Water Cleavage Research Articles

Reduction of chlorinated hydrocarbons with natural sunlight in a platinum-catalyzed water photolysis system

Carbon tetrachloride and trichloroethylene in a water photolysis system (Pt colloid/Ru(bipy)/sub 3//sup 2 +//MV/sup 2 +//EDTA) were reduced to methane and/or ethane during solar illumination. This paper demonstrates that solar energy can be used to excite electron-transfer reactions in the system, which results in the cleavage of water to H/sub 2/ and OH/sup -/. Data suggest chlorinated hydrocarbons added to the system can be dechlorinated and subsequently reduced to low molecular weight hydrocarbons.

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.

Time resolved EPR on photosystem II particles after irreversible and reversible inhibition of water cleavage with high concentrations of acetate

Electron transfer in irreversibly acetate-inhibited PS II preparations from Synechococcus is investigated with EPR. A 1.4 mT wide EPR line with a decay rate consistent with the P + 680 Q − A back reaction is tentatively assigned to be a broadened P + 680 spectrum. With reversible inhibition of water cleavage by the ADRY reagent FCCP added with acetate electron transfer is studied as well. Under these conditions the spectrum of the immediate donor to P + 680 is the same as the spectrum of Z + in systems with irreversibly inhibited water cleavage (signal II fast) and the same as that of D + (signal II slow). The consequences are discussed.

Vectorial phototransfer of electrons across lipid membranes

Abstract

Visible light cleavage of water by CdS photoanode coated with polymer-pendant Ru(bpy) 2+3 film containing RuO 2 dispersions

Simultaneous formation of H 2 and O 2 by visible light cleavage of water was achieved using n-CdS photoanode coated with polymer-pendant Ru(bpy) 2+ 3 film containing RuO 2 dispersions. The Ru complex worked as a relay to transport the holes formed on the CdS surface to the RuO 2 catalyst where water oxidation takes place.

Biological Exploitation of Solar Energy by Photosynthetic Water Splitting

AbstractThe cleavage of water by solar radiation into dioxygen and metabolically bound hydrogen during photosynthesis is of central importance for the existence of higher forms of life on earth. The realization of this process in biological organisms made possible the use of the earth's huge water reservoir for the exploitation of solar energy and, at the same time, led to the creation of an aerobic atmosphere. The dioxygen thereby formed is a powerful oxidant which permits an energetically highly efficient nutrient turnover. In recent years considerable progress has been made in understanding the functional and structural organization of photosynthetic water splitting. This article attempts to give a review of our current state of knowledge with special emphasis on the oxidation of water to O2 in biological systems.

A Novel Route to Azaalkenylidene‐Metal Complexes

The oxime complexes 1 have structures analogous to imine complexes. Such oxime complexes have proven suitable as educts for the synthesis of azaalkenylidene complexes 2 of d‐electronrich transition metals. The cleavage of water from 1 with formal hydridic hydrogen and an N‐bonded OH‐group to give 2 proceeds remarkably smoothly [CRR′ = cyclohexylidene or CMe2; {Os} = (C6H6)(PMetBu2)Os]. equation image

Studies on the protolytic reactions coupled with water cleavage in photosystem II membrane fragments from spinach

The protolytic reactions of PSII membrane fragments were analyzed by measurements of absorption changes of the water soluble indicator dye bromocresol purple induced by a train of 10 μs flashes in dark-adapted samples. It was found that: a) in the first flash a rapid H(+)-release takes place followed by a slower H(+)-uptake. The deprotonation is insensitive to DCMU but is completely eliminated by linolenic acid treatment of the samples; b) the extent of the H(+)-uptake in the first flash depends on the redox potential of the suspension. In this time domain no H(+)-uptake is observed in the subsequent flashes; c) the extent of the H(+)-release as a function of the flash number in the sequence exhibits a characteristic oscillation pattern. Multiphasic release kinetics are observed. The oscillation pattern can be satisfactorily described by a 1, 0, 1, 2 stoichiometry for the redox transitions Si → Si+1 (i=0, 1, 2, 3) in the water oxidizing enzyme system Y. The H(+)-uptake after the first flash is assumed to be a consequence of the very fast reduction of oxidized Q400(Fe(3+)) formed due to dark incubation with K3[Fe(CN)6]. The possible participation of component Z in the deprotonation reactions at the PSII donor side is discussed.

Specific analysis of surface-bound peroxides formed during photoinduced water cleavage in titanium dioxide-based microheterogeneous systems

Photolysis of aqueous dispersions of TiO 2 (anatase) particles loaded with Pt leads to the generation of hydrogen and peroxide. In the pH range investigated (2 ⩽ pH ⩽ 10) the peroxide is entirely adsorbed at the particle surface, presumably in form of a titanium peroxo complex. Using o-tolidine as a redox indicator, we have developed a procedure which allows analysis of the peroxide.

Reaction Sequences from Light Absorption to the Cleavage of Water in Photosynthesis—Routes, Rates and Intermediates

AbstractThe reaction sequence between the primary electron acceptor, the oxidized Chlorophyll‐aII, and the terminal electron donor, the water splitting enzyme system S, is being described in the range from nanoseconds to milliseconds. For the cleavage of water Chlorophyll‐a+II extracts four electrons in four turnovers from the enzyme system S responsible for the water oxidation. For each extraction the electron is moved step by step along the chain that connects the Chlorophyll‐aII center with that of S. Beginning with the transfer from the immediate donor, D1 to Chl‐a+II, the subsequent transfer from D2 to D+I ends in the electron transfer from S to D2+. This final act establishes in S the oxidizing equivalent, probably in the form of oxidized manganese. Coupled with these acts is an intrinsic proton release and a surplus charge formation. After the generation of the 4th oxidizing equivalent in a concerted final action the evolution of O2 from water takes place. Correlations between the events are described quantitatively.

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

Reaction sequences from light absorption to the cleavage of water in photosynthesis

The reaction sequence between the primary electron acceptor, the oxidized Chlorophyll-aII, and the terminal electron donor, the water splitting enzyme system S, is being described in the range from nanoseconds to milliseconds. For the cleavage of water Chlorophyll-aII (+) extracts four electrons in four turnovers from the enzyme system S responsible for the water oxidation. For each extraction the electron is moved step by step along the chain that connects the Chlorophyll-aII center with that of S. Beginning with the transfer from the immediate donor, D1, to Chl-aII (+), the subsequent transfer from D2 to D1 (+) ends in the electron transfer from S to D2 (+). This final act establishes in S the oxidizing equivalent, probably in the form of oxidized manganese. Coupled with these acts is an intrinsic proton release and a surplus charge formation. After the generation of the 4th oxidizing equivalent in a concerted final action the evolution of O2 from water takes place. Correlations between the events are described quantitatively.

Total recovery of O2 evolution and nanosecond reduction kinetics of chlorophyll-a II + (P-680+) after inhibition of water cleavage with acetate

Oxygen evolution and reduction kinetics of the photooxidized Chl-aII (+) have been measured in oxygen-evolving complexes from the thermophilic cyanobacterium Synechococcus sp. 1. Incubation of PS II particles with acetate resulted in an inhibition of oxygen evolution and a retardation of the Chl-aII (+)=reduction kinetics from the nanosecond range to the microsecond range, indicating a modification of the donor side of photosystem II (PS II). 2. After the first two flashes given to a dark-adapted, acetate treated sample, Chl-aII (+) was re-reduced with a half-life time of 160 μs by a component of the donor side of PS II. Under repetitive excitation Chl-aII (+) was re-reduced in 500 μs by electron back reaction from the primary acceptor QA (-) (X-320(-)). Obviously, in the presence of acetate only two electrons are available from the donor side. 3. Both oxygen evolution and nanosecond reduction kinetics of Chl-aII (+) were restored to the control level when acetate was removed. 4. The results indicate a tight coupling between O2 evolution and nanosecond reduction kinetics of Chl-aII (+). 5. The reversible inhibition is probably due to a replacement of Cl(-) by acetate within the water splitting enzyme. 6. Due to its strongly retarded kinetics, the reversibly modified system may facilitate investigations of the mechanism of the donor side.

Sequence of the redox changes of manganese and pattern of the changes of charges during water cleavage in photosynthesis.

Sequence of the redox changes of manganese and pattern of the changes of charges during water cleavage in photosynthesis.

Evidence for the electrochromic identification of the change of charges in the four oxidation steps of the photoinduced water cleavage in photosynthesis

After dark adaptation of oxygen-evolving photosystem (PS) II complexes, oscillatory absorption changes (stable >0.5 s) with a period of 4 were previously detected at 514 nm, probably due to electrochromic band shifts of carotenoids [(1984) FEBS Lett. 176, 83-87]. To support this interpretation, we looked for corresponding phenomena in the 650–714 nm range. Here, oscillations were also observed with a difference spectrum giving evidence for an electrochromic band shift of the chlorophyll a absorption band. The oscillation pattern 0:0:+:+ corresponds to those at 514 nm, supporting the former conclusion that the states S 2 and S 3 have a surplus charge compared to S 0 and S 1. This is possible if the electron release pattern 1:1:1:1 is accompanied by an intrinsic proton release pattern 1:0:1:2 for the transition S 0 → S 1 → S 2 → S 3 → S 0.

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

Photosensitization of semiconductors with transition metal complexes - a route to the photoassisted cleavage of water

Development of artificial (non-biological) devices that achieve fuel generation by visible light is currently an ever growing area of research. Light driven redox reactions on organized assemblies afforded by semiconductor dispersions or colloidal sols provide the impetus. The various strategies used in achieving generation of dihydrogen, H 2, from the photodissociation of water are discussed. One important point that is made is dye sensitization of wide bandgap semiconductors to improve their spectral response to visible light. In practical terms, we present three examples from our recent work, in which the semiconductor particle surface (TiO 2) has been modified by adsorption of various dye molecules and by surface derivatization with ruthenium(II) complexes. In the latter case, we have demonstrated the feasibility of producing both H 2 and O 2 in stoichiometric amounts from the cleavage of water, and this without the need for a sacrificial electron donor.

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.

Oscillatory gas evolution during the visible-light-induced cleavage of water in platinum-free clay-hydroxide suspensions

The visible light irradiation of a mixed colloidal system prepared from sepiolite—Ru(bpy) 3 2+RuO 2 (bpy  2,2′-bipyridine) composite particles and Al x Eu 1− x (OH) 3 gels leads to the oscillatory evolution of hydrogen and oxygen. With respect to the previously reported results obtained with Al x Eu 1− x (OH) 3Pt, the following differences were obtained: (i) the amplitude of the oscillations and the total amount of gas are much smaller; (ii) the descending part of the oscillations is more gradual; (iii) the oscillations are no longer damped. All these features are related to the catalytic properties of platinum. The origin of the oscillations (either physical or chemical) is briefly discussed.