Polarity-resolved fractions of eucalyptus-derived pyroligneous liquid for corrosion inhibition of AISI 1045 steel

Using inhibitors derived from renewable feedstocks to mitigate carbon-steel corrosion in acidic environments remains challenging, particularly when high inhibition must be sustained at elevated temperatures. Pyroligneous liquid (PL), a complex biomass-derived byproduct, has recently emerged as a promising green inhibitor. However, its intrinsic compositional heterogeneity leads to overlapping electrochemical responses arising from the simultaneous adsorption of multiple species, preventing the isolation of individual contributions to charge-transfer processes. In this work, we address this limitation by applying a polarity-guided liquid-liquid extraction (LLE) strategy to pyroligneous liquid derived from Eucalyptus spp. , in order to separate the crude biomass-derived mixture into chemically distinct fractions. Chloroform and n -hexane were used as extraction solvents to obtain fractions with different compositional profiles, which were then evaluated as corrosion inhibitors for AISI 1045 carbon steel in 1.0 M HCl (100-600 ppm). Electrochemical impedance spectroscopy (100 kHz-0.01 Hz) was performed at 298-338 K after 1.5 h stabilization, complemented by potentiodynamic polarization, gravimetric analysis, and FTIR-ATR characterization. The chloroform fraction exhibited superior inhibition efficiency (96.32% at 400 ppm), with a marked increase in polarization resistance, a significant decrease in double-layer capacitance, and adsorption behavior consistent with Langmuir fitting, indicating the formation of a more compact and effective interfacial barrier. These findings show that polarity-selective fractionation can turn complex biomass-derived liquids into experimentally tunable platforms for probing and engineering interfacial electrochemical protection.