Synthesis of ordered mesoporous iron manganese bimetal oxides for arsenic removal from aqueous solutions

• OMIM with large surface area and pore volume was synthesized via the hard template.
• pH affected the removal efficiency of As(III) and As(V) significantly.
• Total arsenic concentration was below 10 ppb both in the As(III) and As(V) systems.
• OMIM plays a dual function for the As(III) removal in aqueous solutions.

A novel ordered mesoporous iron manganese bimetal oxides (OMIM) was synthesized via the hard template approach. The obtained OMIM sample showed excellent performance for the arsenic removal due to its large surface area and pore volume. pH affected the removal efficiency of As(III) and As(V) significantly, and the highest removal occurred in acidic solutions for both arsenic species. The adsorption isotherms were well-described by Freundlich model, and the calculated adsorption capacities of As(III) and As(V) were 67.89 and 93.54 mg/g, respectively. The adsorption kinetics fitted a pseudo-second order model, and intra-particle diffusion was not the only rate-limiting step in the adsorption process. Samples were characterized using SEM-EDS, TEM, XRD and XPS, and the redox states and yields of the arsenic species in aqueous solutions after the reaction of As(III)/As(V) with OMIM were also investigated by HPLC-ICP-MS. The results showed that the changed valence of Mn in OMIM favored As(III) removal and the mechanisms removal of both As(III) and As(V) were complex. In addition, to remove As(III) in aqueous solutions, OMIM plays a dual function as an efficient oxidant of As(III) due to its MnO2 content and subsequently as an excellent adsorbent for As(V).

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