用延展X射线精细结构吸收光谱研究Zn(Ⅱ)-TiO_2体系的颗粒物浓度效应和吸附可逆性  

EXAFS studies on particle concentration effect and adsorption reversibility of Zn(Ⅱ) onto anatase TiO_2

作　　者：李薇[1] 潘纲[1] 陈灏[1] 张美一[1] 何广智[1] 杨玉环[1] 

机构地区：[1]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

出　　处：《核技术》2007年第3期165-170,共6页Nuclear Techniques

基　　金：国家自然科学基金项目(20073060);中国科学院优秀"百人计划"资助

摘　　要：用延展X射线精细结构吸收光谱(EXAFS)研究了不同颗粒物浓度(Cp)下重金属Zn(Ⅱ)在锐钛型TiO2上吸附产物的微观构型,考察了Cp、吸附微观构型与可逆性的关系。宏观的吸附-解吸等温线结果表明,Zn(Ⅱ)-TiO2体系的吸附等温线随Cp的增加而显著降低,有明显的Cp效应;且吸附可逆性随Cp的增加逐渐减小。EXAFS结果表明,Zn(Ⅱ)主要是通过共用水合Zn(Ⅱ)离子及TiO2表面上的O原子结合到TiO2表面上,其平均Zn-O原子间距为(1.98±0.01)。同时,第二配位层(Zn-Ti层)的EXAFS图谱分析结果表明存在两个典型的Zn-Ti原子间距,即R1=(3.26±0.01)(边-边结合的强吸附)和R2=(3.70±0.01)(角-角结合的弱吸附)。吸附密度相近、平衡浓度不同的三个吸附样品,随Cp的增加,强吸附位(N1)基本不变而弱吸附位(N2)减少,两者比值(N1/N2)由0.629增加至0.690。该比值的变化从微观角度解释了宏观吸附-解吸实验中Cp增加,可逆性减小的实验现象。同时,EXAFS实验结果也从微观上证明了亚稳平衡态吸附理论(MEA理论)的吸附密度(Γ)不是状态函数的基本假设。Microscopic structures of Zn （ Ⅱ ） adsorbed onto anatase TiO2 under different particle concentrations （Cp） were studied using the extended X-ray absorption fine structure （EXAFS） spectroscopy. Results of macroscopic adsorption -desorption isotherms indicated that Cp effect was obvious in the adsorption system. Adsorption isotherms decreased substantially with increasing Cp, and reversibility also decreased. Quantitative analysis on the EXAFS spectra showed that Zn （Ⅱ） was adsorbed onto the solid surface in the form of octahedral hydrous Zn （Ⅱ） ions, which were linked to the TiO2 surface by sharing the oxygen atoms, with an average bond length of Rzn-O = （1.98±0.01）A. EXAFS analysis of the second sphere resulted in two Zn-Ti atomic distances of （3.26 ± 0. 01）A and （3.70± 0. 01）A, corresponding to edge-sharing linkage （stronger adsorption site） and corner-sharing linkage （weaker adsorption site） respectively. For three adsorption samples with the same adsorption density and different equilibrium concentration, the number of stronger adsorption sites （N1） remained relatively stable while the number of weaker adsorption sites （N2） decreased with increasing Cp, making the proportion of two adsorption modes （N1/N2） rise from 0.629 to 0.690. These EXAFS results revealed the microscopic mechanism behind the macroscopic adsorption-desorption isotherm experiments. At the same time the basic hypothesis of MEA theory that the adsorption density is not a state variable has been verified.

关 键 词：延展X射线精细结构吸收光谱 Zn(Ⅱ) TIO2 微观构型 颗粒物浓度(Cp)效应 吸附可逆性 

分 类 号：O647[理学—物理化学]