The Experts below are selected from a list of 304482 Experts worldwide ranked by ideXlab platform
J A Baldock - One of the best experts on this subject based on the ideXlab platform.
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assessing the extent of decomposition of natural Organic Materials using solid state 13c nmr spectroscopy
Soil Research, 1997Co-Authors: J A Baldock, J M Oades, Paul N Nelson, T M Skene, A Golchin, P ClarkeAbstract:Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy has become an important tool for examining the chemical structure of natural Organic Materials and the chemical changes associated with decomposition. In this paper, solid-state 13C NMR data pertaining to changes in the chemical composition of a diverse range of natural Organic Materials, including wood, peat, composts, forest litter layers, and Organic Materials in surface layers of mineral soils, were reviewed with the objective of deriving an index of the extent of decomposition of such Organic Materials based on changes in chemical composition. Chemical changes associated with the decomposition of wood varied considerably and were dependent on a strong interaction between the species of wood examined and the species composition of the microbial decomposer community, making the derivation of a single general index applicable to wood decomposition unlikely. For the remaining forms of natural Organic residues, decomposition was almost always associated with an increased content of alkyl C and a decreased content of O-alkyl C. The concomitant increase and decrease in alkyl and O-alkyl C contents, respectively, suggested that the ratio of alkyl to O-alkyl carbon (A/O-A ratio) may provide a sensitive index of the extent of decomposition. Contrary to the traditional view that humic substances with an aromatic core accumulate as decomposition proceeds, changes in the aromatic region were variable and suggested a relationship with the activity of lignin-degrading fungi. The A/O-A ratio did appear to provide a sensitive index of extent of decomposition provided that its use was restricted to situations where the Organic Materials were derived from a common starting material. In addition, the potential for adsorption of highly decomposable Materials on mineral soil surfaces and the impacts which such an adsorption may have on bioavailability required consideration when the A/O-A ratio was used to assess the extent of decomposition of Organic Materials found in mineral soils.
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aspects of the chemical structure of soil Organic Materials as revealed by solid state 13c nmr spectroscopy
Biogeochemistry, 1992Co-Authors: J A Baldock, J M Oades, A G Waters, X Peng, Anthony M Vassallo, Michael A WilsonAbstract:Solid-state cross-polarisation/magic-angle-spinning3C nuclear magnetic resonance (CP/MAS13C NMR) spectroscopy was used to characterise semi-quantitatively the Organic Materials contained in particle size and density fractions isolated from five different mineral soils: two Mollisols, two Oxisols and an Andosol. The acquired spectra were analysed to determine the relative proportion of carboxyl, aromatic, O-alkyl and alkyl carbon contained in each fraction. Although similar types of carbon were present in all of the fractions analysed, an influence of both soil type and particle size was evident.
Michael A Wilson - One of the best experts on this subject based on the ideXlab platform.
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aspects of the chemical structure of soil Organic Materials as revealed by solid state 13c nmr spectroscopy
Biogeochemistry, 1992Co-Authors: J A Baldock, J M Oades, A G Waters, X Peng, Anthony M Vassallo, Michael A WilsonAbstract:Solid-state cross-polarisation/magic-angle-spinning3C nuclear magnetic resonance (CP/MAS13C NMR) spectroscopy was used to characterise semi-quantitatively the Organic Materials contained in particle size and density fractions isolated from five different mineral soils: two Mollisols, two Oxisols and an Andosol. The acquired spectra were analysed to determine the relative proportion of carboxyl, aromatic, O-alkyl and alkyl carbon contained in each fraction. Although similar types of carbon were present in all of the fractions analysed, an influence of both soil type and particle size was evident.
Karl Leo - One of the best experts on this subject based on the ideXlab platform.
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exciton size and binding energy limitations in one dimensional Organic Materials
Journal of Chemical Physics, 2015Co-Authors: Stefan Kraner, R Scholz, Christian Koerner, Felix Plasser, Karl LeoAbstract:In current Organic photovoltaic devices, the loss in energy caused by the charge transfer step necessary for exciton dissociation leads to a low open circuit voltage, being one of the main reasons for rather low power conversion efficiencies. A possible approach to avoid these losses is to tune the exciton binding energy to a value of the order of thermal energy, which would lead to free charges upon absorption of a photon, and therefore increase the power conversion efficiency towards the Shockley-Queisser limit. We determine the size of the excitons for different Organic molecules and polymers by time dependent density functional theory calculations. For optically relevant transitions, the exciton size saturates around 0.7 nm for one-dimensional molecules with a size longer than about 4 nm. For the ladder-type polymer poly(benzimidazobenzophenanthroline), we obtain an exciton binding energy of about 0.3 eV, serving as a lower limit of the exciton binding energy for the Organic Materials investigated. Furthermore, we show that charge transfer transitions increase the exciton size and thus identify possible routes towards a further decrease of the exciton binding energy.
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design proposals for Organic Materials exhibiting a low exciton binding energy
Journal of Physical Chemistry C, 2015Co-Authors: Stefan Kraner, R Scholz, Christian Koerner, Karl LeoAbstract:Organic photovoltaics (OPV) have the potential for a low cost energy conversion from solar to electrical power. However, minimizing voltage losses, inherent to the currently used intermolecular donor–acceptor system, represents the main challenge to make this technology suitable for commercial large area applications. One key parameter to overcome is the high exciton binding energy in Organic Materials. Based on density functional theory (DFT) simulations, it is shown how polar side chains may significantly increase the dielectric constant, which lowers the exciton binding energy and enables charge generation in Organic Materials without a donor–acceptor system. Furthermore, based on time dependent (TD)-DFT calculations, we show another path for low exciton binding energy Organic Materials, by inducing a charge transfer state between two hydrogen bonded oligomers along the backbone. The charge transfer is achieved by fluorination of the acceptor oligomer investigated, leading to a wide-range intermolecula...
J M Oades - One of the best experts on this subject based on the ideXlab platform.
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assessing the extent of decomposition of natural Organic Materials using solid state 13c nmr spectroscopy
Soil Research, 1997Co-Authors: J A Baldock, J M Oades, Paul N Nelson, T M Skene, A Golchin, P ClarkeAbstract:Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy has become an important tool for examining the chemical structure of natural Organic Materials and the chemical changes associated with decomposition. In this paper, solid-state 13C NMR data pertaining to changes in the chemical composition of a diverse range of natural Organic Materials, including wood, peat, composts, forest litter layers, and Organic Materials in surface layers of mineral soils, were reviewed with the objective of deriving an index of the extent of decomposition of such Organic Materials based on changes in chemical composition. Chemical changes associated with the decomposition of wood varied considerably and were dependent on a strong interaction between the species of wood examined and the species composition of the microbial decomposer community, making the derivation of a single general index applicable to wood decomposition unlikely. For the remaining forms of natural Organic residues, decomposition was almost always associated with an increased content of alkyl C and a decreased content of O-alkyl C. The concomitant increase and decrease in alkyl and O-alkyl C contents, respectively, suggested that the ratio of alkyl to O-alkyl carbon (A/O-A ratio) may provide a sensitive index of the extent of decomposition. Contrary to the traditional view that humic substances with an aromatic core accumulate as decomposition proceeds, changes in the aromatic region were variable and suggested a relationship with the activity of lignin-degrading fungi. The A/O-A ratio did appear to provide a sensitive index of extent of decomposition provided that its use was restricted to situations where the Organic Materials were derived from a common starting material. In addition, the potential for adsorption of highly decomposable Materials on mineral soil surfaces and the impacts which such an adsorption may have on bioavailability required consideration when the A/O-A ratio was used to assess the extent of decomposition of Organic Materials found in mineral soils.
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aspects of the chemical structure of soil Organic Materials as revealed by solid state 13c nmr spectroscopy
Biogeochemistry, 1992Co-Authors: J A Baldock, J M Oades, A G Waters, X Peng, Anthony M Vassallo, Michael A WilsonAbstract:Solid-state cross-polarisation/magic-angle-spinning3C nuclear magnetic resonance (CP/MAS13C NMR) spectroscopy was used to characterise semi-quantitatively the Organic Materials contained in particle size and density fractions isolated from five different mineral soils: two Mollisols, two Oxisols and an Andosol. The acquired spectra were analysed to determine the relative proportion of carboxyl, aromatic, O-alkyl and alkyl carbon contained in each fraction. Although similar types of carbon were present in all of the fractions analysed, an influence of both soil type and particle size was evident.
Tomislav Friscic - One of the best experts on this subject based on the ideXlab platform.
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accelerated aging a low energy solvent free alternative to solvothermal and mechanochemical synthesis of metal Organic Materials
Chemical Science, 2012Co-Authors: Matthew J Cliffe, Cristina Mottillo, Robin S Stein, Dejankresimir Bucar, Tomislav FriscicAbstract:We describe a conceptually novel “accelerated aging” approach for the synthesis of metal–Organic Materials. This approach, inspired by natural mineral weathering processes, enables the synthesis of metal–Organic structures from simple and inexpensive solid reactants upon exposure to catalytic amounts of an ammonium salt under conditions of high humidity and mild temperatures (up to 45 °C). Accelerated aging exploits the inherent mobility of molecules and is entirely different from solution-based (precipitation, solvothermal synthesis) or other solvent-free (mechanochemical synthesis) approaches to metal–Organic Materials that require either bulk solvent and/or thermo- or mechanochemical intervention. The present proof-of-principle study of accelerated aging demonstrates the catalysed and topologically specific transformation of ZnO into unusual close-packed varieties of zeolitic imidazolate frameworks (ZIFs) in a static, non-agitated reaction mixture. The reactivity is readily scaled up, as demonstrated by performing selected syntheses of quartz- and diamondoid-topology close-packed ZIFs in ten gram amounts. The latter framework, previously obtained only by using a large excess of reagents under hydrothermal conditions, is transformed into the well-known open framework ZIF-8 by exposure to methanol vapours at room temperature, suggesting an alternative to both solvothermal and mechanochemical approaches to these Materials. A tentative proton-transfer mechanism underpinning the catalytic effect in accelerated aging is proposed, involving protonated imidazole as an intermediate.
