Studies On Host-Guest Assembly Based On Molecular Sieves

The single molecular sieves can meet far from people's needs, and many established molecular sieves applications depend either directly or indirectly on the functionalization. Increasing attention has been paid to the assembly of the guest materials into molecular sieves. The applications involved in the host-guest materials based on microporous molecular sieves are very wide, especially promoting the development of catalyst. The mesoporous molecular sieves have also been synthesized in 1992. The pore size of mesoporous molecular sieves is bigger than the one of microporous molecular sieves, so more classes of guest materials can be assembled into the host materials.In this paper, several host-guest materials based on molecular sieves have been synthesized: 1. Mononuclear univalent zinc has been synthesized in microporous molecular sieves (SAPO-CHA); 2. The organically functionalized hollow silica spheres with a mesostructured shell have been synthesized; 3. Magnetically separable ordered mesoporous carbon with Fe3O4 nanoparticles grafted on the outer surface of the mesoporous carbon material CMK-3 was prepared through a facile route; 4. The Au nanoparticles were assembled into the mesoporous carbon (CMK-3); 5. The host-guest material based on SBA-15 was used as a template for the synthesis of double wall carbon nanotubes (DWCNs).As is known, the normal oxidation state of zinc is either 0 or +2. The interest has also been directed to univalent Zn species. The univalent zinc species can be synthesized in many systems, but the univalent zinc species in these systems exist as diamagnetic (Zn-Zn)2+ pairs, and no ESR signals can be observed. In addition, the mononuclear univalent zinc cation prepared by physical methods is not stable. In our experiment, the metallic zinc gradually vaporized to react with the protons in the cages of microporous silicoaluminophosphate material with the topology of chabazite (SAPO-CHA), and mononuclear univalent zinc was synthesized. The cage of SAPO-CHA is a microspace with isolated Br?nsted acidic sites. In principle, each of these Br?nsted acidic sites can react with one Zn atom to form one Zn+ cation. Two crystallographically independent Zn+ cations have replaced the protons of two different Br?nsted acidic sites, since two crystallographically independent framework O atoms in the structure of SAPO-CHA are associated with a proton. Some strong ESR signals can be observed in the ESR spectrum for the host-guest material. The g factors of the ESR spectrum of the host-guest exhibit anisotropy, and there are two g values corresponding to the two crystallographically independent Zn+ cations. Further more, an obvious antiferromagnetic behavior at low temperatures is seen from the temperature dependence of the susceptibility for the host-guest material. The results of the ESR spectrum and the magnetic susceptibilities against temperature effectively prove the existence of mononuclear Zn+ species. The mononuclear Zn+ cations in SAPO-CHA are stable in dry air, but the mononuclear Zn+ cations react with NH3, and new species have been formed.We study the synthesis of organically functionalized and anionic surfactant templated hollow silica spheres with a mesostructured shell. Anionic surfactant is first used to template the formation of the hollow silica spheres with a mesostructured shell. Anionic surfactants are widely available, and these compounds are much less costly than cationic surfactants. Moreover, it is easy to form organically functionalized mesoporous material by anionic surfactant template. The organical functionalization of the mesoporous materials is particularly attractive because of the possibility to combine the enormous functional variation of organic chemistry with the advantages of a thermally stable and robust inorganic substrate. Two types of hollow spheres were obtained from the same reaction system through varying the initial synthetic reactant ratio. One of the hollow silica spheres consists of monodisperse particles with a diameter of about 200 nm, and the shells of the particles are of multilamellar structure. The hollow spheres with a wider particle size distribution (diameter 100-2000 nm) also are synthesized, and the sphere shells contain circular mesoporous channels in an approximately hexagonal array. All of the two types of organically functionalized hollow spheres can coordinate transition metal ions. We have coordinated Au ion between the layers of the first type of hollow spheres, and highly dispersed Au nanoparticles are anchored in the hollow spheres after reduction.Recently, highly-ordered mesoporous carbons (OMCs) have been attracting increasing interest because these materials find promising applications as catalyst supports, adsorbents, hydrogen storage media. However, small carbon particles are generally difficult to separate from liquid phases and some of their applications, such as in the fields of catalysis and adsorption involving liquids, are restricted to a considerable extent. To overcome this shortcoming, magnetic particles may be introduced to porous carbons, and it is possible to separate the composite support material from the liquid catalytic reaction system using magnets. Here we report a low-cost and convenient route for the preparation of magnetically separable mesoporous carbon material. M?ssbauer spectroscopy and X-ray diffraction prove that the superparamagnetic species in the composite material is Fe3O4 nanocrystal, and the average size of the nanocrystals is estimated to be about 23 nm. Nevertheless, the dispersion of the magnetic nanoparticles on the surface of the CMK-3 material differs depending on preparation temperature. The magnetically separable catalyst was prepared through loading the host-guest material with palladium nanoparticles. The catalytic performance in combination with the magnetically separable property demonstrates that host-guest material is a promising catalyst support with attractive application perspectives.Gold nanocrystals are highly active for selective oxidation. We detailedly study the loading of Au nanocrystals on highly-ordered mesoporous carbons CMK-3. Au/CMK-3 material was prepared by three methods, pore volume impregnation-reduction method, deposition-precipitation method, and gold sol method, respectively. The gold sol method is an easy and effective way of loading Au nanocrystals into CMK-3, and the diameters ranging of Au nanocrystals is 1-4 nm.Molecular sieves have uniform pore diameter and ordered pore structure, which makes them ideally suited as templates for preparing various nanowires/arrays and nanostructures. The smallest carbon nanotubes prepared in the channels of porous zeolite AlPO4-5 (AFI) single crystals was reported, and a Co-MCM-41 catalytic template for the synthesis of uniform-diameter single-walled carbon nanotubes also was reported. In this paper, SBA-15 was modified with ethylenediamine groups, and Co2+ anions were coordinated in the pore of SBA-15. The molybdenum salt was loaded into the pore of SBA-15 by pore volume impregnation. The nanocomposite of Co-Mo-SBA-15 was used as a catalytic template for the synthesis of carbon nanotubes. The TEM results show that the carbon nanotubes templated by the host-guest catalyst are double-walled carbon nanotubes (DWCNs), and the outer diameter ranging of these DWCNs is 3-4 nm. In general, the outer diameter ranging of DWCNs reported in literature is 0.7-2.5 nm. However, the outer diameter of the most of DWCNs prepared by us is bigger, and we conclude that the Co-Mo-SBA-15 catalyst controls the formation of DWCNs.