Synthesis, Characterization And Properties Of Mesoporous Nanocrystalline Metal Oxide Materials

In this thesis, mesoporous nanocrystalline tin oxide materials with high thermal stability were synthesized via the soft-templating method, using long-chain ionic liquids 1-alkyl-3-methylimidazolium bromide (Cnmim+Br-,n= 8,12,14,16) as templates. And also, mesoporous zirconia and titania materials with high BET specific surface area, high thermal stability and high crystallinity were also fabricated via combining the soft-templating with solid-liquid method (CSSL). The resulting samples were mainly characterized by X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), Nitrogen adsorption-desorption, Fourier transform infrared spectrometer (FT-IR) and Thermal analyses.Using 1-alkyl-3-methylimidazolium bromide (Cnmim+Br-, n= 8,12,14,16) as templates and sodium stannate as precursors, mesoporous nanocrystalline tin oxide materials with high thermal stability (up to 700℃) were synthesized via the soft-templating method. The HRTEM and Nitrogen adsorption-desorption results indicated that the obtained mesoporous tin oxide with ordered mesoporous structure in short range possessed high specific surface area (ca.350 m2/g). The pore walls were composed of tin oxide nanocrystallites with size of ca.2.5 nm. The FT-IR analysis showed that the high thermal stability for the obtained mesoporous tin oxide was attributed to the wide interaction between the templating agent C16mim+Br-molecules and tin oxide. It involved the electrostatic interaction and H-bonding between C16mim+Br- molecules and tin oxide, as well asπ-πstacking between the imidazolium rings. In addition, the ordered mesostructures were influenced by the reaction conditions, such as pH values of the hydrolysis of tin salt, the different chain lengths of RTILs and different calcination temperatures.A novel strategy involving the combination of soft-templating and solid-liquid method (CSSL) was designed to synthesize mesoporous nanocrystalline zirconia with high specific surface area. The mesostructured zirconia hybrid was firstly synthesized via cooperative assembly between zirconium sulphate as inorganic precursor and 1-hexadecyl-3-methylimidazolium bromide (C16mim+Br-) as the structure-directing agent, and subsequently ground with solid magnesium nitrate salt followed by heat-treatment in air. Finally, after high-temperature calcination, the mesoporous nanocrystalline zirconia materials were obtained after etching the metal oxide inside the porous channels. The wide-angle XRD results indicated that Mg (NO3)2·6H2O salt transforming into liquid state could infiltrate into the pore channels occupied by templates and be well dispersed in the mesostructured zirconia hybrid when it was heated above its melting point (95℃). The maximum amount of the guest inside the host was 50%(w/w). The TG-DTA analysis suggested that the thermal decomposition of Mg(NO3)2-6H2O salt provided the oxidative atmosphere (O2) and hard pillaring-agent (MgO) inside the pore channels, which contributed to the full decomposition of the templates at low temperature, and the restriction of the quick growth of ZrO2 nanocrystallites in the pore walls, avoiding the collapse of the mesopores. The EDX results showed that the magnesium could not penetrate into the zirconia framework after the impregnation with 10 wt% HCl. On the contrary, more silicon elements could penetrate into the zirconia framework if the hard-templating method was used. The HRTEM and Nitrogen adsorption-desorption results indicated that the zirconia material after calcination at 600 C possessed a wormlike arrangement of mesopores surrounded by tetragonal ZrO2 nanocrystallites of ca.2.3 nm. The BET surface area was 255 m2/g and the pore size was ca.4.3 nm. Contrastingly, as for the sample synthesized via the single soft-templating method, the BET surface area was only 9.5 m2/g. Moreover, the obtained mesoporous zirconia materials exhibited excellent fluorescence features.Mesoporous anatase-brookite nanocrystalline titania was synthesized via the strategy relying on the combination of soft-templating and solid-liquid method (CSSL), using titanium sulphate as precursor and 1-hexadecyl-3-methylimidazolium bromide (C16mim+Br-) as structure-directing agent. The wide-angle XRD results indicated that relying on the solid-liquid method, the magnesium nitrate salt as guest could infiltrate into the pore channels occupied by the templates inside the mesostructured titania hybrid as host. The TG-DTA analysis suggested that the thermolysis of Mg(NO3)2·6H2O salt inside pore channels as guest could not only induce the complete decomposition of the templates at low temperature, but also provide the essential hard-pillaring agent (MgO), resulting in the restriction of the quick growth of the nanocrystalline titania in the pore walls and avoiding the collapse of the mesopores. The XRD and Raman results showed that MgO retaining on the surface of the titania framework induced the phase transformation from anatase phase to brookite and rutile phases, and the amount of the brookite phase increased as the temperature rose. The HRTEM and Nitrogen adsorption-desorption results indicated that the titania material after calcination at 600℃possessed a wormlike arrangement of mesopores. The BET surface area was 255 m2/g, and the pore size was ca.4.1 nm. Contrastingly, as for the sample synthesized via the single soft-templating method, the BET surface area was only 64 m2/g. Moreover, the photocatalytic activities of the resulting titania materials in the degradation of methylene orange under UV irradiation were found to be determined by their surface areas and crystal phase contents.