Coupled Ultrasonication-Milling Synthesis Of Biomassbased Hierarchically Porous Carbon For Energy And Environmental Applications

Porous carbon materials have been widely used in energy storage,adsorption,and catalysis due to their virtues of high specific surface area,porous size,adjustable pore size,electron and heat conductivity,as well as the acid and alkali resistance.Coal,petrochemical products and chemical reagents are often employed as precursor materials to prepare porous carbon,but the unsustainability and high cost restrain their widespread commercial applications.The main components of biomass such as agricultural wastes are cellulose,hemicellulose and lignin.They are widely sourced,renewable and low-cost,and are ideal raw materials for the preparation of porous carbon.Henan is a big agricultural province,which produces a large ammount of non-grain biomass such as corn cob and straw every year.If it can not be effectively utilized,it will bring trouble to agricultural production.Using corn cob and other wastes as raw materials to prepare biomass porous carbon can not only reduce the utilization of fossil resources,but also change waste into treasure.It provides a new way for high-value utilization of agricultural and forestry waste biomass,and has theoretical and practical value.In this paper,for the first time,corn cob,which is abundant and cheap in Henan Province,was used as the raw material to produce hierarchically porous biomass-based carbon materials with high purity and high specific surface area,via the mechanochemical process coupling the ultrasonication and milling treatments.Aiming at to solve the problems of difficulties in removing the impurities?e.g.Si and Al?,low specific surface area and unitary-species of pore structure found for the biomass-based carbon,the ultrasonication and mechanochemistry processing was introduced into the traditional"carbonization-activation"process,so as to efficiently prepare the hierarchically porous carbon with adjustable micro/mesoporous ratio.The XRD,SEM,TEM,XPS,N₂ adsorption-desorption and TG-DSC techniques were used to characterize the compositions and microstructures of the samples.The applications of the carbon materials prepared under the optimized conditions in capacitance energy storage,dye adsorption,heavy metal ion adsorption and non-noble metal electrocatalyst carrier were systematically studied.The main study contents are as follows:?1?The ultrasonication-milling assisted efficient preparation and characterization of high purity porous biomass carbon materials based on corn cob.Superfine modification of corncob carbon was carried out by introducing the coupling mechanochemical effect of ultrasonication-milling for the first time,through which the impurities?such as Si and Al?removing by boiling in NaOH solution was improved.Corncob-based carbon materials with high specific surface area(430-570 m² g^-1)were prepared.The synergistic effect of mechanochemistry,such as ultrasonication and milling,produced superfine carbon particles,and increased the probability of exposure of impurities in carbon particles.On the basis of the carbon materials with high specific surface area,with the appropriate use of the ultrasonication-milling,hierarchically porous carbon materials?UM2h-AC500?with high specific surface area of 2288 m² g^-1,total pore volume of 1.21 cm³ g^-1 and 45%mesoporous biomass were prepared.The effects of ultrasonication,milling and the coupled ultrasonication-milling on the porous carbon pore structure were studied.The results show that the coupling effects of ultrasonication-milling can effectively control the micro/mesoporous ratio in the product.In addition to the pore-forming effect of NaOH,impurities containing Si and Al can be regarded as endogenous templates,which left abundant microporous structure after being removed.?2?The fabrication and energy-storage performance of the corncob-based porous carbon capacitor.The corncob-based carbon material?UM2h-AC500?prepared by the optimized process of ultrasonication-milling was used as the electrode to prepare the capacitor.In aqueous electrolyte(6 mol L^-1),the specific capacitance was as high as465 F g^-1 measure in the three-electrode mode with good rate and cycle stability.The specific capacitance of UM2h-AC500 can reach 135 F g^-1 in organic electrolyte(1 mol L^-1 TEABF₄)when measured in two electrodes mode.The rate performance is good,and the achieved energy density and power density were 25 W h kg^-1 and 2500 W kg^-1,respectively.The comparative study showed that the capacitor performance of porous carbon derived from corncob biomass was significantly higher than that of commercial capacitor carbon YP-50F,either tested in three-or two-electrodes modes.The specific capacitance of porous carbon is obviously affected by ultrasonication-milling process,and the order of influence is ultrasonication-milling>ultrasonication>milling.?3?The performance of the corncob-based porous carbon materials in adsorbing dyes,heavy metal ions and pesticides.The adsorption performance of porous carbon?UM2h-AC500?prepared using the corncob biomass was studied systematically for wastewater containing MB,MO,Cr?VI?,Bentazon and other pollutants.The effects of pH value of the adsorbate solution,dosage of the adsorbent,initial concentration of the adsorbate,adsorption time and temperature on the adsorption performance of the porous carbon were studied.The adsorption isotherm,kinetics,thermodynamics and regeneration properties were analyzed in detail.The results show that the adsorption of MB,MO,Cr?VI?and Bentazon by UM2h-AC500 under 20°C conforms to Langmuir isothermal adsorption model,and the maximum single-layer adsorption capacity is2570,795,760 and 1348 mg g^-1,respectively.The comparisons showed that the adsorption properties of the corncob based porous carbon was superior to that of the commercial carbon SAC-03.?4?The preparation of the non-noble metal electrocatalysts on the corncob-based porous carbon and their electrocatalytic performance of oxygen reduction reaction?ORR?.The corncob-based porous carbon UM2h-AC800 synthesized under the assistance of ultrasonication-milling with high purity and high specific surface was used as carrier for non-noble metal elements such as Fe,Co and Ni to construct carbon-based non-noble metal catalysts.The effects of the catalyst loading amount of single,two or three components,reaction time,the gas flow rate and the adding order of cation precursors on the ORR catalytic performance were studied.The results showed that the1Fe₁Co_0.5@C-20NH₃-800 catalyst exhibited comparable ORR electrocatalytic property to the commercial Pt/C in an alkaline electrolyte:The measured onset potential was0.95 V vs.RHE,the half-wave potential was 0.85 V vs.RHE,the current density was4.66 mA cm^-2,and the current retention after testing for 1800 s was 91%,which is higher than that of Pt/C?72%?under the same conditions.The catalyst has good methanol tolerance.The specific surface area of 1Fe₁Co_0.5@C-20NH₃-800 was as high as 2458 m² g^-1,and the specific surface area of micropore can reach 1880 m² g^-1.The abundant micropore provides a large number of catalytic active sites,which improves the electrocatalytic performance of ORR.