Corrosion inhibition, adsorption behaviour, and thermodynamic studies of red dragon fruit (Selenicereus costaricensis) waste peel extracts on mild steel in acidic environment

Abstract

Metal corrosion is brought about by the oxidation of atoms on the surface resulting in irreversible damage to structures at staggering costs. Hence, the search for efficient and cost-effective corrosion inhibitors is relevant. In this study, the ethanolic extract of Red Dragon Fruit (Selenicereus costaricensis) waste peels (RDF) has been tested for its anti-corrosion property using the weight loss method at different temperatures (303-343 K). The calculated inhibition efficiency of 2% RDF is 97%. Thermodynamic studies reveal that increasing inhibitor concentration raises the activation parameters of mild steel in acidic media such as activation energy (E_a) and changes in enthalpy (DH^o) and entropy (DS^o). Moreover, increased immersion time, inhibitor concentration, and temperature led to increased inhibition efficiency. The spontaneous process (DG^o_ads = -23.47 kJ/mol) of adsorption of RDF on mild steel surfaces obeys the Langmuir isotherm model. Lastly, optical microscopy of the inhibited and uninhibited systems confirms the potential of the RDF against pitting corrosion.