Broad bands around 3500-3600 cm -1 , assigned to stretching vibrations of water molecules in the interlayer and the physically adsorbed surface water, also disappear in the temperature range of 150-250 °C. Bands at ~3650-3700 cm -1 are attributed to OH-stretching of hydroxyl groups. Concurrent decrease of 3500-3600 and 1033 cm -1 bands, Figure , is evidence of decomposition and of dissipation of the interlayer water and carbonates ions. Already at ~150 °C we observe the evolution of a band at ~690 cm -1 , which develops into a strong band at 640 cm -1 with further temperature increase up to 600 °C. After heating the Fe HT80 sample to 600 °C three bands in the 200-1000 cm -1 region can be observed: at 320, 404 and 640 cm -1 . For comparison, the Raman spectrum of the same sample calcined ex situ at 800 °C shows strong bands at 205, 316, 470 and 696 cm -1 , with a shoulder at 640 cm -1 (ESI Figure ). This evolving phase is a mixed oxide pre-spinel phase, which likely changes its composition during the thermal treatment. The bands observed for the ex situ calcined sample are generally consistent with the bands characteristic of MgFe2O4 spinel . The spinel-like phase begins to form as hydrotalcite layers lose hydroxyls at higher temperatures. The second endothermic peak in DTG with the minimum at 416 °C, Table , represents this dehydroxylation / decarbonation process. The in situ Raman data is in agreement with the DTG data, but provides finer detail on the evolution of the structure. ; furthermore, both PXRD and Raman spectra are characteristic of wellcrystalline samples. This leads to the conclusion that the platelets observed in the TEM images are agglomerates of primary crystallites. The platelets are further loosely aggregated into larger structures. The level of aggregation seems to be visibly higher for the sample treated at the higher temperature: the samples were prepared identically for the TEM measurements, but we see more of individual platelets in the image corresponding to the HT 65 sample, compared to that in the image of the HT 80 sample. Based on the literature, an increase in aging temperature results in a higher rate of crystal growth . For the conditions used in this study there is a minor increase in the size of crystallites based on PXRD data, which does not contradict the literature. There is, however, a more pronounced aggregation of the particles upon aging, which should result in the more pronounced changes in the morphology of the materials, specifically their pore structure.