Mesoporous Materials Based On Organic-organic Co-assembly: Synthesis, Mechanism And Properties

Ordered mesoporous carbons possess high surface areas, large pore volumes, high mechanism stability, surface chemical inertness and good conductivity. Therefore, they have potential applications in adsorption, separation, catalysis, electrochemistry, and so on. Traditionally porous carbon materials, especially active carbons, have been widely used. However, the pore sizes are not very uniform, and most of which are miropores, this limited the further applications of such materials in macromolecules adsorption, lithium ion battery and other high technique areas.Recently, organic-organic assembly is explored as a new method for fabricating mesoporous polymers and carbons. Unfortunately, only a few reports have been presented to synthesize mesoporous carbons due to the low thermal and mechanism stabilities of the polymer frameworks. More recently, our group and several other groups have developed a new method to synthesize ordered mesoporous carbons, which have attracted great attentions. However, the structure and morphology of so produced mesoporous carbons are not enough abundance, the mechanisms are not understood very well, and the applications are not widely exploited. Therefore, further investigating the organic-organic assembly method can not only abundance the structure and morphology of mesoporous carbon, but also have great promising for actual applications.This PhD thesis focus on synthesizing mesoporous carbon materials based on the organic-organic assembly method. Mainly from the synthesis, mechanism, and property to enrich the materials, in-depth understanding the synthesis process, and improve the properties of mesoporous carbon materials.In chapter 2, mesoporous carbon multilayer vesicles were synthesized through an emulsion method. A soluble low molecule resol was used as a carbon precursor, TEOS as a silica source, triblock copolymer Pluonic F127 (EO106PO70EO106) as a template. By controlling the sol-gel process of silicate and phenolic resin, a type of mesoporous carbon/silica multilayer vesicles was successfully synthesized in water solution. The product has a particle size of about 100-250 nm. By using base or HF acid to etch silica, pure carbon vesicle can be obtained. On the other hand, removing the organic components under calcination in air or microwave digestion, pure silica multilayer vesicles can be obtained. Comparing the HRSEM images of the vesicles with different components, we find that there are a lot of carbon pillars between the neighboring layers to connect the shells. In chapter 3, the location of silica and phenolic resin in the pore wall of triconstituent mesostructured material was carefully investigated and a "teardown" method to create large mesotunnels on the pore wall of ordered mesoporous silica was propounded. Firstly, triconstituent co-assembly method was used to synthesize a "block copolymer-phenolic resin-silica" triconstituent mesostructured material with 2-D hexagonal symmetry. Then, the organic components were removed by microwave digestion. The space occupied by block copolymer template was transform to the main channels of mesoporous silica, while the space occupied by phenolic resin on the pore wall was transformed to the mesotunnels. The average pore size calculated from the nitrogen adsorption data is as large as 22.9 nm, which is much large than the cell parameter of 14.2 nm, implying the existence of mesotunnels. Combined with the HRSEM images, the mesotunnels are estimated larger than 9.0 nm.In chapter 4, highly ordered mesoporous carbon FDU-16 rhombic dodecahedral single crystals with body-centered cubic structure (space group Im3m) have been successfully synthesized by employing organic-organic assembly of triblock copolymer Pluronic F127 (EO106PO70EO106) and phenol/formaldehyde resol under a basic aqueous solution. Synthetic factors in controlling the formation of rhombic dodecahedral single crystals, including reaction time, temperature, and stirring rate are explored. The optimal stirring rate is controlled at 300±10 rpm, and the reaction temperature is around 66℃. High resolution Scanning Electron Microscope (HRSEM), Scanning Transmission Electron Microscopy (STEM), and a Micro-slicing Technique are applied to study the fine structures of the carbon single crystals. It certificated that the mesopores in body-centered cubic arrangement throughout the whole particle. A layer by layer crystal growth mechanism is raised based on the detailed results to explain the formation of the mesoporous carbon FDU-16 single crystals. The mesoporous carbon single crystals FDU-16 are growth up to the final size within 2 days, following by the structural rearrangement with the reaction time prolongs.In chapter 5, ordered mesoporous glassy carbons with high surface area (～890 m2/g), large pore volume (0.66 cm3/g), and enhanced reversible lithium-ion battery capacity (up to 470 mAh/g) have successfully been prepared through an in situ crystalline growth approach by using transition metals embedded in the pore matrix, such as Cr, Ni, and Mn as a catalyst at relatively low temperature (1000℃). The ordered mesoporous glassy carbons were synthesized by organic-organic assembly via evaporation induced self-assembly (EISA) method. Citric acid chelated metal ions were directly added into the synthesis batch, leading to uniform distribution in the carbon matrix. That plays an important role in the in situ catalytic formation of the mesoporous glassy carbons at low temperature. High-resolution transmission electron microscopy (HRTEM), select area electron diffraction (SAED), Raman and electron energy loss spectroscopy (EELS) were used to characterize the glassy carbon nature. Antiπ*-bonding and antiσ*-bonding of EELS data reveal a fluctuation tendency vertical to the pore channel direction of FDU-15, confirming the distribution of theπ-type carbon inside the glassy carbon phases. All the graphite sheets are winding around the hexagonal arranged pore channels of FDU-15 to form a thick pore wall of～5-6 nm. These graphite sheets have a two-dimensional (2D) crystalline structure but amorphous in 3D. A "short range catalytic" mechanism based on vapor-liquid-solid (VLS) model was proposed to understand the formation process of the ordered mesoporous glassy carbons. Metal Cr seems to be the best catalyst for formation of the mesoporous glassy carbons at a low carbonization temperature without damaging the mesostructure. Fe and Ni could destroy the ordered mesostructure at a high catalyst amount. While the non-catalyst method needs a carbonization temperature high than 2200℃to obtain the glassy carbons, however, their surface areas reduce a lot. The ordered mesoporous glassy carbons gives rise to excellent performances in lithium-ion battery with a reversible capacity of～470 mAh/g, revealing that the crystalline nature, large surface area, and regular mesostructure are good for their electroperformances.In chapter 6, the whole thesis is summarized.