Synthesis of magnetically separable MnFe₂O₄ nanocrystals via salt-assisted solution combustion method and their utilization as dye adsorbent

Abstract

MnFe₂O₄ nanocrystals with spinel structure were prepared by conventional solution combustion synthesis and salt-assisted solution combustion synthesis, respectively, and their adsorption capacities for Congo red (CR) were also investigated. The results showed that the MnFe₂O₄ nanocrystals prepared with KCl salt (K-MFO) exhibited much better adsorption capacity for CR than those prepared without KCl (MFO), because the introduction of KCl into the solution combustion synthesis process results in an obvious dispersion and increment of surface area in the obtained MnFe₂O₄ particles. Meanwhile, the MnFe₂O₄ nanocrystals exhibited a clearly ferromagnetic behavior under applied magnetic field, which allowed their high-efficient magnetic separation from wastewater. The adsorption ratio of MnFe₂O₄ nanocrystals prepared with a KCl/M ratio of 2/3 (K-MFO-c) for CR still reached 81% after 5 cycles. By the calculation of Langmuir model, the maximum monolayer adsorption capacity (q_m) of K-MFO-c is 118.76 mg/g and much higher than that of MFO (30.00 mg/g), which must be associated with the higher surface area of K-MFO-c.