Voci Silvia, Vannoy Kathryn J, Dick Jeffrey E
Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA; Elmore Family School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907, USA.
J Colloid Interface Sci. 2024 May;661:853-860. doi: 10.1016/j.jcis.2024.01.100. Epub 2024 Jan 19.
Interfacial effects are well-known to significantly alter chemical reactivity, especially in confined environments, where the surface to volume ratio increases. Here, we observed an inhomogeneity in the electrogenerated chemiluminescence (ECL) intensity decrease over time in a multiphasic system composed of femtoliter water droplets entrapping femtoliter volumes of the 1,2-dichloroethane (DCE) continuous phase. In usual electrochemiluminescence (ECL) reactions involving an ECL chromophore and oxalate ([CO]), the build-up of CO diminishes the ECL signal with time because of bubble formation. We hypothesised that relative solubilities of chemical species in these environments play a dramatic role in interfacial reactivity. Water droplets, loaded with the ECL luminophore [Ru(bpy)] and the coreactant [CO] were allowed to stochastically collide and adsorb at the surface of a glassy carbon macroelectrode. When water droplets coalesce on the surface, they leave behind femtoliter droplets of the DCE phase (inclusions). We report the surprising finding that the addition of multiple interfaces, due to the presence of continuous phase's femtoliter inclusions, allows sustained ECL over time after successive potential applications at the triple-phase boundary between water droplet|electrode|DCE inclusion. When femtoliter droplets of DCE form on the electrode surface, bright rings of ECL are observed during the simultaneous oxidation of [Ru(bpy)] and [CO]. Control experiments and finite element modelling allowed us to propose that these rings arise because CO that is generated near the 1,2-dichloroethane droplet partitions in due to relative solubility of CO in 1,2-dichloroethane and builds up and/or is expelled at the top of the droplet. The small droplets of the DCE phase act as micropumps, pumping away carbon dioxide from the interface. These results highlight the unexpected point that confined microenvironments and their geometry can tune chemical reactions of industrial importance and fundamental interest.
众所周知，界面效应会显著改变化学反应活性，尤其是在受限环境中，此时表面积与体积之比会增加。在此，我们观察到在一个由飞升级水滴包裹飞升级体积的1,2 - 二氯乙烷（DCE）连续相组成的多相系统中，电致化学发光（ECL）强度随时间的下降存在不均匀性。在涉及ECL发色团和草酸盐（[CO]）的常规电化学发光（ECL）反应中，由于气泡形成，CO的积累会使ECL信号随时间减弱。我们推测化学物质在这些环境中的相对溶解度在界面反应性中起着重要作用。负载有ECL发光体[Ru(bpy)]和共反应物[CO]的水滴随机碰撞并吸附在玻碳宏观电极表面。当水滴在表面合并时，它们会留下飞升级的DCE相液滴（内含物）。我们报告了一个惊人的发现，即由于连续相飞升级内含物的存在而增加的多个界面，使得在水滴|电极|DCE内含物之间的三相边界处连续施加电势后，ECL能够随时间持续。当DCE的飞升级液滴在电极表面形成时，在[Ru(bpy)]和[CO]同时氧化过程中会观察到明亮的ECL环。对照实验和有限元建模使我们能够提出，这些环的出现是因为在1,2 - 二氯乙烷液滴附近生成的CO由于其在1,2 - 二氯乙烷中的相对溶解度而发生分配，并在液滴顶部积累和/或被排出。DCE相的小液滴起到微型泵的作用，将二氧化碳从界面泵走。这些结果突出了一个意想不到的观点，即受限微环境及其几何形状可以调节具有工业重要性和基础研究意义的化学反应。
