Photocatalysts characterization

Pichat, P., 1988, Powder photocatalysts Characterization by isotopic exchanges and photoconductivity, potentialities for metal recovery, catalyst preparation and water pollutant removal, in Photocatalysis and the environment, Schiavello, M., ed., Kluwer Academic Publishers, Dordrecht, The Netherlands, p. 399. 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

Alapi, T., Sipos, P., Ilisz, I., Wittmann, G., Ambrus, Z., Kiricsi, I., Mogyorosi, K., and Dombi, A. (2006) Synthesis and characterization of titania photocatalysts the influence of pretreatment on the activity. Applied Catalysis A General,... 

Choi, Y., Umebayashi, T., and Yoshikawa, M. (2004) Fabrication and characterization of C-doped anatase Ti02 photocatalysts. Journal of Materials Science, 39 (5), 1837-1839. 

Wu, Y., Zhang, J., Xiao, L., and Chen, F. (2009) Preparation and characterization of Ti02 photocatalysts by Fe3+ doping together with Au deposition for the degradation of organic pollutants. Applied Catalysis B Environmental, 88 (3—4), 525—532. 

Stodolny, M. and Laniecki, M. (2009) Synthesis and characterization of mesoporous Ta205—Ti02 photocatalysts for water splitting. Catalysis Today, 142 (3—4), 314-319. 

However, the pathways for these reactions, particularly in the gas phase, have been only -.rtially characterized. In a wide variety of these reactions, coordinatively unsaturated, highly reactive metal carbonyls are produced [1-18]. The products of many of these photochemical reactions act as efficient catalysts. For example, Fe(C0)5 can be used to generate an efficient photocatalyst for alkene isomerization, hydrogenation, and hydrosilation reactions [19-23]. Turnover numbers as high as 3000 have been observed for Fe(C0)5 induced photocatalysis [22]. However, in many catalytically active systems, the active intermediate has not been definitively determined. Indeed, it is only recently that significant progress has been made in this area [20-23]. 

Li, H. Zhang, X. Cui, X. Lin, Y., Ti02 nanotubes/MWCNTs nanocomposite photocatalysts synthesis, characterization and photocatalytic hydrogen evolution under UV-vis light illumination./. Nanoscience andNanotechn. 2012,12 1806-1811. 

Moon, J., Takagi, H., Eujishiro, Y, Awano, M. 2001. Preparation and characterization of the Sb doped TiOj photocatalysts. J Mater Sci 36 949-955. 

In Part I the fundamental aspects of photocatalysis are described. Photoelectrochemical processes at semiconductors are the most important basics for all photocatalytic reactions (Chapter 2). Design, preparation and characterization of active photocatalysts have been an important research subject,... 

Characterization of Ti02 Photocatalysts of Both High Crystallinity and Large Surface Area... 

Design, Preparation and Characterization of Highly Active Metal Oxide Photocatalysts... 

After the finding of photocatalytic water decomposition by Pt Ti02, many new semiconductor photocatalysts which are able to photolyze watei ir. ar. aqueous suspension have been reported.383 These photocatalysts are characterized... 

The coordinative and/or dissociative adsorption of various probe molecules has been used to characterize the surface properties of Ti02) which finds applications as a catalyst, photocatalyst, and sensor. Among the molecules used as probes, we mention CO (37, 38, 563-576), C02 (563, 565, 577), NO (578,579), water (580,581), pyridine (582,583), ammonia (584,585), alcohols (586, 587), ethers (including perfluoroethers) (588), ozone (589), nitrogen oxide (590), dioxygen (591), formic acid (592-594), benzene (584), benzoic acid (595), and chromyl chloride (596). 

Anpo, M. (Ed.) Special issue "Preparation, Characterization, and Reactivities of Titanium Oxide-based Photocatalysts, Topics Catal. 35,1 (2005). 

Thin-lilm photoelectrodes are needed in photoelectrocatalytic systems to apply a bias potential, either for the photoelectrode characterization or to facilitate the photocatalytic reactions. However, to be able to present a more comprehensive view on the performance of different materials, our subsequent discussions will focus on particulate semiconductor photocatalysts since the latter have been much more extensively investigated. Their electronic band structure (i.e., both the bandgap energy and the positions of CB and VB) is the key factor to determine whether or not a semiconductor material is suitable for a specific photocatalytic reaction, as will be demonstrated by reviewing a number of selected metal oxides and cou-pled/composite materials based on various semiconductors. 

Li, D., H. Haneda, S. Hishita and N. Ohashi (2005a). Visible-light-driven N-F-codoped Ti02 photocatalysts. 2. Optical characterization, photocatalysis, and potential application to air purification. Chemistry of Materials, 17(10), 2596-2602. 

Li, Y.Z., D.S. Hwang, N.H. Lee and S.J. Kim (2005c). Synthesis and characterization of carbon-doped titania as an artificial solar light sensitive photocatalyst. Chemical Physics Letters, 404(1-3), 25-29. 

Wang, C., J.C. Zhao, X.M. Wang, B.X. Mai, G.Y. Sheng, P. Peng and J.M. Fu (2002a). Preparation, characterization and photocatalytic activity of nano-sized ZnO/Sn02 coupled photocatalysts. Applied Catalysis B-Environmental, 39(3), 269-279. 

Wang, C.Y., C. BOttcher, D.W. Bahnemann and J.K. Dohrmann (2003a). A comparative study of nanometer sized Fe(III)-doped Ti02 photocatalysts Synthesis, characterization and activity. Journal of Materials Chemistry, 13(9), 2322-2329. 

Dhananjeyan, M.R., Mielczarski, E., Thampi, R.K., Buffat, P., Bensimon, M., Kulik, J., Mielczarski, J. and Kiwi, J. (2001) Photodynamics and surface characterization of Ti02 and Fe203 photocatalysts immobilized on modified polyethylene films. J. Phys. Chem. B 105, 12046-12055. 

Di Paola, A., Marci, G., Palmisano, L., Schiavello, M., Uosaki, K., Ikeda, S. and Ohtani, B. (2002). Preparation of polycrystalline Ti02 photocatalysts impregnated with various transition metal ions Characterization and photocatalytic activity for the degradation of 4-nitrophenol. J. Phys. Chem. B 106(3), 637-645. 

This complexity determines that investigations on heterogeneous photo-catalytic processes sometimes report information only on dark adsorption and use this information for discussing the results obtained under irradiation. This extrapolation is not adequate as the characteristics of photocatalyst surface change under irradiation and, moreover, active photoadsorption centers are generated. Nowadays very effective methods allow a soimd characterization of bulk properties of catalysts, and powerful spectroscopies give valuable information on surface properties. Unfortunately information on the photoadsorption extent under real reaction conditions, that is, at the same operative conditions at which the photoreactivity tests are performed, are not available. For the cases in which photoreaction events only occur on the catalyst surface, a critical step to affect the effectiveness of the transformation of a given compound is to understand the adsorption process of that compound on the catalyst surface. The study of the adsorbability of the substrate allows one to predict the mechanism and kinetics that promote its photoreaction and also to correctly compare the performance of different photocatalytic systems. 

Tubular reactors are probably the most common photocatalytic reactors. Their popularity stems, most likely, from their simplicity. They are characterized by a gas flow along the axis of a tube, which contains the photocatalyst in many possible forms such as a thin coated film on its wall, fluidized particles, a coated monolith, or even as a free powder resting on an appropriate support. The light sources are located, in most cases, externally to the tube, in a parallel configuration relative to its axis. Reflecting surfaces encompass the lamps array, assuring that the only absorbance of photons would be that of the photocatalyst (Figure 7). 

Coated wall annular reactors (Figure 12) are characterized by a thin film of photocatalyst located either on the outer side of inner tube or on the inner side of the outer tube. There are many reasons for preferring the inner side of the outer tube for the coating. The first reason has to do with the flux if is known that at high flux of lighf (>l-2 mW cm ) fhe quantum efficiency is proportional to 1 divided by the square root of fhe intensity. Hence, it is... 

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