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Acta Physico-Chimica Sinica  2007, Vol. 23 Issue (06): 807-812    DOI: 10.3866/PKU.WHXB20070603
Article     
Temperature Effects on Adsorption-Desorption Irreversibility of Zn(II) onto Anatase
LI Wei; PAN Gang; CHEN Hao; ZHANG Mei-Yi; HE Guang-Zhi; LI Jin; YANG Yu-Huan
State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P. R. China
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Abstract  

Microscopic structures and mechanism of Zn(II) adsorbed onto anatase at different temperatures were studied using extended X-ray absorption fine structure (EXAFS) spectroscopy. Macroscopic adsorption-desorption experiments indicated that adsorption isotherms and adsorption reversibility increased substantially with increasing temperature. When temperature increased from 5 ℃ to 40 ℃, the adsorption capacity increased from 0.125 mmol·g-1 to 0.446 mmol·g-1, while the desorption hysteresis angle (θ) decreased from 32.85°to 8.64°. The thermodynamic parameters ⊿H and ⊿S of the reaction were evaluated as 24.55 kJ·mol-1 and 159.13 J·mol-1·K-1, respectively. EXAFS spectra results showed that Zn(II) was adsorbed onto the solid surface in the form of octahedral hydrous Zn(II) ions, which were linked to TiO2 surface by sharing O atoms, with an average bond length RZn-O=(0.199±0.001) nm. EXAFS analysis of the second Zn-Ti coordination sphere resulted in two Zn-Ti atomic distances of (0.325±0.001) nmand (0.369±0.001) nm, corresponding to edge-sharing linkage (stronger adsorption site) and corner-sharing linkage (weaker adsorption site), respectively. The number of stronger adsorption sites (CN1) remained relatively stable while the number of weaker adsorption sites (CN2) increased remarkably as the temperature increased, making the proportion of two adsorption modes (CN1/CN2) drop from0.690 to 0.543. These results revealed that the increased adsorption capacity and reversibility at higher temperature were due to the increase in CN2 and the decrease in CN1/CN2. This result implies that, in a given environment (soils or rivers), the bioavailability of zinc is higher at high temperature than that at low temperature.



Key wordsEXAFS      Microscopic structures      Temperature      Adsorption-desorption      Adsorption reversibility      Zn(II)      Anatase     
Received: 14 December 2006      Published: 27 April 2007
MSC2000:  O642  
Corresponding Authors: PAN Gang     E-mail: gpan@rcees.ac.cn
Cite this article:

LI Wei; PAN Gang; CHEN Hao; ZHANG Mei-Yi; HE Guang-Zhi; LI Jin; YANG Yu-Huan. Temperature Effects on Adsorption-Desorption Irreversibility of Zn(II) onto Anatase. Acta Physico-Chimica Sinica, 2007, 23(06): 807-812.

URL:

http://www.whxb.pku.edu.cn/Jwk_wk/wlhx/10.3866/PKU.WHXB20070603     OR     http://www.whxb.pku.edu.cn/Jwk_wk/wlhx/Y2007/V23/I06/807

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