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

Abstract

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 UIO-SP.Zn solution, achieving a total resistance of 10,350 Ω.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 pull-off 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.