Study On Preparation And Visible-Light Photocatalytic Performance Of Inorganic Material Modified Nano-Titania

Due to the chemical stability and photoinduced properties, enormous efforts have beendevoted to the research of Titanium dioxide（TiO₂） material, which has been applied in areasranging from photovoltaics and photocatalysis to photo-/electrochromics and sensors,especially photocatalytic degradation of pollutants. However, one of the major challenges thathinder the practical applications of pristine TiO₂-based photocatalytic oxidation is the largeband gap of TiO₂（³.2eV for anatase and³.0eV for rutile, respectively） that only absorbUV photons in solar spectrum, consequently, only less than5%solar energy resides in UVregion can be utilized to initial the photocatalytic oxidation process. As such, it is crucial toenhance the light harvesting of TiO₂in the visible region which accounts for more than43%of the total solar energy. As a consequence, more widespread practical applications have beenhampered by its wide band gap. It is therefore evident that any modification of the TiO₂-basedphotocatalysts resulting in a lowering of its band gap or in the introduction of stable opticalsensitizes will represent a breakthrough in the field. For this purpose, many researches arenow focused on the preparation and properties of TiO₂with visible response.In order to further enhance the TiO₂photocatalyst activeness in visible-light range，thisdissertation research the inorganic materials modified nanometer TiO₂as photocatalyticmaterials. The enhanced photocatalytic activity of as-prepared photocatalysts was probed bydegradation reaction of methylene blue （MB） solution under visible-light irradiation. Specificwork focused on the following aspects:1. We report an architecturally controlled synthesis of SiO₂/C-TiO₂/C nanoporouscomposites that exhibit high absorption capability and efficient visible-light photocatalyticactivity. The nanoporous composites are composed of silica particles as the cores and TiCl₄asthe precursor for the TiO₂shell. Polyhydroxy organics are used as the binding agent betweenthe core and the precursory shell, the carbon source, and the porosity promoter. The structure,crystallinity, morphology, and other physical-chemical properties of the samples arecharacterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM）,high-resolution transmission electron microcopy （HRTEM）, X-ray photoelectronspectroscopy （XPS）, N2adsorption-desorption isotherms measurements, UV–vis diffusereflectance spectroscopy （DRS）, photoluminescence, and photoluminescence （PL）. The chemical content of the SiO₂/C-TiO₂/C nanoporous composites were also analyzed by energydispersive x-ray spectra （EDX）. The formation mechanism of the nanoporous composites wasextensively discussed. Methylene blue （MB） solutions were used as model wastewater toevaluate the adsorption and photocatalytic activity of the samples under natural sunlight andvisible light. Fourier transform-infrared spectroscopy （FT-IR） and mass spectrometry （MS）were used to investigate the photodegradated species on the photocatalysts and in solution,respectively. The SiO₂/C-TiO₂/C nanoporous composites samples exhibit remarkablyenhanced visible-light photoactivity than Degussa P25and pure TiO₂, and can be readilycollected for reuse by gravitational sedimentation. The technique presented here seems aneconomical and faster way for the preparation of a highly active photocatalyst. This mayboost applications of the composite, particularly at the industrial scale.2. We report an architecturally controlled synthesis of Se-C-modified porous TiO₂nanocomposites that exhibit efficient photothermocatalytic activity. Se nanoparticles in Sehydrosol were used as seeds to initial the nucleation of a precursory TiO₂shell formed by thehydrolysis of organotitanium molecules. The hybridized jumbles were further calcinated atdifferent temperatures. At low calcination temperature, the samples are Se-C-modifiedamorphous TiO₂porous structures. When the calcination temperature reached to400°C, thesample is SeO2-Se-C/TiO₂composite. UV–visible diffuse reflectance spectroscopy （DRS）showed that the as-synthesized samples have a strong absorption between400–700nm. Thesamples exhibit a synergetic effect between photocatalysis and thermal catalysis in thethermo-photocatalytic degradation of methylene blue （MB） to that of the pure TiO₂nanoparticles. The samples also showed excellent cyclic stability in the photothermocatalyticactivity. The formation mechanism of different porous TiO₂and the photothermocatalyticmechanism are discussed.3. I2sensitized nanoporous TiO₂with Enhanced Photocatalytic Activity underVisible-Light Irradiation were prepared and characterized. A yellow/brown powder of I2sensitized nanoporous TiO₂was obtained via a hydrolysis with TiCl₄and iodine hydrosol asraw material. I2nanoparticles in the hydrosol were used as seeds to initiate the nucleation of aprecursory TiO₂shell. The hybridized jumbles were further calcinated at differenttemperatures. The structure, crystallinity, morphology, and other physical-chemical propertiesof the samples are characterized by XRD, TEM, BET, and UV-vis DRS. The formation mechanism of these I2sensitized nanoporous TiO₂is discussed. Methylene blue solutionswere used as model wastewater to evaluate the visible light photocatalytic activity of thesamples. The results indicate that the calcination temperature has a crucial role in the amountof I2sensitized nanoporous TiO₂. The calcination enhanced the phase transformation of theTiO₂powders form amorphous to anatase phases and crystallization of anatase. Thephotocatalytic activity of the as-prepared samples was higher than that of P25for thedegradation of MB. The sample calcined at400°C shows the highest photocatalytic activity inthe decomposition of methylene blue under visible light due to the enhanced absorption invisible region and the large specific surface area. The degradation of methylene blue （MB）accorded with the first-order reaction model.4. CdSe nanocrystal modified TiO₂nanocomposites were prepared by usingtetrabutylorthotitanate （Ti（OC4H9）4, TBOT） and CdSe nanocrytstal as precursor based onhydrolysis-precipitation method. XRD, TEM, UV-vis, XPS were used to characterize theproducts. The stucture, the photoelectrochemical properties and the photocatalytic propertieswere also studied. MB solutions were used as model wastewater to evaluate the photocatalyticactivity of the samples under visible light. The results showed that CdSe nanocrystal modifiedTiO₂nanocomposites have significantly absorption in the visible region and therecombination rate of the photogenerated electron-hole pairs reduced. The samples whichobtained by different modified methods show different catalytic properties, this is relevant tothe stability of CdSe nanocrystals. The sample thermal treatment in air at200℃showed thehighest photocatalytic activity because of the sensitization of nano-CdSe and the largespecific surface area.