Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, PO Box 534, SE-751 21 Uppsala, Sweden.
ACS Appl Mater Interfaces. 2012 Feb;4(2):672-9. doi: 10.1021/am201253y. Epub 2012 Jan 26.
Photoinduced SO(2) fixation on anatase TiO(2) films was studied by in situ Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The TiO(2) films were prepared by reactive DC magnetron sputtering and were subsequently exposed to 50 ppm SO(2) gas mixed in synthetic air and irradiated with UV light at substrate temperatures between 298 and 673 K. Simultaneous UV irradiation and SO(2) exposure between 373 and 523 K resulted in significant sulfur (S) deposits on crystalline TiO(2) films as determined by XPS, whereas amorphous films contained negligible amounts of S. At substrate temperatures above 523 K, the S deposits readily desorbed from TiO(2). The oxidation state of sulfur successively changed from S(4+) for SO(2) adsorbed on crystalline TiO(2) films at room temperature without irradiation to S(6+) for films exposed to SO(2) at elevated temperatures with simultaneous irradiation. In situ FTIR was used to monitor the temporal evolution of the photoinduced surface reaction products formed on the TiO(2) surfaces. It is shown that band gap excitation of TiO(2) results in photoinduced oxidation of SO(2), which at elevated temperatures become coordinated to the TiO(2) lattice through interactions with O vacancies and form sulfite and sulfate surface species. These species makes the surface acidic, which is manifested in nondetectable adherence of stearic acid to the modified surface. The modified films show good chemical stability as evidenced by sonication and repeated recycling of the films. The results suggest a new method to functionalize wide band gap oxide surfaces by means of photoinduced reactions in reactive gases at elevated substrate temperatures. In the case of anatase TiO(2) in reactive SO(2) gas, we here show that such functionalization yields surfaces with excellent oleophobic properties, as probed by adhesion of stearic acid.
采用原位傅里叶变换红外光谱（FTIR）和 X 射线光电子能谱（XPS）研究了锐钛矿 TiO2 薄膜的光致 SO2 固定化。TiO2 薄膜通过反应性直流磁控溅射制备，然后在 298 至 673 K 的衬底温度下暴露于含有 50 ppm SO2 气体的合成空气中，并辐照紫外光。在 373 至 523 K 之间同时进行紫外辐照和 SO2 暴露，导致 XPS 确定的结晶 TiO2 薄膜上有明显的硫（S）沉积物，而无定形薄膜中则含有可忽略不计的 S。在高于 523 K 的衬底温度下，S 沉积物很容易从 TiO2 上解吸。S 的氧化态从室温下未辐照时吸附在结晶 TiO2 薄膜上的 SO2 的 S(4+)，依次变为辐照时高温下暴露于 SO2 的 S(6+)。原位 FTIR 用于监测 TiO2 表面形成的光诱导表面反应产物的时间演变。结果表明，TiO2 的带隙激发导致 SO2 的光致氧化，在高温下，SO2 通过与 O 空位相互作用而与 TiO2 晶格配位，形成亚硫酸盐和硫酸盐表面物种。这些物种使表面呈酸性，这表现为改性表面上不可检测的硬脂酸粘附。改性后的薄膜表现出良好的化学稳定性，这可以通过超声处理和薄膜的重复回收来证明。结果表明，通过在高温下在反应性气体中进行光致反应，可以为宽能隙氧化物表面赋予新的功能。在反应性 SO2 气体中的锐钛矿 TiO2 的情况下，我们在这里表明，这种功能化可以得到具有优异疏油性的表面，这可以通过硬脂酸的粘附来探测。
