Unraveling the Origin of Visible Light Capture by Core–Shell TiO2 Nanotubes

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• 作者：Jun Li ; Chang-Hai Liu ; Xia Li ; Zhi-Qiang Wang ; Yu-Cheng Shao ; Sui-Dong Wang ; Xue-Liang Sun ; Way-Faung Pong ; Jing-Hua Guo ; Tsun-Kong Sham
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：June 28, 2016
• 年：2016
• 卷：28
• 期：12
• 页码：4467-4475
• 全文大小：557K
• 年卷期：0
• ISSN：1520-5002

文摘

A black TiO₂ nanotube (NT) heterostructure with an anatase-core and an amorphous-shell has been synthesized by NH₃ annealing of amorphous NT grown by the anodization of a Ti substrate. Remarkable photoabsorption behavior of these black TiO₂ NTs is observed: strong absorption throughout the entire optical wavelength region from ultraviolet to near-infrared. X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and resonant inelastic X-ray scattering (RIXS) have been used to elucidate the origin of this spectacular light capture phenomenon. Surface-sensitive XANES recorded in total electron yield and XPS show that the surface layer is amorphous with a chemical composition approaching that of Ti₄O₇. Bulk-sensitive XANES using X-ray partial fluorescence yield and Ti 2p RIXS confirm the presence of a rich amount of Ti³⁺ in the crystalline bulk (core of the NT with anatase structure) of black TiO₂ NTs, which exhibits a dispersive d-d energy loss at ∼2 eV corresponding to the broad visible light absorption at ∼600 nm. Our results suggest that the extraordinary photoabsorption behavior of these black TiO₂ NTs is due to the stabilization of Ti³⁺ in this special N-doped core–shell assembly having structure varying between TiO₂ (bulk anatase) and Ti₄O₇ (surface, amorphous).