Regulating the Helmholtz Plane by Biomass Carbon Quantum Dots for Effective Corrosion Control of Mild Steel

As ecological issues intensify, the use of conventional corrosion inhibitors fails to satisfy developmental demands, prompting researchers to focus on economically viable and environmentally benign alternatives. In this work, an environmentally sustainable biomass carbon quantum dots (BCQDs) corrosion inhibitor was synthesized through a hydrothermal method, utilizing passion fruit peel (PFP) as the primary raw material. Electrochemical analysis, weight loss experiments, and other surface characterization techniques were conducted to investigate the corrosion inhibition properties of BCQDs for Q235 steel in 1 M HCl. The dates of electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) curves, and weight loss experiments indicate that BCQDs can provide an excellent corrosion inhibition effect under acidic conditions. Specifically, the addition of 80 mg/L BCQDs may provide a corrosion inhibition effectiveness of 90%. The linear fitting of the Langmuir adsorption model confirmed the efficacy of BCQDs as mixed-type corrosion inhibitors on steel surfaces. The analysis of the surface morphology of Q235 steel using scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurement (CAM) revealed that BCQDs create a protective film through adsorption, which helps to reduce metal corrosion. Additionally, findings from X-ray photoelectron spectroscopy (XPS), attenuated total reflection–Fourier transform infrared spectroscopy (ATR–FTIR), Raman spectroscopy, and time-of-flight–secondary ion mass spectrometry (TOF–SIMS) further confirm the interaction between the functional groups on the BCQD molecules and the steel surface. This study provides a theoretical foundation for the development of biomass environmentally friendly corrosion inhibitors and the metal pickling industry.