We report the selective removal of perchlorate from water by a cationic coordination polymer in the highest observed capacity and rate to date. Silver bipyridine acetate [Ag­(4,4′-bipy)+]­[CH3CO2 –]·6H2O (bipy = bipyridine) is easily synthesized in water under ambient conditions (60 min with 99.1% yield). The material releases its environmentally benign acetate anions upon perchlorate uptake to 99.9% mol/mol completion in Millipore water. Actual contaminated industrial water from an underground plume (53 ppm initial perchlorate concentration) was treated to 96% mol/mol in 60 min. The uptake capacity is near-record high at 310 mg/g and is 94% complete within 30 min. Perchlorate exchange was also conducted at 1–30 ppm perchlorate typical of underground contaminated source sites, with up to 99.7% mol/mol completion.

An in-depth study of the class of cationic materials [Ag­(4,4′-bipy)+]­[X–] (where X– = CH3CO2 –, NO3 –, BF4 –, ClO4 –, and MnO4 –) has led to key insights on the relationship between anion hydration energy, material structure, solubility, and stability. Since these materials show promise for their potential as water remediation tools, understanding their properties in detail is of significant importance. The structure of the starting and ending materials is the main driving force behind the resultant stability and solubility and can be successfully used to predict the ion exchange capabilities. The solubility trend was determined to be, from most soluble to least soluble, X– = CH3CO2 – > NO3 – ∼ BF4 – > ClO4 – > MnO4 –. Kinetics and thermal stability also follow predictable trends but involve additional factors. For instance, the kinetics of NO3 – to MnO4 – exchange was much slower than expected based on that seen for NO3 – to ClO4 –. Powder X-ray diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the materials. Solubility was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. Ion exchange was analyzed with ion chromatography (IC) and ultraviolet–visible spectroscopy (UV–vis), and thermal stability was determined with thermogravimetric analysis (TGA).

We describe a cationic erbium-based material [Er12(OH)29(H2O)5][O3SCH2CH2SO3]3.5·5H2O. As synthesized, the material is water stable and capable of complete organic anion exchange for a variety of α,ω-alkanedicarboxylates. We chose these anions as initial examples of exchange and as an analog for pharmaceutical waste, some of which have a carboxylate functionality at neutral pH range. Free-floating and partially anchored organosulfonate anions reside between the cationic corrugated layers and allow for exchange. The structure also displays a reversible hydration event above 100 °C. Both the as-synthesized and the exchanged materials are characterized by a variety of analytical techniques.

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