| In recent years, environment pollution issue has been growing along with the development of industry, which also threats the human health and social sustainable development. Heavy metals pollution has become a focus in environmental remediation field. More and more concerns have been paid to chromium pollution in aquatic and soil systems according to its serious threat to human health. Chromium is usually introduce to environment by industries of leather tanning, pub production, wood treatment, electroplating, and metallurgy. Chromium primarily exists in two oxidation states of Cr(Ⅵ) and Cr(Ⅲ). Cr(Ⅵ) of high oxidative property is toxic to plants, animals, and human beings because of its weak adsorption on mineral surfaces. In contrast, Cr(Ⅲ) is relatively low toxicity as it is immobile in most environments due to its low solubility and the formation of strong sorption complexes on the surface of minerals. World Health Organization has set a maximum acceptable guideline concentration of 50 μg·L"1 for total chromium in drinking water, and the United States Environmental Protection Agency set a maximum contaminant limit for total chromium in drinking water of 100μg·L-1. However, Cr(Ⅵ) concentrations in Cr(Ⅵ)-bearing wastewater and Cr(Ⅵ) contaminated natural water resources are far more than the allowable threshold level. Therefore, it is imperative to design new materials and develop effective methods for Cr(Ⅵ) remediation.Adsorption method is an efficient and economical technology for dealing with Cr(Ⅵ) contaminated water problem. Various sorbents, such as carbon materials, mesoporous alumino-silicate, granular titanium dioxide, and magnetite powders (Fe3O4) have been used for Cr(Ⅵ) remediation. Among them, Fe3O4 particles are the most attractive one according to its simply magnetic separable advantage compared with conventional separation, nanoscale magnetite has been applied successfully to the Cr(Ⅵ) removal from electroplating wastewaters recently. Therefore, a series of strategies such as functionalization, immobilization, and modification with other compounds have been applied to the Fe3O4 adsorbent to realize a high efficiency of Cr(Ⅵ) removal.In this study, we synthesized the surface amorphous FeB alloy modified magnetite nanocomposites (Fe3O4-FeB) via reduction of commercial Fe3O4 nanoparticles with NaBH4 solution and investigated their Cr(Ⅵ) removal performance. We found that both quick adsorption and simultaneous reducing of Cr(Ⅵ) happened on the surface of the prepared Fe3O4-FeB nanocomposites, where the amorphous FeB alloy was the major contribution to the high Cr(Ⅵ) removal efficiency of magnetic Fe3O4-FeB, in which boron elements containing many free electrons accelerated the electrons transfer from Fe° to Cr(Ⅵ) as well promoted the Fe(Ⅲ)/Fe(Ⅱ) cycles, thus improved the Cr(Ⅵ) removal efficiency. The high efficiency in Cr(Ⅵ) removal and easy magnetic separation property make this low-cost Fe3O4-FeB nanocomposites a potential material for Cr(Ⅵ) contaminated water treatment.In order to clarify the role of B element on the Cr(Ⅵ) removal with Fe3O4FeB nanocomposites, two kinds of magnetites (Fe3O4) with different morphologies of truncated-cubic (TC) and octahedral (OT) shapes were synthesized by a hydrothermal method by changing the concentration of the KOH solution in ethylene glycol. The TC-Fe3O4 and the OT-Fe3O4 particles were treated with NaBH4 and the Cr(Ⅵ) removal with these modified nanocomposites was studied in detail. A possible Cr(Ⅵ) removal mechanism of the Fe3O4-FeB nanocomposites was proposed on the base of experimental results. |
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