Design of a sodium polyacrylate/carboxymethyl-chitosan-based imprinted cryogel for fluoxetine adsorption in...

Fluoxetine (FLX) contamination in aquatic environments poses significant ecological risks, highlighting the need for efficient and selective removal technologies. In this study, a bio-based macroporous molecularly imprinted cryogel (MIC/NaPA-CMCs) was developed for continuous-flow FLX adsorption. The cryogel was synthesized from sodium polyacrylate and carboxymethyl chitosan by cryopolymerization at -18 °C for 24 h using genipin and N,N'-methylenebis(acrylamide) as crosslinkers, with FLX as the template molecule. Template removal using an acidified solvent (5 % methanol/0.1 M HCl, 1:1 v/v) generated selective recognition cavities, while a non-imprinted cryogel (NIC/NaPA-CMCs) was prepared for comparison. The materials were characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), Brunauer-Emmett-Teller (BET) analysis, and point-of-zero-charge (pH_PZC) determination. MIC/NaPA-CMCs exhibited a pH_PZC of 4.9 and a specific surface area of 36.8 m²/g. Fixed-bed adsorption experiments (pH 8.5, bed height 0.4 cm, 20 ± 2 °C) showed that increasing the FLX inlet concentration (10-40 mg/L) accelerated bed saturation and shifted breakthrough to shorter times, whereas increasing the flow rate (1.5-2.5 mL/min) reduced residence time, decreasing the adsorption capacity from 22.05 to 6.61 mg/g. The Thomas and Yoon-Nelson models accurately described the breakthrough curves (R² > 0.990), indicating that adsorption performance was governed by mass-transfer limitations under dynamic conditions. Competitive adsorption with citalopram confirmed the selective recognition of FLX by MIC/NaPA-CMCs, yielding higher FLX uptake and a relative selectivity coefficient (K' > 1) than the non-imprinted cryogel. These results demonstrate the potential of the developed imprinted cryogel for selective FLX removal under continuous-flow conditions.