In situ characterization of (poly)molybdate and (poly)tungstate ions sorbed onto iron (hydr)oxides by ATR-FTIR spectroscopy

The sorption of (poly)molybdate and (poly)tungstate ions onto four iron (hydr)oxides, hematite (alpha-Fe2O3), goethite (alpha-FeOOH), akaganeite (beta-FeOOH) and lepidocrocite (gamma-FeOOH), was followed by in situ attenuated total reflection infrared spectroscopy. The different behaviors of the ionic species and the surface reactivity of these various solids have been investigated and different inner-sphere complexes have been found. On lepidocrocite and goethite a monodentate structure is preferred, while a polymerization of molybdate and tungstate species has been observed onto hematite surface. Both ions have a different behavior on akaganeite: molybdate ions polymerize while tungstate species seems to have the same monodentate structure than those found on goethite.