Chitosan cross-linked β–cyclodextrin polymeric adsorbent for the removal of perfluorobutanesulfonate from aqueous solution: adsorption kinetics, isotherm, and mechanism

The existence of per- and polyfluoroalkyl substances (PFASs) in water is of serious interest due to their toxic, bioaccumulative, and persistent nature, and adsorption is an effective approach for the PFASs removal. In the present study, we developed a polymeric adsorbent by cross-linking chitosan and β–cyclodextrin using glutaraldehyde (Chi–Glu–β–CD) and evaluated its removal performance for perfluorobutanesulfonate (PFBS) from water. The results indicate that the performance was highly affected by solution pH; under a more acidic condition (e.g., pH 2.0), a higher removal efficiency was detected, and faster adsorption kinetics was observed with the rate constant (k₂) of 0.001 ± 3×10⁻⁴ g mg⁻¹ min⁻¹. Adsorption isotherm data agreed to the Sips model with a maximum heterogeneous adsorption capacity of 135.70 ± 25.70 mg g⁻¹, probably due to protonated amine (NH⁺) and electron-deficient β–CD cavities. The adsorption mechanism was confirmed using energy dispersive X-ray and Fourier transform infrared (FTIR) spectroscopy, showing the role of electrostatic attractions between the protonated amine and the negatively charged PFBS molecule (especially, with sulfonate side (N–H–-O–S)) and host–guest inclusion formations with β–CD cavity in adsorption. Additionally, the synthesized adsorbent was recovered using methanol without any significant decline in adsorption efficiency even after four continuous adsorption/desorption cycles. All these findings suggested that the Chi–Glu–β–CD composite could be a promising adsorbent in the removal of PFBS from water. Graphical abstract: [Figure not available: see fulltext.]