Selective Iodide Recovery from Saline Water Using Electrodeposited Layered Organo-MnO 2 : Elucidation of the Sorption Mechanism

Organo-manganese dioxide (MnO₂) thin films intercalated with cetyltrimethylammonium chloride (CTAC/MnO₂) were successfully fabricated via electrochemical deposition and applied for selective iodide (I^-) recovery from aqueous solutions. The CTAC/MnO₂ thin films exhibited high sorption capacities for I^-, following Langmuir-type monolayer sorption behavior with a maximum sorption capacity of 211 mg g^-1. X-ray photoelectron spectroscopy revealed that iodide sorption proceeded primarily via anion exchange with interlayer Cl^-, without redox transformation of Mn species. Solvent extraction studies confirmed a 1:1 stoichiometry between CTA⁺ and I^- during complex formation. Iodide was electrochemically desorbed under cathodic polarization and resorbed after anodic polarization, demonstrating the reusability of the material. Competitive sorption experiments demonstrated that CTAC/MnO₂ thin films maintained excellent selectivity for I^- even in the presence of excess chloride and sulfate ions, attributed to differences in dehydration energy and structural compatibility within the hydrophobic interlayer space. Furthermore, CTAC/MnO₂ thin films successfully recovered I^- from modified artificial seawater devoid of Ca²⁺ and HCO₃^-, thus highlighting the practical feasibility of this system in the absence of key interfering ions. Additionally, a D2EHPA-based solvent extraction pretreatment was developed to selectively remove Ca²⁺ and HCO₃^- from saline solutions.