Preparation And Catalytic Performance Of Modified TiO₂Nanotubes

Titania (TiO2) has received considerable attention due to its nontoxicity, low cost, high chemical stability and high photoactivity, and was widely used in many applications such as photocatalytic materials, photolectric materials and catalyst support. Compared with TiO22nanoparticles, TiO2nanotubes were more suitable to be utilized as catalyst or catalyst support due to their nanotubular morphologies and higher surface areas. However, wide bandgap, low utilization rate of solar energy, quick recombination of photogenerated electron-hole pairs resulted in low light quantum efficiency of TiO2nanotubes. Moreover, TiO2nanotubes obtained by hydrothermal process had bad structure stability for thermal catalysts. It had been a long-term issue for researchers to improve catalytic performancs of TiO2by reducing the bandgap, inhibiting the recombination of photogenerated electron-hole pairs and increasing the thermal stability of TiO2nanotubes. To overcome the drawbacks of TiO2mentioned above, a series of high catalytic activity and high thermal stability of doped TiO2nanotubes were prepared with different preparation methods in this thesis. The photocatalytic performances of products were evaluated by monitoring their catalytic activities for degradation of methyl orange solution under UV light and simulated sunlight irradiation in the photocatalysis experiments. The primary work was as follows:Using tetrabutyl titanate and sucrose as precursors, carbon-modified TiO2nanotubes (C/TiO2NTs) with various carbon contents were prepared by the combination of sol-gel process with hydrothermal treatment. The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-vis spectroscopy. The influences of calcination temperature and carbon content on catalytic performance of C/TiO2NTs were also discussed. The results indicated that TiO2in the catalysts was anatase. The doped carbon narrowed the band-gap width and increased absorption in the visible range. Compared with pure TiO2nanotubes, C/TiONTs could significantly enhance the photocatalytic efficiency, and the0.90wt.%C/TiO2NTs calcined at400℃exhibited the best photocatalytic activity.Using TiO2NTs as support, Ru3(CO)12and C5H5Mn(CO)3as modification precursor, Ru-C co-modified TiO2nanotubes (Ru-C/TiO5NT5) and Mn-C co-modified TiO2nanotubes (Mn-C/TiO2NTs) were prepared respectively via impregnation-deposition method. The products were characterized with TEM, XRD, UV-vis and XPS, and the synergistic effect comodification elements how to increase the photocatalytic activities were discussed. In the Ru-C/TiO2catalytic system, the conclusions were listed as follows:XRD results showed that although the tubular structure was destroyed calcined at500±, the crystallinity of anatase phase was increased, and appeared the phase transition of small amount anatase to rutile, which was beneficial to improve the catalytic activity. TEM images revealed RuO2nanoparticles with a diameter of3-7nm were uniformly deposited on the surface of TiO2. XPS results revealed that the carbon in Ru-C/TiO2existed as active carbon and carbonate, which benefit the visible light absorbtion, and ruthenium existed as RuO2, which benefit the photo generation electron-hole pairs separation. To the ruthenium and carbon co-modified TiO2, the Ru-C synergistic effect could largely narrow the band gap of TiO2and easily energize more photogenerated electrons and holes. The influences of calcination temperature, calcination atmosphere and contents of C and Ru on the photocatalytic activity of the samples were investigated. Obtained results showed that Ru-C/TiO2NTs exhibited higher photocatalytic activity than P25under UV or simulated sunlight irradiation when Ru and C mole ratio was1.65and calcinated at500±in N2atmosphere.In the Mn-C/TiO2catalytic system, the conclusions were listed as follows:TEM images revealed the specific surface area of TiO2NTs were decreased with the increase of calcinations temperature and exist nanotubes structure with bundles gather state. XPS results revealed that the carbon existed as carbonate, and manganese existed as MnxOy/Mn on the surface of TiO2respectively. UV-vis results revealed that the badgap of TiO2were decreased. To the manganese and carbon co-doped TiO2, the Mn-C synergistic effect could largely enhance the photocatalytic performance under UV light and simulated sunlight irradiation. When the manganese and carbon content were0.15wt.%and1.08wt.%respectively and calcinated at400 ℃, Mn-C/TiO2NTs exhibited the good photocatalytic activities under UV and simulated sunlight irradiation. The preparation method was simple, and achieved the metal and carbon codoping with the modification precursor and without additional carbon source. The method would provide new thought for preparing metal and nonmetal co-modified TiO2.The target product C-Fe co-modified TiO2nanotubes (C-Fe/TiO2NTs) with high thermal stability were successfully synthesized via two-step sol-impregnation method. TEM images showed the better tubular structure of TiO2calcinatied at400℃. XPS results revealed that carbon did not substitute oxygen atom in the lattice of anatase TiO2and the most carbon existed as carbonate. The results revealed that the synergistic effect of C and Fe co-modified could not only decrease the band-gap energy of TiO2nanotubes, but also inhibit recombination of photo generation electron-hole pairs. The photocatalyic performance of C-Fe/TiO2NTs was superior to the activities of TiO2NTs, C-TiO2NTs and Fe-TiO2NTs. When the carbon content was1.45wt.%and calcinated at400℃, C-Fe/TiO2NTs exhibited the best photocatalytic activity.Using stable TiO2NTs as support, IrCl3·3H2O, sucrose and IrCl3·3H2O as modification precursor, Ir modified TiO2(Ir-TiO2) and C-Ir co-modified TiO2(C-Ir/TiO2NTs) were prepared respectively via impregnation-depbsition.The products were characterized with TEM, XRD, UV-vis and XPS. UV-vis results revealed that Ir modified TiO2and C-Ir comodifed TiO2both could broaden the light response range, reduce the bad gap, and enhance the photacatalytic activities to degrade methyl orange solution under UV light and simulated sunlight irradiation. The2.77wt.%Ir-TiO2NTs calcinated at400℃exhibited the best photocatalytic activity. The photocatalytic performances of C-Ir/TiO2were superior to C-TiO2and Ir-TiO2because of the synergistic effect of carbon and Irdium comodified TiO2. When the carbon content was1.24wt.%and calcinated at400℃, the C-Ir/TiO2NTs exhibited the best photocatalytic activity.By using hydrogen titanate nanotubes as support, CuO modified-TiO2nanotubes (CuO/TiO2NTs) with high thermal stability were prepared by impregnation method. The prepared materials were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Their catalytic performances for low-temperature CO oxidation were preliminary discussed. The atomic ratio between Cu and Ti and calcination temperature were also investigated. When the atomic ratio of Cu and Ti was1:2and calcined at300℃, the CuO/TiO2NTs exhibited the best catalytic performance. Other influence factors for catalytic performance and the catalytic principle need to be further researched.