Industrial-scale potential valorization of ecotoxicity-free botanical residues: Uncaria laevigata as a high-efficiency corrosion inhibitor for X80 pipeline steel in acid pickling

Abstract

X80 pipeline steel easily corrodes during acid pickling. However, existing corrosion inhibitors exhibit uncertain toxicity and limited industrialization potential, and few corrosion inhibitors have been specifically designed for X80 pipeline steel. Building on previous studies, this study innovatively proposed Uncaria laevigata extract (ULE) as a potential corrosion inhibitor to address these drawbacks. The main active components of ULE, including alkaloids, flavonoids, and phenolic acids, were identified through spectroscopic characterization. Subsequently, comprehensive evaluation via weight loss and electrochemical tests revealed that ULE exhibited outstanding corrosion inhibition efficiency (>95%) and maintained excellent stability at various temperatures and during prolonged immersion for up to 196 h. Surface measurements (SEM, AFM, XPS, XRD and CA) confirmed that a protective film was generated by ULE on the steel surface, effectively isolating the corrosive medium. The adsorption behavior and corrosion inhibition mechanism of the main molecules from ULE were explained through molecular dynamics simulations and quantum chemical calculations. Importantly, a comprehensive toxicity assessment encompassing acute toxicity, antioxidant enzyme activities, and apoptosis-related gene expression levels was performed. ULE exhibited low acute toxicity (96 h-LC₅₀ = 325.45 mg L⁻¹) and caused no observable elevation in antioxidant-enzyme activities and apoptosis-related gene expression, demonstrating minimal oxidative stress and apoptotic impact and low toxicity for zebrafish. Compared to other plant extracts as well as synthetic and commercial corrosion inhibitors, this study presents ULE as a low cost, high efficiency, environmentally friendly alternative with excellent industrial potential.