Acta Phys. -Chim. Sin. ›› 2005, Vol. 21 ›› Issue (12): 1378-1383.doi: 10.3866/PKU.WHXB20051210

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Zn(II) Adsorption and Precipitation on γ-MnOOH-Water Interfaces DFT and XANES Calculation

ZHU Meng-Qiang;PAN Gang;LIU Tao;LI Xian-Liang;YANG Yu-Huan;LI Wei;LI Jin;HU Tian-Dou;WU Zi-Yu;XIE Ya-Ning   

  1. State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085; 1Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039
  • Received:2005-05-13 Revised:2005-07-14 Published:2005-12-15
  • Contact: PAN Gang

Abstract: Mechanisms of adsorption and precipitation of Zn(II) on γ-MnOOH-water interfaces were studied using DFT (density functional theory) and XANES (X-ray absorption near edge structure) simulation at different pH conditions. Optimal adsorption structures showed that only hydrolyzed clusters of double-edge-link mode could explain the H+ release mechanism and experimental bond-length values. Adsorption energy calculations indicated that the stability sequence of adsorption modes was in the order of double-edge (DE)>double-corner (DC)>single-edge-B (SE-B)> single-edge-A (SE-A). Hydrolysis energy calculations showed that the adsorbed Zn2+ of all the linkage modes hydrolyzed easier than Zn2+ in solution. XANES simulations of optimal adsorption clusters did not accord well with experimental results, indicating that mechanisms other than surface adsorption were involved in the adsorption samples. Surface precipitation species were formed in adsorption samples of pH > 7.5, where mixtures of Zn—O tetrahedron and Zn—O octahedron were arranged in the way similar to that of Zn5(OH)6(CO3)2. Simulated and experimental XANES spectrums of Zn5(OH)6(CO3)2 were very close to that of adsorption samples of pH > 7.5. At pH < 7.0, Zn(II) was mainly adsorbed in edge link mode on the surface of γ-MnOOH.

Key words: DFT, XANES, Surface adsorption, Precipitation, Zn(II), γ-MnOOH