Rational design of a novel multi-functional carbon-based nano-carrier based on multi-walled-CNT-oxide/polydopamine/chitosan for epoxy composite with robust pH-sensitive active anti-corrosion properties

A novel nano-carrier was designed by modifying the MWCNT surface by mussel-inspired polydopamine (PDA), chitosan (CH), and zinc cations. The results of the Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman, field emission scanning electron microscope (FE-SEM), energy dispersive X-ray analysis (EDX), and ultraviolet–visible (UV–vis) spectroscopy affirm the favored adsorption of the PDA, CH, and Zn (II) on the oxidized-MWCNT (OMWCNT) surface. The interactions of PDA, CH, and OMWCNT were theoretically evaluated by density functional theory (DFT-D) methodology. The dual active-barrier potency of the nanocomposites was evaluated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDS), and salt spray assessments. The remarkable enhancement of the total resistance (Rt) of the scratched epoxy coatings after introducing the OMWCNT-PDA-CH-Zn nanostructures (up to 3.6 times) indicates the simultaneous controlled release of the PDA, CH, and Zn(II) from the OMWCNT framework at the damaged area and their active corrosion protection (ACP) ability. The formation of a protective layer of the released inhibitors within the scratched zone was confirmed by FE-SEM/EDX analysis. The inclusion of OMWCNT-PDA-CH-Zn nanocomposite into the epoxy coating endowed the outstanding barrier capability and provided stable corrosion retardation for almost 9 weeks.