Fe3O4@ZnO Core-Shell Nanoparticles—a novel facile fabricated magnetically separable photocatalyst

[Display omitted] •An easily scalable approach is proposed to obtain Fe3O4@ZnO core–shell nanoparticles.•The structure of Fe3O4@ZnO is a sequence of Fe3O4, γ-Fe2O3, α-FeOOH and (0001) ZnO.•Naphthol green B photodegradation reached 77 % in 60 min under UV radiation.•Separation of Fe3O4@ZnO with a magnet is as effective as that with a centrifuge. The current study proposes a simple and inexpensive technique to synthesise core–shell Fe3O4@ZnO as a promising photocatalyst. An easily scalable original procedure was developed based on sequential and simultaneous addition of Zn2+ and OH– ions to Fe3O4 cores, and preheating and subsequent heating of the reaction medium. The structure of Fe3O4@ZnO core–shell nanoparticles was found to be a sequence of layers including magnetite (Fe3O4), maghemite (γ-Fe2O3), goethite (α-FeOOH), and zinc oxide (ZnO) in (0001) orientation. This layer sequence ensures a smooth transition from the Fe3O4 of the core to the ZnO shell. The synthesis conditions affect layer density and thickness, which can be easily used in adjusting Fe3O4@ZnO properties. Photocatalytic degradation of a model persistent dye (naphthol green B) in the presence of Fe3O4@ZnO nanoparticles reached promising 77 % in 60 min under UV radiation, while Fe3O4 cores showed only 20 %. The wide-gap ZnO layer on the surface of the narrow-gap Fe3O4 provides charge separation and suppresses electron-hole recombination, which drastically increases photocatalytic activity of the material. Separation of the photocatalyst with a magnet showed the same result as that with a centrifuge. All of these findings lead to inexpensive fabrication, effective performance, low toxicity and simple separation of Fe3O4@ZnO.