A shield and a signal: Smart polymeric coatings reinforced with zinc-imidazole carboxylate framework for dual corrosion inhibition and corrosion sensing

Abstract

Polymeric coatings are widely employed for the corrosion protection of metallic substrates due to their effective barrier properties; however, they are vulnerable to undetected defects that enable electrolyte ingress and initiate localized corrosion. In this study, we report on the synthesis and development of a multifunctional, smart epoxy-based coating system capable of simultaneously sensing and inhibiting corrosion. The system incorporates a synthesized zinc–imidazole carboxylate framework type MOF (ZIF) carrier, loaded with 2-mercaptobenzimidazole (2MBI) as a corrosion inhibitor and bis-coumarinyl sulfone (bCS) as a fluorescent corrosion sensing agent. The pH-responsive behavior of ZIF ensures the release of 2MBI and bCS upon exposure to 3.5 wt% NaCl solution. Furthermore, density Functional Theory (DFT) analysis of 2MBI and bCS provided molecular-level insights into their electronic properties and active binding sites, supporting their role as effective corrosion inhibitors and fluorescent sensors. The fluorescence spectroscopy results revealed fluorescence enhancement under UV light, due to metal-induced fluorescence enhancement (MEF). Modified epoxy coatings were evaluated for their physicochemical and electrochemical performance. The epoxy coating reinforced with modified ZIF demonstrated enhanced surface hydrophobicity (contact angle of 98.3°) and strong interfacial adhesion (3.59 MPa). Electrochemical impedance spectroscopy (EIS) measurements in 3.5 wt% NaCl solution revealed that modified ZIF coatings exhibited superior long-term barrier properties and corrosion resistance (51.90 GΩ.cm2) compared to blank epoxy coatings (0.03 GΩ.cm2), attributed to the synergistic effect of passive barrier enhancement and active inhibitor release. Additionally, the salt spray immersion test confirmed the coating's ability to visually detect corrosion initiation, offering a reliable means of early failure diagnosis. Thus, extending the service life of metal infrastructures through integrated sensing and inhibition functionalities.