Photocatalytic properties of titania thin films prepared by sputtering versus evaporation and aging of induced oxygen vacancy defects
Photocatalytic properties of titania thin films prepared by sputtering versus evaporation and aging of induced oxygen vacancy defects
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DOI：
10.1016/j.apcatb.2015.06.041
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发表时间：
2016
影响因子：
22.1
通讯作者：
B. Henkel;T. Neubert;Sebastian Zabel;C. Lamprecht;C. Selhuber‐Unkel;K. Rätzke;T. Strunskus;M. Ver
中科院分区：
文献类型：
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作者：
B. Henkel;T. Neubert;Sebastian Zabel;C. Lamprecht;C. Selhuber‐Unkel;K. Rätzke;T. Strunskus;M. Ver
为了了解不同的物理气相沉积技术制备的二氧化钛薄膜的光催化效率的变化，我们研究了两个广泛使用的PVD方法，电子束蒸发和反应脉冲直流磁控溅射的微观结构和所得的性能。此外，我们还研究了在还原性气氛中回火所引起的氧空位缺陷的影响以及时效行为。沉积后，在氧气、空气、氩气和合成气体中进行几个回火系列以控制氧空位缺陷的量。薄膜的结晶度，纹理，晶粒生长，晶粒结构，表面粗糙度，光透射率以及带隙能量进行了表征;通过亚甲基蓝降解的光催化效率进行了测量。结果表明，蒸发法和溅射法制备的二氧化钛薄膜的成核和生长机制不同，从而严重影响了光催化效率。蒸发的薄膜表现出均匀的形核和生长，并且即使在800 ° C下回火1 h后仍保持在马氏体结构。相反，溅射薄膜在与衬底的界面处开始形成晶粒，并表现出异质形核和生长。溅射薄膜经600 ℃回火1h后，已形成金红石结构。与蒸发薄膜（+6%）相比，由于回火而增加的表面积（这促进了光催化反应物的吸附）在溅射薄膜（+29%）中更明显。通过在氩气中回火或在合成气体中回火来保存具有氧空位缺陷的膜，显示出光催化效率的大的改善。然而，样品在19个月内的老化导致效率逐渐下降，最终达到在空气中回火的薄膜水平，该水平在相同的19个月内保持稳定。这强烈地质疑了基于通过氧空位缺陷提高光催化效率的广泛应用的概念。
In order to understand the variations in photocatalytic efficiencies of titania thin films prepared by different physical vapor deposition techniques, we studied the microstructure and resulting properties for the two widely used PVD methods, electron beam evaporation and reactive pulsed DC magnetron sputtering. In addition, we investigated the effect of oxygen vacancy defects induced by tempering in reducing atmospheres and the aging behavior. After deposition, several tempering series in oxygen, air, argon, and forming gas were carried out to control the amount of oxygen vacancy defects. The films were characterized with respect to crystallinity, texture, grain growth, grain structure, surface roughness, light transmission as well as band gap energy; the photocatalytic efficiency was measured via methylene blue degradation. The results show different nucleation and growth mechanisms between evaporated and sputtered titania thin films, resulting in severe influence on photocatalytic efficiency. The evaporated thin films exhibited homogeneous nucleation and growth, and stayed in the anatase structure even after tempering at 800 °C for 1 h. In contrast, the sputtered thin films started to form grains at the interface to the substrate and showed heterogeneous nucleation and growth. Moreover, the sputtered films already formed rutile when tempered at 600 °C for 1 h. The gain in surface area due to tempering, which promotes adsorption of photocatalytic reactants, was more pronounced in sputtered thin films (+29%) compared to evaporated thin films (+6%). Films with oxygen vacancy defects, preserved by tempering in argon or induced by tempering in forming gas, showed a large improvement in photocatalytic efficiency. However, aging of the samples over a period of 19 months lead to a progressive decline in efficiency, finally reaching the level of thin films tempered in air, which had remained stable over the same 19 month period. This strongly questions widely applied concepts based on improving the photocatalytic efficiency via oxygen vacancy defects.