Synthesis And Supercapacitive Properties Of Mesoporous Materials With Nanostructure Or Mesoporous-macroporous Structure

Mesoporous materials have potential applications in many areas, such as catalysis, adsorption, separation, electrode materials, medicine carrier, and host-guest chemistry, etc., because of their ordered pore structure, nanoscale pore size, large specific surface area, and high pore volume. The preparation, property, and application of mesoporous materials have generated a great deal of interest in the fields of chemistry, material, physics, and biology. For general mesoporous materials, the particle sizes are usually about several microns or even larger. The large size of the particles will restrict the utilization of the mesopores and the transfer of the substance in mesopores. The synthesis of mesoporous materials with special nanostructure or hierarchical pore structure is an efficient route to solve the above problems. In this thesis, mesoporous carbon nanofibers, hierarchical mesoporous-macroporous carbons, and mesoporous Co₃O₄, NiO with specical nanostructures were prepared and characterized. The supercapacitive properties of the products were also studied.Mesoporous carbon nanofibers were prepared by using the resol/surfactant mixture to fill the pore of the AAO template. During the preparation process, both the nano-confinement effect of the nanospace for the original self-assembled mesostructure and the strong interaction between the nanofibers and the pore surface of AAO have important effect on the mesostructure of the mesoporous carbon nanofibers. When the resol/surfactant precursor of FDU-15 with 2D hexagonal mesostructure was used for filling the AAO, mesoporous polymer nanofibers with coaxial circular 2D hexagonal mesostructure were firstly obtained and mesoporous carbon nanofibers with new core-shell structure were subsequently obtained after further carbonization. When the resol/surfactant precursor of FDU-16 with 3D Im3m cubic mesostructure was used for filling the AAO, mesoporous polymer nanofibers with quasi-Im3m cubic mesostructure were firstly obtained and mesoporous carbon nanofibers with very large mesopore size were subsequently obtained after further carbonization. During the carbonization, the mesopore size of mesoporous nanofibers increased continuously with increasing the heat treatment temperature. When the resol/surfactant precursor of lamellar mesostructure was used for filling the AAO, mesoporous polymer nanofibers with coaxial circular lamellar mesostructure were firstly obtained and mesoporous carbon nanofibers with another new core-shell structure were subsequently obtained after further carbonization. When the single resol precursor was used for filling the AAO, mesoporous carbon nanofibers with random nanoporous structure were obtained after carbonization. Based on the above results, a new nano-restriction effect of the hard templates for the shrinkage of polymer was proposed for the first time. Furthermore, mesoporous carbon nanofibers with large BET surface areas and favorable pore size distributions were tested by electrochemical characterization. The results indicated that the supercapacitive performances of these mesoporous carbon nanofibers were better than those of general mesoporous carbons.Hierarchical mesoporous-macroporous carbons were prepared by using SiO₂ OPAL as the macropore template and resol/surfactant mixture as the filling precursor. During the carbonization process, the nano-restriction effect of the nanospace of SiO₂ OPAL for the shrinkage of polymer results in an anomalous increase of the mesopore size. Finally, hierarchical mesoporous-macroporous carbons with very large mesopore sizes, high pore volumes, and large mesopore surface areas were obtained. The results of electrochemical tests indicated that the supercapacitive performances of mesoporous-macroporous carbons were better than those of general mesoporous carbons.Mesoporous Co₃O₄ nanoparticles with different textural parameters were prepared by using mesoporous silicas, KIT-6 and SBA-15, as templates and Co(NO3)2·6H2O as precursor via an improved solid-liquid route. The results of N2 adsorption-desorption analysis indicated that mesoporous Co₃O₄ nanoparticles possessed two main pore structures and the calcination temperature did not obviously affect the textural parameters of Co₃O₄ samples. The effects of calcination temperature and textural parameters on the supercapacitive behaviors of Co₃O₄ samples were discussed. The results of electrochemical tests showed the following: the capacitance value of the sample decreases slightly with increasing the calcination temperature; the BET surface area is the crucial factor for the specific capacitance value; for mesopore materials, large pore size and high ordering degree of mesopore facilitate ion transfer; and the mesostructure (2D hexagonal structure or 3D Ia3d cubic structure) of mesoporous Co₃O₄ nanoparticles does not obviously affect the specific capacitance value of the samples, but 2D hexagonal mesoporous structure is more advantageous to ion transfer than 3D Ia3d cubic mesoporous structure.Ni(OH)₂ and Co(OH)₂ with special nanostructures were synthesized by an easy hydrothermal method without using any organic additives. Mesoporous NiO and Co₃O₄ were obtained via heat treatment of the hydrates at low temperature. The results of N2 adsorption-desorption analysis indicated that the metal oxides had high BET surface area and two main pore structures. The results of electrochemical tests showed that the mesoporous metal oxides had fine supercapacitive behaviors. The low temperature heat treatment for the hydrates provides a new method for the preparation of metal oxides with mesoporous structures and large BET surface areas.