Showing papers by "Michael Grätzel published in 1988"

Heterogeneous photochemical electron transfer

Abstract: The present monograph attempts to unify these diverse and exciting new developments within a common framework. First, the physical principles underlying heterogenous electron-transfer processes are outlined in a concise way and are compared to the homogeneous counterpart. This analysis includes the notion of the Fermi level in liquids and solids as well as the distribution of electronic energy levels in solids and liquids. A comparison is made between the salient kinetic features of homogeneous and heterogeneous electron transfer reactions. This establishes the basis for the subsequent treatment of the transduction of excitation energy and photo-initiated electron transfer in organized molecular assemblies, such as micelles, vesicles and monolayers. Transmembrane redox processes are critically reviewed. Particular attention is given to semiconductor electrodes and particles. This includes a discussion of quantum size effects, the nature of space charge layers as well as surface states and the dynamics of charge carrier-induced redox reactions at the semiconductor solution interface. These processes are of fundamental importance in such diverse fields as photochromism, electrochromic displays, electroreprography and photography, information storage, photocatalysis, photodegradation of paints, and solar energy conversion.

Effect of surface hydroxyl density on photocatalytic oxygen generation in aqueous TiO2 suspensions

Abstract: TiO2 powders with various surface hydroxyl densities have been prepared by thermal treatment (600–1000 °C), and their activity for photocatalytic oxygen evolution in aqueous suspensions has been investigated in the presence of various electron acceptors, i.e. AgNO3, K2PtCl4 and KBrO3. The activity increased drastically with the thermal treatment. The oxygen evolution rate was found to be inversely proportional to the surface concentration of OH–, indicating an inhibitory effect of surface hydroxyl groups with respect to photocatalytic oxygen evolution. On highly hydroxylated samples the formation of surface bound peroxides appears to be favoured over oxygen generation.

Room temperature photo-activation of methane on TiO2 supported molybdena

Abstract: Methane is activated at room temperature and atmospheric pressure on TiO2, supported molybdena catalyst excited by band gap illumination. With pure TiO2, complete oxidation to CO2 is observed in the presence of oxygen. The deposition of 4% molybdena has a pronounced effect on methane activation, partial oxidation to CO becoming a competing pathway. CO is the major oxidation product if TiO2 loaded with both MoO3 and H4SiW12O40 is used as a catalyst. MoO3 used alone or in conjunction -with A12O3 or SiO2 as carriers exhibits poor activity in the photoactivation of methane.

Spontaneous oxidation of water to oxygen by the mixed-valence µ-oxo ruthenium dimer L2(H2O)RuIII–O–RuIV(OH)L2(L = 2,2′-bipyridyl-5,5′-dicarboxylic acid)

Abstract: The mixed-valence µ-oxo ruthenium dimer L2(H2O)RuIII–O–RuIV(OH)L2, where L = 2,2′-bipyridyl-5,5′-dicarboxylic acid, converts spontaneously into L2(H2O)RuIII–O–RuIII(H2O)L2 under simultaneous oxidation of water to oxygen under conditions where the driving force of the reaction is less than 0.1 eV per transferred electron.

Preparation of SrTiO3 by sol–gel techniques for the photoinduced production of H2 and surface peroxides from water

Abstract: A method of preparing SrTiO3 by the citrate route and sol–gel freeze-drying technique is presented. These titanates have been produced at relatively low temperatures (550–600 °C) with surface areas up to 40 m2 g–1. The structure of the pure compounds obtained has been verified by X-ray diffraction. Increased photochemical activity to mediate H2 generation is observed for these materials as compared with available commercial samples. The influence of the preparative conditions on the catalysed H evolution has been explored. The concomitant anodic reaction was found to be oxidation of water to surface-bound peroxide. Characterization by surface area measurements (B.E.T.), carbon analysis, X-ray diffraction, diffuse reflectance spectroscopy (d.r.s.), conduction-band position measurements (c.b.) and electron microscopy (e.m.) have been carried out for the titanates under study.

Visible light sensitization of platinized TiO2 photocatalyst by surface-coated polymers derivatized with ruthenium tris(bipyridyl)

Abstract: Preparation de polymeres a base de polystyrene ayant des groupes et revetement du photocatalyseur par evaporation du solvant

Molecular water oxidation catalyst

Abstract: A dimeric composition of the formula: ##STR1## wherein L', L", L'", and L"" are each a bidentate ligand having at least one functional substituent, the ligand selected from bipyridine, phenanthroline, 2-phenylpyridine, bipyrimidine, and bipyrazyl and the functional substituent selected from carboxylic acid, ester, amide, halogenide, anhydride, acyl ketone, alkyl ketone, acid chloride, sulfonic acid, phosphonic acid, and nitro and nitroso groups. An electrochemical oxidation process for the production of the above functionally substituted bidentate ligand diaqua oxo-bridged ruthenium dimers and their use as water oxidation catalysts is described.

Efficient sensitisation of tio2 electrodes using transition metal charge transfer complexes

Abstract: The energy conversion efficiency of photoelectrochemical solar cells using those oxide semiconductor electrodes which are stable in contact with aqueous electrolytes is low because their wide band gaps do not permit a photoresponse to the visible spectrum. By adsorption of a sufficient quantity of a charge-transfer dye with intimate contact to the semiconductor, the electrode can be sensitised to visible radiation. Titanium dioxide electrodes were derivatised by attached ruthenium bis- and tris- bipyridyl and zinc porphyrin dyes and their efficiency as photoelectrochemical solar cell electrodes is reported.

Efficient special sensitisation of tio2 by surface derivatisation with transition metal cyanides

Abstract: Metallocyanide ions such as Fe II (CN) 4− 6 ,Ru II (CN) 4− 6 , Os II (CN) 4− 6 ,Re II (CN) 4− 6 , Mb IV (CN) 4− 8 and W IV (CN) 4− 8 form highly-coloured charge transfer complexes, by analogy with Prussian Blue, Fe 4 [Fe(CN) 6 ] 3 , on TiO 2 surfaces. When illuminated with light of photon energy less than the TiO 2 bandgap there is electron injection from the excited complex into the semiconductor conduction band. Photoelectrochemical systems in which TiO 2 electrodes and colloids are derivatised with these transition metal cyanide complexes are thereby sensitised to light in the visible part of the spectrum. Regenerative photoelectrochemical solar cell performance data are presented.