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

Abstract

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 tbutyloxycarbonyl 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.