Inhibition of Aluminium Corrosion in 1.0 M HCl by Caffeine: Experimental and DFT Studies

Aluminium corrosion inhibition in 1.0 M hydrochloric acid solution by caffeine has been studied using mass loss technique and quantum chemical calculations based on DFT. The inhibition efficiency was found to increase with increasing concentration of caffeine but decreases with a rise in temperature. The molecule shows the highest inhibition efficiency of 74% at 10−2 M for T=303 K. The experimental data were used to fit isotherms including Langmuir, Temkin, Freundlich, and El-Awady. The best fits were obtained with the Langmuir model and the kinetic-thermodynamic adsorption model of El-Awady. However, it was found that the adsorption parameters suit well with the isotherm of El-Awady which was chosen as the appropriate isotherm. To distinguish between physisorption and chemisorption, the Dubinin-Radushkevich adsorption model was used. The thermodynamic parameters governing the adsorption of caffeine onto aluminium and that of the metal dissolution were calculated and discussed. DFT study gave further insight into the mechanism of the inhibiting action of caffeine.