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.

Efficient reactive blue 19 decolorization by the comparison of ozonation membrane contacting process and Fenton oxidation.

The decolorization of Reactive Blue 19 (RB 19) wastewater by an ozonation membrane contactor and Fenton oxidation was studied. The aims of the study were to investigate the affecting parameters and to compare the performance of RB 19 decolorization by two different processes. The results showed that Fe2+ and H2O2 concentrations for Fenton oxidation and ozone concentration with different membranes for the membrane contacting process played the most important roles in RB 19 decolorization. The optimum conditions for RB 19 decolorization by Fenton oxidation were initial pH 3.0, 1.5 mM H2O2 and 0.25 mM Fe2+; in contrast, the optimum conditions for the membrane contactor were initial pH 11 and 40 mg L-1 ozone concentration. Under these conditions, the decolorization of RB 19 by the membrane contactor was almost completed and was higher than by Fenton and photo-Fenton oxidations for 90 min. The decolorizations of RB 19 by Fenton and photo-Fenton oxidations were constant after 30 min, but the decolorization of RB 19 by ozonation with a membrane contactor gradually increased via ozone consumption until 90 min operation, which was higher than that of Fenton oxidations. The use of a PVDF-PAM membrane in the membrane contactor resulted in higher decolorization efficiency than a PVDF membrane. The results demonstrated a COD removal efficiency of 63% by an ozonation membrane contacting process using PVDF-PAM, which was lower than that of Fenton oxidation (73%), but resulted in higher BOD5/COD and NO3 - and SO4 2- releases. Under these conditions, the ozonation membrane contacting process showed the lowest electric energy consumption.

Enhancing the Antibacterial Properties of PVDF Membrane by Hydrophilic Surface Modification Using Titanium Dioxide and Silver Nanoparticles.

This work investigates polyvinylidene fluoride (PVDF) membrane modification to enhance its hydrophilicity and antibacterial properties. PVDF membranes were coated with nanoparticles of titanium dioxide (TiO2-NP) and silver (AgNP) at different concentrations and coating times and characterized for their porosity, morphology, chemical functional groups and composition changes. The results showed the successfully modified PVDF membranes containing TiO2-NP and AgNP on their surfaces. When the coating time was increased from 8 to 24 h, the compositions of Ti and Ag of the modified membranes were increased from 1.39 ± 0.13 to 4.29 ± 0.16 and from 1.03 ± 0.07 to 3.62 ± 0.08, respectively. The water contact angle of the membranes was decreased with increasing the coating time and TiO2-NP/AgNP ratio. The surface roughness and permeate fluxes of coated membranes were increased due to increased hydrophilicity. Antimicrobial and antifouling properties were investigated by the reduction of Escherichia coli cells and the inhibition of biofilm formation on the membrane surface, respectively. Compared with that of the original PVDF membrane, the modified membranes exhibited antibacterial efficiency up to 94% against E. coli cells and inhibition up to 65% of the biofilm mass reduction. The findings showed hydrophilic improvement and an antimicrobial property for possible wastewater treatment without facing the eminent problem of biofouling.