Acid-Catalyzed Oligomerization at the Air-Water Interface Modified by Competitive Adsorption of Surfactants
Acid-Catalyzed Oligomerization at the Air-Water Interface Modified by Competitive Adsorption of Surfactants
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表面活性剂竞争吸附改性的酸催化空气-水界面齐聚
DOI：
10.1021/acs.jpcc.9b07380
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Enami Shinichi
中科院分区：
文献类型：
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作者：
Ishizuka Shinnosuke;Hama Tetsuya;Enami Shinichi
两亲性有机化合物自然地积聚在水性气溶胶的最外层，完全改变了吸附在表面的挥发性有机化合物的吸收和反应机制。通过水相微射流的质谱分析，我们研究了季烷基铵阳离子Me(CH2)n - 1N+Me3（n= 1,4,8,10,12,14）和非离子辛烷-1-醇如何影响气-水界面酸催化的气态异戊二烯（ISO）的齐聚反应。低聚反应由界面水合氢离子与异戊二烯的质子转移（PT）反应引发，形成（ISO）H+，随后发生链传播（CP）反应形成（ISO）m≥2H+。我们发现，虽然（ISO）mH+产物的总质谱信号被烷基铵阳离子或辛烷-1-醇的存在所抑制，但前者的抑制作用远大于后者。即使在5 μM等摩尔烷基铵离子溶液的水微射流中，当气-水界面仅被烷基铵离子稀疏占据时，也观察到这种抑制作用。我们认为是烷基铵阳离子与界面h30 +之间的静电斥力导致了PT反应的阻碍。相反，随后的CP反应没有被烷基铵阳离子或辛烷-1-醇的存在所抑制。我们认为，长链有机表面活性剂的存在阻碍了最初的PT反应，但几乎没有抑制随后的CP反应。我们的研究揭示了迄今为止尚未认识到的影响大气中多相化学的表面活性剂的界面特定作用。
Amphiphilic organic compounds that accumulate naturally on the outermost layers of aqueous aerosols totally change the mechanisms involved in the uptake and reactions of volatile organic compounds adsorbed on the surfaces. By means of mass spectrometry of aqueous microjets, we examined how quaternary alkylammonium cations Me(CH2)n−1N+Me3(n= 1, 4, 8, 10, 12, and 14) and nonionic octan-1-ol influence acid-catalyzed oligomerization of gaseous isoprene (ISO) at the air–water interface. The oligomerization is initiated by proton-transfer (PT) reaction from an interfacial hydronium ion to isoprene to form a (ISO)H+and is subsequently followed by chain-propagation (CP) reaction to form (ISO)m≥2H+. We found that although the total mass spectral signals of (ISO)mH+products were suppressed by the presence of either the alkylammonium cations or octan-1-ol, the suppression by the former surfactants was much larger than that of the latter. The suppression was observed even at aqueous microjets of 5 μM equimolar solution of the alkylammonium cations at which the air–water interface is only sparsely occupied by the alkylammonium cations. We propose that electrostatic repulsions between the alkylammonium cation and the interfacial H3O+cause the hindrance of the PT reaction. In contrast, the subsequent CP reactions were not suppressed by the presence of either the alkylammonium cations or octan-1-ol. We suggest that the presence of long-chain organic surfactants hinders the initial PT reaction but hardly suppresses the subsequent CP reaction. Our study has revealed hitherto unrecognized interface-specific roles of surfactants that affect multiphase chemistry in the atmosphere.