Adsorption studies of fluorotelomer olefin onto granular activated carbon, non-ion and ion exchange resin

Introduction of fluorotelomer into the industry as a replacement for per- and polyfluoroalkyl substances (PFAS) has raised global concern due to its widespread dispersion and potential persistency, bioaccumulation, and toxicity. Adsorption has been recognized as an effective method for removing PFAS from water, however there are lack of studies focusing on fluorotelomer. This study aims to enhance the understanding of fluorotelomer olefin (FTO) adsorption onto different adsorbents, providing valuable insights into potential strategies to eliminate FTO from water systems. Various adsorbents including granular activated carbon (GAC), non-ion exchange resin (XAD-4), and ion exchange resin (IRA958) were examined for adsorption capacity, kinetics, and isotherms under different conditions: adsorbent dosages, contact times, and FTO initial concentrations. Scanning electron microscopy (SEM) images demonstrate that the roughness surface of GAC and smooth surface of XAD-4 remained the same after the adsorption. However, foreign substances were observed on the smooth and cracked surface of IRA958. Brunauer-Emmet-Teller (BET) measurement displayed large surface area of XAD-4 (860.8548 m2/g) followed by GAC (544.1870 m2/g) and IRA958 (2.0381 m2/g). FTO was detected and quantified using gas chromatography-mass spectrometry (GC-MS). The adsorption of FTO on all adsorbents reached equilibrium within 5 h and the data were best-fitted to pseudosecond-order kinetics model (R2 > 0.99). Meanwhile, Freundlich isotherm model was found to be suitable for describing FTO adsorption, with GAC exhibiting the highest adsorption capacity (Kf = 3.0853), followed by IRA958 (Kf = 3.0400) and XAD- 4 (Kf = 0.0009). The findings suggest that the adsorption mechanism of FTO onto adsorbents is characterized by multilayer and chemosorption behavior. Desorption study reveals that FTO was not able to desorb from the adsorbent’s surface using either methanol, ethanol, or n-hexane. Removal of FTO remain high (>80%) with or without the presence of interfering compounds (FTI, FTOH and PFHxI), under optimum adsorption conditions: 1.25 mg adsorbent dosage and 5 h contact time with initial concentration of FTO 100 mg/L and above. The findings from this study have shown the potential of GAC, XAD-4 and IRA958 to be used as adsorbents in water treatment plants to remove FTO from water, hence improving the overall quality of water and environment.