Accurate clarification on assembling and protective mechanisms of β-cyclodextrin/benzothiazole complex for copper in marine environment

Molecular assembly based on cyclodextrins can realize the aqueous utilization of inherently-insoluble corrosion inhibitors for metals; however, the associated protection mechanism is not yet fully understood. Herein, hydrophobic benzothiazole (BT) was assembled with beta-cyclodextrin (beta-CD) forming the complex (CD-BT) for protecting copper in the simulated seawater (SSW). Supramolecular complexing was optimized through response surface methodology, and the host-guest interaction was confirmed by spectral, thermal and morphological examinations besides the disclosed assembling thermodynamics. Electrochemical and surface analyses indicated that CD-BT effectively suppressed copper dissolution in SSW yielding a maximum inhibition efficiency of 97.0%. Density functional theory (DFT) calculations were deployed to clarify the accurate complexing behavior of BT inward beta-CD's cavity. Benefitting from the favorable incorporating configuration of BT and its overwhelming adsorption energy over the assembling counterpart, CD-BT underwent an incubation-guest release-adsorption process at the copper/SSW interface. Adsorption of released BT molecules and its chelation ability towards cuprous/cupric species accounted for the efficient protection of copper in SSW.