Photochemical Cleavage Of Water Research Articles

Computer simulations of photochemical water cleavage systems. 2. Effects of particle size and ion concentration on the production of hydrogen from water mediated with a colloidal catalyst

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComputer simulations of photochemical water cleavage systems. 2. Effects of particle size and ion concentration on the production of hydrogen from water mediated with a colloidal catalystPierre M. Lenoir, Richard E. Sassoon, and John J. KozakCite this: J. Phys. Chem. 1988, 92, 9, 2526–2536Publication Date (Print):May 1, 1988Publication History Published online1 May 2002Published inissue 1 May 1988https://doi.org/10.1021/j100320a027RIGHTS & PERMISSIONSArticle Views34Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Podanden, Coronanden und Kryptanden als neue Komplex-Liganden für Photoelektronentransfer-Reaktionen Synthese und erste photophysikalische Studien / Podands, Coronands and Cryptands as New Complex-Ligands in Photoeleetron Transfer Reactions Synthesis and Photophysical Studies

Podands, coronands and cryptands containing 2,2′-bipyridine-units were synthesized. These Compounds can be used as ligands in Ru(II)-polypyridinecomplexes. This new route principally allows the preparation of tris-heteroleptic complexes using the appropriate cryptands. Ru(II)- polypyridines RuL3 2+ (e.g. Ru(bpy)3 2+) are interesting as sensitizers in photochemical water cleavage. Compared to Ru(bpy)3 2+, the photoanationrate should be reduced in the Ru(cryp)2+ complex.

Computer simulations of photochemical water cleavage systems. 1. A kinetic model for the production of hydrogen on a colloidal catalyst

A mechanism is proposed for the colloidal-catalyst-mediated reduction of water to hydrogen by a reduced electron acceptor. Adsorption of several of the reactants is invoked, and electrons, hydrogen atoms, hydride ions, and molecular hydrogen, all adsorbed on the colloids, are suggested as probable intermediates. Adsorption of H/sup +/ and OH/sup -/ ions onto the catalyst surface at appropriate pH's is also postulated and electrostatic factors are introduced to account for the total electrical charge carried by the colloid. Computer simulations were performed for the change in concentration with time of the reduced methylviologen cation radical, MV/sup +/, in the presence of a colloidal platinum catalyst over the pH range 1-11, the range investigated in earlier pulse radiolysis studies. Values of the rate constants for the individual steps in the reduction process, obtained by optimizing the fits of the computer-simulated decays and growths with those obtained experimentally, are given. The changes occurring with time in the chemical system in the pH range 1-11 are described in detail. The effects on the computer-simulated plots of varying several of the parameters of the system such as the initial concentration of MV/sup +/, the concentration of methylviologen, MV/sup 2 +/, and the concentration ofmore » platinum are also described and in most cases good agreement is obtained with experiment. In particular, deviations from a first-order dependence of the rate of decay of MV/sup +/ on colloid concentration were found in their computer simulations similar to those found experimentally, and are attributed to changes in the coverage of the colloidal particles by adsorbed species as the concentration of catalyst is varied. Possible future refinements to their proposed model are also discussed briefly.« less

A new photosensitizer—catalyst for the photochemical cleavage of water

Decomposition de l'eau, par le complexe Ni(II) bis-[chloro-2 dithiobenzyl] en presence d'EDTA et de methyl viologene

Separation of photoredox products by local potential fields

Polyelectrolytes, ion exchangers and charged colloids can be used to control the rates of photo-induced chemical reactions. In particular, polyelectrolytes possess several additional features which make them attractive as suitable microassemblies in such systems. These include a well-defined structure whose properties of size, shape, charge density etc. may be modified by conventional synthetic techniques, the possibility of attaching specific molecular chromophores chemically to a polyelectrolyte such that they possess the desired properties ( e.g. light absorption, redox potential, solubility etc.) and their possible adsorption to colloidal catalysts and electrodes. Special emphasis on charge separation and the inhibition of photochemical back reactions by polyelectrolytes is therefore made. Charge separation effects are critically reviewed. Large effects on the quantum yields of photochemical electron transfer products are reported. The reactions of zwitterionic quenchers with excited photosensitizers in the presence of polyelectrolytes or charged colloids are also described in which there seems to be a lack of microenvironmental effect on the quantum yields of charge separation. The possible reasons for this are discussed. In general, back reactions are expected to be inhibited in the presence of polyelectrolytes when one of the reacting species lies in the polymer field and the other is an ion bearing the same charge as the polyion. However, the inhibition effect is usually found to be only of one or two orders of magnitude. On the basis of pulse radiolytic measurements of the rate of bimolecular reactions of polyelectrolyte radicals, it can be concluded that polyelectrolytes may lead to the inhibition of back reactions by up to five or six orders of magnitude if the two photochemical transient species are bound to different polyelectrolyte molecules carrying the same electric charge. A photochemical system which fulfils the conditions is described, and ways in which to apply such systems to the photochemical cleavage of water are discussed.

Reply to the Comment on "Factors affecting the efficiency of photochemical water cleavage systems. The reaction between molecular oxygen and the reduced electron acceptor"

Reply to the Comment on "Factors affecting the efficiency of photochemical water cleavage systems. The reaction between molecular oxygen and the reduced electron acceptor"

Optimization of conditions for photochemical water cleavage. Aqueous platinum/TiO2 (anatase) dispersions under ultraviolet light

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOptimization of conditions for photochemical water cleavage. Aqueous platinum/TiO2 (anatase) dispersions under ultraviolet lightJ. Kiwi and M. GraetzelCite this: J. Phys. Chem. 1984, 88, 7, 1302–1307Publication Date (Print):March 1, 1984Publication History Published online1 May 2002Published inissue 1 March 1984https://doi.org/10.1021/j150651a012RIGHTS & PERMISSIONSArticle Views813Altmetric-Citations137LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1009 KB) Get e-Alerts

Factors affecting the efficiency of photochemical water cleavage systems. The reaction between oxygen and the reduced electron acceptor

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFactors affecting the efficiency of photochemical water cleavage systems. The reaction between oxygen and the reduced electron acceptorThomas W. Ebbesen, Bhalachandra L. Tembe, and John J. KozakCite this: J. Phys. Chem. 1984, 88, 4, 683–688Publication Date (Print):February 1, 1984Publication History Published online1 May 2002Published inissue 1 February 1984https://doi.org/10.1021/j150648a014RIGHTS & PERMISSIONSArticle Views65Altmetric-Citations5LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (759 KB) Get e-Alerts

Colloidal TiO2particles as oxygen carriers in photochemical water cleavage systems

By using the redox indicators o-dianisidine and o-toluidine as regents for quantitative analysis, it is shown that in colloidal TiO2–Pt dispersions surface-bound peroxo titanium complexes are formed during photolytic water cleavage in closed systems and as aresult of oxygen photo-uptake.

Photochemical water cleavage: a simple kinetic analysis

We present a simple kinetic model for cyclic water cleavage by a system containing an aqueous solution of a sensitizer, an electron acceptor and two specific catalysts. We illustrate quantitatively how the hydrogen production rate is affected by various parameters such as the concentrations of the solutes, the pH of the solution, the partial pressure of oxygen and hydrogen, the efficiencies of the catalysts, the irradiation intensity and the redox potential of the acceptor. The maximum achievable Φ H 2 is calculated for various operating conditions.

Photosensitised dissociation of water using dispersed suspensions of n-type semiconductors

n-Type semiconductor powders (TiO2 and SrTiO3) were used to sensitise the photochemical cleavage of water using u.v. light (λ < 400 nm) under conditions of room temperature and pressure. Although several methods of platinising these powders were used, one method in particular (involving precipitation of a platinum sol, by addition of an inert electrolyte, in the presence of the semiconductor powder) was found to produce an efficient photocatalyst for water reduction. Many different photocatalysts were tested for water reduction activity, using EDTA as an electron donor, and for water oxidation activity, using Fe3+ as an electron acceptor. In the absence of EDTA and Fe3+, u.v. irradiation of these photocatalysts liberated H2 but O2 evolution was not observed. Reasons for these observations are discussed.

Photochemical cleavage of water by photocatalysis

A bifunctional redox catalyst, composed of Pt and RuO2 co-deposited on a colloidal TiO2 carrier, is a highly potent mediator for water decomposition by visible light1. The system contains apart from the sensitizer (Ru(bipy)2+3) an electron relay—methylviologen. The latter is reduced on light excitation, and the photoreaction is coupled with catalytic steps2 generating H2 and O2 from water. To rationalize the surprisingly high efficiency of this photoredox system, we proposed a mechanism involving species adsorbed at the TiO2 surface. This led us to explore sensitizers which through suitable functionalization show an enhanced affinity for adsorption at the particle–water interface. We describe here the performance of electron relay-free systems capable of efficiently decomposing water into H2 and O2 under visible light illumination. A bifunctional redox catalyst composed of RuO2 and Pt co-supported on colloidal TiO2 particles is used. The only other component present is a sensitizer. Amphiphilic surfactant derivatives of Ru(bipy)2+3 exhibit extremely high activity in promoting the water cleavage process. Adsorption of the sensitizer at the TiO2 particle–water interface and electron ejection into the TiO2 conduction band are evoked to explain the observations. Exposure to UV radiation leads to efficient water cleavage in the absence of sensitizer.

Phatolysis of Water Catalyzed by Transition Metal Dithiolenes

The photoreduction of water processing in neutral solution in the presence of transition metal dithiolene complexes (lambda max approx. 800 nm) is reported. The mechanism of this novel photochemical cleavage of water is still unknown.

Electron Transfer in Monolayer Assemblies with Incorporated Ruthenium (II) Complexes

AbstractAn arrangement for light induced vectorial charge separation is discussed in which the electron of the excited dye is transferred to an acceptor and the dye is recovered by electron tunneling through a high and narrow potential barrier. The possible relevance of the model in connection with photosynthesis is considered. Monolayers of Ru(II)‐bipyridine complexes with long chain hydrocarbon substituents were investigated which may be useful as component in such arrangements.The surface pressure area isotherms of the monolayers were measured for various ionic compositions of the subphase, and the results demonstrate a strong effect of these ions on the structure of the layers. The layers were deposited on different substrates. The luminescence and its change by contacting the sample with water and by subsequent drying were found to be strongly dependent on the architecture of the layer assembly. Attempts of a photochemical cleavage of water with these assemblies failed.The pH‐dependence of the absorption and the luminescence of a Ru(II) bipyridine‐dicarboxylic acid complex in solution is interpreted by assuming that the electron in the excited state is localized in one pyridine part of the substituted ligand, the conjugation with the second half of the bipyridine carboxylic acid being negligible. Monolayer assemblies for measuring the energy transfer from the ruthenium complex to an adequate energy acceptor and from an adequate energy donor to the ruthenium complex were investigated. The results demonstrate that the deactivation of the excited ruthenium complex occurs mainly by passing the luminescent state.Assemblies were investigated for measuring the electron transfer from the excited ruthenium complex to an appropriate electron acceptor positioned in the carboxylate portion at the same interface as the electron donor. With bipyridinium ions as acceptor the ruthenium complex luminescence is quenched at average distances between acceptor molecules of about 10 Å, while this distance is 30, 60 und 75 Å for different cyanine dyes used instead of the ruthenium complex. A correlation between this distance and the ionization energy in the excited state of the donor is observed.

Photochemical reactions in organized monolayer assemblies. III. Photochemical cleavage of water: a system for solar energy conversion using monolayer-bound transition metal complexes

A monolayer film of dilute chloroform solutions of surfactant analogues of tris (2,2'-bipyridine) ruthenium(II)/sup 2 +/ spread on a water-air interface were used to study the photochemical cleavage of water. When the monolayer assemblies were immersed in water and irradiated with a mercury lamp, a steady production of gas (concluded to be O/sub 2/ and H/sub 2/) was observed. This method of preparing O/sub 2/ and H/sub 2/ appears to be an extremely promising means of solar energy conversion. (DDA)

Photochemical Cleavage of Water by Riboflavin. II. Role of Activators

Photochemical Cleavage of Water by Riboflavin. II. Role of Activators