Photocatalytic water reduction with copper-based photosensitizers: a noble-metal-free system.

Of noble descent: a fully noble-metal-free system for the photocatalytic reduction of water at room temperature has been developed. This system consists of Cu(I) complexes as photosensitizers and [Fe(3)(CO)(12)] as the water-reduction catalyst. The novel Cu-based photosensitizers are relatively inexpensive, readily available from commercial sources, and stable to ambient conditions, thus making them an attractive alternative to the widely used noble-metal based systems.

Water oxidation with molecularly defined iridium complexes: insights into homogeneous versus heterogeneous catalysis.

Molecularly defined Ir complexes and different samples of supported IrO(2) nanoparticles have been tested and compared in the catalytic water oxidation with cerium ammonium nitrate (CAN) as the oxidant. By comparing the activity of nano-scaled supported IrO(2) particles to the one of organometallic complexes it is shown that the overall activity of the homogeneous Ir precursors is defined by both the formation of the homogeneous active species and its conversion to Ir(IV)-oxo nanoparticles. In the first phase of the reaction the activity is dominated by the homogeneous active species. With increasing reaction time, the influence of nano-sized Ir-oxo particles becomes more evident. Notably, the different conversion rates of the homogeneous precursor into the active species as well as the conversion into Ir-oxo nanoparticles and the different particle sizes have a significant influence on the overall activity. In addition to the homogeneous systems, IrO(2)@MCM-41 has also been synthesized, which contains stabilized nanoparticles of between 1 and 3 nm in size. This latter system shows a similar activity to IrCl(3)⋅xH(2)O and complexes 4 and 5. Mechanistic insights were obtained by in situ X-ray absorption spectroscopy and scanning transmission electron microscopy.

Laboratory enamel fluoride uptake from fluoride products.

PURPOSE: To evaluate the fluoride concentration in enamel after the use of different fluoride products and 48 hours after the cessation of fluoride use. METHODS: 16 enamel slabs were divided and treated for 15 days as following: Group A, with an amine fluoride toothpaste and mouthrinse (1400 and 250 mg/L(-1), respectively); Group B, with an amine fluoride toothpaste (1400 mg/L(-1)) and mouthrinse without fluoride; Group C, with a sodium fluoride toothpaste (1400 mg/L(-1)) and mouthrinse (250 mg/L(-1)). Chemical biopsy and multiple means were used to determine fluoride concentration. The data were statistically analyzed using the two-way ANOVA and Tukey HSD tests (P<0.05). RESULTS: After 15 days of fluoride product use, Group A samples had the highest fluoride uptake (0.19 microg mm(-2)) (P<0.05). 48 hours after the interruption of fluoride product usage, a higher fluoride concentration was found in Group A samples. Although all fluoride products led to an enamel uptake, amine fluoride products promoted the most effective long-term uptake.

Synthesis and characterization of new iridium photosensitizers for catalytic hydrogen generation from water.

Novel phenylazole ligands were applied successfully in the synthesis of cyclometalated iridium(III) complexes of the general formula [Ir(phenylazole)(2)(bpy)]PF(6) (bpy=2,2'-bipyridine). All complexes were fully characterized by NMR, IR, and MS spectroscopic studies as well as by cyclic voltammetry. Three crystal structures obtained by X-ray analysis complemented the spectroscopic investigations. The excited-state lifetimes of the iridium complexes were determined and showed to be in the range of several hundred ns to multiple µs. All obtained iridium complexes were active as photosensitizers in catalytic hydrogen evolution from water in the presence of triethylamine as a sacrificial reducing agent. Applying an in situ formed iron-based water reduction catalyst derived from [HNEt(3)](+) [HFe(3)(CO)(11)](-) and tris[3,5-tris-(trifluoromethyl)-phenyl]phosphine as the ligand, [Ir(2-phenylbenz-oxazole)(2)-(bpy)]PF(6) proved to be the most efficient complex giving a quantum yield of 16% at 440 nm light irradiation.

Hydrogen evolution from water/alcohol mixtures: effective in situ generation of an active Au/TiO2 catalyst.

Gold standard: Au/TiO(2) catalysts, easily prepared in situ from different Au precursors and TiO(2), generate hydrogen from water/alcohol mixtures. Different alcohols, and even glucose, can serve as sacrificial reductants. The best system produces hydrogen on a liter scale, and is stable for more than two days. Deuteration studies show that proton reduction is likely the rate-limiting step in this reaction.