Unveiling anomalous CO₂-to-N₂ selectivity of graphene oxide

When dry sorbents are considered for CO₂ capture, selective uptake of CO₂ over other gases is highly desirable. However, most dry sorbents suffer from selectivity drop upon temperature increase. Here, we report that graphene oxide (GO) exhibits high CO₂-to-N₂ selectivity, and the selectivity rises anomalously with temperature increase; CO₂-to-N₂ selectivity that starts at 192 at 273 K increases to an extraordinarily high value of 607 at 323 K. These high values and unusual trends in selectivity are attributed to a combined effect of CO₂-philicity from the functional groups of GO and its relatively large macropores that are efficient at releasing N₂. In-depth analysis using FT-IR reveals CO₂-philic electrostatic interactions where CO₂ serves as an electron donor and acceptor simultaneously; while CO₂ can bind with electron-rich oxygen-containing groups of GO, the oxygen of CO₂ can also bind with hydrogen-containing groups at the edges of GO. The current study with GO highlights a design principle for highly selective CO₂ capture represented by CO₂-philic electrostatic sites coupled with relatively large pores for efficient N₂ release.