利用和频振动光谱研究乙醇在气相/熔融石英界面上吸附的亚单层结构。

Structure of the submonolayer of ethanol adsorption on a vapor/fused silica interface studied with sum frequency vibrational spectroscopy.

作者信息

Xu Huijie, Zhang Donghua, Hu Jun, Tian Chuanshan, Shen Y Ron

机构信息

†Department of Physics, State Key Laboratory of Surface Physics, and Key Laboratory of Micro- and Nano-Photonic Structures (MOE), Fudan University, Shanghai 200433, China.

‡Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.

出版信息

J Phys Chem A. 2015 May 14;119(19):4573-80. doi: 10.1021/jp510706u. Epub 2015 Jan 27.

DOI:10.1021/jp510706u

PMID:25580676

Abstract

Sum-frequency vibrational spectroscopy in the CH and OH stretch region was used to study ethanol adsorption on fused silica from vapor of different ethanol partial pressures. It was found that the adsorbed ethanol molecules were oriented with their methyl group tilted away from the surface normal by an average angle of ∼45° at low ethanol vapor pressures and ∼39° when approaching saturated vapor pressure. The spectral change with ethanol vapor pressure and the deduced adsorption isotherm show that ethanol molecules have two distinct adsorption sites on silica: One is the silanol group site to which an ethanol molecule can be strongly hydrogen-bonded, and the other is the siloxane (Si-O-Si) group site to which an ethanol molecule can be weakly bonded. The presence of water in vapor significantly reduced the surface coverage of ethanol on silica due to competitive adsorption between ethanol and water.

摘要

利用CH和OH伸缩振动区域的和频振动光谱研究了不同乙醇分压的蒸汽中乙醇在熔融石英上的吸附情况。研究发现，在低乙醇蒸汽压下，吸附的乙醇分子的甲基与表面法线倾斜，平均角度约为45°；当接近饱和蒸汽压时，平均角度约为39°。乙醇蒸汽压引起的光谱变化以及推导得到的吸附等温线表明，乙醇分子在二氧化硅上有两个不同的吸附位点：一个是硅醇基团位点，乙醇分子可与该位点形成强氢键；另一个是硅氧烷（Si-O-Si）基团位点，乙醇分子与该位点形成弱键。由于乙醇和水之间的竞争吸附，蒸汽中的水的存在显著降低了乙醇在二氧化硅上的表面覆盖率。