Showing papers by "Dong Wang published in 2013"
TL;DR: A novel strategy for the selective synthesis of pyridinic and pyrrolic N atoms and fewer quaternary N atoms is presented, which can enhance the activity of NC materials with sufficient active species that favor ORR and through an increase in electrical conductivity.
Abstract: The development of high-performance and low-cost catalytic materials for the oxygen reduction reaction (ORR) has been a major challenge for the large-scale application of fuel cells. Currently, platinum and platinum-based alloys are the most efficient ORR catalysts in fuel-cell cathodes; however, they cannot meet the demand for the widespread commercialization of fuel cells because of the scarcity of platinum. Thus, the ongoing search for platinum-free catalysts for the ORR has attracted much attention. Graphene, single-layer sheets of sp-hybridized carbon atoms, has attracted tremendous attention and research interest. The abundance of free-flowing p electrons in carbon materials composed of sp-hybridized carbon atoms makes these materials potential catalysts for reactions that require electrons, such as the ORR. However, these p electrons are too inert to be used directly in the ORR. In N-doped electron-rich carbon nanostructures, carbon p electrons have been shown to be activated through conjugation with lone-pair electrons from N dopants; thus, O2 molecules are reduced on the positively charged C atoms that neighbor N atoms. Recently, Hu and co-workers found that as long as the electroneutrality of the sp-hybridized carbon atoms is broken and charged sites that favor O2 adsorption are created, these materials will be transformed into active metal-free ORR electrocatalysts regardless of whether the dopants are electron-rich (e.g., N) or electrondeficient (e.g., B). Nitrogen-doped carbon (NC) materials are considered to be promising catalysts because of their acceptable ORR activity, low cost, good durability, and environmental friendliness. However, their ORR activity is less competitive, especially in acidic media. Relative to commercial Pt/C, the difference in the half-wave potential for ORR is within 25 mV in alkaline electrolytes but is greater than 200 mV in acidic electrolytes. The activity of NC materials can be enhanced through efficient N doping with sufficient active species that favor ORR and through an increase in electrical conductivity. The annealing of graphitized carbon materials, such as carbon nanotubes and microporous carbon black, in NH3 leads to insufficient substitution of nitrogen because of the well-ordered structure of the host materials. Alternatively, the direct pyrolysis of nitrogen-containing hydrocarbons or polymers produces NC materials with good incorporation of nitrogen. However, suitable pyrolysis temperatures are difficult to pinpoint; without optimization, temperatures that are excessively low or excessively high lead to low electronic conductivity or a remarkable loss of active N species, respectively. Recently, mesoporous-alumina-assisted and silica-template-assisted nitrogen incorporation, which can preserve a high content of N in synthesized NC materials, have been reported. However the activities of the resulting NC materials in the ORR were still significantly lower than that of Pt/C, even when the N content was as high as 10.7 atm%. Among three types of N atoms, that is, pyridinic, pyrrolic, and quaternary N, only the pyridinic and pyrrolic forms, which have planar structures, have been proven to be active in the ORR. In contrast, quaternary N atoms, which possess a 3D structure, are not active in the ORR. The low electrical conductivity of NC materials with quaternary N atoms results from the interruption of their p–p conjugation by the 3D structure and is thought to be predominantly responsible for the poor catalysis. Therefore, the synthesis of NC materials with more planar pyridinic and pyrrolic N atoms and fewer quaternary N atoms is important for the preparation of ORR-active catalysts. Herein, we present a novel strategy for the selective synthesis of pyridinicand pyrrolic-nitrogen-doped graphene (NG) by the use of layered montmorillonite (MMT) as a quasi-closed flat nanoreactor, which is open only along the perimeter to enable the entrance of aniline (AN) monomer molecules. The flat MMT nanoreactor, which is less than 1 nm thick, extensively constrains the formation of quaternary N because of its 3D structure but facilitates the formation of pyridinic and pyrrolic N. Nitrogen is well-known to be incorporated into quaternary N in tetrahedral sp hybridization but incorporated into pyridinic and pyrrolic N in planar sp hybridization. The confinement effect of MMT ensures that N is incorporated into the structure and that the graphitization is successful without significant loss of N species. Furthermore, planar pyridinic and pyrrolic N can be [*] Dr. W. Ding, Prof. Z.-D. Wei, Dr. S.-G. Chen, Dr. X.-Q. Qi, Dr. T. Yang, Dr. S. F. Alvi, Dr. L. Li The State Key Laboratory of Power Transmission Equipment and System Security and New Technology, College of Chemistry and Chemical Engineering, Chongqing University Shapingba 174, Chongqing (China) E-mail: zdwei@cqu.edu.cn
643 citations
TL;DR: A self-limiting solid-vapor interface reaction strategy to fabricate highly ordered SCOFs with imine linkage is demonstrated and shows the possibility of a rational design and synthesis of SCOFS with desired functionality.
Abstract: Surface covalent organic frameworks (SCOFs), featured by atomic thick sheet with covalently bonded organic building units, are promised to possess unique properties associated with reduced dimensionality, well-defined in-plane structure, and tunable functionality. Although a great deal of effort has been made to obtain SCOFs with different linkages and building blocks via both “top-down” exfoliation and “bottom-up” surface synthesis approaches, the obtained SCOFs generally suffer a low crystallinity, which impedes the understanding of intrinsic properties of the materials. Herein, we demonstrate a self-limiting solid–vapor interface reaction strategy to fabricate highly ordered SCOFs. The coupling reaction is tailored to take place at the solid–vapor interface by introducing one precursor via vaporization to the surface preloaded with the other precursor. Following this strategy, highly ordered honeycomb SCOFs with imine linkage are obtained. The controlled formation of SCOFs in our study shows the possib...
337 citations
TL;DR: The induction of global homochirality in two-dimensional enantiomorphous networks of achiral molecules via co-assembly with chiral co-absorbers is reported and may reveal important insights into asymmetric heterogeneous catalysis, chiral separation and chiral crystallization.
Abstract: Understanding the chirality induction and amplification processes, and the construction of globally homochiral surfaces, represent essential challenges in surface chirality studies Here we report the induction of global homochirality in two-dimensional enantiomorphous networks of achiral molecules via co-assembly with chiral co-absorbers The scanning tunnelling microscopy investigations and molecular mechanics simulations demonstrate that the point chirality of the co-absorbers transfers to organizational chirality of the assembly units via enantioselective supramolecular interactions, and is then hierarchically amplified to the global homochirality of two-dimensional networks The global homochirality of the network assembly shows nonlinear dependence on the enantiomeric excess of chiral co-absorber in the solution phase, demonstrating, for the first time, the validation of the 'majority rules' for the homochirality control of achiral molecules at the liquid/solid interface Such an induction and nonlinear chirality amplification effect promises a new approach towards two-dimensional homochirality control and may reveal important insights into asymmetric heterogeneous catalysis, chiral separation and chiral crystallization
117 citations
TL;DR: A novel 2D template-directed synthesis of ultrathin single-crystalline Au nanosheets with well-tuned thicknesses of several to tens of nanometers, large areas, and atomically flat surfaces is reported.
Abstract: Thickness-controlled synthesis of nanosheets of nonlayered materials is of scientific significance yet greatly underdeveloped because of the lack of controllable means of inducing anisotropic growth of 2D structures. Here we report a novel 2D template-directed synthesis of ultrathin single-crystalline Au nanosheets with well-tuned thicknesses of several to tens of nanometers, large areas (>100 μm(2)), and atomically flat surfaces. The 2D template is composed of hundred-nanometer-thick water layers sandwiched by lamellar bilayer membranes of a self-assembled nonionic surfactant, dodecylglyceryl itaconate, which appears as an iridescent solution as a result of Bragg reflection of visible light from the periodic lamellar planes. The large-area, ultrathin single-crystalline Au nanosheets enable the fabrication of plasmonic devices. For the first time, the property of surface plasmon polaritons on a patterned single-crystalline Au nanosheet was investigated, and a long propagation length approaching the theoretical expectation was found.
104 citations
TL;DR: Graphene oxide was tailored into GO nanosheets with periodic acid treatment and Interestingly, the latter have a superior sensing performance for the fast and reversible detection of SO(2) compared with the former at room temperature.
Abstract: Graphene oxide was tailored into GO nanosheets with periodic acid treatment. Interestingly, the latter have a superior sensing performance for the fast and reversible detection of SO2 compared with the former at room temperature. Its sensing mechanism was proposed from the structural changes of the GO nanosheets during the sensing and recovering processes.
58 citations
TL;DR: Six new bisbenzylisoquinoline alkaloids (1-6) and seven known compounds (8-14) were isolated from the tubers of Stephania epigaea, in addition to the major alkaloid, cepharanthine, which exhibited cytotoxicity against all six cancer cell lines except ECA109.
Abstract: Six new bisberizylisoquinoline alkaloids (1-6) and seven known compounds (8-14) were isolated from the tubers of Stephania epigaea, in addition to the major alkaloid, cepharanthine (7). The structures of 1-6 were elucidated by combined spectroscopic data analysis and chemical methods, with their configurations determined from their optical rotation values and confirmed using circular dichroism. Compounds 1-6 belong to the oxyacanthine type of bisbenzylisoquinoline alkaloids and have a rare methylenedioxy substituent. Compound 1, a dimer composed of benzylisoquinoline and seco-aristolactam units, represents a new type of bisbenzylisoquinoline alkaloid, while compounds 306 are bisbenzylisoquinoline N-oxides. These compounds were evaluated for their in vitro cytotoxicities against six human cancer cell lines (A-549, ECA109, HL-60, MCF-7, SMMC-7721, and SW480). Cepharanthine (7), the major component of S. epigaea, exhibited cytotoxicity against all of these cancer cell lines except ECA109, while its known analogue, 10, displayed cytotoxicity against all six cancer cell lines.
37 citations
TL;DR: Interestingly, the vesicle gels were observed to be sensitive to temperature, pH, and light; they thin at lower temperatures and become thicker at higher temperatures and the gels become thinner outside of this range.
Abstract: Viscoelastic vesicle gels were prepared by mixing a nonionic surfactant, tetraethylene glycol monododecyl ether (C 12 EO 4 ), and an anionic dye, sodium 4-phenylazobenzoic acid (AzoNa). The gels, which were composed of multilamellar vesicles, were analyzed by cryogenic transmission electron microscopy (cryo-TEM), freeze–fracture transmission electron microscopy (FF-TEM), 2 H NMR spectroscopy, and small-angle X-ray scattering (SAXS). The mechanism of vesicle-gel formation is explained by the influence of anionic molecules on the bilayer bending modulus. Interestingly, the vesicle gels were observed to be sensitive to temperature, pH, and light. The viscoelastic vesicle gels respond to heat; they thin at lower temperatures and become thicker at higher temperatures. The vesicle gels are only stable from pH 7 to 11, and the gels become thinner outside of this range. UV light can also trigger a structural phase transition from micelles to multilamellar vesicle gels.
35 citations
TL;DR: A microscopic investigation of the molecular packing structures of a fused thiophene derivative reveals the important role of intermolecular S···S interaction in directing the 2D self-assembly.
29 citations
TL;DR: In this paper, the three-dimensional network structures of hydrogels were determined by transmission electron microscopy images, scanning electron microscope images, 1H nuclear magnetic resonance, and small-angle X-ray scattering measurements.
Abstract: New hydrogels having high water content, ∼96 wt%, composed of cationic surfactants, alkyltrimethylammonium bromides (C
n
TAB, n = 12, 14, 16, and 18), and a small dye molecule, sodium azobzenzene 4,4′-dicarboxylic acid (AzoNa2), was firstly obtained. The three-dimensional network structures of hydrogels were determined by transmission electron microscopy images, scanning electron microscopy images, 1H nuclear magnetic resonance, and small-angle X-ray scattering measurements. The mechanism of hydrogel formation was also illustrated. The rheological data were obtained to investigate the mechanical strength of hydrogels, which were turned out to be strong mechanical strength (∼104 Pa) materials. We found that the strength of the hydrogel depends on the fiber density, which can be controlled by changing the proportion of the two compounds, concentration of surfactants, temperature, and the chain length of the surfactant. Interestingly, the hydrogels were found to have a multiple-stimulus response property. A reversible thermal, UV–vis, or a chemical response was investigated in the mixtures of cationic surfactants and azoic salt for the first time. These findings may find potential applications such as sensors, actuators, shape memories, and drug delivery systems, etc.
21 citations
TL;DR: An enantioselective direct α-alkylation of 2-oxindoles with Michler's hydrol via an S(N)1-type pathway in the non-covalent activation mode using the bis-cinchona alkaloid and Brønsted acid as a co-catalyst was developed and good to high yields and enantiOSElectivities were obtained.
21 citations
TL;DR: In this article, the role of tethered alkylene spacer in the formation of 2D supramolecular assemblies of the gemini amphiphiles was investigated by scanning tunneling microscopy (STM).
Abstract: The present work investigates the role of tethered alkylene spacer in the formation of 2D supramolecular assemblies of the gemini amphiphiles (Gn-Cn, n = 2, 4, 6, 8, 10) by scanning tunneling microscopy (STM). All Gn-Cn molecules self-organize into the Type I lamellar structure with close-packed alkyl side chains, whereas Type II lamellar structure with interdigitated alkyl side chains is also observed for Gn-C6 and -C8. Two different dipole–dipole interaction modes, that is, collinear and antiparallel arrangement of Schiff base molecular dipole, are proposed to modulate the formation of two types of lamellar assemblies. The results highlight that the tethered alkyl chain length is far from being a passive part of the self-assembled system and plays a definitive role in the supramolecular engineering at the liquid–solid interface.
TL;DR: It is demonstrated that functional groups with strong hydrogen-bond-formation ability are promising building blocks for the guided assembly of nanoporous networks and other hierarchical 2D assemblies.
Abstract: Control over the assembly of molecules on a surface is of great importance for the fabrication of molecule-based miniature devices. Melamine (MA) and molecules with terminal MA units are promising candidates for supramolecular interfacial packing patterning, owing to their multiple hydrogen-bonding sites. Herein, we report the formation of self-assembled structures of MA-capped molecules through a simple on-surface synthetic route. MA terminal groups were successfully fabricated onto rigid molecular cores with 2-fold and 3-fold symmetry through interfacial Schiff-base reactions between MA and aldehyde groups. Sub-molecular scanning tunneling microscopy (STM) imaging of the resultant adlayer revealed the formation of nanoporous networks. Detailed structural analysis indicated that strong hydrogen-bonding interactions between the MA groups persistently drove the formation of nanoporous networks. Herein, we demonstrate that functional groups with strong hydrogen-bond-formation ability are promising building blocks for the guided assembly of nanoporous networks and other hierarchical 2D assemblies.
TL;DR: The unique assembly behaviour of telechelic organics makes them promising structures as important building blocks for the design and construction of complex self-assembled nanoarchitectures.
Abstract: Guiding the self-assembly of different types of functional molecules into well-defined structures on surfaces is beneficial for both fundamental surface and interface study and emerging application fields, especially molecular and organic electronics. This review focuses on understanding the two-dimensional self-assembly process of telechelic organics, which feature alkoxylene chains terminated with carboxyl groups. With the combined flexibility of alkyl chains and directionality of carboxyl groups, telechelic organics show unique assembly behaviour on two-dimensional surfaces. By increasing the length of the alkoxylene chains, the cavities in the nanoporous networks of telechelic trimesic acid (1,3,5-benzene tricarboxylic acid) derivatives change from hexagonal cavities to irregular cavities on a highly oriented pyrolytic graphite surface. The nanoporous networks provide a flexible host template for host-guest supramolecular chemistry because the cavities framed by the flexible alkoxylene chains can be changed in accordance with the sizes/shapes of the guest molecules. Furthermore, the terminal carboxylic group can form a hydrogen bond with another hydrogen bond partner, leading to multi-component structural motifs and hierarchical assemblies. The unique assembly behaviour of telechelic organics makes them promising structures as important building blocks for the design and construction of complex self-assembled nanoarchitectures.
TL;DR: In this paper, a protein-inspired facile approach to synthesize carbon-coated SnO2 nanocrystals (NCs) is presented, which can be readily tuned by adjusting the pH value of the reaction solution.
Abstract: A protein-inspired facile approach to synthesise carbon-coated SnO2 nanocrystals (NCs) is presented. The carbon coating content could be readily tuned by adjusting the pH value of the reaction solution. The obtained carbon-coated SnO2 NCs showed a markedly improved lithium storage ability.
TL;DR: STM results reveal the formation of disordered thin organic films in acetonitrile and the involvement of the radical as an intermediate is evidenced by the negative effect of radical scavengers on organic thin film formation.
Abstract: Surface modifications of a Au(111) electrode with 4-bromobenzenediazonium tetrafluoroborate (BBD) in acetonitrile (ACN) and 0.1 M HClO4 have been characterized by scanning tunneling microscopy (STM). In ACN, STM results reveal the formation of disordered thin organic films. The involvement of the radical as an intermediate is evidenced by the negative effect of radical scavengers on organic thin film formation. In contrast, the 4,4′-dibromobiphenyl monolayer is observed when the aqueous solution is used as a medium to carry out the grafting experiment. The biphenyl compound is considered to be generated by a radical–radical coupling reaction.
TL;DR: In this article, the substituent effect on the adsorption behaviors of four halogen/pseudohalogen-terminated biphenyls (X-BP-X, with X = F, Br, I and CN) on a Au(1.1) surface was investigated by electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry (CV).
TL;DR: In this article, the structural details of the mono-component and the binary assemblies are revealed by high resolution scanning tunneling microscopy (STM) in graphite surfaces. But the electron donors and acceptors are preserved in the binary self-assembly.
Abstract: We have fabricated hybrid molecular chain structures formed by electron acceptor compound 1 and electron donor molecules 2 and 3 at the liquid/solid interface of graphite surface. The structural details of the mono-component and the binary assemblies are revealed by high resolution scanning tunneling microscopy (STM). Compound 1 can form two well-ordered lamellar patterns at different concentrations. In the co-adsorption structures, compounds 2 and 3 can insert into the space between molecular chains of compound 1 and form large area well-ordered nanoscale phase separated lamellar structures. The unit cell parameters for the coassemblies can be “flexibly” adjusted to make the electron donors and acceptors perfectly match along the molecular chains. Scanning tunneling spectroscopy (STS) results indicate that the electronic properties of individual molecular donors and acceptors are preserved in the binary self-assembly. These results provide molecular insight into the nanoscale phase separation of organic electron acceptors and donors on surfaces and are helpful for the fabrication of surface supramolecular structures and molecular devices.
TL;DR: The present work provides direct evidence for understanding the potential-controlled adsorption behaviors of SubPc and SubNc on the Au(111) surface.
Abstract: The adsorption behaviors of subphthalocyanine (SubPc) and subnaphthalocyanine (SubNc) on the Au(111) surface were investigated by electrochemical scanning tunneling microscopy (ECSTM). Two types of ordered adlayer structures of SubPc were observed at 550 mV versus the reversible hydrogen electrode (RHE). All of the SubPc molecules take the Cl-down adsorption configuration on Au(111) in both structures. The ordered adlayers exist in the potential range between 350 and 650 mV. The SubNc molecules adsorb on Au(111) in a less-ordered pattern than the SubPc molecules. The present work provides direct evidence for understanding the potential-controlled adsorption behaviors of SubPc and SubNc on the Au(111) surface.
TL;DR: In this article, a one-dimensional time-dependent FEL code has been developed, in which the imperfection effects of an elliptical permanent undulator are taken into account, and comprehensive simulation results indicate that the residual beam energy chirp and the intrinsic FEL gain may contribute to the degradation of the polarization performance for the crossed planar undulator.
Abstract: The polarization switch of a free-electron laser (FEL) is of great importance to the user scientific community. In this paper, we investigate the generation of controllable polarization FEL from two well-known approaches for Dalian coherent light source, i.e., crossed planar undulator and elliptical permanent undulator. In order to perform a fair comparative study, a one-dimensional time-dependent FEL code has been developed, in which the imperfection effects of an elliptical permanent undulator are taken into account. Comprehensive simulation results indicate that the residual beam energy chirp and the intrinsic FEL gain may contribute to the degradation of the polarization performance for the crossed planar undulator. And the elliptical permanent undulator is not very sensitive to the undulator errors and beam imperfections. Meanwhile, with proper configurations of the main planar undulators and additional elliptical permanent undulator section, circular polarized FEL with pulse energy exceeds 100 $\mu$J could be achieved at Dalian coherent light source.
TL;DR: The aim of the ‘‘Scanning tunneling microscopy: revealing new physical chemistry insight’’ themed issue, is to highlight the role of STM techniques at the interface of chemistry, physics, and material sciences, focusing especially on surface physical chemistry.
Abstract: It has been 30 years since the invention of Scanning Tunnelling Microscopy (STM). STM allows scientists to directly image the nano-world at atomic resolution and has stimulated the development of a large family of probe-based microscopy. More importantly, STM has opened new avenues to explore the fascinating properties associated with nano-sized objects, and has fueled the growth of nanoscience and nanotechnology. As a powerful surface characterization technique, STM is particularly important for physical chemistry research of surfaces and interfaces. The aim of the ‘‘Scanning tunneling microscopy: revealing new physical chemistry insight’’ themed issue, is to highlight the role of STM techniques at the interface of chemistry, physics, and material sciences, focusing especially on surface physical chemistry. The topics covered by the issue include single molecule science, surface physics and chemistry, supramolecular assembly on surfaces and interfaces, and molecular electronics. One of the most fascinating features of STM is not only its ability to obtain the ultimate single molecular resolution, but also to locally probe the electronic properties of the atoms and molecules. It goes without saying that STM has motivated the development of single molecule science. In the perspective article by Wang, Hou, and coworkers (DOI: 10.1039/C3CP51446C), an overview of tip-assisted single molecule chemistry, such as the identification of specific orbitals or states of molecules on surfaces, tipinduced single-molecule manipulation, atomically resolved chemical reactions in photochemistry and tip-induced electroluminescence, has been given. One hot topic in single molecule science is molecular electronics and quantum transport through metallic nanocontacts. By employing the STM-based break junction technique, Mao et al. reported the observation of a multiple subatomic steplength when stretching single atom contacts (DOI: 10.1039/C3CP50473E). Fundamental understanding of surface physical chemistry is of great importance for catalysis, electrochemistry, and many other application fields. The emergence of STM and other advanced surface characterization techniques provides powerful tools to understand surface and interface science. In this collection, Yang and Magnussen present quantitative studies of the diffusion process of adsorbates at electrodes under electrochemical control, using an in situ video STM at a temporal resolution of tens of milliseconds (DOI: 10.1039/ C3CP51027A). Rosei et al. reported the structural characterization of submonolayer Zn on a Pd(111) surface, which is technically important for near-surface alloy heterogeneous catalysis (DOI: 10. 1039/C3CP50793A). The engineering of highly ordered molecular patterns on surfaces represents a prominent bottom-up approach for the fabrication of well-defined molecular architectures at surfaces, which is considered to be an important step towards next-generation molecule-based electronics. Chen et al. present a comprehensive review of supramolecular assemblies of binary nanostructures on graphite surfaces (DOI: 10.1039/ C3CP00023K). Significant attention has been devoted to understanding and tailoring weak but appreciable noncovalent intermolecular interactions, such as hydrogen bonding (DOI: 10.1039/ C3CP50891A), dipole–dipole interaction (DOI: 10.1039/C3CP50808K), and metal– ligand coordination interactions (DOI: 10.1039/C3CP50779C), in order to fabricate sophisticated 2D supramolecular assemblies. On the other hand, the phase transition of cobalt porphyrin adlayers on Au(100) surfaces highlights the important role of substrate structure and substrate–adsorbate interactions for supramolecular assembly (DOI: 10.1039/C3CP50797A). The delicate balance between different weak interactions may result in complicated polymorphs in the adlayers (DOI: 10.1039/C3CP50829C and DOI: 10.1039/C3CP51074C), which on the other hand, provides a great opportunity to understand the underlying driving forces of the self-assembly process. Institute of Chemistry, Chinese Academy of Sciences, and Beijing National Laboratory for Molecular Sciences, Beijing 100190, P. R. China DOI: 10.1039/c3cp90096g
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TL;DR: In this article, the echo-enabled harmonic generation (EEHG) free-electron laser (FEL) has been demonstrated at lower harmonics and the first lasing at third harmonic also has been achieved at Shanghai deep ultra-violet FEL (SDUV-FEL).
Abstract: The echo-enabled harmonic generation (EEHG) free-electron laser (FEL) has been already demonstrated at lower harmonics and the first lasing at third harmonic also has been achieved at Shanghai deep ultra-violet FEL (SDUV-FEL). While the great advantage of much higher harmonic up-conversion efficiency of EEHG over other seeded FELs only shows evidently at much higher harmonics. In this paper, we investigate the possibility of EEHG lasing at 10-th harmonic of the seed laser at SDUV-FEL, both physical designs and numerical simulations have been studied carefully. Two proposals of EEHG at 10-th harmonic have been studied respectively, i.e. with the seed lasers of the same color and two difference colors, the simulation results indicate that both approaches could be the candidate for EEHG lasing at 10-th harmonic at SDUV-FEL, meanwhile the coherent synchrotron radiation does not affect the performance of EEHG-FEL but only slightly shifts the central radiation frequency.
Patent•
04 Dec 2013
TL;DR: In this paper, a preparation method of phyllaemblicin B was proposed, which is simple, practical, short in production cycle, easy in batch production and industrial production.
Abstract: The invention provides a preparation method of phyllaemblicin B. The method includes: subjecting ethanol extract of plant raw materials to column chromatography isolation, enriching phyllaemblicin B parts, concentrating, subjecting to column chromatography purification to obtain coarse phyllaemblicin B, and recrystalizing with ethanol to obtain phyllaemblicin B with the purity larger than 98%. By the method which is simple, practical, short in production cycle, easy in batch production and industrial production, the phyllaemblicin B is high in yield and purity.
TL;DR: The results showed that the content of oxygen-containing groups had great influence on the capacitive performance of SWCNT/GO hybrid films and that the film annealed at 250 degrees C under 5% H2/Ar flow displayed an optimal capacitiveperformance.
Abstract: Homogeneous free-standing SWCNT/GO hybrid network films were fabricated using vacuum filtration method and their performances to be used as flexible electrodes in electrochemical capacitors were studied. Firstly, the SWCNT/GO hybrid films were treated under different temperature to investigate the influence of oxygen-containing groups on GO nanosheets on capacitive performance of them. Our results showed that the content of oxygen-containing groups had great influence on the capacitive performance of SWCNT/GO hybrid films and that the film annealed at 250 degrees C under 5% H2/Ar flow displayed an optimal capacitive performance. For the film with SWCNT/GO mass ratio of 1:4, specific capacitances of 171.85, 162.9, 148.98, 133.8, 112.8 and 82.24 F/g corresponding to discharge current of 5, 10, 20, 40, 80 and 160 A/g, respectively, were achieved. Secondly, the influence of mass ratio of SWCNT/GO on capacitive performance of SWCNT/GO hybrid films was also demonstrated. The hybrid films exhibited extremely high mechanical strength with tensile strength up to 461 MPa and specific capacitance of 105.2 F/g at current density of 5 A/g in case of 1:1 mass ratio of SWCNT/GO. A higher specific capacitance of 206.7 F/s at discharge current of 5A/g was obtained for the films with SWCNT/GO mass ratio of 1:8. Our SWCNT/GO hybrid network films showed good flexibility and durability over 2000 bending cycles test, indicating the potential to be used in flexible energy-storage devices.
TL;DR: In this paper, a novel organocatalytic asymmetric α-alkylation of 2-oxindoles with Michler's alcohol was described, which was catalyzed by the combination of a chiral bis-cinchona alkaloid and a Broensted acid.
Abstract: A novel organocatalytic asymmetric α-alkylation of 2-oxindoles (I) with Michler′s alcohol (II) is described, which is catalyzed by the combination of a chiral bis-cinchona alkaloid and a Broensted acid.
TL;DR: The excellent regioselectivity is controlled by the Pd-catalyst/ligand system and depends on the substrate used.
Abstract: The excellent regioselectivity is controlled by the Pd-catalyst/ligand system and depends on the substrate used.
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TL;DR: In this paper, several polarization control approaches are presented to investigate the great potential on Dalian coherent light source, which is a government-approved novel FEL user facility with the capability of wavelength continuously tunable in the EUV regime of 50 − 150 nm.
Abstract: The property of the FEL polarization is of great importance to the user community. FEL pulses with ultra-high intensity and flexible polarization control ability will absolutely open up new scientific realms. In this paper, several polarizationcontrolapproachesare presentedto investigate the great potential on Dalian coherent light source, which is a government-approvednovel FEL user facility with the capability of wavelength continuously tunable in the EUV regime of 50 − 150 nm. The numerical simulations show that both circularly polarized FELs with highly modulating frequencyand 100 μJ levelpulse energycouldbe generated at Dalian coherent light source.
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TL;DR: In this article, the effect of the slippage effect in the modulator is taken into account to preserve the excellent temporal coherence of seeded FELs in presence of large laser phase errors.
Abstract: Free-electron lasers (FELs) seeded with external lasers hold great promise for generating high power radiation with nearly transform-limited bandwidth in soft x-ray region However, it has been pointed out that the initial seed laser noise will be amplified by the frequency up-conversion process, which may degrade the quality of the output radiation produced by a harmonic generation scheme In this paper, theoretical and simulation studies for laser phase error amplification in seeded FEL schemes with slippage effect taken into account are presented It is found that, the seed laser imperfection experienced by the electron beam can be significantly smoothed by the slippage effect in the modulator when the slippage length is comparable to the laser pulse length This smoothing effect allows one to preserve the excellent temporal coherence of seeded FELs in presence of large laser phase errors For ultra-short UV seed lasers with FWHM around 16 fs, the slippage length in a modulator with ~30 undulator periods is typically comparable to the laser width; for longer seed laser pulses with FWHM around 80 fs, the slippage length can be made comparable to the laser width using a modulator tuned at the sub-harmonic of the UV seed laser Three-dimensional simulations have been carried out for a soft x-ray facility using seed laser pulses with large frequency chirp and the results show that the sensitivity of the bandwidth of the seeded FEL to the initial frequency chirp can be significantly reduced by a proper design of the modulator such that the slippage length is comparable to the laser width Our studies show that the tolerance on laser phase error for generating nearly transform-limited soft x-ray pulses in seeded FELs is much looser than previously thought and fully coherent radiation at nanometer wavelength may be reached with current technologies