One-dimensional TiO₂Nanobelt Surface Heterostructures With Full Solar Spectrum （UV,Visible And Near-infrared）Photocatalytic Properties

One-dimensional (1D) TiO2nanomaterials have been studied extensively and deeply in the field of photocatalysis, water splitting and catalysis, due to their unique properties. However, some negative aspects of1D TiO2nanostructures still exist, including a relatively low specific surface area and a broad band gap, which in turn lead to the lack of an active site, poor quantum efficiency, and a shortage of visible light photocatalytic activity. This restricts their practical applications. Fortunately,1D TiO2nanostructured surface heterostructure (1D TiO2NSH) can be designed and fabricated by assembling secondary phases with special morphology, such as nanoparticles, nanowires, nanorods or other nanostructures, on the surface of the1D TiO2nanostructure. Several published reports have demonstrated that well designed1D TiO2NSHs can preserve the intrinsic characteristics of TiO2, overcome the above-mentioned problems, and even endow the material with some new properties. These new properties include broadening the light absorption band from the visible to the near infrared region, plasmon-enhanced light absorption and highly efficient separation of photo-induced charge carriers, with some special properties that are useful for gas sensors, solar cells, and biomedical applications.The main conclusions are as followings:1. According to the physical mechanism, including band structure matching, P-N junction, surface plasmon resonance and schottky junction, we would like to address the principles and design techniques of1D TiO2NSH, which can get efficient separation of photo-induced charge carriers, broaden the light absorption band from the visible to the near infrared region and achieve effective utilization of the solar spectrum. Based on the morphology of the second phase assembled on the ID TiO2nanostructure, a1D TiO2NSH can also be designed with the following microstructures:OD metal nanoparticles or metal oxide nanoparticles/1D TiO2NSHs,1D nanorods or nanowires/1D TiO2NSHs,2D nanosheets/1D TiO2NSHs. The second phases have different morphologies and structures, which could endow some novel properties with the1D TiO2NSHs.2. CeO2/TiO2nanobelt heterostructures have been prepared by a co-precipitation and hydrothermal method. Both UV and visible photocatalytic activities of CeO2/TiO2 nanobelt heterostructures are greatly enhanced. The optimal CeO2/TiO2ratio of CeO2/TiO2nanobelt heterostructures is2:10. The enhanced broad light wavelength region photocatalytic activities of CeO2/TiO2nanobelt heterostructures are ascribed to the capture-photodegradation-release mechanism. During the photocatalytic process, the pollutant molecules are captured by CeO2nanoparticles, degraded by photogenerated free radicals under UV or visible light, and then released to the solution.3. RuO2/TiO2and Ru/TiO2nanobelt heterostructures were constructed by modifying RuO2and Ru nanoparticles with a small size of2.4±0.5nm and1.4±0.3nm on the surface of TiO2nanobelts, which had enhanced photocatalytic activity under UV and visible light irradiation. Both RuO2/TiO2and Ru/TiO2nanobelts heterostructures exhibited the excellent photocatalytic activity in the decomposition of methyl orange aqueous solution under UV and visible light irradiation, compared with TiO2nanobelts and P25. The enhanced photocatalytic activity of RuO2/TiO2and Ru/TiO2nanobelt heterostructures can be attributed to the energy band matching effect for RuO2/TiO2nanobelt and the schottky barrier effect for Ru/TiO2, respectively. At the same time, the RuO2/TiO2and Ru/TiO2nanobelt heterostructures exhibited excellent gas catalytic activity and selectivity in the oxidation of benzyl alcohol to benzaldehyde.4. We employed TiO2nanobelts as the synthetic template and developed three-dimensional (3D) Bi2MoO6nanosheet/TiO2nanobelt heterostructures with a few-layer and uniform B12MoO6nanosheets by a simple hydrothermal method.The as-prepared Bi2MoO6nanosheet/TiO2nanobelt heterostructure shows a high performance in photocatalytic degradation of the dye molecules under UV and visible light irradiation.The photodegradation rate of Bi2MoO6nanosheet/TiO2nanobelt heterostructure reaches90.4%after80min of visible light irradiation. Nearly100%of MO was degraded with the Bi2MoO6nanosheet/TiO2nanobelt heterostructure after40min of UV irradiation.Importantly, such a heterostructure possesses a high photocatalytic oxygen production and the oxygen production rate is0.668mmol h-1g-1. Moreover, the Bi2MoO6nanosheet/TiO2nanobelt heterostructure shows an enhanced photoelectochemistry (PEC) performance (70uA/cm2) under irradiation of a solar illumination.The enhanced performance can be attributed to its3D flake-like porous surface structure,large specific surface area, large matched energy band of heterostructure, improved charge transfer efficiency and suppressed photoelectron-hole recombination due to the existence of the heterojunction interface structure between Bi2MoO6and TiO2.5. We firstly reported a discovery of near-infrared activity of photocatalyst, Bi2WO6, which has ever been studied as visible photocatalyst. The good near-infrared absorption and photocatalytic performance of Bi2WO6nanosheets can be attributed to the oxygen vacancies. By assembling Bi2WO6nanosheets on TiO2nanobelts, a hybrid nanostructured photocatalyst with enhanced full solar spectrum photocatalytic properties has been constructed, which can harness UV, visible, and near-infrared light to decompose organic contaminants in aqueous solution. Under UV light irradiation, Bi2WO6nanosheets as an electron absorbing agent scavenged the valence electrons of TiO2nanobelts to enhance electron-hole separation. Under visible and near-infrared light irradiation, Bi2WO6nanosheets on the surface of TiO2nanobelts as visible and near-infrared light active component enhanced Bi2WO6/TiO2heterostructure photocatalytic activity. At last, we use the Au nanorods to enhance the near-infrared light absorption of Bi2WO6, thus the enhancement of its near-infrared light photocatalytic property is achieved. This can attribute to the surface plasmon resonance effects and wide range near-infrared light harvesting of Au nanorods.6. Hydrogenated TiO2nanobelt and reduced TiO2nanobelt are prepared by the hydrogen annealing method and NaBH4-reduction method, respectively. Hydrogenated TiO2nanobelt and reduced TiO2nanobelt still keep the belts’structure and get a lot of oxygen vacancies, which make them have enhanced visible photocatalytic activity. Oxygen vacancies allow the creation of carriers by absorption of visible light and inhibit the recombination of photo-generated electron and hole. Then we prepared the carbon quantum dots/hydrogenated TiO2nanobelt heterostructures, which have the full solar spectrum (UV, visible and near-infrared light) photocatalytic properties. The improved UV and visible photocatalytic property can be attributed to improved optical absorption, charge carrier trapping, and hindering of the photogenerated electron-hole recombination of oxygen vacancies and Ti3+ions in TiO2nanobelts created by hydrogenation. The near-infrared photocatalytic activity is from photo-induced electron transfer, electron reservoir, and up-converted PL properties of carbon quantum dots, which can absorb near-infrared light and convert into visible light and transfer to visible photocatalytic active hydrogenated TiO2nanobelts.