Efficient Removal of Cr(VI) with Fe/Mn Mixed Metal Oxide Nanocomposites Synthesized by a Grinding Method

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Abstract

Fe/Mn mixed metal oxides were synthesized facilely by a grinding method and were characterized by TEM, XRD, XPS, and BET. The characterization results revealed that mixed metal oxides were mainly composed of not highly crystallized Fe ₂O ₃and Mn ₃O ₄nanoparticles with a diameter about 3–5 nm. The specific BET surface areas of the composite were affected by the amounts of KCl diluent in the preparation process and about 268 m ²/g of the composite can be achieved. Compared with metal oxide adsorbents existent, the composites showed good adsorption capacity, stability, and regeneration activity for Cr(VI) removal. The enhanced adsorption capacity was speculated to be ascribed to the synergistic effect of the mixed metal oxides. By monitoring the valence change in the adsorption process using XPS characterization, the mechanism for Cr(VI) removal on the composites was found to be a combination of electrostatic attraction and ion exchange. The above results demonstrated that the synthesized metal oxides nanocomposite is of great potential for Cr(VI) removal in the fields of remediation of environmental problems.

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Self-Assembled 3D Flowerlike Iron Oxide Nanostructures and Their Application in Water Treatment

L.-S. Zhong, J. Hu, H-p Liang … (2006)

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Removal and recovery of Cr(VI) from wastewater by maghemite nanoparticles.

Guohua Chen, Jing Hu, Wu-Chia Lo (2005)

Hexavalent chromium existing in the effluent is a major concern for the metal-processing plant. In this study, a new method combining nanoparticle adsorption and magnetic separation was developed for the removal and recovery of Cr(VI) from wastewater. The nanoscale maghemite was synthesized, characterized, and evaluated as adsorbents of Cr(VI). Various factors influencing the adsorption of Cr(VI), e.g., pH, temperature, initial concentration, and coexisting common ions were studied. Adsorption reached equilibrium within 15 min and was independent of initial Cr concentration. The maximum adsorption occurred at pH 2.5. The adsorption data were analyzed and fitted well by Freundlich isotherm. Cr(VI) adsorption capacity of maghemite nanoparticles was compared favorably with other adsorbents like activated carbon and clay. Competition from common coexisting ions such as Na+, Ca2+, Mg2+, Cu2+, Ni2+, NO3-, and Cl- was ignorable, which illustrated the selective adsorption of Cr(VI) from wastewater. Regeneration studies verified that the maghemite nanoparticles, which underwent six successive adsorption-desorption processes, still retained the original metal removal capacity. In addition, the adsorption mechanisms were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopic techniques.