Department of Chemistry, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
Phys Chem Chem Phys. 2010 Dec 14;12(46):15231-9. doi: 10.1039/c0cp00860e. Epub 2010 Nov 2.
Subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) was applied to study (bi)sulfate adsorption on a Pt(111) surface in solutions of variable pH while maintaining a constant total bisulfate/sulfate ((bi)sulfate) concentration without the addition of an inert supporting electrolyte. The spectra were recorded for both the p- and s-polarizations of the IR radiation in order to differentiate between the IR bands of the (bi)sulfate species adsorbed on the electrode surface from those species located in the thin layer of electrolyte. The spectra recorded with p-polarized light consist of the IR bands from both the species adsorbed at the electrode surface and those present in the thin layer of electrolyte between the electrode surface and ZnSe window whereas the s-polarized spectra contain only the IR bands from the species located in the thin layer of electrolyte. A new procedure was developed to calculate the angle of incidence and thickness of the electrolyte between the Pt(111) electrode surface and the ZnSe IR transparent window. By combining these values with the knowledge of the optical constants for Pt, H(2)O and ZnSe, the mean square electric field strength (MSEFS) at the Pt(111) electrode surface and for thin layer of solution were accurately calculated. The spectra recorded using s-polarization were multiplied by the ratio of the average MSEFS for p- and s-polarizations and subtracted from the spectra recorded using p-polarization in order to remove the IR bands that arise from the species present within the thin layer cavity. In this manner, the resulting IR spectra contain only the IR bands for the anions adsorbed on the Pt(111) electrode surface. The spectra of adsorbed anions show little change with respect to the pH ranging from 1 to 5.6. This behavior indicates that the same species is predominantly adsorbed on the metal surface for this broad range of pH values and the results suggest that sulfate is the most likely candidate for this adsorbate.
减法归一化界面傅里叶变换红外反射光谱 (SNIFTIRS) 被应用于研究在 pH 值可变的溶液中，在不添加惰性支持电解质的情况下，保持恒定的总双硫酸盐/硫酸盐 (双硫酸盐) 浓度时，双硫酸盐在 Pt(111) 表面上的吸附。为了区分吸附在电极表面的双硫酸盐物种的 IR 带与位于电解质薄层中的那些物种的 IR 带，记录了 IR 辐射的 p- 和 s- 两种偏振的光谱。用 p 偏振光记录的光谱由吸附在电极表面的物种的 IR 带和电极表面与 ZnSe 窗口之间的电解质薄层中的那些物种的 IR 带组成，而 s 偏振光谱仅包含位于电解质薄层中的物种的 IR 带。开发了一种新的程序来计算 Pt(111)电极表面与 ZnSe 红外透明窗口之间的电解质的入射角和厚度。通过将这些值与 Pt、H2O 和 ZnSe 的光学常数结合起来，可以准确计算 Pt(111)电极表面和薄层溶液中的平均平方电场强度 (MSEFS)。用 s 偏振记录的光谱通过 p 和 s 偏振的平均 MSEFS 的比值相乘，并从用 p 偏振记录的光谱中减去，以去除来自薄层空腔中存在的物种的 IR 带。通过这种方式，得到的 IR 光谱仅包含吸附在 Pt(111)电极表面上的阴离子的 IR 带。吸附阴离子的光谱在 pH 值为 1 到 5.6 的范围内几乎没有变化。这种行为表明，在这个广泛的 pH 值范围内，相同的物种主要吸附在金属表面上，结果表明硫酸盐是这种吸附物最有可能的候选物。
