Development of in situ synthesized Y-based nanoparticle/polyethersulfone adsorptive membranes by adjusting the composition of the coagulation bath for enhanced removal of fluoride

The effects of the composition of the coagulation bath (NaOH solution) on the preparation of in situ generated Y-based nanoparticles (NPs)/polyethersulfone (PES) composite adsorptive membranes were investigated in terms of membrane structure, composition, surface hydrophilicity, water permeability, phase inversion and adsorption performance for defluoridation for the first time. The changes of NaOH concentration in the coagulation bath altered the membrane structure, which was believed to be associated with the change of the phase inversion kinetics in membrane formation process. With the increase in NaOH concentration of the coagulation bath, the demixing way changed from an instantaneous demixing to a delayed demixing process, which led to the suppression of the formation of macro-voids and the generation of more sponger-like structures. Consequently, the surface porosity and permeability of the resulted membranes decreased, e.g. M2-1 > M2-2 > M2-3 > M2-4. From an over view, the contents of Y-based NPs in nanocomposite membrane matrix decreased with slower phase inversion kinetics. The M10-2 showed the best adsorption performance with the maximum adsorption capacity of 51.058 mg g(−1) for fluoride among those prepared membranes, which also contained the most Y-based NPs in membrane. The M10-2 can effectively treat 1770 bed volume of the fluoride contaminated water at neutral pH by continuous filtration, with no leakage of NPs in the permeate. Furthermore, the presence of humic acid and bicarbonate slightly hindered the removal of fluoride in batch and filtration models. This suggested that the prepared in situ nanocomposite adsorptive membranes can be used as a potential membrane for practical treatment of fluoride contaminated water.