Interactions of gaseous HNO3 and water with individual and mixed alkyl self-assembled monolayers at room temperature.
Interactions of gaseous HNO3 and water with individual and mixed alkyl self-assembled monolayers at room temperature.
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室温下气态 HNO3 和水与单独和混合烷基自组装单分子层的相互作用。
DOI：
10.1039/c3cp54118e
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Finlayson-Pitts,BarbaraJ
中科院分区：
文献类型：
--
作者：
Nishino,Noriko;Hollingsworth,ScottA;Stern,AbrahamC;Roeselová,Martina;Tobias,DouglasJ;Finlayson-Pitts,BarbaraJ
大气中气态硝酸(HNO3)的主要去除过程是干沉积和湿沉积在各种表面上。边界层中的表面通常覆盖着有机薄膜，但气态硝酸与它们的相互作用还不是很清楚。为了更好地了解控制气态硝酸在有机薄膜中的吸收和解离的因素，在锗(Ge)衰减全反射(ATR)晶体上沉积了一层薄薄的SiOx，利用C8和C18烷基自组装单分子膜(SAM)的单一组分和混合物进行了研究。为了进行比较，还使用附着在硅粉表面自然氧化层上的C18 SAM进行了漫反射红外傅立叶变换光谱(DRIFT)研究。这些研究表明，自组装膜的烷基链长和有序性/无序性对分子硝酸的吸附或解离/重组没有显著影响。因此，与SAM的性质无关，分子HNO3的相对湿度高达70%-90%。解离后，当除去水时，HNO3分子在所有SAM表面上再生。分子动力学模拟的结果与实验结果一致，表明表面的缺陷和孔洞控制着HNO3分子的吸附、解离和复合。与本文研究的自组装膜相比，边界层表面的有机薄膜将更加不规则，有序性更差，因此在边界层表面可能存在比先前认为的更大程度的未解离HNO_3。这一观察结果与最近显示硝酸在表面上光解增强的研究结果相结合，表明在大气模型中可能需要考虑沉积的硝酸的再氧化作用。
The major removal processes for gaseous nitric acid (HNO3) in the atmosphere are dry and wet deposition onto various surfaces. The surface in the boundary layer is often covered with organic films, but the interaction of gaseous HNO3 with them is not well understood. To better understand the factors controlling the uptake of gaseous nitric acid and its dissociation in organic films, studies were carried out using single component and mixtures of C8 and C18 alkyl self-assembled monolayers (SAMs) attached to a germanium (Ge) attenuated total reflectance (ATR) crystal upon which a thin layer of SiOx had been deposited. For comparison, diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) studies were also carried out using a C18 SAM attached to the native oxide layer on the surface of silicon powder. These studies show that the alkyl chain length and order/disorder of the SAMs does not significantly affect the uptake or dissociation/recombination of molecular HNO3. Thus, independent of the nature of the SAM, molecular HNO3 is observed up to 70–90% relative humidity. After dissociation, molecular HNO3 is regenerated on all SAM surfaces when water is removed. Results of molecular dynamics simulations are consistent with experiments and show that defects and pores on the surfaces control the uptake, dissociation and recombination of molecular HNO3. Organic films on surfaces in the boundary layer will certainly be more irregular and less ordered than SAMs studied here, therefore undissociated HNO3 may be present on surfaces in the boundary layer to a greater extent than previously thought. The combination of this observation with the results of recent studies showing enhanced photolysis of nitric acid on surfaces suggests that renoxification of deposited nitric acid may need to be taken into account in atmospheric models.