Experimental and quantum chemical studies on ethanol extract of Phyllanthus amarus (EEPA) as a green corrosion inhibitor for aluminium in 1 M HCl

Ethanol extract of Phyllanthus amarus (EEPA) is investigated as a possible green corrosion inhibitor for aluminium in solution of HCl. Weight loss, linear and potentiodynamic polarization methods were used to evaluate the inhibition efficiencies of various concentrations of the plant extract. Scanning electron microscopy and Fourier transformed infra red spectroscopy were used to study the surface morphology and engagement of functional groups in the inhibition process. The results obtained at 303 K from weight loss, linear polarization resistance and potentiodynamic polarization methods recorded inhibition efficiencies that ranged from 56.65 to 69.17, 65.00 to 93.93 and from 51.38 to 79.96 % respectively. Generally, inhibition efficiency decreases with increase in concentration but increased with a rise in temperature. Potentiodynamic study, reveals that EEPA acted as a mixed type inhibitor and formed a protective film, which protected the metal against corrosion. Examination of micrographs in the presence and absence of the inhibitor, indicated the formation of a protective film that blocks the active corrosion sites on the surface of the metal. Also, analysis of spectra obtained from Fourier transformed infra red study indicated that EEPA was adsorbed unto the surface of aluminium via C=O and OH functional groups. The adsorption of the inhibitor was spontaneous, exothermic and supported the mechanism of physical adsorption. Calculated quantum chemical parameters for the chemical constituents of EEPA revealed that phyllanthusin D is the most active corrosion inhibitor in the compound. The HOMO and LUMO diagrams of Phyllanthusin D supported the findings from FTIR analysis.