Removal of Low Trace ppb-Level Perfluorooctanesulfonic Acid (PFOS) with ZIF-8 Coatings Involving Adsorbent Degradation

Abstract

For the first time, low trace-level removal of perfluorooctanesulfonic acid (PFOS), i.e., 20–500 μg/L (ppb), from aqueous solutions using zeolitic imidazolate framework-8 (ZIF-8)-coated copper sheet (ZIF-8@Cu) composite is reported here. In comparison with different commercial activated carbon (AC) and all-silica zeolites, the composite showed the highest removal rate of 98%, which remained consistent over a wide range of concentrations. Additionally, no adsorbent leaching from the composite was noticed, which eradicated pre-analysis steps such as filtration and centrifugation, unless needed for other adsorbents studied here. The composite displayed fast uptake with saturation reaching within 4 h, irrespective of the initial concentration. However, the morphological and structural characterization revealed surface degradation of ZIF-8 crystals, along with a decline in the crystal size. The adsorption of PFOS on ZIF-8 crystals was linked to chemisorption, as the surface degradation surges with an increase in PFOS concentration or with cyclic exposure at low concentrations. Methanol seemingly removed surface debris (partially), thus providing access to ZIF-8 beneath the surface debris. Overall, the findings demonstrate that at low trace ppb-level PFOS concentrations ZIF-8 can be considered as a possible candidate for PFOS removal, even though it suffers slow surface degradation, it also removes efficiently PFOS molecules from aqueous solutions.

Metal–Organic Framework-Based Composites for the Adsorption Removal of Per- and Polyfluoroalkyl Substances from Water

“…Recently, significant progress has been made in the research on the removal of PFASs. − The techniques employed to eliminate PFASs from water can be categorized into physical methods, such as adsorption, ion exchange, and membrane treatment, and chemical methods, including electrochemical processes, advanced oxidation, and ultrasonic degradation. − Physical methods have the advantages of low operating costs, simplicity, stability, and no additional pollutants generated during the process. Among these methods, adsorption is the most promising method and has been extensively studied and implemented in practical engineering experiments. − Various adsorbents, including activated carbon, zeolite, graphene, carbon nanotubes, ion-exchange resins, and metal–organic frameworks (MOFs), have been investigated for their effectiveness in removing PFASs from water .…”