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用EXAFS研究pH对Zn(Ⅱ)-TiO2体系吸附和微观构型的影响
引用本文:高爽,陈灏,何广智,潘纲.用EXAFS研究pH对Zn(Ⅱ)-TiO2体系吸附和微观构型的影响[J].高等学校化学学报,2009,30(12):2439-2444.
作者姓名:高爽  陈灏  何广智  潘纲
作者单位: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:应用延展X射线吸收精细结构(EXAFS)方法, 研究了不同pH对Zn(Ⅱ)在锐钛矿型TiO2表面吸附产物的微观构型的影响. 宏观的吸附-解吸实验表明, 随着pH值由5.8增大至6.8, 吸附等温线明显升高, Freundlich吸附常数由1.345 L/g增加到15.385 L/g; 而体系的不可逆性逐渐降低, 不可逆吸附系数(TⅡ)由0.43降低到0.23. 不同pH条件下吸附样品的EXAFS结果表明, Zn(Ⅱ)主要通过共用水合离子及TiO2表面的O原子结合到TiO2表面上, 第一配位层(Zn—O层)原子间距和配位数随着pH值增大逐渐降低, Zn(Ⅱ)在TiO2表面吸附形态从六配位向四配位转化;第二配位层(Zn—Ti层)分析结果表明, 存在2个典型的Zn—Ti原子间距, 即R1=0.319~0.334 nm(双齿方式结合的强吸附)和R2=0.366~0.378 nm(单齿方式结合的弱吸附), 随着pH值的升高, 强吸附位(CN1)逐渐减少而弱吸附位(CN2)逐渐增加, 其比值由2.12降低至0.89, 从而导致其在高pH值的条件下吸附量和可逆性明显增大. EXAFS结果从分子水平说明了该体系在不同pH值条件下表现出的可逆性差异是由于微观吸附状态不同所致.

关 键 词:延长X射线吸收精细结构  pH  吸附可逆性  Zn(Ⅱ)
收稿时间:2009-03-10

EXAFS Studies of pH Effects on Adsorption and Microscopic Strutures of Zn(Ⅱ) onto TiO_2
GAO Shuang,CHEN Hao,HE Guang-Zhi,PAN Gang.EXAFS Studies of pH Effects on Adsorption and Microscopic Strutures of Zn(Ⅱ) onto TiO_2[J].Chemical Research In Chinese Universities,2009,30(12):2439-2444.
Authors:GAO Shuang  CHEN Hao  HE Guang-Zhi  PAN Gang
Institution:GAO Shuang,CHEN Hao,HE Guang-Zhi,PAN Gang(State Key Laboratory of Environmental Aquatic Chemistry,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,Beijing 100085,China)[HJ5][HJ]
Abstract:Microscopic structures and thermodynamic characteristics of Zn( Ⅱ ) adsorbed onto anatase TiO_2 at different pH were studied using extended X-ray absorption fine structure(EXAFS) spectroscopy. Macroscopic adsorption-desorption experiments indicated that as pH increased from 5.8 to 6. 8, the adsorption capacity coefficient(K_F) increased from 1,345 L/g to 15. 385 L/g, while the adsorption irreversibility coefficient (TⅡ) decreased from 0. 43 to 0. 23. EXAFS spectra results showed that Zn(Ⅱ) was adsorbed onto the solid surface in a mixed form of octahedral and tetrahedral hydrous Zn(Ⅱ) ions, which were linked to TiO_2 surface by sharing O atoms. Both the bond length and the coordination number of the first Zn-O coordination sphere decreased as pH increased. Analysis of the second Zn-Ti coordination sphere indicated two Zn-Ti atomic distances: R_1 =0.319-0.334 nm and R_2 =0.366-0.378 nm, referring to bidentate( stronger adsorption site) and monodentate( weaker adsorption site) complexation respectively. The number of stronger adsorption sites( CN1 ) decreased while the number of weaker adsorption sites(CN2) increased remarkably with increasing pH, resulting in a drop of CN1/CN2 from 2.12 to 0.89. EXAFS results revealed that the macroscopic adsorption phenomena were directly related to the changes in microscopic adsorption structures of Zn (Ⅱ) on thesurface of TiO_2 under different pH conditions.
Keywords:pH  Extended X-ray absorption fine structure  pH  Adsorption reversibility
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