Polymer metal-organic cage gels for water purification


Julia Zhao


Julia Zhao, Jeremiah A. Johnson

Author Affiliation: 

Department of Chemistry, Massachusetts Institute of Technology


Polymer metal-organic cage (polyMOC) gels are polymer networks with well-defined MOC junctions formed from the multicomponent assembly of appropriate ligands (L) and metal ions (M), where the cage architecture can vary greatly depending on the bite angle of L. Cages that provide high branch functionality (such as M12L24) produce polyMOC gels with relatively high shear modulus as well as a large number of loop defects. These inelastic loops can be exchanged with functional free ligands at little cost to the modulus, allowing the practical application of polyMOC gels through the incorporation of endo-functionalized free ligands. As a result, this material provides a template that can be tailored to adsorb water pollutants with high specificity: since the nanoenvironment inside each MOC is easily interchangeable with different free ligands, multiple water pollutants can be adsorbed with high affinity by using polyMOC gels in combination. Our modular system uses telechelic tetra-arm poly(ethylene glycol) (PEG), end-functionalized with M12L24-forming bispyridine ligands. The self-assembly of this telechelic PEG with functionalized free ligand and platinum salt produces a robust gel that has been able to withstand up to 12 wash and reuse cycles. Using free ligand endo-functionalized with a fluorinated alkyl chain, we have created a polyMOC gel able to adsorb model compound perfluorooctanoic acid (PFOA) at 95% efficiency ([PFOA]0 = 160 μg/L, [gel] = 6.4 mg/mL). Preliminary results show that contents encapsulated within MOCs can be washed, regenerating the polyMOC gel for reuse.