BIOSURFACTIN AS A BASIS FOR “GREEN” INHIBITORS AND MATERIALS TO ENHANCE THE CORROSION RESISTANCE OF METALS

Abstract

Metal corrosion is a major challenge in modern industry, leading to significant economic losses and reduced equipment reliability. Conventional chemical corrosion inhibitors are often toxic and poorly biodegradable, prompting the search for environmentally friendly alternatives based on natural or biotechnologically derived compounds. Biosurfactants — microbial surface-active agents — have gained attention due to their ability to form protective adsorbed layers on metal surfaces and modulate electrochemical corrosion kinetics. Among these, surfactin, a cyclic lipopeptide produced by Bacillus subtilis, combines a hydrophobic hydrocarbon chain with a hydrophilic peptide moiety, providing high surface activity and stable metal passivation.

Current classifications distinguish two generations of biosurfactants: first-generation bio-based chemically synthesized surfactants from plant or animal feedstocks, and second-generation microbiologically synthesized compounds, including surfactin and its derivatives, which exhibit high biodegradability, low toxicity, and notable biological activity. Literature data highlight surfactin’s potential as a “green” corrosion inhibitor and underscore the need for further studies in neutral aqueous environments.

The inhibitory effect of surfactin was assessed in neutral aqueous-salt solutions, specifically in model solution No. 5 (NaCl – 82.0 mg/dm³, Na₂SO₄ – 74.0 mg/dm³, NaHCO₃ – 80.0 mg/dm³, Ca(NO₃)₂ – 82.0 mg/dm³) and in 3% NaCl. In both media, surfactin effectively suppresses anodic and cathodic components of corrosion. The adsorbed film formed on steel surfaces markedly reduces the limiting diffusion current density, restricting oxygen access and enabling cathodic–anodic corrosion inhibition. These findings support surfactin as an eco-friendly alternative to conventional inhibitors and motivate further investigations into its protective mechanisms across diverse aqueous environments.