Department of Chemical and Biological Engineering, Center for Catalysis Research and Innovation (CCRI), University of Ottawa, 161 Louis-Pasteur St, Ottawa, Ontario K1N 6N5, Canada.
Analyst. 2018 May 29;143(11):2563-2573. doi: 10.1039/c8an00572a.
Infrared spectroscopy is a powerful non-destructive technique for the identification and quantification of organic molecules widely used in scientific studies. For many years, efforts have been made to adopt this technique for the in situ monitoring of reactions. From these efforts, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was developed three decades ago. Unfortunately, because of the complexity of data processing and interpretation, PM-IRRAS had been avoided in lieu of the single potential alteration infrared spectroscopy (SPAIRS) and subtractively normalized interfacial Fourier transform infrared (SNIFTIR). In this work, we present a new approach for PM-IRRAS data processing and presentation, which provides more insight into in situ and surface studies besides dramatically improving the S/N. In this new approach, we recommend three complementary methods of data treatment (eqn (7), (9) and (10)) as the new protocols for presenting PM-IRRAS data. These equations are robust in visualising the surface processes at the solid-liquid and solid-gas interphases. Eqn (7) contrasts the surface adsorbed species with respect to the isotropic background with or without the influence of the applied potential. Eqn (9) highlights the surface potential-driven changes between the sample and the reference spectra. Eqn (10) focuses on the bulk-phase (solution/gas and surface species) potential-driven changes between the sample and the reference spectra, and hence it can be used to track the production of species, which desorb from the surface upon their formation. Examples of ethanol electro-oxidation reaction are provided as a test system for in situ studies and PVP deposited on glassy carbon for thin-film studies to illustrate the utility of the new PM-IRRAS data handling protocol, which is poised to improve the understanding of the chemistry and physics of surface processes.
红外光谱是一种强大的非破坏性技术，用于广泛应用于科学研究中的有机分子的鉴定和定量。多年来，人们一直致力于采用这种技术对反应进行原位监测。从这些努力中，三十年前开发出了偏振调制红外反射吸收光谱（PM-IRRAS）。不幸的是，由于数据处理和解释的复杂性，PM-IRRAS 已经被单电位变化红外光谱（SPAIRS）和减法归一化界面傅里叶变换红外光谱（SNIFTIR）所取代。在这项工作中，我们提出了一种新的 PM-IRRAS 数据处理和表示方法，该方法除了极大地提高信噪比外，还提供了对原位和表面研究的更深入了解。在这种新方法中，我们建议三种互补的数据处理方法（方程（7）、（9）和（10））作为呈现 PM-IRRAS 数据的新方案。这些方程在可视化固-液和固-气界面的表面过程方面非常稳健。方程（7）对比了表面吸附物种相对于各向同性背景的情况，无论是否施加了外加电势。方程（9）突出了表面电势驱动的样品和参考光谱之间的变化。方程（10）关注的是样品和参考光谱之间的体相（溶液/气体和表面物种）电势驱动的变化，因此可以用于跟踪在形成时从表面解吸的物种的产生。提供乙醇电氧化反应的实例作为原位研究的测试系统，以及 PVP 在玻璃碳上的沉积作为薄膜研究的实例，说明了新的 PM-IRRAS 数据处理协议的实用性，该协议有望提高对表面过程的化学和物理的理解。
