Study On Surface Grapheneization And Properties Of Carbon Materials Converted From Organic Precursors

The research on supercapacitors as energy storage devices and wastewater adsorption treatment are important for green sustainable development,both of which require high specific surface area and appropriate pore distribution.Activated carbon obtained from organic precursor has a large specific surface area,but the pore structure is relatively simple,and the preparation process of carbonization and activation is cumbersome.The use of graphene with active edge as the adsorption site can effectively increase the adsorption performance of the material.However,the graphene sheets are easy to agglomerate.Resultantly,the specific surface area and edge structure could not be fully utilized in practical applications.In view of the above problem,in this thesis,a novel carbon material with vertical graphene sheets on surface is prepared by carbonizing organic precursors in NH3,which possesses high specific surface area and wide pore size distribution.Effects of different parameters such as the type of precursor,carbonization atmosphere,carbonization temperature,and carbonization time on the surface graphenization have been investigated.By comparing carbonization of coconut shell,melamine foam,and polyacrylonitrile（PAN）foam in ammonia gas,it was found that the carbon material converted from the PAN foam has more graphene sheets on the surface and possesses the largest specific surface area.By comparison,after carbonizing the PAN foam in argon,the obtained carbon material has a smooth surface.With respect to the carbonization temperatures（800-1200 °C）and holding time（30-240 min）,as the temperature and the holding time increase,the surface vertical graphene structure of the carbon material increases first and then decreases.Under the optimized carbonization parameters of 1100 °C and 120 min holding time,high density vertical graphene structures are obtained on the surface.However,if the temperature is increased or the holding time is extended further,the surface graphene structure is destroyed due to over-etching.The carbon material obtained under the above optimal conditions has a high specific surface area of 1944.7 m²/g,a pore volume of 1.3 cm3/g,and a wide pore size distribution with peaks around 0.6,1.7,and 3.5 nm.The PAN-derived carbon material was used as the electrode material to investigate the influence of the surface graphene structure and pore size distribution on the performance of the electric double layer capacitor.In 6 mol/L potassium hydroxide（KOH）electrolyte,organic electrolyte tetraethylammonium tetrafluoroborate（TEABF₄）,1-ethyl-3-methylimidazolium tetra fluoroboric acid（EMIMBF₄）and trimethyl in propyl ammonium bis-trifluoro methane sulfonimide（TMPTFSI）,with increasing the ionic radius of the electrolyte,the transfer resistance between the material and the electrolyte increases,and the specific capacitance differs greatly.The carbon materials from PAN carbonized at 1100 °C for 120 min were used as the electrode materials to prepare supercapacitors.In TMPTFSI electrolyte,the voltage working window can reach 4.0 V,the specific capacitance is 123.5 F/g,and the energy density is 68.6 Wh/kg,which is better than most carbon materials.The PAN-derived carbon materials obtained under the above optimal conditions are investigated as adsorbent materials.The adsorption capacity of oils and organic solvents such as vacuum pump oil and n-hexane can reach 6-8 times of its own weight.The maximum adsorption capacity for methylene blue dye is 961.3 mg/g.The maximum adsorption capacities of Cu（Ⅱ）,Pb（Ⅱ）,and Cd（Ⅱ）ions are 578.1,319.5,and 127.9 mg/g,respectively.