| Summary: | An innovative method of combustion–calcination of a nitrate–ethanol solution to produce magnetic Co _0.5 Ni _0.5 Fe _2 O _4 nanoparticles was developed. The calcination temperature and the volume of ethanol were two pivotal elements that determine the properties of the Co _0.5 Ni _0.5 Fe _2 O _4 nanoparticles in this study. When the volume of ethanol used was increased from 20 ml to 40 ml, the crystallinity of the Co _0.5 Ni _0.5 Fe _2 O _4 nanoparticles increased; further increase of the volume of ethanol decreased the crystallinity. The smallest nanoparticle was obtained using 20 ml ethanol. As the calcination temperature increased from 400 °C to 700 °C, the saturation magnetization of the Co _0.5 Ni _0.5 Fe _2 O _4 nanoparticles increased from 12.8 emu g ^−1 to 30.8 emu g ^−1 . Co _0.5 Ni _0.5 Fe _2 O _4 nanoparticles fabricated using 20 ml ethanol at 400 °C were used to study the removal of methyl blue (MB) by adsorption. Experimental data revealed that the adsorption was best described by pseudo-second kinetics. The adsorption isotherm applied the Temkin model, which indicated the presence of a single and multilayer associative mechanism in the adsorption of MB on the Co _0.5 Ni _0.5 Fe _2 O _4 nanoparticles. The effect of pH and recycling on the adsorption was measured. At pH values ≥5, the adsorption was high. After eight cycles of use and recycling, the relative removal rate of MB by the Co _0.5 Ni _0.5 Fe _2 O _4 nanoparticles was 75% of the initial adsorption value.
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