Elaboration of lamellar and nanostructured materials based on manganese: efficient adsorbents for removing heavy metals

Abstract

The lamellar and nanostructured manganese oxide materials were chemically synthesized by soft and non-toxic methods. The materials showed a monophasic character, symptomatic morphologies, as well as the predominance of a mesoporous structure. The removal of heavy metals Cd(II) and Pb(II) by the synthesized materials Na-MnO2, Urchin-MnO2 and Cocoon-MnO2 according to the mineral structure and nature of the sites were also studied. Kinetically, the lamellar manganese oxide material Na-MnO2 was the most efficient of the three materials which had more vacancies in the MnO6 layers as well as in the space between the layers. The nanomaterials Urchin-MnO2 and Cocoon-MnO2 could exchange with the metal cations in their tunnels and cavities, respectively. The maximum adsorbed quantities followed the order (Pb(II): Na-MnO2 (297 mg/g)>Urchin-MnO2 (264 mg/g)>Cocoon-MnO2 (209 mg/g), Cd(II): Na-MnO2 (199 mg/g)>Urchin-MnO2 (191 mg/g)>Cocoon-MnO2 (172 mg/g)). Na-MnO2 material exhibited the best stability among the different structures, Na-MnO2 presented a very low amount of the manganese released. The results obtained showed the potential of lamellar manganese oxides (Na-MnO2) and nanostructures (Urchin-MnO2 and Cocoon-MnO2) as selective, economical, and stable materials for the removal of toxic metals in an aqueous medium.