Benzothiazolylhydrazine azomethine derivatives for efficient corrosion inhibition of mild steel in acidic environment: Integrated experimental and density functional theory cum molecular dynamics simulation approach

Abstract

Synthesis of challenging corrosion inhibitors is of prime importance to inhibit hydrogen-induced and localised metallic corrosion occur in the corrosive acidic solution. In this regard, the present research has been focused on the development of functionalised Schiff bases, namely, 1-(benzo[d]thiazol-2-yl)-2-((furan-2-yl)methylene)hydrazine (BTFMH), 1-(benzo[d]thiazol-2-yl)-2-((thiophen-2-yl)methylene)hydrazine (BTTMH), 1-(benzo[d]thiazol-2-yl)-2-((5-methylthiophen-2-yl)methylene)hydrazine (BTMMH) with an aim of effectively curtailing the issues associated to hydrogen-induced cracking and subsequent inhibition of metallic corrosion taking place in the corrosive acidic solution. The corrosion inhibiting performances of the synthesized inhibitors have been assessed for mild steel surfaces exposed in 1 M HCl medium using gravimetric measurement, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization study revealed that the synthesized inhibitor molecules retarded the cathodic hydrogen evolution reaction at cathodic site and subsequently minimized the oxidation of metals at anode; thereby, these Schiff bases acted as the mixed type inhibitors. The EIS study revealed that the corrosion inhibition phenomenon is being controlled through charge transfer processes. All of these three synthesized inhibitor molecules showed approximately 96–98 % corrosion inhibiting efficiency at exceedingly low concentration (0.5 mM). The inhibition efficacy obtained for these synthesized inhibitor molecules follows the order: BTMMH > BTTMH > BTFMH. The adsorption nature of these inhibitor molecules on mild steel surfaces have been revealed through surface morphology, topography and water contact angle studies. Thereafter, the insight of corrosion inhibition mechanism at atomic level have been explored by density functional theory (DFT). The optimized geometrical structure, electron density distribution of frontier molecular orbitals and their corresponding energy parameters obtained from DFT as well as Fukui indices analysis have been explored to unveil the plausible modes of adsorption or the reactive sites present within the inhibitor molecules which facilitate their interactions with surface atoms of metals. The non-covalent interaction based on reduced density gradient have been explored to study intrinsic feeble interaction acting with the molecules. Afterwards, molecular dynamics simulation has been employed to validate the spontaneity along with the nature of interaction at the metal inhibitor interface. Furthermore, the equilibrium adsorption configuration of the synthesized inhibitor molecules on the targeted metal surface atoms have been envisaged and the interfacial phenomenon has been explained.