Thermodynamic and kinetic insights into the role of amino acids in improving the adhesion of iota-carrageenan as a natural corrosion inhibitor to the aluminum surface

The effect of amino acids on improving the corrosion inhibition performance of i-carrageenan through increasing the polymer adhesion to the aluminum surface in 2 M HCl solution was evaluated by using weight loss measurements at temperatures ranging from 25°C to 45°C. The studied amino acids, including Glycine, Alanine, Isoleucine, Serine, and Cysteine, are believed to play an adsorption mediating role to reach a coherent protection layer on the metal surface. The obtained weight loss data are used to calculate the activation parameters of the transition state formation (Ea, ΔHact0, and ΔSact0) to explain the mechanism of inhibition. A thermodynamic insight into the adsorption phenomenon of the inhibitor on the aluminum surface in the presence and absence of amino acids is provided by calculating the standard Gibbs free energy (ΔGads0), enthalpy (ΔHads0), and entropy (ΔSads0) of the adsorption process. The results show a significant enhancement in the inhibition efficiency of i-carrageenan in the presence of amino acids. The obtained ΔGads0 values are negative and become more negative with the addition of amino acid to the medium. This indicates that the inhibitor adsorption on the metal surface has a spontaneous nature, and this spontaneity increases in the presence of amino acids. It is also found that the adsorption process of i-carrageenan in the presence of amino acids is driven by a change in entropy, whereas it is controlled by changes in both enthalpy and entropy in the absence of amino acids.

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