Removal of aqueous Pb(II) by adsorption on Al2O3-pillared layered MnO2

In the present study, Al2O3-pillared layered MnO2 (p-MnO2) was synthesized using delta-MnO2 as precursor and Pb(II) adsorption on p-MnO2 and delta-MnO2 was investigated. To clarify the adsorption mechanism, Al2O3 was also prepared as an additional sorbent. The adsorbents were characterized by X-ray fluorescence analysis, powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and N-2 adsorption-desorption. Results showed that in comparison with pristine delta-MnO2, Al2O3 pillaring led to increased BET surface area of 166.3 m2 g(-1) and enlarged basal spacing of 0.85 nm. Accordingly, p-MnO2 exhibited a higher adsorption capacity of Pb(II) than delta-MnO2. The adsorption isotherms of Pb(II) on delta-MnO2 and Al2O3 pillar fitted well to the Freundlich model, while the adsorption isotherm of Pb(II) on p-MnO2 could be well described using a dual-adsorption model, attributed to Pb(II) adsorption on both delta-MnO2 and Al2O3. Additionally, Pb(II) adsorption on delta-MnO2 and p-MnO2 followed the pseudo second-order kinetics, and a lower adsorption rate was observed on p-MnO2 than delta-MnO2. The Pb(II) adsorption capacity of p-MnO2 increased with solution pH and co-existing cation concentration, and the presence of dissolved humic acid (10.2 mg L-1) did not markedly impact Pb(II) adsorption. p-MnO2 also displayed good adsorption capacities for aqueous Cu(II) and Cd(II). Findings in this study indicate that p-MnO2 could be used as a highly effective adsorbent for heavy metal ions removal in water. (C) 2017 Elsevier B.V. All rights reserved.