Synthesis And Application Of Mesoporous Materials Templated By Specific Polymer

Mesoporous materials hold important potential for various applications,including energy storage and conversion,catalysis,and biomedicine as well as adsorption and separation,due to their intrinsic properties such as ultrahigh specific surface area,very large pore volume,special pore structure and precise controllable pore size.After more than 20 years of research and development,the synthesis of silicon-based mesoporous materials has been relatively mature.However,the design and synthesis of non-silicon-based mesoporous materials still faces the following challenges:?1?Expanding the synthesis system of mesoporous materials.Compared with the silicon-based precursors,it is really of hardship to control the hydrolysis and condensation process of the non-silicon-based precursors especially the metal chlorides and metal alkoxides.Therefore,the synthesis of non-silicon based mesoporous materials is only suitable for organic solvent synthesis system;?2?Accurate control of crystal structures and pore frameworks of mesoporous materials.?3?Developing a low-cost and high-yield synthesis strategy to promote the industrialization of mesoporous materials.The synthesis of mesoporous materials requires the use of expensive surfactants or block copolymers as templates,and their synthesis periods lasts for several days or even a week,which greatly limit the large-scale production and industrial application of mesoporous materials.?4?Enriching the members of mesoporous materials with novel structures.The molecular self-assembly technology and nano-casting technology have been not suitable for the synthesis of mesoporous materials with ultrahigh crystallization temperatures and complex structures,such as sodium super ionic conductor structure materials,perovskite materials,spinel materials,etc.Therefore,in order to meet the increasing application requirements,we need to explore and develop the new synthesis strategies to prepare mesoporous materials with novel structures.In this paper,we synthesize a series of mesoporous materials with large specific surface area and high crystallinity by using specific polymers as porogens and systematically investigate the effect of porous structure,specific surface area,morphology and crystallinity on the photocatalytic activity and electrochemical performance.In chapter 2,we demonstrate a facile and versatile polymer-oriented self-assembly strategy for the synthesis of a series of mesoporous metal oxides with ultrahigh specific surface areas,including TiO₂,Al₂O₃,HfO₂,Nb₂O₅,Ta₂O₅,ZrO₂,and SnO₂,by using cheapnonsurfactantcationicpolymerspolyethylenimineor polydimethyldiallylammonium chloride as porogens,metal alkoxides as metal oxide precursors,acetic acid as pH regulator and coordination agent in a robust aqueous synthesis system.In this approach,the pore structures,crystal structures and morphologies of the materials can be precisely controlled by tailoring the interactions between metal oxide precursors and cationic polymers.Taking the mesoporous TiO₂ as the representative,the specific surface area of the samples can be controlled in a wide range from 226 m² g^-1 to 733 m² g^-1.In the photocatalytic water splitting test,the mesoporous TiO₂ shows excellent photocatalytic activity and the hydrogen production rate is as high as 3.68 mmol h^-1 g^-1.In chapter 3,we develop a polymer-assisted coordination-mediated self-assembly strategy to prepare mesoporous TiO₂ polymorphs with large specific surface area by using titanium tetrachloride as metal oxide precursor,polyethylenimine as the porogen,hydrochloric acid and acetic acid as the coordination agents,and deionized water as the solvent.Using this method,the crystal phases?monophase,biphase,and triphase?and phase compositions?0-100%?are readily adjusted by changing the amount and type of acidic media.In the photocatalytic water splitting test,the triphasic TiO₂ photocatalyst displays the optimal photocatalytic activity as compared to the Degussa P25 and other polymorphs due to the synergistic effects of mesostructure and heterophase junctions.Moreover,the effect of heterophase junctions on the photocatalytic activity is investigated in detail by diffused reflectance UV-vis spectroscopy,Mott-Schottky plots,and valence band XPS spectra.We propose the possible electron and hole transfer pathway in triphasic TiO₂ photocatalyst,which provides a new insight for the subsequent study of photocatalysis mechanism.In chapter 4,we report a facile and scalable solvent-free self-assembly strategy to synthesize a library of mesoporous materials with large surface area and high crystallinity,including single-component mesoporous materials?e.g.,SiO₂,TiO₂,Ta₂O₅,Nb₂O₅,HfO₂,Al₂O₃,and ZrO₂?and multi-component mesoporous materials,such as doped mesoporous materials?e.g.,yNb-doped TiO₂?,composite mesoporous materials?e.g.,Nb₂O₅-TiO₂ composite?,and polymetallic oxide?e.g.,TiNb₂O₇?.Compared with the traditional solution-based self-assembly route,this technology does not need any solvent and uses cationic polymer polyethyleneimine as template instead of expensive surfactant,which greatly reduces the consumption of cost and energy as well as the environmental pollution.The self-assembly of polymer and inorganic precursor can be completed by mortar grinding at room temperature for five minutes,which makes the method can produce mesoporous materials on a large scale,and promotes the industrial application of mesoporous materials.These mesoporous materials have high crystallinity and good porosity can be readily tailored for various applications.In chapter 5,we report a facile polymer-assisted spinodal decomposition method to prepare highly interconnected hierarchical porous sodium super ionic conductor structure materials,including Li₃V₂?PO₄?₃,Na₃V₂?PO₄?₃,K₃V₂?PO₄?₃,Na₂TiV?PO₄?₃,and Na₄MnV?PO₄?₃,using block copolymer as the structure-directing agents in a tetrahydrofuran/ethanol/H₂O synthesis system.Based on the boiling point of solvents,the selective volatilization of the solvents induces both macrophase separation and mesophase separation.Nanoscale X-ray computed tomography,scanning electron microscopy and transmission electron microscopy indicate these materials consist of densely packed carbon-coated nanocrystals and have the interconnected macro/mesostructures.The resulting hierarchical porous Na₃V₂?PO₄?₃ exhibit superior electrochemical performances in sodium-ion batteries.We believe that the present approach is of great significance to the synthesis of hierarchical porous materials with ultrahigh crystallization temperatures and complex structures.