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The distribution of reactive Ni2+ in 2D Mg2-xNixAl-LDH nanohybrid materials determined by solid state 27Al MAS NMR spectroscopy

Abstract

Layered double hydroxides (LDH), especially (doped) with transition metals, as well as nanohybrid and 2D materials derived from these, are interesting materials due to their catalytic and electrochemical properties. Their reactivity is determined by the atomic level distribution of the transition metal in the LDH cation layer, which is essential to control for design of LDH with optimized properties. However, low crystallinity, absence of long range order, and/or isoelectronic ions often prevents atomic level structural characterization. A series of poorly crystalline Mg2-xNixAl-NO3 LDH were investigated by ultrafast 27Al MAS NMR spectroscopy to determine the distribution of Ni2+ in these as well as possible superstructure and miscibility gaps. Four Ni2Al-LDH interlayer distances ranging from 7.6 to 17.5 Å were prepared to assess the contribution of inter- and intralayer magnetic interactions. The effect of Ni2+ content and the atomic level distribution of Ni2+ were probed by ultrafast 27Al MAS NMR spectroscopy: The Al distribution can be modeled by a binomial distribution and neithter a superstructure was identified for the MgNiAl-LDH sample or a miscibility gap was identified. The 27Al isotropic shift, δiso(27Al) is a very sensitive probe of the number of neighboring Ni2+ in the first metal ion sphere, but to a smaller degree also affected by intercalated anion (interlayer distance). These results were used for detailed characterization a exfoliated (2D)-restacked Mg1.83Ni0.17Al-LDH and a Mg1.83Ni0.17Al-LDH-alginate nanohybrid material, which 27Al MAS NMR showed to maintain its structure and partial dissolution of the LDH, respectively. In contrast, both powder X-ray diffraction and vibrational spectroscopies (IR and Raman) reflected only the overall change in sample composition.

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Publication details

The article was received on 16 Aug 2018, accepted on 10 Sep 2018 and first published on 10 Sep 2018


Article type: Paper
DOI: 10.1039/C8CP05243C
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    The distribution of reactive Ni2+ in 2D Mg2-xNixAl-LDH nanohybrid materials determined by solid state 27Al MAS NMR spectroscopy

    N. D. Jensen, C. Forano, S. S. C. Pushparaj, Y. Nishiyama, B. Bekele and U. G. Nielsen, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP05243C

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