Ti/RuO2-Ir-Ti4O7 composite electrocatalytic membrane for PFOA removal and transformation: Cross-flow vs. dead-end operation, transformation pathways, and toxicogenomic response evolution.

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.