Porous aromatic frameworks with anion-templated pore apertures serving as polymeric sieves.

Owing to environmental pollution and energy depletion, efficient separation of energy gases has attracted widespread attention. Low-cost and efficient adsorbents for gas separation are greatly needed. Here we report a family of quaternary pyridinium-type porous aromatic frameworks with tunable channels. After carefully choosing and adjusting the sterically hindered counter ions via a facile ion exchange approach, the pore diameters are tuned at an angstrom scale in the range of 3.4-7 Å. The designed pore sizes may bring benefits to capturing or sieving gas molecules with varied diameters to separate them efficiently by size-exclusive effects. By combining their specific separation properties, a five-component (hydrogen, nitrogen, oxygen, carbon dioxide and methane) gas mixture can be separated completely. The porous aromatic frameworks may hold promise for practical and commercial applications as polymeric sieves.