Bishydrazone ligand and its Zn-complex: synthesis, characterization and estimation of scalability inhibition mitigation effectiveness for API 5L X70 carbon steel in 3.5% NaCl solutions

Abstract

Bishydrazone ligand, 2,2′-thiobis(N′-((E)-thiophen-2-ylmethylene) acetohydrazide), H₂TTAH and its Zn- complex were prepared and characterized through elemental analysis and various spectroscopic performances as well as (IR, ¹H and ¹³C NMR, mass and (UV-Vis) measurements. The synthesized complex exhibited the molecular formula [Zn₂(H₂TTAH)(OH)₄(C₅H₅N)₃C₂H₅OH] (Zn-H₂TTAH). To assess their potential as anti-corrosion materials, the synthesized particles were assessed for their effectiveness for API 5L X70 C-steel corrosion in a 3.5% NaCl solution using electrochemical methods such as potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). Additionally, X-ray photoelectron spectroscopy (XPS) was employed to examine the steel surface treated with the tested inhibitors, confirming the establishment of an adsorbed protecting layer. The results obtained from the PP plots indicated that both H₂TTAH and Zn-H₂TTAH act as mixed-type inhibitors. At a maximum concentration of 1 × 10⁻⁴ M, H₂TTAH and Zn-H₂TTAH exhibited inhibition efficiencies of 93.4% and 96.1%, respectively. The adsorption of these inhibitors on the steel surface followed the Langmuir adsorption isotherm, and it was determined to be chemisorption. DFT calculations were achieved to regulate the electron donation ability of H₂TTAH and Zn-H₂TTAH molecules. Additionally, Monte Carlo (MC) simulations were conducted to validate the adsorption configurations on the steel surface and gain insight into the corrosion inhibition mechanism facilitated by these molecules.