Long-Range and Short-Range Structures of Multimetallic Layered Double Hydroxides

Layered double hydroxides (LDHs) are a family of anionic clays that have wide applications in environmental remediation, catalysis, and nanocomposite materials. These excellent performances heavily depend on the cation arrangements of LDHs, and thus, a thorough understanding of this cation arrangement is of significance to the functional optimization of LDHs. The cation arrangements of LDHs, however, remain obscure because of the small particle size and stacking defects. This study synthesized seven multimetallic layered double hydroxides (LDHs) with a composition of [Me0.66Al0.33(OH)2](CO3, NO3)0.17–0.33·(0.79–1.01)H2O (Me = Co, Ni, and/or Zn) through a coprecipitation method at pH 7.5. Multiple advanced techniques, including pair distribution function, extended X-ray absorption fine structure, wavelet transform analysis, and nuclear magnetic resonance spectroscopy, were employed to characterize the cation arrangement. The results suggest that Co, Ni, and/or Zn are distributed randomly with Al in the seven LDHs, all of which reside in the octahedral site coordinated by six oxygen atoms. The random distribution of Co/Ni/Zn and Al deviates from Pauling's rule, which would require no edge sharing of AlO6 octahedra in LDHs with a ratio of Me2+/Me3+ equal to 2. The cation disorder of the seven LDHs is likely related to the neutral pH used in the synthetic process. This study provides detailed structural information of the seven LDHs at the atomic level, which helps shed light on the future understanding of the structure–function relationship of short-range structural ordering nanomaterials.