Hierarchical iron containing γ-MnO2 hollow microspheres: A facile one-step synthesis and effective removal of As(III) via oxidation and adsorption

The hierarchical flower-like iron containing γ-MnO 2 hollow microspheres assembled by ultrathin nanosheets have been successfully fabricated via a facile one-step co-precipitation route in the absence of additional templates or surfactants. Structural characterization show that iron element is uniformly incorporated into γ-MnO 2 framework, and no segregated iron oxide appears. The resulting iron containing MnO 2 hollow microspheres exhibit a noticeable enhanced performance for As(III) removal compared to that of the undoped counterparts, accompanied by 102.84   mg/g of the saturated removal capacity towards As(III). The excellent performance for the arsenic removal may be attributed to the unique structural characteristics of highly accessible surface and fully exposed active sites inherited from the hierarchical iron containing γ-MnO 2 samples. The co-existence of oxidation and adsorption is another key factor for the improvement of As(III) removal efficiency, in which manganese dioxide is mainly responsible for oxidizing As(III) to As(V) and ferrous species may serve to the adsorption of the generated As(V), as evidenced by X-ray photoelectron spectroscopy (XPS) analysis. Importantly, the composites exhibit an excellent regenerative ability over three cycles without a significant decrease in its removal efficiency towards As(III). Furthermore, the relatively large micrometer-scale particles can be easily separated by filtration, accompanied by fewer secondary contaminants risks than nanoparticles. Therefore, the fabricated hierarchical Fe-containing γ-MnO 2 hollow spheres in the present study will be an excellent candidate for the arsenic transformation and removal from the contaminated water based on the synergistic effects of effective oxidizing and adsorptive performance, good regeneration together with the convenient separation.