High-temperature X-ray powder diffraction as a tool for characterization of smectites, layered double hydroxides, and their intercalates with porphyrins

We have analyzed expandable clay minerals and layered double hydroxides with different interlayer ions by high-temperature X-ray powder diffraction (HT-XRD) with comparison to thermal analysis (DTG/DTA) coupled with evolved gas analysis (EGA). We described in detail their thermal behaviour with emphasis to the differences among samples related to their crystallochemical characteristics. Porphyrin-intercalated smectites have a quite unique thermal behaviour as monitored by HT-XRD; the intercalates with tetrakis(1-methyl-4-pyridinio)porphyrin have a basal spacing of about 1.4 nm and are thermally stable up to ca. 600 °C. The resolution of the individual dehydration steps of smectites (from 2-layer hydrate via 1-layer hydrate to the anhydrous form) is much better in HT-XRD then in DTG/EGA curves. Layered double hydroxides (LDHs) have a varying thermal stability depending on their chemical composition and crystallinity. LDHs intercalated with porphyrin anions are thermally stable up to 350-400 °C.