Markedly enhanced coercive field and Congo red adsorption capability of cobalt ferrite induced by the doping of non-magnetic metal ions

• CoFe2−xMxO4 (M = Al3+, In3+ and Cu2+) ferrites were synthesized by a facile hydrothermal method.
• The hypothesis of water magnetized by the coercive fields of doped cobalt ferrites was proposed.
• The sample In3 with the largest coercive force of 2014.2 Oe possessed the highest CR adsorption capacity (605.4 mg g−1).

In this contribution, a series of CoFe2−xMxO4 (M = Al3+, In3+ and Cu2+) ferrites were synthesized by a facile hydrothermal method. On the premise of spinel structure, the coercive forces and adsorption capabilities of the doped CoFe2O4 ferrites are significantly enhanced. It is first reported that coercive field of magnetic material shows more important influence on the adsorption capacity than that of specific surface area. Water magnetized mechanism was proposed to explain the relation between the coercive field and adsorption capacity. To the best of our knowledge, the CR adsorption value of 605.4 mg g−1 may be the best among the reported magnetic adsorbents with spinel structure.