Activated carbons prepared by the KOH activation of a hydrochar from garlic peel and their CO2 adsorption performance
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摘要: 以大蒜皮为碳源，先采用水热法制备炭前驱体，再经KOH活化法制备了高比表面积和高孔体积的多孔炭材料。采用氮气吸附仪、扫描电子显微镜（SEM）和X-射线衍射（XRD）仪对所制多孔炭的孔结构和形貌特性进行表征。结果表明，活化温度对多孔炭材料的比表面积和孔体积影响较大，当活化温度为800℃和KOH/炭前驱体浓度比为2时，得到的多孔炭材料（AC-28）比表面积和孔体积分别高达1 262 m2/g和0.70 cm3/g；当活化温度为600℃和KOH/炭前驱体浓度比为2时，多孔炭材料（AC-26）比表面积和孔体积分别为947 m2/g和0.51 cm3/g。虽然AC-26样品的比表面积和孔体积均较低，但其微孔率高达98%，使得此材料CO2吸附性能优异，在25℃和1 bar时的CO2吸附量高达4.22 mmol/g。常压下影响多孔炭材料中CO2吸附量的主要因素是微孔率，并不是由比表面积和孔体积决定。当具有合适的孔径结构和比表面积时，生物质基多孔炭材料中微孔率的增加会有效增加CO2吸附量。Abstract: Biomass is regarded as a promising low-cost precursor for the preparation of activated carbons. However, direct carbonization of biomass usually produces a low-surface-area or even non-porous carbons that are useless for CO2 capture. In this work, garlic peel was first transformed to a hydrochar by hydrothermal carbonization and then chemically activated by KOH to obtain activated carbons with high-surface-areas and large pore volumes. The microstructure and morphology of the activated carbons were characterized by N2 adsorption, SEM and XRD. Results indicate that their surface area and pore volume are mainly determined by the activation temperature and KOH/hydrochar mass ratio. Activated carbon (AC-28) obtained by KOH activation with a KOH/hydrochar ratio of 2 at 800℃ has a well-developed porosity with a surface area and pore volume of 1262 m2/g and 0.70 cm3/g, respectively, while a reduction of the activation temperature to 600℃ (AC-26) results in a material whose corresponding values are 947 m2/g and 0.51 cm3/g. Although AC-26 exhibits a much lower surface area and pore volume compared with AC-28, it has the larger CO2 uptake of up to 4.22 mmol/g at 25℃ and 1 bar due to its higher microporosity of up to 98% and abundant narrow micropores, implying that the microporosity is one of the main factors for CO2 capture besides the traditionally-believed surface area and pore volume. The isosteric heat of CO2 adsorption indicates that the affinity between the activated carbon and CO2 molecules increases with the volume of narrow micropores less than 0.8 nm and the number of surface oxygen-containing functional groups.
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Key words:
- Biomass /
- Hydrothermal carbonization /
- Porous carbons /
- Activation /
- CO2 capture
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