Thermo-Regenerable Anion-Exchange Composites for the Removal of Diclofenac and Ibuprofen

Anion-exchange resins (AER) are widely applied in water treatment, although their chemical-intensive regeneration remains a bottleneck for the consumption of chemicals and generation of wastes. This study presents a thermo-regenerable AER composite (TR@AER) prepared via the interpenetration of poly(acrylic acid-co-acrylamide) (p(AA-co-AM)) within the AER matrix. TR@AER exhibits thermoresponsive hydrophilicity and surface charge, evidenced by a decrease in contact angle from 88.1° (25 °C) to 76.7° (50 °C) and a drop in ζ-potential from +36.9 mV (25 °C) to +31.1 mV (50 °C). In situ variothermal FTIR and molecular dynamics simulations reveal that this dual response is triggered by the dissociation of hydrogen bonds between -COOH and -CONH₂ groups in p(AA-co-AM). The dissociation simultaneously drives the hydrophobic-to-hydrophilic transition and deprotonation of -COOH groups in p(AA-co-AM), which subsequently interact with quaternary ammonium (-NR₃⁺) moieties of AER and alter surface charge characteristics. This enables a switchable adsorption and desorption of organic contaminants. At 25 °C, TR@AER rapidly adsorbs diclofenac and ibuprofen through synergistic electrostatic and hydrophobic interactions. Heating to 50 °C disrupts these interactions, significantly enhancing desorption. The desorption efficiency correlates with p(AA-co-AM) content in TR@AER. At the optimal p(AA-co-AM) loading (26-37 wt%), diclofenac desorption reached 92.2% and ibuprofen desorption reached 96.0% at 50 °C, representing 1.7- and 1.8-fold that of 25 °C, respectively. By circumventing chemical-intensive regeneration protocols, this work highlights an innovative strategy for stimuli-responsive adsorbent design with excellent regeneration capabilities.