Investigation of the Adsorption Properties of Electrically Conductive Pyrolyzed Polyacrylonitrile Modified with Chromium (III) Oxide to Obtain Highly Efficient Gas Sensors

Abstract

   Introduction. Obtaining highly sensitive gas sensors is an urgent task, the solution to which will allow you to accurately and quickly assess changes in the air-gas composition of a given medium. Gas sensors based on metal-containing pyrolyzed polyacrylonitriles (Me-pPAN) are among the cheapest and most environmentally friendly gas-sensitive materials with a fast response. One of the types of sensor materials included in the Me-pPAN list is pyrolyzed polyacrylonitrile (pPAN) modified with a chromium (III) oxide molecule. The reasons for selective adsorption of pPAN and Me-pPAN to pollutant gases, which would allow controlling this process and obtaining sensory materials with increased sensitivity to gases, are not enough studied.   Therefore, the aim of this work was to establish the main causes of selective adsorption of semiconductor electrically conductive films by modeling methods in the framework of molecular and quantum mechanics.   Materials and Methods. The authors used modeling methods in the framework of molecular and quantum mechanics (MM2), the density functional theory (COSMO) method and the semi-empirical PM7 method in the MOPAC software package.   Results. MM2 and PM7 methods were used to obtain models of adsorption complexes of "Cr-pPAN – gas-pollutant" systems. Thermodynamic parameters of the system were calculated for standard environmental conditions. The dependence of the adsorption of pollutant gases on the surface of Cr-pPAN on temperature has been established.   Discussion and Conclusion. As a result of calculating the thermodynamic parameters of gas-pollutant–pPAN/Me-pPAN systems and obtaining positive values of Gibbs energies of these systems, it was confirmed that the adsorption of polluting gases on the surface of Cr-pPAN was not a spontaneous phenomenon and was effective at high temperatures. Considering that when chromium (III) oxide was introduced into the pPAN matrix, the charge on nitrogen atoms increased. It could be concluded that a chromium (III) oxide molecule had a positive effect on the semiconductor properties of pPAN. It was found that the adsorption of polluting gases (SO2 and NO2) was most likely on the surfaces of pPAN and Cr-pPAN. The results obtained in the work can be used to obtain gas-sensitive materials with specified metrological characteristics.