NSC94-EPA-Z-008-004

4.2 Photoreduction under visible light with InVO 4InVO4 photocatalysts were prepared with various preparation variables, including: (1)loading me tal, NiO, (2) different amount of NiO loading (0.5 wt%, and 1.0 wt%), (3)reduction-oxidation pretreatment.4.2.1 Effect of various amount of NiO loadingThe aqueous solution of nickel nitrate hexahydrate was added respectively into thesurface of the InVO4 powders. Water of the suspension was evaporated by a water bath understirring. Following, the dried powder was calcined at 350 O C for 1 hr in air using a mufflefurnace.4.2.1.1 XRDFigure 4.16 shows the XRD patterns of the as-prepared InVO 4 with various loadingmetal. The XRD patterns of InVO 4 samples prepared by solid reaction at 1123K wellconsisted with orthorhombic InVO 4-III phase spectrum, space group Cmcm, indicated that thesamples were fully crystallized InVO 4 (Figure 4.1A). The crystal lattice parameters wererefined as follows: a=5.7531(1) Å, b=8.5201(1) Å and c=6.5781(2) Å. The indexed result is ingood agreement with that reported in the JCPDS database card (No. 48-0898).Ye et al. (2002) has reported the structural of InVO 4 . The InVO 4 compound belongs tothe orthorhombic system, space group Cmcm, a = 5.7542(1), b= 8.5229(1) and c= 6. 5797(1)Å. The structure is com posed of two kinds of polyhedra: InO 6 octahedron and VO 4tetrahedron. The InO 6 octahedron connects to each other by sharing edge to form chains along[0 0 1] direction, which were linked together by the VO 4 tetrahedra. The band structure ofoxides is generally defined by d-level and O 2p-level, as confirmed by the theoreticalcalculations based on the first principles method for TiO 2 and InMO 4 (M= V, Nb, and Ta)photocatalysts (Lee et al., 2000). Figure 4.1B is a pattern of InVO 4 samples loaded NiO, oneaddition XRD peak appeared near 55.861 o (0 0 4) (Touboul et al., 1995), which might becausethe crystalline distortion induced by NiO loadings.4.2.1.2 SEMFigure 4.17 shows the SEM photographs of the InVO 4 samples prepared with variousloading amount of nickel. Figure 4.17A is a micrograph of InVO 4 samples, the particlediameters of InVO 4 samples were less than 6μm. The particles agglomerated in irregularshape with ca. 3~6 μm. Figure 4.17B is a micrograph of InVO 4 samples loaded with 0.5 wt%NiO on the catalysts, many pellets and pin-holes were observed on NiO/InVO 4 particles.Figure 4.17C is a micrograph of InVO 4 samples loaded with 1.0 wt% NiO on the catalysts,many pellets and pin-holes were observed on NiO/InVO 4 particles. It should be noted thatsuch Ni particles were not so homogeneously dispersed over InVO 4 support. However, it isdifficult to infer from a SEM photograph whether the Ni particles are located at the surface orbetween layers. The SEM-EDS results of InVO 4 prepared with various amount of NiO36