Heterostructured TiO₂ nanoparticles/nanotube arrays (NPs/NTAs) are produced from as-anodized amorphous TiO₂ nanotube arrays in water at a temperature as low as 90 °C. The phase and morphology transformation of the as-anodized amorphous TiO₂ nanotube in water can be attributed to a water-induced dissolution and recrystallization mechanism in which the as-anodized amorphous TiO₂ NTAs are gradually self-sacrificed, and then spontaneously morphing into the composite NPs/NTAs structure consisting of anatase NPs and thinner amorphous NTs. The composite can be further crystallized into anatase TiO₂ NPs/NTAs consisting of anatase NT and anatase NPs by annealing in air at 450 °C for 3 hours. The composite anatase TiO₂ NPs/NTAs have a surface area that is 1.4 times larger than that of the anatase TiO₂ NTAs and possess enhanced photocatalytic activity in the photodecomposition of organic pollutants and water splitting. The photodecomposition rate of the organic pollutant rhodamine B by the anatase TiO₂ NPs/NTAs photocatalyst is two times higher than that by the annealed anatase TiO₂ NTAs. The enhanced photocatalytic activity of the hererostructured TiO₂ NPs/NTAs arises from the large surface area of the TiO₂ NPs and superior electron transport in anatase TiO₂ NT. The in situ hydrothermal conversion of the microstructure from amorphous TiO₂ NTAs into hererostructured TiO₂ NPs/NTAs in water is very simple thereby enabling the design and fabrication of highly photoactive one-dimensional TiO₂-based functional materials applicable to photocatalysis and solar energy conversion.

Although human eyes are quite insensitive to ultraviolet (UV) light, most of the longer wavelength UV light (the UV-A band between 320 and 400 nm) does reach the earth surface and after prolonged exposure, the radiation can cause health concerns especially skin cancer. Therefore, it is extremely important to explore ways to effectively monitor the radiation. Herein we report for the first time a new high-performance UV photodetector made of an individual Nb₂O₅ nanobelt. Quasi-aligned Nb₂O₅ nanobelts 100–500 nm wide and 2–10 μm long were synthesized using a hydrothermal treatment of a niobium foil in a KOH solution followed by proton exchange and calcination treatment. A nanostructured photodetector was constructed from an individual Nb₂O₅ nanobelt and its optoelectronic properties were evaluated. The detector exhibited linear photocurrent characteristics, excellent light selectivity, and high external quantum-efficiency (EQE) of 6070%. Long-term stability of the photocurrent over a period of 2500 s at an applied voltage of 1.0 V was achieved. The photodetector performance was further enhanced by improving the crystallinity and eliminating the defects in the Nb₂O₅ nanobelt crystals. These excellent optoelectronic properties demonstrate that Nb₂O₅ nanobelts are suitable for visible-blind UV-light sensors and optoelectronic circuits, especially those operating in the UV-A range.

Quasi-aligned cylindrical and conical core–shell nanofibers consisting of carbon shells and TiO₂ nanowire cores are produced in situ on Ti foils without using a foreign metallic catalyst and template. A cylindrical nanofiber has a TiO₂ nanowire core 30–50 nm in diameter and a 5–10 nm-thick cylindrical carbon shell, while in the conical nanostructure the TiO₂ nanowire core has a diameter of 20–40 nm and the thickness of the carbon shell varies from about 200 nm at the bottom to about 5 nm at the tip. Electrochemical analysis reveals well-defined redox peaks of the [Fe(CN)₆]^3−/4− redox couple and heterogeneous charge-transfer rate constants of 0.010 and 0.062 cm s⁻¹ for the cylindrical and conical nanofibers, respectively. The coverage of exposed edge planes on the cylindrical and conical carbon shells is estimated to be 2.5 and 15.5 % respectively. The more abundant exposed edge planes on the conical nanofiber decrease the overpotential and increase the voltammetric resolution during electrochemical detection of uric acid and ascorbic acid. Our results suggest that the density of edge-plane sites estimated from Raman scattering is not necessarily equal to the density of exposed edge-plane sites, and only carbon electrodes with a large density of exposed edge planes or free graphene sheet ends exhibit better electrochemical performance.