Analytical Evaluation of Corrosion Inhibition Efficiency of Citrus limonum Extract on Zn Metal in 0.1M HNO3

Abstract

The corrosion inhibition potential of Citrus limonum extract for zinc in nitric acid 
(HNO₃) medium was investigated using weight-loss measurements, Fourier 
Transform Infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). 
The inhibition behaviour and corrosion mechanism were evaluated for zinc immersed 
in 0.1 M HNO₃ containing different concentrations of the plant extract over a 
temperature range of 303–333 K. Weight-loss results demonstrated that inhibition 
efficiency (IE) increased with increasing inhibitor concentration but decreased with 
increasing temperature throughout the test period. This temperature-dependent 
behaviour suggests that adsorption of Citrus limonum constituents onto the zinc 
surface occurs predominantly through physisorption. Kinetic and thermodynamic 
analyses revealed that both inhibited and uninhibited corrosion reactions of zinc in 
HNO₃ medium were spontaneous, followed first-order kinetics, were exothermic, and 
proceeded with an increasing degree of order. Analysis of the adsorption behaviour 
showed that the experimental data were best described by the Langmuir adsorption 
isotherm, indicating systematic surface coverage by adsorbed inhibitor species. SEM 
examination further revealed substantial differences between inhibited and 
uninhibited zinc surfaces, confirming that the Citrus limonum extract formed a 
protective covering on the metal surface, thereby reducing direct interaction 
between zinc and the corrosive acidic medium. Complementary FTIR analysis 
identified changes in characteristic functional groups of the extract, suggesting 
that some functional groups participated in bond formation and development of an 
adsorbed interfacial layer between zinc and inhibitor molecules. These findings 
confirm significant interactions between the inhibitor constituents and zinc surface 
and demonstrate the corrosion-protection potential of Citrus limonum in 0.1 M HNO₃.