Direct imaging of visible-light-induced one-step charge separation at the chromium oxide/strontium titanate interface
Direct imaging of visible-light-induced one-step charge separation at the chromium oxide/strontium titanate interface
复制标题
氧化铬/钛酸锶界面可见光诱导一步电荷分离的直接成像
DOI：
10.1039/d1ta08950a
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发表时间：
2022
影响因子：
11.9
通讯作者：
Miyauchi Masahiro
中科院分区：
文献类型：
--
作者：
Wardhana Aufandra Cakra;Yasuhara Sou;Yu Min-Wen;Yamaguchi Akira;Nagao Tadaaki;Ishii Satoshi;Miyauchi Masahiro
高效的可见光活性光催化剂在实际应用中具有重要意义。第一排过渡金属氧化物纳米团簇被负载到紫外光驱动的半导体上，在可见光照射下进行了几种光催化反应。然而，引发这些反应的激发机制尚不清楚。在本文中，我们使用一层涂覆在SrTiO_3衬底上的超薄CrO_2O_3薄膜(Cr2O_3/SrTiO_3薄膜系统)作为明确的光催化剂模型，阐明了这些材料之间独特的界面电荷传输路径(即还原剂到带电荷转移(RBCT))。开尔文探针力显微镜(KPFM)测量表明，在可见光照射下，Cr2O3薄膜的表面电位差(SPD)发生了负移。考虑到对照样品(Cr2O_3/石英(SiO_2)、Cr2O_3/Al_2O_3(Al_2O_3)/SrTiO_3和氧化铜(CuO_X)/SrTiO_3)的SPD结果，负移是由于从Cr2O_3薄膜的价带(Vb)到SrTiO_3衬底的导带(Cb)的一步电子激发，在薄膜上留下了空穴。Cr2O3SPD信号的厚度依赖关系表明，空穴分布在距界面90 nm以内。此外，原子力显微镜(AFM)对光沉积的金或锰氧化物(MnOx)颗粒的观察表明，还原反应和氧化反应分别在SrTiO_3衬底和Cr2O_3薄膜上进行，两种反应都发生在距离薄膜边缘数百纳米的横向位置。这项研究为开发由界面电荷转移驱动的高效可见光敏感光催化剂提供了见解。
Efficient visible-light-active photocatalysts are of great interest for practical applications. First-row transition metal oxide nanoclusters have been loaded onto ultraviolet (UV)-driven semiconductors for several photocatalytic reactions under visible-light illumination. However, the excitation mechanisms, which initiate these reactions, are yet to be understood. Here, using an ultrathin Cr2O3 film that was coated on a SrTiO3 substrate (a Cr2O3/SrTiO3 thin-film system) as a well-defined photocatalyst model, we elucidated a unique interfacial charge transport pathway (i.e., reductant-to-band charge transfer (RBCT)) between these materials. The Kelvin probe force microscopy (KPFM) measurement on the Cr2O3 thin film showed a negative shift in the surface potential difference (SPD) during visible-light irradiation. Taking into account the SPD results of the control samples (Cr2O3/quartz (SiO2), Cr2O3/alumina (Al2O3)/SrTiO3, and copper oxide (CuOx)/SrTiO3), the negative shift was due to the one-step electron excitation from the valence band (VB) of the Cr2O3 thin film to the conduction band (CB) of the SrTiO3 substrate, leaving holes in the thin film. The thickness dependence of the SPD signals of Cr2O3 suggested that the distribution of the holes was within 90 nm from the interface. Moreover, the atomic force microscopy (AFM) observation of the photo-deposited gold or manganese oxide (MnOx) particles indicated that the reduction and oxidation reactions proceeded on the SrTiO3 substrate and Cr2O3 thin film, respectively; both reactions took place laterally at distances of several hundred nanometres from the edge of the thin film. This study provides insights into the development of efficient visible-light-sensitive photocatalysts that are driven by the interfacial charge transfer.