Structural-chemical disorder of manganese dioxides II.: Influence on textural properties

被引:26
作者
Prélot , B
Villiéras, F
Pelletier, M
Razafitianamaharavo, A
Thomas, F
Poinsignon, C [1 ]
机构
[1] Ecole Natl Super Electrochim & Electrome Grenoble, Inst Natl Polytech Grenoble, Lab Electrochim & Phys Chim Mat & Interfaces, CNRS,UMR 5631, BP 75, F-38402 St Martin Dheres, France
[2] CNRS, UMR 7569, INPL ENS Geol, Lab Environm & Mineral, F-54501 Vandoeuvre Les Nancy, France
关键词
D O I
10.1016/S0021-9797(03)00394-1
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Relationships between structural parameters of MnO2 and their surface properties at the solid-gas interface were investigated. The studied series ranged from ramsdellite to pyrolusite and encompassed disordered gamma-MnO2 samples. The structural model used takes into account structural defects: Pr (rate of pyrolusite intergrowth in the ramsdellite network) and Tw (rate of microtwinning). Analysis of the N-2 adsorption isotherm evidenced positive correlations between specific surface area and Tw for gamma-MnO2 only and between the energetic constant C and (1-Pr). No microporosity is evidenced. Water adsorption isotherms evidenced the dependence of the H2O monolayer volume on Tw and showed a positive correlation between the cross-section area of water molecules adsorbed in the first monolayer and Pr, ranging from 13.5 Angstrom(2) for Pr = 1 to 6.3 Angstrom(2) for Pr = 0.2 (12 sites/nm(2)). Energetic heterogeneity is quantified from Ar and N-2 low-pressure adsorption isotherms with the DIS procedure and correlated with H2O adsorption. High-energy adsorption domains are quantified and assigned to the different crystal faces: (110) faces with a common 1 x 1 octahedra layer of pyrolusite and ramsdellite and the (001) face of ramsdellite with 2 x 2 octahedra on which channels and plateaus are differentiated. The specific surface area ratio of ramsdellite high-energy sites to total ramsdellite content is shown to depend on Tw. The dependence on microtwinning of low cross-sectional area of N-2 and much lower cross-sectional of residual H2O molecules leads us to assume that their adsorption sites on grain boundaries are represented by the twin planes between the structured nanocrystals generated by oxygen evolution during MD synthesis. (C) 2003 Elsevier Inc. All rights reserved.
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页码:343 / 353
页数:11
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