Topochemical Synthesis, Anion Exchange, and Exfoliation of Co−Ni Layered Double Hydroxides: A Route to Positively Charged Co−Ni Hydroxide Nanosheets with Tunable Composition

Abstract

This paper describes the topochemical synthesis of Co−Ni layered double hydroxides (LDHs) from brucite-like Co−Ni hydroxides through a novel oxidative intercalation process employing bromine as an oxidizing agent, and their exfoliation into positively charged unilamellar nanosheets in formamide after anion-exchange treatment. In this protocol, hexagonal microplatelets of brucite-like Co−Ni hydroxides in variable composition were prepared by homogeneous precipitation of a mixed solution of divalent cobalt and nickel ions via hexamethylenetetramine hydrolysis. Subsequent treatment of the brucite-like Co−Ni hydroxides with excessive bromine in acetonitrile promoted partial oxidation of Co2+ into Co3+, producing Br−-intercalated Co−Ni LDHs inheriting the hexagonal morphology. This rational topochemical approach was applicable for realizing a pure phase of Co−Ni LDHs with nickel content up to 50% (metal content). Chemical analyses indicated that as-prepared Co−Ni−Br LDHs were unexceptionally characterized by a...