Synthesis of Tubular Magnéli Phase Titanium Suboxide Reactive Electrochemical Membrane in Water Treatment

This study presents the fabrication and application of tubular reactive electrochemical membranes (REMs) based on Magnéli phase titanium suboxide (Ti4O7) for PFOA degradation. Using a lab-developed slip-casting method, we produced two membrane variants: Membrane-1 with TiO2 slurries, and Membrane-2 with added sodium hexametaphosphate (SHMP) as a dispersant. Characterization by SEM, XRD, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) revealed that Membrane-1 exhibited a superior electroactive surface area of 3320.56 ± 1230.33 cm² and a roughness factor of 814.37 ± 154.02, compared to Membrane-2 which have 663.3 cm² electroactive surface area and 196.5 roughness factor. SEM analysis showed Membrane-1 had a porosity of 20 - 40% versus the denser Membrane-2 of 21%, contributing to its increased reactivity. Electrochemical oxidation testing with oxalic acid (OA) and terephthalic acid (TA) as probes for direct electron transfer (DET) and hydroxyl radicals, respectively, confirmed Membrane-1 high reactivity. Membrane-1 achieved a PFOA degradation rate of 42.8 ± 6 mmol h⁻¹ m⁻² at 4.2 V/SHE, substantially higher than prior flow-through rates. This enhanced performance is attributed to Membrane-1 increased surface roughness and porosity, facilitating superior mass transfer and active site availability. A maximum fluoride yield of 77.9 ± 5.5% at 4.7 V/SHE was achieved, highlighting the electrode efficiency in achieving complete degradation. These results underscore the potential of in-lab synthesized Ti4O7 REMs as cost-effective alternatives to commercial membranes, achieving efficient PFOA degradation by leveraging increased surface area and reactivity. Further work will aim to optimize fabrication for greater flux and stability across diverse treatment scenarios.