Development of pH-Sensitive UiO-66/Polyaniline Nanohybrids with Self-Healing Anticorrosive Performance in Epoxy Coatings

Abstract

The present research focused on the corrosion protection behaviors of epoxy coatings filled with polyaniline (PANI) and its nanohybrid with a Zr-based metal–organic framework (MOF), i.e., UiO-66. Hybrid nanoparticles were synthesized at various weight percentages of UiO-66 in the nanohybrid, including 5, 25, and 50 wt % named H5, H25, and H50, respectively. The morphological features of the nanoparticles characterized with various techniques showed that the nanohybrids with higher UiO-66 content, i.e., H25 and H50, provided a core–shell microstructure with a porous core covered by the PANI outer shell. Analysis of the saline solution (3.5 wt % NaCl) containing the nanoparticles indicated the pH-sensitive release of organic compounds and Zr cations from UiO-66, which could act as active inhibitors against corrosion. The corrosion behavior of the mild steel plate immersed in a saline solution containing the extracts of the nanoparticles, investigated by the Tafel polarization method and electrochemical impedance spectroscopy (EIS), showed that the hybrid nanoparticles played strong active inhibition compared with neat PANI. Among the nanohybrids, H25 exhibited maximum inhibition performance with 56.7% inhibition after 24 h of immersion. Active (self-healing) corrosion behavior of scratched epoxy coatings containing 0.15 wt % nanoparticles was revealed that the epoxy coating with H25 and H50 exhibited 170 and 155% improvement (total resistance (Rt)) at optimal immersion times of 5 and 3 h, respectively. Field emission scanning electron microscopy (FE-SEM) observation of the scratched area after corrosion, confirmed by energy-dispersive X-ray spectroscopy (EDS) analysis, revealed the formation of inhibitor films in those areas, which increased the protectiveness of the coatings.