Preparation of nickel-doped ZnFe₂O₄ composites and their algal removal properties

Harmful algal blooms (HABs) outbreaks due to eutrophication of water bodies are becoming increasingly serious, posing a great threat to the water environment and human health. In this paper, magnetic and recoverable nickel-doped ZnFe₂O₄ (Ni-ZFO) adsorbents were prepared by a simple hydrothermal method for the removal of Microcystis aeruginosa from water bodies. The materials were characterized by SEM, XRD, EDS, XPS and VSM. The algal cell removal of Ni-ZFO composites was up to 99.09% within 30 min and remained above 90.41% at 25℃ and pH = 3-8. In addition, the saturation magnetization intensity of Ni-ZFO was 67.93 emu/g, which was 10.74 emu/g higher than that of ZnFe₂O₄ (ZFO), and it was easy to be recycled. The content of algal bile proteins did not increase in the adsorption process, and the algal cells would not be ruptured during the adsorption process, which avoids the secondary pollution caused by Microcystins entering the water environment. The algal removal rate remained above 75% after four times of recycling. The Ni-ZFO adsorbent synthesized in this paper has strong removal efficiency for algal cells and does not cause secondary pollution, which shows great potential in the practical application of mitigating eutrophication of water bodies, and also enriches the application of modified ZFO in the field of adsorption.