Mesoporous crystalline metal oxides

Metallic oxides;Mesoporous materials

Yue, Wenbo ; Zhou, Wuzong ; Zhou, Wuzong

University:University of St Andrews

Department:Chemistry (School of)

关键词: Metallic oxides;    Mesoporous materials;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/830/WenboYuePhDThesis.pdf?sequence=6&isAllowed=y

来源: DR-NTU

【 摘 要 】

Mesoporous monocrystalline metal oxides (e.g. Co₃O₄, Cr₂O₃, NiO, CeO₂, In₂O₃and WO₃) templated by SBA-15 or KIT-6 were synthesised successfully by using asimple solvent-free approach, the so-called solid-liquid method, which was theprincipal development of methodology in this project. A metal-containing precursor,whose melting point is lower than its decomposition temperature, was directly groundwith a mesoporous silica and impregnated into the pores of the silica template aftermelting when the temperature was increased above its melting point. The liquidprecursor then decomposed to form metal oxide inside the silica pores when thetemperature was further increased to its decomposition temperature andcrystallization temperature of the oxide. The structural characterisations of theseporous metal oxides were performed by using TEM, XRD and N₂adsorption/desorption techniques. The solid-liquid method is convenient andsolvent-free. On the other hand, its limitation is that the precursor must have amelting point lower than its decomposition temperature.A novel porous single crystal of rutile TiO₂ as well as anatase nanocrystal-silicacomposite was also synthesised successfully for the first time using SBA-15 andKIT-6 as templates. These materials have interesting properties of proton conductivity,Li insertion and photoactivity. Likewise, the characterisation of porous TiO₂ wasachieved by using XRD, TEM, SAED and N₂ adsorption/desorption. The residualSiO₂ component in porous TiO₂ was detected by using the EDX technique.Porous cubic metal oxides of Co₃O₄, NiO, CeO₂ and In₂O₃ were prepared usingnovel mesoporous silicas FDU-12 and SBA-16, which contain spherical nanocavitieslinked together by smaller windows. These porous materials have larger surface areasthan those templated by SBA-15 and KIT-6. Unlike the cubic metal oxides, synthesesof porous crystals of non-cubic metal oxides such as rhombohedral Cr₂O₃, Fe₂O₃ andhexagonal TiO₂, WO₃ were not successful when using cage-containing mesoporoussilicas as templates. The three-dimensional arrangements of nanospheres in porous crystals of cubic oxides mentioned above were observed by TEM and thecorresponding larger surface areas were confirmed by N₂ adsorption/desorptiontechnique.Additionally, fabrication of porous crystals of other metal oxides such as MgO,ZnO and ZrO₂ were unsuccessful by using either mesoporous silicas or mesoporouscarbons as templates. Possible drawbacks of using mesoporous silica and carbon astemplates were discussed.