Removal of aqueous Pb(II) by adsorption on Al 2 O 3 -pillared layered MnO 2

Abstract In the present study, Al 2 O 3 -pillared layered MnO 2 (p-MnO 2 ) was synthesized using δ-MnO 2 as precursor and Pb(II) adsorption on p-MnO 2 and δ-MnO 2 was investigated. To clarify the adsorption mechanism, Al 2 O 3 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 δ-MnO 2 , Al 2 O 3 pillaring led to increased BET surface area of 166.3 m 2 g −1 and enlarged basal spacing of 0.85 nm. Accordingly, p-MnO 2 exhibited a higher adsorption capacity of Pb(II) than δ-MnO 2 . The adsorption isotherms of Pb(II) on δ-MnO 2 and Al 2 O 3 pillar fitted well to the Freundlich model, while the adsorption isotherm of Pb(II) on p-MnO 2 could be well described using a dual-adsorption model, attributed to Pb(II) adsorption on both δ-MnO 2 and Al 2 O 3 . Additionally, Pb(II) adsorption on δ-MnO 2 and p-MnO 2 followed the pseudo second-order kinetics, and a lower adsorption rate was observed on p-MnO 2 than δ-MnO 2 . The Pb(II) adsorption capacity of p-MnO 2 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-MnO 2 also displayed good adsorption capacities for aqueous Cu(II) and Cd(II). Findings in this study indicate that p-MnO 2 could be used as a highly effective adsorbent for heavy metal ions removal in water.