Infrared Study of (Poly)tungstate Ions in Solution and Sorbed into Layered Double Hydroxides: Vibrational Calculations and In Situ Analysis

In situ attenuated total reflection infrared spectroscopy (ATR-FTIR) was used to study the speciation of (poly)­tungstate ions in solution and the sorption process into layered double hydroxides (LDHs). In the first section, the W­(VI) speciation in solution was performed by comparison of thermodynamical calculations and infrared spectroscopy of solutions as a function of pH. Then, the exchange mechanism within LDHs was followed in real time with the in situ ATR technique and compared with batch experiments characterized by powder X-ray diffraction (PXRD), elemental analysis, and FTIR. Decomposition of the (W–O) stretching vibration bands, between 800 and 1000 cm^–1, has allowed the identification of the high affinity of LDHs for the polytungstate species, W₇O₂₄^6–, despite the presence of carbonate ions and higher charged polytungstate ions in solution. This was confirmed by the DFT methods used to investigate the structure and the vibrational modes of this anion, and very good agreement with experimental spectra has been obtained. The affinity series W₇O₂₄^6– > CO₃^2– > WO₄^2– > SO₄^2– has been directly deduced from those results