Covalent organic framework (COF)-enhanced carbon hollow sphere (CS): a novel nano-porous material for robust epoxy composite coating intelligent corrosion protection

In this research, carbon hollow spheres (CSs) were synthesized by carbonizing polysaccharide shells deposited on silica spheres as hard templates to obtain graphenic carbon shells. Melamine-based covalent organic framework (COF) 3D nanostructures (NSs) were synthesized onto the surface of CSs to enhance their compatibility with the epoxy matrix and their capacity for encapsulating zinc cations and green L-glutamate (ZG) as corrosion inhibitors. Corrosion protection studies of the CS@ZG-COF extract showed an increase in the total impedance of immersed steel from 2298.5 to 14,502.2 Ω cm2 after 24 h, compared to the control solution. The potentiodynamic polarization (PP) test revealed an inhibition efficiency of 82.43% for the CS@ZG-COF extract. The EP/CS@ZG-COF coating demonstrated exceptional self-healing ability, corrosion protection, and barrier properties, forming a robust and uniform protective layer due to the release of encapsulated ZG complexes, which enhanced its electrochemical performance compared to other tested coatings. Furthermore, the incorporation of CS@ZG-COF NSs increased both dry and wet adhesion strength of the epoxy coatings, while the cathodic delamination radius was reduced from 7.6 to 4.4 mm in their presence.