Polyaniline-wrapped nitrogen-doped graphene nanocomposites as protective functional fillers in epoxy coatings for remarkable enhancement of corrosion inhibition performance

Corrosion, a major concern in many industries, is primarily accountable for high maintenance costs, material degradation, frequent repair/replacement, and poor lifespan of structural installations. Eventually, corrosion can lead to a high risk of catastrophic equipment failures and environmental threats such as leakage from pipelines and chemical containers. Protective coatings enriched with nanostructured fillers that impart enhancement of corrosion inhibition properties are gaining immense interest. In the present work, nanocomposites comprising N-doped graphene (NGr) wrapped by emeraldine salt form of polyaniline (PANI-ES) are developed as highly effective protective functional fillers to epoxy coatings for mild steel corrosion inhibition. The NGr-PANI-ES nanocomposites furnished excellent structural strengthening to epoxy coatings and are able to impede the penetration of corrodents to a significant extent. The corrosion inhibition performance of the NGr-PANI-ES nanocomposites-based epoxy coatings is evaluated by electrochemical impedance spectroscopy and salt spray tests. The nitrogen incorporation into graphene skeleton introduced ample electron-rich nitrogen-based functionalities as revealed by XPS analysis, which synergistically amplified corrosion inhibition performance with PANI-ES. The NGr-PANI-ES nanocomposites in epoxy coatings enhanced the total impedance in a highly aggressive corrosive electrolyte (3.5 % NaCl) by a magnitude of 12 orders, corroborating with excellent corrosion inhibition performance results based on salt spray tests. The improved corrosion inhibition properties are collectively attributed to the structural barrier by 2D N-doped graphene, compatibility of NGr-PANI-ES nanocomposites with epoxy matrix to strengthen the coatings, and the synergistic inhibition of the anodic reactions by PANI-ES and N-doped graphene that underpin the corrosive events.