Highly efficient, rapid and selective CO2 capture by thermally treated graphene nanosheets

Graphene, by virtue of its unique molecular structure and many interesting properties, is receiving considerable attention as an adsorbent for separation and purification of gases. In this study, graphene nanosheets were subjected to heat treatment in the temperature range of 200–800 °C under flowing N2 to improve their textural characteristics (surface area, pores size, and total pore volume) for efficient removal of CO2 from flue gases. The resulting graphene materials showed highly ordered structure, large surface area (up to 484 m2 g−1) and interconnected hierarchical pore networks with narrow pore size distribution in the large-micropore/small-mesopore range. As a consequence, the heat-treated graphene samples demonstrated significantly greater CO2 uptake capabilities (up to 2.89 mmol g−1) compared to pristine graphene (0.81 mmol g−1) at 0 °C and 1 bar. More importantly, the materials displayed rapid adsorption kinetics with ultrahigh selectivity for CO2 over N2, as well as stable and readily reversible adsorption/desorption cycling behavior. The isosteric heat of adsorption had an unusual dependence on surface loading because of the presence of attractive intermolecular forces between the adsorbed quadrupolar CO2 molecules. These findings demonstrate for the first time that thermal treatment at high-temperatures can have a positive influence on the single component CO2 adsorption characteristics of graphene sheets and should be explored further as an effective strategy in the design and development of graphene-based porous solid adsorbents for CO2 abatement.