NEW VARIETIES OF ZINC-CHROMIUM-SULFATE LAMELLAR DOUBLE HYDROXIDES

摘要

The synthesis of zinc-chromium lamellar double hydroxides (LDHs) intercalated by sulfate anions is carried out with a onestep method that combines coprecipitation and anionic exchange, The materials obtained in a reactor containing a sodium sulfate solution are compared with those prepared from lithium, potassium, and ammonium sulfate solutions. The compounds are characterized by chemical analysis, powder X-ray diffraction, and infra-red spectroscopy. Depending on pH conditions, the washing process, and the nature of the monovalent cation, the sulfate intercalated compounds exhibit two 2H hexagonal varieties with different layer spacings d approximate to 8.9 Angstrom and d approximate to 11 Angstrom at room temperature; this last phase is related to the insertion of alkaline interlamellar cations. Under dry air, the loss of intercalated water leads to a 3R rhombohedral variety with d approximate to 8.2 Angstrom. A second rhombohedral variety with d approximate to 10.9 Angstrom is reversibly obtained from the ''8.9 Angstrom'' phase under high relative humidity. These four [Zn-CrSO4] LDHs differ by their stacking sequences and interlamellar distances and can be selectively obtained. (C) 1997 Academic Press. [References: 19]