Photocatalysis, electrochemically

White JR, Bard AJ (1985) Electrochemical investigation of photocatalysis at CdS suspensions in the presence of methylviologen. J Phys Chem 89 1947-1954... 

P.V. Kamat, Electrochemically assisted photocatalysis titania particulate film electrodes for photocatalytic degradation of 4-chlorophenol, J. Phys. Chem. 97 (1993) 9040-9044. 

Microscopic observation of Ti02 photocatalysis using scanning electrochemical microscopy, J. Phys. Chem. B 103 (1999) 3213-3217. 

A number of works are devoted to the electrochemical preparation of ZnO, which may have application in photocatalysis, ceramics, piezoelectric transducers, chemical sensors, photovoltaics, and others. ZnO has the same band-gap energy as Ti02, and the oxygenation capacities for both compounds should be similar. Ya-maguchi et al. [155] prepared photoactive zinc oxide films by anodizing a zinc plate. Such films could decompose gaseous acetaldehyde with the aid of black lights. 

Various polyoxometalates can be reduced electrochemically and reversibly by several electrons at modest potentials (Section VILA), and these properties are exploited in photocatalysis and eiectrocatalysis. In both cases, redox properties of heteropolyanions (Fig. 49) and the organic reactants (Table XXXV) are the principal properties that control the catalytic performance. The selection of the electrode is also important in eiectrocatalysis. Photocatalysis by hereopoly-anions has been reported extensively, but there are only a few reports of eiectrocatalysis by these compounds. 

As reported by Augugliaro et al. [64] the photocatalysis can be combined with chemical or physical operations. In the first case, when the coupling is with ozonation [65, 66], ultrasonic irradiation, photo-Fenton reaction or electrochemical treatment, which influence the photocatalytic mechanism, an increase of the efficiency of the process is obtained. 

A comparison of these new processes with Ti02 photocatalysis for the degradation of aniline [148] showed that the former are faster. Although all these methods are considered to proceed via OH radicals, some different intermediates were detected in the electrochemical and photocatalytic experiments. p-Benzoquinone and NH4+ appeared in all solutions tested. A recent study [149] reports 87% and 99% TOC removals after 4 hr of... 

In a single-crystal semiconductor (n-type) based photoelectrochemical cell, the problem of achieving charge separation is easily overcome by applying an anodic bias as was first demonstrated by Honda and Fujishima [263]. Using a single crystal Ti02, they were able to carry out the photoelectrolysis of water under the influence of an anodic bias. This concept to manipulate the photocatalytic reaction by electrochemical method can be extended to nanostructured semiconductor thin films [39,116]. The principle of electrochemically assisted photocatalysis is illustrated in Fig. 10. 

Figure 11 The absorption spectrum of a 0.2-mM NBB dye solution recorded at different time intervals following electrochemically assisted photocatalysis. An immobilized Ti02 particulate film cast on a conducting glass electrode was maintained at an electrochemical bias of 0.8 V SCE during the photocatalytic degradation experiment. (From Ref. 265.)...

Vinodgopal, K. Stafford, U. Gray, K. A. Kamat, P. V. Electrochemically assisted photocatalysis. II. The role of oxygen and reaction intermediates in the degradation of 4-chlorophenol on immobilized Ti02 particles, J. Phys. Chem 1994, 98, 6797. 

Goeringer S, Chenthamarakshan CR, Rajeshwar K. Synergistic photocatalysis mediated by Ti02 mutual rate enhancement in the photoreduction of Cr(VI) and Cu(II) in aqueous media. Electrochem Commun 2001 3 290-292. 

To improve the photoprocess performance, diverse combinations of heterogeneous photocatalysis with chemical and physical operations have been proposed, including among others, photo-Fenton, ozonization, biological or electrochemical treatment, and ultrasonic irradiation these attempts were recently reviewed and analysed [107],... 

Agrios AG, Pichat P. State of the art and perspectives on materials and applications of photocatalysis over Ti02. J Appl Electrochem 2005 35 655-63. 

This review concentrates on John Albery s work in the field of colloidal semiconductor photoelectrochemistry. John s major contributions to this area, as in so many others, have been through his astounding facility for generating useful asymptotic solutions for highly complex kinetic models of electrochemical systems. So as to put John s work in colloidal photoelectrochemistry into context. Sections 9.1-9.3 of this chapter provide a review of the more salient kinetic models of semiconductor photocatalysis developed over the last 20 years or so. Section 9.4 then concentrates on the Alberian view and presents, for the first time, John s model of the chronoamperometric behaviour of colloidal CdS. 

Bulk semiconductor photocatalysts (Section 4), such as TiC>2 and Ti02-containing materials (Sections 2.1 and 4), have continued to gain attention, because of their application to the electrochemical photolysis of water (Fujishima and Honda, 1972) and also because of their importance in photocatalysis (Anpo, 2005). 

Hattori, A., Y. Tokihisa, H. Tada and S. Ito (2000). Acceleration of oxidations and retardation of reductions in photocatalysis of a Ti02/Sn02 bilayer-type catalyst. Journal of the Electrochemical Society, 147(6), 2279-2283. 

Vinodgopal, K. and Kamat, P. V. (1995). Electrochemically assisted photocatalysis using nanocrystalline semiconductor thin-films. Solar Energy Mater. Solar Cells 38(1 4), 401 410. 

Light with supraband gap energy absorbed by a semiconducting particle (e.g., Ti02) can excite an electron from its valence band to the conduction band. This process also creates a positive hole in the valence band, which is an oxidizer and may react with adjacent oxygenated species to produce OH radicals. At the same time, the excited electron is capable of directly or indirectly reducing species in contact with the semiconductor. Such phenomena are electrochemical in nature—they are under intense study for application in the environmental remediation arena where they are globally called photocatalysis. 

B) Electrochemically-assisted photocatalysis As discussed above, photocatalytic processes are electrochemical in nature. A clever enhancement approach involves the application of a judiciously selected potential bias to a semiconductor electrode. The potential promotes a better charge-separation, thus decreasing the electron-hole recombination and increasing the yield of the target processes. This approach is called electrochemically... 

Ibanez, J. G. Mena-Brito, R. Fregoso-Infante, A., Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 8. Microscale Photocatalysis, J. Chem. Educ. 2005, 82, 1549-1551. 

One of the most prominent feature of polypyridine complexes is that they can be easily oxidized and reduced both photochemically and electrochemically. This opens an enormous potential for applications in photocatalysis (Section 5.4.9) and electrocatalysis. 

Thus, in general, a reduced and an oxidized product are obtained, in complete analogy with a classical electrochemical reaction. Except for a very few examples, almost all reactions photocatalyzed by semiconductors fall within this scheme and we have proposed to classify such reactions as semiconductor photocatalysis type A [45]. 

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