Electrosynthesis of Layered Organo-Manganese Dioxide Framework-Doped with Cobalt for Iodide Sensing

Aqueous Mn²⁺ ions were anodized at 70 °C with Co²⁺ in the presence of cationic surfactant, cetyltrimethylammonium (CTA). X-ray diffraction (XRD) analysis revealed that the deposited film possesses a layered structure of MnO₂, the interlayer of which is occupied with the assembled CTA molecules. Inclusion of Co ions in the MnO₂ film was evidenced by X-ray photoelectron spectroscopy (XPS). They were located in the MnO₂ framework, not in the interlayer. The thus-obtained film, CTA-intercalated Co-framework-doped layered MnO₂ (CTA/Co-MnO₂), was applied as an electrochemical sensor toward iodide (I^-), a hydrophobic anion. The organic phase between MnO₂ layers could extract I^- ions from solution, providing a better sensitivity than a film consisting of layered MnO₂ with hydrated alkali metals. On the other hand, the Co-doped layers of MnO₂ achieved faster electron transfer kinetics for the oxidation of I^-, which resulted in a drastic reduction in response time compared to the nondoped CTA/MnO₂.