Natural
halloysite nanotubes (HNTs) have attracted great interest
as smart nanocontainers of corrosion inhibitors. The adsorption behavior
of corrosion inhibitors on HNTs will affect their loading capacity,
a crucial property of smart nanocontainers. This work modified the
surface of HNTs by preadsorbing metal cations (M2+: Fe2+, Zn2+, or Cu2+) to improve the adsorption
of benzotriazole (BTA) on HNTs. The results based on the thermal gravimetric
analysis showed that the loading capacities of BTA in Fe2+-, Zn2+-, and Cu2+-adsorbed HNTs were 8.25,
8.39, and 9.74 wt %, respectively, which are significantly higher
than those in pristine HNTs of 4.57 wt %. Furthermore, density functional
theory calculations exhibited that the adsorption energies of BTA
on the M2+-adsorbed surfaces increased compared to that
on the clean surface. Notably, the increasing trend of adsorption
energies is in good agreement with that of measured loading capacities.
Moreover, the presence of metal cations significantly enhances the
charge transfer between BTA and the surface. The density of states
analysis indicated that the adsorbed metal cations shifted the valence
bands of the surface close to the Fermi level, thereby enhancing the
coupling between the occupied bands of HNTs and the unoccupied orbitals
of BTA.