Polyamide/UiO-66-NH2 nanocomposite membranes by polyphenol interfacial engineering for molybdenum(VI) removal

Introducing porous nanomaterials into polyamide thin layer has been identified to be a desirable approach to improve separation performance of nanofiltration membrane. In this work, a novel sandwich-like thin-film nanocomposite membrane (TFNi) featuring an interlayer was prepared. The interlayer, composed of porous UiO-66-NH2 metal organic framework and adhesive tannic acid (TA), was formed between amphiphilic poly(vinylidene fluoride)-grafting-poly(acrylic acid) substrate and polyamide top layer by self-assembly and interfacial polymerization. TFNis were characterized by FT-IR, SEM, AFM, XRD, water contact angle, zeta potential, molecular weight cut off, flux and ion retention. Results showed that the introduction of interlayer could enhance efficiently membrane flux and ion removal. TFNi-3 membrane constructed by an optimized stepwise deposition, had a high permeate flux (65.4 L m−2 h−1), and good removal efficiencies towards single molybdenum(VI) (Mo(VI)) (98.1 %), single salt (30.8 % for NaCl, 96.5 % for Na2SO4) and mixed solutions (37.0 % for NaCl-Mo(VI), 93.6 % for Na2SO4-Mo(VI), 76.1 % for NaCl-Na2SO4-Mo(VI)). The adsorption experiment and density functional theory (DFT) calculations were also carried out. Amino and zirconium oxygen clusters in UiO-66-NH2 and polyphenol in TA were main adsorption sites. In addition, TFNi-3 had the favorable stability. Perhaps it has a potential application for desalination and Mo(VI) removal from wastewaters.