Titania photocatalyst

Titania photocatalyst is used for air and water purification, photo-splitting of water to produce hydrogen, odor control and disinfectant. Crystal structure and crystallite size of titania particles are one of the most important factors that affect on the photoactivity. Photoactivity of anatase is higher than that of rutile, and increases with crystallite size [1]. Therefore, to increase photoactivity, it is desirable to find a route for the synthrais of the pure anatase titania with large crystallite size. 

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,... 

Baiju, K.V., Shukla, S., Biju, S., Reddy, M.L.P., and Warrier, K.G.K. (2009) Morphology-dependent dye-removal mechanism as observed for anatase-titania photocatalyst. Catalysis Letters,... 

Zhang, X. and Liu, Q. (2008) Visible-light-induced degradation of formaldehyde over titania photocatalyst co-doped with nitrogen and nickel. Applied Surface Science, 254 (15), 4780-4785. 

The silver-loaded titania photocatalysts possess high activity in the photocatalytic decomposition of ozone [38], photoreduction of various thiols [39], photodestruction of 1,4-dichlorobenzene [40], dehydrogenation and oxidation of alcohols (e.g. of 2-propanole [41,42]), decoloration of textile waste water [43], photokilling of bacteria [44], and others. For additional detailed information on this topic, one can use a number of review articles and books [e.g. 45-48]. 

Dependences of 2R on Tcaic for several pure or mixed semiconductor oxides are presented in Fig. 8.4. Iron doped titania photocatalysts with different iron contents at Tcalc below 400°C had iron ions uniformly distributed in the anatase-Ti02 phase [114]. At Tcalc > 400°C, 1 wt % Fe samples performed the same behaviour of 2R as without iron, and at Tcalo > 600°C in the samples with 10 wt % Fe content, the formation of hematite phases interacted with the titania phases was observed in XRD experiments. The crystalline structure of Ti02 phases was distorted at high Tcalc which also resulted in 5-fold decrease of 2R as compared to 1 wt % Fe case (Fig. 8.4). 

Guiflard, C., Disdier, J., Monnet, C., Dussaud, J., Malato, S., Blanco, J., Maldonado, M.I. and Herrmann, J.-M. (2003a) Solar efficiency of a new deposited titania photocatalyst Chlorophe-nol, pesticide and dye removal applications. Appl. Catal. B Environ. 46, 319-332. 

Visinescu, C. M., Sanjines, R., Levy, F., Marcu, V. and Parvulescu, V. I. (2005). Tantalum doped titania photocatalysts Preparation by dc reactive sputtering and catalytic behavior. J. Photochem. Photobiol. A-Chem. 174(2), 106-112. 

To estimate the thermodynamic feasibility of interfacial redox reactions at a hitherto unknown semiconductor surface, it is therefore of basic importance to know the position of the quasi-Fermi level. The quasi-Fermi level of electrons of powders or thin films of modified titania photocatalysts can be easily obtained by the suspension method developed by Bard et al. (9,10) and modified by Roy et al. (11) for titania and cadmium sulfide. It is based on the pH-dependence of the flat-band potential of Ti02-... 

Recently, it was reported that also the halogenides of Ru(III), Ir(IV), and Au(III) are able to form visible light active titania photocatalysts (60). 

It can be said that not only the above mentioned nano-structure but also other ordinary physical or structural properties measured for photocatalysts have not been proved to be decisive factors for the photocatalytic activities. It is true that photocatalytic activities of photocatalysts of certain components prepared or treated in different ways or under different conditions may be different and this is because physical and structural properties of those photocatalysts differ depending on the preparation/treatment conditions, that is, physical and structural properties must control the photocatalytic activity 49). A problem is we, at least the author, do not know how properties affect photocatalytic activity. A possible reason is that those properties, though we do not know how many properties are required for analysis, are changed at the same time. For example, when titania photocatalysts are prepared by hydrolysis of a titanium compound such as titanium(IV) sulfate or tetra (2-propoxide) followed by calcination in air, higher-temperature... 

In femto-second pump-prove transition photoabsorption measurements, titania photocatalysts gave visible-light photoabsorption of trapped e" within ca. 100 fs pump pulse without showing photoabsorption of e in the CB. See Section IV.C. 

Early examples are the preparation of a titania photocatalyst on a stainless steel plate [224] and of alumina (as a catalyst support) on metallic gauzes [225]. The properties of the layers are controlled by the composition and the pH of the solution as well as the voltage and the current density that is applied. Vorob eva [225] used an acidic solution of isopropanol and obtained an initial alumina sol that was composed of nanoparticles of boehmite AIO(OH). The deposited layer thickness on wires 50 pm in diameter could be varied between 1 and 15 pm by adjusting the voltage and the deposition time. 

Silica-titania photocatalysts were prepared from Si(OEt)4 (TEOS) and Ti(OBu)4 as silica and titania sources by the following sol-gel method, as summarized in scheme 1. A clear mixture of TEOS, EtOH, H2O, and HCl (mol ratio = 1 4 1 0.6) was stirred at room temperature for x min. A yellow and clear mixture of Ti(OBu)4, EtOH, and (CH3C0)2CH2 (mol ratio = 0.01 1 0.005) was added and stirred for y min at room temperature. The clear mixed solution was stirred and dried at 353 K typically for 1 h until clear gel was obtained. The wet gel was dried at 383 K ovemi t, then calcined in air... 

In preparation of silica-titania photocatalysts by sol-gel method, both hydrolysis and condensation time were clarified to be the important parameters to obtain... 

Ismail, A.A. and Bahnemann, D.W. (2011) Mesoporous titania photocatalysts preparation, characterization and reaction mechanisms. J. Mater. Chem., 21, 11686-11707. 

Dagan, G., S. Sampath, and O. Lev, Preparation and utilization of organically modified silica-titania photocatalysts for decontamination of aquatic environments,... 

Partial or complete heterogeneous photocatalytic oxidation of neat toluene and 4-picoline in liquid organic oxygenated dispersions containing pure or iron-doped titania photocatalysts. /. Mol Catal A. Chem., 104 (3), 329-339. 

Yagi K., Shibata S., Yano T., Yasumori A., Yamane M., Dunn B. Photo stability ofthe laser dye DCM in various inorganic-organic host. J. Sol-Gel Sci. Technol. 1995 4 67-73 Yamazaki S., Honjo H., Hata S., Kai Y. Sol-Gel products news. Development of hydrophilic outside mirror coated with titania photocatalyst. J. Sol-Gel Sci. Technol. 2002 23 267-268. 

Zhang X, Liu Q. Preparation and characterization of titania photocatalyst co-doped with boron, nickel, and cerium. Mater Lett 2008 62 2589-2592. 

B. Ohtani, Titania Photocatalysts Beyond Recombination A Critical Review, Catalyst, 3, 942-53 (2013). 

G. Li, L. Chen, M. E. Graham, and K. A. Gray, A Comparison of Mixed Phase Titania Photocatalysts Prepared by Physical and Chemical Methods The Importance of the Solid-Solid Interface, J. Mol. Catal. Chem. A 275, 30-35 (2007). 

At present the most efficient solid photocatalyst for CO2 reduction by H2 is based on Ti02, a semiconductor that is suitably modified to increase the efficiency under solar light irradiation and contain co-catalysts to increase production rate and selectivity of the process. One of the most efficient photocatalysts has been reported by Grimes and coworkers who have used anodized titania nanotubes in the anatase phase doped with nitrogen and platinum and copper nanoparticles as photocatalyst for the gas phase CO2 reduction by H2O production rates to methane as high as 75 ppm cm h have been achieved for this type of titania photocatalyst under solar light illumination [23, 25]. 

Palmisano L, Augugliaro V, Bellardita M, Di Paola A, Garcia-Lopez E, Loddo V, Marci G, Palmisano G, Yurdakal S (2011) Titania photocatalyst for selective oxidations in water. ChemSusChem 4 1431-1438... 

---