Particle photocatalysis

Dye sensitization of semiconductor surfaces is not considered here, nor are issues related to semiconductor particles, photocatalysis and photoelectrolysis per se. These companion topics may be found elsewhere in Volumes I, IV and V. The discussion is phenomenological and is designed to provide an intuitive grasp of the key issues rather than detailed derivations that would have been prohibitive in terms of space constraints in any case. Indeed, the available theoretical framework is only examined in terms of how and with what confidence the pertinent conclusions can be experimentally verified with semiconductor electrodes. 

Arakawa, H. and Sayama, K., Water photolysis by Ti02 particles—significant effect of Na2C03 addition on water splitting, Photocatalysis, Science and Technology, Kaneko, M. and Okura, I. (Eds), Kodansha/Springer, Berlin, 2002, Chap. 14. 

Heterogeneous particle morphology, in polymer colloids, 20 387 Heterogeneous photocatalysis, 19 73, 103 principles of, 29 74-75 Heterogeneous polymer blends, 20 343. 

Mass market soap manufacture, 22 723 Mass Mean Diameter (MMD), 23.T87 Mass of catalyst, in photocatalysis, 19 77-78 Mass particle diameter, 78 134 Mass polymerization, 70 206 ABS, 7 422... 

Photocatalysis uses semiconductor materials as catalysts. The photoexcitation of semiconductor particles generates electron-hole pairs due to the adsorption of 390 run or UV light of low wavelength (for Ti02). If the exciting energy employed comes from solar radiation, the process is called solar photocatalysis [21],... 

Other composite photocatalysts were prepared by mounting immobilized anatase particles on mesoporous silica and silica beads [189-191], The behavior of anatase-mounted activated carbons was also studied in detail [192-194], It was even suggested that carbon-coated anatase exhibits better performance in photocatalysis than anatase itself, demonstrating high adsorptivity, inhibition of interaction with organic binders, etc. [195,196],... 

CO oxidation, 28 108 iron catalyst, 30 168 kinetics, 28 250-257 complicated, 28 257-263 latest developments in, 5 1 over amorphous metal alloys, 36 372-374 over iron, 36 24-25 on alumina support, 36 47 antipathetic behavior, 36 150, 152 particle size and, 36 131-132 promotion by potassium, 36 36-37 over rhenium. 36 24-25 promotion by potassium, 36 37 photocatalysis over perovskites, 36 304 Anunoxidation, 30 136-137 allyl alcohol, 30 157-158... 

The limiting factors that control photocatalysis efficiency are rapid recombination between photo-generated charge carriers, and the backward reaction leading to recombination of the formed molecular hydrogen and oxygen. To retard these processes efforts have typically focused on surface modification of the semiconductor particles using metals or metal oxides. 

Abstract A colloidal solution of titanium dioxide (TiO ) nanoparticles was prepared by the solvothermal method and dip-coated onto a polypropylene fabric with TMOS binder. The prepared TiO particles, colloidal solution and the coated fabrics were characterized by X-ray diffraction, SEM and TEM. The results showed that the TiO particles prepared by the solvothermal method were composed of anatase which uniformly coated the snbstrate. Photocatalysis induced bactericidal properties of coated fabrics were tested by measuring the viability of Escherichia coli. It was fonnd that solvothermally prepared TiO coatings have the ability to kill E. coli. This nniqne property of TiO makes it an ideal candidate in producing self-sterilizing protective masks and in providing bactericidal and self-cleaning properties to a variety of snrfaces. 

There are several factors caused by the change of the particle size that affect the activity of particulate photocatalysis (1) surface area, (2) band energy shift, (3) accessibility to the surface, and (4) space for charge separation. 

In the process of photocatalysis, the electrons and holes produced on photoirradiated Ti02 powders are trapped at the particle surface to form unpaired-electron species (step (4) in Fig.D.3). Photocatalytic reactions are actually the reactions of these radicals with reactant molecules at the Ti02 surface. Electron spin resonance (ESR) spectroscopy has been used for the detection of the photoproduced radicals on Ti02 at low temperatures such as 77 K. It has been reported that photoproduced electrons are trapped at various different sites titanium atoms on the surface or inside the particles, or oxygen molecules adsorbed on the surface. On the other hand, photoproduced holes are trapped at lattice OAygen atoms near the particle surface or at surface hydroxyl groups. We analyzed these radical species for several Ti02 photocatalysts that are commercially available, and found that the differences in the photoproduced radicals resulted from different heat-treatment conditions and the reactivity with several molecules.17)... 

Sonophotocatalysis is photocatalysis with ultrasonic irradiation or the simultaneous irradiation of ultrasound and light with photocatalyst. Tnis method includes irradiation with alternating ultrasound and light. Ultrasound effects on heterogeneous photocatalytic reaction systems have been demonstrated by Mason,1 Sawada et al.,2) Kado et al.,3) and Suzuki et al.4) In these papers, not only acceleration of photocatalytic reactions but increase in product selectivity by ultrasonic irradiation has also been reported. It was postulated that ultrasound effects, such as surface cleaning, particle size reduction and increased mass transfer, were the result of the mechanical effects of ultrasound.1,5) Lindley reviewed these and other effects.5)... 

Fig. 5.3 Processes of photocatalysis at semiconductor particles. The numbers correspond to those in the text, Path increased by decreasing the particle size are shown by increase. ...

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