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10DOI: 10.6060/ivkkt.20206304.6008 УДК: 544.03
МОЛЕКУЛЯРНОЕ МОДЕЛИРОВАНИЕ АДСОРБЦИИ ГАЗОВ-ПОЛЛЮТАНТОВ НА КАДМИЙСОДЕРЖАЩЕМ ПОЛИАКРИЛОНИТРИЛЕ
М.М. Авилова, Е.А. Марьева, О.В. Попова, Т.Г. Иванова
Марта Маисовна Авилова*, Екатерина Александровна Марьева, Ольга Васильевна Попова* Кафедра экологии и безопасности жизнедеятельности Института управления в экономических, экологических и социальных системах Южного федерального университета, пер. Некрасовский, 44, Таганрог, Ростовская область, Российская Федерация, 347928
Е-mail: m.avir89@yandex.ru*, ekaterina_maryeva@mail.ru, ovpopova@sfedu.ru* Татьяна Геннадьевна Иванова
Кафедра химической технологии, Южно-Российский государственный политехнический университет им. М.И. Платова, ул. Просвещения, 132, Новочеркасск, Ростовская область, Российская Федерация, 346428
Е-mail: tgalikyan@rambler.ru
В публикации представлены теоретические исследования адсорбции газов-поллю-тантов на поверхности кадмийсодержащего полиакрилонитрила (Cd-полиакрилонитрила) при отсутствии и наличии в окружающей среде молекул воды и молекул кислорода. Определен перечень газов, к которым поверхность Cd-полиакрилонитрила может проявлять наибольшую чувствительностью. В качестве газов-загрязнителей выбраны диоксид азота, метан, аммиак, оксид серы (II), сероводород, озон, монооксид углерода, оксид углерода (II), хлор. Для моделирования в работе использованы программные пакеты: HyperChem, Gaussian 09, Chemoffice 2010. По итогам работы в HyperChem, Gaussian 09 получены модели макромолекул полиакринонитрила, из которых для получения кластера Cd-полиакрилонитрила выбрана макромолекула пентамера. Затем, реализуя метод молекулярной механики в Chemoffice 2010, а именно в подпрограмме Chem3D, произведено построение модели кластера Cd-полиакрилонитрила. Далее методом молекулярного моделирования определены термодинамические показатели систем: «кластер Cd-полиакрилонитрила - молекула газа», «кластер Cd-полиакрилонитрила - молекула кислорода», «кластер Cd-полиакрилонитрила - молекула воды», «кластер Cd-полиакрилонитрила - молекула кислорода - молекула газа», «кластер Cd-полиакрилонитрила - молекула воды - молекула газа». В результате молекулярного моделирования установлено, что Cd-полиакрилонитрил в атмосферном воздухе проявляет чувствительность к газообразному хлору и монооксиду углерода; в бескислородной среде -также к сероводороду. Результаты молекулярного моделирования подтверждают ранее полученные экспериментальные данные по оценке газочувствительности Cd-полиакрилонит-рила и указывают на действие сил Ван-дер-Ваальса между поверхностью Cd-полиакрило-нитрила и адсорбирующейся молекулой газа. Наличие или отсутствие в атмосферном воздухе молекул воды не должно сказываться на изменении чувствительности Cd-полиакрило-нитрила к газам-поллютантам.
Ключевые слова: полиакрилонитрил, кадмий-содержащий полиакрилонитрил, молекулярное моделирование, влияние молекул воды (кислорода), адсорбция газов-поллютантов, силы Ван-дер-Ваальса
Для цитирования:
Авилова М.М., Марьева Е.А., Попова О.В., Иванова Т.Г. Молекулярное моделирование адсорбции газов-поллютан-тов на кадмийсодержащем полиакрилонитриле. Изв. вузов. Химия и хим. технология. 2020. Т. 63. Вып. 4. С. 49-54 For citation:
Avilova М.М., Maryeva E.A., Popova O.V., Ivanova ^G. Molecular modeling of adsorption of pollutant gases on cadmium-containing polyacrylonitrile. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. [Russ. J. Chem & Chem Tech.]. 2020. V. 63. N 4. P. 49-54
MOLECULAR MODELING OF ADSORPTION OF POLLUTANT GASES ON CADMIUM-CONTAINING POLYACRYLONITRILE
M.M. Avilova, E.A. Maryeva, O.V. Popova, T.G. Ivanova
Marta M. Avilova*, Ekaterina A. Mar'yeva, Olga V. Popova*
Department of Ecology and Life Safety, Institute of Management in Economic, Environmental and Social Systems of the Southern Federal University, Nekrasovskiy line, 44, Taganrog, Rostov region, 347928, Russia E-mail: m.avir89@yandex.ru*, ekaterina_maryeva@mail.ru, ovpopova@sfedu.ru*
Tat'yana G. Ivanova
Department of Chemical Technology, South-Russian State Technical University named after M.I. Platov, Prosveshcheniya st., 132, Novocherkassk, Rostov region, 346428, Russia E-mail: tgalikyan@rambler.ru
The paper presents theoretical studies of the adsorption of pollutant gases on the surface of cadmium-containing polyacrylonitrile (Cd-polyacrylonitrile) in the absence and presence of water molecules and oxygen molecules in the environment. The list of gases to which the Cd-polyac-rylonitrile surface may have the highest sensitivity is determined. Nitrogen dioxide, methane, ammonia, sulfur oxide (II), hydrogen sulfide, ozone, carbon monoxide, carbon oxide (II), chlorine were chosen as pollutant gases. The following software packages are used for modeling: Hyper-Chem, Gaussian 09, Chemoffice 2010. Polyacrylonitrile macromolecule models were obtained from HyperChem, Gaussian 09, from which a pentamer macromolecule was chosen to produce a Cd-polyacrylonitrile cluster. Then, implementing the molecular mechanics method in Chemoffice 2010, namely in the Chem3D subroutine, the Cd-polyacrylonitrile cluster model is constructed. Further, using the molecular modeling method, the following thermodynamic parameters were determined: «Cd-polyacrylonitrile cluster - gas molecule», «Cd-polyacrylonitrile cluster - oxygen molecule», «Cd-polyacrylonitrile cluster - water molecule», «Cd-polyacrylonitrile cluster - oxygen molecule gas molecule», «Cd-polyacrylonitrile cluster - water molecule - gas molecule». As a result of molecular modeling, it was established that Cd-polyacrylonitrile in the atmospheric air exhibits selective sensitivity to gaseous chlorine and carbon monoxide; in an oxygen-free environment - also to hydrogen sulfide. The results of molecular modeling confirm the previously obtained experimental data on the evaluation of the gas sensitivity of Cd-polyacrylonitrile and indicate the presence of van der Waals forces between the Cd-polyacrylonitrile and the adsorbed gas molecule. The presence or absence of water molecules in atmospheric air should not affect the change in the sensitivity of Cd-polyacrylonitrile to pollutant gases.
Key words: polyacrylonitrile, cadmium-containing polyacrylonitrile, molecular modeling, water (oxygen) molecules effect, pollutant gases adsorption, Van der Waals forces
INTRODUCTION
Modified polyacrylonitrile (PAN) is used to create supercapacitors, flexible electronic devices, self-cleaning coatings, photocatalysts, gas sensors, as a material for creating highly porous activated carbons [1-6]. The introduction of alloying additives into the PAN allows one to change its physicochemical, electrical, mechanical properties, which makes it possible to synthesize composite materials with given parameters of properties. After thermal treatment by IR annealing, PAN acquires the properties of sensitivity to atmospheric air gases at room temperature [7-12] and can serve as the basis for the synthesis of metal-containing composites, which, in turn, have the property of selective sensitivity to polluting gases. To improve the metrological indicators of polyacrylonitrile films,
they often resort to varying the time and temperature parameters for producing PAN films, as well as the type and concentration of modifying additives (transition metal salts) [9, 10]. One example of a PAN-based nanocomposite material is Cd-PAN, which has selective sensitivity to hydrogen sulfide [10, 11]. However, to obtain a highly efficient gas-sensitive material, theoretical studies of the causes of the selective gas-sensitivity of Cd-PAN films are required, as well as the effect of various components in the analyzed air-gas medium on the adsorption of gases.
The purpose of this paper is to study the gas sensitivity of Cd-PAN according to the results of molecular modeling of the interaction of a Cd-PAN cluster with molecules of pollutant gases with different atmospheric air composition.
М.М. Авилова, Е.А. Марьева, О.В. Попова, Т.Г. Иванова
RESEARCH TECHNIQUES
The method of quantum chemical calculations in the HyperChem program using semi-empirical computational schemes (MNDO) was used to obtain spatial configurations of PAN pentamer macromolecules. Further, for maximum accuracy of the results in the Gaussian09 software package using the Pople base set (6-31 G*) within the framework of the density functional theory (DFT), we calculated the thermodynamic indicators of PAN macromolecules [13-15].
To obtain the Cd-PAN cluster and estimate its gas sensitivity, the molecular modeling method (or minimization of the potential energy of the system in a modified version of the force field (MM2) developed by Ellinger [16]) was used in the Chem3D sub-program of the Chemoffice program [13, 17-21].
Synthesis of Cd-PAN films is carried out by the method of pyrolysis under the influence of IR radiation under low vacuum [10]. Cadmium (II) chloride dissolved in dimethylformamide is used as the alloying component. As a rule, IR annealing of Cd-PAN films is carried out at temperatures not exceeding 350-400 °C. Since the melting point of cadmium chloride is 568.5 °C [22], cadmium salts are likely to be present in films of thermally stabilized Cd-PAN).
According to the foregoing, as a model of a Cd-PAN cluster, we take a system consisting of chains of macromolecules of PAN and cadmium chloride molecules located in the interlayer space. To simplify, we consider a system of 2 parallel oriented macromo-lecular chains of pentamers and one molecule of cadmium parallel to each other. When implementing the molecular mechanics method in the Chem3D software package, we set different positions for the location of the cadmium chloride molecule: (1) from the edge and (2) in the center of the interlayer space (Fig. 1). We establish that the most energetically favorable arrangement of CdCl2 is in the central part of the interlayer space (2).
(1) (2)
Fig. 1. Introduction of cadmium chloride in the PAN system: (1) - on the edge of the PAN cluster (Emm = 1467.42 kJ / mol); (2) - in the
center of the PAN cluster (Emm = 1401.22 kJ / mol) Рис. 1. Внедрение хлорида кадмия в систему ПАН: (1) - с краю кластера ПАН (Emn = 1467,42 кДж/моль); (2) - в центр кластера ПАН (Emm =1401,22 кДж/моль)
At the next stage, the possibility of adsorption of pollutant gases (nitrogen oxide (IV), ammonia, sulfur oxide (II), hydrogen sulfide, ozone, carbon oxide (IV), carbon oxide (II), chlorine) on the surface of the Cd-PAN cluster was investigated. At the same time, different positions of gas molecules were set: (1) - inside the cluster and (2) - (12) - in the middle of the cluster at a distance of 2-10 A from the surface (Fig. 2).
(12) 1=10 A
Fig. 2. The location of gas molecules at interacting with the surface of a Cd-PAN cluster Рис. 2. Расположение молекул газов при взаимодействии с поверхностью кластера Cd-ПАН
At this stage, the thermodynamic characteristics (steric energy of the system (Emm), binding energy (AE), energy minimum points (lmin)) and geometric indicators (distances between gas molecules and the Cd-PAN cluster (l)) were identified.
Then, similarly to the above, the systems "PAN cluster - oxygen molecule" and «PAN cluster -water molecule» were studied, namely the steric energy of this system (ECd-PAN + O2 and ECd-PAN + H2O), the binding energy between the oxygen / water molecule and the surface of the PAN cluster (AE), the points with the minimum energy (lmin), and also the distances between the molecules of pollutant gases and the oxygen molecule (LO2) / water (LH2O). At the last stage of implementation of the molecular modeling method, the systems Cd-PAN cluster - oxygen molecule - gas molecule and Cd-PAN cluster - water molecule - gas molecule were investigated.
According to the results of the comparison of the thermodynamic parameters of the studied systems, first of all their steric energies, the possibility of interaction of gas molecules with Cd-PAN was evaluated.
RESULTS AND DISCUSSION
As a result of molecular modeling of the Cd-PAN cluster, it was found that the steric energy of this cluster is 1401.22 kJ/mol, the steric energy of
the «Cd-PAN cluster - oxygen molecule» system is 1397.62 kJ/mol, and the steric energy of the «cluster Cd-PAN is a water molecule» - 5206.33 kJ/mol. Based on the obtained results, it can be concluded that oxygen adsorption is most likely due to the fact that Emm Cd-PAN + O2 < Emm Cd-PAN. In this case the interaction with the water molecule of this cluster is excluded (Emm Cd-PAN << Emm Cd-PAN+H2O), therefore, the effect of humidity on the adsorption of pollutant gases in this case is unlikely. This is also confirmed by the study [11]. The results of molecular modeling of the adsorption of pollutant gases on the surface of Cd-PAN in various gaseous medium are presented below in tables 1-3 and in fig. 3 and 4.
Table 1
Steric energy of the system Cd-PAN cluster - water / oxygen molecule - gas molecule Таблица 1. Стерическая энергия системы «кластер Cd-ПАН - молекула воды / кислорода - молекула газа»
Gas Emin, kJ/mol
Cd-PAN Cd-PAN + Н2О Cd-PAN + О2
Cl2 1358.48 5206.33 1392.97
CO 1398.45 5175.07 1389.57
О3 6271.05 7383.83 2446.88
NO2 3545.87 7782.97 10156.85
H2S 1395.90 5485.63 1706.88
СО2 2061.65 5665.42 2081.17
SO2 2288.75 6042.02 2278.06
NH3 4787.03 7263.41 4864.13
Table 2
Bond energy of the system Cd-PAN cluster - water / oxygen molecule - gas molecule Таблица 2. Энергия связи системы «кластер Cd-ПАН - молекула воды / кислорода - молекула газа»
Gas AE, kJ/mol
Cd-PAN Cd-PAN + Н2О Cd-PAN + О2
Cl2 12.46 9.09 0.71
CO 2.85 4.44 4.15
О3 18.98 8.34 1.76
NO2 86.10 6.45 4.78
H2S 5.36 8.25 1.38
СО2 8.88 46.84 4.73
SO2 3.18 22.12 6.33
NH3 9.43 12.99 1.68
The minimum values of steric energy were obtained for the interactions of the Cd-PAN cluster with chlorine and carbon monoxide molecules and hydrogen sulfide. Regardless of whether there are oxygen or water molecules in the environment, Cd-PAN films will be sensitive to Cl2 and CO. When interacting in an
oxygenated and humid environment of Cd-PAN with H2S molecules, the energy costs will be relatively low due to the small AEmm value, which may indicate the presence of hydrogen sulfide sensitivity under the indicated conditions.
Table 3
Points with the minimum energy of the Cd-PAN cluster - water / oxygen molecule - gas molecule" system and
the distance of gas molecules from H2O/O2 Таблица 3. Точки с минимальной энергией системы «кластер Cd-ПАН - молекула воды / кислорода - молекула газа» и расстояния молекул газов от Н2О/О2
Gas 1 A Amm? A l,A l,A
Cd-PAN Cd- PAN+H2O Cd- PAN+O2 Н2О O2
Cl2 3.5 3.5 6 5.4 3.2
CO 3.7 3.2 3 2.9 2.7
О3 3.7 6 6 2.7 3.5
NO2 2.5 3.7 6 2.7 5.8
H2S 3.7 3.5 6 3.1 4.7
СО2 3.2 3.4 3 3.3 3.1
SO2 4 3.2 3 2.6 3.4
NH3 3 2.5 4 4.7 2.7
Fig. 3. The dependence of steric energy on the distance to the gas molecule for the system «cluster Cd-PAN - gas molecule». 1 - CO;
2 - Cl2; 3 - H2S; 4 - CO2; 5 - SO2; 6 - NO2; 7 - NH3; 8 - O3 Рис. 3. Зависимость стерической энергии от расстояния до молекулы газа для системы «кластер Cd-ПАН - молекула газа». 1 - CO; 2 - Cl2; 3 - H2S; 4 - CO2; 5 - SO2; 6 - NO2; 7 - NH3; 8 - O3
М.М. Авилова, EA. Марьева, О.В. Попова, Т.Г. Иванова
Fig. 4. The dependence of steric energy on the distance to the gas molecule for the systems «cluster Cd-PAN - oxygen molecule -gas molecule» (at the top) and «Cd-PAN cluster - water molecule -gas molecule» (at the bottom): 1 - CO; 2 - Ck; 3 - H2S; 4 - CO2 Рис. 4. Зависимость стерической энергии от расстояния для систем «кластер Cd-ПАН - молекула кислорода - молекула газа» (вверху) и «кластер Cd-ПАН - молекула воды - молекула газа» (внизу): 1 - CO; 2 - Ck; 3 - H2S; 4 - CO2
The analysis of the obtained binding energies (AE) between the gas molecules and the cluster surface showed that in most cases, van der Waals interaction forces arise between the components of the system. An exception is the interaction of nitrogen dioxide molecules with a Cd-PAN cluster in an oxygen-free environment, where the binding energy reaches a higher value than in the case of other gases, which is explained by the possible coordination interaction of PAN with NO2 dimers according to the following scheme:
Since in the case of adsorbed nitrogen dioxide molecules, sufficiently high energy costs are required, exceeding the energy of the Cd-PAN cluster (Cd-PAN / Cd-PAN + O2), the interaction of NO2 with the cluster surface at standard temperature is excluded.
For the gases considered, the smallest points with the minimum energy are in most cases within 2.5-
3.7 A from the Cd-PAN cluster (Table 3). This distance between the gas molecule and the surface of the cluster allows intermolecular interactions, but excludes the possibility of overlapping electron clouds and the appearance of a chemical bond. For this reason, the appearance of a chemical bond is also excluded between the oxygen / water molecule and the gas molecule (LO , LH O).
CONCLUSION
Studies carried out by molecular modeling have established that Cd-PAN will be sensitive to chlorine, carbon monoxide and, in an oxygen-free environment, also to hydrogen sulfide in atmospheric air. Assuming that the binding energy in most cases does not exceed the value of 20 kJ/mol, we can assume that Van der Waals forces act between the gas molecules and the Cd-PAN surface.
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Поступила в редакцию 25.02.2019 Принята к опубликованию 20.02.2020
Received 25.02.2019 Accepted 20.02.2020
