Thermodynamics of nitroaromatic compound adsorption from water by smectite clay
Thermodynamics of nitroaromatic compound adsorption from water by smectite clay
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DOI：
10.1021/es035054y
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发表时间：
2004-10-15
影响因子：
11.4
通讯作者：
Boyd, SA
中科院分区：
文献类型：
--
作者：
Li, H;Teppen, BJ;Boyd, SA
硝基芳香族化合物通过炸药、杀虫剂、溶剂和染料、香水和药物制造中的合成中间体进入环境。最近的研究发现，许多硝基芳香族化合物被蒙脱石，特别是K+饱和蒙脱石强烈保留。当硝基芳香族化合物取代与粘土相关的水并在K+和-NO2基团之间形成络合物时，就会发生吸附。本研究试图从能量学的角度进一步理解硝基芳烃与粘土的相互作用。在4℃~ 37℃的温度范围内，测定了饱和K+和Ca2+的蒙脱石（SWy-2）对水溶液中1,3-二硝基苯、1,4-二硝基苯和1,3,5-三硝基苯的吸附等温线，确定了摩尔微分吸附焓。发现同种离子K+-和Ca2+-蒙脱石的吸附均为放热过程。Ca-SWy-2对硝基芳烃的吸附焓较小，与K-SWy-2对硝基芳烃的吸附量较小是一致的。我们对1,3,5-三硝基苯与K-SWy-2相互作用的焓的最佳估计是-124 kJ/mol，这是参考气相1,3,5-三硝基苯，校正了层间水的位移，可以直接与文献中的量子化学焓进行比较。我们对1,3-和1,4-二硝基苯相互作用焓的可比估计接近- 90kj /mol。我们得出的结论是，我们的吸附焓结果与假设一致，即硝基芳香族化合物被K-蒙脱石强烈吸附，因为它们在粘土夹层中与K+阳离子形成了内球和/或外球配合物。事实上，在硝基芳香族化合物存在的情况下，重湿粘土膜的基底间距意味着水分子不能有效地与吸附的硝基苯竞争K-SWy-2上的活性位点。
Nitroaromatic compounds enter the environment through their use as explosives, pesticides, solvents, and synthetic intermediates in the manufacturing of dyes, perfumes, and drugs. Recent studies have found that many nitroaromatic compounds are strongly retained by smectites, especially K+-saturated smectites. Sorption occurs when nitroaromatic compounds replace water associated with the clay and form complexes between K+ and -NO2 groups. This study seeks to further understand nitroaromatic-clay interactions from the viewpoint of energetics. Adsorption isotherms of 1,3-dinitrobenzene, 1,4-dinitrobenzene, and 1,3,5-trinitrobenzene from aqueous solution by K+- and Ca2+- saturated smectite (SWy-2) were measured at several temperatures between 4 degreesC and 37 degreesC to determine the molar differential adsorption enthalpies. Adsorption was found to be an exothermic process on both homoionic K+- and Ca2+- smectite. The smaller adsorption enthalpy on Ca-SWy-2 was consistent with its much smaller adsorption capacity for nitroaromatics compared to K-SWy-2. Our best estimate for the enthalpy of 1,3,5-trinitrobenzene interactions with K-SWy-2 is -124 kJ/mol, which is referenced to gas-phase 1,3,5-trinitrobenzene, corrected for the displacement of interlayer water, and can be directly compared with quantum chemical enthalpies from the literature. Our comparable estimates for 1,3- and 1,4-dinitrobenzene interaction enthalpies are near -90 kJ/mol. We conclude that our adsorption enthalpy results are consistent with the hypothesis that nitroaromatic compounds are sorbed strongly by K-smectites because they form inner- and/or outer-sphere complexes with K+ cations in clay interlayers. Indeed, the basal spacings of rewetted clay films in the presence of nitroaromatic compounds imply that water molecules cannot effectively compete with the adsorbed nitrobenzenes for reactive sites on K-SWy-2.