Graphene has attracted extensive research interest in recent years because of its fascinating physical properties and its potential for various applications. The band structure or electronic properties of graphene are...Graphene has attracted extensive research interest in recent years because of its fascinating physical properties and its potential for various applications. The band structure or electronic properties of graphene are very sensitive to its geometry, size, and edge structures, especially when the size of graphene is below the quantum confinement limit. Graphene nanoribbons （GNRs） can be used as a model system to investigate such structure-sensitive parameters. In this review, we examine the fabrication of GNRs via both top-down and bottom-up approaches. The edge-related electronic and transport properties of GNRs are also discussed.展开更多
By using the first-principles calculations, the electronic properties of graphene nanoribbon （GNR） doped by boron/nitrogen （B/N） bonded pair are investigated. It is found that B/N bonded pair tends to be doped at ...By using the first-principles calculations, the electronic properties of graphene nanoribbon （GNR） doped by boron/nitrogen （B/N） bonded pair are investigated. It is found that B/N bonded pair tends to be doped at the edges of GNR and B/N pair doping in GNR is easier to carry out than single B doping and unbonded B/N co-doping in GNR. The electronic structure of GNR doped by B/N pair is very sensitive to doping site besides the ribbon width and chirality. Moreover, B/N pair doping can selectively adjust the energy gap of armchair GNR and can induce the semimetal-semiconductor transmission for zigzag GNR. This fact may lead to a possible method for energy band engineering of GNRs and benefit the design of graphene electronic device.展开更多
In the present work, we report nitrogen and phosphorus co-doped 3-D structured carbon nanotube intercalated graphene nanoribbon composite. The graphene nanoribbons are prepared via partial exfoliation of multi-walled ...In the present work, we report nitrogen and phosphorus co-doped 3-D structured carbon nanotube intercalated graphene nanoribbon composite. The graphene nanoribbons are prepared via partial exfoliation of multi-walled carbon nanotubes. In the graphene nanoribbons/CNTs composite, carbon nanotubes play a role of skeleton and support the exfoliated graphene nanoribbons to form the stereo structure. After high temperature heat-treatment with ammonium dihydrogen phosphate, the unique structure reserves both the properties of carbon nanotube and graphene, exhibiting excellent catalytic performance for the ORR with excellent onset and half-wave potential, which is similar to commercial Pt/C electrocatalysts.展开更多
In pristine graphene ribbons,disruption of the aromatic bond network results in depopulation of covalent orbitals and tends to elongate the edge,with an effective force of fe~2 eV/Å(larger for armchair edges than...In pristine graphene ribbons,disruption of the aromatic bond network results in depopulation of covalent orbitals and tends to elongate the edge,with an effective force of fe~2 eV/Å(larger for armchair edges than for zigzag edges,according to calculations).This force can have quite striking macroscopic manifestations in the case of narrow ribbons,as it favors their spontaneous twisting,resulting in the parallel edges forming a double helix,resembling DNA,with a pitchλt of about 1520 lattice parameters.Through atomistic simulations,we investigate how the torsionτ~1/λt decreases with the width of the ribbon,and observe its bifurcation:the twist of wider ribbons abruptly vanishes and instead the corrugation localizes near the edges.The length-scale(λe)of the emerging sinusoidal“frill”at the edge is fully determined by the intrinsic parameters of graphene,namely its bending stiffness D=1.5 eV and the edge force fe withλe~D/fe.Analysis reveals other warping configurations and suggests their sensitivity to the chemical passivation of the edges,leading to possible applications in sensors.展开更多
Sandwich structured graphene-wrapped FeS-graphene nanoribbons （G@FeS-GNIKs） were developed. In this composite, FeS nanoparticles were sandwiched between graphene and graphene nanoribbons. When used as anodes in lith...Sandwich structured graphene-wrapped FeS-graphene nanoribbons （G@FeS-GNIKs） were developed. In this composite, FeS nanoparticles were sandwiched between graphene and graphene nanoribbons. When used as anodes in lithium ion batteries （L1Bs）, the G@FeS-GNR composite demonstrated an outstanding electrochemical performance. This composite showed high reversible capacity, good rate performance, and enhanced cycling stability owing to the synergy between the electrically conductive graphene, graphene nanoribbons, and FeS. The design concept developed here opens up a new avenue for constructing anodes with improved electrochemical stability for LIBs.展开更多
A nanocomposite material of SnO2-reduced graphene oxide nanoribbons has been developed. In this composite, the reduced graphene oxide nanoribbons are uniformly coated by nanosized SnO2 that formed a thin layer of SnO2...A nanocomposite material of SnO2-reduced graphene oxide nanoribbons has been developed. In this composite, the reduced graphene oxide nanoribbons are uniformly coated by nanosized SnO2 that formed a thin layer of SnO2 on the surface. When used as anodes in lithium ion batteries, the composite shows outstanding electrochemical performance with the high reversible discharge capacity of 1,027 mAh/g at 0.1 A/g after 165 cycles and 640 mAh/g at 3.0 A/g after 160 cycles with current rates varying from 0.1 to 3.0 A/g and no capacity decay after 600 cycles compared to the second cycle at a current density of 1.0 A/g. The high reversible capacity, good rate performance and excellent cycling stability of the composite are due to the synergistic combination of electrically conductive reduced graphene oxide nanoribbons and SnO2, The method developed here is practical for the large-scale development of anode materials for lithium ion batteries.展开更多
A hexaazatriphenylene（HAT） derivative that bears two n-octyl chains was designed and synthesized.Its photophysical and electrochemical properties have been investigated.SEM study revealed that it could self-assemble...A hexaazatriphenylene（HAT） derivative that bears two n-octyl chains was designed and synthesized.Its photophysical and electrochemical properties have been investigated.SEM study revealed that it could self-assemble into well-ordered 1D nanoribbons or 2D microsheets,which depends on the polarity of the solvents used.展开更多
The microstructural characteristics and microhardness of nanostructured Al-4.6Cu-Mn ribbons produced by melt spinning were investigated using field-emission gun scanning electron microscopy, transmission electron micr...The microstructural characteristics and microhardness of nanostructured Al-4.6Cu-Mn ribbons produced by melt spinning were investigated using field-emission gun scanning electron microscopy, transmission electron microscopy, and hardness testing, and the results were compared to those of similar ribbons manufactured by direct-chill casting. It is shown that the nanostructure of the as-melt-spun ribbons consists of α-Al dendrites with a secondary dendrite arm spacing of approximately 0.55-0.80 μm and ultrafine eutectic crystals of a nanosized scale of approximately 100-200 nm on dendritic boundaries. The solidification time and cooling rate of 46-μm-thick ribbons were estimated to be 1.3 × 10-6 s and 4.04 × 106 K·s-1, respectively. At an aging temperature of 190°C, the coherent θ″ phase in aged ribbons gradually transforms into nanoscale θ′-phase platelets as the aging time is extended from 2 to 8 h; the rod-like morphology of the T(Al20Cu2Mn3) dispersoid with 120-160-nm diameter also forms, which results in peak aging hardness. The precipitation behaviors of aged ribbons cannot be changed at the high cooling rates of as-cast ribbons. However, a finer and more uniformly distributed microstructure and a supersaturated solid solution at a high cooling rate can shorten the time required to obtain a certain aging hardness before peak hardness.展开更多
Dual-phase heterointerface electrocatalysts(DPHE)constructed by oxygen reduction reaction(ORR)-and oxygen evolution reaction(OER)-active elements exhibit excellent bifunctional activity and long-term durability due to...Dual-phase heterointerface electrocatalysts(DPHE)constructed by oxygen reduction reaction(ORR)-and oxygen evolution reaction(OER)-active elements exhibit excellent bifunctional activity and long-term durability due to the abundant interface exposure and synergistic catalytic effect.Herein,low-dimensional N-doped graphene nanoribbons(N-GNRs)coupling with ultrathin CoO nanocomposites(N-GNRs/CoO)were controllably fabricated through a facile two-step approach using synthesized Co(OH)_2 nanosheet as CoO precursor.Density functional theory(DFT)calculations and experimental characterizations prove that the formation of interface between N-GNRs and CoO can induce local charge redistribution,contributing to the improvement of catalytic activity and stability.The optimal N-GNRs/CoO DPHE possesses hierarchically porous architectures and presents outstanding bifunctional activities with a small potential gap of 0.729 V between the potential at 10 mA·cm^(-2)for OER and the halfwave potential for ORR,which outperforms Pt/C+IrO_(2)and the majority of noble-metal-free bifunctional catalysts.Liquid-and solid-state rechargeable Zn-air batteries assembled with N-GNRs/CoO as the cathode also display high peak power density and fantastic cycle stability,superior to that of benchmark Pt/C+IrO_(2)catalyst.It is anticipated to offer significant benefits toward high activity,stability and mechanical flexibility bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries.展开更多
Graphene,as star versatile materials having extraordinarily high electric conductivity,electron mobility,thermal conductivity,thermal stability,optical transparency,and mechanical strength,has attracted much attention...Graphene,as star versatile materials having extraordinarily high electric conductivity,electron mobility,thermal conductivity,thermal stability,optical transparency,and mechanical strength,has attracted much attention from scientists and engineers in the field of materials,chemistry,physics,energy,and environment in the last decade and achieved fruitful accomplishment.This review discusses preparation strategies,functionality,characterization,and applications for two dimensional nanosheet and quasi-onedimensional nanoribbon of graphene through direct exfoliation of graphite,chemical vapor deposition of hydrocarbon,laser-induced direct synthesis of graphene,laser etched graphene oxide in the dry state without the use of toxic reducing agent hydrazine,unzipping carbon nanotube,and polycondensation of polycyclic aromatics on the basis of 178 representative references mostly in 2015.The stabilization of graphene oxide prepared in chemical preparation in " top-down" is emphasized.Several vital classic methods of characterizing molecular structure,C/O ratio,defect,morphology,single-or few-layered( 2 to 10 layers) structure,porous and hollow structures,including Raman spectroscopy,AFM,SEM,TEM,STM,electron diffraction,X-ray diffraction,and X-ray photoelectron spectroscopy are systematically introduced.Because graphene possesses novel incomparable multifunctionalities,its versatile applications as novel conducting additives,reinforcing filler,separation membrane,sensor,anticorrosive coating,catalyst,electromagnetic shield,lubricant,and flexible electrode materials in electrochemical and electronic devices,including photovoltaic cells,supercapacitors,rechargeable batteries,sensors,field effect transistors,light emitting diodes,separation membranes,adsorbents and absorbents,catalysts,electro-optic modulator,terahertz emitter and detector,and semiconductors,have been mentioned.Especially in the aspect of both high performance and cost-effectiveness,graphene is expected to be even superior to the expensive carbon nanotubes.展开更多
Unlike graphene sheets, graphene nanoribbons （GNRs） can exhibit semiconducting band gap characteristics that can be tuned by controlling impurity doping and the GNR widths and edge structures. However, achieving suc...Unlike graphene sheets, graphene nanoribbons （GNRs） can exhibit semiconducting band gap characteristics that can be tuned by controlling impurity doping and the GNR widths and edge structures. However, achieving such control is a major challenge in the fabrication of GNRs. Chevron-type GNRs were recently synthesized via surface-assisted polymerization of pristine or N-substituted oligophenylene monomers. In principle, GNR heterojunctions can be fabricated by mixing two different monomers. In this paper, we report the fabrication and characterization of chevron-type GNRs using sulfur-substituted oligophenylene monomers to produce GNRs and related heterostructures for the first time. First-principles calculations show that the GNR gaps can be tailored by applying different sulfur configurations from cyclodehydrogenated isomers via debromination and intramolecular cyclodehydrogenation. This feature should enable a new approach for the creation of multiple GNR heterojunctions by engineering their sulfur configurations. These predictions have been confirmed via scanning tunneling microscopy and scanning tunneling spectroscopy. For example, we have found that the S-containing GNRs contain segments with distinct band gaps, i.e., a sequence of multiple heterojunctions that results in a sequence of quantum dots. This unusual intraribbon heterojunction sequence may be useful in nanoscale optoelectronic applications that use quantum dots.展开更多
We have investigated the electronic properties of WTe2 armchair nanoribbons with defects. WTe2 nanoribbons can be categorized depending on the edge structure in two types： armchair and zigzag. WTe2 in its bulk form h...We have investigated the electronic properties of WTe2 armchair nanoribbons with defects. WTe2 nanoribbons can be categorized depending on the edge structure in two types： armchair and zigzag. WTe2 in its bulk form has an indirect band gap but nanoribbons and nanosheets of WTe2 have direct band gaps. Interestingly, the zigzag nanoribbon is metallic while the armchair nanoribbons are semiconducting. Thus they can find applications in device fabrication. Therefore, it is very important to study the effect of defects on the electronic properties of the armchair nanoribbons as these defects can impair the device properties and characteristics. We have considered defects such as： vacancy, rough edge, wrap, ripple and twist in this work. We report the band gap variation with these defects. We have also studied the change in band gap and total energy with varying degrees of wrap, ripple and twist.展开更多
Substantial effort has been made to search for electrode materials of Na-ion batteries with high energy/power density. The application of S-saturated zigzag MoS2 nanoribbons （MoSzNRs） for Na-ion batteries has been e...Substantial effort has been made to search for electrode materials of Na-ion batteries with high energy/power density. The application of S-saturated zigzag MoS2 nanoribbons （MoSzNRs） for Na-ion batteries has been explored through density function theory （DFT）. The theoretical maximum specific capacity reaches 386.4 mAh,g t via dou- ble-side and special edge adsorption mode. The electronic structure reveals that there exists charge transfer between Na and MoS2NRs. The diffusion barrier on MoS2NRs （0.17 eV） is much lower than that of bulk MoS2 （1.15 eV）, indicating an excellent diffusion kinetics, in addition, the S-edge in MoS2NRs plays a key role. Firstly, the Mo edge was half saturated by S, which helps to stabilize the MoS2NRs as well as offer more intercalation sites for Na. On the other hand, Na migrates much faster on the S edge route in MoS2NRs. Our computational results show that S-saturated MoSzNRs exhibit a great potential as electrode materials for Na-ion batteries with high performance.展开更多
We present a study of electronic properties of zigzag graphene nanoribbons （ZGNRs） substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near t...We present a study of electronic properties of zigzag graphene nanoribbons （ZGNRs） substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near the Fermi level sepa- rate due to the asymmetric nitrogen-doping. The ground states of these systems become ferromagnetic because the local magnetic moments along the undoped edges remain and those along the doped edges are suppressed. By controlling the charge-doping level, the magnetic moments of the whole ribbons are modulated. Proper charge doping leads to interest- ing half-metallic and single-edge conducting ribbons which would be helpful for designing graphene-nanoribbon-based spintronic devices in the future.展开更多
In this paper, nanotubes and nanoribbons of sodium titanate structures were synthesized via hydrothermal methods in alkaline solution. CdS decorated titanate nanotubes and nanoribbons were therefore constructed for ex...In this paper, nanotubes and nanoribbons of sodium titanate structures were synthesized via hydrothermal methods in alkaline solution. CdS decorated titanate nanotubes and nanoribbons were therefore constructed for exploring the performance of hydrogen evolution and synergistic effect of CdS based titanate structures. CdS decorated titanate nanotubes and nanoribbons were characterized by high resolution transmission electron microscopy （HRTEM）, X-ray diffraction （XRD）, UV-vis, Brunauer- Emmett-Teller （BET） and X-ray photoelectron spectroscopy （XPS） measurements. CdS encapsuled in titanate nanotubes （CdS-ETNTs） showed the best capacity of H2 evolution by water splitting and stability than that from the other two structures, i.e., CdS doped titanate nanotubes （CdS-DTNTs） and CdS doped titanate nanoribbons （CdS-DTNRs）, which could be explained by the synergistic effect of decorated CdS with sodium titanate structures and confinement effect of CdS nanoparticles encapsuled inside展开更多
A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol （PEG） （GEMINI protocol）. Previous work provided evidence that this is i...A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol （PEG） （GEMINI protocol）. Previous work provided evidence that this is in fact possible. Other fusogens might improve current results. In this study, we aimed to assess the effects of PEGylated graphene nanoribons （PEG-GNR, and called ＂TexasPEG＂ when prepared as lwt% dispersion in PEG600） versus placebo （saline） on locomotor function recovery and cellular level in a rat model of spinal cord transection at lumbar segment 1 （L1） level. In vivo and in vitro experiments （n -- 10 per experiment） were designed. In the in vivo experiment, all rats were submitted to full spinal cord transection at L1 level. Five weeks later, behavioral assessment was performed using the Basso Beattie Bresnahan （BBB） locomotor rating scale. Immunohistochemical staining with neuron marker neurofilament 200 （NF200） antibody and astrocyt- ic scar marker glial fibrillary acidic protein （GFAP） was also performed in the injured spinal cord. In the in vitro experiment, the effects of TexasPEG application for 72 hours on the neurite outgrowth of SH-SYSY cells were observed under the inverted microscope. Results of both in vivo and in vitro experiments suggest that TexasPEG reduces the formation of glial scars, promotes the regeneration of neurites, and thereby contributes to the recovery of locomotor function of a rat model of spinal cord transfection.展开更多
Fabricating single-atom catalysts(SACs)with high catalytic activity as well as great stability is a big challenge.Herein,we propose a precise synthesis strategy to stabilize single atomic ruthenium through regulating ...Fabricating single-atom catalysts(SACs)with high catalytic activity as well as great stability is a big challenge.Herein,we propose a precise synthesis strategy to stabilize single atomic ruthenium through regulating vanadium defects of nickel vanadium layered double hydroxides(NiV-LDH)ultrathin nanoribbons support.Correspondingly,the isolated atomically Ru doped NiV-LDH ultrathin nanoribbons(NiVRu-R)were successfully fabricated with a super-high Ru load of 12.8 wt.%.X-ray absorption spectrum(XAS)characterization further confirmed atomic dispersion of Ru.As catalysts for electrocatalytic hydrogen evolution reaction(HER)in alkaline media,the NiVRu-R demonstrated superior catalytic properties to the commercial Pt/C.Moreover,it maintained exceptional stability even after 5,000 cyclic voltammetry cycles.In-situ XAS and density functional theory(DFT)calculations prove that the Ru atomic sites are stabilized on supports through forming the Ru-O-V structure,which also help promote the catalytic properties through reducing the energy barrier on atomic Ru catalytic sites.展开更多
Motivated by recent successful synthesize of segmented graphene nanoribbons(GNRs)with junctions,we explore electronic properties of a novel form of GNR with sawtooth-like structure using the density-functional theory ...Motivated by recent successful synthesize of segmented graphene nanoribbons(GNRs)with junctions,we explore electronic properties of a novel form of GNR with sawtooth-like structure using the density-functional theory method.It is found that the unique edge structures of the sawtooth-like GNR induce richer band-gap features than the straight GNR counterpart with either armchair or zigzag edges.The effect of external electric fi eld on the electronic properties of the sawtooth-like GNR is also studied.The theoretical results may be useful for designing GNR-based fi eld-effect transistors.展开更多
基金Acknowledgements This work was supported by the National Natural Science Foundation of China （NSFC, Grant Nos. 61325021, 11574361, and 61390503）, the National Basic Research Program of China （973 Program, Grant Nos. 2013CB934500 and 2013CBA01602）, and the Key Research Program of Frontier Sciences （Grant No. QYZDB-SSW-SLH004）.
文摘Graphene has attracted extensive research interest in recent years because of its fascinating physical properties and its potential for various applications. The band structure or electronic properties of graphene are very sensitive to its geometry, size, and edge structures, especially when the size of graphene is below the quantum confinement limit. Graphene nanoribbons （GNRs） can be used as a model system to investigate such structure-sensitive parameters. In this review, we examine the fabrication of GNRs via both top-down and bottom-up approaches. The edge-related electronic and transport properties of GNRs are also discussed.
基金supported by the Science and Technology Program of Hunan Province,China (Grant No.2010DFJ411)the Natural Science Foundation of Hunan Province,China (Grant No.11JJ4001)the Fundamental Research Funds for the Central Universities,China (Grant No.201012200053)
文摘By using the first-principles calculations, the electronic properties of graphene nanoribbon （GNR） doped by boron/nitrogen （B/N） bonded pair are investigated. It is found that B/N bonded pair tends to be doped at the edges of GNR and B/N pair doping in GNR is easier to carry out than single B doping and unbonded B/N co-doping in GNR. The electronic structure of GNR doped by B/N pair is very sensitive to doping site besides the ribbon width and chirality. Moreover, B/N pair doping can selectively adjust the energy gap of armchair GNR and can induce the semimetal-semiconductor transmission for zigzag GNR. This fact may lead to a possible method for energy band engineering of GNRs and benefit the design of graphene electronic device.
基金supported by the National Natural Science Foundation of China (Nos. 21306060, 21573083)the Program for New Century Excellent Talents in University of Ministry o Education of China (No. NCET-13-0237)+2 种基金the Doctoral Fund o Ministry of Education of China (No. 20130142120039)the Fundamental Research Funds for the Central University (Nos 2013TS136, 2014YQ009)the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences (No. DE-SC0012704)
文摘In the present work, we report nitrogen and phosphorus co-doped 3-D structured carbon nanotube intercalated graphene nanoribbon composite. The graphene nanoribbons are prepared via partial exfoliation of multi-walled carbon nanotubes. In the graphene nanoribbons/CNTs composite, carbon nanotubes play a role of skeleton and support the exfoliated graphene nanoribbons to form the stereo structure. After high temperature heat-treatment with ammonium dihydrogen phosphate, the unique structure reserves both the properties of carbon nanotube and graphene, exhibiting excellent catalytic performance for the ORR with excellent onset and half-wave potential, which is similar to commercial Pt/C electrocatalysts.
基金the Air Force Research Laboratory and by the Robert Welch Foundation(C-1590).
文摘In pristine graphene ribbons,disruption of the aromatic bond network results in depopulation of covalent orbitals and tends to elongate the edge,with an effective force of fe~2 eV/Å(larger for armchair edges than for zigzag edges,according to calculations).This force can have quite striking macroscopic manifestations in the case of narrow ribbons,as it favors their spontaneous twisting,resulting in the parallel edges forming a double helix,resembling DNA,with a pitchλt of about 1520 lattice parameters.Through atomistic simulations,we investigate how the torsionτ~1/λt decreases with the width of the ribbon,and observe its bifurcation:the twist of wider ribbons abruptly vanishes and instead the corrugation localizes near the edges.The length-scale(λe)of the emerging sinusoidal“frill”at the edge is fully determined by the intrinsic parameters of graphene,namely its bending stiffness D=1.5 eV and the edge force fe withλe~D/fe.Analysis reveals other warping configurations and suggests their sensitivity to the chemical passivation of the edges,leading to possible applications in sensors.
文摘Sandwich structured graphene-wrapped FeS-graphene nanoribbons （G@FeS-GNIKs） were developed. In this composite, FeS nanoparticles were sandwiched between graphene and graphene nanoribbons. When used as anodes in lithium ion batteries （L1Bs）, the G@FeS-GNR composite demonstrated an outstanding electrochemical performance. This composite showed high reversible capacity, good rate performance, and enhanced cycling stability owing to the synergy between the electrically conductive graphene, graphene nanoribbons, and FeS. The design concept developed here opens up a new avenue for constructing anodes with improved electrochemical stability for LIBs.
文摘A nanocomposite material of SnO2-reduced graphene oxide nanoribbons has been developed. In this composite, the reduced graphene oxide nanoribbons are uniformly coated by nanosized SnO2 that formed a thin layer of SnO2 on the surface. When used as anodes in lithium ion batteries, the composite shows outstanding electrochemical performance with the high reversible discharge capacity of 1,027 mAh/g at 0.1 A/g after 165 cycles and 640 mAh/g at 3.0 A/g after 160 cycles with current rates varying from 0.1 to 3.0 A/g and no capacity decay after 600 cycles compared to the second cycle at a current density of 1.0 A/g. The high reversible capacity, good rate performance and excellent cycling stability of the composite are due to the synergistic combination of electrically conductive reduced graphene oxide nanoribbons and SnO2, The method developed here is practical for the large-scale development of anode materials for lithium ion batteries.
文摘A hexaazatriphenylene（HAT） derivative that bears two n-octyl chains was designed and synthesized.Its photophysical and electrochemical properties have been investigated.SEM study revealed that it could self-assemble into well-ordered 1D nanoribbons or 2D microsheets,which depends on the polarity of the solvents used.
基金financial support from the Aeronautical Science Foundation of China (No. 2012ZF53080)the Shaanxi Province Science and Technology Research and Development Program of China (No. 2013K08-11)the 111 Project of China (No. B08040)
文摘The microstructural characteristics and microhardness of nanostructured Al-4.6Cu-Mn ribbons produced by melt spinning were investigated using field-emission gun scanning electron microscopy, transmission electron microscopy, and hardness testing, and the results were compared to those of similar ribbons manufactured by direct-chill casting. It is shown that the nanostructure of the as-melt-spun ribbons consists of α-Al dendrites with a secondary dendrite arm spacing of approximately 0.55-0.80 μm and ultrafine eutectic crystals of a nanosized scale of approximately 100-200 nm on dendritic boundaries. The solidification time and cooling rate of 46-μm-thick ribbons were estimated to be 1.3 × 10-6 s and 4.04 × 106 K·s-1, respectively. At an aging temperature of 190°C, the coherent θ″ phase in aged ribbons gradually transforms into nanoscale θ′-phase platelets as the aging time is extended from 2 to 8 h; the rod-like morphology of the T(Al20Cu2Mn3) dispersoid with 120-160-nm diameter also forms, which results in peak aging hardness. The precipitation behaviors of aged ribbons cannot be changed at the high cooling rates of as-cast ribbons. However, a finer and more uniformly distributed microstructure and a supersaturated solid solution at a high cooling rate can shorten the time required to obtain a certain aging hardness before peak hardness.
基金financially supported by the National Natural Science Foundation of China(No.51972150)the Natural Science Foundation of Jiangsu Province(Nos.BK20210769 and BK20210780)Start-up Foundation for Senior Talents ofJiangsu University(No.21JDG041)。
文摘Dual-phase heterointerface electrocatalysts(DPHE)constructed by oxygen reduction reaction(ORR)-and oxygen evolution reaction(OER)-active elements exhibit excellent bifunctional activity and long-term durability due to the abundant interface exposure and synergistic catalytic effect.Herein,low-dimensional N-doped graphene nanoribbons(N-GNRs)coupling with ultrathin CoO nanocomposites(N-GNRs/CoO)were controllably fabricated through a facile two-step approach using synthesized Co(OH)_2 nanosheet as CoO precursor.Density functional theory(DFT)calculations and experimental characterizations prove that the formation of interface between N-GNRs and CoO can induce local charge redistribution,contributing to the improvement of catalytic activity and stability.The optimal N-GNRs/CoO DPHE possesses hierarchically porous architectures and presents outstanding bifunctional activities with a small potential gap of 0.729 V between the potential at 10 mA·cm^(-2)for OER and the halfwave potential for ORR,which outperforms Pt/C+IrO_(2)and the majority of noble-metal-free bifunctional catalysts.Liquid-and solid-state rechargeable Zn-air batteries assembled with N-GNRs/CoO as the cathode also display high peak power density and fantastic cycle stability,superior to that of benchmark Pt/C+IrO_(2)catalyst.It is anticipated to offer significant benefits toward high activity,stability and mechanical flexibility bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51273148)the Foundation of State Key Laboratory of Pollution Control and Resource Reuse(Tongji University),China(Grant No.PCRRY14003)
文摘Graphene,as star versatile materials having extraordinarily high electric conductivity,electron mobility,thermal conductivity,thermal stability,optical transparency,and mechanical strength,has attracted much attention from scientists and engineers in the field of materials,chemistry,physics,energy,and environment in the last decade and achieved fruitful accomplishment.This review discusses preparation strategies,functionality,characterization,and applications for two dimensional nanosheet and quasi-onedimensional nanoribbon of graphene through direct exfoliation of graphite,chemical vapor deposition of hydrocarbon,laser-induced direct synthesis of graphene,laser etched graphene oxide in the dry state without the use of toxic reducing agent hydrazine,unzipping carbon nanotube,and polycondensation of polycyclic aromatics on the basis of 178 representative references mostly in 2015.The stabilization of graphene oxide prepared in chemical preparation in " top-down" is emphasized.Several vital classic methods of characterizing molecular structure,C/O ratio,defect,morphology,single-or few-layered( 2 to 10 layers) structure,porous and hollow structures,including Raman spectroscopy,AFM,SEM,TEM,STM,electron diffraction,X-ray diffraction,and X-ray photoelectron spectroscopy are systematically introduced.Because graphene possesses novel incomparable multifunctionalities,its versatile applications as novel conducting additives,reinforcing filler,separation membrane,sensor,anticorrosive coating,catalyst,electromagnetic shield,lubricant,and flexible electrode materials in electrochemical and electronic devices,including photovoltaic cells,supercapacitors,rechargeable batteries,sensors,field effect transistors,light emitting diodes,separation membranes,adsorbents and absorbents,catalysts,electro-optic modulator,terahertz emitter and detector,and semiconductors,have been mentioned.Especially in the aspect of both high performance and cost-effectiveness,graphene is expected to be even superior to the expensive carbon nanotubes.
基金Acknowledgements Work at lOP and UCAS was supported by grants from the National Key Research and Development Program of China （No. 2016YFA0202300）, the National Natural Science Foundation of China （Nos. 61390501, 61471337, 51210003, and 51325204）, National Basic Research Program of China （No. 2013CBA01600）, the CAS Pioneer Hundred Talents Program, the Transregional Collaborative Research Center TRR 61, and the Chinese Academy of Sciences and the National Supercomputing Center in Tianjin. A portion of the research was performed in CAS Key Laboratory of Vacuum Physics. Work at the Max Planck Institute for Polymer Research were supported by the EC graphene flagship （No. CNECT-ICT-604391） and ERC NANOGRAPH. Work at Vanderbilt University was supported by Department of Energy grant DE-FG02- 09ER46554 and by the McMinn Endowment.
文摘Unlike graphene sheets, graphene nanoribbons （GNRs） can exhibit semiconducting band gap characteristics that can be tuned by controlling impurity doping and the GNR widths and edge structures. However, achieving such control is a major challenge in the fabrication of GNRs. Chevron-type GNRs were recently synthesized via surface-assisted polymerization of pristine or N-substituted oligophenylene monomers. In principle, GNR heterojunctions can be fabricated by mixing two different monomers. In this paper, we report the fabrication and characterization of chevron-type GNRs using sulfur-substituted oligophenylene monomers to produce GNRs and related heterostructures for the first time. First-principles calculations show that the GNR gaps can be tailored by applying different sulfur configurations from cyclodehydrogenated isomers via debromination and intramolecular cyclodehydrogenation. This feature should enable a new approach for the creation of multiple GNR heterojunctions by engineering their sulfur configurations. These predictions have been confirmed via scanning tunneling microscopy and scanning tunneling spectroscopy. For example, we have found that the S-containing GNRs contain segments with distinct band gaps, i.e., a sequence of multiple heterojunctions that results in a sequence of quantum dots. This unusual intraribbon heterojunction sequence may be useful in nanoscale optoelectronic applications that use quantum dots.
基金the Department of Science and Technology of the government of India for partially funding this work
文摘We have investigated the electronic properties of WTe2 armchair nanoribbons with defects. WTe2 nanoribbons can be categorized depending on the edge structure in two types： armchair and zigzag. WTe2 in its bulk form has an indirect band gap but nanoribbons and nanosheets of WTe2 have direct band gaps. Interestingly, the zigzag nanoribbon is metallic while the armchair nanoribbons are semiconducting. Thus they can find applications in device fabrication. Therefore, it is very important to study the effect of defects on the electronic properties of the armchair nanoribbons as these defects can impair the device properties and characteristics. We have considered defects such as： vacancy, rough edge, wrap, ripple and twist in this work. We report the band gap variation with these defects. We have also studied the change in band gap and total energy with varying degrees of wrap, ripple and twist.
文摘Substantial effort has been made to search for electrode materials of Na-ion batteries with high energy/power density. The application of S-saturated zigzag MoS2 nanoribbons （MoSzNRs） for Na-ion batteries has been explored through density function theory （DFT）. The theoretical maximum specific capacity reaches 386.4 mAh,g t via dou- ble-side and special edge adsorption mode. The electronic structure reveals that there exists charge transfer between Na and MoS2NRs. The diffusion barrier on MoS2NRs （0.17 eV） is much lower than that of bulk MoS2 （1.15 eV）, indicating an excellent diffusion kinetics, in addition, the S-edge in MoS2NRs plays a key role. Firstly, the Mo edge was half saturated by S, which helps to stabilize the MoS2NRs as well as offer more intercalation sites for Na. On the other hand, Na migrates much faster on the S edge route in MoS2NRs. Our computational results show that S-saturated MoSzNRs exhibit a great potential as electrode materials for Na-ion batteries with high performance.
基金supported by the National Natural Science Foundation of China(Grant Nos.10834012 and 11374342)National Key Basic Research and Development Program of China(Grant No.2009CB930700)the Knowledge Innovation Foundation of the Chinese Academy of Sciences(Grant No.KJCX2-YW-W35)
文摘We present a study of electronic properties of zigzag graphene nanoribbons （ZGNRs） substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near the Fermi level sepa- rate due to the asymmetric nitrogen-doping. The ground states of these systems become ferromagnetic because the local magnetic moments along the undoped edges remain and those along the doped edges are suppressed. By controlling the charge-doping level, the magnetic moments of the whole ribbons are modulated. Proper charge doping leads to interest- ing half-metallic and single-edge conducting ribbons which would be helpful for designing graphene-nanoribbon-based spintronic devices in the future.
基金financially supported by the Natural Science Foundation of China(No.81660708)Natural Science Foundation of Jiangsu Province of China(Nos.BK20150692,BK20171389)+3 种基金the Key Project of Science and Technology of Tibet(No.2015XZ01G70)the Key Project of Tibet Tibetan Medicine Bureau(No.2017005)open fund by Jiangsu Engineering Technology Research Center of Environmental Cleaning Materials(No.KHK1507)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘In this paper, nanotubes and nanoribbons of sodium titanate structures were synthesized via hydrothermal methods in alkaline solution. CdS decorated titanate nanotubes and nanoribbons were therefore constructed for exploring the performance of hydrogen evolution and synergistic effect of CdS based titanate structures. CdS decorated titanate nanotubes and nanoribbons were characterized by high resolution transmission electron microscopy （HRTEM）, X-ray diffraction （XRD）, UV-vis, Brunauer- Emmett-Teller （BET） and X-ray photoelectron spectroscopy （XPS） measurements. CdS encapsuled in titanate nanotubes （CdS-ETNTs） showed the best capacity of H2 evolution by water splitting and stability than that from the other two structures, i.e., CdS doped titanate nanotubes （CdS-DTNTs） and CdS doped titanate nanoribbons （CdS-DTNRs）, which could be explained by the synergistic effect of decorated CdS with sodium titanate structures and confinement effect of CdS nanoparticles encapsuled inside
基金supported by a grant from the National Research Foundation(NRF)funded by the Korean government(NRF-2015M3A9C7030091 and NRF-2015R1C1A1A02037047)
文摘A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol （PEG） （GEMINI protocol）. Previous work provided evidence that this is in fact possible. Other fusogens might improve current results. In this study, we aimed to assess the effects of PEGylated graphene nanoribons （PEG-GNR, and called ＂TexasPEG＂ when prepared as lwt% dispersion in PEG600） versus placebo （saline） on locomotor function recovery and cellular level in a rat model of spinal cord transection at lumbar segment 1 （L1） level. In vivo and in vitro experiments （n -- 10 per experiment） were designed. In the in vivo experiment, all rats were submitted to full spinal cord transection at L1 level. Five weeks later, behavioral assessment was performed using the Basso Beattie Bresnahan （BBB） locomotor rating scale. Immunohistochemical staining with neuron marker neurofilament 200 （NF200） antibody and astrocyt- ic scar marker glial fibrillary acidic protein （GFAP） was also performed in the injured spinal cord. In the in vitro experiment, the effects of TexasPEG application for 72 hours on the neurite outgrowth of SH-SYSY cells were observed under the inverted microscope. Results of both in vivo and in vitro experiments suggest that TexasPEG reduces the formation of glial scars, promotes the regeneration of neurites, and thereby contributes to the recovery of locomotor function of a rat model of spinal cord transfection.
基金supported by the National Natural Science Foundation of China(Nos.51932001,51872024,52022097,and 22022508)the National Key Research and Development Program of China(No.2018YFA0703503)+1 种基金the Foundation of the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2020048)China Postdoctoral Science Foundation(No.2022M712167).
文摘Fabricating single-atom catalysts(SACs)with high catalytic activity as well as great stability is a big challenge.Herein,we propose a precise synthesis strategy to stabilize single atomic ruthenium through regulating vanadium defects of nickel vanadium layered double hydroxides(NiV-LDH)ultrathin nanoribbons support.Correspondingly,the isolated atomically Ru doped NiV-LDH ultrathin nanoribbons(NiVRu-R)were successfully fabricated with a super-high Ru load of 12.8 wt.%.X-ray absorption spectrum(XAS)characterization further confirmed atomic dispersion of Ru.As catalysts for electrocatalytic hydrogen evolution reaction(HER)in alkaline media,the NiVRu-R demonstrated superior catalytic properties to the commercial Pt/C.Moreover,it maintained exceptional stability even after 5,000 cyclic voltammetry cycles.In-situ XAS and density functional theory(DFT)calculations prove that the Ru atomic sites are stabilized on supports through forming the Ru-O-V structure,which also help promote the catalytic properties through reducing the energy barrier on atomic Ru catalytic sites.
基金supported by grants from the DOE(DE-FG02-04ER46164),NSF(CHE-0427746,CHE-0701540,and CMMI-0709333)the Nebraska Research Initiative,NSFC(#20628304)by the Research Computing Facility at University of Nebraska-Lincoln and Holland Computer Center at University of Nebraska-Omaha.
文摘Motivated by recent successful synthesize of segmented graphene nanoribbons(GNRs)with junctions,we explore electronic properties of a novel form of GNR with sawtooth-like structure using the density-functional theory method.It is found that the unique edge structures of the sawtooth-like GNR induce richer band-gap features than the straight GNR counterpart with either armchair or zigzag edges.The effect of external electric fi eld on the electronic properties of the sawtooth-like GNR is also studied.The theoretical results may be useful for designing GNR-based fi eld-effect transistors.
