Polymeric smart coatings containing modified capped halloysite nanotubes for corrosion protection of carbon steel

Abstract

A newly designed smart self-healing epoxy coating system comprised of modified halloysite nanotubes (HNTs) having capping is proposed for corrosion protection of steel. In the first step, HNTs were loaded with 8-hydroxyquinoline (8HQ), used as a corrosion inhibitor. Then the HNTs were sealed/capped using cobalt (II), aiming for an efficient and controlled release of the loaded inhibitor. The smart coatings were developed by reinforcing loaded HNTs into the epoxy matrix. The structural, thermal, mechanical, and electrochemical properties of capped modified HNTs and smart coatings were studied using various techniques. UV–Vis analysis depicted that the capping of the metal-inhibitor complex was decomposed at acidic pH resulting in a controlled release of the loaded inhibitor into HNTs. Electrochemical impedance spectroscopic (EIS) analysis of blank and smart coatings demonstrated that the low-frequency impedance modulus of smart coatings is 109 Ω.cm2 for 20 days compared to blank coatings (105 Ω.cm2), reflecting their excellent corrosion inhibition performance. The superior corrosion protection properties of these smart coatings can be ascribed to the controlled and efficient release of the loaded inhibitor from the capped HNTs. Finally, X-ray photoelectron spectroscopy (XPS) analysis of the steel substrate after the corrosion analysis revealed the adsorption of 8HQ on the steel surface, confirming the formation of iron complex due to the release of loaded inhibitor. This work demonstrated the adeptness of 8HQ in mitigating the corrosion due to the controlled and effective release of the inhibitor from capped HNTs because of dissociation of the metal-inhibitor complex (Co-8HQ).