Reversible, Selective Trapping of Perchlorate from Water in Record Capacity by a Cationic Metal–Organic Framework

We report the capture of ppm-level aqueous perchlorate in record capacity and kinetics via the complete anion exchange of a cationic metal–organic framework. Ambient conditions were used for both the synthesis of silver 4,4′-bipyridine nitrate (SBN) and the exchange, forming silver 4,4′-bipyridine perchlorate (SBP). The exchange was complete within 90 min, and the capacity was 354 mg/g, representing 99% removal. These values are greater than current anion exchangers such as the resins Amberlite IRA-400 (249 mg/g), Purolite A530E (104 mg/g), and layered double hydroxides (28 mg/g). Moreover, unlike resins and layered double hydroxides, SBN is fully reusable and displays 96% regeneration to SBN in nitrate solution, with new crystal formation allowing the indefinite cycling for perchlorate. We show seven cycles as proof of concept. Perchlorate contamination of water represents a serious health threat because it is a thyroid endocrine disruptor. This noncomplexing anionic pollutant is significantly mobile and environmentally persistent. Removal of other anionic pollutants from water such as chromate, pertechnetate, or arsenate may be possible by this methodology.