Synthesis And Property Studies On New Layered Double Hydroxides And Their Intercalated Compounds

When a guest species is encapsulated in a host, composite host-guest compounds with unusual properties may form. Layered inorganic materials have been extensively consider as a good host to incorporate functional guest species which yield a variety of useful applications as catalyst, ion conductors, shape-selective adsorbents, ion exchangers, photofunctional materials, etc., and many novel assembly structures can be tailored at the molecular level through the design of the host and the guest species. In this thesis, we describe some new host-guest systems related to layered double hydroxides.We synthesized four types of Cd-containing LDHs: alkyl sulfate intercalated Cd/Cr LDH and nitrate intercalated Cd/Ga LDH through the method of co-precipitation. The powder X-ray diffraction patterns indicate that the as-synthesized samples exhibit high structural order. The typical diffraction peaks correspond to intercalated layered double hydroxides with layer separations in good agreement with those reported previously. There is a difference between the two LDHs in structure that DS- plays an important roll with the layered structure of Cd/Cr-DS LDH while the Cd/Ga-NO3 LDH exhibits a perfect hydrotalcite structure.Using the organic-inorganic multiple compound of Cd/Cr-DS LDH as a precursor, for the first time we prepared CdS nanocrystals and CdS/ZnS that are implanted and stabilized in the layer matrices through a gas/solid reaction route. Depending on the Cd/M (M is trivalent metal) ratio in the precursor, the size of the CdS nanoparticles can be controlled and tuned. The XRD patterns of the CdM-LDH after sulfurization reaction show three broad peaks corresponding to the (111), (220) and (311) reflections of cubic CdS. CdS nanoparticles appear to be a predominant hexagonal phase containing a small amount of cubic CdS phase if trivalent cations were not added. It indicates the MIII play an important effect on the formation of the nanocrystals.I2/I- intercalated Cd/Ga LDH was synthesized through direct synthesizing method. This compound shows excellent stability against air, water, organic solvents and temperatures under 400K while the interlayer iodine remains reactive and it can be released at the temperature of 500K under ambient pressure. It was studied that the interlayer I- was intercalated as the charge balancing anion of layered double hydroxides but the interlayer crystalline hydrate seemed more or less replaced by I2 molecules that existed as the form of"crystalline iodine".Microrods/microtubes was prepared from layered metal hydroxides salt compound (Cd2(OH)3(DS)·nH2O) through hydrothermal reaction.Microrods/microtubes (long: 5-10μm; diameter: about 1μm) were obtained by the synthesis of the layered hydroxides salt compound followed by hydrothermal reaction at 100 oC for 12h. The hydrothermal temperature and the period can influence the yield of the microrods/microtubes. If the hydrothermal temperature is above 120 oC or the hydrothermal period below 6h, we can't get the microrods/microtubes. Also, the the microrods/microtubes decompose if the hydrothermal period is above 15h. The surfactant and keeping still while reacting are indispensable conditions which answer for the formation of the microrods/microtubes. However, hydrothermal method insure the reaction speed and the stability of the products. We deduced the concomitant mechanisms from the formation of the microrods/microtubes. The crystalizing-solving-recystalizing process may well explain the formation of microrods/microtubes.