Preparation and N2, CO2 and H2 adsorption of super activated carbon derived from biomass source hemp (Cannabis sativa L.) stem

A series of activated carbons (ACs) were prepared by chemical activation of hemp (Cannabis sativa L.) stem with KOH. The porous structure of the samples was characterized by N2, CO2 and H2 adsorption, and the surface property was analyzed by IR. All samples show type I isotherms with multimodal pore size distributions in the <10 nm region, and a super AC with BET surface area of 3241 m2/g and total pore volume of 1.98 cm3/g is obtained. Hydrogen uptakes are linear function of specific surface area, total pore volume, and micropore volume, and the maximum hydrogen uptakes are 3.28 wt.% at −196 °C, 1.0 bar. The hydrogen adsorption mainly takes place in micropores but not absolutely, and mesopores in the range 2–5 nm also make important contribution. The gas adsorption amount is dominated by ultramicropores at lower pressure, and then lager micropores and mesopores make major contributions at higher pressure.

The gas adsorption behavior of hemp-based activated carbons is characterized by gases adsorption measurements of N2 (Fig. a), CO2 (Fig. b) and H2 (Fig. c), respectively. The gas adsorption amount is dominated by ultramicropores at lower pressure, and then lager micropores and mesopores make major contributions at higher pressure. The hydrogen adsorption mainly takes place in micropores but not absolutely, and mesopores in the range 2–5 nm also make important contribution.Figure optionsDownload as PowerPoint slideHighlights
► The natural ordered porous structure of hemp stem is favorable for activation.
► The structure of hemp stem supplies suitable adsorption site for hydrogen storage.
► The maximum of H2 adsorption capacity for hemp based ACs is 3.28 wt.%.
► Both micropore and mesopore in 2–5 nm make contribution to hydrogen uptake.
► Gas adsorption is a stepwise process dominated by pore size and its distribution.