Solvent extraction mechanism studied by vibrational sum frequency generation spectroscopy

Kusaka, Ryoji  ; Watanabe, Masayuki   

In general solvent extraction, an aqueous phase where metal ions are dissolved and an organic phase where an extractant is dissolved are brought into contact with each other, and the metal is extracted from the aqueous phase to the organic phase as a metal complex. Since the extractant used is poorly soluble in water and surface active, it is considered that complex formation between metal and extractant takes place at the interface and then the metal is extracted into the organic phase. However, due to experimental difficulties, the phase transfer mechanism occurring at the interface is unknown. One of the reasons for the difficulties to observe the metal complex at the interface is that the metal complex moves to the organic phase after the complex formation at the interface. In order to observe the metal complex at the interface, we removed the organic phase so that we can trap the metal complex at the extractant/water interface (the surface of aqueous solution). The structure of the metal complex at the interface is investigated using sum frequency generation (VSFG) spectroscopy to elucidate the solvent extraction mechanism.