Ti/RuO₂-Ir-Ti₄O₇ composite electrocatalytic membrane for PFOA removal and transformation: Cross-flow vs. dead-end...

Selecting anode materials is critical for electrocatalytic membrane treatment of perfluorooctanoic acid (PFOA), affecting activity, stability, and mass transfer. Three Ti-based electrodes were screened to construct a composite electrocatalytic membrane (CEM) comprising a Ti substrate, RuO₂-Ir interlayer, and Ti₄O₇ surface layer. The composite exhibited an oxygen evolution potential of 2.67 V, a charge-transfer resistance of 11.8 Ω, and 722 h accelerated lifetime. After optimization, C/C₀ reached 0.34 and 0.03 after 3 h under dead-end and cross-flow modes, corresponding to approximately 66% and 97% parent-PFOA removal, respectively. Polarity reversal every 15 min improved removal by up to 19.34 percentage points over the control, suggesting partial alleviation of surface passivation. Differential radical-quenching experiments suggested the involvement of radical-associated oxidation, while substantial residual parent-PFOA removal after alcohol quenching suggested contributions from additional interfacial oxidation pathways. HRMS-detected transformation products were consistent with possible decarboxylation followed by progressive carbon-chain shortening, although multiple pathways may coexist in the CEM system. Because fluoride release and CO₂ evolution were not quantified, defluorination and overall mineralization could not be determined. Toxicogenomic assessment showed that transcriptional stress decreased after 1 h and then increased, indicating that parent-PFOA removal did not correspond to a monotonic decrease in toxicogenomic response.