A new approach for design and synthesis of Co-II and Co-II,Co-III hydroxide materials

A synthetic investigation on the formation of cobalt hydroxides has been ca rried out under low pH and atmosphere-controlled conditions. It was found t hat various phases and compositions of cobalt hydroxides can be tailor-prep ared via a careful control of preparative parameters such as the initial co ncentration ratio of [OH-]/[Co2+], preparative atmosphere and aging time. T hrough elemental and structural determinations, the formation sequence of a major cobalt hydroxide in air has been shown as: turbostratic Co-II hydrox ide, Co-II hydrotalcite-like phase, Co-II,Co-III hydrotalcite-like phase an d Co-II brucite-like phase. It is indicated that the oxidation of divalent cobalt in Co-II brucite-like phase becomes more difficult when the hydroxid e is synthesized with a higher [OH-]/[Co2+] ratio. Defective crystallites a nd large interlayer spacing are attributed to be the two major factors cont ributing to the oxidation of divalent cobalt. In contrast to the samples pr epared in air, the Co-II brucite-like phase is readily formed under a nitro gen atmosphere even at a low [OH-]/[Co2+] ratio. Thermal decomposition of p repared hydroxides has also been conducted, which confirms the findings rev ealed by the synthetic experiments and compositional and structural analyse s. (C) 2000 Elsevier Science Ltd. All rights reserved.