Induced π–complexation properties of smectites impregnated by Ni, Cu and Ag transition metals: The highly efficient styrene uptake

Abstract

Two natural smectite minerals (montmorillonite and beidellite) differing in structural charge location were impregnated with varying amounts of transition metals: Ni(II), Cu(I) or Ag(I). The modification aimed to increase the affinity of the minerals towards styrene vapors. The structure, texture, chemical composition and surface chemistry of the materials were studied by XRD, FTIR, Raman, N2 adsorption/desorption, XRF and XPS. The experiments examined the influence of the starting smectite and the type of introduced metal on styrene adsorption efficiency. The styrene uptake mechanisms were investigated through solid state analysis and supported by DFT calculations. The study demonstrated that the small content of introduced metals (<2% wt.) substantially increased styrene uptake (∼200–350% wt.) surpassing values reported for surfactant-intercalated smectites (∼40–80% wt.) and activated carbons (∼30% wt.). This enhancement was attributed to the π-complexation between dispersed d-block metals and π-electron-rich styrene molecules, subsequently leading to polystyrene formation. The DFT calculations were consistent with experimental findings, indicating a higher affinity of the raw beidellite towards styrene than the raw montmorillonite connected to the charge location. Moreover, the observed trends in calculated adsorption energies and lengths of weak hydrogen bonds allowed to explain a significant adsorption increase observed for the Ni- and Cu-impregnated montmorillonite-based materials.