Computationally Designed Perrhenate Ion Imprinted Polymers for Selective Trapping of Rhenium Ions

Abstract

Computationally designed ion imprinted polymers (IIP) were synthesised for selective binding of perrhenate ion from CMSX-4 superalloy leach solutions. A library of functional monomers was screened using Density Functional Theory (DFT) based on their binding energy with perrhenate ion. DFT calculations were also employed to determine the template:monomer ratio of 1:2 from binding energy calculation of the complex formed, and perrhenate ion formed the most stable complex with protonated 4-vinylpyridine (4VP) at 1:2 molecular ratio. An optimum imprinting ratio of 2:4:40 for the functional monomer:cross-linker:perrhenate ion template was calculated using molecular dynamics simulation of a fixed number of component molecules in a periodic boundary and isothermal conditions (NVT-Molecular Dynamics) using MM+ force field. The perrhenate ion selective IIPs were synthesised via bulk polymerisation and combinatorial screening of the imprinting porogen composition was employed to compliment the computational screening. The resulted IIPs showed fast kinetics, high binding capacity (122 mg Re/g polymer), and adsorption processes governed by pseudo-second order kinetics. The IIP synthesised using 4-vinylpyridine and ethylene glycol dimethylacrylate (EGDMA) show superior selectivity towards perrhenate ion in the presence of the oxides, hydroxides, and chlorides of Al, Co, Cr, Hf, Mo, Ni, Ta, Ti, and W in the feed leach solution at pH = 7.0. The perrhenate ion IIPs demonstrated excellent chemical and physical stability towards extreme acidic stripping conditions, and storage for an extended period. Therefore, the use of perrhenate ion imprinted polymers for separation as part of the industrial recycling of rhenium from superalloy leach solutions is recommended.