Influence of fuel nature on sol–gel microwave-ignited combustion synthesis of nanosized cobalt and nickel spinel ferrites

CoFe$_{2}$O$_{4}$ and NiFe$_{2}$O$_{4}$ spinel ferrites were obtained by microwave-assisted sol–gel combustion synthesis using three different types of chelating/combustion agents: maleic acid, citric acid, and urea. The nanomaterials produced were characterized from the structural, morphological, textural, and magnetic viewpoints. The spinel ferrites prepared were employed as adsorbents for the removal of Orange-II dye from synthetic wastewaters. The nickel ferrite sample prepared using urea as fuel exhibited distinctive properties such as the smallest crystallite size and the highest specific surface area. Likewise, this material was the most efficient for the adsorption of the organic pollutant (50.32 mg/g) from aqueous solutions