Preparation And Properties Of Lignin-based Carbon Nanofibers

Lignin,as the second most abundant natural biomass feedstock,was considered as a good carbonaceous precursor for preparing carbon materials owing to its low price,abundant sources and high carbon content.The Lignin-based carbon fibers（LCFs）usually appeared obvious pore structures,resulting low mechanical properties,which indicated that the oxygen structure units of Lignin could acquire the functional LCFs with pore structure and surface functional group.Therefore,in this paper,the Lignin-based carbon nanofibers（LCNFs）were prepared by using the Lignin and polyacrylonitrile（PAN）as raw materials through the electrospinning,stabilization and carbonization processes.The corresponding nanofibers were characterized by Thermogravimetric analysis（TG）,Fourier transform infrared spectroscopy（FT-IR）,Scanning electron microscope（SEM）,N₂ adsorption,X-ray photoelectron spectroscopy（XPS）and Electron spin-resonance spectroscopy（ESR）.It is aimed to reveal the influence of Lignin units on the porous texture and surface chemistry of LCNFs,to inverstigate the stabilization behavior of Lignin-based nanofibers,and to analysis the electrochemical properties of LCNFs.The results proved that the oxygen structre units of Lignin were helpful to prepare the carbon fibers with structural and functional integration feature,and the LCNFs as the self-supporting electrode material showed excellent perfromace for supercapacitors.The main contents and conclusions of this thesis were as follows:（1）The as-spun fibers with the diameter aobut 196 nm were uniform when the Lignin content was less than 20%.The newly formed N-O group between Lignin and PAN was helpful to improve the thremostability of fibers and to reduce the heat release during the stabilization and carbonization process.The LP20-CF had high surface areas of 389 m²/g,and possessed interconnected multidimension network with fiber bonding.Moreover,LP20-CF contained more oxygen functional groups of C=O,COOR and nitrogen functional groups of N-6,N-Q than the pristine CFs.（2）The introduced Lignin could be beneficial to reduce the cyclization degree of nanofibers,accomplishing their stabilization process at a lower temperature.Meanwhile,the introduced Lignin could be helpful to attenuate the exothermal reaction of PAN,accomplishing their stabilization process at a higher heating rate.In the low stabilization temperature stage（<240℃）,the abundant oxygen-containing groups in Lignin acted as a free-radical scaveenger to slow down the ionic cyclization rate of fibers.In the high stabilization temperature stage（>260℃）,the carboxyl in Lignin served as an initiating agent to accelerate the free radical cyclization rate of nanofibers.（3）The LCNFs had a high specific area and abundant oxygen and nitrogen functional groups without any activation.The LP20-CF800 electrode exhibited excelletnt capactive performances with a special capactive of 167 F/g at currnt density of 0.5A/g and a high rate performance of 74%at currnt density of 5A/g.In summary,the carbon nanofibers with developed porosity and abundant surface chemistry could prepared with Lignin.Therefore,this work not only realized the development of the Lignin products with high value-added,but also provided a feasible routes for designing the structural and functional integrated materials.