Chelation-Mediated Aqueous Synthesis of Metal Oxyhydroxide and Oxide Nanostructures: Combination of Ligand-Controlled Oxidation and Ligand-Cooperative Morphogenesis

Graphical Abstract

Nanosheets and nanoflakes of FeOOH or Na_xMnO₂ and CoOOH, respectively (see picture), were generated from the corresponding divalent metal salts and ethylenediaminetetraacetate (L) by a one-pot synthesis in alkaline aqueous solution under ambient conditions. The chelating agent L controlled both the reaction, by inhibiting precipitation of M^II(OH)₂ and mediating oxidation to M^III by dissolved oxygen, and the morphogenesis to M^IIIOOH or M^III/IVO₂ nanostructures (see reaction scheme).

Abstract

We have synthesized nanostructures of iron and cobalt oxyhydroxides and manganese oxides in aqueous solution containing a chelating agent. Nanosheets of FeOOH and Na_xMnO₂ and nanoflakes of CoOOH were generated from the corresponding divalent metal salts and ethylenediaminetetraacetate (EDTA) by one-pot synthesis under ambient conditions. The chelating agent fulfilled multiple roles in the reaction process and morphogenesis leading to two-dimensional nanostructures. Coordination to the divalent metal ions inhibited rapid precipitation of metal hydroxides and mediated oxidation to tri- and tetravalent species by dissolved oxygen. Along with the deposition, the two-dimensional and single-crystal nanostructures were also associated with interactions of the chelating agent. Therefore, this approach can be regarded as a combination of ligand-controlled oxidation and ligand-cooperative morphogenesis. Parallel control of the reaction and the morphology was achieved by a simple approach. The model cases suggest that tailoring chelation can facilitate the design of other metal oxide nanomaterials.