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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >An Approach to the Estimation of Adsorption Enthalpies of Polycyclic Aromatic Hydrocarbons on Particle Surfaces
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An Approach to the Estimation of Adsorption Enthalpies of Polycyclic Aromatic Hydrocarbons on Particle Surfaces

机译：估算颗粒表面多环芳烃吸附焓的方法

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Current atmospheric models incorporate the values of vaporization enthalpies, Delta H-vap, obtained for neat standards, thus disregarding the matrix effects on volatilization. To test the adequacy of this approximation, this study measured enthalpies of vaporization for five polycyclic aromatic hydrocarbons (PAHs) in the form of neat standards (Delta H-vap) as well as adsorbed on the surface of silica, graphite, and graphene particles (Delta H-vap(eff)), by using simultaneous thermogravimetry-differential scanning calorimetry (TGA-DSC). Measurement of the corresponding activation energy values, E-a(vap) and E-a (eff)(vap), by TGA using a derivative method was shown to be the most reliable and practical way to assess Delta H-vap and Delta H-vap(eff). Enthalpies of adsorption (Delta H-ads) were then calculated from the differences between E-a(vap) and E-a (eff)(vap), thus paving a way to modeling the solid-gas phase partitioning in atmospheric particulate matter (PM). The PAH adsorption on silica particle surfaces (representing n-pi* interactions) resulted in negative values of Delta H-ads, indicating significant interactions. For graphite particles, positive Delta H-ads values were obtained; i.e., PAHs did not interact with the particle surface as strongly as observed for PM. PAHs on the surface of graphene particles evaporated in two stages, with the bulk of the mass loss occurring at temperatures lower than those with the neat standard, just as on graphite. Yet, unlike graphite, a small PAH fraction did not evaporate until higher temperatures compared to case of the neat standards and other particle surfaces (37.4-145.7 K), signifying negative, more PM-relevant values of Delta H-ads, apparently reflecting pi-pi* interactions and ranging between -7.6 and +32.6 kJ mol(-1), i.e., even larger than for silica, -3.3 to +8.3 kJ mol(-1). Thus, current atmospheric models may underestimate the partitioning of organic species in the particle phase unless matrix adsorption is taken into account.
机译：当前的大气模型结合了为纯净标准品获得的蒸发焓值Delta H-vap，因此忽略了基质对挥发的影响。为了测试这种近似的充分性，本研究测量了五种多环芳烃（PAH）的汽化焓，它们以纯净标样（ΔH蒸气）形式以及吸附在二氧化硅，石墨和石墨烯颗粒的表面上（ Delta H-vap（eff）），使用同时热重分析-差示扫描量热法（TGA-DSC）。用导数法通过TGA测量相应的活化能值Ea（vap）和Ea（eff）（vap）被证明是评估Delta H-vap和Delta H-vap（eff）的最可靠，最实用的方法）。然后根据E-a（vap）和E-a（eff）（vap）之间的差异计算出吸附焓（Delta H-ads），从而为模拟大气颗粒物（PM）中固相分配的方法铺平了道路。 PAH在二氧化硅颗粒表面的吸附（代表n-pi *相互作用）导致Delta H-ads值为负值，表明存在明显的相互作用。对于石墨颗粒，获得了正Delta H-ads值。即，PAHs与颗粒表面的相互作用不如PM观察到的强。石墨烯颗粒表面的PAHs分两阶段蒸发，大部分质量损失发生在温度低于纯净标准品的温度下，就像在石墨上一样。然而，与石墨不同，与纯净标准品和其他颗粒表面（37.4-145.7 K）相比，只有少量的PAH馏分直到更高的温度才蒸发，这表明Delta H-ads的负相关，与PM相关的值更多，显然反映了pi。 -pi *相互作用，范围为-7.6至+32.6 kJ mol（-1），即，甚至大于二氧化硅的-3.3至+8.3 kJ mol（-1）。因此，除非考虑基质吸附，否则当前的大气模型可能会低估有机物在颗粒相中的分配。

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