Sustainable carbon quantum dots-chitosan hydrogel composite for corrosion protection of mild steel in 1 M sulfuric acid.

Chitosan, a biodegradable and non-toxic biopolymer, has shown promising potential in corrosion inhibition applications. Traditional corrosion inhibitors for mild steel often rely on toxic and expensive organic or inorganic compounds, prompting a shift toward eco-friendly alternatives. In this study, we developed a green corrosion inhibitor based on a chitosan-carbon quantum dot (CQD) hydrogel, leveraging the excellent optical properties and functionalization potential of biomass-derived CQDs. It was found that the hydrogel effectively inhibited mild steel corrosion in 1 M H₂SO₄ when tested using weight loss analysis, potentiodynamic polarization, and electrochemical impedance spectroscopy. At an optimum concentration of 40 ppm, the hydrogel achieved a highest inhibition efficiency of 89.22 % (EIS), 83.63 % (PDP), and 82.60 % (weight loss), indicating strong surface protection. However, at 35 °C, the efficiency decreased to 77.20 % (weight loss), indicating a reduction in performance with rising temperature. Surface characterisation using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), verified the existence of the protection film on the mild steel surface, elucidating the inhibition mechanism. This study demonstrates the potential of CQD-chitosan hydrogel as a cost-effective and environmentally benign corrosion inhibitor.