Defective magnesium ferrite nano-platelets for the adsorption of As(V): The role of surface hydroxyl groups.

Abstract

In this work, magnesium ferrite (MgFe2O4) nano-platelets with rich defects and abundant surface hydroxyl groups were synthesized, and used for the removal of low concentration As(V) in aqueous solution. Results from scanning electron microscopy (SEM) showed that the as-synthesized MgFe2O4 nano-platelets were consisted of many individual nanospheres. Rietveld refinement of X-ray diffraction (XRD) data indicated that the Mg2+ ions substituted the Fe3+ ions at both the octahedral and the tetrahedral sites of the crystal structure. Batch adsorption experiment showed that the equilibrium concentration of As(V) could be reduced down to 4.9 μg·L-1 when the initial concentration of As(V) is 1 mg·L-1, which complied with the drinking water standard of WHO (10 μg·L-1). The adsorption capacity of synthesized MgFe2O4 towards As(V) was higher than commonly used iron oxide adsorbents (Fe3O4, γ-Fe2O3 and α-Fe2O3). Mechanistic studies proved that the superior adsorption capacity was attributed to: (1) increased amount of surface hydroxyl groups that resulted from the surface defects. (2) formation of tridentate hexanuclear surface complexes instead of bidentate binuclear complexes, and (3) formation of excess Mg-OH surface hydroxyl groups and As-Mg monodentate mononuclear surface complexes. This work disclosed the correlation of the superior As(V) adsorption ability with the surface hydroxyl groups in defective MgFe2O4, and propose MgFe2O4 as a potential candidate for the remediation of As-contaminated water.