Modification of PVDF membranes using BiOBr precursor in-situ deposition and tannic acid self-assembly for effectively removing organic pollutants

Currently, conventional technologies for water treatment are not sufficiently efficient to completely mineralize refractory organic pollutants, and most of the existing reports only deal with multiple organic pollutants individually. Therefore, designing a hydrophilic membrane that is easy to fabricate and has multiple active sites for simultaneous separation of blended complex organic pollutants is urgently required. Therefore, the aim of this study was to share a new perspective for designing high-performance membranes by functionally modifying the membranes. First, we combined water-induced precipitation properties of BiOBr with polyvinylidene fluoride (PVDF) phase inversion to enable in-situ growth and firm enchasing of hydrophilic BiOBr nanomaterials in the micro-clusters of the PVDF membrane, avoiding the disadvantages of easy aggregation and masking of nanomaterials. Second, we adopted a simple method to self-assemble the tannic acid (TA) and halloysite nanotubes on the membrane surface enhanced hydrophilicity and anti-fouling performance. The electrostatic force between TA and the [Bi2O2]2+ electric double layer of BiOBr makes the two stably combined. The TA/BiOBr/PVDF membrane designed herein demonstrated high efficiency in the instantaneous separation of recalcitrant blended organic molecules. The removal efficiency of the TA/BiOBr/PVDF membrane for methylene blue, methyl orange, rhodamine B, tetracycline, and bisphenol A was 99.6%, 97.7%, 99.8%, 90.7%, and 85.5%, respectively. The evaluation of SEM, EDS, atomic force microscopy, XRD and XPS results demonstrated not only the compatibility of in-situ preferential deposition of BiOBr for PVDF but also a hydrophilic nano-layer of TA self-assembled on the surface of the BiOBr/PVDF membrane. The stable blended pollutants flux (Jw, 144.4 L·m−2·h−1·bar−1) and water contact angle (47.46°) of the TA/BiOBr/PVDF membrane were higher than those of a pristine PVDF membrane (102.7 L·m−2·h−1·bar−1 and 87.08°, respectively). In addition, the composite membrane showed high stability for recycling and anti-pollution activities.