Empowering TiO2–coated PVDF membranes stability with polyaniline and polydopamine for synergistic separation and photocatalytic enhancement in dye wastewater purification

Photocatalytic membranes are effective in removing organic dyes, but their low UV resistance poses a challenge. To address this, self-protected photocatalytic PVDF membranes were developed using polyaniline (PANI) and polydopamine (PDA), whaich are anti-oxidation polymers, as interlayers between the membrane and TiO₂. PVDF membranes were first modified by a self-polymerization layer of either PANI or PDA and then coated with titanium dioxide (TiO₂). The TiO₂ remained firmly attached to the PANI and PDA layer, regardless of sonication and prolonged usage. The PANI and PDA layers enhanced the durability of PVDF membrane under UV/TiO₂ activation. After 72 h of irradiation, PVDF-PDA-TiO₂ and PVDF-PANI-TiO₂ membranes exhibited no significant change. This process improved both separation and photocatalytic activity in dye wastewater treatment. The PVDF-PDA-TiO₂ and PVDF-PANI-TiO₂ membranes showed enhanced membrane hydrophilicity, aiding in the rejection of organic pollutants and reducing fouling. The modified membranes exhibited a significant improvement in the flux recovery rate, attributed to the synergistic effects of high hydrophilicity and photocatalytic activity. Specially, the flux recovery rate increased from 17.7% (original PVDF) to 56.3% and 37.1% for the PVDF-PDA-TiO₂ membrane and PVDF-PANI-TiO₂ membrane. In dye rejection tests, the PVDF‒PDA‒TiO₂ membrane achieved 88% efficiency, while the PVDF‒PANI‒TiO₂ reached 95.7%. Additionally, the photodegradation of Reactive Red 239 (RR239) by these membranes further improved dye removal. Despite an 11% reduction in flux, the PVDF-PDA-TiO₂ membrane demonstrated greater durability and longevity. The assistance of PANI and PDA in TiO₂ coating also improved COD removal (from 33 to 58-68%) and provided self-protection for photocatalytic membranes, indicating that these photocatalytic membranes can contribute to more sustainable wastewater treatment processes.