Unlocking the potential of a zirconium-based MOF for advanced protective coatings: Delve into the UIO-66 smart release functioning for a bio-based Zn2+complex

In recent years, the incorporation of nanoreservoirs into epoxy coating (EP) formulations has gained significant traction, primarily for their role in delivering self-healing capabilities. This research endeavor is centered around the synthesis and application of a zirconium-based metal-organic framework (MOF) known as UIO-66, specifically designed for the encapsulation of corrosion inhibitors. A novel breakthrough is achieved by simultaneously loading of a green organic inhibitor (Spand extract) and inorganic zinc cations into the highly porous UIO-66, yielding a pioneering bio-based controlled-release nanoreservoir, denoted as UIO-SP.Zn. The UIO-SP.Zn nanoreservoir is characterized through multiple techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller surface area analysis, thermogravimetric analysis, and field emission scanning electron microscopy. The controlled-release and pH-sensitive behavior of the UIO-SP.Zn structure are thoroughly evaluated through inductively coupled plasma and UV-vis spectroscopic analyses at three separate pH levels. Electrochemical impedance spectroscopy results underscore the remarkable enhancement in corrosion protection for steel components exposed to a saline medium (3.5 % NaCl) upon the addition of a 1000 ppm UIOSP.Zn solution, achieving a total resistance of 10,350 Omega.cm2 after a 96 h immersion. The self-healing and active protection of scratched nano-coatings are meticulously examined through electrochemical techniques, revealing that the EP-coated panel incorporating UIO-SP.Zn nanoreservoirs (EP/UIO-SP.Zn) exhibits a substantial impedance (exceeding 60 kohm.cm2) even after prolonged exposure (72 h). Furthermore, the coating's dry pulloff strength registers a notable increase (40.3 %), while delamination is reduced by 50.1 % compared to the unmodified EP coating, signifying the promising adhesion properties of EP/UIO-SP.Zn.