Showing papers by "Michael Grätzel published in 1984"
TL;DR: In this paper, electron transfer from the conduction band of CdS to that of TiO2 particles occurs in alkaline suspensions containing SH- ions and is exploited to improve the performance of a system that decomposes H2S with visible light.
Abstract: Electron transfer from the conduction band of CdS to that of TiO2 particles occurs in alkaline suspensions containing SH– ions and is exploited to improve the performance of a system that decomposes H2S with visible light.
246 citations
TL;DR: In this article, a lattice-defect model is invoked to explain the behavior of CdS particles in the presence of acceptors such as methyl viologen (MV2+): 10−8 mol dm−3 MV2+ suffices to quench 50% of the emission.
Abstract: Colloidal particles of CdS are produced by adding H2S to aqueous solutions of Cd(NO3)2(method 1) or rapid mixing of Na2S and Cd(NO3)2 solutions (method 2). Single crystals with cubic structure are obtained, their size being 50 and 20 A, respectively. Type 1 particles are associated as dimers or trimers while type 2 particles form larger clusters of 2000–3000 A size in aqueous solution.Luminescence studies, carried out mainly with type 1 sol, show the presence of a red emission (λmax≈ 700 nm) arising from sulphur vacancies and a very weak green fluorescence (λmax≈ 515 nm) due to free-carrier recombination. The red luminescence is extremely sensitive to the presence of acceptors such as methyl viologen (MV2+): 10–8 mol dm–3 MV2+ suffices to quench 50% of the emission. Kinetic analysis shows that only one MV2+ per CdS aggregate is required to quench completely the red luminescence. This effect is exploited to determine the aggregation number of CdS particles. MV2+ also induces a green emission (λmax≈ 530 nm, ϕ= 4 × 10–3) which is attributed to the formation of Cd vacancies.A green emission (λmax≈ 520 nm) is also obtained by substitutional doping of type 1 sol with chloride, and this arises from interstitial sulphur. Doping with Cu2+ produces the characteristic emission of this activator (λmax≈ 820 nm) only if particles are prepared under aerobic conditions or illuminated in the presence of oxygen. A lattice-defect model is evoked to explain this behaviour.
210 citations
TL;DR: In this article, the feasibility of direct probing of microscopic particles of semiconductor materials (TiO2, CdS and Se) suspended in a nonpolar liquid medium was demonstrated.
Abstract: The electronic properties of small particles of semiconducting materials have attracted considerable attention because they can mediate the photolytic decomposition of water1–6; a property which may prove useful in solar energy storage devices. Information about the initial electron–hole state formed on photolysis and the subsequent conduction and electron transfer processes occurring at the particle–solvent interface has previously been gained indirectly through steady-state and flash-photolysis studies of colloidal solutions that also contain well known electron donor and/or acceptor molecules. A more direct, ‘electrical’ method of probing such systems might be expected to lead to a more detailed understanding of the primary photoionization event and the ensuing bulk and surface electronic processes. We demonstrate here the feasibility of such direct probing of microscopic particles of semiconductor materials (TiO2, CdS and Se) suspended in a nonpolar liquid medium.
50 citations
TL;DR: In this paper, the steric effects arising from steric factors cause significant differences in the absorption and emission spectra and triplet lifetimes of the title porphyrin systems as compared to their non-methyl-substituted analogs.
41 citations
TL;DR: In this paper, band gap illumination of TiO2 (anatase) dispersions in weakly alkaline solutions of nicotinamide-adenine-dinucleotide (NAD+) leads was investigated.
Abstract: — Band gap illumination of TiO2 (anatase) dispersions in weakly alkaline solutions of nicotinamide-adenine-dinucleotide (NAD+) leads in the presence of rhodium trisbipyridyl complex [Rh(bipy)3+3], to continuous generation of biologically active cofactor NADH. Effects of pH, NAD+ and Rh(bipy)3+3 concentration on the efficiency of this photoconversion process are investigated. The reaction proceeds already in aqueous solution in the absence of external electron donors but it is enhanced significantly in the presence of 10% methanol.
37 citations
TL;DR: In this article, the phase distribution and kinetics of phase exchange were derived for TTF in aqueous/CTAC micellar solution, comprising cyclic voltammetry and rotating disc kinetic studies.
33 citations
01 Jan 1984
TL;DR: In this article, the authors present a Web of Science Record created on 2006-02-21, modified on 2017-05-12 for the LPI-ARTICLE-1984-015.
Abstract: Reference LPI-ARTICLE-1984-015View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12
31 citations
TL;DR: In this article, a review of the research in the area of photochemical conversion and storage of solar energy has been presented, focusing on several areas such as H2, O2 production from water in homogeneous dye-based systems using redox catalysts, studies related to characterisation of catalysts and mechanism of their operation, heterogeneous photocatalysis and photodissociation of water using semiconductor dispersions and colloids, photogalvanic and photoelectrolysis-galvanic cells, dye-sensitization phenomena and other related topics
Abstract: Research activity in the area of photochemical conversion and storage of solar energy has grown enormously in recent years and currently involves interdisciplinary efforts from many areas such as photochemistry, electrochemistry, catalysis, solid state chemistry and photobiology. The coverage of this review is restricted to publications which appeared in the year 1983 and is discussed under several areas: H2, O2 production from water in homogeneous dye-based systems using redox catalysts, studies related to characterisation of catalysts and mechanism of their operation, heterogeneous photocatalysis and photodissociation of water using semiconductor dispersions and colloids, photogalvanic and photoelectrolysis-galvanic cells, dye-sensitization phenomena and other related topics. Photoelectrochemical studies with semiconductor electrodes (both for the conversion of visible light to electrical energy in regenerative cells and for direct photogeneration of useful chemicals) is one of the major areas in the photochemical solar energy conversion. The present coverage excludes a discussion of all such studies, except to provide a classified, annotated bibliography in the appendix. Fortunately, monitoring of the progress in the area of photochemical solar energy conversion is facilitated by the appearance of several review articles (Calvin, 1983a,b; Fox, 1983; Gratzel, 1983a; Harriman, 1983; Kutal, 1983; Gurevich and Pleskov, 1983; Zamarev and Parmon, 1983) and monographs (Claesson and Holmstrom, 1982; Gratzel, 1983b). There are numerous studies which can play a very important role in the eventual design of photochemical devices for the solar energy conversion which are again omitted in this coverage. These include studies on the improving of the efficiency of charge separation and the prevention of back reactions in photoredox quenching of molecular excited states-both by synthesis of novel sensitizers with appropriate tuning of ground, excited state properties and by the use of various organised assemblies such as micelles, vesicles, polymers, polyelectrolytes, microemulsions, monoand multilayer assemblies, and other multiphase systems such as cyclodextrins, clays, zeolites, etc. Similarly, mention should be made of various photobiological model systems for energy conversion: studies with isolated chloroplasts, chlorophyll or porphyrinquinone complexes, reaction center preparations, enzymes either as isolated ones or immobilised on various supports for water reduction and oxidation. There appears to be a very low level of activity on studies of photochemical energy storage via valence isomerisation (Childs et al., 1983; Jones et al., 1983: Olmsted et al., 1983; Philippopovlos et al., 1983). Porter has addressed the question of thermodynamic efficiency limits for a photochemical system that converts visible light into chemical potential (Porter, 1983).
31 citations
TL;DR: In this paper, it was shown that surface-bound peroxo titanium complexes are formed during photolytic water cleavage in closed systems and as aresult of oxygen photo-uptake.
Abstract: 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.
27 citations
TL;DR: The activity of TiO2 particles for photocatalytic oxygen evolution in the presence of Ag+ ions as an electron acceptor is increased 10 times by the removal of surface hydroxy groups through thermal treatment.
Abstract: The activity of TiO2 particles for photocatalytic oxygen evolution in the presence of Ag+ ions as an electron acceptor is increased 10 times by the removal of surface hydroxy groups through thermal treatment.
27 citations
TL;DR: In this article, the authors presented a method to construct an LPI-ARTICLE-1984-011, which is used in the Web of Science Record (WORR).
TL;DR: In 2 O 3 powder has a band gap of 2.5 ± 0.2 eV as derived from reflectance spectroscope as mentioned in this paper, where the conduction band position of these partic
TL;DR: In this paper, two TiO 2 anatase powders have been derived by silanization followed by quaternization of 1-methyl-4,4′-bipyridyl.
TL;DR: In this article, the photocatalytic cleavage of H2S in alkaline aqueous media and mediated by irradiation of low band-gap (2.4 eV) semiconductor dispersions of CdS is described.
Abstract: Processes are described which are of potential interest in solar energy conversion devices. In particular, reference is made to the photocatalytic cleavage of H2S in alkaline aqueous media and mediated by irradiation of low band-gap (2.4 eV) semiconductor dispersions of CdS. Hydrogen evolution is sustained for longer periods in the presence of SO32- to produce S2O32-. We review here some of our recent work and indicate a possible cyclic system that might prove useful in converting the sun's energy to useful fuels (H2) and chemicals (S2O32-). Moreover, this process has the added advantage of attacking yet another problem, namely that of disposing of two significant environmental pollutants, H2S and SO2.
01 Jan 1984
TL;DR: In this article, the authors studied the characteristics of various catalytic systems capable of generating H by water-photolysis, including completely biological sytems where natural electron carriers such as ferredoxin, flavodoxin, cytochrome c3 or NAD reduced by illuminated chloroplasts are coupled to hydrogen3ses, and semibiological systems where photosynthetically reduced natural or synthetic electron relays (e.g. viologens, metatungstate, cobalt complexes, etc.) are coupled with hydrogenase or Pt for H2 production.
Abstract: We have been studying the characteristics of various catalytic systems capable of generating H by water-photolysis. These include (a) completely biological sytems where natural electron carriers such as ferredoxin, flavodoxin, cytochrome c3 or NAD reduced by illuminated chloroplasts are coupled to hydrogen3ses; (b) semibiological systems wherein photosynthetically reduced natural or synthetic electron relays (e.g. viologens, metatungstate, cobalt complexes, etc.) are coupled to hydrogenase or Pt for H2 production and (c) completely artificial systems using semiconductors, (TiO , RuO , CdS, etc.) as photo and redox catalysts for the photogener2ation 2f H2 by coupling to Pt (see Cuendet, Gratzel 1982a, Rao, Hall 1983). At present we are concerned with the stabilisation of the H generating system and also with the optimisation of the electron an2d proton transfer reactions to achieve the maximum light and catalytic conversion efficiencies. With this objective we are studying (a) the effect of various additives to the medium, (b) the effect of entrapment of photosynthetic membranes in polyurethane, and (c) the efficiency of different synthetic relays on the rate and longevity of H evolution reaction.