Visible-Light Excitated Photocatalytic Activity of Rare Earth Metal-Ion-Doped Titania

The rare earth ion Ce 4+ doped TiO 2 was prepared by sol-gel method. The average particle sizes are about 10 nm for sol phase and 55 nm for polycrystalline phase. The photocatalytic activities to degrade Reactive Brilliant Red Dye X-3B were investigated. The result reveals that the spectrum response of Ce 4+-TiO 2 has extended to visible region from the UV region(λ<387 nm) of pure TiO 2. Amorphous phase Ce 4+-TiO 2 sol with an electron scavenger (1.0% atom fraction Ce 4+ ion doping amount) shows the capability of the photocatalytic degradation of the dye X-3B as well as the nanocrystallite Ce 4+-TiO 2 with an interband trap site. Despite of the difference in the morphology of Ce 4+-TiO 2 photocatalyst, there is no apparent difference in respect of the decoloring effects. Whereas, polycrystalline phase Ce 4+-TiO 2 exhibits strong photomineralization power in comparison with the amorphous phase. The photocatalytic oxidation mechanisms of the dye molecule mainly involved in the self-photo-sensitization photolysis process by the first excited singlet oxygen ( 1O 2) and photocatalysis process by hydroxyl radicals(·OH) under visible light irradiation.

Synthesis of CeO_2/fly ash cenospheres composites as novel photocatalysts by modified pyrolysis process

A novel fly ash cenospheres（FACs）-supported CeO2 composite（CeO2/FACs） was successfully synthesized by the modified pyrolysis process.The prepared composites were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, X-ray photoelectron spectroscopy（XPS）, and diffuse reflection spectra（DRS） techniques.XRD results indicated that the CeO2 film coated on cenospheres was a face-centered cubic structure.SEM images confirmed that the CeO2 film was relatively compact.XPS results showed that Ce was present as both Ce4＋ and Ce3＋ oxidation states in CeO2 film coated on FACs substrate.The bandgap of the composite was narrower compared with the pure CeO2.The as-prepared material exhibited good photocatalytic activity for the decolorization of methylene blue（MB） under visible light irradiation, and the first-order reaction rate constant（k） of 0.0028 min–1 for CeO2/FACs composite was higher than 0.0015 min–1 of pure CeO2.The fact that they floated on water meant that CeO2/FACs composites were easily recovered from water by filtration after the reaction.The recycling test revealed that the composites were quite stable during the MB photocatalytic decolorization.The CeO2/ FACs catalyst was therefore promising for practical use in the degradation of pollutants or water cleanup.

Photocatalytic degradation of aqueous Methyl Orange using nitrogen-doped TiO_2 photocatalyst prepared by novel method of ultraviolet-assisted thermal synthesis

A nitrogen-doped titanium dioxide composite photocatalyst（N–TiO2） with heterojunction structures is synthesized by three different approaches： a novel UV-assisted thermal synthesis, annealing, and microwave technique. Photocatalytic activities of synthesized photocatalysts are evaluated by the degradation of Methyl Orange under ultraviolet light types A（UV-A）, B（UV-B）, and C（UV-C）, visible light, and direct sunlight irradiation. Results show that by using N–TiO_2 photocatalyst prepared by the UV-assisted thermal synthesis and annealing, the degradation increases by 16.5% and 20.4%, respectively, compared to that by bare TiO2. The best results are obtained at a nitrogen to TiO2 mass ratio of 0.15（N：TiO2）. The enhancement of the photocatalytic activity observed in the visible range is mainly attributed to the increasing separation rate of photogenerated charge carriers. The novel UV-assisted thermal synthesis has produced encouraging results as a preparation method for the nitrogen-doped TiO2 photocatalyst; thus, further studies are recommended for process optimization, immobilization, and scale-up to evaluate its applicability in wastewater treatment.