In-situ growth of polyvinylpyrrolidone modified Zr-MOFs thin-film nanocomposite (TFN) for efficient dyes removal

The major challenges in fabricating excellent thin film nanocomposite (TFN) membranes are the aggregation of the nanofiller and the organic-inorganic incompatibility. In this work, to overcome such challenges, polyvinylpyrrolidone (PVP) assisted in-situ growth method was utilized to synthesize Zr-MOFs (PVP-UiO-66-NH2). The resultant Zr-MOFs has well dispersibility in water, negatively charged, high surface area and uniform shape. PVP-UiO-66-NH2 was incorporated into polyvinyl alcohol (PVA) aqueous solution and drop-coated on the surface of HPAN supporting layer. The influences of PVP-UiO-NH2 nanofillers on the TFN membranes were systematically studied. Compared with the unfilled TFC membrane, the TFN membranes reveal better hydrophilicity and filtration properties. The optimized membrane (PVP-UiO-66-NH2 content of 0.3 wt%) has a water permeability of 130.9 ± 2.9 L m−2 h−1 MPa−1, remarkable rejection (99.89%∼100%) for four dyes (Congo red, Methyl blue, reactive Black 5 and Direct red 23), low rejection for monovalent salt (5.2%, 6.0% for NaCl and MgCl2) and moderate rejection for bivalent salt (10.2%, 22.3% for MgSO4 and Na2SO4). The membrane also demonstrated a good stability in continuing operation for 50 h. Overall, the prepared membranes show an exciting prospect for dye/salt separation owing to their excellent filtration performance.