Visible light assisted Fenton-like degradation of Orange II on Ni3Fe/Fe3O4 magnetic catalyst prepared from spent FeNi layered double hydroxide

• Magnetic catalysts were synthesized using spent FeNi-LDH as precursor.
• The materials exhibited high efficiencies in Orange II degradation.
• The strong magnetism of the materials provided great convenience in separation.
• The developed spent adsorbent reutilizing method proved to be facile.

Magnetic Ni3Fe/Fe3O4 catalyst was prepared by using spent FeNi layered double hydroxide derived from the adsorption of organic dyes as precursor via heat treatment under nitrogen atmosphere. X-ray diffraction results indicated that the obtained materials were composed of Ni3Fe and Fe3O4. Thermogravimetric analysis, X-ray photoelectron spectroscopy, elemental analysis, and thermomagnetic curves characterization results demonstrated that Fe3+ and Ni2+ could be reduced to low valence by organic contaminants, and the obtained materials possessed strong magnetism. Visible light assisted Fenton-like experiment results showed that the obtained materials possessed high catalytic activities and the degradations at pH of 3–6 and pH 7 preferred to followed Langmuir–Hinshelwood and Eley–Rideal mechanism, respectively. In addition, the possible effects of Fe0 and Ni species were briefly discussed as well. On the other hand, comparing to the heated products of FeNi layered double hydroxide the obtained materials presented much superiority including variety in metal valences, higher amount of −OH surface group, stronger magnetism and higher Curie point, and higher catalytic activities. This work provided a facile method for reutilizing the spent layered double hydroxide adsorbent with special metal elements (e.g., Fe and Ni) as well as synthesizing functional material (e.g., catalyst).

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