Mechanisms for the adsorption of substituted nitrobenzenes by smectite clays
Mechanisms for the adsorption of substituted nitrobenzenes by smectite clays
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DOI：
10.1021/es010663w
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发表时间：
2001-11-01
影响因子：
11.4
通讯作者：
Johnston, CJ
中科院分区：
文献类型：
--
作者：
Boyd, SA;Sheng, GY;Johnston, CJ
为了更全面地了解硝基芳香族化合物在土壤和底土中的迁移潜力，测定了一系列对位和间位取代的硝基苯(SNBS)在K蒙脱石粘土上的吸附。吸附等温线符合Freundlich方程，所得Freundlich吸附系数(log(K-f))与Hammett取代基常数呈正相关(r(2)=0.80)。这个关系式和一个正的反应常数(Rho=1.15)表明吸附反应是由吸电子取代基促进的。这些结果与先前提出的电子给体(蒙脱石)-受体(取代硝基苯)机理是一致的。然而，量子计算没有揭示Hammett常数与芳环上的电子密度之间的任何系统关系，这可以解释施主-受体关系。相反，由硝基苯上的第二个取代基提供的电子密度似乎被硝基占用，保持环电子密度不变。傅里叶变换红外光谱显示，1，3，5-三硝基苯(TNB)吸附到K+-蒙脱石上后，其-NO2振动模式发生了变化，这与K+被-NO2基团络合的情况相一致。对于饱和了更强水合阳离子(即Na+、Mg~(2+)、Ca~(2+)和Ba2+)的SWY-1，没有观察到这样的TNB振动位移。分子动力学模拟表明，多个NO2基团同时与交换性K+相互作用。蒙脱石粘土对SNBS的吸附可能是层间K+离子与-NO2基团和二次取代基加和作用的结果。吸附发生的程度或多或少取决于取代基对额外层间阳离子的络合能力和SNBS的水溶解度。我们的结论是，SNBS在K-SAZ-1上的吸附趋势可以在没有假设的电子供体-受体络合物的情况下得到解释。
To more fully understand the potential for transport of nitroaromatic compounds in soils and subsoils,the adsorption of a series of para- and meta-substituted nitrobenzenes (SNBs) by K-smectite clay was measured. Adsorption isotherms were fit to the Freundlich equation, and the resultant Freundlich adsorption coefficients (log(K-f)) were positively correlated with the Hammett substituent constant (r(2) = 0.80). This relationship and a positive reaction constant (rho = 1.15) indicate that the adsorption reaction is favored by electron-withdrawing substituents. These results are consistent with an electron donor (smectite)-acceptor (substituted nitrobenzene) mechanism offered previously. However, quantum calculations did not reveal any systematic relationship between the Hammett constant and the electron density on the aromatic ring, which would explain a donor-acceptor relationship. Rather, electron density donated by a second substituent on nitrobenzene appears to be appropriated by the nitro group leaving ring electron density unchanged. Fourier transform infrared spectroscopy revealed shifts in the -NO2 vibrational modes of 1,3,5-trinitrobenzene (TNB) upon adsorption to K+-smectite that were consistent with the complexation of K+ by -NO2 groups. Such TNB vibrational shifts were not observed for SWy-1 saturated with more strongly hydrated cations (i.e., Na+, Mg2+, Ca2+, and Ba2+). The simultaneous interaction of multiple -NO2 groups with exchangeable K+ was indicated by molecular dynamic simulations. Adsorption of SNBs by smectite clays appears to result from the additive interactions of -NO2 groups and secondary substituents with interlayer K+ ions. Adsorption occurs to a greater or lesser extent depending on the abilities of substituents to complex additional interlayer cations and the water solubilities of SNBs. We conclude that the adsorption trends of SNBs on K-SAz-1 can be explained without recourse to hypothetical electron donor-acceptor complexes.