Studies On Host-guest Assembly Based On Layered Materials

When a guest species is encapsulated in a host, composite host-guestcompounds with unusual properties may form. Layered inorganic materials havebeen extensively considered as good hosts to incorporate functional guest specieswhich yield a variety of useful applications as catalyst, ion conductors,shape-selective adsorbents, ion exchangers, photofunctional materials, etc., andmany novel assembly structures can be tailored at the molecular level through thedesign of the host and the guest species. In this dissertation, we describe some newhost-guest systems related to layered materials.(1) A novel azobenzene derivative modified magadiite has been prepared by thereaction between the interlayer hydroxyl groups of magadiite and the azobenzenederivative using dodecyltrimethylammonium-exchanged magadiite as theintermediate. The formation of the silylated magadiite-azobenzene system wasconfirmed by X-ray diffraction, IR and MAS NMR spectroscopies. The organicgroups of the azobenzene molecules are grafted onto the interlayer surface ofmagadiite by covalent bond, affording compounds different from those derived byion exchange. The composite compound is stable in water and other commonorganic solvents. The orientation and reorientation of the azobenzene derivative inthe magadiite have been examined through observing its photoinduced anisotropybehavior. Because the azobenzene derivatives are grafted on the interlayer surface ofmagadiite, the rigid inorganic layers of pDRSiM act as a "wall"to prevent theazobenzene molecules from getting entangled with the polymer chains of PMMA. Inother words, the inorganic layers of magadiite provide a relatively free space aroundthe azobenzene groups, rendering the azobenzene free to reorient. The freeorientation of azobenzene groups leads to the faster reversal of the inducedanisotropy to isotropy. Furthermore, the photoinduced anisotropy behavior of thecomposite material can be observed even at 95 C. Our approach provides an oalternative route for the construction of new materials which can be used forreversible photoinduced anisotropy study.(2) We synthesized four types of Cd-containing LDHs compounds (CdCr-LDH,ZnCdCr-LDH, CdAl-LDH, CdDS) containing alkyl sulfate as the interlamellaranion through a coprecipitation technique. The powder X-ray diffraction patternsindicate that the as-synthesized samples exhibit high structural order. The typicaldiffraction peaks correspond to intercalated layered double hydroxides with layerseparations in good agreement with those reported previously. The UV-vis spectrareveal the existence of mononuclear state of CrIII in a nearly octahedral OH-environment within the hydroxide layer of the Cr-containing LDHs.Antiferromagnetic interactions between the CrIII centers have been observed for theas-prepared CdCr-LDH and ZnCdCr-LDH. The introduction of zinc influences theligand field of CrIII and the CrIII-CrIII interactions in the Cr-containing LDHcompound. It is found that both CdCr-LDH and ZnCdCr-LDH can be delaminatedby dispersion in formamide, leading to translucent and stable colloidal solutions.Dodecyl sulfate (DS) has been used as the anion to intercalate the layers of theseCr-containing compounds which exhibit high structural order and can be exfoliatedinto single layers in formamide solution, providing new precursors to be used inassembly chemistry.(3) Using these LDHs compounds mentioned above as precursors, for the first timewe prepared CdS nanocrystals and CdS/ZnS those are implanted and stabilized inthe layer matrices of the four types of compounds through a gas/solid reaction route.Depending on the Cd/M (M is trivalent metal) ratio in the precursor, the size of theCdS nanoparticles can be controlled and tuned. The XRD patterns of the CdM-LDHafter sulfurization reaction show three broad peaks corresponding to the (111), (220)and (311) reflections of cubic CdS, whereas the XRD patterns of the ZnCdCr-LDHafter sulfurization reaction show three broad peaks corresponding to the mixture ofcubic CdS and cubic ZnS. In contrast, the CdS nanoparticles in CdDS aftersulfurization reaction appear to be a predominant hexagonal phase contains a smallamount of cubic CdS phase. It indicates the MIII plays an important effect on theformation of the nanocrystals. It is also found that the photocatalyic performance ofthe CdAl-LDH implanted with CdS nanocrystals is distinctly superior to those ofbulk CdS and even nanosized TiO2 for the degradation of rhodamine B under UVand visible light irradiation. In principle, our preparation approach can begeneralized to extend to other nanocrystals implanted in layer matrices, and a varietyof functional composites with nanocrystals of controlled size may be prepared in asimilar way.(4) Preparation of microrods/microtubes from single metal layered hydroxides saltcompound (Cd2(OH)3(DS)·nH2O) through hydrothermal reaction.Microrods/microtubes (long: 5-30 μm; diameter: about 1-3 μm) were obtained bythe synthesis of the layered hydroxides salt compound followed by hydrothermaltreatment at 100 C for 12h. The hydrothermal temperature and the period can oinfluence the yield of the microrods/microtubes. If the hydrothermal temperature isabove 120 oC or the hydrothermal period below 4h, we can't get themicrorods/microtubes. The hydrothermal reaction and the surfactant are...