Yu. A. Azarova

Imidazole-containing chitosan derivative: a new synthetic approach and sorption properties

A novel method for the synthesis of a hetaryl-containing chelate amino polymer, namely, N-(4(5)-imidazolylmethyl)chitosan (IMC), with a degree of substitution up to 0.3 was proposed. The “synthesis in gel” approach involves direct substitution of the hydroxyl group in 4(5)-imidazolylmethanol. The structures of these polymers were confirmed by 1H NMR data. For sorption studies, IMC samples were crosslinked with epichlorohydrin and diglycidyl ethers of ethylene glycol and diethylene glycol. The degrees of swelling and sorption properties of the polymers largely depend on the crosslinking agent and the degree of crosslinking. The sorption capacities of IMC for AuIII, PtIV, and PdII ions are higher than those of the nonmodified polymer. The extraction of noble metal ions from chloride solutions becomes more selective with increasing degree of crosslinking. The sorption capacity of IMC for CoII and NiII ions is higher than those of chitosan and its known N-heterocyclic derivatives.

N-2-(2-pyridyl)ethyl chitosan: Synthesis in gel and sorption properties

A procedure was developed for preparing a new heterocyclically substituted chelating aminopolymer, N-2-(2-pyridyl)ethyl chitosan, by direct addition of 2-vinylpyridine to chitosan under the conditions of synthesis in gel. The resulting polymer has the degree of substitution of up to 1. The ability of the samples obtained to sorb transition and noble metal ions was evaluated.

Application of chitosan and its derivatives for solid-phase extraction of metal and metalloid ions: a mini-review

Here we review chitosan-based materials for solid-phase extraction of metal and metalloid ions prior to their determination by atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, mass spectrometry, and some other spectrometric techniques. We show that nearly zero affinity of chitosan and its derivatives to alkali and alkali-earth metal ions is very beneficial for separation of analytes from the salt matrix, which is always present in natural waters, waste streams, and geological samples and interferes with analytical signals. Applicability of chitosan to selective recovery of different metal and metalloid ions can be significantly improved via functionalization with N-, S-, and O-containing groups imparting chitosan with additional electron donor atoms and capability to form stable five- and six-membered chelate rings with metal ions. Among most promising materials for analytical preconcentration, we discussed chitosan-based composites; carboxyalkyl chitosans; chitosan derivatives containing residues of aminoacids, iminodiacetic acid, ethylenediaminetetraacetic and diethylenetriaminepentaacetic acids; chitosans modified with aliphatic and aromatic amines, heterocyclic fragments (pyridyl, imidazole), and crown ethers. We have shown that most chitosan derivatives provide only group selectivity toward metal ions; however, optimization of recovery conditions allows metals and metalloids speciation and efficient separation of noble and transition metal ions.

Application of chitosan and its N-heterocyclic derivatives for preconcentration of noble metal ions and their determination using atomic absorption spectrometry.

Chitosan and its N-heterocyclic derivatives N-2-(2-pyridyl)ethylchitosan (2-PEC), N-2-(4-pyridyl) ethylchitosan (4-PEC), and N-(5-methyl-4-imidazolyl) methylchitosan (IMC) have been applied in group preconcentration of gold, platinum, and palladium for subsequent determination by atomic absorption spectroscopy (AAS) in solutions with high background concentrations of iron and sodium ions. It has been shown that the sorption mechanism, which was elucidated by XPS, significantly influences the sorption capacity of materials, the efficiency of metal ions elution after preconcentration, and, as a result, the accuracy of metal determination by AAS. We have shown that native chitosan was not suitable for preconcentration of Au(III), if the elution step was used as a part of the analysis scheme. The group preconcentration of Au(III), Pd(II), and Pt(IV) with subsequent quantitative elution using 0.1M HCl/1M thiourea solution was possible only on IMC and 4-PEC. Application of IMC for analysis of the national standard quartz ore sample proved that gold could be accurately determined after preconcentration/elution with the recovery above 80%.

Preparation of a sorbent for metal ions based on N-(5-methylimidazol-4-ylmethyl) chitosan with medium degree of substitution

A procedure was developed for preparing a heterocycle-containing chelating amino polymer, N-(5-methylimidazol-4-ylmethyl) chitosan, by polymer-analogous transformations of chitosan in reaction with 4-chloromethyl-5-methylimidazole. The procedure allows synthesis of the polymer with the degree of substitution of up to 0.8, with simultaneous formation of the cross-linked structure. The structure of the polymers prepared was proved by IR and 13C NMR spectroscopy. The ability of N-(5-methylimidazol-4-ylmethyl) chitosan with the degree of substitution of 0.54 to sorb Cu2+ and Ni2+ ions was evaluated. According to the sorption isotherms, the sorption capacity of this derivative exceeds that of the unmodifi ed polymer by a factor of 5.

Sr2+ sorption by synthetic and technogenic silicate materials

We have studied Sr2+ sorption by silicate sorbents prepared in different multicomponent systems, examined sorption kinetics, and identified the sorption mechanism.

Kinetics of the sorption of heavy-metal ions by a sorbent obtained from boric acid production waste

The results of studies of kinetic regularities of sorption of heavy-metals ions (Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Mn2+) by a sorbent based on calcium hydrosilicate (hereinafter referred to as silicate sorbent) produced from manmade waste formed during the processing of the boron-containing mineral raw materials (boron–gypsum) have been presented.

Study of the Composition, Structure, and Sorption Properties of Nanostructured Aluminosilicates

Sorption properties of synthetic nanostructured potassium aluminosilicates with Si/Al ratios from 1 to 5 fabricated in a multicomponent system KOH–Al2(SO4)3·18H2O–SiO2·nH2O–H2O under static sorption conditions at various temperatures and nitrate salt background have been investigated; the activation energy of cesium ions sorption has been evaluated.

Sorption of 137Cs from seawater onto resorcinol–formaldehyde resin

Sorption of 137Cs from seawater onto a selective cation exchanger based on resorcinol–formaldehyde resin was studied. The maximal distribution coefficient of 137Cs at the ratio S: L = 1: 1000 is (4.1–4.5) × 103 cm3 g–1. The sorption-selective characteristics of the resin are negatively affected by alkaline earth meal ions. In the dynamic regime, the operation life of the resorcinol–formaldehyde resin exceeds 700 bed volumes with more than 95% efficiency of cesium sorption. More than 95% of 137Cs is eluted with a 1–3 M HNO3 solution. The eluate volume does not exceed 10 bed volumes.