General Insights into Structural Evolution of Layered Double Hydroxide: Underlying Aspects in Topochemical Transformation from Brucite to Layered Double Hydroxide

The topochemical transformation from transition-metal brucite hydroxide (Co1-xFex(OH)(2), Co(OH)(2), Co1-xNix(OH)(2)) to corresponding (Co2+-(Co3+)-Fe3+, Co2+-(Ni2+)-Co3+) LDH under oxidizing halogen agents (iodine, bromine) exhibits different staging phenomena depending on the metallic composition/ratio in starting brucite. A plausible charge hopping mechanism based on valence interchange between redoxable charge center (Fe3+/Co3+) and neighboring divalent sites in the host sheet is proposed to understand the restoration of electron donor sites at the interface between brucite crystallites and halogen agents, which ensures a continual oxidative reaction, and a staged intercalation/diffusion of in situ reduced halide anions into the interlayer gallery commensurate with the host charge propagation. The discussion on the correlation between staging product and metallic composition/ratio offers a general perspective and new insights into M2+/M3+ ratio and cation ordering, host layer charge, and phase evolution in LDH structure.