Controllable Synthesis Of Porous Carbon Nanospheres

Porous carbon nanospheres have important applications in the fields of adsorption,catalysis,energy storage,environment and life medicine due to their symmetric structure,high specific surface area,tunable pore structure,resistance to high temperature and water vapor environment,and good chemical stability.In response to the differentiation of application requirements,it is a long-term and unremitting pursuit of researchers to design the structure design,targeted synthesis and functional integration of porous carbon nanospheres by chemically oriented design of molecular assembly processes.The key to the synthesis of porous carbon nanospheres is the adjustment of structure and efficient preparation,and the difficulties are focused on the precise regulation of particle size distribution(PSD),morphology,and structure at the nanoscale.And it is still a great challenge to design and construct the required structures according to the needs of practical applications.Based on the principle of molecular assembly,a series of porous carbon iiinanospheres were synthesized by the molecular interaction and the confinement effect.And the PSD,surface roughness and graphitization of porous carbon nanospheres were investigated and precisely regulated.Specifically,this thesis includes the following three parts:(1)In nanoscale,there are problems such as limited regulation of the PSD and poor monodispersity due to heterogeneous nucleation of carbon nanosphere precursors,Oswald ripening and higher surface free energy.Based on the nucleation and growth theory,a kinetic regulation method is developed to regulate the PSD of monodisperse carbon nanospheres.The method uses benzoxazine-based polymer spheres as precursors and regulates the surface tension of the solution during nucleation growth by varying the concentration of surfactant F127(CF127),which in turn regulates the nucleation rate of the polymer spheres and achieves the regulation of the PSD of the monodisperse carbon nanospheres.The prepared carbon nanospheres have a uniform size and morphology,and the size of the carbon spheres is precisely regulated in the range of 41-114 nm.The mechanism of CF127 on the regulation of PSD and monodispersity of carbon spheres is investigated:(ⅰ)CF127 regulates the surface tension and the nucleation rate of polymer nanospheres,which ultimately regulates the size of polymer nanospheres.(ⅱ)F127 molecule can not only stabilize the nucleated polymer spheres to avoid the free energy-driven agglomeration.(ⅲ)Suitable CF127 can lead to lower viscosity of the solution,avoiding high viscosity to limit the diffusion rate of the monomer and the migration of the particles,keeping homogeneous nucleation and growth.The kinetic regulation method provides experimental support and theoretical basis for the PSD regulation of other monodisperse nanomaterials.(2)The carbon nanospheres suffer from agglomeration and uncontrollable morphology during direct pyrolysis at high temperatures.Based on the electrostatic interaction of heterogeneously charged colloids,a surface charge-driven interfacial self-assembly method is developed to prepare carbon nanospheres with rough surfaces(RCNS).The RCNS prepared by this method have tunable surface roughness.abundant surface mesopores and good water dispersibility.The mechanism of surface roughness regulation of RCNS is investigated.The SiO2 spheres construct discrete confined structures on the surface of PNS through electrostatic attraction;SiO2 spheres provide deposition sites for volatile carbon species during the pyrolysis process;the higher the pyrolysis temperature,the more pronounced the deposition effect and the higher the surface roughness of RCNS after silica removal.The presence of SiO2 avoids sintering of adjacent RCNS under high temperature conditions,resulting in good dispersity of RCNS.A coating model was developed to achieve precise regulation of the surface roughness of RCNS by adjusting the surface coverage of PNS and the pyrolysis temperature.Such charge-driven interfacial self-assembly method provides experimental support and theoretical basis for the surface roughness regulation of other types of carbon nanomaterials.(3)Common graphitization methods for carbon spheres suffer from uncontrollable graphitization structure and underdeveloped pores.Based on surface charge-driven interfacial self-assembly,an outside-in catalytic graphitization method was developed to prepare graphitized carbon nanospheres(GPCSs).The GPCSs prepared by this method have tunable graphitization,well-developed pores,uniform morphology and good dispersion in both water and ethanol.The mechanism of outside-in catalytic graphitization is investigated.The electrostatic self-assembly between oppositely charged monodisperse polymer spheres(PNS)and nickel-magnesium-aluminium hydrotalcite nanosheets(NiMgAl-LDH).The generation of nickel nanoparticles on the outer surface of the carbon spheres.The dissolution and reprecipitation of nickel particles drive the continuous migration of nickel particles from the outer surface to the inside,accompanied by a catalytic graphitization process.The internal graphitisation of the GPCSs is precisely regulated by varying the charge ratio,pyrolysis time and pyrolysis temperature.The higher the charge ratio,the longer the pyrolysis time and the higher the pyrolysis temperature,the higher the Graphitization of GPCSs.NiMgAl-LDH not only provides nickel particles for the catalytic Graphitization,but also can overcome the agglomeration.Such outside-in catalytic graphitization method provides a theoretical basis for the precise regulation of the graphitization of other morphological carbon materials,and provides new ideas for the design and synthesis of graphitized carbon nanomaterials.