Gravimetric study of corrosion inhibition of mild steel in H2SO4 environment using watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) leaf extract as inhibitor

ABSTRACT This work presents gravimetric study of corrosion inhibition of mild steel in H2SO4 environment using watermelon (Citrullus lanatus) leaf extract as inhibitor. The extract was characterized in terms of phytochemical status and functional groups. Its efficiency in the corrosion inhibition was optimized using response surface methodology (RSM). In the RSM, interactive effects of inhibitor concentration, temperature and time on the efficiency of the extract were monitored using central composite design of design expert software. Analysis of the results show that watermelon leaf extract successfully inhibited corrosion of mild steel in H2SO4 environment. Predominant functional groups of watermelon leaf include; C-H stretch (2851.4 cm-1), N-H symmetric and asymmetric stretch (3267.7 cm-1), C=H stretch (2195.4 cm-1), =C-O-C stretch (1241.2 cm-1), C=O symmetric and asymmetric stretch (17722.0 cm-1), C-F (1155.5 cm-1) and =C-H bend (674.0 cm-1). It contains polar atoms of nitrogen and oxygen. Its major phytochemicals are alkaloids (243.14 ±0.03 mg/100g) and tannins (216.32 ±0.02 mg/100g). The extract possesses good inhibitive properties. Weight loss, corrosion rate, inhibition efficiency and degree of surface coverage were influenced by time of immersion of the mild steel, temperature and concentration. The watermelon leaf extract exhibited high inhibition efficiency. Hence, it can be used to inhibit corrosion of mild steel in H2SO4 solution. Quadratic equation reliably connects the inhibition efficiency with the considered factors. Optimum Inhibition efficiency of 92.96% was attained by the watermelon leaf extract.