| Since1972, Fujishima et al reported photocatalytic production of hydrogen from water using TiO2electrode, TiO2has been received widely attention due to its many advantages. TiO2has presented the promising applications for high efficiency for degradation of difficult-to-remove pollutants. But it can be excited only by irradiating with ultraviolet (UV) light due to the wide band gap energies. At the same time, high recombination rate of photogenerated electron-hole pair results in inefficient use of energy absorbed.So,it is a a profound negative effect on its application.In1986, Sato et al. first reported the N-doped TiO2photocatalyst with visible light photocatalytic activity,But people don’t feel it is very important. Until2001, Asahi et al. obtained a visible light active TiO2-xNx films, it not only dosn’t reduce UV absorption but also increase visible response.It rekindled a great attentionin TiO2as a visible light photocatalyst.In this paper, Specific contents are as follows:In the second section, we use a low-temperature hydrothermal method to prepare sodium titanate nanotubes (Na2Ti2O4(OH)2nanotubes). Ammoniu titanate nanotubes ((NH4)2Ti2O4(OH)2) were produced from sodium titanate nanotubes (Na2Ti2O4(OH)2) by ion exchange using NH4Cl.Then. it was calcined in air at between100and600℃for3h to yield N-TiO2. They were characterized by TEM and XRD for their morphologies and crystal structure. It can be found that after ion exchange reaction, calcining (NH4)2Ti2O4(OH)2at100and200℃,TEM indicates that the ion exchange process did not significantly change the morphology of the nanotube. XRD shows the crystal structure of samples belong to an orthorhombic system.UU-VIS DRS shows the band edge of the nanotubes shifted to a longer wavelength afer N doped and reduced the value of Eg. When calcining at300and400℃, the crystal form gradually transferred into anatase phase.At the same time, the nanotubes fractured,samples creased visible light aborption.And the value of Eg further reduced, Further Calcining at500and600℃caused the disappearance of the tubular pore of the nanotubes,which translated into short nanorods or nanoparticles. At the same time, the value of Eg didn’t further reduced. And the visible light aborption of the samples decreased. In this section, we also discussed the decomposable condions of ammonium titanate and mechanism of N doped samples.In the third chapter, when we used a hydrothermal method, meanwhile we joined5ml ammonia solution into sodium titanate. And postsynthesis was treated by sintering at different temperatures (200℃,300℃,400℃,500℃) in a NH3flow atmosphere, in a nitrogen atmosphere, in air and in ammonia solution atmosphere. XRD shows the crystal form of samples still belong to an orthorhombic system.TEM shows the samples still keep nanotubes until calcining at500℃. UV-VIS DRS shows different visible light aborption in different atmosphere.In the forth chapter, we use the same method to prepare N doped samples as in the third section.The only difference is that we use100ml0.1M HCl to wash pH=7. Then we wash the precipitate to remove NaCl. XRD shows the samples still keep orthorhombic system in a NH3flow atmosphere, in a nitrogen atmosphere and in air before calcining at400℃.However, calcination at400℃in ammonia solution atmosphere cause a phase transformation from hydrogen titanate to TiO2(B) phase and anatase phase. When at500℃all samples transfer into the hybid phases including anatase phase and TiO2(B) phase. TEM shows that the morphology of the nanotube translated into nanoparticle when calcining in a NH3flow atmosphere and in a nitrogen atmosphere. UV-VIS DRS shows different visible light absorption in different atmosphere. Further, XPS results indicated that the nitrogen concentration sintered in a NH3flow atmosphere was slightly higher than those of the samples calcined in a nitrogen atmosphere. And this resulted in the substitutable dope and the formation of N-Ti-O bonds. Under the other conditions, the interstitial nitrogen doped into the TiO2lattice and the formation of Ti-O-N bonds. In summary, we realized the adjustment of the crystallization, the crystal structures, nitrogen state on the surface and nitrogen concentration of N-doped nanomaterials and also discussed the decomposable conditions of ammonium titanate and mechanism of N doped samples. |
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