A search for selectivity to enable CO2 capture with porous adsorbents

Fundamental aspects and actual developments of selective CO2 capture from relevant sources (flue gas or air) by reversible physisorption are critically reviewed. Thermodynamic as well as kinetic principles of CO2 adsorption in the presence of other gases are linked to current approaches of materials development. Whilst hundreds or even thousands of porous materials have been evaluated for CO2 capture, research in this field is still full of challenges, as for instance a feasible physical adsorbent for CO2 capture for direct capture from air has still not been found. Current attempts towards the optimization of materials in terms of CO2 uptake/selectivity, regenerability, tolerance against water, and cost most often exclude each other. The aim of this article is not to summarize all recent attempts towards tailoring of materials for selective CO2 capture but to discuss the most fundamental aspects of adsorptive CO2 separation in order to illuminate the "sweet spot'' to be explored when electronic structure, polarity, and pore size/geometry are rationally balanced and optimized - just like nature does when exerting selective binding of gases.