Adsorptive Removal of Per- and Polyfluoroalkyl Substances (PFAS) by Polyaniline (PANI) and Chitosan-Graft- Polyaniline (CS-PANI)

Abstract

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals widely used in various industrial and consumer products due to their resistance to heat, water, and oil. However, their persistence, bioaccumulation potential, and adverse effects on human health and the environment have raised significant global concern. Owing to their strong C-F bonds and weak intermolecular interactions, PFAS are extremely resistant to degradation and are difficult to remove using conventional treatment technologies. In this study, polyaniline (PANI), a low-cost, easily synthesized conductive polymer, was investigated as an adsorbent for PFAS removal. To enhance adsorption performance, a chitosan-graft- polyaniline (CS-PANI) composite was synthesized via in situ chemical oxidative polymerization of aniline in the presence of chitosan, a bio-based polymer rich in amino and hydroxyl functional groups. Both PANI and CS-PANI were synthesized at optimized monomer ratios and comprehensively characterized using FE-SEM, BET, DLS, FTIR, and XPS analyses, confirming successful chitosan incorporation and improved surface functionality. When evaluated in raw drinking water spiked with eight PFAS compounds (5 µg/L each) at an adsorbent dosage of 5 mg/L, both PANI and CS-PANI achieved adsorption equilibrium within 1 h, exhibiting faster kinetics than a commercial powdered activated carbon (F400). In the same water matrix, the surface area-normalized maximum adsorption capacities (qmax, µg/m2) derived from isotherm models were more than an order of magnitude higher for PANI and CS-PANI than for F400, with CS-PANI showing the highest capacity. The superior performance of CS-PANI was attributed to an increased density of active sites and favorable surface characteristics, as supported by characterization and isothermal titration calorimetry (ITC) analyses. Overall, this study demonstrates that PANI-based polymeric adsorbents are highly effective for PFAS removal, and that chitosan incorporation significantly improves adsorption kinetics, capacity, and selectivity. These findings highlight CS-PANI as a sustainable, high-performance adsorbent with strong potential for advanced PFAS removal in water treatment applications.