Study On Biomass-based Porous Materials And Their Application In Supercapacitors

Porous materials have special pore structure and high specific surface area,so they have a wide range of applications in many fields,such as adsorption and supercapacitor.With the increasingly serious problems of energy crisis and environmental pollution,it is of great significance to prepare porous materials using renewable resources.Biomass is the only carbon source in renewable resources,and it is an important precursor of biomass-based porous materials.Using biomass as raw materials to develop porous materials with controllable structure and properties can,not only save cost,but also alleviate the pressure of environment pollution caused by incineration of waste biomass,to achieve the high value utilization of biomass,is one of the main topic in this research field.In the present study,the preparation and characterization of porous materials based on biomass system were studied,such as biomass-based porous carbon materials,biomass based gel and composite gel,and their applications on supercapacitor and adsorption were explored.The existing problems are pointed out,and the future development trend is prospected.The main contributions of this thesis are as follows:1.Biomass-based porous carbon materials were prepared through one step carbonization method.The non-fibrous?corn cob?and fibrous biomass?Bagasse,Ganoderma lucidum residue and Melaleuca?are used as the carbon precursor respectively and KOH as activating agent.The results showed that this method is suitable for different kinds of biomass.Because biomass itself contains natural pore structure to facilitate the entry of activator,we can prepare activated carbon with high performance using only a small amount of activating agent.For example,the prepared porous carbons partially preserve the natural hierarchical structure of corncob biomass and exhibit excellent capacitance performance.A specific capacitance of394.9 F g^-1 in 6 mol L^-1 at a current density of 1 A g^-1 is achieved when the corncob carbon was adopted as the supercapacitor electrode.2.Self-template biomass-based porous carbon materials were prepared though two step carbonization with suitable ratio of activator,activation temperature and heating rate.The fiber biomass?Sugarcane bagasse,Ganoderma lucidum residue and Melaleuca etc.?with natural fiber structure is used as raw material.In this method,we first fixed fiber structure at low temperature and then got pore at high temperature.The porous carbon material prepared by this method has good electrochemical performance,performing good potential application in energy storage.3.Two kinds of carbon materials based on biomass were prepared by two steps carbonization method using nitrogen containing soybean as biomass material.Fluorescent soybean carbon dots?SCDs?with inherent nitrogen-doping were obtained in the first low-temperature carbonization step,while hierarchical porous carbon with an interconnected microstructure was obtained by follow-up high-temperature carbonization with the insoluble residues.This method improves the utilization efficiency of biomass materials greatly,and provides a new idea for the high value utilization of biomass.4.Cellulose aerogels were successfully prepared by sol-gel polymerization using microcrystalline cellulose and dissolved wood pulp as raw materials and ionic liquids as solvents.The synthesized aerogel can be used as an adsorbent to remove contaminants such as dyes,oils,and organic solvents.The surface morphology and physical properties were characterized and compared.Results indicate that the cellulose aerogels with high degrees of polymerization have much better mechanical strength and adsorption properties than the cellulose aerogels with low degrees of polymerization.5.Highly tough cellulose/graphene composite gels were prepared by regenerating the mixture of wood pulp and reduced graphene oxide from their ionic liquid?IL?solution using deionized water as coagulant and vitamin C as the reducing agent.Cellulose/graphene composite gel was prepared by using graphene as an inorganic enhancer.The addition of graphene obviously improved the mechanical properties and thermal stability of the composite gels.Over four times higher compressive Young's modulus was obtained with 0.5wt%doping of graphite oxide?GO?in cellulose.6.Cellulose fiber/graphene composite gels were obtained by ascorbic acid reduction.The cellulose fibers were mixed with graphene oxide in water directly.Graphene would be embedded in the cellulose network or wrapped in cellulose fiber by the self-assembled effect of graphene oxide during reduction,which can prevent the agglomeration of graphene effectively and improve the conductivity and mechanical properties of cellulose/graphene composite porous material.The electrical measurements show the self-assemble composite aerogel has a sheet resistance of 4?/sq.7.In order to improve the conductivity and effective surface area of biomass-based porous carbon material,the graphene was composited with porous carbon.As prepared material was used as electrode material for supercapacitor,showing an improved rate performance and stability.The retention of capacitance is kept as high as 81.6%at a current density of 20 A g^-1.