Chitosan biopolymer effect on copper corrosion in 3.5 wt.% NaCl solution: Electrochemical and quantum chemical studies

Abstract

The inhibition of copper corrosion by chitosan biopolymer in 3.5 wt.% NaCl solution was assessed using electrochemical impedance spectroscopy, potentiodynamic polarization and quantum chemical methods. Results obtained show that Chitosan inhibited copper dissolution in the corrosive medium. The adsorption of the studied inhibitor on the metallic surface was found to follow Langmuir adsorption model. The inhibition efficiency increased with the inhibitor concentration. From polarization measurements, Chitosan can be classified as mixedtype corrosion inhibitor. The Gibbs free energy of adsorption value revealed that the adsorption process of chitosan is endothermic and mainly by a physisorption mechanism following Langmuir adsorption isotherm model. Surface analysis performed using optic microscopy has confirmed the existence of a protective film of chitosan molecules onto copper surface. Moreover, quantum chemical calculations at B3LYP level with 6-31G (d, p) basis set lead to molecular descriptors such as E HOMO (energy of the highest occupied molecular orbital), E LUMO (energy of the lowest unoccupied molecular orbital), ΔE (energy gap) and μ (dipole moment). The global reactivity descriptors such as χ (electronegativity),  (global hardness), S (global softness) and ω (electrophilicity index) were derived using Koopman's theorem and analyzed. The local reactivity parameters, including Fukui functions and dual descriptor were determined and discussed. Experimental and theoretical data were in good agreement.