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Synthesis and Characterization of Modified TiO_2Nanoparticles and Their Applications in Photocatalysis

Muhammad Nasir  
【摘要】:Titanium dioxide has been proved as a promising photocatalyst for the environmental cleanup in the field of photocatalysis because of its high activity, low cost, easy availability, non-toxicity and chemical robustness. However, there are certain shortcomings, which hinder its photoactivity such as its large band gap of3.2eV and fast recombination of electrons and holes. Therefore, there is a dire need to modify it in order to make it feasible for the photocatalysis under visible light irradiation and to reduce the recombination of electrons and holes. The main focus of the thesis was laid upon the single element doping and codoping with the nonmetals and transition metals in order to shift the absorption of TiO2towards the visible light region and reduce the recombination of photoexcited charge carriers to make it active under the visible light irradiation. The details of my works are as follows: 1-In my first work, Ce and N codoped TiO2samples were successfully prepared by keeping in mind the advantages of Ce as a very powerful electron scavenger (even more than oxygen) with the ability to generate labile oxygen vacancies and bulk oxygen species, also N proved as a good candidate for the narrowing of the band gap and enhancement of the visible light response. The samples were prepared through the hydrothermal method by using less expensive precursors such as cerium nitrate, tetrabutyl orthotitanate (TBOT) and urea. These prepared samples were characterized by various techniques such as, X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Fourier Transformation Infrared Spectroscopy (FTIR), Thermogravimetric Analysis and Differential Thermal Analysis (TG/DTA), UV-Visible Diffuse Reflectance Spectroscopy (UV-vis DRS) and Photoluminescence Spectroscopy (PLS). The XRD and Raman spectra showed only anatase phase of TiO2for the single doped and codoped samples. The XPS of Ce showed the presence both Ce3+and Ce4+oxidation states. The PLS of the samples showed first decrease in the recombination centers when Ce was introduced in codoped TiO2with the maximum decrease for0.05Ce/N codoped TiO2and then started increasing with the increase of Ce in the samples. There have been founded a direct relationship between the number of recombination centers and photoactivity of the samples, which was measured by the decolorization of25mg/L solution of Acid Orange7(AO-7). The activities of codoped samples were highly increased by the incorporation of Ce with the maximum degradation exhibited by0.05Ce/N-TiO2sample. 2-Inspired by the previous results of the idea of codoping Ce with the N, here in this part we tried the replacement of N with S, to check its effect on the efficiency of the degradation of the pollutant under the visible light. Hence, Ce and S codoped TiO2nanoparticles were prepared through simple sol-gel method and various characterization techniques were applied. The prepared samples showed the anatase type of structure with the increase of the specific surface area and decrease of the pore size with the increase in the Ce amount in the samples as indicated by the XRD and BET. The photoluminescence spectra revealed first decrease in the intensity of the spectra sync with the reduction of recombination of electrons and holes. Also, the Ce and S codoping induces the formation of Ti3+together with the increase in the surface hydroxyl radical with the increase in the amount of Ce in the samples. Thus, the increased photoactivity of the samples was attributed to the increase of the surface area, increase of the surface hydroxyl groups and decrease of the recombination of electrons and holes as well as the formation of Ti3+by the synergistic effect of the Ce and S. 3-In the third part we replaced the S with the C in the Ce-TiO2to find out the effect on the photocatalytic activity of the prepared samples. The samples showed a slight increased in the surface area and decrease in the crystal sizes with the increase in the Ce amount in the samples. Also, the XPS of the samples indicated the decrease in the electron density on the Ti and an increase in the surface hydroxyl groups with the increase in the Ce concentration in the samples. The visible light photocatalytic activity of the prepared codoped samples was significantly increased as compared to the single C-doped TiO2due to the number of factors, such as a decrease of the crystal size and increase of the surface area, increase of the surface hydroxyl groups along with the decrease of the recombination of electrons and holes etc. 4-In the fourth part we tried scandium and carbon codoped TiO2catalyst prepared through simple sol-gel synthesis method by using scandium nitrate as scandium dopant precursor, glucose as carbon and tetrabutyl orthotitanate as titanium precursor and calcined at450℃for3h. The XRD of the samples showed the decrease in the crystal size with the subsequent increase in the specific surface area as shown by BET. The UV-vis DRS displayed the blue shift in the absorption together with the PLS revealed first the decrease in the recombination of electrons and holes by the addition of the scandium and then after the certain optimum value the further increase of the scandium further increased the recombination of electrons and holes. The photocatalytic activity of the samples was investigated by the help of degradation of AO-7, which showed that the codoped samples significantly improved the photocatalytic activity.


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