–H···O hydrogen bonds manifest themselves in the spectra of ZnZrF
6
·
n
H
2
O (
n
=5, 3) crystallohydrates by broad structureless bands in the region of stretching, bending, and libration vibrations.
Manganese oxides have been prepared on the surface of carbon fiber by simple methods: coprecipitation of manganese salts of different valence in the presence of fiber as a support or ...electrodeposition from Mn(II) salt solution on a carbon fiber cathode, in the presence of chitosan including, under oxidation with air oxygen conditions. The obtained samples have been characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Sorption properties of the composites toward As(V) have been studied. The relationships between sorption properties, structure, Mn valence, and manganese oxide surface morphology have been discussed.
Brown coals with high Au and PGE concentrations from six deposits in the southern Russian Far East were analyzed for elemental composition, acid-base properties, and the molecular-size distribution ...of humic acids (HA). The ash contents of the coals were determined to be negatively correlated with their Au concentrations, and the content of “organic Au” (which is chemically bound to humic substances, HS) reaches 95%. The most probable mode of Au occurrence in the brown coals is submicrometer-sized particles of elemental gold stabilized by HA. Quantum-mechanical calculations of interactions between Au(0) clusters with model HS fragments confirm that HS could be originally strongly chemically adsorbed on the surface of elemental gold particles. Different stability of colloids during centrifuging of alkali extracts of the gold-bearing brown coals was proved to be likely responsible for the selective separation of free HA and those bound with gold particles, and this can be used to develop a technology for gold recovery from coals without decomposing their organic matrix.
Space-charge wave (SCW) excitation is studied under the influence of an external magnetic field in GaAs:Cr depending on the orientational angle of the exciting oscillating sinusoidal interference ...pattern to the external electric field. It was found that the tilt of the SCW propagation direction induced by the magnetic field results in a shift of the orientational dependence curve. This feature allows determining the deviation angle of charge carriers’ trajectory and their sign. A quantitative theoretical explanation of the effects is proposed and a theoretical expression for the SCW ac-current is given.
