One-pot synthesis of hierarchical magnetic porous γ-Fe2O3@NiFe2O4 composite with solid-phase morphology changes promoted by adsorption of anionic azo-dye

Hierarchical magnetic porous gamma-Fe2O3@NiFe2O4 composite was synthesized in air by sol-gel auto-combustion method. Through nitrogen physisorption analysis was found a very large surface area of 220 m(2)/g. Due to the strong molecular host-guest interaction, complemented by the noticeable magnetic properties (M-s = 25 emu/g and H-c = 137 Oe), gamma-Fe2O3@NiFe2O4 shows outstanding adsorption performance over anionic dyes, including but not limited to methyl orange. The adsorption process is spontaneous and the pseudo-second-order kinetic model and the Langmuir isotherm model well described the adsorption process. Unquestionably, the excellent adsorption capacity of MO azo dye of 1.66 g/g, according to Langmuir isotherm, promotes morphology changes from porous-like material to fibrous-like structure. The inherent features of morphology changes enhance the photocatalytic activity of the composite by increasing the surface exposure to the visible light. Compared with previously published data, the adsorption capacity of gamma-Fe2O3@NiFe2O4 ranks at the top.