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 Ni8-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 Ni8-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 (kobs) of 0.99 g mg-1 h-1 and large maximum uptake capacity (qmax) of 268.5 mg g-1 for perfluorooctanoic acid and kobs of 0.77 g mg-1 h-1 and qmax of 142.1 mg g-1 for perfluorooctanesulfonic acid.