Abstract
Hydrocalumite structured layered double hydroxides (LDHs) with various Fe3+ ratios were prepared through a coprecipitation method. In order to control the Fe3+ content in LDH, binary Ca–Fe LDHs were first synthesized with various Ca/Fe ratios. The X-ray diffraction pattern showed that only a limited Ca/Fe ratio resulted in LDH formation. The Fe3+ content in LDH was controlled by applying Al3+ while the divalent and trivalent metal ratio was set to 2. Through X-ray diffraction patterns, ternary LDHs with Ca–Al–Fe composition were successfully synthesized without significant impurities, with the Al increasing crystallinity. Quantification showed that Al moiety participated in the formation of the LDH framework more than Ca and Fe, implying a structural stabilization in the presence of Al. In order to investigate the global and local structure of Fe moiety in the LDH, both solid state UV-vis and X-ray absorption spectroscopies were carried out. Both spectroscopies revealed that the existence of Al induced slight local distortion in coordination but global crystal stabilization.
Highlights
Layered double hydroxide (LDH) is a family of 2-dimensional layered inorganics having positively charged nanolayers and charge compensating anions [1,2,3,4]
The structure and composition of hydrocalumite type LDH with Ca–Al–Fe composition were investigated in this study
It was confirmed that pure binary LDH with Ca–Fe composition could only be obtained with a limited metal ratio of 2/1
Summary
Layered double hydroxide (LDH) is a family of 2-dimensional layered inorganics having positively charged nanolayers and charge compensating anions [1,2,3,4]. A layer is composed of M(OH) octahedrons having either divalent or trivalent metal ions, and the metal hydroxide units are linked in the crystallographic ab-plane direction by sharing each other’s edges [22]. When Ca2+ is involved in the layer structure, there is a slight distortion in the lattice; relatively large Ca2+ ions are stabilized in a capped octahedron geometry with a coordination number of 7 [24]. This specific phase of LDH is often referred to as hydrocalumite, in which
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