Removing Perfluoro Pollutants PFOA and PFOS by Two-Pronged Design of a Ni₈-Pyrazolate Porous Framework

Inspired by the practical need to remove persistent perfluoro pollutants from the environment, we leverage cutting-edge crystal engineering approaches. For this, we set our eyes on a recent porous coordination framework system based on the Ni 8 -oxo cluster and pyrazolate linkers as it is known for its stability to bases and other harsh environmental conditions. Our designer linker molecule here features (1) pyrazole donors masked by t -butyloxycarbonyl and (2) ethynyl side units protected by triisopropylsilyl groups. The former solvothermally demasks to assemble the Ni 8 -pyrazolate framework, in which the triisopropylsilyl groups can be post-synthetically cleaved by guest fluoride ions to unveil the terminal alkyne group (−CCH). The ethynyl groups of the framework solid offer versatile reactions for functionalization, as with perfluorophenyl azide (via a click reaction) to afford the two prongs of the 1,2,3-triazole base unit and the perfluoro unit. Together, these two functions make for an effective adsorbent for the topical acid pollutants of perfluorooctanoic acid and perfluorooctanesulfonic acid, with a high apparent rate constant ( k obs ) of 0.99 g mg –1 h –1 and large maximum uptake capacity ( q max ) of 268.5 mg g –1 for perfluorooctanoic acid and k obs of 0.77 g mg –1 h –1 and q max of 142.1 mg g –1 for perfluorooctanesulfonic acid.