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

Abstract

A black TiO 2 nanotube (NT) heterostructure with an anatase-core and an amorphous-shell has been synthesized by NH 3 annealing of amorphous NT grown by the anodization of a Ti substrate. Remarkable photoabsorption behavior of these black TiO 2 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 Ti 4 O 7 . Bulk-sensitive XANES using X-ray partial fluorescence yield and Ti 2p RIXS confirm the presence of a rich amount of Ti 3+ in the crystalline bulk (core of the NT with anatase structure) of black TiO 2 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 TiO 2 NTs is due to the stabilization of Ti 3+ in this special N-doped core−shell assembly having structure varying between TiO 2 (bulk anatase) and Ti 4 O 7 (surface, amorphous).

Preparation of PAN@TiO2 Nanofibers for Fruit Packaging Materials with Efficient Photocatalytic Degradation of Ethylene

“…Pure PAN nanofibers exhibited no absorption in UV region, while the TiO 2 -coated nanofibers had great absorption in the range of UV spectrum. The result are consistent with a previous study showing that TiO 2 nanotubes absorbed UV light in the 300–400 nm range [25].…”

Tuning defects in oxides at room temperature by lithium reduction

“…4d–f , some peaks at ~2 eV appear for the oscillator strength of the transition from gap states to the CB. Such results clearly suggest that the gap states induced by O v can enhance the photoadsorption through d−d transitions between Ti 3+ ions and its resonance 47 . It should be noted that the oscillator strength of Ti 4+ does not have such kind of feature.…”

Synergetic Enhancement of Light Harvesting and Charge Separation over Surface-Disorder-Engineered TiO2 Photonic Crystals

“…As the proportion of UV light in solar light is small, strategies for improving photon absorption and reducing the recombination of charge carriers of TiO 2 are crucial to achieve a high photocatalytic performance. [15][16][17] Photonic crystal (PC)-based materials offer a unique way to enhance light harvesting and have attracted considerable attention in photocatalysis. [18][19][20][21][22] PCs have a periodic dielectric structure with unique optical and structure properties, such as controlling and manipulating incident light, high light absorption efficiency, a uniform macroporous structure, and large specific surface area.…”