Nanostructured spinel-type M(M = Mg, Co, Zn)Cr2O4 oxides: novel adsorbents for aqueous Congo red removal

Nanostructured spinel-type M(M = Mg, Co, Zn)Cr 2 O 4 oxides with novel adsorbents for aqueous Congo red removal were synthesized by a polyacrylamide gel method and studied for their phase structure, microstructure, adsorption performance, and multiferroic behavior. The phase structure and purity analysis revealed that the nanostructured spinel-type M(M = Mg, Co, Zn)Cr 2 O 4 oxides presented a spinel-type cubic structure, and the formation of a secondary phase such as Cr 2 O 3 , MgO , ZnO, or Co 3 O 4 was not observed. The microstructure characterization confirmed that the spinel-type MCr 2 O 4 oxides grew from fine spherical particles to large rhomboid particles. Adsorption experiments of spinel-type MCr 2 O 4 oxides for adsorption of Congo red dye were fitted well with the pseudo-second-order kinetics. The adsorption capacity of the ZnCr 2 O 4 oxide (44.038 mg/g, pH 7, temperature 28 °C, initial dye concentration 30 mg/L) was found to be higher than that of MgCr 2 O 4 oxide (43.592 mg/g, pH 7, temperature 28 °C) and CoCr 2 O 4 oxide (28.718 mg/g, pH 7, temperature 28 °C). The effects of initial adsorbent concentration, initial dye concentration, pH, and temperature between the ZnCr 2 O 4 oxide and Congo red dye at which optimal removal occurs, were performed. The thermodynamic studies confirmed that a high temperature favors the adsorption of Congo red dye onto ZnCr 2 O 4 oxide studied. The nanostructured spinel-type M(M = Mg, Co, Zn)Cr 2 O 4 oxides that exhibited high adsorption performance for adsorption of Congo red dye can be ascribed to the synergistic effect of electrostatic interaction , pore filling, and ion exchange. The present work suggested that the nanostructured spinel-type M(M = Mg, Co, Zn)Cr 2 O 4 oxides have excellent adsorption performance and multiferroic behavior, which shows potential applications for removal of the Congo red dye from wastewater, magnetic memory recording media, magnetic sensor, energy collection and conversion device, and read/write memory.