The Synthesis, Characterization And Properties Of Polyanions-intercalated Layered Double Hydroxides

Heteropolyanion-Pillared Hydrotalcites (HTLCs一POMs) are a new type of materials. They can be synthesized by ion-exchange method directly. Because both POMs and hydrotalcites have catalytic activities, their combinationobtain can improve each's catalytic activity obtain multiple-founction catalysts.Mg₂Al-CoW₁₂(1) and Mg₂Al- Ce(PW₁₁O₃₉)₂(2) ,Mg₂Al- Pr(PW₁₁O₃₉)₂(3) were synthysized by the ion-exchange method. This thesis relates to a systemic study on the preparation of HTLCs一POMs by intercalation and assembly through nitrate hydrotalcites, and on the relationship between the composition, the structure and the property of the products thereby obtained. The IR property and thermal stability of the polyanions-pillared hydrotalcites have been studied by XRD, FTIR and TG-DTA. The results show that the polyanions-pillared hydrotalcites, with a high degree of anion exchange, have similar crystal appearances to their precursors. The interlayer distance depends on the arrangement of the polyanions, as well as their size. The arrangement of the polyanions is influenced by the amount of the interlayer water molecules, the composition of the brucite layers and the degree of anion exchange.Cyclic voltammetry, magnetic properties and fluorescent activity of these compounds have been studied respectively. Magnetic susceptibility measurement for 1 and 3 in the temperature range 2-300K reveal the occurrence of weak antiferromagnetic interactions between neighbor magnetic centers in both compounds. The emission spectrum result shows weak photoluminescence of compound 3. The catalytic activities of the HTLCs-POMs were extensively studied. It was observed that the catalytic activities of the HTLCs-POMs are higher than that of the pure POM or LDH, this mainly attributed to the synergetic effect between POMs and HTLCs.