Novel mechanochemical process for facile and rapid synthesis of a Co–Fe layered double hydroxide

Abstract

This paper presents a novel mechanochemical method for the rapidly and straightforward synthesis of a crystalline cobalt–iron (Co2+–Fe2+–Fe3+) layered double hydroxide (LDH) with intercalated Cl−. In this method, an acidic cobalt chloride solution is ball-milled at room temperature for 6h in a tumbling mill with steel balls. This method does not require any reagent as the iron source or alkali for precipitating the metal hydroxides and adjusting the pH. Furthermore, no heating of the solution is required. The resulting LDH sample appeared as aggregates of slender nanoplatelets with a long lateral length of 100–200nm, showing high crystallinity and purity. The result shows that this method successfully provides a Cl−-form Co–Fe LDH that is almost identical to the one synthesized by conventional methods. A possible mechanism for the mechanochemical synthesis of the LDH is proposed as follows. Iron ions gradually elute from the steel balls during ball-milling. At the same time, electrons are generated, which decompose water molecules, leading to the production of hydroxide ions. This provides automatic pH control and enables the coprecipitation of cobalt and iron as hydroxides, resulting in the formation of Co–Fe LDH crystals.