Membrane filtration and adsorption are two prominent methods for the effective removal of per- and poly-fluoroalkyl substances (PFAS) from water. Thin-film composite (TFC) nanofiltration (NF) membranes exhibit acceptable PFAS removal (<90%), but the presence of rejected PFAS in the concentrate stream necessitates an additional separation process. Our previous study reported the fabrication of adsorptive TFN NF membranes, incorporating superfine activated carbon (SFAC), for enhanced perfluorooctanesulfonic acid (PFOS) removal via adsorption during water filtration. The SFAC-TFN-0.5 membranes (0.5 wt% loading) of SFAC embedded inside the polyamide layer of TFN demonstrated 94% PFOS removal, with over 80% adsorption, and an increased permeability of 22 LMH/bar compared to the bare TFC. Although the results were impressive, the selectivity of the membranes towards different PFAS (long-chain PFOS and short-chain perfluorobutane sulfonate, PFBS), and in the presence of other components was not investigated. In this project, we investigated the selectivity of the adsorptive membrane toward different PFAS in the presence of NOM. Initial static adsorption results revealed limited PFBS adsorption on SFAC (45%), while it showed 93 % adsorption towards PFOS. To enhance the adsorbent's selectivity for different PFAS, SFAC was further fluorinated, as fluorination increases fluorophilic interactions with short-chain PFAS — an essential mechanism for their adsorption. The selectivity of PFOS in the presence of NOM on the SFAC membrane was observed to decrease to 70 % from 90 %. Therefore, the hypothesis is that fluorophilic interaction can boost the affinity of SFAC towards PFOS rather than NOM. In addition, the incorporation of SFAC in the IP process led to SFAC aggregation and disruption of the polyamide layer as reported in our previous study. In this project, fluorinated SFAC is grafted onto the active layer to prevent aggregation and better control surface properties.
