Reversible perchlorate trapping from water using a highly recyclable coordination polymer

We report an easily recyclable cationic coordination polymer (CP) for the selective removal of high perchlorate (ClO₄^-) concentrations through an anion exchange reaction. Ambient conditions were used for both the synthesis of the starting silver 2,3'-bipyridine nitrate (2,3'-SBN, [Ag(C₅H₄N)₂][NO₃]) and the perchlorate exchange product, silver 2,3'-bipyridine perchlorate (2,3'-SBP, [Ag(C₅H₄N)₂][ClO₄]). Exchange reactions are 80% complete within 10 min and 86% complete after 1 h, with a capacity of 380 mg ClO₄^- per g 2,3'-SBN. Unlike commercially available resins, 2,3'-SBN can be regenerated under brine-free aqueous conditions at room temperature using only two-fold molar excess sodium nitrate in 1 h, which is outstanding for a cationic coordination polymer. The average percent recovery across four cycles was 95%. Since regeneration involves the formation of new 2,3'-SBN crystals, the material can potentially be used for the trapping of perchlorate indefinitely. The collected perchlorate can then be concentrated and disposed of with a significant reduction in cost compared to current remediation processes. Both materials were characterized by powder X-ray diffraction (PXRD), single crystal X-ray diffraction (SCXRD), scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), thermogravimetric analysis (TGA), elemental analysis and Fourier transform infrared spectroscopy (FTIR).