Novel cucurbit[6]uril-based [3]rotaxane supramolecular ionic liquid as a green and excellent corrosion inhibitor for the chemical industry

Abstract The corrosion of steel materials in alkaline-saline media is the largest problem in industry. Economical and environmentally friendly corrosion inhibitors are crucial for corrosion protection. The present work is the first to introduce a novel cucurbit[6]uril-based [3]rotaxane supramolecular ionic liquid (CB6-based [3]rotaxane) as a green and efficient corrosion inhibitor for the chemical industry. The correlation between the supramolecular ionic liquid system and inhibition behaviour was studied first. The inhibition characteristics of CB6-based [3]rotaxane in 1 M OH– + 1 M Cl– solution were first fully investigated by thermodynamic, gravimetric, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), electrochemical noise (EN), cyclic voltammetry (CV), density functional theory (DFT), molecular dynamics (MD) simulation, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) methods. The experimental results confirmed that CB6-based [3]rotaxane exhibited excellent corrosion resistance, and its inhibition efficiency was 97.97% at 100 mg/L and 0.032 mM. The electrochemical results suggested that (i) CB6-based [3]rotaxane was a mixed-type corrosion inhibitor with anodic dominance; (ii) the supramolecular part of selected ionic liquid is responsible for notably blocks the charge transfer process on the metal surface. The theoretical findings correlated well with the experimental results and revealed that the protonated form of this supramolecular structure exhibited better performance than its neutral form. MD simulations results suggested that the bond length of the Fe(surface)-inhibitor (3.127 A) is less than 3.5 A, which indicates that chemisorption is dominant in the investigated adsorption system. Molecular electrostatic potential analysis confirmed that the studied ionic liquid-supramolecular system contained most favourable nucleophilic centres, which are responsible for excellent inhibition performance.