The currently used radial distribution functions (pair correlation of particles) are time-and space-averaged quantities, and reconstructing the size and structure of individual molecular groups of liquids from them cannot be solved unambiguously. In the article, using liquid water under normal conditions as an example, it is shown that its structure is best represented by the instantaneous spatial distribution of oxygen atoms over distances. This distribution was calculated from the structure of a water cluster (H2O)56 without taking into account molecules subject to the edge effect. The cluster structure was calculated by the nonempirical quantum chemical method in the HF LCAO approximation with the 6-31G basis set. The data on the exact positions of each oxygen atom of several molecules located near the cluster center were selected as the origin of coordinates for calculating the radial distribution function g(r) in the usual way. The shape of g(r) strongly depends on the integration step. With a minimum integration step of 0,1 & Aring; at r < 5.6 & Aring;, it has 10 peaks, the number of which decreases to three with its increase. In this case, the g(r) diagram acquires a normal form, and information about its fine structure is lost. The most reliable and visual interpretation can be obtained by jointly analyzing the radial distribution diagram of the number density of particles and the spatial distribution of particles by distances.

Знание формы ионов четвертичных аммониевых оснований необходимо для корректной интерпретации свойств их солей, однако, информация о численных значениях геометрических параметров их молекул практически отсутствует. В статье приводятся данные ab initio расчета (HF/6-31G) структуры полноатомной модели кластера, содержащего одну ионную пару тетрабутиламмония бромида TBA+Br- в вакууме и водной среде. Такие же расчеты сделаны для его нейтрального структурного аналога тетрабутимлметана (ТBМ). Найдены следующие геометрические параметры: расстояния от центрального атома до терминальных атомов углерода и водорода: расстояния между терминальными атомами; избыточные заряды на атомах водорода и углы между атомами, характеризующие структуру; объемы структур, аппроксимирующих реальные частицы; средние количества и длинны водородных связей молекул воды в зависимости от расстояния до центрального атома частиц. Ими оказались неправильные тетраэдры с плотно упакованными углеводородными радикалами. Форма и размер ТBА+ и ТBМ практически одинаковы и не зависит от окружающей среды или наличия электрического заряда на центральном атоме

A set of studies necessary to determine the suitability of a fibrous anion exchanger with ternary amino groups based on industrial polyacrylonitrile fiber Nitron C as a component of ion substrates was carried out. A laboratory-prepared ion exchanger sample had a working exchange capacity equal to 0.9 meq/g for the nitrate anion, which limits the biological productivity of the substrate for growing plants, in the physiological pH range = 5.5–7.5 and the concentration of the equilibrium nutrient solution is 0.02 eq/l. This capacity is at the level of the best granular ion exchangers and significantly exceeds the capacity of the previously used fibrous ion exchangers for growing plants in zero gravity conditions on space stations in 1970–1994 (Mir, Soyuz TM-10 – TM-17). The synthesized ion exchanger is a polyampholyte and contains three types of ion exchange groups, has high hydrophilicity and mechanical properties that allow it to be processed into textiles and used for any purpose, in which fibrous ion exchangers can be used (air and water purification, human protection means, etc.).

The shape of ions of quaternary ammonium bases should be known to correctly interpret the properties of their salts; however, there is almost no available numerical data on geometric parameters of their molecules. We report ab initio (HF/6-31G) calculation data on the structure of an all-atom model of the cluster containing one ion pair of tetrabutylammonium bromide TBA+Br– in a vacuum and in a water environment. The same calculations are performed for its neutral structural analogue tetrabutylmethane (TBM). The following geometric parameters are reported: distances from the central atom to the terminal carbon and hydrogen atoms; distances between terminal atoms; excess charges on hydrogen atoms and angles between atoms characterizing the structure; volumes of structures approximating real species; average numbers and lengths of hydrogen bonds in water molecules depending on the distance to the central atom of the species. It is shown that the determined shapes correspond to irregular tetrahedra with densely packed hydrocarbon radicals. The shape and size of TBA+ and TBM are almost identical and do not depend on the environment or the electric charge on the central atom.

A fibrous carboxylic ion exchanger, obtained by post-radiation grafting of polyacrylic acid to polypropylene fiber, in the ammonium form has an abnormally low swelling in water, corresponding to 10 moles of water per equivalent, and in the form of tetraethylammonium ion (NEt4+) – abnormally high 25 moles of water/eq. Considering that NH4+ is a hydrophilic particle and NEt4+ is hydrophobic, this fact seems paradoxical. The article attempts to explain this phenomenon using molecular modeling (ab initio calculations of the structure of hydrate complexes in the HF MO LCAO approximation with the 6-31G basis set) in combination with the Predominant Hydrates Model, which made it possible to calculate the theoretical water sorption isotherms of the ion exchanger and compare them with experimental data. The abnormally low swelling of the ion exchanger in the NH4+-form is caused by the formation of a strong bond between the carboxylate anion and ammonium with a significant degree of covalence due to the superposition of the Coulomb interaction of the ions and the formation of a hydrogen bond between them. The abnormally high swelling of NEt4+-forms is caused by the absence of a strong interaction between cations and carboxylate groups due to the impossibility of their convergence due to steric reasons. The high swelling of the ion exchanger is caused by the absence of blocking of the hydrophilic carboxylate groups of the ion exchanger by hydrogen bonds with the cation. The ion exchanger matrix does not contain a cross agent and does not create a spatial restriction for the high swelling of the ion exchanger.

By the method of potentiometric titration of a fibrous aminocarboxylic polyampholyte with a predominant content of carboxyl groups, the equilibrium of the cation exchange of calcium, magnesium, and potassium ions for a hydrogen ion was studied. Due to the low solubility of calcium and magnesium hydroxides in these cases, titration was carried out by Ca(OH)2 and Mg(OH)2, which are formed in solution upon contact with the H-form of the ion exchanger оf increasing portions of solid CaO and MgO. This made it possible to obtain titration curves in a wide range of pH and calcium and magnesium chlorides concentration (0–0.1 eq./L). The dependences of the swelling of ion exchangers on the neutralization degree with the bases of the studied cations are obtained. The coefficients of ion-exchange equilibria are calculated. It was found that the swelling of the ion exchanger is relatively little dependent on its ionic form. The ion exchanger has a higher affinity for calcium than magnesium ion.

Based on the data of ab initio calculation of the structure of (RSO3)2Mg (H2O)18 and (RSO3Rb)2(H2O)16 clusters, which simulate the structure of swollen sulfostyrene ion exchangers in the corresponding ionic forms and a water cluster of comparable size, the numbers of water molecules directly bound to cations and their coordination numbers, including the oxygen atoms of the sulfonic groups linked to the cation, were calculated. It is shown that the first molecular layer around the magnesium ion is formed from water molecules with the highest binding energy with the cluster, and around the rubidium ion – from the molecules of the nearest environment with the lowest binding energies. This is explained by the fact that the transfer of water molecules from its volume to magnesium hydrate is energetically favorable, but not to rubidium hydrate. Therefore, the magnesium ion builds its hydrate mainly from water molecules with the highest binding energy in order to obtain the greatest energy gain, and the rubidium ion – from molecules with the lowest energy, which provides the smallest energy loss.

Titration curves of H-forms of the fibrous chelating sorbent with iminodiacetic groups based on industrial polyacrylonitrile fiber Nitron with potassium hydroxide in 1M KCl solution in the presence of Ni2+, Co2+, Cu2+ and Ca2+ chlorides were obtained. The method used made it possible to simultaneously measure the pH of the solution and the concentration of the divalent cation at each point of the titration curve. From these data, the dependences of their sorption values on the pH of the equilibrium solution were calculated. The curves of direct and back titration practically coincided in all cases. As the pH changed during titration, precipitation was observed at pH values of precipitation of the corresponding hydroxides. In this case, the increase in pH was suspended or greatly slowed down by adding alkali to the titration cell. The formation of a precipitate occurred mainly in a solution for Co2+ and Ni2+ (pH 8), when the ion exchanger was saturated with a metal ion. In the case of Cu2+ (precipitate formation pH 4), Cu2+ sorption occurs at both lower and higher pH due to ionization of carboxyl groups and partial dissolution of the precipitate. In all cases, the maximum sorption of Ni2+, Co2+, Cu2+, Ca2+ corresponded to the formation of sorption complexes of the R–N(CH2COO-)2Me2+ type.

Curves of potentiometric titration of fully protonized fibrous ion exchangers with potassium hydroxide against the background of 1 M KCl in the presence of chlorides of Ni2+, Со2+, Сu2+ and Ca2+ were obtained. The ion exchangers were synthesized by modifying of industrial polyacrylonitrile fiber with diethylenetriamine and triethylenetetraamine and predominantly contained functional groups R-CO-NH- (CH2CH2NH)nH (n = 2 or 3) and a small amount of carboxyl groups. The sorption of Ni2+, Со2+, Сu2+ и Ca2+by ion exchangers was calculated from the data obtained depending on the pH of the medium. It was found that the investigated ion exchangers with high selectivity sorb heavy metal ions in a wide range of acidity of solutions (pH 2–9) due to the formation of metal-polymer complexes with polyamine functional groups. The maximum sorption capacity is 1.5–2.7 and 4–5 meq/g for ion exchangers with n = 2 and 3, respectively.

Structural and electronic characteristics of molecular models of swollen polyacrylic and sulfostyrene-type cation exchangers in sodium and potassium ionic forms are calculated within the non-empirical HF/basis set method using the MINI Huzinaga basis set and the Firefly program. The obtained data are compared with those for water clusters of a comparable size. The molecular models include four and two monomeric units of corresponding polymers with ten water molecules per functional group; the water clusters contain 20 and 40 water molecules. The following characteristics of the model structure are obtained: the number and the types of the nearest neighbors of cations and water molecules; the distances between the interacting ions and the atoms; the orders of interionic and ion-molecular bonds; binding energy distribution of water molecules in the systems; number and length distributions of hydrogen bonds; the number and character of RCO_2^-⋯I^+, RSO_3^-⋯I^+ and H_2O⋯I^+ bonds. The lengths of hydrogen bonds and the total number of intermolecular and ion-molecular bonds per water molecule in water clusters are established to be similar to those in Na+ and K+ molecular models of ion exchangers. The first coordination layer around both ions is filled with oxygen atoms of water molecules and fixed anions. The coordination numbers of Na + and K + are almost equal to those in aqueous solutions. The calculations indicate that direct interaction of Na + and K + with the anionic groups is responsible for the difference between their ion exchange selectivities on carboxylic and sulfostyrene ion exchangers. The Na + ion forms direct largely covalent chemical bonds with the fixed carboxylate anion. The K + ion forms long electrostatic bonds with the carboxylate group. This accounts for a higher selectivity of Na + on carboxylic ion exchangers than that of K + . The K + ion forms long direct electrostatic bonds with the fixed sulfonate anion. The Na + ion does not form direct bonds with the sulfonate due to strong hydration of the former. This accounts for a higher selectivity of K + on sulfonic acid resins that that of Na + .

The structural parameters of the molecular model of a swollen sulfostyrene ion exchanger in lithium form were calculated. The calculations were performed using the non-empirical method (HF/basis using the Mini Huzinaga basis) and the Firefly software for the (RSO3Li)(2)center dot(H2O)(20) cluster. The distances between the Li+ ions and the oxygen atoms in the cluster, which belong to the water molecules and sulfonic groups, were found and sorted in ascending order. The obtained data allowed one to establish that in the first molecular layer, strictly four oxygen atoms of water molecules are present around the Li+ ion, and the ion itself does not form a direct bond with the sulfonic group. A sharp jump in the Li+-O distances takes place between the first and second molecular layers around the cation.

Polyampholytes, containing aminodiacetic functional groups, on the base of polyacrylonitrile fiber Nitron C were obtained by the amination reaction of nitrile groups with polyamines (number of repeating units from 1 to 5) and subsequent alkylation with monochloroacetic acid. The experimental results of potentiometric titration and sorption of supporting electrolyte (kCl) ions by synthesized ion exchangers were obtained, which made it possible to determine the acidity parameters of functional groups: the presence of four types of cation exchange and two types of anion exchange groups was detected in polyampholytes, the sequence of their neutralization in the titration process was established.

Структурные и электронные характеристики молекулярных моделей набухших катионитов полиакрилового и сульфостирольного типа в натриевой и калиевой ионных формах рассчитаны неэмпирическим методом HF/basis set с использованием базиса MINI Huzi­naga и программного пакета Firefly. Полученные результаты сопоставлены с такими же данными для кластеров молекул воды соизмеримого размера. Молекулярные модели включали четыре и две мономерные единицы соответствующих полимеров с десятью молекулами воды на функциональную группу; кластеры воды содержали 20 и 40 молекул. получены следующие характеристики модельной структуры: число и тип ближайших соседей катионов и молекул воды; расстояния между взаимодействующими ионами и атомами; порядок межионных и ион-молекулярных связей; распределение молекул воды в кластерах по энергии связи; распределение водородных связей по числу и длине, а также количество и характер связей RCO2–⋯I+, RSO3–⋯I+ и H2O⋯I+. Длина водородных связей и общее число межмолекулярных и ион-молекулярных связей на молекулу воды в кластерах воды и в молекулярных моделях ионитов в ионных формах Na+ и K+ оказались одинаковыми. Первый координационный слой вокруг обоих ионов заполнен атомами кислорода молекул воды и фиксированных анионов. Координационные числа Na+ и K+ оказались практически такими же, как и в водных растворах. Из результатов расчетов следует, что прямое взаимодействие Na+ и K+ с фиксированными анионными группами обусловливает разницу в их ионообменной селективности на карбоксильных и сульфостирольных ионитах. Ион Na+ образует прямые химические связи с фиксированным карбоксилатным анионом, имеющие заметную долю ковалентности. Ион K+ — длинные электростатические связи с карбоксилатной группой. Это объясняет более высокую селективность Na+ по сравнению с K+ на карбоксильных ионитах. K+ образует длинные прямые электростатические связи с фиксированным сульфонат-анионом, а у Na+ нет прямых связей с сульфогруппой из-за его сильной гидратации. Это объясняет более высокую селективность K+ по сравнению с Na+ на сульфостирольных смолах.

A mathematical model for description of the sorption capacity of ion exchangers on alkaline compounds protonizable in aqueous solutions (exemplified by ammonia, mono-, diand triethylamine) was proposed. The Henry’s constants for these substances were experimentally determined. The model accounts for the concentration and acid-base properties of the sorbate, relative air humidity, acid-base properties and exchange capacity of the ion exchanger, as well as spatial availability of functional groups for interaction under conditions of limited permeability of polymeric ion exchanger. The applicability of the model is illustrated by processing the experimental results on the sorption of ammonia and ethylamines by fibrous carboxylic and sulfonic cation exchangers. Good agreement between the calculated and experimental data is observed.

On the base of fibrous ion exchangers, indicator materials were obtained for sorbates of an alkaline and acidic nature, intended to visualize the working time of the filter layer during ion exchange air purification. The optimal conditions for their production and operation were determined. The practical applicability for the manufacture of indicator cartridges for filters of deep air purification and personal protective equipment for human respiratory organs and skin with the aim of timely visualizing of the sorption resource depletion, due to the contrast and sensitivity of the color change, was demonstrated.

С помощью неэмпирических квантово-химических расчетов (в рамках теории функционала плотности с использованием уровня DFT/B3LYP/6-31G(3d,p)) рассчитаны геометрические характеристики сорбционных комплексов диоксида серы с первичными, вторичными и третичными аминогруппами анионитов, которые синтезированы аминированием нитрильных групп полиакрилонитрильного волокна этилендиамином или диметиламинопропиламином, визуализированы их структуры. Установлены основные закономерности сорбции SO2 из воздуха и особенности протекающих взаимодействий в фазе полимеров: 1) SO2 с первичными и вторичными аминогруппами анионита в основном взаимодействует с молекулами воды и практически не образует связей непосредственно с азотом функциональной группы; введение молекулы кислорода не изменяет состояние системы; 2) в фазе анионита с третичными аминогруппами SO2, взаимодействуя с молекулами воды, самопроизвольно трансформируется в гидросульфит-ион с передачей протона на третичный азот; при наличии в системе молекулы кислорода происходит безбарьерное образование аниона пероксокислоты (SO3OO2-) с возможным дальнейшим окислением гидросульфита в гидросульфат.

Geometrical and electronic parameters of the microstates of the molecular models of polyacrylamide and co-polymers of acrylamide-acrylic acid in aqueous solutions of sodium and potassium chlorides were computed by the non-empirical SCF MO LCAO method with the use of the basis MINI Huzinaga. The models contained four monomeric units of the polymer, including two metal carboxylate groups, 80 water molecules and two pairs of ions Na+ and Cl– or K+ and Cl–. It follows from the calculation results that there is a principal difference in the hydration of Na+ and K+: the Na+‧‧‧О2– bond is shorter than the sum of the radii of the interacting ions, while the k+‧‧‧O2– bond is equal or longer. This indicates that in the first case, the bonds are partially covalent, while in the second one they are pure electrostatic. All elements of the molecular models in the both cases are combined by the intermolecular bonds forming a spatial net. The polymer molecules have a flexible chain with oxygen containing functional groups that are built into the structure of the salt solutions without distorting it. We assume that this is the main reason for the good solubility of the studied polymers in the aqueous salt solutions.

A recipe for the nutrient granular substrate for growing plants (the working name is "Zion") has been developed. The substrate contains all necessary for plant nutrient elements in the chemically bound state in high concentration; it does not contain any organic matter and nitrates, and does not need additional fertilization during the plant vegetation. All nitrogen in the substrate is contained in ammonium form. The substrate has been tested in the laboratory conditions in pot experiments for fertility and nitrates concentration in the biomass of the two cultures accumulating a large amount of nitrates that is leaf salad (Lactuca sativa L.) cultivar Afficion and ryegrass (Lolium perenne L.). The plants were grown on a 100 % substrate as well as on its mixtures (3-10 %) with different fruitless media - quartz sand, peat, and vermiculite. It appeared that in all the cases, when Zion has been used, the maximal content of nitrates in the plant biomass was 209 mg/kg dry, the minimal one was less than 50 mg/kg dry, which is lower by an order of magnitude than the admitted sanitary norm for the plants used in the study.

A fibrous anion exchanger with ternary amino groups of dimethylaminopropylamine was obtained on the base of a polyacrylonitrile fiber by the previously proposed method of catalytic amination of nitrile groups. A fibrous anion exchanger with strong base functional groups was synthesized on the base of this material by the reaction of alkylation of its groups with epichlorohydrin solutions. Their exchange capacities, acid-base properties, sorption of acetic acid vapors from air with different relative humidity were determined. The boundary and optimal conditions of application of the obtained ion exchangers in the processes of air purification from acetic acid and the dynamic characteristics of filtration layers were established.

The equilibrium distribution of ammonia, ethylamine, diethylamine and triethylamine between their aqueous solutions and the gas phase at 25 ± 0.1 °C have been investigated under equilibrium conditions. Based on the results obtained (using the equations of Henry’s law and the ionization constant), Henry’s constants for these substances have been calculated with the consideration of their interaction with water. It was established that Henry’s law is valid, at least, in the range of amine concentrations in the air 0–200 mg/m3.