Study On Templating Synthesis And Electrochemical Performance Of Lignin-derived Mesoporous Carbon

As one of the three typical recalcitrant components of lignocellulosic renewable biomass,lignin possesses vast reserves and a high carbon content over 50%,becoming a promising ideal precursors for mesoporous carbons.Amongst all mesoporous carbons preparation methods,template route feathers an excellent performance on tailoring the pore texture precisely.However,when fabricating mesoporous carbons separately using porous silica templates or amphiphilic surfactant templates,the complicated amorphous structure of industrial lignin can induce the pore collapse,resulting in a random pore structures and poor porosity.Considering the structural properties of lignin molecule,this dissertation describes the synthesis of lignin-derived meso-structured carbons by employing nano-sized MgO and Pluronic F127 as templates,with technological conditions and electrochemical performance as supercapacitor electrode materials systematically investigated.After that,thermochemical behaviors of all components in precursor composite were explored during carbonization with dual-template route.Finally,lignin-derived mesoporous carbons were further modified by physical/chemical activation so as to improve the capacitance.The followed summarize main research contents and results of this dissertation.?1?Synthesis and electrochemical performance of lignin-derived mesoporous carbons via template route Using residual lignin in the wheat straw pulping black liquor as carbon precursor,mesoporous carbons were synthesized via dual-template route,with technological conditions systematically investigated,such as functions of templates,precursors mixing ratios,and ways to exsiccate precursor composites.MgO nano-particles functioned as substrates and main template by a space occupying effect,while Pluronic F127 worked as soft template as well as dispersant preventing the agglomeration of Mg²⁺.The specific surface area and pore volume of as-made mesoporous carbons can reach 712 m²/g and 0.90 cm³/g with dominating pore width of 9 nm and mesopore content over 83%.Besides,the optimal carbon exhibited a specific capacitance of 186.3 F/g,with a high retention of 93.4%after 5 000 cycles.?2?Study on thermochemical behavior in preparing lignin-derived mesoporous carbons via template route.Pyrolysis products and thermochemical behavior of precursor composite were investigated in real time by simulating the carbonization process by TG-FTIR-MS in combination with FTIR characterization of chars at different carbonization stages.Research results indicated that almost no char was formed after the pyrolysis of templates,and lignin was the only carbon precursor.Besides,pyrolysis products mainly consisted of small molecules like CO,H₂O,CO₂,methane,acetaldehyde,etc,and some transition state fragment ions including C₂^+·,O^+·,CH₂^+·,C₂H₆^+·,C₃H₆⁺,etc.Besides,with carbonization temperature increasing,aliphatic C–C bond and C–O bonds ruptured firstly,then the pyrolysis of F127 and Mg?CH₃COO?₂.4H₂O was completed.Meanwhile,the C–H,C=C and C–C bonds that originally linked with benzene ring in lignin began to fracture,followed by the cracking of benzene ring after 600?.Finally,the pyrolysis of precursor composite was almost completed after 800? with oxygen-containing functionalities left on the surface of char.?3?Study on physical/chemical activation of lignin-derived mesoporous carbons and corresponding capacitance performance For the purpose of meeting the rapid ions transportation,lignin-derived mesoporous carbons were further activated by employing CO₂ and KOH as activation agents,producing hierarchical porous carbons with pore sizes of 0.8,1.2,and 10 nm,simultaneously.Moreover,charge storage capability was significantly enhanced with the increasing specific surface area.During CO₂ activation,the carbon with 46.4%burn off degree exhibited a specific surface area and pore volume of 1 945 m²/g and 2.47 cm³/g,almost 3 times as large as those of mesoporous carbon without activation,and corresponding specific capacitance reached 320.9 F/g.While the specific surface area and pore volume of carbon with 200%KOH loading in precursor reached1 490 m²/g and 1.32 cm³/g,respectively,with a higher specific capacitance of 350.1 F/g.