BioMOF@PAN Mixed\nMatrix Membranes as Fast and Efficient\nAdsorbing Materials for Multiple Heavy Metals’ Removal

Heavy metal ions are a common source of water pollution.\nIn this\nstudy, two novel membranes with biobased metal–organic frameworks\n(BioMOFs) embedded in a polyacrylonitrile matrix with tailored porosity\nwere prepared via nonsolvent induced phase separation methods and\ndesigned to efficiently adsorb heavy metal ions from oligomineral\nwater. Under optimized preparation conditions, stable membranes with\nhigh MOF loading up to 50 wt % and a cocontinuous sponge-like morphology\nand a high water permeability of 50–60 L m<sup>–2</sup> h<sup>–1</sup> bar<sup>–1</sup> were obtained. The\ntortuous flow path in combination with a low water flow rate guarantees\nmaximum contact time between the fluid and the MOFs, and thus a high\nheavy metal capture efficiency in a single pass. The performances\nof these BioMOF@PAN membranes were investigated in the dynamic regime\nfor the simultaneous removal of Pb<sup>2+</sup>, Cd<sup>2+</sup>,\nand Hg<sup>2+</sup> heavy metals from aqueous environments in the\npresence of common interfering ions. The new composite adsorbing membranes\nare capable of reducing the concentration of heavy metal pollutants\nin a single pass and at much higher efficiency than previously reported\nmembranes. The enhanced performance of the mixed matrix membranes\nis attributed to the presence of multiple recognition sites which\ndensely decorate the BioMOF channels: (i) the thioether groups, deriving\nfrom the <i>S</i>-methyl-l-cysteine and (<i>S</i>)-methionine amino acid residues, able to recognize and\ncapture Pb<sup>2+</sup> and Hg<sup>2+</sup> ions and (ii) the oxygen\natoms of the oxamate moieties, which preferentially interact with\nCd<sup>2+</sup> ions, as revealed by single crystal X-ray diffraction.\nThe flexibility of the pore environments allows these sites to work\nsynergically for the simultaneous capture of different metal ions.\nThe stability of the membranes for a potential regeneration process,\na key-factor for the effective feasibility of the process in real\nlife applications, was also evaluated and confirmed less than 1% capacity\nloss in each cycle.