| Semiconductor photocatalytic has been an important approach for solving theproblems of energy crisis and environmental pollution as a result of its advantages,such as high efficiency, energy efficiency, environment friendly, and so on. However,the use of conventional semiconductor materials (TiO2，Nb2O5) is impaired by theirwide band gap, which require ultraviolet light irradiation for photocatalytic reaction,and the ultraviolet light accounts for only5%of solar energy. In recent years,researchers found doping could improve its photocatalytic activity under visible lightirradiation. Normally, doping can be classified into metal doping and nonmetaldoping in accordance with the doping element. Metal doping refers trace metal atomsinto crystal of the semiconductor, replacing the metal lattice, improving thephotocatalytic activity of the semiconductor by changing the composite rate of theelectron and hole, and transferring rate of the interfacial electron. Nonmetal dopingrefers some nonmetal atoms into the lattice of the semiconductor, replacing the spaceof O atom, narrowing its band gap, which can be irradiated by the visible light, so asto improve the photocatalytic activity under visible light. Compared withmetal doping, nonmetal doping is used more widely by researchers because of simpleoperation, low cost, and higher photocatalytic efficiency. In this paper, we had synthesized spherical C doped TiO2mesoporous materials,C doped Nb2O5mesoporous materials and C, F codoped Nb2O5mesoporous materialsusing the solvothermal method, and we also studied its morphologyand photocatalytic activity.The research contents include the following aspects:1) C doped TiO2mesoporous materials with spherical morphology have beensynthesized by solvothermal method in the system of ethanol, using TBOT as thetitanium source. The synthesized samples have been characterized by XRD，SEM，N2adsorption-desorption, XPS, UV-Vis and photocatalytic degradation of dye. Wefind that, synthesized samples are pure phase anatase TiO2, and the synthesizedsamples show uniform size ball with the accumulation of the nanoparticles.The crystallinity and morphology of the synthesized samples changes with the volumeof adding acetic acid during the synthesis process. With the addition acetic acidincreasing, the crystallinity increases, and the TiO2balls also gradually becomessmaller, and the size of nanoparticles which composed of TiO2ball also increases.Nitrogen adsorption desorption data shows that the synthesized samples aremesoporous materials, and the mesoporous structure is in disorder as a result of theaccumulation of nanoparticles. XPS data shows traces of C atoms getting intothe TiO2lattice, replacing the site of O atom. UV-Vis data indicates that the lightabsorption of the synthesized samples shifts towards long wavelength, and thephotocatalytic degradation experiments also prove its excellent photocatalyticactivity under visible light.2) Nb2O5is a kind of semiconductor material, which is similar to TiO2. Itslarge band gap greatly limits the absorption of visible-light, and seriously affectsits promotion and application. In this paper, we have synthesized C-doped Nb2O5,and the C atoms were incorporated in the lattice of the niobium pentoxide byoccupying the O sites, forming the bonding of Nb-C, which can narrow the bandgap of Nb2O5, and improve its photocatalytic property. During the experiments,mesoporous C-Nb2O5materials with a high surface area had been preparedthrough solvothermal synthetic strategy using NbCl5as precursor, ethanol as solvent. The structure, morphology and property of the obtained material wereverified by the combination of powder X-ray diffraction (PXRD),High-resolution transmission microscopy (HRTEM), N2adsorption and X-rayphotoelectron spectrum (XPS), photodegradation and H2evolution. Due to itssmall size (3-8nm), it was difficult to identify the phases of the sample bypowder XRD pattern. In this case, high resolution transmission electronmicroscopy (HRTEM) was employed to investigate the obtained samples. Thesamples were identifies as TT phase. Proved by XPS data, the obtained samplescontained elements of Nb, O, C, and the Nb exists in the form of state+5, the Catom is incorporated in the lattice of the niobium pentoxide by occupying the Osites, forming the bonding of Nb-C. N2Nitrogen adsorption-desorption datademonstrates the surface area of the sample is up to344m2/g, and it is richmesoporous structure, which is very important for photocatalytic procedure.UV-Vis data proves C-doped Nb2O5with strong visible light absorption resultingfrom the doping. This mesoporous C-doped Nb2O5is turned out to be a highlyefficient photocatalyst by the experiments of photodegradation and H2evolutionunder visible-light irradiation (>420nm). Meanwhile, the influences of syntheticfactors on the photocatalytic activity of the samples were also studied. Thecalcination temperature and crystallization temperature have great influence onthe morphology, surface area, and C content, thus affect the photocatalyticactivity of the samples. While the amount of acetic acid and crystallization timehas slight influence on the structure, morphology and C content, and thus has nodifference on its photocatalytic activity.3) It has been reported that the F ion physically absorbed on the surface of theTiO2, without onto its internal lattice, can be helpful for the formation for thesurface·OH, thus contributes to improve its photocatalytic activity. In thischapter，we had prepared C, F-doped Nb2O5base on the synthesis of C-dopedNb2O5by adding HF during preparation process. The morphology, chemicalcomposition and photocatalytic activity had been characterized by a series ofcharacterization methods. The results show the F ions can promote the growth of Nb2O5along the direction of [001]. The F ions were not incorporated into thelattice of Nb2O5by occupying the O atoms, but physically adsorbed on thesurface of Nb2O5nanocrystals. It can accelerate the photocatalytic reaction byenhancing the generation of free·OH radicals over the surface of Nb2O5. |
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