Preparation Of Complex Catalysts Based On Mesoporous Titinia And Study On Their Photocatalytic Performance

Titanium dioxide possesses relatively high specific surface area, well-developed and ordered mesoporous structure as well as low price. Besides, titanium dioxide still has no toxicity and its surface is easy to be modified. Thus titanium dioxide exhibits extensively applying value. There are still limited factors on the photocatalytic activity of titanium dioxide, such as wide band gap, narrow light-response region, collapse and reunion during calcination. Therefore, modifying its surface, enhancing its stability and broadening its light-response to visible region have been the urgent problems to be solved in the process of titanium dioxide wide application.By employing the liquid crystal of surfactant cetyltrimethyl ammonium bromide(CTAB), tetrabutyl titanate, ammonium metavanadate and silver nitrate as template, titanium source and doping-ion precursors, respectively, vanadium-doped and silver-doped mesoporous titanium dioxide(V/MT or Ag/MT) were obtained by sol-gel method. The structure of obtained samples was characterized via X-ray diffraction(XRD), nitrogen adsorption-desorption, thermogravimetry-differential thermal(TG-DTA), X-ray photoelectron spectroscope(XPS), UV-visible diffuse reflection(UV-vis) and transmission electronic microscope(TEM). Choosing methylene blue(MB) as the target degradation product, the photocatalytic performance of prepared samples was discussed by the degradation of MB under ultraviolet lighting and visible irradiation. The results show that doping vanadium or silver can reduce the particle size of MT, inhibit photo-electron and hole recombination and increase specific surface area as well as the concentration of titanium ion and hydroxyl. Thus V/MT and Ag/MT exhibit an optimum catalytic activity compared to pure MT and P25. In addition, doping silver can also decrease the MT band-gap energy and improve its catalytic activity under visible light. The optimal photocatalytic activity can be obtained at the vanadium and silver doping content of 1.5 % and 1.0 %, respectively, the V/MT concentration of 0.83 g/L, Ag/MT concentration of 0.6 g/L and MB concentration of 1mg /L.To further inhibit the photo-induced electron and hole recombination rate, graphene(GR) was successfully linked with Ag ion-doped-mesoprous TiO2(GR-Ag/MT) by a sol-gel method with the aid of liquid crystal template. The as-prepared photocatalysts were analyzed by XRD, BET, XPS, TEM and so on. The visible-light driven photocatalytic performance of catalysts were investigated by degradation of MB dye solution. The results indicate that the introduction of graphene can inhibit the charge recombination rate, increase the specific surface area and the concentration of hydroxyl radicals. GR-Ag/MT composites exhibit the highest degradation efficiency among pure MT, GR/MT and Ag/MT under visible-light irradation. It is attributed to the introduction of graphene and the doping with Ag+. Owing to the formation of Ti-O-C bonds in complex catalyst, the synergistic effects among GR, Ag and MT generate, and further prevent charge recombination and reduce band gap energy. Additionally, GR-Ag/MT possesses highly photocatalytic stability under visible irradiation, and effects of GR on the misostructure of MT endowed the high photocatalytic activity of composite with a graphene mole ratio of 1.2 %. The effects of catalyst amount, pH value, and initial MB concentration have been examined as operational parameters. A photocatalytic mechanism based GR-Ag/MT was proposed under visible light.In addition, mesoporous TiO2 film electrode(MTFE) was fabricated with coating and calcination by using the liquid crystal of CTAB, tetrabutyl titanate and FTO conductive glass as template, titanium source and substrate, respectively. Subsequently, the graphene-quantum-dot(GQD) sensitized mesoporous titania film(MTFE)(GQD/MTFE) was snythesized by a controllable electrophoretic method. The photoelectrocatalytic activity of GQD/MTFE was also discussed under visible light. These results demonstrated that titania films show visible-light-driven photoelectroactivity with the assistant of GQD, because the GQD could effectively extend the light absorption edge of the titania to visible light region and accelerate the separation of photo-generated electrons and holes. These lead to high photoelectroactivity of GQD/MTFE for AO7 degradation, and it remain high photoelectrocatalytic performance in recycling. Furthermore, GQD/MTFE possesses higher visible-light driven photoelectrocatalytic performance than than GQD sensitized nonporous TiO2 films(GQD/NTFE) due to the excellent capability of adsorption from nonmesoporous structure, smaller particle size, relatively low complex band energy and higher concentration of hydroxyl.