Electrochemical reactions in the LiS batteries are considered as a multistep reaction process with at least 2–3 equilibrium states. Here we report a possibility of having a conversion of Li2S into ...sulfur without detectible formation of polysulfides. That was confirmed by using a novel material system consisting of carbon coated Li2S particles prepared by carbothermal reduction of Li2SO4. Two independent in operando measurements showed direct oxidation of Li2S into sulfur for this system, with almost negligible formation of polysulfides at potentials above 2.5 V vs. Li/Li+. Our results link the diversity of first charge profiles in the literature to the Li2S oxidation mechanism and show the importance of ionic wiring within the material. Furthermore, we demonstrate that the Li2S oxidation mechanism depends on the relative amount of soluble sulfur in the electrolyte. By controlling the type and the amount of electrolyte within the encapsulating carbon shell, it is thereby possible to control the reaction mechanism of Li2S activation.
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•Mechanism of Li2S activation.•Direct conversion of Li2S to sulfur.•Impact of ionic conductivity on Li2S batteries behavior.•Absence of polysulfides during charging.
Irradiation of silicon-bridged 1ferrocenophane Fe(η-C5H4)2SiMe2 (1) in the presence of substitutionally labile Lewis bases such as 4,4′-dimethyl-2,2′-bipyridine (Me2bpy) initiates ring-opening ...polymerization and oligomerization via cleavage of an iron−cyclopentadienyl bond. A distribution of cyclic polyferrocenylsilane c-PFS (PFS = Fe(η-C5H4)2SiMe2 n ) and a series of cyclic oligomers (2 2 −2 7 ) were isolated by column chromatography and fully characterized. Varying temperature and concentration were found to influence the molecular weight distribution and the ratio of polymer to oligomer products, enabling the formation of c-PFS with molecular weights >100 kDa. Cyclic polymer samples were found to possess lower hydrodynamic radii and viscosity and higher glass transition temperatures than those of their linear PFS counterparts (l-PFS) of comparable molecular weight. Compared with crystalline samples of l-PFS of similar molecular weights, c-PFS formed smaller spherulites, as observed by polarizing optical microscopy. While the wide-angle X-ray scattering (WAXS) patterns from lower molecular weight l-PFS were found to differ from those from higher molecular weight samples, those obtained for lower and higher molecular weight samples of c-PFS are identical and resemble diffraction patterns of high molecular weight l-PFS. The electrochemical behavior of each cyclic oligomer 2 2 −2 7 was studied by cyclic and differential pulse voltammetry and was found to depend on whether the oligomer contains an odd or even number of ferrocene units. In contrast to linear analogs, two reversible redox processes of varying intensities were observed for cyclic oligomers containing an even number of iron centers, while three reversible redox processes of varying intensities were observed for cyclic oligomers containing an odd number of iron centers. As the oligomer chain length increased, the electrochemical behavior of all cyclic oligomers approached that of both cyclic and linear high molecular weight polymers.
We present an efficient synthesis of a modified carbon nitride photocatalyst by using supramolecular complexes of cyanuric acid, melamine, and 2,4-diamino-6-phenyl-1,3,5-triazine as precursors. We ...combined a self-templating approach for morphology control with the modification of photophysical properties by altering the chemical structure of the material. The resulting carbon nitrides exhibit high surface areas, defined morphologies, and a strong enhancement of light absorption in the visible-light region. A detailed analysis shows that the ratio changes of the three raw monomers resulted in different carbon nitride morphologies, absorption, and emission properties, along with the incorporation of different numbers of phenyl groups in the resulting carbon nitride structures. The modified carbon nitrides exhibit superior activity in the photodegradation of rhodamine B, up to 16 times that of bulk carbon nitride. The pyrolysis of rationally chosen supramolecular hydrogen-bonded precursors constitutes a synthetic pathway for the simple one-pot preparation of efficient, metal-free carbon nitride photocatalysts.
A biomimetic receptor for glucose Tromans, Robert A; Carter, Tom S; Chabanne, Laurent ...
Nature chemistry,
01/2019, Letnik:
11, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Specific molecular recognition is routine for biology, but has proved difficult to achieve in synthetic systems. Carbohydrate substrates are especially challenging, because of their diversity and ...similarity to water, the biological solvent. Here we report a synthetic receptor for glucose, which is biomimetic in both design and capabilities. The core structure is simple and symmetrical, yet provides a cavity which almost perfectly complements the all-equatorial β-pyranoside substrate. The receptor's affinity for glucose, at K
~ 18,000 M
, compares well with natural receptor systems. Selectivities also reach biological levels. Most other saccharides are bound approximately 100 times more weakly, while non-carbohydrate substrates are ignored. Glucose-binding molecules are required for initiatives in diabetes treatment, such as continuous glucose monitoring and glucose-responsive insulin. The performance and tunability of this system augur well for such applications.
Herein we report a general liquid-mediated pathway for the growth of continuous polymeric carbon nitride (C3N4) thin films. The deposition method consists of the use of supramolecular complexes that ...transform to the liquid state before direct thermal condensation into C3N4 solid films. The resulting films exhibit continuous porous C3N4 networks on various substrates. Moreover, the optical absorption can be easily tuned to cover the solar spectrum by the insertion of an additional molecule into the starting complex. The strength of the deposition method is demonstrated by the use of the C3N4 layer as the electron acceptor in a polymer solar cell that exhibits a remarkable open-circuit voltage exceeding 1 V. The easy, safe, and direct synthesis of carbon nitride in a continuous layered architecture on different functional substrates opens new possibilities for the fabrication of many energy-related devices.
Non-spherical nanostructures derived from soft matter and with uniform size-that is, monodisperse materials-are of particular utility and interest, but are very rare outside the biological domain. We ...report the controlled formation of highly monodisperse cylindrical block copolymer micelles (length dispersity < or = 1.03; length range, approximately 200 nm to 2 microm) by the use of very small (approximately 20 nm) uniform crystallite seeds that serve as initiators for the crystallization-driven living self-assembly of added block-copolymer unimers with a crystallizable, core-forming metalloblock. This process is analogous to the use of small initiator molecules in classical living polymerization reactions. The length of the nanocylinders could be precisely controlled by variation of the unimer-to-crystallite seed ratio. Samples of the highly monodisperse nanocylinders of different lengths that are accessible using this approach have been shown to exhibit distinct liquid-crystalline alignment behaviour.
Metallopolymers with emerging applications Eloi, Jean-Charles; Chabanne, Laurent; Whittell, George R. ...
Materials today,
April 2008, 2008-04-00, 20080401, Letnik:
11, Številka:
4
Journal Article
Recenzirano
Odprti dostop
A wide variety of metal-containing polymers, or ‘metallopolymers’, have become readily available over the past decade. This has led to a rapidly expanding interest in their properties and uses. These ...new materials combine the processing advantages of polymers with the functionality provided by the presence of metal centers. We illustrate a selection of applications of metallopolymers in areas such as sensors, memory and light-emitting devices, solar cells, nanolithography, photonic crystal displays, controlled release, and catalysis.
Skeletal Ni, produced by the selective leaching of Al from a Ni/Al alloy, has been successfully employed in the catalytic dehydrogenation of various amine–borane adducts. The combination of low cost ...and facile single-step synthesis make this system a potentially attractive alternative to the previously described precious metal and other first-row metal catalysts. The heterogeneous nature of the catalyst facilitates convenient product purification, and this is the first such system to be based on a first-row transition metal. Catalytic dehydrocoupling of Me2NH·BH3 (1) and Et2NH·BH3 (5) was demonstrated using 5 mol % skeletal Ni catalyst at 20 °C and produced Me2N–BH22 (2) and Et2N–BH22/Et2NBH2 (6), respectively. The related adduct iPr2NH·BH3 (7) was also dehydrogenated to afford iPr2NBH2 (8) but with significant catalyst deactivation. Catalytic dehydrocoupling of MeNH2·BH3 (9) was found to yield the cyclic triborazane MeNH–BH23 (10) as the major product, whereas high molecular weight poly(methylaminoborane) MeNH–BH2 n (11) (M w = 78 000 Da, PDI = 1.52) was formed when stoichiometric quantities of Ni were used. Similar reactivity was also observed with NH3·BH3 (12), which produced cyclic oligomers and insoluble polymers, NH2–BH2 x (14), under catalytic and stoichiometric Ni loadings, respectively. Catalyst recycling was hindered by gradual poisoning. A study of possible catalyst poisons suggested that BH3 was the most likely surface poison, in line with previous work on colloidal Rh catalysts. Catalytic dehydrogenation of amine–borane adducts using skeletal Cu and Fe was also explored. Skeletal Cu was found to be a less active dehydrogenation catalyst for amine–borane adducts but also yielded poly(methylaminoborane) under stoichiometric conditions on reaction with MeNH2·BH3 (9). Skeletal Fe was found to be completely inactive toward amine–borane dehydrogenation.
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