Clay nanotubes for corrosion inhibitor encapsulation: release control with end stoppers

Halloysite clay tubes of 50 nm diameter and ca. 1000 nm length were analyzed as potential nanocontainers for loading, storage and induced sustained release of chemical agents. Halloysite is a natural aluminosilicate mineral with hollow cylindrical geometry and submicron size. Halloysite nanotubes loaded with the corrosion inhibitor benzotriazole can be admixed into paint to improve its anticorrosion performances as well as the coating tensile strength. Corrosion protection of such coating was evaluated by direct exposure of the coated metal (copper) to highly corrosive media. Loading and release characteristics of benzotriazole from these nanotubes were optimized. Benzotriazole release kinetics correspond to the time needed for the formation of a metal protective layer through copper complexation. For formation of the tube end stoppers, benzotriazole loaded halloysite was exposed to the solution of Cu(II) ions, and kinetics of the stopper complex formation was analyzed. Tunable release of benzotriazole was achieved by controlling the strength of the stopper complexes, and the release time may be varied from ten to hundreds of hours. A possibility for the tube on/off release switch was demonstrated.