PMMA-Silica Nanocomposite Coatings Modified by Functionalized Carbon Dots for Corrosion Protection of Aluminum Alloys

The demand for ecological and efficient anticorrosive coatings for metallic components is the focus of present research. Composite materials containing carbon nanostructures, such as carbon quantum dots (CDs), have received special attention as corrosion inhibitors in this field. This is due to the possibility of tuning the surface properties of CDs by functional groups, with emphasis on the use of nitrogen and sulfur (N-CDs and N,S-CDs) capable of providing inhibitory and self-healing functionality. In this study, coatings with active properties were developed by incorporating N-CDs and N,S-CDs into poly(methyl-methacrylate) (PMMA)-silica nanocomposite. The CDs were synthesized by the hydrothermal method involving the pyrolysis of citric acid and functionalized with urea and thiourea to obtain N-CDs and N, S-CDs, respectively. The PMMA-silica hybrids were prepared by combining polymerization reactions and the sol–gel process and deposited by immersion as a few μm-thick coatings onto the AA7075 alloy. Among the structural, morphological, and mechanical characterization techniques used in different stages of the study, atomic force and transmission electron microscopies, infrared, UV–visible, photoluminescence, and X-ray photoelectron spectroscopies were employed, in addition to adhesion and contact angle measurements. The structural and morphological results were correlated with the anticorrosive performance of the coatings investigated by electrochemical impedance spectroscopy in 3.5% NaCl solution and salt spray tests. The results demonstrate that the N-CDs, N,S-CDs impart long-term protection and self-healing ability to the PMMA-silica coatings through complex coordination reactions of amine, thiocarbonyl, and carboxyl groups, evidenced after corrosive and mechanical failure in saline environments. The combination of passive and active protection results in high-performance and environmentally friendly nanocomposite coatings for anticorrosion protection of aerospace components.