Delgado Hernan E, Rumbach Paul, Bartels David M, Go David B
Department of Chemical and Biomolecular Engineering, University of Notre Dame.
Department of Aerospace and Mechanical Engineering, University of Notre Dame;
J Vis Exp. 2018 Jan 24(131):56833. doi: 10.3791/56833.
The total internal reflection absorption spectroscopy (TIRAS) method presented in this article uses an inexpensive diode laser to detect solvated electrons produced by a low-temperature plasma in contact with an aqueous solution. Solvated electrons are powerful reducing agents, and it has been postulated that they play an important role in the interfacial chemistry between a gaseous plasma or discharge and a conductive liquid. However, due to the high local concentrations of reactive species at the interface, they have a short average lifetime (~1 µs), which makes them extremely difficult to detect. The TIRAS technique uses a unique total internal reflection geometry combined with amplitude-modulated lock-in amplification to distinguish solvated electrons' absorbance signal from other spurious noise sources. This enables the in situ detection of short-lived intermediates in the interfacial region, as opposed to the bulk measurement of stable products in the solution. This approach is especially attractive for the field of plasma electrochemistry, where much of the important chemistry is driven by short-lived free radicals. This experimental method has been used to analyze the reduction of nitrite (NO2(aq)), nitrate (NO3(aq)), hydrogen peroxide (H2O2(aq)), and dissolved carbon dioxide (CO2(aq)) by plasma-solvated electrons and deduce effective rate constants. Limitations of the method may arise in the presence of unintended parallel reactions, such as air contamination in the plasma, and absorbance measurements may also be hindered by the precipitation of reduced electrochemical products. Overall, the TIRAS method can be a powerful tool for studying the plasma-liquid interface, but its effectiveness depends on the particular system and reaction chemistry under study.
本文介绍的全内反射吸收光谱法（TIRAS）使用廉价的二极管激光器来检测低温等离子体与水溶液接触时产生的溶剂化电子。溶剂化电子是强还原剂，据推测它们在气态等离子体或放电与导电液体之间的界面化学中起重要作用。然而，由于界面处反应物种的局部浓度很高，它们的平均寿命很短（约1微秒），这使得它们极难检测。TIRAS技术采用独特的全内反射几何结构并结合幅度调制锁相放大，以将溶剂化电子的吸收信号与其他杂散噪声源区分开来。这使得能够原位检测界面区域中的短寿命中间体，而不是溶液中稳定产物的整体测量。这种方法对于等离子体电化学领域特别有吸引力，在该领域中许多重要的化学反应是由短寿命自由基驱动的。该实验方法已用于分析等离子体溶剂化电子对亚硝酸盐（NO2(aq)）、硝酸盐（NO3(aq)）、过氧化氢（H2O2(aq)）和溶解二氧化碳（CO2(aq)）的还原作用，并推导有效速率常数。该方法的局限性可能出现在存在意外平行反应的情况下，例如等离子体中的空气污染，并且吸收测量也可能受到还原电化学产物沉淀的阻碍。总体而言，TIRAS方法可以成为研究等离子体 - 液体界面的有力工具，但其有效性取决于所研究的特定系统和反应化学。
