title: EXAFS studies on adsorption-desorption reversibility at manganese oxide-water interfaces. II. Reversible adsorption of zinc on delta-MnO2.
abstract: Microscopic structures of Zn(II) adsorbed at delta-MnO(2)-water interfaces were studied using extended X-ray absorption fine structure (EXAFS) spectroscopy. In a 0.1 M NaNO(3) solution of pH 5.50, hydrous Zn(II) was adsorbed onto the solid surface in the form of octahedral coordination. Adsorbed octahedral Zn(II) was located above and below the vacancy sites of delta-MnO(2). Each Zn was coordinated on one side to H(2)O molecules forming an H(2)O sheet and on the other side to oxygen atoms shared with layer MnO(6) octahedra forming a corner-sharing octahedral interlayer complex. The average Zn-O and Zn-Mn distances were 2.07+/-0.01 and 3.52+/-0.01 A, respectively. Macroscopic adsorption-desorption isotherms showed that, in contrast to that of the Zn-gamma-MnOOH system, adsorption of Zn(II) on delta-MnO(2) was highly reversible. EXAFS results indicated that the highly reversible adsorption was due to the weak adsorption mode of the corner-sharing linkage between the adsorbate and adsorbent polyhedra.
authors.affiliation: State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China.
authors.forename: Xianliang
authors.initials: X
authors.lastname: Li
authors.forename: Gang
authors.initials: G
authors.lastname: Pan
authors.forename: Yanwen
authors.initials: Y
authors.lastname: Qin
authors.forename: Tiandou
authors.initials: T
authors.lastname: Hu
authors.forename: Ziyu
authors.initials: Z
authors.lastname: Wu
authors.forename: Yaning
authors.initials: Y
authors.lastname: Xie