Effect of Sulfide Ions on the Inhibition Performance and Mechanism of Metal–Organic Frameworks for Copper in Marine Environments

Background: Metal–organic framework (MOF)-based corrosion inhibitors are susceptible to interference from environmental ions in practical applications; however, the underlying failure mechanisms are poorly understood. In particular, the influence of sulfide ions (S2−) on the ability of MOFs to prevent copper corrosion has not been systematically investigated. Methods: Three isostructural MOFs—Zn-zeolitic imidazolate framework (ZIF), Co-ZIF, and Ni-ZIF—were synthesized and applied as copper corrosion inhibitors. Their protective performance was systematically evaluated in sulfide-containing environments using electrochemical techniques. The structural evolution of the MOFs upon sulfide exposure was characterized to elucidate the mechanism of inhibition failure. Results: All three materials efficiently inhibited corrosion at a sulfide ion concentration of 50 mg/L, with inhibition efficiencies reaching 90.06% (Zn-ZIF), 93.39% (Co-ZIF), and 89.31% (Ni-ZIF). However, when the sodium sulfide nonahydrate (Na2S·9H2O) concentration was increased to 10 mg/L, the inhibition efficiencies dropped to 15.54%, 18.11%, and 4.00%, respectively. Mechanistic analysis uncovered a novel failure pathway, namely competitive coordination between sulfide ions and MOF metal centers, which induces structural collapse of the framework and consequently destroys the protective film previously formed on the copper surface. Conclusions: This study reveals a quantitative relationship between sulfide ion concentration and the performance of MOF-based corrosion inhibitors, defines the applicability boundaries of MOF-based inhibitors under complex sulfur-containing service conditions, and provides critical practical guidance for the deployment of such inhibitors while elucidating a fundamental failure mechanism driven by competitive coordination.