Self-cleaning BiOBr/Ag photocatalytic membrane for membrane regeneration under visible light in membrane distillation

In this study, an innovative electrospun photocatalyst self-cleaning BiOBr/Ag membrane is introduced for the MD treatment of dyeing wastewater coupled with post-MD UV and visible light exposure for fouled membrane regeneration. The E-BiOBr/Ag membrane was fabricated by successfully coating an electrospun membrane with BiOBr/Ag catalyst particles using electrospray technology, with the goal to achieve higher hydrophobicity and the reproducible property. Along with the E-BiOBr/Ag membrane, two commercial polyvinylidene difluoride (PVDF) and polytetrafluoroethylene (PTFE) membranes were tested for comparison. The fouling processes on all three membranes were monitored in real-time using optical coherence tomography (OCT). The coating of BiOBr/Ag particles on the E-BiOBr/Ag membrane's surface accelerated dye foulant degradation through the electron-holes’ strong oxidization capacity when exposed to UV. Meanwhile, after Ag nanoparticles were coated on the BiOBr photocatalyst by UV deposition method, not only improved the efficiency of electron separation and transfer but also lessened the electron recombination phenomenon effectively. Correspondingly, compared to the two commercial membranes, the BiOBr/Ag photocatalyst membrane achieved significant improvements in the recovery efficiencies of the water contact angle (95.6%) and water flux (92.2%) under UV illumination, pointing to its potential for fouled membrane regeneration. In addition, the deposition of Ag on BiOBr as cocatalyst enhanced the visible light harvesting. Finally, the BiOBr/Ag photocatalyst membrane maintained good flux recovery and dye rejection (99.9%) over a 5-cycle MD test coupled with visible light exposure, suggesting the application of the novel self-cleaning photocatalyst membrane as a potential alternative for upscaling MD technology to the industrial level.