Addition of PBA-CC cathode in a FCDI system enabling flexible regulation of degradation of tetracycline and synergistic ionic byproduct removal

This study successfully developed a novel dual-cathode flow electrode capacitive deionization (DC-FCDI)/peroxymonosulfate (PMS) coupled system for simultaneous tetracycline (TC) degradation and removal of PMS reaction byproduct ions. The system integrates a high-performance Prussian blue analogue-modified carbon cloth (PBA-CC) as a dedicated inner-circuit reaction cathode with external flowing electrodes responsible for continuous ion migration and desalination. The PBA-CC plays a pivotal role in the coupled system by providing abundant redox-active Fe/Co sites and nitrogen-containing functional groups, which enable efficient PMS activation through mixed-valence Fe(II)/Fe(III) and Co(II)/Co(III) cycling under the applied electric field. Besides, the PBA-CC also facilitates localized electron transfer and transient cation accumulation at the electrode/influent interface, thereby enhancing PMS utilization efficiency and alleviating the competition between pollutant degradation and ion removal. Mechanistic studies, via quenching experiments and EPR tests, identified SO₄• − , •OH, O₂• − , and 1 O₂ as key reactive oxygen species. Crucially, the system exhibited excellent long-term operational stability over five cycles, maintaining high removal rates for both TC (72.3%) and ions (40.7%). In summary, this innovative DC-FCDI/PMS system offers a highly effective, stable, and energy-efficient solution for simultaneous organic pollutant degradation and byproduct ion desalination, presenting a promising advance in sustainable water treatment technologies.