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In this study, Zn-doped Fe₃O₄ nanoparticles were successfully synthesized by a facile solvothermal method in the presence of sodium dodecyl sulfate (SDS). The morphology, magnetic properties and electromagnetic wave absorbing properties of these materials were characterized. Results showed that Zn${}^{2+}$ played a significant role in the formation of Zn-doped Fe₃O₄. With the protection of SDS, highly dispersed Fe₃O₄ nanoparticles were obtained. The nanoparticle size decreased after Zn${}^{2+}$ doping, and the dispersity deteriorated with increasing Zn${}^{2+}$ doping concentration. Zn-doped Fe₃O₄ exhibited excellent electromagnetic wave absorbing property, which resulted in magnetic loss and dielectric loss at an appropriate doping concentration. The minimum reflection loss (RL) was approximately $-27.2$dB at 16.9GHz. As the coating layer thickness increased to 4.0mm, the bandwidth was approximately 5.0GHz corresponding to RL below $-10$dB, which nearly covered the entire S band (2–4GHz) and C band (4–8GHz). The peak frequency of RL and the number of peaks matched the quarter-wave thickness criteria. It was believed that the Zn-doped Fe₃O₄ could be a potential electromagnetic wave absorbing material in S and C bands.

Zn-doped Fe₃O₄ has been employed as a catalyst for the photo-Fenton process. At the present study, the influence of Zn content in the Zn-doped Fe₃O₄ on the catalytic activity for the photo-Fenton process was studied. Monodispersed Zn_xFe${}_{3-x}$O₄ particles were facilely synthesized with higher surface area and several nm of diameter, where $x=0$, 0.4 and 1.0. Rhodamine B (Rh B), as one of the positive dyes, was selected as a model pollutant. The decolorization efficiency of the Fe₃O₄ ($x=0$) for Rh B reached about 90% in 120min under visible light. The Zn content increase in the Zn-doped Fe₃O₄ inhibited the Fenton process. The higher molar ratio of Fe${}^{2+}$ to Fe${}^{3+}$, smaller band-gap, and more negative zeta potential of the Fe₃O₄ induced the most excellent photo-Fenton performance for the Rh B degradation.