| Titania (TiO2) is an important multifunctional oxide finding various applications in photocatalysis, dye-sensitized solar cells, gas sensors, and Li-ion batteries (LIBs). As a promising photocatalyst, TiO2 possesses attractive merits of abundance, biocompatibility, and excellent chemical stability. Nanostructured TiO2 such as nanowires, nanorods, nanoflowers, nanotubes, and nanobelts, has been widely studied to achieve an improved photocatalytic performance. Among them, TiO2 nanobelts integrate the merits of two-dimensional (2D) nanomaterials, that is, extremely high specific surface area, with enhanced charge transport that is characteristic of ID configuration, which hence attracted much attention in fields of gas sensors, photocatalysis, and LIBs.TiO2 nanobelts are typically fabricated through an alkaline hydrothermal treatment followed by a subsequent proton exchange and heat treatment, which usually exhibit a large thickness and a low surface area. The preparation process has to be carried out at high temperature and pressure, which is not appropriate mass productions. Therefore, to explore a method for preparing nanobelt arrays under the open system is of practical significance.In the current investigation, a precursor solution was developed. Under a mild open environment, the precursor solution is capable of deposting ultrathin TiO2 nanobelt arrays, as well as hierarchical "belt-on-wire" and "belt-on-belt" TiO2 arrays based on 1D TiO2 nanostructures. The relationship between the structure and photocatalytic properties was studied in detail. Fllows are the main results abotained.A solution combustion procedure was firstly adopted to prepare a black water-proof precursor, which, after interacting with H2O2 at ambient temperature, resulted in a precursor solution that is capable of precipitating hydrogen titanate (H2Ti2O5·H2O) nanobelt arrays on metallic Ti substrates at 60 ℃. A subsequent calcination in air at 400 ℃ achieved arrays of ultrathin anatase TiO2 nanobelt ca.2-4 nm in thickness. The additive of nickel nitrate in the combustion solution achieved the Ni-doping into the resultant TiO2 nanobelts, which did not alter the nanobelt structure but significantly reduced the band gap from 3.2 eV to 2.9 eV. When compared with the commonly alkali-hydrothermal synthesized anatase TiO2 nanobelts, the present ultrathin nanobelts exhibited much improved photocatalytic activity when utilized to assist photodegradation of rhodamine B in water. The ultrathin nanobelt structure is believed to contribute to the high specific surface area, much reduced charge migration path, and the enhanced charge transport along the longitude direction. The appropriate Ni-doping further enhanced the photocatalytic performance, because of the increased light harvesting efficiency and reduced charge recombination.The precursor solution can also be used to fabricate 1D TiO2 hierarchical nanostructures. When immersing TiO2 nanowire array or nanobelt array, which were synthesized by the alkali-hydrothermal technique, into the precursor solution for 60 min under 60 ℃, hierarchical "belt-on-wire" and "belt-on-belt" TiO2 arrays can be easily obtained, respectively. The nanobelts can grow on the nanowire/nanobelt substrates directly, without any seed layers. The trunck is in anatase single-crystal structure and the branch is in polycrystalline structure. It can be ovserved that the nanobelt will grow rapidly once the nucleation process initiates. When compared with 1D TiO2 nanowire/nanobelt arrays, the "belt-on-wire" and "belt-on-belt" TiO2 arrays possess much higher performance to assist photodegradations of rhodamine B in water, thanks to the higher specific surface area. The Ni-doping of the nanobelt branch further enhanced the photocatalytic properties of the TiO2 hierarchical nanostructure arrays. |
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