Combustion synthesis of Fe3O4 and properties of the resulted powders have been discussed in relation to reaction atmosphere (in air/in the absence of air) and used fuel (sucrose, citric acid and glucose). Conducting the combustion reactions in air caused the rapid oxidation of Fe2+ to Fe3+ under the influence of the atmospheric oxygen; therefore the final reaction product was a mixture of α‐Fe2O3 and γ‐Fe2O3. In order to avoid the oxidation of Fe2+ to Fe3+ a simple but efficient solution has been suggested: combustion reactions were carried out in a round bottom flask and the evolving gases were bubbled in a beaker filled with water. This solution allowed the preparation of Fe3O4 nanopowders, with crystallite size varying from 10 nm (glucose) to 18 nm (citric acid). Depending on the used fuel, the specific surface area of the magnetite powders varied between 56 m2/g (citric acid) and 106 m2/g (glucose). The saturation magnetization of Fe3O4 powders prepared in the absence of air ranged between 55.3 emu/g (glucose) and 59.4 emu/g (sucrose).

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A magnetic iron oxide nanopowder (MnP) prepared by a new combustion technique was characterized and tested as adsorbent for methylene blue (MB) removal from aqueous solution. The effects of pH, adsorbent dose, initial dye concentration, contact time, and temperature on the amount of MB adsorbed were studied. The adsorption kinetics were described by a pseudo-second-order model, and the equilibrium experimental data were well fitted to the Langmuir isotherm, yielding a maximum adsorption capacity of 25.54 mg g -1 . The adsorption mechanism is governed by electrostatic forces and is highly dependent on the pH. The MnP adsorbent demonstrated excellent stability, showing good removal efficiency even after eight cycles of reuse, suggesting its potential large-scale application for the removal and recovery of MB from wastewater.