Novel polydopamine/metal organic framework thin film nanocomposite forward osmosis membrane for salt rejection and heavy metal removal

[Display omitted] •A new PDA/MOF-TFN membrane is developed for heavy metal removal and salt rejection.•The preferentially deposited PDA provided strong adhesion to MOF-801.•MOF-801 is added in PA layer without agglomeration under the influence of PDA.•The stability of the MOF-801 is improved under the influence of PDA.•The high rejection of heavy metals was affected by adsorption and size exclusion. A novel polydopamine/metal organic framework thin film nanocomposite (PDA/MOF-TFN) forward osmosis (FO) membrane was developed for salt rejection and heavy metal ion removal. The polyamide layer of the PDA/MOF-TFN membrane was formed by the interfacial polymerization of an MPD/PDA aqueous phase and a TMC/MOF organic phase. MOF-801 strongly adhered to preferentially deposited PDA, which caused an increased amount of MOF-801 to be uniformly distributed in the polyamide layer without agglomeration. Studies have shown that MOF nanocrystals in the polyamide layer introduce additional water channels, which significantly improves the water permeability of the membrane. At the same time, MOF nanocrystals, having a frame structure, increased the pore tortuosity of the polyamide layer, thereby improving the salt rejection performance of the membrane. Compared to conventional thin film composite (TFC) membranes, the PDA/MOF-TFN membrane showed a water flux (Jv) increase of 30%, a reverse salt flux decrease of 44% and a specific salt flux (Js/JV) increase of 56%. Due to its size exclusion and adsorption properties, the PDA/MOF-TFN membrane showed high heavy metal ion (2000 ppm of Cd2+, Ni2+ and Pb2+) rejection (>94%). These results indicate the potential of PDA/MOF-TFN membranes for salt rejection and heavy metal wastewater treatment.