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Synthesis of polymer/CNTs composites for the heterogeneous asymmetric hydrogenation of quinolines
No full textThe development of heterogeneous catalytic processes is crucial for the synthesis of chiral compounds for both academic and industrial applications. However, thus far, such achievements have remained elusive. Herein, we report the heterogeneous asymmetric hydrogenation of 2-methylquinoline over solid chiral catalysts, which were prepared by the one-pot polymerization of (1R,2R)-N-(4-vinyl-benzenesulfonyI)-1,2-diphenylethane-1,2-diamine (VDPEN) and divinylbenzene (DVB) in the presence or absence of activated carbon (C) or carbon nanotubes (CNTs), followed by Ru coordination and anion exchange. The solid chiral catalysts were fully characterized by N2 sorption analysis, elemental analysis, TEM, FT-IR spectroscopy, and C-13 CP-MAS NMR. All the solid chiral catalysts could efficiently catalyze the asymmetric hydrogenation of 2-methylquinoline to afford 2-methyl-1,2,3,4-tetrahydroquinoline with 90% ee. Studies have shown that polymer/C and polymer/CNTs composites are more active than pure polymers. The polymer/CNTs composite exhibited the highest activity among all the solid chiral catalysts under identical conditions, owing to the unique morphology of CNTs. The recycling stabilities of the solid chiral catalysts were greatly improved when ionic liquids (ILs) were employed as solvents; this is mainly attributed to the decreased leaching amount of anions owing to the confinement effect of ILs on ionic compounds. (C) 2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved
A moisture absorbing gel electrolyte enables aqueous and flexible supercapacitors operating at high temperatures
No full textGel electrolytes are of great importance for supercapacitors (SCs) operating at high temperatures. However, it is a fundamental challenge for SCs using aqueous gel electrolytes at elevated temperatures to ensure good work durability due to the evaporation of water. Here we report a "water-in-salt" gel electrolyte that exhibits superior water-retention and even water-absorption capability. What is noteworthy is that a quasi-solid-state SC utilizing the gel electrolyte is able to work and exhibit long cycling life across a wide temperature range from room temperature up to 120 degrees C in an extremely dry atmosphere, representing the best record among the previously reported aqueous gel-based SCs, as far as we know. This strategy may provide a new way to develop reliable aqueous gel electrolytes for SCs operating at high temperatures
Training Foundation for Scientific Research of Talents Project, Hebei Province[A2016005004]
No full textRuO2 Particles Anchored on Brush-Like 3D Carbon Cloth Guide Homogenous Li/Na Nucleation Framework for Stable Li/Na Anode
No full textLithium (sodium)-metal batteries are the most promising batteries for next-generation electrical energy storage due to their high volumetric energy density and gravimetric energy density. However, their applications have been prevented by uncontrollable dendrite growth and large volume expansion during the stripping/plating process. To address this issue, the key strategy is to realize uniform lithium (sodium) deposition during the stripping/plating process. Herein, a thin lithiophilic layer consisting of RuO2 particles anchored on brush-like 3D carbon cloth (RuO2@CC) is prepared by a simple solution-based method. After infusion of Li, the RuO2@CC transfers to Li-Ru@CC. Ru nanoparticles not only play a role in leading Li+ (Na+) to plate on the 3D carbon framework, but also lower local current density because of the good electrical conductivity. Furthermore, density functional theory calculations demonstrate that Ru metal, the reaction product of alkali metal and Ru, can lead Li+ to plate evenly around carbon fiber owing to the strong binding energy with Li+. The Li-Ru@CC anode shows ultralong cycle life (1500 h at 5 mA cm(-2)). The full cell of Li-Ru@CC|LiFePO4 exhibits lower polarization (90% capacity retention after 650 cycles). In addition, sodium metal batteries based on Na-Ru@CC anodes can achieve similar improvement
Particulate Oxynitride Photoanodes Assembled with Transparent Electron-Collecting Oxide Nanorod Arrays
No full textThe collection of photogenerated electrons is commonly a bottleneck in photoelectrochemical water oxidation on a particulate photoanode. Herein, a new strategy called "array insertion" for particulate photoanode preparation is proposed to improve electron collection. ZnO nanorod arrays are inserted between LaTiO2N particles and Al-doped ZnO (AZO) substrates via epitaxial electrodeposition, which make electronic connections. Using this methodology, charge separation efficiency is improved drastically, and the photocurrent at 1.23 V-RHE is enhanced by more than 1 order of magnitude, because the obstacle of electron collection in the particulate LaTiO2N photoanodes is overcome
Atomic-Scale Observation of Bimetallic Au-CuOx Nanoparticles and Their Interfaces for Activation of CO Molecules
No full textSupported gold nanoparticles with sizes below 5 nm display attractive catalytic activities for heterogeneous reactions, particularly those promoted by secondary metal (e.g., Cu) because of the well-defined synergy between metal compositions. However, the specific atomic structure at interfaces is less interpreted systematically. In this work, various bimetallic Au-CuOx catalysts with specific surface structures were synthesized and explored by aberration-corrected scanning transmission electron microscopy (AC-STEM), temperature-programmed experiments and in situ DRIFT experiments. Results suggest that the atomic structure and interfaces between gold and CuOx a are determined by the nucleation behaviors of the nanoparticles and result in subsequently the distinctive ability for CO activation. Bimetallic CuO*/Au sample formatted by gold particles surrounded with CuOx nanoclusters have rough surface with prominently exposed low-coordinated Au step defects. Whereas the bimetallic Au@CuO sample formatted by copper precursor in the presence of gold nanoparticles have core-shell structure with relatively smooth surface. The former structure of CuO*/Au displays much accelerated properties for CO adsorption and activation with 90% CO converted to CO2 at 90 degrees C and nice stability with time on stream. The results clearly determine from atomic scale the significance of exposed gold step sites and intrinsic formation of defected surface by different nucleation. The above properties are directly responsible for the induced variation in chemical composition and the catalytic activity
Unraveling the coordination structure-performance relationship in Pt-1/Fe2O3 single-atom catalyst
No full textHeterogeneous single-atom catalyst (SAC) opens a unique entry to establishing structure-performance relationship at the molecular level similar to that in homogeneous catalysis. The challenge lies in manipulating the coordination chemistry of single atoms without changing single-atom dispersion. Here, we develop an efficient synthetic method for SACs by using ethanediamine to chelate Pt cations and then removing the ethanediamine by a rapid thermal treatment (RTT) in inert atmosphere. The coordination chemistry of Pt single atoms on a Fe2O3 support is finely tuned by merely adjusting the RTT temperature. With the decrease in Pt-O coordination number, the oxidation state of Pt decreases, and consequently the hydrogenation activity increases to a record level without loss of chemoselectivity. The tunability of the local coordination chemistry, oxidation states of the metal, and the catalytic performance of single atoms reveals the unique role of SACs as a bridge between heterogeneous and homogeneous catalysis
Covalent Functionalization of Graphene Oxide with a Presynthesized Metal-Organic Framework Enables a Highly Stable Electrochemical Sensing
No full textThis paper reports the covalent functionalization of graphene oxide (GO) by a presynthesized metal-organic framework NH2-MIL-101(Fe) via ultrasonication of the two components. The formation of Fe-O covalent bonding in the NH2-MIL-101(Fe)-GO nanohybrid is clearly evidenced, and the covalent bonding still remains after electrochemical reduction. The morphology and structure of the nanohybrid are characterized via scanning electron microscopy, transmission electron microscopy, UV-vis spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. The electrode based on electrochemically reduced NH2-MIL-101(Fe)-GO shows ultrastable and high-sensitive performance in simultaneous electrochemical sensing of three purine metabolic derivatives (uric acid, xanthine, and hypoxanthine); in particular, no signal fading is seen even after running for 120 times. The covalent bonding within the nanohybrid is obviously the key to maintain such a stability