Comparison of adsorption isotherms of single-ringed compounds between carbon nanomaterials and porous carbonaceous materials over six-order-of-magnitude concentration range

Understanding the mechanisms controlling the differences in adsorption properties between carbon nanomaterials (CNMs) and porous carbonaceous materials—particularly, the structure–activity correlations—is critical for exploring CNMs as special adsorbents for environmental applications. In this study, batch adsorption isotherms of 4-chloronitrobenzene (planar, aromatic) to three CNMs (single-walled carbon nanotubes/SWNT, multi-walled carbon nanotubes/MWNT, and graphene) and three porous carbonaceous materials (two activated carbons/ACs, and a template-synthesized mesoporous carbon/CMK-3) were compared with those of trans-1,2-dichlorocyclohexane (nonplanar, aliphatic) to the respective adsorbents. The isotherms covered a concentration range of over six orders of magnitude. After being normalized by the adsorbent total surface area, adsorption of 4-chloronitrobenzene to CNMs was stronger than to ACs and CMK-3, likely due to strong π–π stacking between 4-chloronitrobenzene and the well-crystallized and open accessed graphitic surfaces of CNMs. In contrast, the surface area-normalized adsorption of trans-1,2-dichlorocyclohexane was stronger to ACs and CMK-3 than to CNMs, which can be attributed to the stronger micropore-filling effect with porous carbonaceous materials. The proposed adsorption mechanisms were verified by examining the adsorption properties of 1,2-dichlorobenzene and 1,4-dichlorobenzene to SWNT and one of the ACs, as well as modeling the adsorption data with Polanyi theory-based Dubinin–Ashtakhov model.