Abstract: The growing focus on environmental sustainability has spurred significant interest in plant extracts as eco-friendly alternatives to conventional corrosion inhibitors. This study presents a novel approach to enhance the corrosion resistance of cold-rolled steel (CRS) by utilizing a combination of sodium dodecylbenzene sulfonate (SDBS) and Camellia oleifera fruit shell extract (CFSE). The inhibition performance of the CFSE/SDBS complex on CRS in 0.50 M sulfamic acid (SA) solution was evaluated through weight loss methods and electrochemical methods. The results demonstrate an impressive inhibition efficiency of 93.2% with 200 mg L^-1 CFSE and 50 mg L^-1 SDBS at 20 °C, supported by a synergism parameter (S_θ) exceeding 1. CFSE, SDBS, and the CFSE/SDBS complex act as mixed-type inhibitors, primarily influencing the cathodic reaction. Surface analyses conducted using X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS) confirm that the active components in CFSE and SDBS can adsorb onto CRS surfaces, creating a robust protective film. Quantum chemical (QC) calculations identify reactive sites in morin (MR), DL-methionine (DL-Met), and lysine (Lys), highlighting heteroatoms and conjugated double bonds as key contributors. Molecular dynamic (MD) simulations reveal that these compounds form an impermeable film on Fe(001) surfaces, effectively reducing the migration rate of corrosive ions (NH₂SO₃^-, H₃O⁺). This research challenges conventional compounding methods and offers innovative insights into the development of eco-friendly corrosion inhibitors derived from plant extracts.

Key words: Cold rolled steel, Camellia oleifera fruit shell extract, Sodium dodecylbenzene sulfonate, Synergistic effect, Sulfamic acid