Synthesis, Characterization, Catalytic And Optical Properties Of Three Dimensionally Ordered Macroporous Functional Materials

Three dimensionally ordered macroporous (3DOM) materials have attracted much research attention in recent years due to their special structural and functional properties. 3DOM materials can be utilized as photonic crystals, catalyst, supports, absorbents and electrodes etc., and show great prospective in applications of catalysis, environment, chemical engineering and electronic industries. Currently, 3DOM materials is becoming a hot research area in materials science, and the researches in this field are mainly focused on: (1) development of synthesis technology; (2) modulation of porous structure and pore size; (3) construction with various materials systems; (4) surface fictionalization; (5) exploration of novel functionality of 3DOM structures. However, all these research aspects are somehow difficult to be achieved. Applications of 3DOM materials in various areas still face challenges such as improving the pore wall compactness and mechanical stability, forming ordered structure in large scale, and finding simple synthesis route to decrease synthesis cost.In the present thesis, novel colloidal crystal template methods were developed to synthesize 3DOM materials with controllable pore sizes, improved pore wall compactness and mechanical stability, and well defined three dimensionally ordered porous periodicity. The effects of preparation methods and reaction conditions on the structure, pore size and porous periodicity of 3DOM structures were systematically studied. Furthermore, 3DOM Au/CeO₂ catalysts were synthesized by loading Au nanoparticles onto the 3DOM CeO₂ structure. The catalytic performance of the as-prepared 3DOM Au/CeO₂ catalysts on formaldehyde oxidation reaction was tested. Finally, the 3DOM rare earth phosphors were synthesized via the colloidal crystal template method, and the fluorescence properties were investigated.The main results of the thesis were summarized as below:1. Monodisperse polystyrene (PS) beads with diameters of 200-2000 nm were prepared by using dispersion polymerization and soap-free-emulsion polymerization technique. PS colloidal crystal template was assembled with the obtained monodisperse PS via natural sedimentation, vertical deposition technique and centrifugation method. By using the PS colloidal crystal as templates, 3DOM Dy₂O₃, Fe₂O₃, Y₂O₃:Eu³⁺and CeO₂ materials were fabricated. Transmission electron microscope (TEM), scanning electron microscope (SEM) and infrared spectra (IR) were used to characterize the resulting 3DOM materials. The results showed that 3DOM materials with adjustable pore sizes in ranges of 80-1500nm were obtained by using this colloidal crystal template method. The obtained 3DOM materials showed three dimensionally ordered porous periodicity with high density. These materials are believed to be good candidates for catalytic support and catalyst uses.2. The 3DOM CeO₂ materials were used as catalytic supports to prepare a series of novel 3DOM Au/CeO₂ nanocatalysts with adjustable pore sizes and different Au loading amount via a deposition-precipitation by in-situ Au nanoparticles onto the 3DOM CeO₂ catalyst supports. The catalytic performance of the obtained 3DOM Au/CeO₂ nanocatalysts on formaldehyde oxidation reaction were investigated. The effects of the pore structure, size, Au loading amount, reaction temperature and pre- or post-treatment on the catalytic activity of the 3DOM nanocatalysts were systematically evaluated. Furthermore, the catalytic efficiency, stability and lifetime were mainly estimated, and the catalytic mechanism was discussed as well. The results indicated that the pore size, Au loading amount and annealing treatment had significantly influences on the catalytic performance of the nanocrystals on formaldehyde oxidation reaction. The nanocatalysts with 80 nm pore size, Au 3wt% loading amount and dying at 60℃showed the best efficiency on formaldehyde oxidation reaction. The formaldehyde oxidation tests revealed that the 3DOM Au/CeO₂ catalysts exhibit superior catalytic activity with 100% formaldehyde conversion at -75℃, 30℃lower than previously reported powder Au/CeO₂ catalysts. This is mainly due to the uniform macroporous structures leading to good distribution of catalytic species of Au nanoparticles with less aggregation. The novel 3DOM Au/CeO₂ nanocatalysts showing much stable, efficient and long catalytic activity may find applications in in-door air purification and industrial catalysis.3. By using the mixture of nitrates and citric acid as precursors, 3DOM Y₂O₃: Eu³⁺ phosphors were fabricated via the colloidal crystal template method. The obtained 3DOM Y₂O₃: Eu³⁺ phosphors were studied by means of XRD, SEM and fluorescence spectroscopy. The effects of the porous structure and heating treatment on the fluorescent properties were examined.