Exchange Capability of Cationic Silver 4,4′-Bipyrdine Materials for Potential Water Remediation: Structure, Stability, and Anion Exchange Properties

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).