No abstract

Nanocrystalline TiO2 was synthesized by the solution combustion method using titanyl nitrate and various fuels such as glycine, hexamethylenetetramine, and oxalyldihydrazide. These catalysts are active under visible light, have optical absorption wavelengths below 600 nm, and show superior photocatalytic activity for the degradation of methylene blue and phenol under UV and solar conditions compared to commercial TiO2, Degussa P-25. The higher photocatalytic activity is attributed to the structure of the catalyst. Various studies such as X-ray diffraction, Raman spectroscopy, Brunauer-Emmett-Teller surface area, thermogravimetric-differential thermal analysis, FT-IR spectroscopy, NMR, UV-vis spectroscopy, and surface acidity measurements were conducted. It was concluded that the primary factor for the enhanced activity of combustion-synthesized catalyst is a larger amount of surface hydroxyl groups and a lowered band gap. The lower band gap can be attributed to the carbon inclusion into the TiO2 giving TiO(2-2x)C(x) VO2**.

The W, V, Ce, Zr, Fe, and Cu metal ion substituted nanocrystalline anatase TiO2 was prepared by solution combustion method and characterized by XRD, Raman, BET, EPR, XPS, IR TGA, UV absorption, and photoluminescence measurements. The structural studies indicate that the solid solution formation was limited to a narrow range of concentrations of the dopant ions. The photocatalytic degradation of 4-nitrophenol under UV and solar exposure was investigated with Ti1 - x M x O2 ± δ. The degradation rates of 4-nitrophenol with these catalysts were lesser than the degradation rates of 4-nitrophenol with undoped TiO2 both with UV exposure and solar radiation. However, the photocatalytic activities of most metal ion doped TiO2 are higher than the activity of the commercial TiO2, Degussa P25. The decrease in photocatalytic activity is correlated with decrease in photoluminescence due to electron states of metal ions within the band gap of TiO2.

No abstract

The structure and chemical nature of Pt in combustion-synthesized Pt/CeO2 catalysts have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and temperature-programmed reaction (TPR). Catalytic oxidation of CO over Pt/CeO2 is correlated with its structure. High-resolution XRD studies show that the structure could be refined for the composition of Ce1 - x Pt x O2 - δ in the fluorite structure with 6% oxide ion vacancy. TEM images show very few Pt particles on the CeO2 crystallite surface in as-prepared samples and a decrease in the density of Pt metal particles is observed on heating. XPS studies demonstrate that Pt is dispersed mostly in +2 (72%) and +4 (21%) oxidation states on CeO2, whereas only 7% is present as Pt metal particles. On heat treatment, Pt2+ species increase at the cost of Pt4+ ions. EXAFS studies show the average coordination number of 1.3 around the platinum ion in the first shell of 1% Pt/CeO2 at a distance of 1.98 Å, indicating oxide ion vacancy around the platinum ion. On heating, the average oxygen coordination of Pt and oxygen increases to 2.3. The second shell at 2.97 Å is due to Pt−Pt coordination, which is absent in PtO2 and PtO. The third shell at 3.28 Å is not observed either in Pt metal or any of the platinum oxides, which could be attributed to Pt2+−Ce4+ correlation. Thus, Pt/CeO2 forms a Ce1 - x Pt x O2 - δ type of solid solution having −□−Pt2+−O−Ce4+− kinds of linkages.