Removal of methylene blue from aqueous solution using a polarizable nanolayered manganese oxide film

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 (Et(4)N) cations was deposited potentiostatically at +1.0 V (vs. Ag/AgCl) from an aqueous Mn(2+) solution containing Et(4)NCl. Et(4)N cations were sandwiched between negatively charged MnO(x) layers. When the Et(4)N/MnO(x) film was immersed in a solution containing MB alone, the intercalated Et(4)N cations were replaced with MB in a solution phase by an ion-exchange mechanism. The uptake capacity of the Et(4)N/MnO(x) film for MB was estimated to be 45.3 mg per 1.0 g of MnO(2). 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.