Chinese Acad Sci, State Key Lab Environm Aquat Chem, Res Ctr Ecoenvironm Sci, Beijing 100085, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing Synchrotron Radiat Facil, Beijing 100039, Peoples R China
Mechanisms of adsorption and precipitation of Zn(II) on gamma-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-comer (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 Zn-5(OH)(6)(CO3)(2). Simulated and experimental XANES spectrums of Zn-5(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 gamma-MnOOH.