Ultrahigh aniline-removal capacity of hierarchically structured layered manganese oxides: trapping aniline between interlayers

Abstract

A significant improvement in adsorption capacity and selectivity for pollutants from wastewater over adsorbents is intrinsically limited by the disordered intra-granule pores of traditional adsorbents. Herein, we propose an unprecedented strategy of trapping pollutants between the interlayers of inorganic layered materials for the high-capacity and highly selective treatment of wastewater, utilizing the interlayer gaps of layered materials containing ordered two-dimensional (2D) nanoscaled channels for intra-lattice trapping of foreign species with sizes smaller than the interlayer gaps. Using such a trapping-between-interlayers mechanism, the layered matrixes can function as “sponges”, absorbing pollutants by transforming the surface-adsorption of traditional adsorbents into bulk absorption. As a proof of concept, the trapping of toxic aniline with a diameter of 0.58 nm from alkaline aqueous solutions between interlayers of K⁺-preintercalated layered manganese oxides (δ-MnO₂ or birnessite) with an interlayer gap of 0.73 nm via a K⁺/aniline exchange process is verified and rationalized by both experiments and density functional theory (DFT) simulations. An equilibrium aniline-removal capacity as high as 940.2 mg g⁻¹ is therefore achieved over hierarchically structured Mn₃O₄@δ-MnO₂, one order of magnitude higher than that of traditional adsorbents. The proposed and verified strategy on trapping pollutants between the interlayers of inorganic layered materials opens a new avenue towards the high-capacity and highly selective treatment of wastewater.