Preparation And Photocatalytic Properties Of The Doping BiFeO₃ And KNbO₃ Nanoparticles

In recent years, the researchers are trying to design and prepare photocatalytic materials which have high efficiency under visible light. Among these materials, perovskite-based materials have be considered to be a promising materials because of its ferroelectricity and altered band structure. In this thesis, firstly, we prepared the Bi1-xRexFe O3( Re = Sm3+,Tb3+,Ho3+;x = 0.0,0.07,0.10,0.15) and the [KNb O3]1-x[Ba Ni1/2Nb1/2O3-δ]x( x = 0.0- 0.5) by a sol-gel method and a polymeric precursor method, respectively. We used two different cations on the perovskite A-site or/and B-site to change the crystal structure. Then we could acquire the high efficiency of photocatalytic materials under visible light by improving the ability of visible-light-absorbing. Finally, we discussed the results about the crystal structure from the date of X-ray diffraction(XRD) and Raman scattering spectroscopy. The morphology observed from Scanning electron microscope, and the optical band gap from diffuse reflectance spectroscopy, and other factors which could affect the photocatalytic activity of nanoparticles under the visible light were also analyzed. The main results are summarized as follows:1. In terms of Bi1-xRexFe O3( Re = Sm3+,Tb3+,Ho3+) nanoparticles: The crystal structure of doping samples remains substantially the rhombohedral phase with R3 c space group when x ≤ 0.10, and the transitions to the orthorhombic phase with Pnma space group while x = 0.10- 0.15 occurred; The particle size of the samples tends to be smaller and then to be bigger with the increasing of the doping concentrations; The optical band gap of Bi1-xRexFe O3 have an abrupt decline at the phase transition edge.2. The optimum photocatalytic performance for Bi1-xRexFe O3( Re = Sm3+,Tb3+,Ho3+) nanoparticles is at x = 0.1, which can be attributed to the smaller particle size. The smaller nanoparticle size enhances the active surface area of the Bi1-xRexFe O3 nanoparticles and improve the absorption rate and photocatalytic performance.3. The X-ray diffraction and Raman scattering spectroscopy show that the KNb O3 is the orthorhombic crystal system with Cmm2 space group, while the [KNb O3]1-x[Ba Ni1/2Nb1/2O3-δ]x( x = 0.1- 0.5) remains substantially cubic perovskite with Pm3 m space group; Compared with that of KNb O3, the particle size of [KNb O3]1-x[Ba Ni1/2Nb1/2O3-δ]x is smaller. The ability of visible-light-absorbing of doping samples has improved when x = 0.3- 0.5.4. Compared with that of KNb O3, the photocatalytic performance of [KNb O3]1-x[Ba Ni1/2Nb1/2O3-δ]x(x = 0.1- 0.5) nanoparticles has be improved. But the photocatalytic performance for all the doped samples are not ideal, which may be attributed to the lower ability of visible-light-absorbing resulting from relative lower substitution rate of Ba and Ni introduced into the perovskite A-site and B-site, respectively.