Construction of Hierarchically Porous Frameworks for PFAS Removal and Sensing

Metal-organic frameworks (MOFs) are crystalline polymeric materials featuring nanosized pores for transporting energy and matters. However, most MOFs feature micropores smaller than 2 nm, largely limiting the ingress of guest molecules and their practical applications. Herein, I have developed both top-down and bottom-up methodologies to engineer the pore sizes of MOFs, yielding hierarchically porous MOFs consisting of both micropores and mesopores (2-50 nm). The enlarged pore sizes significantly enhance mass transfer and make the active sites in MOFs more accessible. Most importantly, the hierarchically porous MOFs demonstrate excellent performance in sustainable applications, such as the removal of polyfluoroalkyl substance (PFAS), an emerging contaminant widely observed in drinking water in the US. Based on the sorption experiments, the MOF named PCN-1002 features an exceptionally high capacity of perfluorooctanoic acid （PFOA), with a uptake value over 600 mg/g, which is the highest value among all reported MOFs. Mechanism studies based on density functional theory (DFT) calculation and 13C{1H} Magic Angle Spinning (MAS) nuclear magnetic resonance (NMR) indicate that the PFOA is captured through the synergistic binding with the open metal sites and free hydroxyl groups. Besides, the hierarchically porous MOFs also feature record-breaking luminescence sensitivity and selectivity towards a broad range of small molecules, benefiting from the enlarged pore sizes and well-tailored chemical environment. Such innovation in synthetic methodology will bring inspiration for the future development of sustainable materials to address grand challenges in environmental remediation and chemical production.