RAMAN-SPECTROSCOPIC STUDIES OF INTERCALATED MOLYBDATE IONS IN LAYERED METAL-HYDROXIDES

X-ray diffraction and Raman spectroscopy have been used to investigate the chemistry of MoO4(2-) and Mo7O24(6-) ion-exchanged into the interlayers of layered metal hydroxide compounds. In the case of LiAl2(OH)6.1/2MoO4, exposure of the sample to air leads to destruction of the layered structure as manifested by the diffraction pattern. Raman spectroscopy indicates that this occurs due to hydrolysis of the MoO4(2-) followed by reaction of OH- with CO2. It is proposed that this process occurs due to charge imbalance between the framework and the intercalated ions. For Mg2Al(OH)6.1/6Mo7O24, the heptamolybdate ion was found to survive treatments up to 400-degrees-C, although the layer structure is lost at temperatures of 300-degrees-C. The drastic differences between the thermal behavior of molybdates and an earlier reported study of vanadates on magnesium aluminate arise from the distinct hydrolysis chemistry of these two systems.