Porous Nanobimetallic Fe-Mn Cubes with High Valent Mn and Highly Efficient Removal of Arsenic(III).

Iron (Fe) oxides are the most commonly used adsorbent materials for the aqueous removal of Arsenic (As), but they have deficiencies, including low uptake and poor removal of the relatively higher toxicity As(III). Introduction of transition metals into Fe-containing adsorbents, an inexpensive method of altering Fe chemical states, is likewise of interest for removing As(III) from water by means of adsorption. Porous cubic Fe-Mn structures with BET surface area of 450 m2 g-1 were herein prepared via chemical etching of Mn-substituted Prussian Blue analogues (PBAs). Cyclic voltammetry showed a "protective" role of polyvinylpyrrolidone (PVP) during the preparation process, so that Mn with high valence state was readily preserved in this binuclear corner-sharing structure. The calculated reaction Gibbs free energy, which was the most negative of the studied adsorbents, indicated that the adsorption was promoted in the presence of high valence Mn. The structures were capable of directly capturing As(III) oxyanions to below the acceptable limits in drinking water standards, and the saturation uptake capacity of 460 mg g-1 was substantially higher than comparable materials under consideration. The work therefore presents a new benchmark for As-adsorbent materials and demonstrates the promise of the porous Fe-Mn structure for rapid removal of other metal ions from contaminated water for environmental remediation.