Fractal-like kinetics for enhanced boron adsorption on heterogeneous magnetic composite surfaces

Co-precipitated 14 nm γ-Fe₂O₃ and 35 nm MgO nanoparticles (NPs) decorated on zeolite 5 A (Z5A) templates were systematically studied. ⁵⁷Fe Mössbauer and transmission electron microscopy data indicated a broad particle size distribution. The spinel structure of γ-Fe₂O₃ is strongly affected by size effects (particles smaller than 10 nm in size have an octahedral/tetrahedral iron site ratio of 7/3 instead of 5/3 found in bulk). ²⁷Al nuclear magnetic resonance (NMR) showed the formation of octahedral Al species after boric acid reaction with MgO NPs. ¹¹B NMR spectra indicated adsorption of B on the MgO/Z5A surface, whereas B adsorption in the pure Z5A framework is absent. Adsorption isotherms and kinetic studies of the nanohybrids showed that the B-rich species adsorption is described by Freundlich and fractal-like models, respectively. B adsorption occurs dominantly by the MgO fraction. The nanohybrids presented a good B removal efficiency when compared with other materials reported in literature.