ORIGINAL PAPER Inhibitive effect of bithiophene carbonitrile derivatives on carbon steel corrosion in 1 M HCl solution: experimental and theoretical approaches M. A. Bedair 1 & A. S. Fouda 2 & M. A. Ismail 2 & Aliaa Mostafa 2 Received: 30 September 2018 /Revised: 5 November 2018 /Accepted: 19 November 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract The effect of [2,2′:5′,2″-terthiophene]-5-carbonitrile and its derivatives on carbon steel surface in 1 M HCl solution was delib- erated at (25 °C) using weight loss technique in addition to electrochemical techniques such as electrochemical frequency modulation, potentiodynamic polarization, and electrochemical impedance spectroscopy. Results gained from all techniques employed are in good coincidence with each other. Results illustrate that [2,2′:5′,2″-terthiophene]-5-carbonitrile is considered as the best inhibition efficiency at 18 × 10 -6 M additive concentration. Efficiency was found to rise with rising concentration and decrease with rising temperature. Adsorptions of organic derivatives on the carbon steel surface follow the Langmuir isotherm. Polarization studies showed that inhibitors are mixed type. From weight loss technique at different temperature data, we calculated the thermodynamic functions of adsorption process and analyze the mechanism between inhibitor and carbon steel surface. The morphology of steel surface was estimated by using SEM, EDX, AFM, and FT-IR. The inhibition performance had been discussed also using theoretical study by quantum chemical calculations and molecular dynamic simulation. Keywords Bithiophenes . Polarization . Electrochemical impedance spectroscopy . Density functiontheory . Molecular dynamics Introduction Corrosion process has an important role in the field of eco- nomics and safety. CS has been used a lot under different conditions in petroleum industries [1]. Acidic media are great- ly used in industries for pickling, acid cleaning of boilers, descaling and oil well acidizing [2–5]. Mostly, sulfuric and hydrochloric acids are employed for such purposes [6]. Inhibitors used in corrosion especially the organic compounds containing oxygen, sulfur, and nitrogen are used in the steel industry in different process for production and plating of steel strips, which permit an adsorption on the surface of metal [7–10]. Inhibitor adsorbs on metal surface and blocks the ac- tive surface sites to minimize the rate of corrosion. Four types of adsorption may occur by inhibitor molecules at interface between metal/solution: (i) electrostatic attraction between the charged molecules and charged metal, (ii) interaction of un- charged pairs in the molecules with the metal, (iii) interaction of π electrons with the metal, and (iv) combination of (i) and (iii). Bithiophene derivatives have structure that able them to be used as inhibitors such other organic inhibitors [11–13]. The advantages of using these inhibitors are low cost, high efficiency, anticancer, and antioxidant. Quantum calculations are very important in doing correlation between molecular structure and chemical reactivity and relation with corrosion inhibition process. Inhibitor efficiency in a chemical reaction is related to electronic molecular structures [14]. The purpose of this current study is to investigate the corrosion retardation effect of these organic derivatives in CS in 1 M HCl by chem- ical and electrochemical techniques and the agreement with each other and with the quantum study. Materials and experimental methods Materials Carbon steel sheets used in this study possess the following composition (weight %): 0.200 C, 0.003 Si, 0.024 P, 0.350 Mn, and the rest Fe. * M. A. Bedair m_bedier@yahoo.com; m_bedier@hotmail.com 1 Department of Chemistry, Faculty of Science (Men’ s Campus), Al-Azhar University, Nasr City, Cairo 11884, Egypt 2 Department of Chemistry, Faculty of Science, El-Mansoura University, El-Mansoura 35516, Egypt Ionics https://doi.org/10.1007/s11581-018-2811-0