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ORIGINAL PAPER

Polyaniline emeraldine salt as selective electrochemical sensor for HBr over HCl: a systematic density functional theory study through oligomer approach Bilal Ahmad Farooqi 1 & Muhammad Yar 2 & Ayesha Ashraf 1 & Umar Farooq 1 & Khurshid Ayub 2 Received: 21 August 2020 / Accepted: 26 October 2020 / Published online: 4 November 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Density functional theory (DFT) calculations are performed to rationalize the experimentally observed sensitivity and selectivity of polyaniline emeraldine for hydrogen bromide over hydrogen chloride. The interaction behaviour is studied at UB3LYP method of density functional theory through oligomer approach. The properties for polymers are obtained extrapolation through second-degree polynomial fit. Optimized of geometries, interaction energies, Mulliken and natural bond orbital charges are analysed to study the sensing behaviour. In the preferred orientation modes, emeraldine salt acts as a hydrogen donor, whereas HBr and HCl are hydrogen acceptors (nucleophile). Basis set superposition error corrected interaction energies are calculated for accurate determination of interaction strength between sensor and analyte. The basis set superposition error is significant for HBr complex compared to HCl. The decrease in energy gap between highest occupied and lowest unoccupied molecular of conducting polymer (sensor) on complex formation with both analytes has been studied. The results of computational study show that polyaniline emeraldine salt shows more selectivity towards HBr as compared to HCl and this outcome is in agreement with reported results based on experimental observations. Keywords Density functional theory . Sensors . Conducting polymers . Polyaniline Emeraldine salt . Halogen acids

Introduction Sensing phenomenon brings about several changes in the chemistry of sensing material upon interaction with analytes. Some of these changes such as change in colour, temperature or electrical conductivity are very much noticeable and have become the basis of detection and sensor phenomenon. Some of the changes are better explained theoretically than experimentally. Chemical sensors are the devices used to monitor

Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s00894-02004590-3. * Khurshid Ayub [email protected] 1

Institute of Chemistry, University of the Punjab, Lahore, Pakistan

2

Department of Chemistry, COMSATS University, Abbottabad Campus, Islamabad 22060, Pakistan

specific chemical species in a given system. Different classes of materials have been used as sensors; however, conducting polymers possess certain advantages such as rapid response, remarkable sensitivities, suitable mechanica1 properties and wide range working temperature [1, 2]. These properties have led to the development of a number of sensors based on conducting polymers [3]. These materials are used as these films incorporated as an integral part of sensin