Pillared sheet hydroxides

The structure of the layered double hydroxides is the reverse of that of the clays. They are anionic materials in which the sheets are intercalated with anions instead of cations. These ions can be exchanged with several different anions. The cationic nature of the layers lends itself to pillaring by large Keg-gin anions. 

The results in Table II suggest that molybdate- and vanadate-pillared hydrotalcites contain both acidic and basic sites, the basic sites located on the metal hydroxide sheets, and the acidic sites located on the polyoxometalate pillars. 

Challier and Slade [175] reported the synthesis of nanocoinposite materials consisting of polyaniline molecules encapsulated between ultra-thin mixed metal hydroxide sheets which are propped apart by spacers of terephthalate or hexacyanoferrate(II) ions acting as pillars. The layered double hydroxides (LDHs) were prepared by the method of Drezdon [176] which were refluxed with aniline to synthesize aniline intercalated LDHs. In thermo-gravimetric studies, terephthalate/Cu/Cr LDHs as well as hexa-cyanoferrate(lI)/Cu/Al LDHs showed weight losses in two steps attributed to the removal of trapped water and thermal breakdown of the intercalated systems. The former material exhibited somewhat better thermal stability than the latter one. 

---