| Porous materials have been widely applied in catalysis, adsorption and separation due to their opened frameworks, large specific surface areas and ordered pore structures. After years of efforts and discussion, the porous composite materials with adjusted pores, all kinds of components, different morphologies and pore channels have been synthesized. However, many challenges and difficulties need to be overcome in the reasonable design and application of ordered mesoporous materials and hierarchical porous materials. The synthetic methods with simple, fast, inexpensive and environmental-friendly properties must be developed to obtain the porous materials with high quality and multifunction. The potential function of porous materials should be studied further for their widely application in areas of catalysis, environment field, adsorption and separation, etc. This procedure is full of opportunities and challenges.As a result, in this thesis, we firstly focus on the development of new type of mesoporous catalysts for the fuel conversion process. We have demonstrated a chelate-assisted multi-component co-assembly method to synthesize ordered mesoporous carbon with uniform metal nanoparticles using acetylacetone as a chelating agent, resol as a carbon source, metal nitrates as metal sources, and amphiphilic copolymers as a template. The obtained nanocomposites have a 2-D hexagonally arranged pore structure, uniform pore size (～4.0 nm), high surface area (～500 m2/g), large pore volume (～0.30 cm3/g), uniform and highly dispersed Fe2O3 nanoparticles and constant Fe2O3 contents around 10 wt%. By adjusting acetylacetone amount, the size of Fe2O3 nanoparticles is readily tunable from 8.3 to 22.1 nm. More importantly, it is found that the nanoparticles are partially embedded in the carbon framework with remaining part exposed in the mesopore channels. This unique semi-exposure structure not only provides an excellent confinement effect and exposed surface for catalysis but also helps to tightly trap the nanoparticles and prevent aggregating during catalysis. Fischer-Tropsch synthesis results show that, as the size of iron nanoparticles decreases, the mesoporous Fe-carbon nanocomposites exhibit significantly improved catalytic performances with C5+selectivity up to 68%, much better than any reported promoter-free Fe-based catalysts due to the unique semi-exposure morphology of nanoparticles confined in the mesoporous carbon matrix. It is believed that this chelate-assisted co-assembly can be used as a general synthetic method for designing various function-integrated nanostructures containing incorporated functional nanoparticles for diverse applications.Nowadays, it is well accepted that CO2 looping cycling using solid CaO-based sorbents is a great alternative technology for capturing CO2 due to their high efficiency, and low cost in sorbents. However, the major and most challenge for the employment of CaO based sorbents in CO2 looping cycles is their rapid decrease of the reversibility for the carbonation reaction, which is typically explained by sorbent sintering and attrition at high temperature. Concerning about this problem, we have demonstrated a wet coating process to the core/shell structured CO2 carriers with CaO based pellets as cores and mesoporous SiO2/ZrO2 mixed oxides or pure ZrO2 as shells resulting in a novel sinter-resistant sorbent for cyclic CO2 capture. It was found that the silica/zirconia mixed oxide or pure zirconia could be not only coated as a layer with tunable thickness from 1 μm to 5 μm around the pellet, but also infiltrated into the inner void of the pellets isolating the CaO crystalline grains and forming a unique segregation effect during the high-temperature CO2 capture. During the cyclic calcination-carbonation process, the core/shell pellets exhibited much better stability than their original cores, the synthetic Cadomin pellets (CP), due to the segregation effect which could prevent the contact of CaO crystalline grains and their sintering. The core/shell pellet with 1 μm zirconia shell showed the best CO2 uptake capacity of 7.2 moles CO2/kg calcined sorbent and lowest activity loss of only 30.8% after 20 cycles, whereas, CO2 uptake capacity and activity loss of sample CP is only 5.6 moles CO2/kg calcined sorbent and up to 51.2%, respectively. The zirconia shell provided an excellent protection for the active CaO cores in forming a rigid and stable skeleton. At the same time, the mesopores exiting in the zirconia framework favored fine CO2 diffusion during all 20 cycles.Microspheres (MS) with well-controlled porosity can provide ready access to a relatively large surface by reducing diffusion lengths compared to their bulk counterparts due to their large surface-to-volume ratio. However, it still remains a big challenge to synthesize mesoporous carbon microspheres, especially to precisely control their morphology, internal mesostructure and porosity. Moreover, direct and controllable integration of ordered mesoporous carbons with functional components (e.g. catalytic nanoparticles) has not yet been reported achieved. In our following work, a general confined co-assembly process has been demonstrated to produce discrete uniform mesoporous carbon microspheres with particle size of 0.8-1μm using 3-D ordered macroporous silica as the template. The obtained mesoporous carbon microspheres have uniform and discrete spherical morphology, variable symmetry (hexagonal p6mm or cubic Im3m) of mesostructures, high specific surface areas (500-1100 m2/g), large pore volumes (0.6-2.0 cm3/g) and highly accessible large mesopores (7-10.3 nm). The particle size of the carbon microspheres can be easily tuned by simply using templates with different macropore sizes. It was found that the smaller MC-MSs (330 nm) with higher surface-to-volume ratio tend to shape into integral monolithic MC-MSs matrix, while larger MC-MSs (> 800 nm) with lower surface-to-volume ratio to discrete spherical morphology. This feature is attributed to the difference in shrinkage behavior of mesoporous carbon spheres confined in the macropores caused by the interaction between the silica wall and carbon microspheres. Adsorption experiments indicate that the cobalt-based nanoparticles incorporated mesoporous carbon microspheres exhibit excellent size selectivity for protein adsorption in a complex solution and good magnetic separability for easy recycling.Unique heterogeneous catalysts, especially metallic ones like noble metals are often referred to nano-sized particles ranging in size from roughly 1-50 nm, which can increase the exposed surface area of the active component of the catalyst, thereby enhancing the contact between reactants and catalyst dramatically and mimicking the homogeneous catalysts. However, owing to their high surface energies, metallic nanoparticles are normally unstable and tend to coagulate towards sintering in catalytic reactions along with a sharp drop compared with their initial activity and selectivity. Another major obstacle remained in the application of nanoparticulate catalysts is the separation of nanoparticles from a complex heterogeneous system for recycling. In this regards, we have demonstrated a facile and versatile synthesis of multicomponent and multifunctional microspheres Fe3O4@C-Pd@mSiO2 with well-defined core/shell structures, confined catalytic Pd nanoparticles and accessible ordered mesopore channels by combining the sol-gel process, interfacial in-situ deposition, and surfactant-templating approach. It exhibited excellent catalytic performance and reusability in Suzuki-Miyaura cross-coupling reactions.Up to now, by using different synthesis strategies, researchers are now able to synthesize various kinds of mesoporous materials with controllable morphologies, framework compositions, pore structures and pore sizes. Although mesopores provide high surface areas and shape-selectivity for guest molecules, they exhibit great resistance of diffusion. So far the pore size of mesoporous materials synthesized using the conventional methods is restricted in the range of 2-60 nm and the entrance size of mesopores is very small (< 35 nm), which may limits their practical applications involving large molecules, such as protein enrichment, confined space enzymolysis of biomolecule and separation. In the last section of this thesis, for the first time, we presented a controlled synthesis of hierarchically ordered macro-/mesoporous silicate materials with adjustable macropore window sizes (0-160 nm) via a dual-templating approach which combines colloidal crystal templating and amphiphilic surfactant templating. Various synthesis conditions affecting macropore entrance size have been investigated, including the prehydrolysis time of silica source, the concentration of acid and sintering conditions of colloidal crystal templates. The obtained hierarchically ordered porous silica monolithic materials exhibits excellent size selectivity for adsorption of biomacromolecules.In Chapter 7, the whole thesis is summarized. |
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