Adsorptive removal of toxic Methylene Blue and Acid Orange 7 dyes from aqueous medium using cobalt-zinc ferrite nanoadsorbents

Cobalt-zinc ferrite nanoparticles of general formula Co1-xZnxFe2O4 (0.0 <= x <= 1.0) were synthesized by means of chemical co-precipitation method. Impedance analysis was used to study the grain and inter-grain conductivities. The changing of complex conductivity with composition confirmed the semiconducting behavior. A significant influence of Zn concentration on dielectric properties was observed. The obtained Co-Zn ferrites were examined as magnetic adsorbents using both cationic and anionic dyes as model pollutants. Substitution of zinc ions with cobalt ones resulted in changes in sorption characteristics. The efficiency of Methylene Blue (MB) dye removal was increased with increasing Co content. On contrary, efficiency of Acid Orange 7 dye removal was increased with increasing Zn content. The adsorption of the both anionic and cationic dyes onto ferrite nanoparticles agreed well with the Langmuir isotherms. The maximum adsorption capacity for the Acid Orange 7 dye was reached up to 31 mg/g using ZnFe2O4, while the maximum adsorption capacity for the cationic Methylene Blue dye was found to be 3.4 mg/g on Co0.9Zn0.1Fe2O4. The relation of adsorption efficiency with ionic-covalent and acid-base parameters of the ferrite surface was also discussed.