Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Solar Energy”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed2006

Mechanisms for photogeneration and recombination of multiexcitons in semiconductor nanocrystals: implications for lasing and solar energy conversion.

One consequence of strong spatial confinement of electronic wave functions in ultrasmall semiconductor nanocrystals is a great enhancement of carrier-carrier interactions, which has a dramatic effect on the spectral and dynamical properties of both single and multiexciton states. Strong carrier-carrier interactions open new nanocrystal-specific energy relaxation and recombination channels associated, e.g., with electron-hole energy transfer and ultrafast nonradiative Auger recombination. Further, they lead to extremely efficient direct photogeneration of multiple electron-hole pairs (excitons) by single photons known as carrier (or exciton) multiplication. This review focuses on the effect of Coulomb interactions on carrier recombination and photogeneration mechanisms in nanocrystals based on II-VI (e.g., CdSe) and IV-VI (e.g., PbSe) compounds. The specific topics discussed here include the fine structure of the band-edge optical transitions and its effect on temperature-dependent single-exciton recombination dynamics, Auger recombination of multiexcitons in size- and shape-controlled nanocrystals with a specific emphasis on optical-gain properties of nanocrystalline materials (including quantum rods and multicomponent core-shell heterostructures), and the direct generation of multiple excitons via carrier multiplication and its implications in photovoltaic technologies.

Journal Article↗
PubMed1975

Reaction of tris(bipyridine)ruthenium(III) with hydroxide and its application in a solar energy storage system.

Irradiation of Ru(bipy)(3) (2+) (bipy = 2,2'-bipyridine) with light below 560 nm results in the formation of a charge-transfer excited state potentially capable of reducing water to dihydrogen with concomitant production of Ru(bipy)(3) (3+). The latter may be reduced by hydroxide [Formula: see text] to form dioxygen and regenerate the starting complex. The use of these reactions in a cell designed to bring about the photochemical decomposition of water is proposed.The stoichiometry, kinetics, and mechanism of the Ru(bipy)(3) (3+)-hydroxide reaction have been investigated by conventional and stopped-flow spectrophotometry. The dioxygen yield is a sharp function of pH, attaining its maximum value (about 80%) at pH 9. At low pH (3 and 4.8) the production of ruthenium(II) is first order with k(obsd) = (1.41 +/- 0.04) x 10(-4) sec(-1) (25 degrees , ionic strength mu = 1.00 M with sodium sulfate). In the intermediate pH range (7.9-10.0) complex kinetics are observed. In the hydroxide range 0.01-0.50 M, ruthenium(II) production is predominantly first order with k(obsd) = k(a)[OH(-)] + k(b)[OH(-)](2) sec(-1); k(a) = 148 M(-1) sec(-1) and k(b) = 138 M(-2) sec(-1) (25 degrees , mu = 1.00 M, sodium sulfate). For the k(a) term, the activation parameters are DeltaH(double dagger) = 15.3 +/- 1.0 kcal mol(-1) and DeltaS(double dagger) = 7 +/- 3 cal deg(-1) mol(-1) (1 cal = 4.184 J). An intermediate species (lambda(max) 800 nm) forms at the same rate as ruthenium(II) in this hydroxide range. It disappears with k(obsd) = 1.2 + 1.1 x 10(2) [OH(-)] sec(-1) at 25 degrees . Similarly absorbing (lambda(max) 750 to 800 nm) species are generated by the addition of hydroxyl radical to M(bipy)(3) (2+/3+) [M = Fe(II), Os(II), Ru(II), Cr(III), Ru(III)] in pulse radiolysis experiments. The kinetics above pH 7 are described in terms of rate-determining nucleophilic attack by hydroxide on the bound bipyridine ring. The hydroxide adduct so generated is tentatively identified with that observed in the pulse radiolysis experiments with Ru(bipy)(3) (2+).For reduction of Ru(bipy)(3) (3+) by hydrogen peroxide ruthenium(II) production is first order with k(obsd) = k(c)[HO(2) (-)] + k(d)[H(2)O(2)] where k(c) = 5.4 x 10(7) M(-1) sec(-1) and k(d) = 8.3 M(-1) sec(-1) (25 degrees , mu = 1.00 M, pH 3.5 to 9.7). This reaction produces dioxygen in 83 +/- 15% yield at pH 6.8 and in 1.0 N sulfuric acid.

Journal Article↗
PubMed1998

[Efficiency of oxidant gas generator cells powered by electric or solar energy].

Diseases caused by microbial contaminants in drinking water continue to be a serious problem in countries like Mexico. Chlorination, using chlorine gas or chlorine compounds, is one of the best ways to treat drinking water. However, difficulties in handling chlorine gas and the inefficiency of hypochlorite solution dosing systems--due to sociopolitical, economic, and cultural factors--have reduced the utility of these chlorination procedures, especially in far-flung and inaccessible rural communities. These problems led to the development of appropriate technologies for the disinfection of water by means of the on-site generation of mixed oxidant gases (chlorine and ozone). This system, called MOGGOD, operates through the electrolysis of a common salt solution. Simulated system evaluation using a hydraulic model allowed partial and total costs to be calculated. When powered by electrical energy from the community power grid, the system had an efficiency of 90%, and in 10 hours it was able to generate enough gases to disinfect about 200 m3 of water at a cost of approximately N$8 (US $1.30). When the electrolytic cell was run on energy supplied through a photoelectric cell, the investment costs were higher. A system fed by photovoltaic cells could be justified in isolated communities that lack electricity but have a gravity-fed water distribution system.

Chlorine↗