Green inhibitor loaded functional halloysite nanotubes modified coatings for improving corrosion protection of carbon steel

In this study, halloysite nanotubes (HNTs) were first etched with H2SO4 or NaOH and then loaded with a green corrosion inhibitor (sodium benzoate, SB) under vacuum. Subsequently, a thin layer of tetraethyl orthosilicate (TEOS) was coated for the controlled release of SB. The dispersion of the coated HNTs in epoxy resin was improved by amino functionalization with (3-aminopropyl) triethoxysilane (APTES). The obtained S24HNTs-SB-TEOS-APTES nanocapsules were analyzed by Brunauer-Emmett-Teller (BET), showing that after etching with 5 mol/L of H2SO4 for 24 h, the pore size inside the HNTs increased, and the tubular morphology was maintained. According to the results of UV–visible spectroscopy, SB was released faster in acidic (pH=3) and alkaline conditions (pH=11) than neutral condition. Furthermore, nanocapsules were successfully embedded in epoxy coating used for corrosion protection of carbon steel. The electrochemical impedance spectroscopy (EIS) and salt spray experiments demonstrated that the smart composite coating exhibited outstanding corrosion resistance, and the addition of 3 wt% S24HNTs-SB-TEOS-APTES having the most excellent anticorrosion performance with its impedance at 0.01 Hz maintaining 3.11 × 106 Ω⋅cm2 even after 3 weeks of corrosion immersion.