Li Wei, Pan Gang, Zhang Meiyi, Zhao Dongye, Yang Yuhuan, Chen Hao, He Guangzhi
State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
J Colloid Interface Sci. 2008 Mar 15;319(2):385-91. doi: 10.1016/j.jcis.2007.11.028. Epub 2007 Dec 26.
Adsorption irreversibility of Zn(II) on TiO2 at various temperatures was studied using a combination of classical macroscopic methods and extended X-ray absorption fine structure (EXAFS) spectroscopy. When the temperature was increased from 5 to 40 degrees C, the Zn(II) adsorption capacity increased by 130%, and adsorbed Zn(II) became more reversible. The standard Gibbs free energy change (DeltaG 0) of the adsorption reaction at 5, 20, and 40 degrees C was determined to be -19.58+/-0.30, -22.28+/-0.10, and -25.14+/-0.21 kJ mol(-1), respectively. And the standard enthalpy (DeltaH 0) and entropy (DeltaS 0) were 24.55+/-2.91 kJ mol(-1) and 159.13+/-0.53 J mol(-1)K(-1), respectively. EXAFS spectra results showed that the hydrated Zn(II) was adsorbed through fourfold coordination with an average ZnO bond distance of 1.98+/-0.01 A. Two ZnTi atomic distances of 3.25+/-0.02 and 3.69+/-0.03 A were observed, which corresponded to an edge-sharing linkage mode (strong adsorption) and a corner-sharing linkage mode (weak adsorption), respectively. As the temperature increased from 5 to 40 degrees C, the number of strong adsorption sites (N1) remained relatively constant while the number for the weak adsorption sites (N2) increased by 31%. These results indicate that the net gain in adsorption capacity and the decreased adsorption irreversibility at elevated temperatures were due to the increase in available weak adsorption sites (N2) or the decrease in the ratio of N1/N2. Both the macroscopic sorption/desorption equilibrium data and the molecular level evidence of this study suggest that in a given environmental system (e.g., soils or natural waters) zinc and other similar heavy metals are likely more mobile at higher temperatures.
采用经典宏观方法与扩展X射线吸收精细结构（EXAFS）光谱相结合的方式，研究了不同温度下Zn(II)在TiO₂上的吸附不可逆性。当温度从5℃升高到40℃时，Zn(II)的吸附容量增加了130%，且吸附的Zn(II)变得更具可逆性。在5℃、20℃和40℃下，吸附反应的标准吉布斯自由能变化（ΔG⁰）分别测定为-19.58±0.30、-22.28±0.10和-25.14±0.21 kJ·mol⁻¹。标准焓（ΔH⁰）和熵（ΔS⁰）分别为24.55±2.91 kJ·mol⁻¹和159.13±0.53 J·mol⁻¹·K⁻¹。EXAFS光谱结果表明，水合Zn(II)通过四重配位吸附，平均ZnO键距为1.98±0.01 Å。观察到两个Zn-Ti原子距离分别为3.25±0.02 Å和3.69±0.03 Å，分别对应边共享连接模式（强吸附）和角共享连接模式（弱吸附）。当温度从5℃升高到40℃时，强吸附位点数量（N1）保持相对恒定，而弱吸附位点数量（N2）增加了31%。这些结果表明，高温下吸附容量的净增加和吸附不可逆性的降低是由于可用弱吸附位点（N2）的增加或N1/N2比值的降低。本研究的宏观吸附/解吸平衡数据和分子水平证据均表明，在给定的环境系统（如土壤或天然水体）中，锌和其他类似重金属在较高温度下可能更具迁移性。
