| Carbon nanospheres, including solid/hollow spheres and core-shell spheres, have attracted considerable attention owing to their distinctive properties such as high surface areas, good wearability and isotropy, which show great potential for applications in adsorption, catalysis, drug delivery, energy storage and conversion. Moreover, the carbon spheres can be used as block units to assemble monolith materials and the space between the spheres can act as the channels for the transport of substances. Up to date, there are many reports about the synthesis of carbon nanospheres. However, the practical applications of carbon spheres were limited due to their lack in porosity diversity and weak adsorption capacity of the hollow cavity. In order to solve these issues, this thesis is focused on the fabrication and microstructure manipulation of carbon nanospheres. The strategy is mainly based on the controlled synthesis of diverse polymer nanospheres through the weak interactions of the molecules followed by the confined nanospace pyrolysis in core-shell nanostructures. Specifically, the work includes the following aspects.(1) We have developed a novel method of manipulating the microstructure (cavity volume and porosity) of the hollow carbon nanospheres based on the self-activation mechanism in a confined nanospace. The synthesis principle of hollow polymer nanospheres was based on the weak acid-base interaction (-COO-/NH4+/-COO-) induced assembly using2,4-Dihydroxybenzoic acid and formaldehyde as the precursor and ammonia as the catalyst. Subsequently, hollow polymer nanospheres were coated with a silica shell through the typical sol-gel process to create core-shell structures. Hollow carbon nanospheres were obtained after confined nanospace pyrolysis and SiO2removal processes. The study found that the hollow core volume of the sample via confined pyrolysis was～25times larger than that of the carbon obtained by direct pyrolysis of polymer analogue. Meanwhile, the specific surface area of hollow carbon spheres was increased from560m2g-1to787m2g-1. The hollow carbon nanospheres were then used as adsorbent for the removal of Cr(VI) in an aqueous solution. The Cr(VI) in100mL solution with concentration of10ppm was removed completely, which is better than that of similar materials reported in literature.(2) Based on the confined effect of core-shell structure, we prepared large-pore (pore size～10.8nm) mesoporous carbon nanospheres. The mesoporous polymer nanospheres were synthesized through the hydrothermal method using resorcinol and hexamethylene tetramine (HMT) as the monomers, surfactant Pluronic F127as structural directing agent. Subsequently, mesoporous polymer nanospheres were coated with silica shells. Large-pore mesoporous carbon nanospheres with a pore size of10.8nm were obtained through confined nanospace pyrolysis followed by SiO2removal processes. The mesoporous carbon spheres show a very high BET specific surface area of840m2g-1and a total pore volume of0.86cm3g-1. While, the pore size of carbon spheres obtained by direct pyrolysis of polymer spheres is approximately concentrated on1.0nm. This result indicated that the confined nanospace pyrolysis avoided the pores shrink phenomenon during traditional pyrolysis of mesoporous polymers. The obtained mesoporous carbon spheres were used as electrode for supercapacitor and showed an excellent suitability for high-rate operation. A slightly decrease in the capacitance is observed when current density is increased from10A g-1to50A g-1and the capacitances are103A g-1and96A g-1, respectively, corresponding to a capacity retention of93%.(3) A new type of core-shell nanocarbon with tertiary structure was synthesized. The synthesis started from the synthesis of solid polymer spheres with size of ca.370nm using resorcinol and formaldehyde as precursor and hexamethylenediamine as the catalyst. Then, the core-shell nanocarbon was obtained after confined nanospace pyrolysis and the silica removal process. The obtained carbon nanosphere showed a three-tier structure:a mesoporous shell, a hollow cavity, and a microporous core. The microporous carbon core was anchored to the mesoporous carbon shell. The BET surface area of the nanocarbons pyrolyzed at900℃was up to1038m2g-1. Importantly, the obtained yolk-shell nanocarbons exhibit ultrahigh thermal stability up to1200℃. By taking full advantages of the core-shell carbons, the obtained carbon nanosphres were chosen as carbon host to loading sulfur for Li-S batteries application. The electrode gave superior electrochemical performance with high specific capacity of615mA h g-1at a0.5C rate after100cycles, corresponding to a capacity retention of93%, and excellent cycling stability and rate capability, ca.457mA h g-1at a rate of2.0C. |
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