Adsorption behavior and removal mechanism of arsenic on graphene modified by iron–manganese binary oxide (FeMnOx/RGO) from aqueous solutions

Abstract

Iron–manganese binary oxide (FeMnO_x) is considered highly effective for arsenic adsorption, however, the agglomeration effect hindered its practical application. In this study, graphene has been used as a supporting matrix to disperse FeMnO_x due to its huge specific surface area, and the synthesized novel composite adsorbent (FeMnO_x/RGO) was employed for arsenic removal. Results demonstrated that FeMnO_x/RGO (mass ratio of FeMnO_x to FeMnO_x/RGO nanocomposites is 45%) has larger specific surface area (411 m² g⁻¹) in comparison with bare FeMnO_x, and showed 10.16 mg As g⁻¹ FeMnO_x and 11.49 mg As g⁻¹ FeMnO_x adsorption capacities for As(III) and As(V), respectively, with 1 mg L⁻¹ initial concentration. Increased in the initial concentration to 7 mg L⁻¹, the adsorption capacities of As(III) and As(V) reached to 47.05 mg As g⁻¹ FeMnO_x and 49.01 mg As g⁻¹ FeMnO_x, respectively. The removal process perfectly obeys pseudo second-order kinetic model for both As(III) and As(V). And PO₄³⁻ was found to strongly inhibit arsenic adsorption. Furthermore, adsorption tests and characterization analyses confirmed that MnO₂ played a key role on the oxidation of As(III), while iron(III) oxide was found crucial to As(V) removal. Electrostatic interaction and surface complexation mechanisms involved in the adsorption. These findings suggested that the adsorbent could be used in real arsenic-contaminated water treatment.