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- ItemVanadium pentoxide/carbide-derived carbon core-shell hybrid particles for high performance electrochemical energy storage(London [u.a.] : RSC, 2016) Zeiger, Marco; Ariyanto, Teguh; Krüner, Benjamin; Peter, Nicolas J.; Fleischmann, Simon; Etzold, Bastian J.M.; Presser, VolkerA novel, two step synthesis is presented combining the formation of carbide-derived carbon (CDC) and redox-active vanadium pentoxide (V2O5) in a core–shell manner using solely vanadium carbide (VC) as the precursor. In a first step, the outer part of VC particles is transformed to nanoporous CDC owing to the in situ formation of chlorine gas from NiCl2 at 700 °C. In a second step, the remaining VC core is calcined in synthetic air to obtain V2O5/CDC core–shell particles. Materials characterization by means of electron microscopy, Raman spectroscopy, and X-ray diffraction clearly demonstrates the partial transformation from VC to CDC, as well as the successive oxidation to V2O5/CDC core–shell particles. Electrochemical performance was tested in organic 1 M LiClO4 in acetonitrile using half- and asymmetric full-cell configuration. High specific capacities of 420 mA h g−1 (normalized to V2O5) and 310 mA h g−1 (normalized to V2O5/CDC) were achieved. The unique nanotextured core–shell architecture enables high power retention with ultrafast charging and discharging, achieving more than 100 mA h g−1 at 5 A g−1 (rate of 12C). Asymmetric cell design with CDC on the positive polarization side leads to a high specific energy of up to 80 W h kg−1 with a superior retention of more than 80% over 10 000 cycles and an overall energy efficiency of up to 80% at low rates.
- ItemThe Contrasting Character of Early and Late Transition Metal Fluorides as Hydrogen Bond Acceptors(Washington, DC : ACS Publications, 2015) Smith, Dan A.; Beweries, Torsten; Blasius, Clemens; Jasim, Naseralla; Nazir, Ruqia; Nazir, Sadia; Robertson, Craig C.; Whitwood, Adrian C.; Hunter, Christopher A.; Brammer, Lee; Perutz, Robin N.The association constants and enthalpies for the binding of hydrogen bond donors to group 10 transition metal complexes featuring a single fluoride ligand (trans-[Ni(F)(2-C5NF4)(PR3)2], R = Et 1a, Cy 1b, trans-[Pd(F)(4-C5NF4)(PCy3)2] 2, trans-[Pt(F){2-C5NF2H(CF3)}(PCy3)2] 3 and of group 4 difluorides (Cp2MF2, M = Ti 4a, Zr 5a, Hf 6a; Cp*2MF2, M = Ti 4b, Zr 5b, Hf 6b) are reported. These measurements allow placement of these fluoride ligands on the scales of organic H-bond acceptor strength. The H-bond acceptor capability β (Hunter scale) for the group 10 metal fluorides is far greater (1a 12.1, 1b 9.7, 2 11.6, 3 11.0) than that for group 4 metal fluorides (4a 5.8, 5a 4.7, 6a 4.7, 4b 6.9, 5b 5.6, 6b 5.4), demonstrating that the group 10 fluorides are comparable to the strongest organic H-bond acceptors, such as Me3NO, whereas group 4 fluorides fall in the same range as N-bases aniline through pyridine. Additionally, the measurement of the binding enthalpy of 4-fluorophenol to 1a in carbon tetrachloride (−23.5 ± 0.3 kJ mol–1) interlocks our study with Laurence’s scale of H-bond basicity of organic molecules. The much greater polarity of group 10 metal fluorides than that of the group 4 metal fluorides is consistent with the importance of pπ–dπ bonding in the latter. The polarity of the group 10 metal fluorides indicates their potential as building blocks for hydrogen-bonded assemblies. The synthesis of trans-[Ni(F){2-C5NF3(NH2)}(PEt3)2], which exhibits an extended chain structure assembled by hydrogen bonds between the amine and metal-fluoride groups, confirms this hypothesis.
- ItemProximal Soil Sensing - A Contribution for Species Habitat Distribution Modelling of Earthworms in Agricultural Soils?(San Francisco, California, US : PLOS, 2016) Schirrmann, Michael; Joschko, Monika; Gebbers, Robin; Kramer, Eckart; Zörner, Mirjam; Barkusky, Dietmar; Timmer, JensBackground: Earthworms are important for maintaining soil ecosystem functioning and serve as indicators of soil fertility. However, detection of earthworms is time-consuming, which hinders the assessment of earthworm abundances with high sampling density over entire fields. Recent developments of mobile terrestrial sensor platforms for proximal soil sensing (PSS) provided new tools for collecting dense spatial information of soils using various sensing principles. Yet, the potential of PSS for assessing earthworm habitats is largely unexplored. This study investigates whether PSS data contribute to the spatial prediction of earthworm abundances in species distribution models of agricultural soils. Methodology/Principal Findings: Proximal soil sensing data, e.g., soil electrical conductivity (EC), pH, and near infrared absorbance (NIR), were collected in real-time in a field with two management strategies (reduced tillage / conventional tillage) and sandy to loam soils. PSS was related to observations from a long-term (11 years) earthworm observation study conducted at 42 plots. Earthworms were sampled from 0.5 x 0.5 x 0.2 m³ soil blocks and identified to species level. Sensor data were highly correlated with earthworm abundances observed in reduced tillage but less correlated with earthworm abundances observed in conventional tillage. This may indicate that management influences the sensor-earthworm relationship. Generalized additive models and state-space models showed that modelling based on data fusion from EC, pH, and NIR sensors produced better results than modelling without sensor data or data from just a single sensor. Regarding the individual earthworm species, particular sensor combinations were more appropriate than others due to the different habitat requirements of the earthworms. Earthworm species with soil-specific habitat preferences were spatially predicted with higher accuracy by PSS than more ubiquitous species. Conclusions/Significance: Our findings suggest that PSS contributes to the spatial modelling of earthworm abundances at field scale and that it will support species distribution modelling in the attempt to understand the soil-earthworm relationships in agroecosystems.
- ItemElectrospinning of ultrafine metal oxide/carbon and metal carbide/carbon nanocomposite fibers(London : RSC Publishing, 2015) Atchison, Jennifer S.; Zeiger, Marco; Tolosa, Aura; Funke, Lena M.; Jäckel, Nicolas; Presser, VolkerElectrospinning has emerged as a facile technology for the synthesis of ultrafine fibers and even nanofibers of various materials. While carbon nanofibers have been extensively investigated, there have also been studies reported on metal oxide and metal carbide fibers. Yet, comparative studies, especially following the same general synthesis approach, are lacking. In our comprehensive study, we use a sol gel process by which a carrier polymer (cellulose acetate or polyvinylpyrrolidone) is mixed with titanium butoxide, zirconium(IV) acetylacetonate, or niobium n-butoxide to yield nanotextured titania/carbon, zirconia/carbon, or niobia/carbon nonwoven textiles. Carbothermal reduction between 1300 °C and 1700 °C effectively transforms the metal oxide/carbon fibers to metal carbide/carbon nanocomposite while preserving the fiber integrity. As a beneficial effect, the fiber diameter decreases compared to the as-spun state and we obtained ultrafine fibers: 294 ± 108 nm for ZrC/C, 122 ± 28 nm for TiC/C, and 65 ± 36 nm for NbC/C. The highly disordered and porous nature of the carbon matrix engulfing the metal carbide nanocrystals enables a high specific surface area of up to 450 m2 g−1 (TiC/C) after carbothermal reduction.
- ItemDimethyl carbonate synthesis from carbon dioxide using ceria–zirconia catalysts prepared using a templating method: characterization, parametric optimization and chemical equilibrium modeling(London : RSC Publishing, 2016) Kumar, Praveen; With, Patrick; Srivastava, Vimal Chandra; Shukla, Kartikeya; Gläser, Roger; Mishra, Indra ManiIn this paper, a series of CexZr1−xO2 solid solution spheres were synthesized by exo- and endo-templating methods and tested for dimethyl carbonate (DMC) synthesis using direct conversion of CO2. The synthesized catalysts were characterized by X-ray diffraction (XRD), N2-physisorption, scanning electron microscopy (SEM), and CO2/NH3-temperature-programmed desorption (TPD). Formation of CexZr1−xO2 solid solutions with tetragonal and cubic crystal structures depending on cerium/zirconium compositions was confirmed by XRD analysis. The specific surface area of the mixed oxide decreased and the average pore diameter increased with an increase in the ceria content, with the exception of the mixed oxides with x = 0.4–0.5 i.e. Ce0.4Zr0.6O2 and Ce0.5Zr0.5O2. The basic and acidic site density of the synthesized catalysts was in the order: ZrO2 < CeO2 < Ce0.5Zr0.5O2, and the basic and acidic site density per unit area followed the same order. The best Ce0.5Zr0.5O2 catalyst was further used for the optimization of reaction conditions such as reaction time, reaction temperature, catalyst dose and reusability for DMC synthesis. Furthermore, study of chemical equilibrium modeling was done using the Peng–Robinson–Stryjek–Vera equation of state (PRSV-EoS) along with the van der Waals one-fluid reaction condition so as to calculate change of Gibbs free energy (ΔG°) and heat of reaction (ΔH°).