Electrochemically-controlled Capture and Release of PFOA via Redox-tunable Polyaniline

Abstract

Per- and poly-fluoroalkyl substances (PFAS) are persistent environmental pollutants due to their exceptional chemical stability and widespread use, posing significant environmental and biological risks. Among them, perfluorooctanoic acid (PFOA) has drawn particular attention because of its high toxicity and persistence in the environment, emphasizing the urgent need for more effective treatment technologies. However, existing methods have several limitations, necessitating the exploration of alternative approaches. In this study, we investigated electrochemically-mediated modulation of oxidation state of polyaniline (PANI), particularly leucoemeraldine and emeraldine, and their collective effects on capture and reversible regeneration. The successful formation of these states was confirmed using X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The adsorption performance of PANI structures was investigated using a combination of experimental analyses and density functional theory (DFT) calculations, revealing that the emeraldine salt form is the most effective for PFOA capture due to synergistic electrostatic and hydrophobic interactions. Desorption experiments were carried out after adsorption to investigate how the adsorption mechanism influences the reversibility and regeneration of PANI electrodes, as well as the desorption behavior of PFOA. To gain deeper insight into the desorption mechanism, molecular dynamics (MD) simulations were conducted, revealing that PFOA adsorption—primarily driven by electrostatic interactions—occurs in a vertical configuration, where the carboxylate end of PFOA aligns vertically with the amine groups of emeraldine PANI. This configuration enables optimal desorption under negative polarization. The ease of desorption facilitates the integration of capture and release with tandem advanced oxidation using boron-doped diamond (BDD) electrodes, allowing both capture and degradation to occur within a single device. Finally, PFOA adsorption experiments were extended to real wastewater samples to evaluate the electrode’s performance under practical conditions using an up-scaled system. All these results prove the practical applicability of the PANI-based redox systems for real-world use.