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•The colloid-chemical properties of individual and mixed colloid solutions of nanoscale crystal chitin and manganese oxide were studied.•The heteroaggregation of ChNC-MnO2 hybrid ...dispersions occurs according to the “charge neutralization – charge reversal” mechanism.•Using of organomineral composite sorbents was followed to trend Ni 2+ > Cu2+ > Sr2+ for the heavy metal ion removal.•The rate and degree of degradation of the polymer component can be controlled by adjusting the amount of manganese oxide.
The article presents the results of the synthesis and research of a new biodegradable hybrid nanosized polymer-inorganic system possessing the double nature of heavy metal ions extraction from solutions. Firstly, the sorption of metal ions takes place by the ion-exchange properties of porous manganese oxide and, secondly, due to specific interaction and chelating with functional groups of polysaccharides in terms of nanochitin (ChNC). The synthesis is based on the colloid-chemical processes of interaction between polysaccharide and manganese oxide nanosized particles. Using the mathematical model of the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, it has been shown that this interaction occurs due to the formation of hydrogen bonds and electrostatic interactions of oppositely charged particles. Hybrid sorbents were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, Transmission electron and Atomic force microscopy. The highest value of sorption capacity for hybrid materials was obtained for Ni2+ extraction and reached 114.0 ± 1.1 mg/g. It was shown that biodegradation of hybrid sorbents increases with the concentration of manganese oxide nanoparticles and almost complete degradation of the organic part can be performed within 6 days. The obtained biodegradable sorbents were designed to address ecological problems connected with the pollution of natural waters by toxic metallic ions.
Using formulas of J. Moser for finite-dimensional Toda lattices, we derive the evolution law for moments of the spectral measure of the semi-infinite Jacobi operator associated with the Toda lattice. ...This allows us to construct solutions of semi-infinite Toda lattices for a wide class of unbounded initial data by using well-known results from the classical moment problem theory.
A dynamic inverse problem for a dynamical system that describes the propagation of waves in a Krein string is considered. The problem is reduced to an integral equation, and an important special case ...is considered where the string density is determined by a finite number of point masses distributed over the interval. An equation of Krein type, with the help of which the string density is restored, is derived. The approximation of constant density by point masses uniformly distributed over the interval and the effect of the appearance of a finite wave propagation velocity in the dynamical system are also studied.
Abstract
We establish relationships between the classical moments problems which are problems of a construction of a measure supported on a real line, on a half-line or on an interval from prescribed ...set of moments with the Boundary control approach to a dynamic inverse problem for a dynamical system with discrete time associated with Jacobi matrices. We show that the solution of corresponding truncated moment problems is equivalent to solving some generalized spectral problems.
We study the inverse dynamic problem of recoverying the potential in the one-dimensional dynamical system with memory. The Gelfand–Levitan equations are derived for the kernel of the integral ...operator which is inverse to the control operator of the system. The potential is reconstructed according to the solution of these equations.
The carbene transfer from N-heterocyclic carbene complexes of Group 11 metals (NHC–M
C
) (especially silver and copper) to other metals is considered a convenient and universal, sometimes having no ...alternative, method for the synthesis of a wide range of important N-heterocyclic carbene complexes of transition metals. As the number of successful examples of transmetalation with the formation of the target product has increased, the data were accumulated on alternative or unexpected results of the interaction of NHC–M
C
complexes with compounds of other metals. This review considers the examples of NHC–M
C
reactions with compounds of other metals which proceed with a change in the metals oxidation state, conversion of (NHC)M
C
X into cationic homoleptic (NHC)
2
M
C
+
forms, transmetalation retaining the other metal in the coordination sphere of the product, or formation of heterometallic adducts preserving the M
C
–C
carbene
bond, rather than these occurring according to the standard reaction pathway. Unusual “reverse” carbene transfer reactions have been considered separately. The review material reveals a promising new synthetic potential of NHC–M
C
in the reactions with other metals and discusses the possible mechanisms and driving forces of such transformations. The most important aspects of the application of the obtained products, primarily in various catalytic processes, have been considered as well.
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•The photoformation and separation of charge carriers in traps in VLA titania ceramics and titania powder were examined.•Thermoprogrammed annealing (TPA) spectra of Ti3+ color centers ...photoinduced in VLA TiO2 displayed temperature dependencies.•Highest rate of recombination of holes released into the valence band with Ti3+ centers was due to extra charged centers.•Rate of photodesorption of O2 occurrence in specific channel to activate VLA TiO2 by photoexcitation of Ti3+ centers.
We herein report on the photophysics of color centers in visible-light-active (VLA) rutile titania ceramics and titania powder resulting from the photoformation and separation of charge carriers explored by a diffuse reflectance (DR) spectroscopic and kinetic study using a cryostat-type accessory for a Cary 5000 spectrophotometer after exposure of the titanias to UV radiation and Vis-light illumination. The action spectrum of the photoformation of Ti3+ at 90 K accorded fully with the absorption spectrum of intrinsic defects in the as-synthesized TiO2. The photoinduced absorption spectra consisted of a set of individual absorption bands attributable to several different Ti3+ centers. Analysis of the dependencies of the photoformation of separate centers on the wavelength of illumination and light exposure provided extraction of specific Ti3+ centers putatively attributed to centers with excess negative charge {2Ti3+ + Vo2+} ⟵→ {Tiδ+ + Vo2+} with 3 > δ > 2 formed at significantly high concentration upon maximal exposure to Vis-light illumination. Thermoprogrammed annealing (TPA) spectra of Ti3+ color centers photoinduced in VLA TiO2 displayed temperature dependencies of the rate of detrapping of the photoinduced holes observed optically through annihilation of the Ti3+ centers. The TPA spectra in the range 90–500 K consisted of a set of first-order peaks corresponding to the traps, whose depths ranged from ∼0.2 eV (peak at 130 K in powder specimen) to 1.06 eV (peak at 455 K in the ceramics). The highest rate of recombination of holes released to the valence band with Ti3+ centers, an event attributable to the Tiδ+ centers, provided TPA spectra that clearly manifested the existence of shallow traps. We also report mass spectrometric evidence of the photoformation of electrons and holes in VLA TiO2 under Vis-light illumination through an examination of the photoadsorption of molecular oxygen and the photodesorption of photoadsorbed oxygen from the surface of powdered VLA titania specimens. Moreover, kinetics of the photodesorption of O2 under orange light illumination, after the photoadsorption of O2 stimulated by blue light excitation, provided experimental proof of the occurrence of an additional specific channel toward the photoactivation of VLA TiO2 via the photoexcitation of photoinduced Ti3+ color centers.
The inverse dynamic problem for the wave equation with a potential on a real line is considered. The forward initial-boundary value problem is set up with the help of boundary triplets. As an inverse ...data, an analog of the response operator (dynamic Dirichlet-to-Neumann map) is used. Equations of the inverse problem are derived; also, a relationship between the dynamic inverse problem and the spectral inverse problem from a matrix-valued measure is pointed out.
The problem of reconstruction of the Cauchy data for the wave equation in ℝ
1
from the measurements of its solution on the boundary of a finite interval is considered. This is a one-dimensional model ...for the multidimensional problem of photoacoustics, which was studied previously. The method was adapted and simplified for the one-dimensional situation. The results of numerical testing to see the rate of convergence and the stability of the procedure are given. Some hints are also given on how the procedure of reconstruction can be simplified in the 2d and 3d cases.
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