Imperial College London, South Kensington Campus, London, SW7 2AZ, UK.
Phys Chem Chem Phys. 2013 Jun 7;15(21):8254-63. doi: 10.1039/c3cp44513e. Epub 2013 Apr 24.
Anatase TiO2 thin-films were formed on glass by a sol-gel dip-coating method and annealed at 500 °C. Ag nanoparticles were grown on the surface of TiO2 by a photo-assisted process from AgNO3 salt using either UVC - 254 nm or UVA - 365 nm light. The size, shape and coverage of the particles were assessed by scanning electron microscopy. Changes in surface plasmon properties were investigated by UV-visible spectroscopy. A greater level of spherical Ag nanoparticles grew on TiO2 when using UVA light (365 nm); with particles 96 ± 33 nm wide on average and covering 29% of the surface. In the case of UVC light (254 nm), particles were 78 ± 14 nm wide on average and covered 13% of the surface. EXAFS measurements performed in situ of the Ag K-edge showed that the photo-assisted growth was more rapid when UVA light was used, leading to the full conversion of the AgNO3 salt layer in ≈1900 seconds. When UVC light was used, ≈50% of the salt layer was converted in ≈6100 seconds. The inhibited growth under UVC conditions was attributed to the absorption of light by the Ag nanoparticles as they formed (as opposed to the semiconductor beneath). The films also displayed reversible photochromism. The change in phase from the coloured (metallic Ag) to the bleached state (oxidized Ag) was identified using EXAFS spectroscopy. By comparing the EXAFS pattern with simulated model structures, it was shown that the transition from cubic Ag to cubic Ag2O was most likely, with an ≈70% conversion with 12 hours of white light irradiance. We believe that this is the first time the bleached form of silver in photochromic Ag-TiO2 thin-films has been identified by a direct method. In addition, we believe that this is the first case in which the photo-assisted formation of Ag-TiO2 has been monitored in situ under ambient temperature and pressure.
锐钛矿 TiO2 薄膜通过溶胶-凝胶浸涂法在玻璃上形成，并在 500°C 下退火。Ag 纳米粒子通过光辅助过程从 AgNO3 盐在 UVC-254nm 或 UVA-365nm 光下生长在 TiO2 表面上。通过扫描电子显微镜评估颗粒的尺寸、形状和覆盖率。通过紫外可见光谱研究表面等离子体特性的变化。使用 UVA 光（365nm）时，在 TiO2 上生长出更多球形 Ag 纳米粒子；平均粒径为 96±33nm，覆盖面积为 29%。在 UVC 光（254nm）的情况下，颗粒的平均宽度为 78±14nm，覆盖面积为 13%。原位进行的 Ag K 边 EXAFS 测量表明，使用 UVA 光时，光辅助生长更快，导致 AgNO3 盐层在 ≈1900 秒内完全转化。当使用 UVC 光时，≈50%的盐层在 ≈6100 秒内转化。在 UVC 条件下生长受到抑制归因于 Ag 纳米粒子形成时吸收光（与半导体下方相反）。该薄膜还表现出可逆光致变色性。使用 EXAFS 光谱鉴定了从有色（金属 Ag）到漂白状态（氧化 Ag）的相变化。通过将 EXAFS 图案与模拟模型结构进行比较，表明最有可能从立方 Ag 到立方 Ag2O 发生转变，在 12 小时的白光辐照下，转化率约为 70%。我们相信，这是首次通过直接方法鉴定光致变色 Ag-TiO2 薄膜中漂白形式的银。此外，我们相信这是首次在环境温度和压力下原位监测 Ag-TiO2 的光辅助形成。
