Facile preparation of recyclable and flexible BiOBr@TiO2/PU-SF composite porous membrane for efficient photocatalytic degradation of mineral flotation wastewater

Various semiconductor nanopowders can photodegrade wastewater efficiently, but their practical application is grievously limited due to poor recycling performance, insufficient sunlight utilization and potential secondary pollution. Membrane materials have been widely used for water treatment, including oil-water separation, desalination and sewage purification. In this paper, a novel BiOBr@TiO2/PU-SF composite porous membrane was prepared via a facile blending-phase separation-impregnation-precipitation method, and this was the first time that the novel membrane material was used as a photocatalyst for mineral flotation wastewater disposal. The PU-SF composite membrane with irregular porous structure acted as a loading substrate, which not only provided abundant space to immobilize BiOBr and TiO2 nanoparticles but also offered more photocatalytically active sites. The as-prepared BiOBr@TiO2/PU-SF composites were well characterized and exhibited higher photocatalytic activity as compared to BiOBr/PU-SF and TiO2/PU-SF. Combining the result of the character-ization and free radical capture experiments with correlative theoretical calculations, we confirmed that the significant enhanced photocatalytic performance of BiOBr@TiO2/PU-SF membranes was attributed to the Z -scheme heterojunction formed between BiOBr and TiO2. In addition, the novel composite membrane material is flexible, it can be sheared, folded, and stretched arbitrarily. More importantly, the BiOBr@TiO2/PU-SF mem-brane can be readily taken out from the photocatalytic reaction system by tweezers, and the catalytic activity was essentially unchanged after being reused for 3 times. This novel recyclable flexible photocatalytic membrane will have promising prospect in field of actual mineral flotation wastewater treatment.