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.

α-MnO2 (2×2 tunnel structure) nanorods and δ-MnO2 (2-D layered structure) nano-fiber clumps were synthesized in a facile way in an aqueous solution and characterized by TEM, FE-SEM, XRD and BET-N2 adsorption techniques. The structural analysis shows that α-MnO2 is needle shaped nanorods and δ-MnO2 consists of 2-D platelets of fine needle-like fibers arranged in ball-like aggregates. Further batch experiments confirmed that both nanoadsorbents are potential candidates for the adsorption of As(V) with a capacity of 19.41 and 15.33 mg g−1 for α-MnO2 and δ-MnO2, respectively. The presence of As3d peak in XPS study indicates that arsenic on the surface of nanoadsorbents is in the stable form of As(V) with a percentage of arsenate onto α-MnO2 is 0.099% as compared to 0.021% onto δ-MnO2, clearly indicating the higher adsorption of As(V) in case of α-MnO2 as compared to δ-MnO2, which is in good agreement with the adsorption studies results.Figure optionsDownload as PowerPoint slide