Metal-organic frameworks based on heterocyclic ligands and some transition metals as effective carbon steel corrosion inhibitors in aqueous environment
By Fouda, Abd El Aziz S.; Etaiw, Safaa Eldin H.; Sobhy, Sally
Published in Journal of Molecular Liquids
2022
Abstract
A variety of corrosion inhibitors, including inorganic salts and organic compounds containing heteroatoms and electron clouds, were utilized as corrosion inhibitors for metals in diverse corrosive environments”. The presence of Nano cages and hollow spheres in metal organic frameworks expands their applicability in the field of electrochemistry. Metal-organic frameworks (MOFs) containing 2,6-pydinedicarboxylic acid ligands (2,6-pydcH2) as well as Cd and Mn were synthesized to investigate their influence on C-steel corrosion inhibition in 1 M hydrochloric acid solution. 2-Asymmetric units of each MOFs1 and 2 represent a repeat structure which contains 2-metal cations coordinated to two 2,6-pydc ligands and 3-molecules of H2O with one free 2,6-pydcH2 as guest molecule. The network structures of 1 and 2, contains 2-similar Cd (II) or Mn (II) atoms surrounded by 7- atoms adopting unusual distorted pentagonal bipyramidal geometry. The prevention of C-steel corrosion was studied using weight loss (WL), “Tafel polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM)”. Inhibition efficacy rises with raising inhibitor concentration, decreases with rise in temperature and reached 91.42% at 25 °C for MOF (1) at 1 × 10-4 M. On the other hand, it increases with improvement of concentration and in rise in temperature and reached 85.98% at 45 °C for MOF (2) at 1 × 10-4 M. Polarization measurements revealed that these MOFs operated as a mixed kind of inhibitors. The activation and adsorption thermodynamic properties were estimated and discussed. The value of free energy of adsorption determined at 25 °C (ΔGoads = 16.96, 41.61 kJ mol−1 for MOFs 1 and 2, respectively), suggested a physisorption for MOF (1) and Chemisorption for MOF (2) compounds. The adsorption of these inhibitors was shown to follow the Langmuir adsorption isotherm. The surface morphology of a C-steel sample was done using scanning electron microscopy (SEM) technique. All tests conducted that MOFs 1 and 2 acted as good corrosion inhibitors.