Mechanism Elucidation of Nitrogen in Functional Porous Carbon Materials Prepared by Pyrolysis of Organic Solid Waste
Author:Cheng Bin Hai
Supervisor:jiang hong zeng jian xiong
The excessive consumption of fossil fuels cause energy crisis and environmental problems.In recent years,developing new sustainable clean energy has become a research hotspot,among which,obtaining resources from renewable biomass is a promising way.In addition,the disposal of a large number of organic solid wastes has cause a lot of environmental problems.However,since the high content of organic matter in the organic solid waste,it has the potential of resource recycling.On the one hand,as a sustainable precursor of carbon materials,biochar can be functionalized to obtain functional porous carbon materials,which are widely used in energy storage and conversion,catalysis,environmental remediation and other aspects.On the other hand,by means of pyrolysis,C can be largely fixed in biochar to reduce carbon emissions.In addition,heteroatoms(N,P,O,etc.)contained in biomass can be used as endogenous dopants to improve the performance of final carbon materials,and also can be largely fixed in carbon materials to prevent secondary pollution,such as the emission of NOx.However,the effect of N and P on the properties of the prepared porous carbon during pyrolysis is not clear.The main contents and results of this thesis are as follows:1.Phosphamide resin is synthesized,wherein the special N-P structure is chemically bonded as the nodes for linking the monomers into polymers.The transformation of N and P in the pyrolysis of phosphamide resin and its effect on the formation of porous carbon material are studied.The N and P in the PAR framework can be transformed to NH4H2PO4 during carbonization.The well-distributed NH4H2PO4 acts as the in situ activating agent to form micro/mesopores,which has better effect on activation than post-added NH4H2PO4.The as-prepared PCMPAR has a high SS A of 2,620 m2 g-1 and pore volume of 1.49 cm3 g-1 and fine micro/mesoporous structure.Electrochemical tests show that PCMPAR has approximately rectangular CV curves and triangular GCD profiles.This finding indicates that PCMPAR is a typical EDLC electrode.The PCMPAR exhibits a specific capacitance of 440 F g-1 at 0.5 A g-1 and 278 F g-1 at 20 A g-1,as well as high stability(retention of 93%over 10,000 cycles).The high capacitance retention at high charge-discharge rates signifies that PCMPAR has fine micro/mesoporous structure for the transport of electrolyte ions.The results illustrate that the N and P in the structure of polymers can improve the formation of porosity under the appropriate pyrolysis conditions.2.Porous carbon materials(PCMs)are prepared using corn gluten meal(CGM)waste by fast pyrolysis combined with chemical activation by KOH,and the capacitance performance of the resulting PCMs was investigated.The specific capacitance of PCMP500(fast pyrolysis at 500℃)is 488 F g-1 at a current density of 0.5 A g-1,which is better than those of PCMs obtained at other pyrolytic temperatures(PCMp300 and PCMp400).Under the same conditions,the PCMs prepared by the HTC process exhibit relatively lower supercapacitance performance,i.e.,PCMH250(HTC at 250℃)is 433 F g-1.The high performance of PCMP500 is mainly attributed to the high specific surface area and pore structure,which depends on the thermal treatment methods.Furthermore,the doped N can also change the wettability and conductivity of the carbon materials,and participate in Faraday reaction,so as to improve the capacitance performance.3.The CO2 produced in the pyrolysis process will increase the greenhouse gas effect.The cycloaddition of CO2 to epoxide is an effective method for CO2 fixation and recycling.Currently,the mainly used metal-contain homogeneous catalyst for cycloaddition of CO2 could bring out metal leaching problem,which is harmful to the environment.Herein,a metal-free N/O co-doped carbon material(N/O@C-cO2)is successfully synthesized from directly pyrolysing chitosan under CO2 atmosphere.The doped nitrogen comes from the-NH2 in chitosan molecules,while the doped oxygen is derived from the co-effect of-OH in chitosan and CO2 pyrolysis atmosphere.N/O@C-CO2 shows enhanced solid acid-base properties,measured by NH3-TPD and CO2-TPD.This material is found to be efficient in the cycloaddition of CO2 to epoxides without adding co-catalyst and solvent.Control experiments of CO2 cycloaddition reaction using chitosan derived material under Ar atmosphere and cellulose derived material under CO2 atmosphere reveal that the doped nitrogen and oxygen exhibit synergistic effect in cycloaddition of CO2 to epoxides.Furthermore,we demonstrate that the catalytic efficiency can be changed through regulating the content of doped nitrogen and oxygen.A mechanism is proposed that CO2 and epoxide molecules are adsorbed and activated by the integrated acid-base active sites,which are provided by the functional nitrogen and oxygen groups and high specific surface area of the carbon material.The high activity and recyclability of the N/O@C-CO2 in the cycloaddition reaction of epoxides to CO2 under the mild reaction condition might offer an opportunity for designing an efficient heterogeneous catalyst for chemical fixation of CO2 in the future.