Surface Interaction and Corrosion Inhibition of Mild Steel in Hydrochloric Acid Using Pyoverdine, an Eco-Friendly Bio-molecule

Pyoverdine, an yellowish-green, water-soluble fluorescent siderophore, was predominantly produced by the species of Pseudomonas, P. aeruginosa , is used as a corrosion inhibitor for mild steel in 0.5 M HCl, and its efficiency was studied by gravimetric method, electrochemical impedance spectroscopy and polarization techniques at temperatures of 303, 308 and 313 K. Pyoverdine being a strong iron chelator shows excellent inhibition efficiency at all these temperature regions. The adsorption of pyoverdine on mild steel surface increases the charge transfer resistance and activation energy of metal corrosion. 97.55 % of protection efficiency was reported for 10 ppm inhibitor at 303 K; the bacterial biofilm can protect the metal even at 308 and 313 K, and efficiency reduced to only 73 and 68 %. Pyoverdine inhibited both anodic and cathodic reactions and hence worked as a mixed type inhibitor. The results of electrochemical studies also support this observation. The surface morphology of mild steel was examined with scanning electron microscopy and atomic force microscopy. The inhibitor got adsorbed on the metal surface, and the process of adsorption follows Langmuir and Temkin isotherms.