Insights into the uses of two azine decorated d10-MOFs for corrosion inhibition application on mild steel surface in saline medium: Experimental as well as theoretical investigation

Abstract

Recently, the use of metal–organic frameworks (MOFs) as an efficient corrosion inhibitor has been focused on due to their unique excellent properties such as being rich in π-electron system, chemical and thermal robustness and supramolecular task-specific functionality etc. The present work demonstrates the judicious synthesis of two d10-MOFs namely CI@Cd-MOF and CI@Zn-MOF utilizing organic struts like 4,4′-oxybisbenzoic acid (OBA) and (1E,2E)-1,2-bis(1-(pyridine-4-yl)ethylidene)hydrazine (BPD) and investigated as efficient inhibitor for mild steel corrosion in an adverse corrosive medium i.e. in 3.5 wt% saline medium. The applications of MOFs as heterogenous inhibitor for mild steel corrosion in saline medium have been assessed via potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) studies. The EIS analysis shows that the effectiveness of corrosion inhibition rises with increasing inhibitor concentrations, reaching 90.15 % with the application of 50 ppm of CI@Zn-MOF. PDP study reveals that both MOFs act as a mixed kind of inhibitor. Post-corrosion study of the mild steel surface has been characterised by Field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) analysis and 3D-surface profilometer study demonstrating that the application of inhibitors results in a significant reduction of the corrosion process. The water contact angles on the steel surface increased from 49° to 104.2° and 108.1° due to the adsorption of inhibitors on the steel surface following the Langmuir adsorption isotherm model. Furthermore insightful explanations and correlations with density functional theory (DFT) have been provided for the experimentally observed corrosion inhibition performance as well as adsorption capability. Molecular dynamics (MD) simulation has been conducted to mimic the interactions of the inhibitors with metal surface atoms and corrosive species in an actual corrosive medium. The high binding energy (1328.12 kJ/mol for CI@Zn-MOF) provides evidence that inhibitors are able to spontaneously adsorb on steel surfaces. Additionally, the pivotal role of non-covalent intermolecular interactions in a confined space has been assessed using non-covalent interaction based on the reduced density gradient (NCI-RDG) technique.