Large scale selective synthesis of α-Co(OH)2 and β-Co(OH)2 nanosheets through a fluoride ions mediated phase transformation process

In this work, α-Co(OH)2 and β-Co(OH)2 nanosheets were selectively synthesized through an epoxide precipitation reaction under mediation of fluoride ions. The protonation and ring opening reaction of propylene oxide promoted the hydrolysis [Co(H2O)6]2+ to form a mixed phase of α-Co(OH)2 and Co2(OH)3Cl in the condition of no existence of fluoride ions. Due to the enhanced hydrolysis of [Co(H2O)6]2+ under function of fluoride ions, pure phases of α-Co(OH)2 and β-Co(OH)2 were formed respectively at different concentration of fluoride ions. The mild reaction condition of this route allows for large scale synthesis of cobalt hydroxide nanosheets, which is only limited by volume of the vessel used as reactor.

► α- and β-Co(OH)2 nanosheets were selectively synthesized through an epoxide precipitation route. ► The phase purity of hydroxides depended on the reactivity of anions in reaction with epoxide. ► The polymorph type of cobalt hydroxide was controlled by concentration mediation of fluoride ions. ► The synthesis was carried out at mild conditions on large scale.