Facile assembly of a hierarchical core@shell Fe3O4@CuMgAl-LDH (layered double hydroxide) magnetic nanocatalyst for the hydroxylation of phenol

Abstract

Novel hierarchical core@shell structured magnetic nanocatalysts of various morphologies involving ternary Cu-based layered double hydroxide CuMgAl-LDH shells and Fe₃O₄ cores were prepared via one-pot coprecipitation assembly and systematically characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning/transmission electron microscopy (SEM/TEM)/high-resolution (HR) TEM, vibrating-sample magnetometry (VSM), H₂-temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The nanocatalyst Fe₃O₄@CuMgAl-1 is revealed as a ca. 50 nm thick CuMgAl-LDH nanoshell consisting of 20 nm plate-like LDH particles horizontally coated onto the surface of the Fe₃O₄ core (ca. 500 nm in diameter), while Fe₃O₄@CuMgAl-2 shows honeycomb-like morphology with ca. 200 nm hexagonal plate-like LDH particles vertically grown on the surface of the Fe₃O₄ core. Both magnetic nanocatalysts exhibit higher catalytic activity for phenol hydroxylation by H₂O₂ than pure CuMgAl-LDH, and the former is better than the latter. These results can be rationally explained by a hydroxyl radical mechanism, resulting from Cu²⁺/Fe²⁺ and H₂O₂via a Fenton-like reagent, enhanced by the synergetic effect between the CuMgAl-LDH shell and the Fe₃O₄ core, possibly via a Cu–O–Fe linkage. In addition, the as-prepared magnetic nanocatalysts possess strong magnetic properties and a high magnetic reuse efficiency.