Application of Crosslinked Ionic Poly(Vinyl Alcohol) Nanogel as Adsorbents for Water Treatment

Core-shell smart ionic nanogels based on poly(vinyl alcohol) (PVA) core and poly(N-isopropylacrylamide/acrylic acid) p(NIPAm-AAc) shell particles were successfully synthesized through a one-step surfactant-free emulsion polymerization method (SFEP). Different mole ratios of p(NIPAm-AAc) shells were synthesized. The morphologies of PVA/p(NIPAm-AAc) nanogels were investigated by transmission electron microscope (TEM). The data showed the formation of spherical nanoparticles and well-defined core-shell nanogels. PVA/p(NIPAm-AAc) core-shell nanogels were applied as a novel polymeric adsorbent to remove heavy metal pollutants from aqueous solution. Copper(II) (Cu²⁺) ions were selected as the target pollutant to evaluate these nanoparticles’ adsorption capability. The influence of the uptake conditions such as pH, weight ratio of nanoparticles, time, initial feed concentration, and adsorption temperature on the metal ion binding capacity of nanogels was also tested. Adsorption equilibrium data were calculated according to Langmuir and Freundlich isotherms. It was found that the sorption of Cu²⁺ was better suited to the Freundlich adsorption model than the Langmuir adsorption model. Also, the selectivity of the nanogels toward the different metal ions such lead (Pb²⁺) and cadmium (Cd²⁺) were tested. The maximum of Cu²⁺ ions adsorbed on to PVA/p(NIPAm-AAc) core-shell nanogels adsorbent was 94 mg/g obtained under simple and fast experimental conditions, indicating these nanogels can be used as effective and practical polymeric adsorbents.     

The structure and dynamics of the copper(II)—l-proline 1:2 complex in solution

The ¹³C relaxation times (T₁ and T₂) and isotropic contact shifts (Δω) of a one molar aqueous solution of l-proline at pH = 11 (or pD = 11.4) containing ca 10^?4 M copper(II) perchlorate are measured at 62.86 MHz over a temperature range of 26–70°C. The purely dipolar longitudinal relaxation of carbon-13 nuclei contrasting with purely scalar transverse relaxation allowed us to extract carbon-to-metal distances (through T₁ measurements) and hyperfine coupling constants and dynamic parameters (from T₂ and Δω measurements). The structure of the complex in solution is found closely similar to that in the solid state. Curve-fitting procedures allowed us to derive the hyperfine electron—carbon coupling constants A_c = ?1.95, + 0.42, + 1.90 and ?1.70 MHz for carbons α, β, γ, δ, of the pyrrolidinic ring, the reorientation correlation time of the complex, τ_R (25°C) = 1.15 × 10^?10 sec, the l-proline exchange rate, k_M (25°C) = 4.0 × 10⁵ sec^?1 (and the corresponding activation parameters ΔH^≠ = 9.0 kcal mol^?1 and ΔS^≠ = ?0.7 e.u.), and the electronic relaxation time, T_1e = 1.13 × 10^?8 sec (at 25°C). The latter value was found in agreement with the one computed from ESR data and the above τ_R value, showing the predominant contributions of spin—rotation interaction and, to a lesser extent, of the effect of g-tensor anisotropy to the electronic relaxation rate.     

Zeolite ZSM-5 containing copper ions: The effect of the copper salt anion and NH<Subscript>4</Subscript>OH/Cu<Superscript>2+</Superscript> ratio on the state of the copper ions and on the reactivity of the zeolite in DeNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir’s monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in N₂O decomposition. The amount of Cu²⁺ that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu²⁺ cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO _x ) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO _x properties of Cu-ZSM-5 depend considerably on the NH₄OH/Cu²⁺ ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NH₄OH/Cu²⁺ = 6–10 stabilize, in the Cu-ZSM-5 structure, Cu²⁺ ions bonded with extraframework oxygen, which are more active in DeNO _x than isolated Cu²⁺ ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NH₄OH/Cu²⁺ = 3).     

Magnetic resonance studies of copper (II) sorbitol complex,in solution,reveal a supramolecular structure compatible to the crystal structure

Although the Cu²⁺-sorbitol complex [Cu²⁺-Sorb] structure in crystalline state has been determined by X rays, it is not known in solution, where most studies of this complex are performed. Therefore, the goal of this work was to obtain information about the structure of this complex in aqueous solution using nuclear magnetic resonance and electron paramagnetic resonance spectroscopies. The magnetic resonance results indicate that the complex is formed at approximately pH 12. In this pH the sorbitol ¹H relaxation times were so short (broad line) that was not possible to use standard nuclear magnetic resonance parameters (nuclear Overhauser effect and spin–spin coupling constants values) to solve the three-dimensional structure. However, valuable structural information about the complex in solution was obtained. The relaxation results indicate that the Cu²⁺ ions are buried in the structure and not accessible to solvent; the ¹H and ¹³C spectra shows strong paramagnetic shift effect indicating short distance between these nuclei and Cu²⁺ in the structure. No electron paramagnetic resonance signal was observed in pH 12 indicating strong Cu²⁺- Cu²⁺ dipolar interaction, compatible to Cu²⁺-Cu²⁺ distances measured in crystal, from 1.148 to 1.393 Angstroms. The complex self-diffusion coefficient (D) of 1.58 × 10⁻¹⁰ m²/s value, determined by Diffusion-Ordered Spectroscopy, is compatible to a molecular weight of 3–6 KDa. Therefore, these results corroborate that the [Cu²⁺-Sorb] complex is assembled in solution, at pH 12, with several structural parameters compatible to the toroidal hexadecacuprate supramolecular structure determined in solid state.     

Cu2+-complexes of polyamino acids in aqueous solutions catalytic activity (H202-decomposition) and structure

The decomposition of H₂O₂ (8 · 10^?3M ) catalyzed by complexes of Cu²⁺ (4 · 10^?4M ) with various oligomers and polymers of glycine, L-lysine or L-glutamic acid was investigated in aqueous solution in the pH range 5–11, at 24°C and at low ionic strength. Previous investigations have shown that the decomposition of H₂O₂ is catalyzed by Cu²⁺-complexes capable of forming Cu²⁺-peroxocomplexes. With increasing pH the catalytic activity of Cu²⁺-complexes with glycine or glycylglycine (1:1) increases while the activity of Cu²⁺-complexes with tri- or tetraglycine (1:1) is comparatively small at higher pH values apparently because in the latter cases the coordination positions of the copper become progressively occupied by the peptides. This interpretation is in accordance with the pH-dependence of the light-absorption spectra of the latter complexes. Cu²⁺-complexes with poly-α, L -lysines of various molecular weights (molar ratios Cu²⁺: lysine residues = 1:15) have a catalytic activity comparable to or higher than that of the complex Cu²⁺-ethylenediamine (1:1), indicating two available coordination positions for formation of peroxo-complexes. On the other hand, the system Cu²⁺-L -lysine (1:15) showed no significant activity probably because all coordination positions at the Cu²⁺ are occupied by lysine. Despite the excess of ligand groups over Cu²⁺ in the polylysine systems the structure of this polyamino acid apparently does not allow its full coordination with these groups under the conditions investigated. Two adjacent chelating ε-amino groups are considered as the main ligand groups of the polymer to each copper ion. The Cu²⁺-poly-α, L -glutamic acid complex examined (Cu²⁺: glutamic acid residues = 1:5) shows comparatively little activity. In this case, absorption spectra indicate formation of hydroxo-complexes at higher pH. Besides the effects of structure, the electrostatic fields of the charged polyelectrolytes polylysine or polyglutamic acid are also considered to affect the rates of catalysis.     

Performance Evaluation of Hybrid Gas–Liquid Pulse Discharge Plasma-Induced Degradation of Polyvinyl Alcohol-Containing Wastewater

A multi-needle-to-plate pulsed discharge plasma reactor was designed to investigate its potential for polyvinyl alcohol-containing wastewater (PVA) treatment. The effects of some operational parameters such as PVA initial concentration, pulse peak discharge voltage, air flow rate, solution pH value, and iron additives on PVA degradation were examined. The results indicated that PVA could be effectively degraded from aqueous solutions. PVA degradation efficiency was 76.0 % within 60 min’s discharge plasma treatment with 1.5 mmol L^?1 Fe²⁺ addition. Decreasing PVA initial concentration and increasing pulse peak discharge voltage were both beneficial for PVA degradation. There existed appropriate air flow rate for obtaining great PVA degradation efficiency in the present study. A little acid environment was conducive to PVA degradation. The presence of Fe²⁺ and Cu²⁺ could both benefit PVA degradation, and the increment of Fe²⁺ and Cu²⁺ concentrations to a certain extent could enhance its degradation efficiency, as well as energy yield. PVA possible degradation mechanisms were discussed, and the degradation processes were mainly triggered by the reactions of PVA with \(^{ \cdot } {\text{OH}}\) radicals.     

Paramagnetic ion binding to amino acids,structural and dynamical information on a Mn(II) complex of L-proline from 13C relaxation data

The ¹³C relaxation times (T₁ and T₂) and isotropic contact shift (Δω) of 1.28 molar aqueous solutions of L-Proline at pH = 11 (or pD = 11.4) containing 10^?4 - 10^?5 M manganese perchlorate are measured at 62.86 MHz over a temperature range of 28–80°C. Under these conditions, the Mn²⁺ cation is bound to three L-Proline molecules in their dibasic form, and a fast exchange is occurring between bound and bulk L-Proline molecules. The longitudinal relaxation of carbons α, β, γ, δ of L-Proline molecules in this complex is shown to be purely dipolar, and is controlled by the rotational reorientation of the complex. The transverse relaxation of bound L-Proline molecules is mainly scalar and is controlled by the electronic relaxation. Overall relaxation rates and paramagnetic shifts also depend on the ligand exchange rate k_M (from bound to free sites) at lower temperatures. The measurement of these quantities allow us to determine (i) the structure of the complex: the Mn(II) cation may be positioned with respect to each proline ligand, the sites of coordination are the unchanged nitrogen and one carboxylic atom, the distance to the Mn²⁺ cation are respectively 2.08 and 1.97 Å; (ii) Hyperfine coupling constants: A= + 0.16; 0.08; 0.25 and 0.22 MHz for carbons α, β, γ, δ, respectively. (iii) Electronic relaxation parameters: assuming that T_1e ( = 2.18 x 10^?8 s at 25°C) is controlled by the modulation of the quadratic crystalline zero-field splitting interaction allows us to estimate the trace of the corresponding tensor: Δ = 0.0305 cm^?1, and a correlation time τν(25°C) = 1.32 ps for the impact of solvent molecules against the Mn²⁺-L-Proline complex (iv) Kinetic parameters for ligand exchange: k_M(25°C) = 7.41 x 10⁴s^?1; ΔH³ = 15.6 kcal.mol.^?1; ΔS³ = 16.1 e.u.     

Synthesis of imidazole‐terminated hyperbranched polymers with POSS‐branching points and their pH responsive and coordination properties

An imidazole‐terminated hyperbranched polymer with octafunctional POSS branching units denoted as POSS‐HYPAM‐Im was prepared by the polymerization of excess amounts of tris(2‐aminoethyl)amine with the first‐generation methyl ester‐terminated POSS‐core poly(amidoamine)‐typed dendrimer, reacting with methyl acrylate, and ester‐amide exchange reaction with 3‐aminopropylimidazole. The imidazole‐terminated hyperbranched poly(amidoamine) denoted as HYPAM‐Im was also synthesized with 1‐(3‐aminopropyl)imidazole from a methyl ester‐terminated hyperbranched poly(amidoamine) by the ester‐amide exchange reaction. The transmittance of the POSS‐HYPAM‐Im solution drastically decreased when the solution pH was greater than 8.2. On the other hand, the transmittance of the HYPAM‐Im solution gradually decreased when the solution pH at 8.5 and was greater than 9. Spectrophotometric titrations of the hyperbranched polymer aqueous solutions with Cu²⁺ ions indicated the variation of the coordination modes of POSS‐HYPAM‐Im from the Cu²⁺–N₄ complex to the Cu²⁺–N₂O₂ complex and the existence of the only one complexation mode of Cu²⁺–N₄ between Cu²⁺ ion and HYPAM‐Im with increasing the concentrations. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2695–2701     

Properties of N,N-Dimethyl-N′-(2-Hydroxybenzyl)ethylenediamine as a Ligand to Copper(II)

The acid-basic and complexing properties of N,N-dimethyl-N-(2-hydroxybenzyl)ethylenediamine (HL) in aqueous propan-2-ol were characterized by spectrophotometry, pH-metry, and mathematical simulation of equilibria in solutions (T = 25 ± 0.1°C, = 0.1 M KNO₃). Dimer H₂L₂ was found to predominate in solution at c _HL = 0.01 mol/l. Three protonated dimeric (H₃L₂ ⁺, H₄L₂ ²⁺, and H₅L₂ ³⁺), diprotonated monomeric (H₃L²⁺), and triprotonated tetrameric forms (H₇L₄ ³⁺) were detected in the system, depending on pH. At lower ligand concentrations (c _HL = 0.0015 mol/l), the solution contains both dimers and monomers of this compound. The higher dentate number of HL compared to 2-alkylaminomethylphenols allows it to form more number of both mono- and binuclear complexes ([Cu(HL)]²⁺, [Cu(HL)₂]²⁺, [CuL₂], [CuL₂OH]^–, [Cu₂(HL)₂]⁴⁺, and [Cu₂(HL)₂L₂]²⁺), making them more stable.     

Spectrophotometric Study of Complexation of Bis(ethylenediamine)gold(III) with the Chloride Ion in an Aqueous Solution

The interaction of Au(En)₂ ³⁺ with the chloride ion in an aqueous solution at I = 2.5 mol/l and T = 20°C was studied by spectrophotometry. The equilibrium constant of formation of the Au(En)₂Cl²⁺ penta coordinated complex was determined.     

Copper and copper-palladium catalysts of aliphatic thiols oxidation in biological objects: Quantum-chemical DFT simulation

DFT calculations (M06, PBE0/Def2-TZVP) of coordination compounds used in reactions of selective oxidation of thiols to disulfides were performed. Primary active centers of the catalysts are polynuclear scaffolds {L₂M(μ-OH)₂ML₂}²⁺ and {L₂M(μ-OH)₂M′(μ-OH)₂ML₂}²⁺ (M = Cu^I, Cu^II, Pd^II; M' = Cu^II; L = NH₃). Cu^II ions in combination with PdII ions are capable of formation of polynuclear active center {PdII(μ-OH)₂Cu^II(μ-OH)₂Pd^II}²⁺ bringing together a large number of mutually oriented RS^– groups and thus affecting the rate of formation of disulfide R₂S₂.     

Electrochemically driven reversible solid state metal exchange processes in polynuclear copper complexes

The electrochemical characteristics of polynuclear di-copper and tetra-copper complexes of an expanded "Robson-type" macrocyclic ligand are explored by solid state voltammetry in aqueous media. When adhered to a graphite electrode surface in the form of microcrystalline powders and immersed in aqueous buffer solution, these water-insoluble polynuclear copper complexes show well-defined voltammetric reduction and re-oxidation responses. The di-copper metal complexes [Cu₂(H₃L)(OH)][BF₄]₂ and the tetra-copper complexes [Cu₄(L)(OH)][NO₃]₃ with an O₄N₄ octadentate macrocyclic ligand L are shown to exhibit inter-related and proton concentration sensitive solid state voltammetric characteristics. At sufficiently negative potential, copper is extracted from the complexes to form a solid copper deposit and the neutral form of the insoluble free ligand. Upon re-oxidation of the copper deposit, Cu²⁺ undergoes facile re-insertion into the ligand sphere to re-form solid di- and tetra-copper complexes at the electrode surface. The reduction process occurs in two stages, with two Cu²⁺ cations being extracted in each step. The ability of the macrocyclic ligand to efficiently release and accumulate copper is demonstrated. Electronic Publication     

Chelation of manganese(II) with quinaldic acids. An NMR relaxation study

Manganese(II) enhanced spin-lattice relaxation rates (1/T_1p) of ¹H and ¹³C nuclei in quinoline-2-carboxylic acid, 8-methoxyquinoline-2-carboxylic acid, 8-hydroxyquinoline-2-carboxylic acid, 8-aminoquinoline-2-carboxylic acid, and 6-(hydroxymethyl)pyridine-2-carboxylic acid were measured in aqueous solution at various temperatures. Relative metal-nucleus distances were calculated from the r^?6 dependence of 1/T_1p. The results indicate that the Mn²⁺ ion in the 8-methoxyquinaldic acid chelate is coordinated to the carboxyl oxygen atom and the nitrogen atom but not t the methoxyl oxygen atom.     

Fluorescence Turn‐On Detection of Nitric Oxide in Aqueous Solution Using Cationic Conjugated Polyelectrolytes

A fluorescent turn‐on detection for nitric oxide in aqueous solution is developed using cationic conjugated polymers. The assay benefits from the sensitivity of optical signals from conjugated polymers and the simplicity of fluorescence measurement techniques. The assay contains three elements: a cationic conjugated polymer that contains imidazole moieties, Cu²⁺ ions, and the target nitric oxide. The highly fluorescent conjugated polymer coordinates to Cu²⁺ ions through weak N · · · Cu interactions, and its fluorescence is efficiently quenched by a photo‐induced electron transfer process (‘off’ state). In the presence of nitric oxide, the transformation of the paramagnetic Cu²⁺ ion into a diamagnetic Cu¹⁺ ion inhibits the quenching and, therefore, the fluorescence of the conjugate polymer is recovered (‘on’ state). Other biologically relevant reactive nitrogen species, such as NOBF₄, NaNO₂, and NaNO₃ don't exhibit the fluorescence recovery of the conjugated polymer under the same conditions as nitric oxide. The cationic conjugated polymer/Cu²⁺ complex can thus be used as a platform to detect nitric oxide in aqueous solution with high sensitivity and selectivity.

     

Identification of the Chromophore in the Apatite Pigment [Sr10(PO4)6(CuxOH1−x−y)2]: Linear OCuO− Featuring a Resonance Raman Effect,an Extreme Magnetic Anisotropy,and Slow Spin Relaxation

A new chromophore has been identified in copper‐doped apatite pigments having the general composition [Sr₁₀(PO₄)₆(Cu_xOH_1?x?y)₂], in which x=0.1, 0.3 and y=0.01–0.42. By using X‐ray absorption spectroscopy, low‐temperature magnetization measurements, and synchrotron X‐ray powder structure refinement, it has been shown that the oxygenated compounds contain simultaneously diamagnetic Cu¹⁺ and paramagnetic Cu³⁺ with S=1. Cu³⁺ is located at the same crystallographic position as Cu¹⁺, being linearly coordinated by two oxygen atoms and forming the OCuO^? anion. The Raman spectroscopy study of [A₁₀(PO₄)₆(Cu_xOH_1?x?y)₂,], in which A=Ca, Sr, Ba, reveals resonance bands at 651–656 cm^?1 assigned to the symmetric stretching vibration (ν₁) of OCuO^?. The strontium apatite pigment exhibits a strong paramagnetic anisotropy with an unprecedentedly large negative zero‐field splitting parameter (D) of ≈?400 cm^?1. The extreme magnetic anisotropy causes slow magnetization relaxation with relaxation times (τ) up to 0.3 s at T=2 K, which relates the compounds to single‐ion magnets. At low temperature, τ is limited by a spin quantum‐tunneling, whereas at high temperature a thermally activated relaxation prevails with U_eff≈48 cm^?1. Strong dependence of τ on the paramagnetic center concentration at low temperature suggests that the spin‐spin relaxation dominates in the spin quantum‐tunneling process. The compound is the first example of a d‐metal‐based single‐ion magnet with S=1, the smallest spin at which an energy barrier arises for the spin flipping.     

Proton,phosphorus and carbon nuclear magnetic relaxation studies on the interaction of poly(riboadenylic acid) with Cu2+

Interaction between poly(riboadenylic acid) (poly(A)) and Cu²⁺ in neutral aqueous (D₂O) solution has been studied by ¹H, ³¹P, and ¹³C nuclear magnetic resonance. electron-nuclear hyperfine coupling constant and apparent electron-nuclear distances were determined by measurement of T₁ and T₂ values as a function of temperature. The apparent distance from Cu²⁺ to H(2), H(8), H(1′), and phosphorus nuclei were estimated to be 4.1, 3.7, 5.1, and 3.1 Å from these results. Cu²⁺ was found to coordinate directly to the phosphate groups of poly(A) (Type I complex). Simultaneously there are bindings of Cu²⁺ directly to one of the nitrogen atoms of adenine ring, mainly to N(7) (Type II complex) and either N(1) or N(3) (Type III complex).     

A fluorescent probe based on N-butylbenzene-1,2-diamine for Cu(II) and its imaging in living cells

A fluorescent probe LZ-N with naphthalimide as fluorophore and N-butylbenzene-1,2-diamine as a new recognition moiety for copper ion was designed and synthesized. The probe LZ-N exhibits high selectivity for Cu²⁺ ion in aqueous media (CH₃CN:H₂O = 1:1) over all the other metal ions in our study, more than 20-fold fluorescence enhancement by coordinating with Cu²⁺, and the maximum emission intensity independence in the range of pH 2.06–9.25. The results of ¹H-NMR titration, time-resolved fluorescence decay measurement, and computational optimization illuminate the mechanisms of Cu²⁺ and probe LZ-N. Confocal fluorescence images and cell viability values test show the high fluorescence enhancement of probe LZ-N for exogenous Cu²⁺ in living cells.     

Extraction of metal picrates by lipophilic hexamide and hexamine derivatives of azacrown [18]-N6

To determine the metal ion complexing ability of high molecular weight macrocyclic polyamines and polyamides, lipophilic derivatives of azacrown [18]-N₆ (hexacyclen) were prepared. Transition and heavy metal picrates, but not alkali and alkaline earth picrates, were extracted from water into chloroform and transported from water through chloroform into a second water phase by the hexa-4-dodecyloxybenzoyl and hexa-3,4-bis-dodecyloxybenzoyl amide derivatives1 and2 and by the hexa-4-dodecyloxybenzyl amine derivative3 of [18]-N₆ (hexacyclen). The relative amounts of picrates extracted by hexamine3 from a pH 5 aqueous solution were Cu²⁺Ag⁺Pb²⁺> Hg²⁺>Zn²⁺>Co²⁺>Ni²⁺Cd²⁺. Using a pH 7 receiving phase, none of the metal ions were transported rapidly through chloroform, and only Co²⁺, Cu²⁺, and Pb²⁺, were transported rapidly into a pH 11 aqueous phase. The hexamide2, but not hexamide1, extracted significant amounts of the picrates of Cu²⁺, Ag⁺, and Hg²⁺, and transported Cu²⁺ and Ag⁺ but not Hg²⁺.     

Dissociation and coordinating ability of 1,2,3,4-tetrahydro-8-hydroxyquinoline in aqueous solution

The state of 1,2,3,4-tetrahydro-8-hydroxyquinoline is studied spectrophotometrically in the near-UV and visible regions at different pH in an aqueous solution in the presence and absence of Cu²⁺, Zn²⁺, and Cd²⁺ cations. The dissociation constant (pK ₁ ≈ 5.6 (293 K)) is (293 K)) is estimated from the pH-metric data. The stability of the complexes formed decreases in the series Cu²⁺ > Zn²⁺ ≥ Cd²⁺. The influence of tetrahydro atoms on the dissociation, complexation, and change in the state of 1,2,3,4-tetrahydro-8-hydroxyquinoline in an aqueous solution is discussed.     

Kinetics of Cu<Superscript>2+</Superscript> binding to the poly(acrylic acid) hydrogel

Isothermal kinetics of copper (ion) binding to poly(acrylic acid) (PAA) hydrogel at 20, 25, 35 and 45°C was investigated. Isothermal conversions and kinetic curves of Cu²⁺ binding to the PAA hydrogel were determined. It was found that the well-known kinetic models of Peppas cannot be applied to describing the entire process of Cu²⁺ binding. The new method for the determination of the kinetic model of the Cu²⁺ binding process, as well as the activation energy density distribution functions of PAA hydrogel interaction with Cu²⁺, were established. It was found that Cu²⁺ diffusion to the active centers (with E _a = 9 kJ/mol) has a dominant influence on the kinetics of the process at temperatures T ≥ 30°C, but at T ≥ 30°C and for the degree of bound Cu²⁺ α ≥ 0.2, the interaction of Cu²⁺ from the adsorption center with E _a = 26 kJ/mol is dominant. The text was submitted by the authors in English.