An in-situ investigation of LDH–acetate prepared in polyol, under moderate thermal treatment

Pure NiAl-Layered double hydroxides (LDH) intercalated by acetate anions is prepared by polyol method. Intercalation of acetate anions gives rise to expanded LDH with a basal spacing of 1.24 nm (±0.01). In-situ X-ray diffraction (XRD) measurements of the as-prepared hybrid material evidence a contraction (0.29 nm) of the interlamellar domain under either moderate thermal treatment from 80 to 200 °C or under dynamic vacuum, which is related to the release of physisorbed and interlayer water molecules. The contracted–dehydrated phases are found to quickly recover the initial interlayered distance upon cooling to room temperature or at ambient pressure, evidencing a completely reversible phenomenon. To better understand these transient metastable phases, the contraction phenomenon is further investigated by in-situ XAFS at Ni K-edge combined with Raman spectroscopy during the heating process. Whatever the techniques of investigation, the results reveal a complete reversibility of the contraction, which is assigned to a reorientation of acetate anions into the interlamellar space under dehydration–rehydration process.