Experimental Study On Organic Potassium Salt-assisted One-pot Synthesis Of Bio-derived Porous Carbon

The recycling of biomass resources is an important subject for the sustainable development of mankind,and it is of great significance to solve the current energy and environment issues.The preparation of bio-derived porous carbon by simple and easy thermochemical conversion is undoubtedly one of the best solutions.The recent researches about preparations of bio-derived porous carbon mostly focused on the selection of raw material and subsequent etching process whereas less concern has been taken on the growth mechanism of carbon skeleton and its influence on subsequent etching.Extensively thinking through the formation of carbon skeleton together with etching reaction,this study attempts to explore the method for preparing porous carbon with high raw-material flexibility,high pore-generation efficiency and simple implementation,and to present an effective pore structure adjustment strategy.The main contents and conclusions are as follows:First,starting with self activation,we explored the effect of heating rate,carrier gas flow and intrinsic inorganics on the prepared porous carbon via modulating carbon skeleton growth and pore formation.For self-activating preparation of porous carbon through enhanced etching reaction,the increase of heating rate is favorable for the formation of amorphous carbon skeleton and pore widening,thus mesoporous volume increases and micropores decline.Enhancing etching reaction by lowering carrier gas flow,the increase of heating rate facilitates formation of defects and pores.For the preparation of porous carbon by etching and template effect of inorganic components,the heating rate weakens the etching and template perfomance of inorganics,thus the micro-and mesoporous volume reduce.For the biomass-derived organic salt,the increase of heating rate facilitates the formation of small-sized pores,and also inhibites pore formation;Second,we explored the unique pore-forming characteristics and behavior of typical organic potassium salt.Organic potassium salt has a similar activation performance to KOH under one-pot method treatment,while the organic salt can produce narrow mesopores with more concentrated distribution and less template-induced pores;For different AAEM acetates,potassium salts mainly form microporous pores,while sodium,magnesium and calcium salts perform poor etching capability,mainly exhibiting a large mesoporous template effect.The carbonization process under the addition of potassium acetate can be divided into three stages:in stage of 100⁴00°C,molten potassium acetate penetrates into the particles,and the dispersibility of potassium acetate in char is improved by hydrogen bonding.Potassium acetate decomposes in the 400⁶00°C stage to form a new carbon skeleton,covering the surface of char,and generating potassium species to initially etch the carbon skeleton and produce micropores.Above 600°C,the main potassium species K₂CO₃ further etches the carbon skeleton,creating new pores and further widening.Based on the above mechanism,potassium acetate performs excellent activation capability for main components of biomass,and obtained porous carbon is used as active material of supercapacitor electrode,the specific capacitance can reach 200²40 F/g at a current density of 1 A/g;Third,we studied the effect of various preparation conditions on the pore structure of porous carbon prepared by potassium acetate assisted one-pot method,and the influnce of biomass characteristics on the pore structure of porous carbon.Increasing the final temperature of carbonization to 900°C will lead to pore collapse,while excessive potassium acetate addition will reduce the etching effect.Increase of heating rate will lower the yield,but the pore structure is significantly developed.High carrier gas flow rate is favorable to the development of the pore structure.On the other hand,Increase of heating rate and flow rate also promote the formation of amorphous carbon skeleton.The specific surface area and pore volume of the porous carbon can reach 2265.59 m²/g and 1.10 cm³/g at high heating rate and flow rate.Potassium acetate showed excellent activation effect on various kinds of lignocellulosic biomass.The specific surface area and pore volume of porous carbon obtained from different biomass are in the range of 1822²358 m²/g and 0.97¹.41 cm³/g.Hemicellulose is beneficial to pore widening.The presence of inorganic template components results in significant development of large mesopores.This method is also applicable to microalgae and polysaccharide biomass,but not to chitosan.