Abstract: Biological carbon dots as pickling inhibitors offer renewability, environmental compatibility, and abundant surface-active groups, facilitating the synergy between efficient inhibition and green sustainability. Macadamia integrifolia shell (MIS) biomass carbon dots (MI-BCDs) containing a graphene structure with an average particle size of 2.4 nm were prepared via hydrothermal method. The -C=C-, -NH₂ and -C=O existed in MI-BCDs were easily reactive sites, which could interact with steel through these active sites in a nearly parallel or tilted configuration. MI-BCDs were adsorbed on steel surfaces through single-molecule adsorption by geometric coverage mechanism to inhibit both cathodic and anodic corrosion reactions. MI-BCDs have negative charges in acid media, but steel surfaces excess positively charged after adsorption of MI-BCDs due to the existence of protonation reaction. The protonation reaction, aggregation effect and chelation reaction with Fe²⁺ of MI-BCDs made them adsorb on steel surfaces under physisorption and chemisorption. The maximum inhibition efficiency of 300 mg L^-1 MI-BCDs at 40 °C was 92.5 %. To the best of our knowledge, this is the first report utilizing MIS to develop N-containing carbon dots for corrosion inhibition, offering an eco-friendly and cost-effective approach.

Key words: Biomass carbon dots, Pickling inhibitor, Macadamia integrifolia shell, Adsorption, Inhibition mechanism