Effect of Doping Al Cations into MgFe2O4 Magnetic Structure for Efficient Removals of Methyl Orange Dye from Water

Magnetic spinels MgAlxFe2-xO4 (x = 0, 0.2, 0.4, and 0.6) were synthesized by the gel-combustion method to be used as an adsorbent in the process of methyl orange (MO) dye removal from aqueous solutions. The quantity of MgFe2O4 was reduced by Al doping, which can be attributed to the formation of a mixed structure of MgAlFe spinel or separate spinel phase of MgAl2O4. The surface morphology of the adsorbents also showed a reduction in the particle size upon doping Al cations. A reduction in the crystalline size and particle size increased the surface area of the samples containing Al cations. However, the magnetic properties of MgFe2O4 insignificantly decreased by doping the Al cation (0.4 mol). When these synthesized samples were utilized in the adsorption process, the MgAl0.4Fe1.6O4 sample was a better adsorbent in removing MO molecules from the aqueous medium. A contact time = 10 min, adsorbent dosage = 1 g/L, temperature = 25 °C, agitation speed = 200 rpm, and pH   5 were obtained as optimum conditions by using the best adsorbent in the adsorption process. Investigation of adsorption isotherms for the sample revealed that the adsorption process followed the Freundlich model, and the maximum adsorption capacity for this sample was 274.6 mg/g. Kinetic studies also showed that the pseudo-second-order model is consistent with the adsorption process. The process was thermodynamically spontaneous and exothermic. Thus, the MgAl0.4Fe1.6O4 magnetic sample, which is synthesized easily and economically, can be a very suitable adsorbent for the removal of dye pollutants from water.