Core-shelled mesoporous CoFe2O4-SiO2 material with good adsorption and high-temperature magnetic recycling capabilities

Residues of organic dye in industrial effluents cause severe water system pollution. Although several methods, such as biodegradation and activated carbon adsorption, are available for treating these effluents before their discharge into waterbodies, secondary pollution by adsorbents and degrading products remains an issue. Therefore, new materials should be identified to solve this problem. In this work, CoFe₂O₄-SiO₂ core-shell structures were synthesized using an improved Stöber method by coating mesoporous silica onto CoFe₂O₄ nanoparticles. The specific surface areas of the synthesized particles range from 30 m²/g to 150 m²/g and vary according to the dosage amount of tetraethoxysilane. Such core-shelled nanoparticles have the following advantages for treating industrial effluents mixed with dye: good adsorption capability, above-room-temperature magnetic recycling capability, and heat-enduring stability. Through adsorption of methylene blue, a typical dyeing material, the core-shell-structured particles show a good adsorption capability of approximately 33 mg/L. The particles are easily and completely collected by magnets, which is possible due to the magnetic property of core CoFe₂O₄. Heat treatment can burn out the adsorbed dyes and good adsorption performance is sustained even after several heat-treating loops. This property overcomes the common problem of particles with Fe₃O₄ as a core, by which Fe₃O₄ is oxidized to nonmagnetic α-Fe₂O₃ at the burning temperature. We also designed a miniature of effluent-treating pipeline, which demonstrates the potential of the application.