Detlef W. Bahnemann

Understanding TiO2 Photocatalysis: Mechanisms and Materials

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

Photocatalytic production of hydrogen peroxides and organic peroxides in aqueous suspensions of titanium dioxide, zinc oxide, and desert sand

The formation of H_2O_2 and organic peroxides in illuminated aqueous suspensions of ZnO, TiO_2, and desert sand in the presence of O_2 and organic electron donors has been studied. The photocatalytic rate of formation of H_2O_2 on ZnO was shown to depend on the O_2 partial pressure, on the concentration of organic electron donors, and on the concentration of H_2O_2.

Photocatalysis in water environments using artificial and solar light

This paper presents a review of part of the work done on photocatalytic reactors. Being aware of the comprehensive reports already existing on the chemistry of these reactions [A.M. Braun, L. Jakob, E. Oliveros, C.A. Oller do Nascimento, Adv. Photochem. 18 (1993) 235; O. Legrini, E. Oliveros, A.M. Braun, Chem. Rev. 93 (1993) 671; D. Bahnemann, J. Cunningham, M.A. Fox, E. Pelizzetti, P. Pichat, N. Serpone, in: G.R. Helz, R.G. Zepp, D.G. Crosby (Eds.), Aquatic and Surface Photochemistry, Lewis Publishers, Boca Raton, FL, 1994, p. 261; M.R. Hoffmann, S.T. Martin, W. Choi, D.W. Bahnemann, Chem. Rev. 95 (1995) 69; D. Bahnemann, in: P. Boule (Ed.), The Handbook of Environmental Chemistry, Part I, Vol. 2, Environmental Photochemistry, Springer, Berlin, 1999, p. 285] we have focused our work on two main themes: (i) light absorption evaluation when artificial light is used and (ii) description of reactor configurations and applications when solar radiation is employed. A classification is proposed for both topics and typical examples have been chosen to illustrate the specified concepts.

Advanced oxidation of a reactive dyebath effluent: comparison of O3, H2O2/UV-C and TiO2/UV-A processes

In the present study the treatment efficiency of different AOPs (O3/OH- H2O2/UV-C and TiO2/UV-A) were compared for the oxidation of simulated reactive dyebath effluent containing a mixture of monochlorotriazine type reactive dyes and various dye auxiliary chemicals at typical concentrations encountered in exhausted reactive dyebath liquors. A525 (color), UV280 (aromaticity) and TOC removal rates were assessed to screen the most appropriate oxidative process in terms of reactive dyebath effluent treatment. Special emphasis was laid on the effect of reaction pH and applied oxidant (O3, H2O2) dose on the observed reaction kinetics. It was established that the investigated AOPs were negatively affected by the Na2CO3 content (= 867 mg/L) which is always present at high concentrations in dychouse effluents since it is applied as a pH buffer and dye fixation agent during the reactive dyeing process. The ozonation reaction exhibited almost instantaneous decolorization kinetics and a reasonable TOC reduction rate. It appeared to be stable under the investigated advanced oxidation conditions and outranked the other studied AOPs based on the above mentioned criteria. Besides, the electrical energy requirements based on the EE/O parameter (the electrical energy required per order of pollutant removal in 1 m3 wastewater) was calculated for the homogenous AOPs in terms of decolorization kinetics. In view of the electrical energy efficiency, ozonation and H2O2/UV-C oxidation at the selected treatment conditions appear to be promising candidates for full-scale dyehouse effluent decolorization.

A comparative study of nanometer sized Fe(III)-doped TiO2 photocatalysts: synthesis, characterization and activity

Fe(III)-doped TiO2 nanoparticles have been prepared in three different ways using inorganic or organic precursors, respectively. Transmission electron microscopic (TEM) structure characterization of the obtained particles reveals that TiO2 particles with and without the Fe(III) dopant possess the crystal structure of anatase. Cryo-TEM of vitrified samples confirms earlier assumptions that TiO2 nanoparticles tend to form three-dimensional networks in solution. A novel energy transfer mechanism is suggested employing these three-dimensional networks as antenna systems which lead to improved photocatalytic activities of the colloidal preparations. The performance of the nanostructured TiO2 with and without Fe-dopant for the photocatalytic oxidation of methanol producing HCHO is strongly dependent on the preparations and the Fe-content. Fe(III)-doped TiO2 nanoparticles prepared from organic precursors by the novel method (≤2.5 atom% Fe) exhibit a greatly enhanced photocatalytic activity (quantum yield of HCHO up to ca. 15%).

Mesoporous titania photocatalysts: preparation, characterization and reaction mechanisms

Titanium dioxide is a very important semiconductor with a high potential for applications in photocatalysis, solar cells, photochromism, sensoring, and various other areas of nanotechnology. Increasing attention has recently been focused on the simultaneous achievement of high bulk crystallinity and the formation of ordered mesoporous TiO2 frameworks with high thermal stability. Mesoporous TiO2 has continued to be highly active in photocatalytic applications because it is beneficial for promoting the diffusion of reactants and products, as well as for enhancing the photocatalytic activity by facilitating access to the reactive sites on the surface of photocatalyst. This steady progress has demonstrated that mesoporous TiO2 nanoparticles are playing and will continue to play an important role in the protection of the environment and in the search for renewable and clean energy technologies. This review focuses on the preparation and characterisation of mesoporous titania, noble metals nanoparticles, transition metal ions, non-metal/doped mesoporous titania networks. The photocatalytic activity of mesoporous titania materials upon visible and UV illumination will be reviewed, summarized and discussed, in particular, concerning the influence of preparation and solid-state properties of the materials. Reaction mechanisms that are being discussed to explain these effects will be presented and critically evaluated.

Advanced chemical oxidation of reactive dyes in simulated dyehouse effluents by ferrioxalate-Fenton/UV-A and TiO2/UV-A processes

Abstract Effective degradation of various mono- and bifunctional aminochlorotriazine reactive dyes in simulated dyehouse wastewater was achieved by the application of ferrioxalate-photo-Fenton [Fe(C 2 O 4 ) 3 3− /H 2 O 2 /UV-A; 300 nm>λ>400 nm] and titanium dioxide-mediated heterogeneous photocatalytic (TiO 2 /UV-A) treatment processes. These so-called advanced oxidation processes were studied in a novel batch photoreactor that was irradiated by a solar simulating installation. Decolorization by the ferrioxalate-photo-Fenton oxidation process was found to proceed three times faster than the photocatalytic process, while the latter was more efficient in reducing the optical density at 280 nm wavelength (UV 280nm ). Complete decolourization and partial mineralization with 17–23% total organic carbon (TOC) and 73–86% UV 280nm removals were achieved by the ferrioxalate-Fenton/UV-A and TiO 2 /UV-A processes, respectively, within a 1-h treatment time. Emphasis was placed on the effect of dyehouse effluent strength on decolourization kinetics, along with possible advantages of the ferrioxalate-Fenton/UV-A process over the conventional photo-Fenton (Fe 2+ /H 2 O 2 /UV-C) process. The results of these experiments showed that the more dilute the dyehouse effluent the faster the decolourization rate. On the basis of spectrophotometric measurements, dye decomposition could be successfully fitted to the empirical Langmuir–Hinshelwood kinetic model.

The application of TiO2 photocatalysis for disinfection of water contaminated with pathogenic micro-organisms: a review

The use of semiconductor photocatalysis for treatment of water and air has been the topic of intense research activity over the past 20 years. This powerful process has also been extended to the disinfection of environments contaminated with pathogenic micro-organisms. This review summarizes recent developments concerned with the photocatalytic treatment of water contaminated with pathogenic micro-organisms presenting a potential hazard to animals and human beings.

Mechanistic studies of water detoxification in illuminated TiO2 suspensions

Abstract The destruction of toxic halogenated hydrocarbons in waste water effuents or ground water wells is a problem of growing importance in our industrial society. Since conventional methods such as chemical oxidation or microbial treatment are often not efficient for the destruction of these toxins, alternative routes for detoxification are required. It has been shown that semiconductor particles can be used as photocatalysts which are capable of inducing the complete mineralization of many of these hazardous compounds. Detailed mechanistic studies are presented here which have been carried out to investigate the potential use of concentrated solar illumination as the source of irridiance in those photocatalytic systems. Thus the influence of light intensity, temperature and pH on the overall yield of the destruction of halogenated hydrocarbons in aqueous suspensions containing titanium dioxide powder has been studied in detail. Models are presented to explain the observations made with chloroform as the probe molecule and to enable predictions of the efficiency of this method for “real world” applications.

Heterogeneous photocatalytic reactions comparing TiO2 and Pt/TiO2

Abstract Two commercial samples, namely Degussa P-25 and Sachtleben Hombikat UV 100, and platinized modifications of these samples have been tested comparatively as photocatalysts for EDTA oxidation and for Cr(VI) reduction in the absence and in the presence of EDTA. Platinized photocatalysts were prepared by photoimpregnation of H 2 PtCl 6 on TiO 2 by prolonged irradiation in the presence of methanol. Only slight differences in efficiency were found between both pure commercial forms, except for the Cr(VI) reduction in the presence of EDTA, where Hombikat UV 100 samples were more active. Platinized Hombikat UV 100 was found to be less active for Cr(VI) reduction in water. The concentration of dissolved molecular oxygen was crucial for EDTA oxidation and had no influence on Cr(VI) reduction. From kinetic profiles, initial photonic efficiencies ( ζ ) and conversion degrees have been calculated. Platinization did not improve Cr(VI) reduction but increased the initial photonic efficiency for EDTA oxidation. However, after prolonged irradiation, the conversion of EDTA was lower employing platinized samples instead of pure samples. The effect of platinum on titania was analyzed on the basis of proposed mechanisms.