Researches On The Behaviours Of Ions Doption And Mechanism Of TiO₂ Photocatalytic Material

This paper systemically studied 13 metal ions doping mechanism of ion-doped powders, and put forward the interaction model existed between doping ions and powders. The influences of doping ions and the concentrations of doping on the photocatalytic degradation of methyl-orange on TiO₂ material have been analyzed from the chemical properties, including the kinds of ions, the concentrations of ions, the radius of ions, valence state of ions, the charge of ions, the electronic affinity of ions and oxide enthalpy of formation, and phase analysis (X-ray diffraction), spectra analysis (UV-vis absorption spectra and FT-IR spectra), defect analysis (positron annihilation technique), ect. In addition, the energy levels of several ions in TiO₂ were established elementary by spectra study ranging from UV to FT-IR, and the separation or recombination of electron/hole pair in TiO₂ material caused by doping ions was analyzed from the semiconductor energy theory. And the influences of ion-doped TiO₂ powders on photocatalytic activity were explored in nature. The main results of this paper are following:(1) Influences of the chemical character of doping ions on photocatalytic activity on TiO₂ powdersPhotocatalytic activity of TiO₂ powders is related with the types of doping ions. Doping V5+, La3+, W6+, Fe3+, Ni2+, Ag+ can enhance the photocatalytic activity of TiO₂ obviously, while doping Cr3+, Al3+, Zn2+, Pb2+, Cu2+, Co2+ have little influence on the photocatalytic activity of TiO₂, doping Mn2+ decreases the photocatalytic activity to some extents. The photocatalytic activity of TiO₂ powders doped the same ion on different concentrations is different. With the increase of doping concentration, the photocatalytic activity increases; However, with the futher increase of concentration, the photocatalytic activity decreases instead. The different ions have different optimum doping concentrations, in which the optimum concentration of V5+, La3+, W6+, Mn2+, A13+, Co2+ is 6.04 X 1015 /cm3, Fe3+, Ni2+, Ag+, Cu2+, Pb2+ is 6.04X1017/crn3,Zn2+is6.04X1018/cm3 respectly.The photocatalytic activity of TiO₂ powders is related with the radius of ions, valencestate of ions, the charge of ions, the electronic affinity of ions and the oxide enthalpy of formation.(2) Influence of doping ions on matter appearance of TiO₂By the XRD analysis of TiO₂ of doping 13 ions, It can be found that the sizes of crystal and the contents of anatase have changed compared with undoped TiO₂. After doping ions, the sizes of crystal TiO₂ decrease and the contents of anatase increase, in which the contents of anatase doping Cr3+ ,Fe3+, Co2+, Ni2+ and Pb2+-TiO₂ powders increase from 63.04% to 80%, while the contents of doping Zn2+, La3+, W6+-TiO₂ have little change. Moreover, when choosing V5+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+ test the doping concentration on the influence of XRD, it can be found that the photocatalytic activity is related with the contents of anatase. If the contents are too large or too small, the photocatalytic activity will be inhibited.(3) Influence of doping ions on defectBy analyzing the influences of TiO₂ defect on doping ions, it can be seen that TiO₂ crystal of doping ions have two types of defects: free volume defect and ting hole defect; and positron everage lifetime is related to the structures and types of doping ions; by studying the I1/I2 of doping ions versus the photocatalytic activity, It can be found that with the increase of I1/I2 when Pb2+, La3+, Cr3+, Co2+are doped, the photocatalytic activity decreases; In addition, except Fe3+, with the drop of positron lifetime, the photocatalytic activity increases obviously.(4) Influence of doping ions on intrinsic absorptionBy analyzing the UV spectra of 13 ions doping TiO₂, it can be found that the band energy edge of TiO₂ essence absorption always shows red shift when ions are doped, and different ions have different values of red shift. For the different doping concentrations of the same ion, the intrinsic absorptions are different.