Analytical Sciences

Removal of Methylene Blue from Aqueous Solution Using a Polarizable Nanolayered Manganese Oxide Film

Masaharu NAKAYAMA, Shinya NAKAMOTO, Chihiro IIDA, and Makoto YOSHIMOTO

Department of Applied Chemistry, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japa

A layered manganese oxide film grown electrochemically was applied to remove methylene blue (MB), a cationic dye, from an aqueous solution. A layered MnO_x film intercalated with tetraethylammonium (Et₄N) cations was deposited potentiostatically at +1.0 V (vs. Ag/AgCl) from an aqueous Mn²⁺ solution containing Et₄NCl. Et₄N cations were sandwiched between negatively charged MnO_x layers. When the Et₄N/MnO_x film was immersed in a solution containing MB alone, the intercalated Et₄N cations were replaced with MB in a solution phase by an ion-exchange mechanism. The uptake capacity of the Et₄N/MnO_x film for MB was estimated to be 45.3 mg per 1.0 g of MnO₂. In the presence of KCl, the MB sorption was seriously restricted because the interlayer space was occupied by K⁺ ions. However, the MnO_x film anodized at +0.8 V can selectively take up MB molecules from the KCl solution. This can be ascribed to an increase in the interlayer space available to the sorption of MB due to the extraction of K⁺ ions, where the MnO_x surface probably has a specific affinity toward MB molecules.

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