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)Cr2O4 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)Cr2O4 oxides presented a spinel-type cubic structure, and the formation of a secondary phase such as Cr2O3, MgO, ZnO, or Co3O4 was not observed. The microstructure characterization confirmed that the spinel-type MCr2O4 oxides grew from fine spherical particles to large rhomboid particles. Adsorption experiments of spinel-type MCr2O4 oxides for adsorption of Congo red dye were fitted well with the pseudo-second-order kinetics. The adsorption capacity of the ZnCr2O4 oxide (44.038 mg/g, pH 7, temperature 28 degrees C, initial dye concentration 30 mg/L) was found to be higher than that of MgCr2O4 oxide (43.592 mg/g, pH 7, tem-perature 28 degrees C) and CoCr2O4 oxide (28.718 mg/g, pH 7, temperature 28 degrees C). The effects of initial adsorbent concentration, initial dye concentration, pH, and temperature between the ZnCr2O4 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 ZnCr2O4 oxide studied. The nanostructured spinel-type M(M = Mg, Co, Zn)Cr2O4 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)Cr2O4 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. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Nanostructured spinel-type M(M = Mg, Co, Zn)Cr2O4 oxides with novel adsorbents showed excellent adsorption performance for aqueous Congo red removal. Among them, ZnCr2O4 oxide exhibited higher adsorption capacity than MgCr2O4 and CoCr2O4 oxides. The adsorption process was best described by pseudo-second-order kinetics.