Enhancing Epoxy Coating Durability on Q235 Carbon Steel via Cu-Doped ZIF-8 Encapsulated Benzotriazole: A Bimetallic MOF with Synergistic Barrier and Active Inhibition

Abstract Aiming at the shortcomings of conventional epoxy coatings such as insufficient barrier property, lack of active protection function and short service life, bimetallic Cu-ZIF-8 nanomaterials with different Cu2+/Zn2+ molar ratios were synthesized via a room-temperature method, and the optimal doping ratio was determined as Cu2+/Zn2+ = 1:3. Cu-ZIF-8@BTA composite filler was further obtained by in situ loading of benzotriazole (BTA) and then introduced into epoxy resin to fabricate pH-responsive anti-corrosion composite coatings. The microstructure, chemical composition and thermal stability were characterized by SEM, EDS, XRD, FTIR, XPS and TGA. The corrosion resistance, long-term stability and interfacial adhesion were systematically evaluated by electrochemical impedance spectroscopy, neutral salt spray test and pull-off adhesion test. Results show that Cu2+ is successfully doped into ZIF-8 framework through isomorphous substitution, and the complete rhombic dodecahedron morphology can be well retained at an appropriate doping content. BTA is uniformly distributed in the pores and on the surface without damaging the main structure. The Cu-ZIF-8@BTA/EP coating exhibits significantly improved physical barrier, interfacial bonding strength and long-term corrosion resistance compared with Neat EP and ZIF-8/EP coatings. It maintains a high impedance modulus after 56 days of immersion in 3.5 wt % NaCl solution and presents notable active corrosion inhibition performance in salt spray test, forming an integrated synergistic protection mechanism of “physical shieldingpH-responsive release behaviormulti-component synergistic corrosion inhibition”. This work provides a strategy for designing and preparing high-performance long-acting pH-responsive anti-corrosion epoxy coatings for Q235 carbon steel in harsh marine and petrochemical environments, as evidenced by 56 day immersion and 21 day salt spray testing.