Synthesis and Characterization of Polyoxovanadate-Pillared Zn−Al Layered Double Hydroxides: An X-ray Absorption and Diffraction Study

Zn−Al layered double hydroxides (LDHs) have been prepared with Cl - and CO 3 2 - interlayer anions and with Zn/Al ratios of 2 and 3. The corresponding polyoxovanadate-containing LDHs were then prepared by anion exchange reaction at different pH values. The products were characterized by atomic absorption, PXRD, FT-IR spectroscopy, TG analysis, and transmission electron microscopy (TEM). The resulting vanadate-containing LDHs, depending on the pH and the Zn/Al ratio, consisted of one or more phases. PXRD patterns corresponding to layered compounds with different gallery heights (7.0, 4.6, and 2.6 Å for V 10 O 28 6 -, V 4 O 12 4 - and (VO 3 ) n n - chains, respectively) were observed. X-ray absorption spectroscopy has been also used to assess the local geometry of vanadium ions in the different samples, and results indicate the presence of V 5+ ions in octahedral and/or tetrahedral coordination depending upon the conditions of the synthesis.