Efficient reduction of hexavalent chromium by Fe-Mn bimetallic nanoparticles: Performance and role of manganese

Modification of zero-valent iron by manganese doping is a potential way to improve the properties of zero-valent iron, but the role of manganese in Fe/Mn bimetallic nanoparticles during the reduction process of hexavalent chromium is not yet fully recognised. Nano-Fe/Mn bimetals (NFMB) was synthesized through one-step chemical reduction method and characterized by Transmission Electron Microscope (TEM), Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS) and X-ray Photoelectron Spectroscopy (XPS). The results showed that dispersed particles owned a rough surface and six functional groups, namely, C-O, C=O, O-H, and -COOH, Fe-O, Mn-O. XPS analysis results showed that four elements in NFMB: Fe, Mn, C, and O, along with Fe0, Mn0, Fe2O3, and FeOOH were confirmed. The composition analysis indicated an approximate content of Fe (16.74 %) and Mn (12.59 %), with the detection of Cr (1.51 %) after the reaction. The batch experiments revealed a significant enhancement of reduction efficiency of Cr (VI) at a lower pH level and higher temperature, with a consistent removal rate of around 99.9 % within the pH range of 3-9, showcasing the adaptability of NFMB across a wide pH range. The maximum removal capacity of Cr (VI) by NFMB was determined to be 35.54 mg·g−1. The removal process involved the adsorption of Cr (VI) to the surface of NFMB, followed by a series of chemical reduction and precipitation processes, and the final removal from the aqueous solution. Therefore, the Fe/Mn bimetallic nanocomposites was proved to be promising for the removal of Cr (VI) from aqueous environments.