Photocatalysis photocatalytic reactors

Thus, photocatalysis and photogenerated catalysis indeed open up rather reach opportunities in fine organic synthesis, including some new reactions and nontraditional pathways for some known reactions. More efforts should be made in engineering of appropriate photocatalytic reactors for such synthesis. 

Solar-grade silicon, production of, 22 507-508 Solar heat control, use of gold in, 12 703 Solarization effect, 19 203 Solar photocatalysis, 23 23-24 Solar photocatalytic detoxification, 19 76 Solar photocatalytic processes, 19 100-101 Solar photocatalytic reactor, using deposited titania, 19 99 Solar photoreactors, 19 95-99 Solar salt harvesting, 22 802, 806-808 Solar spectrum, 23 2 Solar still, 26 89-92 Solar thermal converters, 23 10-13 Solar transmittance, for thin films, 23 19 Solatene, 24 558 Solder, 3 53... 

Savinov, Evgueni N. is a Head of the Laboratory of photocatalysis on the semiconductors at the Boreskov Institute of Catalysis since 1987. Since 1996 he is a Head of the Chemical Physical Department at the Novosibirsk State University. His area of interest is the photocatalytic and photochemical processes in liquid and gas phase. This includes preparation and characterisation of photocatalysts study the mechanism of photocatalytic reactions design of photocatalytic reactors application of photocatalytic technology to the industry. 

Light sources are among the most important parts of photocatalytic devices, based on the fact that photons are often regarded as the most expensive component of photocatalytic reactors (Nicolella and Rovatti, 1998). Hence, it is obvious that criteria for effective use of photons should be very important in the design and operation of photocatalytic devices. Unfortimately (or not), the odds that lamp manufacturers will produce UV lamps especially designed for photocatalysis for a competitive price are very slim. As a consequence, the design and even the size of a feasible reactor is very much constrained by the commercial availability of the radiation source (Imoberdorf et al., 2007). 

FIGURE 2.4. Schematic representation of the optical-fiber bundled array photocatalytic reactor system (Reprinted with permission from Environ. Sci. Tech., 32(3), N.J. Peill and M.R. Hoffmann, Mathematical model of a phtoocatlaytic piber-optic cable reactor for heterogeneous photocatalysis, 398-404. Copyright 1998 American Chemical Society ). 

In summary, there are a number of available photocatalytic reactor configurations for the photoconversion of water pollutants. These reactors are based on either suspended or immobilized Ti02- It is expected that enhanced energy efficiencies could be achieved by improving the engineering of the above-described designs. This could considerably expand the prospects of the use of photocatalysis for water purification. 

The removal of airborne contaminants is an area of promising applications for photocatalysis. The challenges to be faced involve the treatment of relatively large gas flows in devices with low pressure-drops, good photocatalyst irradiation and efficient reactant species-photocatalyst contacting (Dibble and Raupp, 1992). In the near future photocatalytic reactors, incorporating the use of solar energy, are also anticipated to be developed. 

Photoconversion of air contaminants in photocatalytic reactors has been considered through a diversity of reactor configurations and designs. The high quantum yields observed, sm passing the value of 1, suggest that this approach will become a major area for futm e applications of photocatalysis. 

A successful implementation of photocatalysis requires very efficient catalysts, illumination sources and reactors. In addition, auxiliary equipment for photocatalytic reactors is of major importance to assess the effectiveness of the reactor and of the kinetic reactor modeling. Uiis requires proper characterization of the near-UV lamps used, in the case of artificially powered photocatalytic reactors, and the characterization of the photons absorbed in the photocatalytic reactor unit. 

Various experiments, carried out with different photocatalytic reactors and commercial pervaporation membranes, by varying the relative weight of pervaporation with respect to photocatalysis, have demonstrated that the intensification factor depends solely on the parameter 5 previously defined, as is apparent in Fig. 3.7. 

In Fig. 21.7 a laboratory scale PMR coupling photocatalysis with MF is shown. The PMR was applied for the removal of trichloroethylene (TCE) from water (Choo et al., 2008). The system was composed of a photocatalytic reactor (volume of 700 cm ) and a hollow fiber MF module (effective membrane surface area of 20.7 cm ). A UV-A light source was placed in the inner chamber of the photoreactor, whereas in the outer chamber the solution undergoing the photocatalytic reaction was flowing. Feed from the feed tank was pumped through the photoreactor to the membrane module. The PMR was operated either in batch or in continuous mode. In batch operations, the permeate and retentate were recycled to the photoreactor. In continuous mode, the permeate was discharged and the same volume of the solution was fed into the reactor. Thus the working volume of the photoreactor was maintained at a constant level. 

The Photocatalytic reactor, used in this study, has been described in detail in our earlier publications for hydrogen production, phenol degradation and other applications [7,8]. The contaminated water samples with bacteria (80 ml) were irradiated using Nd YAG laser, at different incident laser energies, varying amounts of photocatalyst and for different times. To find the effect of the catalyst identity on the inactivation of the coliforms, micron-WOs (p-WOs), Pd-free w-WOs and w-Pd/n-WOs catalysts were used. Furthermore, to find out the effectiveness of either photocatalyst or laser radiation on removal of coliforms, photocatalysis was performed in the cases of photocatalyst without laser radiation as well as laser irradiation without a photocatalyst. During this study, the laser energy per pulse was kept at 100 mj and the contaminated water samples were irradiated for 10 minutes. The treated water samples were collected at different time intervals to observe the removal. 

Photocatalysis, i.e., using semiconductor particles under band gap irradiation as little micro reactors for the simultaneous reduction and oxidation of different redox systems, has been intensively studied during the last 25 years since the pioneering work of Carey et al [1]. The main focus of these studies seems to be the investigation of the principal applicability of photocatalytic systems for the efficient treatment of water and air streams polluted with toxic substances. Several review articles on this topic have recently been published [2]. In some cases, pilot-scale or even commercially available reactors have already been constructed, especially when titanium dioxide is used as the photocatalyst [3]. 

Studies on heterogeneous photocatalysis have been undertaken extensively worldwide, employing significantly diverse experimental conditions including illumination, photocatalyst preparation, and reactor design. To allow the comparison of experimental data between different research laboratories, a unified, unambiguous definition of the efficiencies of photocatalytic processes is compulsory. 

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