Preparation And Photocatalytic Property Of Ultrathin Titanium Dioxide Nanobelts And Heterostructures

TiO2 is a kind of metal semiconductor with several outstanding performances, which have a wide range of potential applications due to its special characteristics, for example, photocatalytic degradation, photocatalytic hydrogen evolution and photocatalytic air treatment. One dimensional (ID) TiO2 has been widely studied because of the fast electron transition along the in longitudinal axis direction, good sedimentation ability in waste water and good substrate to be hetero with other nanomaterials. However, TiO2 has a narrow response range of solar spectrum due to its wide bandgap, which limits its practical application. According to previous studies, anatase-rutile bi-phase TiO2, for example commercial TiO2-P25, can efficiently promote the separation of photogenerated carriers due to the band matching between anatase and rutile. 1D TiO2 surface nanoheterostructures prepared by assembling other semiconductors of metal nanoperticles on TiO2 can not only maintain the basic properties of TiO2, but also broaden the response range of solar spectrum of the photocatalysts and suppress the recombination of the photogenerated electron-hole pairs.In this thesis, ultrathin TiO2 (U-TiO2) nanobelts with amounts of highly active facet exposed were prepared via a solvothermal method. Based on this material, U-TiO2-based nanobelt heterostrucutres were synthesized and their photocatalytic activities were studied.The main contents of research in this thesis are shown as follows:1. Through controlling the volume ratio of the component of organic solvent, bi-phase U-TiO2 nanobelts consisting of both anatase and rutile phases have been successfully synthesized via a one-step solvothermal process by using tetrabutyl titanate as the Ti source and acetic acid/N,N-dimethylformamide (DMF) as the blended organic solvent. Based on the refinement result of the X-ray diffraction (XRD) patterns of U-TiO2 nanobelts, the ratio of anatase and rutile phases in the as-synthesized TiO2 nanobelts were calculated to be 90.8 wt% and 9.2 wt%, respectively. The SEM and TEM results show that U-TiO2 nanobelts have a length of about 200-300 nm, a width of 10-20 nm and a thickness of lower than 5 nm. Their main exposed facet is (010) of anatase, which have a good photocatalytic activity. Besides, U-TiO2 nanobelts have large specific surface area of about 98.5 m2·g-1 and good sedimentation ability. The bi-phase and active facet exposure characteristics endow the ultrathin TiO2 nanobelt with high photocatalytic activity, which is superior to P25. The photodegradation results of P25, TiO2 nanobelts synthesized by alkali-hydrothermal method (H-TiO2) and U-TiO2 that H-TiO2 has the worst photocatalytic activity and U-TiO2 is even better than P25.2.Based on U-TiO2 nanobelts, four kinds of noble metal/U-TiO2 nanobelt heterostrucutres (Au/U-TiO2, Ag/U-TiO2, Pt/U-TiO2 and Pd/U-TiO2) were synthesized by photo-reduction method at ambient temperature. The average sizes of Au、Pt and Pd nanoparticles are under 5 nm, while that of Ag nanoparticles is around 10-20 nm. The results of spectral analysis indicate that the light response range of all noble metal/U-TiO2 nanobelt heterostrucutres increase. The results of photocatalytic hydrogen evolution show that Pd/TiO2 nanobelt heterostructure has the best catalytic activity, the rate of hydrogen production of which is about 1487 μmol·h-1·g-1. The worst is Ag/TiO2 nanobelt heterostructure, which can be abscribed to less active sites resulting from the large particle size of Ag nanoparticles.3. Based on U-TiO2 nanobelts, the PdO/TiO2 ultrathin nanobelt heterostructures with different weight ratios were synthesized at ambient temperature by using ultrathin nanobelts as substrates. TEM image shows that the average size of PdO nanoparticles is only 1.34 nm. Compared with individual U-TiO2 nanobelts, which exhibited outstanding photodegradation activity with methyl orange and Rhodanime B, excellent hydrogen generation, and observably enhanced photoelectrochemical activity under simulated solar irradiation.4.Based on U-TiO2 nanobelts, the MoS2/U-TiO2 nanobelt heterostructures were synthesized by wrapping U-TiO2 with MoS2 nanosheets via hydrothermal method. The belt-like morphorlogy maintained. The few-layered MoS2 nanosheets coated onto the TiO2 nanobelts not only broaden the photocatalytic light region from UV to visible, but also enhances the photocatalytic activity of the nanobelt heterostructures due to band matching between MoS2 and TiO2.In summary, bi-phase ultrathin TiO2 nanobelts consisting of both anatase and rutile phases have been successfully synthesized via a one-step solvothermal process, which have high photocatalytic activity. Moreovee, PdO/U-TiO2 and noble metal/U-TiO2 nanobelt heterostrucutres were prepared based on the U-TiO2 nanobelt. The results of photocatalytic measurement reveal that the construction of nanoheterostrucutres efficiently suppress the recombination of photogenerated carriers, leading to better photocatalytic activities. U-TiO2 based nanoheterostrucutres will have great potential in applications for photocatalytic water treatment and hydrogen generation because of the facile synthesis process and superior photocatalytic activity.