Selective sorption of iodide onto organo-MnO2 film and its electrochemical desorption and detection.

This paper reports an electrochemically grown film consisting of layered MnO2 intercalated with hexadecylpyridinium cations (HDPy(+)), which can selectively sorb and detect iodide anions in aqueous solution amperometrically. Sorption of iodide by the HDPy/MnO2 film did not occur via ion exchange, but through hydrophobic interactions between the interlayer organic phase of the film and iodide ions in solution. The sorption rate increased with the deposited amount of MnO2. During the sorption process, the interlayer spaces expanded, and new diffraction peaks appeared that were attributed to the incorporated species. Anodic polarization of the iodide-sorbed HDPy/MnO2 film led to electron transfer from the incorporated iodide to the underlying substrate through the MnO2 sheets. The oxidized iodide was expelled from the film as molecular I2, while the expanded interlayer spaces were restored to their original state. Thus, the MnO2 layers and the incorporated HDPy can synergistically sorb/desorb iodide anions, resulting in a unique "self-cleaning" function that can operate electrochemically. This property allowed amperometric detection of iodide at a concentration as low as 0.0186 µM, which was below the detection limits reported for previous iodide sensors.

Effective and selective sorption of iodide by thin film of multilayered MnO(2) intercalated with cationic surfactants.

We have fabricated a thin film of multilayered MnO2 whose interlayer is occupied with hexadecylpyridinium (HDPy) cations, using a simple anodic approach. The resulting film can effectively sorb iodide anions from aqueous solutions, even in the presence of NaCl or Na2SO4. The maximum sorption capacity was estimated to be 256 mg/g-MnO2, whereas a layered MnO2 film intercalated with K(+) ions showed no significant sorption. The layered structure of the HDPy/MnO2 composite remained unchanged after a sorption experiment. This indicates the incorporation of I(-) ions between MnO2 layers due to their specific affinity toward HDPy.