Activated carbons prepared by the KOH activation of a hydrochar from garlic peel and their CO2 adsorption performance

By Gege Huang, Yi-fei Liu, Xingxing Wu, Jinjun Cai. Carbon, 2019

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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 CO 2 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 N 2 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 °C has a well-developed porosity with a surface area and pore volume of 1 262 m 2 /g and 0.70 cm 3 /g, respectively, while a reduction of the activation temperature to 600 °C (AC-26) results in a material whose corresponding values are 947 m 2 /g and 0.51 cm 3 /g. Although AC-26 exhibits a much lower surface area and pore volume compared with AC-28, it has the larger CO 2 uptake of up to 4.22 mmol/g at 25 °C 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 CO 2 capture besides the traditionally-believed surface area and pore volume. The isosteric heat of CO 2 adsorption indicates that the affinity between the activated carbon and CO 2 molecules increases with the volume of narrow micropores less than 0.8 nm and the number of surface oxygen-containing functional groups.

Subfields: Biomedical Engineering, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/de6487c25642096553e340de8d8f2f0d8625ad9a