Mechanistic insights into electrosorption of diverse organic compounds: Is the molecular structure a barrier?

Electrosorption is a promising strategy for removing ionic organic pollutants and in-situ adsorbent regeneration; however, a lack of mechanistic understanding hinders its broader application. This study systematically investigates the potential-dependent adsorption of 21 structurally diverse persistent, mobile, and potentially toxic compounds (PMs/PMTs), spanning cationic, anionic, zwitterionic, and neutral species with and without aromatic moieties. Experiments were conducted at trace concentrations in realistic tap water matrix using activated carbon felt electrodes with tailored surface chemistries across a potential range of -1 V to +1 V (vs. Ag/AgCl). Results demonstrate that electrosorption is governed by superimposed electrostatic and non-electrostatic interactions, strongly modulated by molecular structure. Non-aromatic ions exhibit electrostatically dominated behavior, following bell-shaped curves with maxima at moderate opposite-charge potentials, with adsorption coefficients (K_d) varying by up to 5 log units. In contrast, aromatic compounds show enhanced adsorption under cathodic polarization regardless of charge, indicating potential-induced strengthening of π-π interactions. Oxygen-rich surface chemistries attenuate these effects, limiting K_d variations to ≤ 2 orders of magnitude. Desorption hysteresis in aromatic species identifies a critical boundary for electrode regenerability, suggesting tailored designs for aromatic vs. non-aromatic fractions. This work provides a foundation for the predictive design of electrosorption processes in realistic water treatment scenarios.