Study On Silver And Nitrogen Doped Nano-TiO₂Photocatalyst

TiO2is a promising photocatalyst due to its characteristics of great photocatalytic activity, chemical stability, low cost and non-toxic in the field of environmental pollution control. However TiO2as photocatalyst has two major problems. Firstly its solar energy utilization is very low due to its wide band gap (3.23eV). It requires ultraviolet irradiation (λ<387nm) for photocatalytic activity. Ultraviolet light energy accounts for only a small fraction (about4%) of the solar energy. Secondly its photo quantum yield value is also very low due to its photo-excited electron-hole pairs easily recombining. Therefore a variety of methods are used in order to broaden the range of its response to visible light and reduce recombination rate between the photo-excited electrons and holes. Researchers use a variety of methods to modify TiO2, such as noble metal depositing, ion doping, dye sensitizing and semiconductor compounding. Ion doping is usually considered as one of the most efficient methods. Noble metal ion doped TiO2as ion doping is especially focused. In this paper, under the guidance of the theoretical calculation by our group, the Ag-TiO2and Ag-N-TiO2photocatalyst were prepared by sol-gel and microwave chemical method. The samples were characterized by XRD, FT-IR, XPS, TEM, Nano particle size analyzer, UV-Vis and PL. Furthermore, in order to test the photocatalytic activity of the samples, the methyl blue (MB) degradation was investigated under the irradiation of fluorescent lamp. The main work and results are as the follows:1. Ag-TiO2photocatalystThe Ag-TiO2powders were prepared by sol-gel method in which distilled water as the solvent and AgNO3as Ag source. The influences of sintered temperature and Ag content on crystalline structure, spectral absorption performance and photocatalytic activity of Ag-TiO2samples were investigated. According to photocatalytic activity of Ag-TiO2sample, the optimal preparation condition is as the following:reaction temperature60℃, Ag content Ag:TiO2=0.1at%, sintered temperature400℃for3h and pH value2.5. The results show that Ag mainly deposites on the surface of TiO2and only a small amount of Ag is doped into the lattice of TiO2. Under the irradiation of fluorescent lamp, the methyl blue (MB) degradation rate by Ag-TiO2sample under the optimal preparation condition is87.06%within8h, which is higher than that of P25(59.37%) under the same experimental condition. The stability of Ag-TiO2sample is good. The photocatalytic activity of Ag-TiO2sample has little change after recycling the photocatalytic reaction five times.2. Ag-N-TiO2photocatalystThe Ag-N-TiO2powders were prepared by sol-gel method combined with microwave chemical method in which distilled water as the solvent, AgNO3as Ag source and urea as nitrogen source. The influences of sintered temperature and Ag content on crystalline structure, spectral absorption performance and photocatalytic activity of Ag-N-TiO2samples were investigated. According to photocatalytic activity of Ag-N-TiO2sample, the optimal preparation condition is as the following:reaction temperature60℃, Ag content Ag:TiO2=0.05at%, sintered temperature600℃for4h, pH value2.5, urea content lOg and microwave reaction pressure10.342×105Pa. The results show that the co-doped samples show better photocatalystic activity than the single doped samples due to the synergistic effect of suitable Ag ions and N ions.Under the irradiation of fluorescent lamp, the methyl blue (MB) degradation rate by Ag-N-TiO2sample under the the optimal preparation condition is93.44%within5h, which is higher than that of P25(39.40%) under the same experimental condition. The stability of Ag-N-TiO2sample is good. The photocatalytic activity of Ag-N-TiO2sample has little change after recycling the photocatalytic reaction five times.The novelties of the work are mainly focused on the following aspects:(1) The experiment can effectively overcome the blindness and repeatability of the recent research due to the guidance of the theoretical calculation by our group.(2) Noble metal deposition method is used at home and abroad. Noble metal ion doped TiO2, noble metal ion and N ion co-doped TiO2seems to be seldom reported. Ag as doping element is selected due to its low cost. The influences of Ag and Ag-N co-doping TiO2on crystalline structure, spectral absorption performance and photocatalytic activity are studied. The mechanism of single doping and co-doping is analyzed in detail.