EXAFS Studies of pH Effects on Adsorption and Microscopic Strutures of Zn(Ⅱ) onto TiO2

Chem. J. Chinese Universities ›› 2009, Vol. 30 ›› Issue (12): 2439.

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EXAFS Studies of pH Effects on Adsorption and Microscopic Strutures of Zn(Ⅱ) onto TiO₂

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

Received:2009-03-10 Online:2009-12-10 Published:2009-12-10
Contact: PAN Gang. E-mail: gpan@rcees.ac.cn
Supported by:
国家自然科学基金(批准号: 20777090, 20537020)资助.

Abstract

Abstract:

Microscopic structures and thermodynamic characteristics of Zn(Ⅱ) adsorbed onto anatase TiO₂ 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 TiO₂ 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: R₁=0.319—0.334 nm and R₂=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 the surface of TiO₂ under different pH conditions.

Key words: Extended X-ray absorption fine structure; pH; Adsorption reversibility; Zn(Ⅱ)

TrendMD:

GAO Shuang, CHEN Hao, HE Guang-Zhi, PAN Gang*. EXAFS Studies of pH Effects on Adsorption and Microscopic Strutures of Zn(Ⅱ) onto TiO₂[J]. Chem. J. Chinese Universities, 2009, 30(12): 2439.

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EXAFS Studies of pH Effects on Adsorption and Microscopic Strutures of Zn(Ⅱ) onto TiO₂

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