The Porous Carbon Derived From Biomass For Gas Adsorption And Supercapacitors

Porous carbon materials can be widely applied in gas adsorption,chemical energy storage,catalyst carrier and other fields,because of their high specific surface area,well-developed pore structure,good electrical conductivity,low cost and excellent physicochemical stability.There are many precursors for the preparation of porous carbon materials,but biomass is regarded as a promising carbonaceous precursor,due to the characteristics of huge amount,renewable,environmental friendly and low cost.Therefore,the preparation of porous carbon materials with biomass can reduce the cost and realize the effective utilization of biomass resources.In this paper,we report the facile synthesis of porous carbon materials with a large surface area that is derived from bamboo shoot shells and garlic peels.Further regulating the structure of porous carbon,the porous carbon can be more suitable for CO₂ adsorption and supercapacitor,and the influence of CO₂ adsorption and capacitive performance on porous carbon structure were also studied.The main research contents of this paper are as follows:First,we report a facile method to synthesize N-doped hierarchical carbons from hydrothermal carbonization followed by a mild KOH activation,using agricultural biowastes of bamboo shoot shells as raw materials and melamine as nitrogen source.The porous carbon without N element has high mesoporous ratio,certain amount of micropores and suitable specific surface area,showing the CO₂ uptake of up to 5.23and 3.29 mmol/g for 25 ^oC and 0 ^oC at 1 bar.N-doped porous carbons showing the highest surface areas of 3350 m²/g with main mesopores centering at 2.8 nm.The carbons used as electrodes for supercapacitor showed excellent capacitive performance with capacitance of 209 F/g in 6 M KOH electrolytes at 0.5 A/g,and remained to be 188 F/g even at high current density of 10 A/g.In addition,the as-assembled supercapacitor also exhibited superior cycling stability with capacity retention of 95%at 10 A/g even after 10000 cycles.Second,garlic peels as one of typical agricultural biowastes were chemically activated by KOH to obtain porous carbons and the porous carbons possesses the surface areas is highly up to 2893 m²/g and the pore volumes up to 0.68 cm³/g.The results indicated that the main factor for the CO₂ capture on porous carbons is the microporosity not the traditionally believed surface area or pore volume,and the increase in microporosity for biomass carbons with special pore size and moderate surface area will result in the enhancement of CO2 uptakes.Porous carbons from garlic peels shows the high CO₂ uptake of 4.10 mmol/g for 25 ^oC at 1 bar.This result has important implications for the design and synthesis of biomass porous carbon and the preparation of efficient CO₂ adsorbents from common agricultural waste resources.Finally,considering the advantages of hydrothermal carbonation,we still take the agricultural waste garlic peels as the carbon source,and the resulting porous carbon with a specific surface area of 941 m²/g through hydrothermal carbonation and KOH activation.Although its specific surface area is not high,the microporosity is up to98.04%,showing the high CO₂ uptake of 4.22 mmol/g for 25 ^oC at 1 bar.The CO₂adsorption capacity are higher than that of the directly activated activated garlic peels porous carbons,indicating that the prepared porous carbon can be a good CO₂adsorption material.