The mechanistic pathways of extracellular polymeric substances in the inhibition of carbon steel corrosion

This study examined the corrosion inhibition mechanisms of extracellular polymeric substances (EPS) from <i>Lactobacillus reuteri</i>, <i>Pseudomonas fluorescens</i>, and <i>Escherichia coli</i> on carbon steel. Using UV spectrophotometry, LC-MS, infrared spectroscopy, and atomic force microscopy (AFM), it was apparent that all three EPS effectively inhibited corrosion, with optimal concentrations of 300 mg/L for <i>Lactobacillus reuteri</i> and 400 mg/L for the other species, yielding inhibition efficiencies of 28.25%, 23.87%, and 21.72%, respectively. The carboxyl group content was critical, with <i>Lactobacillus reuteri</i> EPS having the highest proportion. Functional group analysis showed it contained 12.39% and 12.93% more carboxyl groups than those from <i>Pseudomonas fluorescens</i> and <i>Escherichia coli</i>. Iron ion adsorption was primarily physical and occurred in a monolayer, with a greater capacity for Fe³⁺ than Fe²⁺, peaking at 600 mg/L.