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End date: 2019 × Start date: 2019 × Type: Article × Type: Text × Publisher: Cambridge : Royal Society of Chemistry × WGL Institute: IFWD ×

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Now showing 1 - 10 of 24
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    Improving the zT value of thermoelectrics by nanostructuring: Tuning the nanoparticle morphology of Sb2Te3 by using ionic liquids
    (Cambridge : Royal Society of Chemistry, 2016) Schaumann, Julian; Loor, Manuel; Ünal, Derya; Mudring, Anja; Heimann, Stefan; Hagemann, Ulrich; Schulz, Stephan; Maculewicz, Franziska; Schierning, Gabi
    A systematic study on the microwave-assisted thermolysis of the single source precursor (Et2Sb)2Te (1) in different asymmetric 1-alkyl-3-methylimidazolium- and symmetric 1,3-dialkylimidazolium-based ionic liquids (ILs) reveals the distinctive role of both the anion and the cation in tuning the morphology and microstructure of the resulting Sb2Te3 nanoparticles as evidenced by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). A comparison of the electrical and thermal conductivities as well as the Seebeck coefficient of the Sb2Te3 nanoparticles obtained from different ILs reveals the strong influence of the specific IL, from which C4mimI was identified as the best solvent, on the thermoelectric properties of as-prepared nanosized Sb2Te3. This work provides design guidelines for ILs, which allow the synthesis of nanostructured thermoelectrics with improved performances.
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    Magnetic superexchange interactions: Trinuclear bis(oxamidato) versus bis(oxamato) type complexes
    (Cambridge : Royal Society of Chemistry, 2015) Abdulmalic, Mohammad A.; Aliabadi, Azar; Petr, Andreas; Krupskaya, Yulia; Kataev, Vladislav; Büchner, Bernd; Zaripov, Ruslan; Vavilova, Evgeniya; Voronkova, Violeta; Salikov, Kev; Hahn, Torsten; Kortus, Jens; Meva, Francois Eya’ane; Schaarschmidt, Dieter; Rüffer, Tobias
    The diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) was treated with an excess of RNH2 in MeOH to cause the exclusive formation of the respective o-phenylenebis(N(R)-oxamides) (opboH4R2, R = Me 1, Et 2, nPr 3) in good yields. Treatment of 1–3 with half an equivalent of [Cu2(AcO)4(H2O)2] or one equivalent of [Ni(AcO)2(H2O)4] followed by the addition of four equivalents of [nBu4N]OH resulted in the formation of mononuclear bis(oxamidato) type complexes [nBu4N]2[M(opboR2)] (M = Ni, R = Me 4, Et 5, nPr 6; M = Cu, R = Me 7, Et 8, nPr 9). By addition of two equivalents of [Cu(pmdta)(NO3)2] to MeCN solutions of 7–9, novel trinuclear complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me 10, Et 11, nPr 12) could be obtained. Compounds 4–12 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 4–10 and 12 have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 8 and 9 (1%) in the host lattice of 5 and 6 (99%) (8@5 and 9@6), respectively, in the form of single crystals have been made available, allowing single crystal ESR studies to extract all components of the g-factor and the tensors of onsite CuA and transferred NA hyperfine (HF) interaction. From these studies, the spin density distribution of the [Cu(opboEt2)]2− and [Cu(opbonPr2)]2− complex fragments of 8 and 9, respectively, could be determined. Additionally, as a single crystal ENDOR measurement of 8@5 revealed the individual HF tensors of the N donor atoms to be unequal, individual estimates of the spin densities on each N donor atom were made. The magnetic properties of 10–12 were studied by susceptibility measurements versus temperature to give J values varying from −96 cm−1 (10) over −104 cm−1 (11) to −132 cm−1 (12). These three trinuclear CuII-containing bis(oxamidato) type complexes exhibit J values which are comparable to and slightly larger in magnitude than those of related bis(oxamato) type complexes. In a summarizing discussion involving experimentally obtained ESR results (spin density distribution) of 8 and 9, the geometries of the terminal [Cu(pmdta)]2+ fragments of 12 determined by crystallographic studies, together with accompanying quantum chemical calculations, an approach is derived to explain these phenomena and to conclude if the spin density distribution of mononuclear bis(oxamato)/bis(oxamidato) type complexes could be a measure of the J couplings of corresponding trinuclear complexes.
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    Sc3CH@C80: selective 13C enrichment of the central carbon atom
    (Cambridge : Royal Society of Chemistry, 2016) Junghans, Katrin; Rosenkranz, Marco; Popov, Alexey A.
    Sc3CH@C80 is synthesized and characterized by 1H, 13C, and 45Sc NMR. A large negative chemical shift of the proton, -11.73 ppm in the Ih and -8.79 ppm in the D5h C80 cage isomers, is found. 13C satellites in the 1H NMR spectrum enabled indirect determination of the 13C chemical shift for the central carbon at 173 ± 1 ppm. Intensity of the satellites allowed determination of the 13C content for the central carbon atom. This unique possibility is applied to analyze the cluster/cage 13C distribution in mechanistic studies employing either 13CH4 or 13C powder to enrich Sc3CH@C80 with 13C.
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    Stimuli-responsive nanogel composites and their application in nanomedicine
    (Cambridge : Royal Society of Chemistry, 2015) Molina, Maria; Asadian-Birjand, Mazdak; Balach, Juan; Bergueiro, Julian; Miceli, Enrico; Calderón, Marcelo
    Nanogels are nanosized crosslinked polymer networks capable of absorbing large quantities of water. Specifically, smart nanogels are interesting because of their ability to respond to biomedically relevant changes like pH, temperature, etc. In the last few decades, hybrid nanogels or composites have been developed to overcome the ever increasing demand for new materials in this field. In this context, a hybrid refers to nanogels combined with different polymers and/or with nanoparticles such as plasmonic, magnetic, and carbonaceous nanoparticles, among others. Research activities are focused nowadays on using multifunctional hybrid nanogels in nanomedicine, not only as drug carriers but also as imaging and theranostic agents. In this review, we will describe nanogels, particularly in the form of composites or hybrids applied in nanomedicine.
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    A crystalline anionic complex of scandium nitride endometallofullerene: Experimental observation of single-bonded (Sc3N@Ih-C80−)2 dimers
    (Cambridge : Royal Society of Chemistry, 2016) Konarev, Dmitri V.; Zorina, Leokadiya V.; Khasanov, Salavat S.; Popov, Alexey A.; Otsuka, Akihiro; Yamochi, Hideki; Saito, Gunzi; Lyubovskaya, Rimma N.
    Reduction of scandium nitride clusterfullerene, Sc3N@Ih-C80, by sodium fluorenone ketyl in the presence of cryptand[2,2,2] allows the crystallization of the {cryptand[2,2,2](Na+)}2(Sc3N@Ih-C80−)2·2.5C6H4Cl2 (1) salt. The Sc3N@Ih-C80˙− radical anions are dimerized to form single-bonded (Sc3N@Ih-C80−)2 dimers.
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    Hydrophilic non-precious metal nitrogen-doped carbon electrocatalysts for enhanced efficiency in oxygen reduction reaction
    (Cambridge : Royal Society of Chemistry, 2015) Hao, Guang-Ping; Sahraie, Nastaran Ranjbar; Zhang, Qiang; Krause, Simon; Oschatz, Martin; Bachmatiuk, Alicja; Strasser, Peter; Kaskel, Stefan
    Exploring the role of surface hydrophilicity of non-precious metal N-doped carbon electrocatalysts in electrocatalysis is challenging. Herein we discover an ultra-hydrophilic non-precious carbon electrocatalyst, showing enhanced catalysis efficiency on both gravimetric and areal basis for oxygen reduction reaction due to a high dispersion of active centres.
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    A faux hawk fullerene with PCBM-like properties
    (Cambridge : Royal Society of Chemistry, 2014) San, Long K.; Bukovsky, Eric V.; Larson, Bryon W.; Whitaker, James B.; Deng, S.H.M.; Kopidakis, Nikos; Rumbles, Garry; Popov, Alexey A.; Chen, Yu-Sheng; Wang, Xue-Bin; Boltalina, Olga V.; Strauss, Steven H.
    Reaction of C60, C6F5CF2I, and SnH(n-Bu)3 produced, among other unidentified fullerene derivatives, the two new compounds 1,9-C60(CF2C6F5)H (1) and 1,9-C60(cyclo-CF2(2-C6F4)) (2). The highest isolated yield of 1 was 35% based on C60. Depending on the reaction conditions, the relative amounts of 1 and 2 generated in situ were as high as 85% and 71%, respectively, based on HPLC peak integration and summing over all fullerene species present other than unreacted C60. Compound 1 is thermally stable in 1,2-dichlorobenzene (oDCB) at 160 °C but was rapidly converted to 2 upon addition of Sn2(n-Bu)6 at this temperature. In contrast, complete conversion of 1 to 2 occurred within minutes, or hours, at 25 °C in 90/10 (v/v) PhCN/C6D6 by addition of stoichiometric, or sub-stoichiometric, amounts of proton sponge (PS) or cobaltocene (CoCp2). DFT calculations indicate that when 1 is deprotonated, the anion C60(CF2C6F5)− can undergo facile intramolecular SNAr annulation to form 2 with concomitant loss of F−. To our knowledge this is the first observation of a fullerene-cage carbanion acting as an SNAr nucleophile towards an aromatic C–F bond. The gas-phase electron affinity (EA) of 2 was determined to be 2.805(10) eV by low-temperature PES, higher by 0.12(1) eV than the EA of C60 and higher by 0.18(1) eV than the EA of phenyl-C61-butyric acid methyl ester (PCBM). In contrast, the relative E1/2(0/−) values of 2 and C60, −0.01(1) and 0.00(1) V, respectively, are virtually the same (on this scale, and under the same conditions, the E1/2(0/−) of PCBM is −0.09 V). Time-resolved microwave conductivity charge-carrier yield × mobility values for organic photovoltaic active-layer-type blends of 2 and poly-3-hexylthiophene (P3HT) were comparable to those for equimolar blends of PCBM and P3HT. The structure of solvent-free crystals of 2 was determined by single-crystal X-ray diffraction. The number of nearest-neighbor fullerene–fullerene interactions with centroid⋯centroid (⊙⋯⊙) distances of ≤10.34 Å is significantly greater, and the average ⊙⋯⊙ distance is shorter, for 2 (10 nearest neighbors; ave. ⊙⋯⊙ distance = 10.09 Å) than for solvent-free crystals of PCBM (7 nearest neighbors; ave. ⊙⋯⊙ distance = 10.17 Å). Finally, the thermal stability of 2 was found to be far greater than that of PCBM.
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    Thermal activation of catalytic microjets in blood samples using microfluidic chips
    (Cambridge : Royal Society of Chemistry, 2013) Restrepo-Pérez, Laura; Soler, Lluís; Martínez-Cisneros, Cynthia S.; Sanchez, Samuel; Schmidt, Oliver G.
    We demonstrate that catalytic microjet engines can out-swim high complex media composed of red blood cells and serum. Despite the challenge presented by the high viscosity of the solution at room temperature, the catalytic microjets can be activated at physiological temperature and, consequently, self-propel in diluted solutions of blood samples. We prove that these microjets self-propel in 10× diluted blood samples using microfluidic chips.
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    SEI-component formation on sub 5 nm sized silicon nanoparticles in Li-ion batteries: The role of electrode preparation, FEC addition and binders
    (Cambridge : Royal Society of Chemistry, 2015) Jaumann, Tony; Balach, Juan; Klose, Markus; Oswald, Steffen; Langklotz, Ulrike; Michaelis, Alexander; Eckert, Jürgen; Giebeler, Lars
    Silicon is a promising negative electrode for secondary lithium-based batteries, but the electrochemical reversibility of particularly nanostructured silicon electrodes drastically depends on their interfacial characteristics, commonly known as the solid electrolyte interface (SEI). The beneficial origin of certain electrolyte additives or different binders is still discussed controversially owing to the challenging peculiarities of interfacial post-mortem investigations of electrodes. In this work, we address the common difficulties of SEI investigations of porous silicon/carbon nanostructures and study the addition of a fluoroethylene carbonate (FEC) as a stabilizing additive as well as the use of two different binders, carboxymethyl cellulose/styrene-butadiene rubber (CMC/SBR) and polyacrylic acid (PAA), for the SEI formation. The electrode is composed of silicon nanocrystallites below 5 nm diameter allowing a detailed investigation of interfacial characteristics of silicon owing to the high surface area. We first performed galvanostatic long-term cycling (400 times) and carried out comprehensive ex situ characterization of the cycled nanocrystalline silicon electrodes with XRD, EDXS, TEM and XPS. We modified the preparation of the electrode for post-mortem characterization to distinguish between electrolyte components and the actual SEI. The impact of the FEC additive and two different binders on the interfacial layer is studied and the occurrence of diverse compounds, in particular LiF, Li2O and phosphates, is discussed. These results help to understand general issues in SEI formation and to pave the way for the development of advanced electrolytes allowing for a long-term performance of nanostructured Si-based electrodes.
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    High-defect hydrophilic carbon cuboids anchored with Co/CoO nanoparticles as highly efficient and ultra-stable lithium-ion battery anodes
    (Cambridge : Royal Society of Chemistry, 2016) Sun, Xiaolei; Hao, Guang-Ping; Lu, Xueyi; Xi, Lixia; Liu, Bo; Si, Wenping; Ma, Chuansheng; Liu, Qiming; Zhang, Qiang; Kaskel, Stefan; Schmidt, Oliver G.
    We propose an effective strategy to engineer a unique kind of porous carbon cuboid with tightly anchored cobalt/cobalt oxide nanoparticles (PCC–CoOx) that exhibit outstanding electrochemical performance for many key aspects of lithium-ion battery electrodes. The host carbon cuboid features an ultra-polar surface reflected by its high hydrophilicity and rich surface defects due to high heteroatom doping (N-/O-doping both higher than 10 atom%) as well as hierarchical pore systems. We loaded the porous carbon cuboid with cobalt/cobalt oxide nanoparticles through an impregnation process followed by calcination treatment. The resulting PCC–CoOx anode exhibits superior rate capability (195 mA h g−1 at 20 A g−1) and excellent cycling stability (580 mA h g−1 after 2000 cycles at 1 A g−1 with only 0.0067% capacity loss per cycle). Impressively, even after an ultra-long cycle life exceeding 10 000 cycles at 5 A g−1, the battery can recover to 1050 mA h g−1 at 0.1 A g−1, perhaps the best performance demonstrated so far for lithium storage in cobalt oxide-based electrodes. This study provides a new perspective to engineer long-life, high-power metal oxide-based electrodes for lithium-ion batteries through controlling the surface chemistry of carbon host materials.