特别选题
李晋,潘纲,陈灏,李薇.用EXAFS研究Zn(Ⅱ)在γ-MnOOH上的吸附热力学行为[J].环境科学学报,2006,26(10):1600-1605
用EXAFS研究Zn(Ⅱ)在γ-MnOOH上的吸附热力学行为
- EXAFS studies on irreversible adsorption thermodynamics of Zn(Ⅱ) at γ-MnOOH water interface
- 基金项目：国家自然科学基金(No.20073060);中科院优秀"百人计划"资助项目
- 作者
- 单位
- 李晋
- 中国科学院生态环境研究中心环境水质学国家重点实验室, 北京 100085
- 潘纲
- 中国科学院生态环境研究中心环境水质学国家重点实验室, 北京 100085
- 陈灏
- 中国科学院生态环境研究中心环境水质学国家重点实验室, 北京 100085
- 李薇
- 中国科学院生态环境研究中心环境水质学国家重点实验室, 北京 100085
- 摘要：用延展X射线吸收精细结构光谱(EXAFS)研究了不同温度下重金属Zn(Ⅱ)在水锰矿(γ-MnOOH)上吸附产物的微观构型,从微观角度研究了宏观的吸附热力学行为.宏观热力学实验结果表明,Zn(Ⅱ)-水锰矿体系的吸附反应是吸热反应,随着温度的升高吸附量显著升高,不可逆性明显减小.EXAFS结果表明,Zn(Ⅱ)主要是通过共用水合Zn(Ⅱ)离子的O原子及水锰矿表面上的O原子形成Zn—O键,从而结合到水锰矿固体表面上,其平均Zn—O原子间距为(2.01±0.01)×10-10m.同时,对第二配位层(Zn—Mn相互作用)的EXAFS图谱分析证明,存在2个典型的Zn—Mn原子间距,即R1=(3.06±0.02)×10-10m(边-边结合的强吸附)和R2=(3.52±0.02)×10-10m(角-角结合的弱吸附).当温度升高时,强吸附位基本不变而弱吸附位增加,两者比值(N1/N2)由0.428降至0.158.该比值的变化从微观角度解释了宏观吸附-解吸等温线中吸附量增加、不可逆性减小的实验现象.
- Abstract：Microscopic structures of Zn (Ⅱ) surface complexes adsorbed on γ-MnOOH MnOOH under different temperatures were studied using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Macroscopic thermodynamic results indicated that the adsorption was an endothermic reaction, and the adsorption isotherms increased substantially with increasing temperature, while irreversibility decreased. Quantitative analysis on the EXAFS spectra showed that Zn (Ⅱ) was adsorbed onto the solid surface in form of octahedral hydrated Zn (Ⅱ) ions, which were linked to the octahedral MnO6 of manganite by sharing oxygen atoms (Zn—O bond), with an average bond length RZn—O = (2.01 ±0.01)×10-10 m. EXAFS analysis of the second sphere resulted in two Zn—Mn atomic distances of (3.06 ±0.02)×10-10 m and (3.52 ±0.02)×10-10 m, corresponding to edge-sharing linkage (stronger adsorption site) and corner-sharing linkage (weaker adsorption site) respectively. The number of stronger adsorption sites (N1) remained relatively stable while the number of weaker adsorption sites (N2) increased remarkably along with increasing temperature, making the proportion of the two adsorption modes (N1/N2) drop from 0.428 to 0.158. These EXAFS results revealed the microscopic mechanism behind the macroscopic adsorption-desorption isotherm experiments that the increased adsorption density and reversibility at higher temperature were due to the increase in N2 and the decrease in N1/N2.
- Key words：EXAFS Zn γ-MnOOH adsorption thermodynamics microscopic structures adsorption reversibility
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