Cooperative CO₂ adsorption promotes high CO₂ adsorption density over wide optimal nanopore range

Abstract

Separation of CO2 based on adsorption, absorption, and membrane techniques is a crucial technology necessary to address current global warming issues. Porous media are essential for all these approaches and understanding the nature of the porous structure is important for achieving highly efficient CO2 adsorption. Porous carbon is considered to be a suitable porous media for investigating the fundamental mechanisms of CO2 adsorption, because of its simple morphology and its availability in a wide range of well-defined pore sizes. In this study, we investigated the dependence of CO2 adsorption on pore structures such as pore size, volume, and specific surface area. We also studied slit-shaped and cylindrical pore morphologies based on activated carbon fibers of 0.6–1.7 nm and carbon nanotubes of 1–5 nm, respectively, with relatively uniform structures. Porous media with larger specific surface areas gave higher CO2 adsorption densities than those of media having larger pore volumes. Narrower pores gave higher adsorption densities because of deep adsorption potential wells. However, at a higher pressure CO2 adsorption densities increased again in nanopores including micropores and small mesopores. The optimal pore size ranges of CO2 adsorption in the slit-shaped and cylindrical carbon pores were 0.4–1.2 and 1.0–2.0 nm, respectively, although a high adsorption density was only expected for the narrow carbon nanopores from adsorption potentials. The wider nanopore ranges than expected nanopore ranges are reasonable when considering intermolecular interactions in addition to CO2–carbon pore interactions. Therefore, cooperative adsorption among CO2 in relatively narrow nanopores can allow for high density and high capacity adsorption.

Electrospun Composites Made of Reduced Graphene Oxide and Polyacrylonitrile-Based Activated Carbon Nanofibers (rGO/ACNF) for Enhanced CO2 Adsorption

“…In fact, the adsorption isotherms obtained from the various pressures and specific temperature explained the equilibrium adsorption capacity of the ACNFs. The isotherms were found to be Type I, being in line with the findings based on N 2 isotherms, i.e., the microporous features that were induced to achieve the high adsorption of CO 2 [ 58 ].…”

“…In fact, the adsorption isotherms obtained from the various pressures and specific temperature explained the equilibrium adsorption capacity of the ACNFs. The isotherms were found to be Type I, being in line with the findings based on N 2 isotherms, i.e., the microporous features that were induced to achieve the high adsorption of CO 2 [58]. Table 3 summarized the comparison between CO 2 uptakes by different carbon fibers-based adsorbents and their composites from previous literature with the rGO/ACNF composites produced in this study.…”

Boosting CO2 adsorption and selectivity in metal–organic frameworks of MIL-96(Al) via second metal Ca coordination

“…However, CO 2 adsorption decreases to about 5.26 mmol g À1 in MIL-96(Al)-Ca4 because further increasing in Ca 2+ content leads to decrease in the BET surface area, pore-volume, micropore content. 54 It seems that the pore volume expands when the high pressure is applied. Therefore, CO 2 uptake is dramatically increased in the MIL-96(Al)-Ca samples with the Ca 2+ content lower than 0.74%.…”

Carbon Spheres as CO2 Sorbents

“…Investigation of Chen et al [49] showed that the adsorption of CO 2 molecules in the 0.3 nm slit pores, due to the similar size of CO 2 molecules, was very poor. In contrast, the highest CO 2 adsorption was noticed in the 0.4 nm pores.…”