Coating processes – Electrical product produced – Welding electrode
Patent
1985-12-27
1987-08-04
Newsome, John H.
Coating processes
Electrical product produced
Welding electrode
2041575, 20415752, 427 541, 427215, B05D 306
Patent
active
046845372
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the sensitization of a semiconductor-based oxidation/reduction photocatalyst, to the photocatalyst thus obtained and also to the use of the said photocatalyst for the photooxidation of aqueous or aqueous-organic liquids or the photodecomposition of aqueous liquids in visible light. One of the purposes will be the photoproduction of hydrogen. The subject of the present invention is defined in the claims.
The immediate problem encountered with photoelectrochemical cells or with systems for the photochemical generation of hydrogen, especially systems based on solar energy conversion, is the efficiency of this energy conversion. A variety of solutions are currently being proposed to overcome this problem, such as modification of the surface of the photocatalyst with photoreactive dyes or doping of the said photocatalyst with suitable substances.
To solve the problems of the efficiency of solar energy conversion in applications such as the photodecomposition of aqueous liquids, it would be of interest to possess photocatalysts having a light absorption band in or near the visible region. It has been observed that, by forming a complex of titanium oxide (TiO.sub.2) using a complex of titanium and 8-hydroxyquinoline, it is possible to sensitize the particles of titanium oxide so as to enable them to be used in visible light [see in this connection J. Am. Chem. Soc. 105, 5695 (1983)]. However, the use of this type of photocatalyst is restricted by the fact that it is not possible to produce oxygen by the photodecomposition of water.
The object of the present invention is to purpose a sensitized photocatalyst which makes it possible to generate hydrogen and oxygen, with a satisfactory efficiency, by the photodecomposition of aqueous liquids in visible light. This is achieved by sensitizing a semiconductor-based oxidation/reduction photocatalyst by means of the process claimed.
It has in fact been discovered, surprisingly, that the desired effect is achieved by fixing to the surface of a semiconductor-based oxidation/reduction photocatalyst, such as titanium oxide, for example, a chromophore consisting of a fragment of a complex of a transition metal with a ligand of the bipyridyl or phenanthrolyl type.
According to the invention, the said chromophore most generally consists of a fragment of a ruthenium, chromium or iron complex, preferably a complex fragment of the formula: 2,2'-bipyridyl-4,4'-dicarboxylate. A chromophore of this type is perfectly stable under the conditions of use of the photocatalyst and causes the light absorption of the photocatalyst to shift beyond 600 nm. The stability of such as chromophore can be explained by the chemical fixation of the complex fragment: formation of Ru-O-Ti bonds as illustrated below: ##STR1## (L=diisopropyl 2,2'-bipyridyl-4,4'-dicarboxylate).
It has been found that a photocatalyst sensitized in this way makes it possible to obtain hydrogen, with a satisfactory efficiency, by irradiating aqueous or aqueous-organic liquids at a wavelength of between 590 and 665 nm. The photodecomposition of water to give hydrogen and oxygen respectively has been carried out just as efficiently.
According to the invention, the photocatalyst is sensitized by fixing the chosen chromophore to the surface of the semiconductor by any suitable method. In a preferred method of carrying out the process of the invention, the photocatalyst is irradiated in the presence of an acid aqueous solution of a complex of the formula: example, chlorine.
The TiO.sub.2 -based oxidation/reduction catalyst can advantageously be prepared by the methods described in the literature; the solution of the complex defined above can be obtained from commercial products.
For the irradiation, the chosen quantity of catalyst is suspended in a dilute aqueous solution of complex, which is of the order of 0.5 to 5.times.10.sup.-4 molar according to the particular case. If necessary, the pH of the solution is adjusted to the prescribed value, which is generally between 1 and 3, by the addit
REFERENCES:
patent: 4105517 (1978-08-01), Ryason
Duonghong Dung
Graetzel Michael
Serpone Nick
Newsome John H.
R. E. Stiftung
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