Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

Understanding TiO2 photocatalysis: mechanisms and materials.

The presence of transition metal ions in photocatalytic reactions is reviewed according to two main approaches: (a) the influence of transition metal ions on the rate of photocatalytic reactions (mainly oxidation) and (b) the transformation of the ions to less toxic species or their deposition on the semiconductor catalyst surface for recovery of expensive and useful metals. Most of the proposed mechanisms are discussed, together with experimental physicochemical evidences that support the involved pathways. Practical applications related to environmental protection and industrial processes are described.

Heterogeneous photocatalysis: Transition metal ions in photocatalytic systems

Chromium-, manganese- and cobalt-doped titanium dioxide photocatalysts containing 0.2, 0.5 or 1 at.% of metal-dopant were investigated by UV–VIS, FT-IR, near-IR and electron paramagnetic resonance (EPR) spectroscopic techniques. The presence of the doping ions in the titania structure caused significant absorption shift to the visible region compared to pure TiO 2 powder (P25 Degussa). The EPR spectra of TiO 2 powders containing chromium showed the superposition of three types of individual paramagnetic species (β-, γ- and δ-signals), whose relative EPR intensity is significantly dependent on the dopant concentration, as well as on the photocatalysts preparation and treatment. The EPR spectra of the chromium-doped photocatalysts heated in H 2 /N 2 atmosphere corresponded to the Cr(III) ions occupying vacated cation sites in the rutile or anatase crystal lattice. The characteristic feature of the EPR spectra of the Mn/TiO 2 samples is a sharp six-line Mn(II) component centered on g eff =1.99, flanked by shoulders with a weak feature, which appeared on g eff =2.66 and 4.32. The photocatalytic activity of the various metal-doped TiO 2 samples was tested in aqueous or dimethylsulfoxide (DMSO) suspensions using EPR spin trapping technique with 5,5-dimethyl-1-pyrroline N -oxide (DMPO) spin trap. The ability of the irradiated photocatalysts to generate reactive oxygen species, namely hydroxyl radicals and super-oxide anion radicals, which were trapped as the corresponding DMPO-adducts was investigated.

Investigations of metal-doped titanium dioxide photocatalysts

Nanotechnology, the engineering and art of manipulating matter at the nanoscale (1-100 nm), offers the potential of novel nanomaterials for treatment of surface water, groundwater, and wastewater contaminated by toxic metal ions, organic and inorganic solutes, and microorganisms. Due to their unique activity toward recalcitrant contaminants and application flexibility, many nanomaterials are under active research and development. Accordingly, literature about current research on different nanomaterials (nanostructured catalytic membranes, nanosorbents, nanocatalysts, and bioactive nanoparticles) and their application in water treatment, purification and disinfection is reviewed in this article. Moreover, knowledge regarding toxicological effects of engineered nanomaterials on humans and the environment is presented.

Nanotechnology and Water Treatment: Applications and Emerging Opportunities

Iron-ion-doped anatase titanium (IV) dioxide (TiO2) samples were prepared by hydrothermal hydrolysis and crystallization in octanol-water solution. The samples were characterized by X-ray diffraction, BET-specific surface area determination, UV-Vis diffuse reflectance spectroscopy and electron paramagnetic resonance spectroscopy. UV-Vis diffuse reflectance spectra showed a slight shift to longer wavelengths and an extension of the absorption in the visible region for almost all the ion-doped samples, compared to the non-doped sample. The photocatalytic activity of those catalysts was investigated for the liquid phase photocatatlytic degradation of active yellow XRG dye diluted in water under UV and visible light irradiation. It was found that the catalysts doped with FeCl3 have better catalytic activity for photodegradation of XRG than those doped with FeCl2. The amount of doped iron ion plays a significant role in affecting its photocatalytic activity and iron doped with optimum content can enhance photocatalytic activity, especially under visible light irradiation.

Characterization of Fe–TiO2 photocatalysts synthesized by hydrothermal method and their photocatalytic reactivity for photodegradation of XRG dye diluted in water

Specimens of iron-doped titania containing different amounts of Fe (0.5–5%) were prepared from TiO2 (Degussa P-25) and Fe(III) acetylacetonate by the wet impregnation method. Samples were characterized by X-ray diffraction analysis, specific surface area (BET) measurements, SEM-EDX, atomic absorption and IR and diffuse reflectance spectra. From the structural point of view, the samples were similar to those obtained with Fe(NO3)3 · 9H2O as the precursor, but with a more homogeneous distribution of iron for each mixed oxide sample on the particle surfaces but not between particles. The photocatalytic activity of these samples under near-UV irradiation was better for oxalic acid degradation than for EDTA, and similar for both types of mixed oxide samples. Mixed oxides showed however lower activity than TiO2. Some photodegradation under visible irradiation, not occurring with TiO2, could be observed for oxalic acid when using 5% Fe-containing samples.

JoséA. Navío

Papers

Synthesis, characterization and photocatalytic properties of iron-doped titania semiconductors prepared from TiO2 and iron(III) acetylacetonate