Preparation, Characterization And Photocatalytic Properties Of Nanosized ZnO-Zn₂TiO₄, α-Fe₂O₃-TiO₂Complex Materials

The semiconductor compound photocatalyst prepared by coupling method cannot only reduce the needed energy when inspired, broaden the spectral response scopeof the composite catalysts, but also can promote the separation of the electron hole incomposite catalyst. As a result, its photocatalytic activity will be improved. In orderto get the photocatalyst with higher activities, the ZnO-Zn₂TiO₄nanocompositematerials were prepared by the template method and the sol-gel method respectively,and the α-Fe₂O₃-TiO₂heterogeneous nanocomposites were synthesized via the twostep methods （low-temperature hydrothermal method and dipping-thermal conversionmethod） in this thesis. Then, the thermal stability, morphologies, size, structure andoptical absorption properties of the materials were characterized by varioustechniques. At the room tempreture, their photocatalytic properties were evaluated byusing the degradation of dye rhodamine B （RB） solution as model reaction under theUV-light. Moreover, the impact of calcining temperature, calcining time, and elementmass ratios or components on their photocatalytic properties were considered in thesame systems.This thesis mainly consists of three major parts:Part one: A facile template method was employed to prepare ZnO-Zn₂TiO₄hollow fiber materials by using defatted cotton fibers template. The structure,morphology, composition and optical absorption properties of the prepared sampleswere characterized by thermogravimetry （TG）, X-ray diffraction （XRD）, scanningelectron microscopy （SEM）, and UV-vis absorbance spectroscopy. The resultsindicated that the samples replicated the morphology of original cotton fibers verywell and had hollow fiber structure; the obtained sample from the precursor withsuitable element mass ratios （8%） was calcinated under650oC for2.5h shows theoptimal photocatalytic property. For example, on the surface of ZnO-Zn₂TiO₄hollownano-fiber material, the decolorizing efficiency of RB solution was to96.44%and the first-order catalytic degradation kinetics constant （k1） reached1.142h^-1whenirradiation time was2h under UV-light. In addition, the photocatalyst has goodstability because the decolorizing rate remained above86%when it was repeatedlyused for5times and easily removed from the system.Part two: A series of ZnO-Zn₂TiO₄nano-composite photocatalytic material wasprepared via Sol-Gel method. And their structure, morphology, composition andoptical absorption properties were characterized by X-ray diffraction （XRD）,scanning electron microscopy （SEM）, energy dispersive spectrometry （EDS）, andUV-vis absorbance spectroscopy. The results indicated that the obtained sample withsuitable element mass ratios （8%） was calcinated under400oC for2h shows theoptimal photocatalytic property. For example, on the surface of the ZnO-Zn₂TiO₄nano-composite material, the decolorizing efficiency of RB solution was to99.6%and the first-order catalytic degradation kinetics constant （k1） reached0.675h^-1whenirradiation time was4h under UV-light. In addition, the photocatalyst has goodstability because the decolorizing rate remained above90%when it was repeatedlyused for5times and easily removed from the system.Part three: Alpha ferric oxide （α-Fe₂O₃） nanocrystals were prepared usingiron（III） nitrate nonahydrate （Fe（NO₃）₃·9H₂O） by a low-temperature hydrothermalmethod, and α-Fe₂O₃-TiO₂heterogeneous photocatalysts with different mass ratiosvia impregnation of Ti4+on the surface of α-Fe₂O₃were synthesized by adipping-thermal conversion method, using tetrabutyl titanate （TBT） and the preparedalpha ferric oxide as raw materials. The obtained materials were characterized byX-ray diffraction （XRD）, transmission electron microscope （TEM） and UV-Vistechniques （UV-Vis）. The results show that50%α-Fe₂O₃-TiO₂nanocompositecalcined under3h at550oC possesses a higher photocatalytic activity, and thefirst-order catalytic degradation kinetics constant （k1） of10.0mg/L rhodamine Bsolution reaches0.93h^-1within2.5hours, however, the k1only reaches0.05h^-1onthe pure α-Fe₂O₃nanoparticles under the same conditions. The good photocatalytic activity is attributed to the synergy between TiO₄₂and α-Fe₂O₄₃. As comparisons, in adifferent way, a series of heterogeneous α-Fe₂O₄₃-TiO₄₂nanocomposite materials weresynthesized by the same method and characterized by the above technique, but theresults show their photocatalytic performances is worse.