Broad spectrum corrosion inhibition: corrosion and microbial (SRB) growth inhibiting effects of Piper guineense extract

To assess the prospect of exploiting biomass extracts for the simultaneous control of chemical- and microbial-influenced corrosion, we herein describe experimental and computational studies to probe the corrosion inhibition and biocidal efficacy of aqueous extracts of Piper guineense (PG). Proximate phytochemical analysis of PG revealed the presence of alkaloids (3.1%), tannins (0.9%) and saponins (11.0%). The corrosion-inhibiting effect of the extract was appraised on low-carbon steel corrosion in 1-M HCl and 0.5-M H₂SO₄ using gravimetric and electrochemical techniques, whereas the agar disc diffusion method was employed to determine the biocidal effect of the extract on the corrosion-associated sulfate-reducing bacteria (SRB), Desulfotomaculum species. PG was found to be an excellent inhibitor for both corrosion and SRB growth. Both effects are attributed to the phytochemical constituents present in the extract. The corrosion process was inhibited by adsorption of the extract organic matter on the steel surface, whereas the antimicrobial effect results from disruption of the growth and essential metabolic functions of the SRB. We have relied on quantum chemical computations and molecular dynamics simulations to highlight the individual contributions of some extract constituents to the observed corrosion-inhibiting effect.