| The global pollution is becoming more and more serious, and the environment we live in is deteriorating. How to deal with the environment pollution, especially the water pollution, has been an important issue that the human must face and solve. At present, the traditional methods in domestic and foreign countries used to deal with the organic pollutants in the water include:micro-biological treatment, activated carbon adsorption, membrane extraction chemical reduction, ultrasonic degradation and so on. These methods play a key role in controlling the water pollution. But some of them with low efficiency can not sweep out the pollutants and may bring the second pollution, or have narrow application just used for the specific pollutants, or have high energy costs and difficulties in reactor design and can not be used widely. Therefore, developing a novel method with high efficiency, low energy costs and wide application is of great importance in both theory and practice. As a new and efficient method, the photocatalytic degradation of organic compounds has become a hot research topic in recent years.As a wide band gap semiconductor, TiO2 is an ideal photocatalyst with excellent photocatalytic activity, good chemical stability and light resistance. With the rapid development of nanoscience and nanotechnology, TiO2 nanomaterials have demonstrated great vitality in both energy development and environmental purification, which have enormous economical, environmental and social benefits in many fields. However, previous studies have focused on titanium dioxide particles or thin films, and there are few studies on titanium dioxide nanobelts. When TiO2 particles are used in the field of wastewater treatment, the catalysts in the photocatalytic process will easily aggregate, and they are difficult to separate and reuse. The emergence of one-dimensional nanomaterials can solve the difficult problem of recovery. In addition, one-dimensional TiO2 nanomaterials can be used as catalyst supporters. When the heterostructures are grown on the surface of the TiO2 nanobelts, its photocatalytic properties can be greatly improved.In the dissertation, different heterostructures based on nanobelts are prepared by acid-assisted hydrothermal method, photocatalytic reduction method and the liquid phase method. The photocatalytic activity of TiO2 nanobelts heterostructures are also studied to provide a theoretical basis for future practical applications such as wastewater treatment.The main conclusions are as follows:1. Titania-based nanobelts from commercial TiO2 were successfully synthesized via an alkali-hydrothermal process. The influence of heating temperature and holding time on crystal phase and morphology, and their photocatalytic properties were studied. After treated at 600℃for 1 h, the TiO2 nanobelts with typical width of 50 to 200 nm, thicknesses of about 50 nm, were up to tens of micrometers in length. With the increase of heating temperature and holding time, the morphology of nanobelts may be undermined to some extent. If you want to get pure anatase phase, the heat treatment temperature should be 800℃. The product is the mixture of anatase and TiO2-B under the other conditions. The photocatalytic activity of the nanobelts treated at 600℃for 1 h is the best.2. TiO2 nanoparticles@TiO2 nanobelts heterostructrues were prepared by corrosion of H2Ti3O7 nanobelts with sulfuric acid. The influence of different temperature, different concentrations and different reaction time on the crystalline phase and morphology were studied. The photocatalytic properties of different products were also investigated. The higher reaction temperatures, the increasing acid concentration, or the longer reaction time is not only conducive to the formation of the heterostructures, but also the anatase crystalline phase. With the same etching time and acid concentration, the photocatalytic property of the sample obtained from 60℃is far below than that of the products obtained from 100℃or 140℃. With the same temperature and etching time, the influence of acid concentration on the photocatalytic properties is not obvious. The photocatalytic performance of the products obtained with 0.02 mol/L and 1 mol/L H2SO4 is better than that of the samples obtained with 0.1 mol/L and 0.5 mol/L H2SO4. After considering all the acid corrosion conditions, the best condition is 100℃,0.02 mol/L. In addition, the longer the reaction time is, the better photocatalytic performance of the sample is. The heterostructrued nanobelts with corrosion by 0.02 mol/L H2SO4 solution at 100℃for 24 h possess the same photocatalytic property as that of P25. The photocatalytic property of TiO2 nanoparticles@TiO2 nanobelts heterostructrue is enhanced greatly due to the unique structure. This is the result of many factors, such as the size effect of nanoparticles, an appropriate amount of defects, high specific surface area, more active surface, and level of the coupling interaction.3. Ag nanoparticles@TiO2 nanobelts heterostructures were prepared by photocatalytic reduction method. The influences of different solvents and reaction time on the morphologies and the photocatalytic properties of different products were studied. Ag+is reduced to form Ag nanoparticles which in situ self-assemble on the surface of the TiO2 nanobelts. Under the same illumination time, the size of Ag particles generated with ethanol as solvent is bigger than that of Ag particles generated with ethanol and water as solvent, whish is bigger than that of Ag particles generated with water as solvent. The size of Ag particle increases with the illumination time in the same solvent. There is no obvious difference in the photocatalytic properties of the different products. The degradation rate of methyl orange varies between 38% and 44.9%. Compared with the common nanobelts, the degradation rate of Ag@ TiO2 heterostructure is nearly doubled. The photocatalytic performance of Ag nanoparticles@ TiO2 nanobelts heterostructures is improved greatly. This is because Ag nanoparticles deposited on surfaces of nanobelts to form a Schottky barrier, that is to say, Ag particles can easily capture electrons and reduce the hole-electron pair recombination rate; in addition, the abundant electrons on Ag particles combine with O2 on the surface of nanobelts, forming superoxide anion radical (·O2-), which can further degrade of organic compounds.4. CdS nanoparticles@TiO2 nanobelts heterostructures were successfully synthesized through the liquid phase method. The photocatalytic properties of the products were also studied. The products are CdS nanoparticles self-assembled on the surface of TiO2 nanobelts. The nanobelts are 50～200nm in width and several tens of micrometers in length, while the size of CdS nanoparticles is about 10 nm. The photocatalytic activity of CdS@ TiCO2 heterostructure is improved greatly compared with that of the common nanobelts. This is attributed to the different band energy structure of the two semiconductors, facilitating efficient charge separation and migration.5. The double heterostructures (Ag nanoparticles@TiO2 nanoparticles@TiO2 nanobelts) were prepared by the combination of sulfuric acid corrosion and photocatalytic reduction method. The photocatalytic properties of different double heterostructures were also studied. This double heterostructure is able to self-revival. Even if it is oxidized in the air, the photoelectrons of TiO2 induced by UV irradiation can reduce it to Ag, thereby maintaining photocatalytic performance of the double-heterostructures for long time. The results show that the photocatalytic activity of double heterostructures is much higher than that of single heterostructures. The double heterostructures with corrosion for 12 h possess the same photocatalytic performance as P25, while the double heterostructures with corrosion for 16 h or 24 h possess higher photocatalytic performance than P25. The reasons for the enhancement of the photocatalytic activity are as follows:one is the combination effect of two single heterostructures; the other is the growth of the number of defects and structural distortions, which also can reduce the hole-electron pair recombination rate. |
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