Epoxy coating reinforced with graphene-PANI nanocomposites for enhancement of corrosion-resistance performance of mild steel in saline water

Protective coatings enriched with different types of chemical additives, functional fillers, and nanostructured materials are gaining immense interest to minimize corrosion. Present work demonstrates the synthesis of chemically functionalized reduced graphene oxide (rmGO) and emeraldine salt form of polyaniline (PANI-ES)-based rmGO-PANI-ES nanocomposites as protective functional fillers for epoxy coating to inhibit mild steel corrosion. The oxidative polymerization of aniline into PANI-ES is initiated on nitrogen-rich active sites of rmGO and it propagates along the basal plane of rmGO, eventually enwrapped the graphene sheets by interfacially grown PANI-ES. The synthesis of rmGO-PANI-ES nanocomposites and their chemical, morphological, crystalline, and structural characteristics are examined by the FTIR, 13C NMR, XPS, XRD, Raman, SEM, and HRTEM analyses. The multiple interactions between the highly polar nitrogen-rich rmGO-PANI-ES nanocomposites and the epoxy matrix strengthened the coating and increased the hardness and elastic modulus. The corrosion inhibition performance of epoxy coating enriched with the rmGO-PANI-ES nanocomposites is probed by electrochemical impedance spectroscopic (EIS) and salt spray tests using an accelerated corrosive environment (3.5 wt% NaCl). The rmGO-PANI-ES-15 nanocomposite having 0.15 wt% rGO in epoxy coating showed superior corrosion inhibition performance. The total electrochemical impedance of epoxy coating (8.7 ×103 Ω.cm2) increased to 4.7 ×1015 Ω.cm2 after incorporating 1 wt% rmGO-PANI-ES-15 nanocomposite. The enhancement of electrochemical impedance by ~12 orders of magnitude demonstrates the effectiveness of the rmGO-PANI-ES nanocomposites for corrosion mitigation in a harsh corrosive environment. The high surface area and remarkable structural barrier of the 2D chemically functionalized graphene furnished excellent protective coverage. The PANI-ES of rmGO-PANI-ES nanocomposites formed a passive layer of fully reduced leucoemeraldine base of PANI (PANI-LEB) on the coating-mild steel interface by accepting the electrons, generated during the anodic oxidation of iron. These events collectively increase the impedance by multifolds and inhibit steel corrosion. The present findings revealed that graphene-enriched conductive polymeric nanocomposites-based coatings can be promising solution to mitigate corrosion of metal-based installations in a marine environment.