Controlled Synthesis Of Monodisperse Hierarchical Porous Nano-carbon Spheres And Their Applications

Owing to the unique features such as high surface area,tunable porosity and strong skeleton rigidity,porous materials are tremendously useful in the fields of energy storage and conversion,adsorption,catalysis,separation,biomedicine,sensors,etc.According to the size of pore,porous materials can be divided into three types:microporous materials?pore diameter<2nm?,mesoporous materials?2nm<pore diameter<50nm?and macroporous materials?pore diameter>50nm?.As is known to all,micropore provides a large surface area,a high porosity and a narrow size distribution,while the existence of mesoporous and macroporous pores can increase accessibility of the microporous surface by enhanced diffusion,resulting in increasing overall efficiency.So a particular attention has been focused on hierarchically porous materials,which contain pores across multiple length scales from micro-to meso-and macropores.Hierarchically porous carbon materials?HPCs?is an important kind of hierarchically porous materials.In recent years,a large number of achievements have been made in synthesis of well-defined HPCs.Although hierarchically porous carbons have been successfully prepared through many approaches,the described methods are too much dependent on the templating methods,in while the synthesis and removal of the templates are severe and harmful to the environment.In addition,by far,it is still difficult to adjust and control the pore size distribution for HPCs,while most HPCs obtained are monolithic materials and have no ordered morphology,which restricts their properties and limits their applications in many significant fields.Take together,a facile method to synthesize HPCs with controlled porosity and ordered morphology are highly desirable and challenging.This thesis proposes a new method to prepare monodisperse HPCs by using the vesicle bilayers as templates.In the past decade,the main research of our group is focused on polymer self-assembly.So,can we use the self-assembly method to prepare HPCs?As we all know,hyperbranched polymers can form vesicles by self-assembly in water.The thickness of the vesicles'bilayer is uniform although the size of the vesicles is polydisperse.Thus,uniform polymer nanoparticles can be obtained by using the bilayers as templates and controlling intra-vesicular free-radical polymerization of the monomers.Then the polymer nanoparticles can be hyper-crosslinked to get microporous hypercrosslinking polymer nanoparticles.At last,hypercrosslinking polymer nanoparticles can be carbonized to obtain HPCs.Based on this idea,two kinds of HPCs have been achieved by utilizing the vesicles'bilayer templating method and their performances of CO₂ adsorption and supercapacitor were preliminary studied in this thesis.The specific research contents and conclusions are summerized as bellow:1.Controlled synthesis of monodisperse small-sized hierarchical porous carbon spheres based on VBC and their applicationsBy using the bilayers of vesicles formed by the self-assembly of amphiphilic hyperbranched block copolymers in water as templates and vinylbenzyl chloride?VBC?as well as divinyl benzene?DVB?as monomers,monodisperse?PDI=0.049?poly?vinylbenzyl chloride??PV?with the size of 61 nm were obtained.And then utilized hypercrosslinking technology,monodisperse hypercrosslinking poly?vinylbenzyl chloride??HPV?nanoparticles were obtained.Nitrogen adsorption-desorption isotherms measurement indicates that the BET surface area(S_BET)of HPV nanoparticles is up to 1362 m² g^-1,the micropore surface area(S_micro)is 1067 m² g^-1,the ratio of micropore area(S_micro/S_BET)is 78.34% and the pore volume(V_total)is 0.72 cm³ g^-1,the micropore volume(V_micro) is 0.55cm³ g^-1,the ratio of V_microicro 76%.This extremely high ratio of micropore is very beneficial for CO₂ adsorption.The CO₂ adsorption measurement implies that the obtained HPV nanoparticles show the highest CO₂adsorption ability(2.87 mmol g^-1)among“Davankov Resins”.At last,HPV nanoparticles were carbonized to obtain HPCs?HPC_V?at 900 ?.Nitrogen adsorption-desorption isotherms measurement was taken to demonstrate the HPC_V's surface area and porosity parameters,the S_BET is922 m² g^-1,S_micro is 684 m² g^-1 and V_total is 0.69 cm³ g^-1,V_micro is 0.38 cm³g^-1.The ratio of S_micro and V_micro descreased to 74% and 69% compared with HPV nanoparticles.It implied that there formed some mesopores and macropores during the carbonization resulting in the decrease of S_BET and the ratio of S_micro and V_micro,and increase of the ratio of external surface area and volume.But the CO₂ adsorption capacity was incresead to4.61mmol g^-1?273K,1bar?and 3.41 mmol g^-1?298K,1bar?.It indicated that the mesopores or macropores are beneficial for CO₂ adsorption.At last,in order to improve the conductivity of the HPCs,melamine was mixed with HPV nanoparticles to obtain N-doped hierarchically porous carbon materials?NHPC_V?.The galvanostatic charge-discharge curves indicated that specific capacitance is 176.9 F g^-1,which is much higher than HPC_V.2.Controlled synthesis and application of monodisperse small-sized hierarchical porous carbon spheres based on VBC/MMAA series of monodisperse poly?vinylbenzyl chloride-co-methyl methacrylate??PVM?nanoparticles were prepared according to the ratio of VBC,DVB and methyl methacrylate?MMA??VBC/DVB=40,VBC/MMA=5,4,3,2,1?via vesicle bilayer templating method,and the size of them ranged from 22 to 52 nm.And then the hypercrosslinking poly?vinylbenzyl chloride-co-methyl methacrylate??HPVM?nanoparticles were obtained through hypercrosslinking.Nitrogen adsorption-desorption isotherms measurement demonstrated that the S_BETET of HPVM nanoparticles was up to ca.1500 m² g^-1 and all of them possessed many micropores.As the ratio of MMA/VBC increased,the S_BET and V_total both decreased,but the ratio of S_micro and V_microicro were almost the same which indicated that the introduction of MMA had no influence on hypercrosslinking.After carbonization,the PMMA in the HPVMs were degraded and became mesopores while PVBC became the microporous carbon skeleton,and thus the monodisperse hierarchically porous carbon materials based on VBC/MMA(HPC_VM)were achieved.As the ratio of MMA/VBC increased,the ratio of micropore decreased gradually,while the mesopore and macropore increased.When VBC/MMA=5 and 4,there were still many micropores;when VBC/MMA=3 and 2,there came out many mesopores and macropores;when VBC/MMA=1,the carbon skeleton collapsed completely to get almost pore-free materials,which indicated that controlled synthesis of hierarchically porous carbon materials was realized.