Showing papers by "Michael Grätzel published in 1980"

Photophysical and Photochemical Processes in Micellar Systems

Abstract: Reference LPI-ARTICLE-1980-008View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Light Induced Redox Reactions of Water Soluble Porphyrins, sensitization of hydrogen generation from water by zincporphyrin derivatives

Abstract: The photoredox behaviour of two water soluble derivatives of zincporphyrin, 5,10,15,20-tetra-p-sulfonatophenyl (1) and 5,10,15,20-tetra-p-N-methylpyridiniochloride (2), was investigated using laser and continuous photolysis techniques. Photoexcitation produces triplet states whose lifetimes in aqueous solution exceeds 1 ms. These triplet states can be quenched reductively by donors such as EDTA and oxidatively by acceptors such as methylviologen (MV2+). Electron transfer to MV2+ is greatly influenced by the charge of the porphyrin, rate constants being 1.4 x 1010M−1S−1 and 2 × 106M−1S−1 for 1 and 2, respectively. In the presence of colloidal Pt catalyst, the cationic porphyrin sensitizes photoreduction of water to hydrogen with remarkable efficiency.

Photochemical methods for the conversion of light into chemical energy

Abstract: This paper is concerned with reaction systems in which fuel production is achieved by illumination of aqueous solutions. Research interest in this field focusses on photoredox reactions in which R and S are solutes of which one is excited by light. Major problems to overcome for practical use of these systems are the retardation of the back reaction and the back conversion of R− and S+ under production of a fuel. To accomplish the production of the back reaction microscopically, heterogeneous solutions containing molecular assemblies such as micelles or vesicles have been employed. Here, through judicious choice of the molecular system, in particular the use of functional electron relays, charge separation can be achieved. This concept has been coupled with the use of colloidal redox catalysts to bring about hydrogen and oxygen formation from water Systems which produce hydrogen and/or oxygen from water through illumination with visible light will be reviewed and most recent experimental results from our and other laboratories discussed. Diese Arbeit behandelt Reaktionssysteme, bei denen die Brennstofferzeugung durch Belichtung wasriger Losungen erreicht wird. Das Hauptinteresse der Forschung konzentriert sich in diesem Gebiet auf Photoredoxreaktionen bei denen R und S geloste Stoffe sind, von denen einer durch Licht angeregt wird. Grosere Probleme, die fur die praktische Anwendung dieser Systeme bewaltigt werden mussen, sind die Verzogerung der Ruckreaktion und die Ruckumwandlung von R− und S+ bei der Produktion eines Brennstoffes. Um die Ruckreaktion verschwindend klein zu halten, wurden heterogene Losungen, die molekulare Systeme wie Mizellen oder Vesikeln enthalten, verwandt. Hier kann durch eine zweckentsprechende Wahl des molekularen Systems, insbesondere durch die Verwendung von funktionellen Elektronenschaltstellen, die Ladungstrennung erreicht werden. Dieses Konzept wurde mit dem Einsatz kolloidaler Redoxkatalysatoren zur Bildung von Wasserstoff und Sauerstoff aus Wasser gekoppelt. Es wird ein Uberblick uber Systeme, die bei Belichtung mit sichtbarem Licht Wasserstoff und/oder Sauerstoff erzeugen, gegeben, und die neuesten experimentellen Ergebnisse aus unserem und anderen Laboratorien werden diskutiert.

Cyclic Water Cleavage by Visible Light: Drastic Improvement of Yield of H2 and O2 with Bifunctional Redox Catalysts†

Abstract: The performance of a new cofunctional redox catalyst which achieves astonishingly high quantum yields in the water splitting process is described. The new catalyst contains Pt and RuO/sub 2/ codeposited on a common carrier, i.e., colloidal TiO/sub 2/.

LIGHT‐DRIVEN REDOX PROCESSES IN FUNCTIONAL MICELLAR UNITS—III. Zn‐TETRAPHENYLPORPHYRIN SENSITIZED REACTIONS IN METHYL VIOLOGENE SURFACTANT ASSEMBLIES

Abstract: — The photoreduction of methyl viologene by ZnTPP triplet excited states was studied in mixed micelles containing the functional surfactant JV-dodecyl, N-methyl viologene (C12MV2+) as one and Cetyltrimethylammoniumchloride (CTAC) as the other component. Using the laser photolysis technique the kinetics of the redox reaction were studied at various CTAC/C12MV2+ ratios. The average time for the electron transfer decreases linearly with the C12MV2+ occupancy. The back transfer from C12MV2+ to ZnTPP2+ can be intercepted if a donor such as NADH is cosolubilized in the micelle. In such a system irreversible methyl viologene reduction is achieved which in the presence of a suitable redox catalyst can be used to produce hydrogen from water.

Ruthenium Dioxide Electrodes as Suitable Anodes for Water Photolysis

Abstract: This paper presents a cell system in which a photoinduced redox reaction occurs in the cathodic compartment which is coupled to a RuO2-anode. The light induced oxidation of the ruthenium complex Ru (bipy) by peroxodisulfate is used to illustrate that even under diffuse room light irradiation the photopotentials developed at the Pt-cathode are sufficient to afford water oxidation in the anode compartment. The oxygen produced at the RuO2-electrode stands in a stochiometric relation to the current passed through the circuit. Implications for a cell system in which H2 and O2 are produced in separate compartments under illumination are discussed.