Synthesis, characterization and study of arsenate adsorption from aqueous solution by α- and δ-phase manganese dioxide nanoadsorbents

Single-phase α-MnO2 nanorods and δ-MnO2 nano-fiber clumps were synthesized using manganese pentahydrate in an aqueous solution. These nanomaterials were characterized using the Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FE-SEM), Powder X-ray diffraction (XRD) and the Brunauer–Elmet–Teller nitrogen adsorption technique (BET-N2 adsorption). The structural analysis shows that α-MnO2 (2×2 tunnel structure) has the form of needle-shaped nanorods and δ-MnO2 (2D-layered structure) consists of fine needle-like fibers arranged in ball-like aggregates. Batch adsorption experiments were carried out to determine the effect of pH on adsorption kinetics and adsorption capacity for the removal of As(V) from aqueous solution onto these two types of nanoadsorbents. The adsorption capacity of As(V) was found to be highly pH dependent. The adsorption of As(V) onto α-MnO2 reached equilibrium more rapidly with higher adsorption capacity compared to δ-MnO2.