Structural Differentiation between Layered Single (Ni) and Double Metal Hydroxides (Ni-Al LDHs) Using Wavelet...

Area of Science:

• Materials Science
• Geochemistry
• Environmental Chemistry

Background:

• Layered double hydroxides (LDHs) are anionic clays with applications in environmental chemistry, geochemistry, and materials science.
• Extended X-ray absorption fine structure (EXAFS) signal processing, particularly wavelet transformation (WT), is used to identify metals in LDHs.
• Previous studies suggest WT plots of LDHs should differ from single metal hydroxides, but direct comparisons are lacking.

Purpose of the Study:

• To systematically analyze Ni-rich mineral standards using WT.
• To compare WT plots of Ni-Al LDHs, single metal Ni hydroxides, and Ni-rich silicates.
• To determine if WT can differentiate between LDHs and single metal hydroxides based on their first metal shell.

Main Methods:

• Systematic analysis of Ni-rich mineral standards including Ni-Al LDHs, α-Ni(OH)2, and Ni-rich silicates.
• Application of wavelet transformation (WT) to extended X-ray absorption fine structure (EXAFS) data.
• Comparison of WT plots to differentiate mineral structures.

Main Results:

• WT plots for α-Ni(OH)2 and Ni-Al LDHs were often indistinguishable, showing similar two-component plots.
• The WT of the first metal shell is insufficient to differentiate between LDHs and single metal hydroxides.
• Interlayer anions adsorbed to α-Ni(OH)2, invisible in Fourier transform (FT), were clearly resolved by WT.

Conclusions:

• Wavelet transformation of the first metal shell in EXAFS data cannot reliably differentiate between layered double hydroxides and single metal hydroxides.
• WT is a valuable tool for detecting interlayer anions in minerals like α-Ni(OH)2, which are not discernible using traditional FT methods.