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1.
Nat Commun ; 10(1): 3302, 2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-31341162

RESUMO

Rechargeable sodium metal batteries with high energy density could be important to a wide range of energy applications in modern society. The pursuit of higher energy density should ideally come with high safety, a goal difficult for electrolytes based on organic solvents. Here we report a chloroaluminate ionic liquid electrolyte comprised of aluminium chloride/1-methyl-3-ethylimidazolium chloride/sodium chloride ionic liquid spiked with two important additives, ethylaluminum dichloride and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide. This leads to the first chloroaluminate based ionic liquid electrolyte for rechargeable sodium metal battery. The obtained batteries reached voltages up to ~ 4 V, high Coulombic efficiency up to 99.9%, and high energy and power density of ~ 420 Wh kg-1 and ~ 1766 W kg-1, respectively. The batteries retained over 90% of the original capacity after 700 cycles, suggesting an effective approach to sodium metal batteries with high energy/high power density, long cycle life and high safety.

2.
J Nanosci Nanotechnol ; 15(12): 9856-60, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26682424

RESUMO

SnO2 nanowires (NWs) were grown on a catalyst-coated silicon wafer via the thermal evaporation of SnO powder at 20-30 mTorr. Three types of catalyst, namely Fe, Pt, and Au, were used for the synthesis of the SnO2 NWs. The results show that Pt and Au can be used for the formation of SnO2 NWs. Depending on the experimental conditions, the diameter and length of the SnO2 NWs obtained with Au catalyst are in the ranges of 20-65 nm and a few hundred nanometers to a few micrometers, respectively. The size of the Au nanocatalyst greatly affects the diameter of the SnO2 NWs. With increasing particle size of the Au catalyst, the diameter of the SnO2 NWs increased. In addition, the results show that the synthesis of SnO2 NWs can be conducted at 500 degrees C, which is compatible with low-temperature processes.

3.
Sci Rep ; 5: 10976, 2015 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-26042359

RESUMO

A field-emission light source with high luminance, excellent luminance uniformity, and tunable luminance characteristics with a novel lateral-gate structure is demonstrated. The lateral-gate triode structure comprises SiC nanowire emitters on a Ag cathode electrode and a pair of Ag gate electrodes placed laterally on both sides of the cathode. The simple and cost-effective screen printing technique is employed to pattern the lateral-gates and cathode structure on soda lime glass. The area coverage of the screen-printed cathode and gates on the glass substrate (area: 6 × 8 cm(2)) is in the range of 2.04% - 4.74% depending on the set of cathode-gate electrodes on the substrate. The lateral-gate structure with its small area coverage exhibits a two-dimensional luminance pattern with high brightness and good luminance uniformity. A maximum luminance of 10,952 cd/cm(2) and a luminance uniformity of >90% can be achieved with a gate voltage of 500 V and an anode voltage of 4000 V, with an anode current of 1.44 mA and current leakage to the gate from the cathode of about 10%.

4.
ACS Nano ; 8(1): 443-8, 2014 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-24359599

RESUMO

Graphene is expected to enable superior corrosion protection due to its impermeability and chemical inertness. Previous reports, however, demonstrate limited corrosion inhibition and even corrosion enhancement of graphene on metal surfaces. To enable the reliable and complete passivation, the origin of the low inhibition efficiency of graphene was investigated. Combining electrochemical and morphological characterization techniques, nanometer-sized structural defects in chemical vapor deposition grown graphene were found to be the cause for the limited passivation effect. Extremely fast mass transport on the order of meters per second both across and parallel to graphene layers results in an inhibition efficiency of only ∼50% for Cu covered with up to three graphene layers. Through selective passivation of the defects by atomic layer deposition (ALD) an enhanced corrosion protection of more than 99% was achieved, which compares favorably with commercial corrosion protection methods.

5.
Dalton Trans ; 41(3): 723-6, 2012 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-21869983

RESUMO

An α-Fe(2)O(3) nanoflake urchin-like structure is formed via the thermal oxidation of micrometre-sized iron spheres in air at temperatures of 300-400 °C. The material consists of α-Fe(2)O(3) nanoflakes grown perpendicularly to the sphere surface, a layer of a mixture of α-Fe(2)O(3) and Fe(3)O(4) as the oxidation shell, and an iron core. The ranges of the tip diameters of the nanoflakes are 20-30 nm (300 °C), 30-50 nm (350 °C), and 60-100 nm (400 °C). A composite consisting of the α-Fe(2)O(3) nanoflake urchin-like structure and an epoxy resin exhibits an excellent electromagnetic (EM) wave absorption ability. A small tip diameter (20-30 nm) and a high density (3 × 10(13) nanoflakes m(-2)) lead to a good network structure and good EM wave absorption. A minimum reflection loss (RL) of -33.8 dB (99.93% of EM wave absorption) at 7.8 GHz can be achieved using a 70 wt% urchin-like material as the filler in the resin matrix. In addition, a composite containing 60 wt% unchin-like material exhibits dual-frequency EM wave absorption. The peaks of the minimum RL values are located at 9.7 GHz (-26.2 dB) and 25.2 GHz (-21.0 dB). The unique morphology of the α-Fe(2)O(3) nanoflake urchin-like material is believed to be a key factor in the enhancement of the EM wave absorption.

6.
J Nanosci Nanotechnol ; 12(12): 8949-54, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23447943

RESUMO

Platelet graphite nanofibers (GNFs) and turbostratic carbon nanofibers (CNFs) are synthesized by the thermal evaporation and decomposition of a polymer-based mixture at 700 degrees C using Ni as a catalyst. The mixture consists of poly(ethylene glycol) (PEG), serving as the carbon source, and hydrochloric acid solution (HCl(aq)), serving as the promoter/additive for the growth of CNFs. High-purity zigzag-shaped platelet GNFs form with 10 wt% HCl(aq) as an additive in the PEG. The diameters of the platelet GNFs are in the range of 40-60 nm, with lengths of a few micrometers. High-resolution transmission electron microscopy images indicate a high degree of graphitization and well ordered graphene layers along the fiber axis. In contrast, high-purity turbostratic CNFs form with 20 wt% HCl(aq) in the PEG. The diameter and length of the turbostratic CNFs are 20-40 nm and a few micrometers, respectively. The participation of HCl in the thermal process leads to the formation of Ni-Cl compounds. The amount of chlorine affects the shape of the Ni catalyst, which determines the type of CNF formed.

7.
ACS Appl Mater Interfaces ; 3(8): 3084-90, 2011 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-21774492

RESUMO

A three-dimensional urchin-like α-Fe(2)O(3) microstructure is formed via a simple, template-free, and one-step thermal oxidation of Fe spheres in an air atmosphere at temperatures in the range of 300-450 °C. The urchin-like α-Fe(2)O(3) microstructure consists of crystalline α-Fe(2)O(3) nanoflakes grown perpendicularly on the surface of the sphere, a shell layer of α-Fe(2)O(3)/Fe(3)O(4), and an Fe core. During the oxidation process, the nanoflakes germinate and grow from cracks in the oxidation layer on the surface. The length of the nanoflakes increases with oxidation time. The tip diameters of the nanoflakes are in ranges of 10-20 nm at 300 °C, 20-30 nm at 350 °C, and 40-60 nm at 400 °C; the length can reach up to a few micrometers. The field-emission characteristics of the samples are experimentally studied and simulated. The results show that the urchin-like emitter has a low turn-on field of 2.8 V/µm, high field-enhancement factor of 4313, excellent emission uniformity of over 4 cm(2), and good emission stability during a 24 h test.


Assuntos
Compostos Férricos/química , Cristalização , Óxido Ferroso-Férrico/química , Nanofios/química , Nanofios/ultraestrutura , Oxirredução , Tamanho da Partícula , Temperatura Ambiente
8.
J Nanosci Nanotechnol ; 11(3): 2315-20, 2011 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-21449387

RESUMO

A carbonyl iron/carbon fiber material consisting of carbon fibers grown on micrometer-sized carbonyl iron sphere, was synthesized by chemical vapor deposition using a mixture of C2H2 and H2. The hollow-core carbon fibers (outer diameter: 140 nm and inner diameter: 40 nm) were composed of well-ordered graphene layers which were almost parallel to the long axis of the fibers. A composite (2 mm thick) consisting of the carbonyl iron/carbon fibers and epoxy resin demonstrated excellent electromagnetic (EM) wave absorption. Minimum reflection losses of -36 dB (99.95% of EM wave absorption) at 7.6 GHz and -32 dB (99.92% of EM wave absorption) at 34.1 GHz were achieved. The well-dispersed and network-like carbon fibers in the resin matrix affected the dielectric loss of the EM wave while the carbonyl iron affected the magnetic loss.


Assuntos
Ferro/química , Nanotubos de Carbono/química , Nanotubos de Carbono/ultraestrutura , Absorção , Cristalização/métodos , Campos Eletromagnéticos , Teste de Materiais , Nanotecnologia/métodos , Tamanho da Partícula , Refratometria , Espalhamento de Radiação
9.
J Nanosci Nanotechnol ; 10(12): 8278-85, 2010 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21121328

RESUMO

Vapor-grown carbon fibers (VGCFs), platelet graphite nanofibers (PGNFs), turbostratic carbon nanofibers (CNFs), and carbon spheres were continuously produced by the thermal decomposition of ethanol in the presence of an Fe catalyst and a sulfur promoter at 1100 degrees C under a nitrogen/hydrogen atmosphere in a vertical chemical vapor deposition reactor. The sulfur concentration dramatically affected the morphology and microstructure of the carbon materials produced. A large amount of sulfur in the catalytic precursor led to the direct pyrolysis of hydrocarbons and the formation of carbon spheres (Fe:S = 1:10) while a lower amount of sulfur led to the formation of fibrous carbon materials, including VGCFs (Fe:S = 1:0.2), PGNFs (Fe:S = 1:2), and turbostratic CNFs (Fe:S = 1:5). The degree of poisoning of the catalysts determined the precipitation of the graphene layers, allowing the different types of carbon material to form.

10.
J Nanosci Nanotechnol ; 9(5): 2813-9, 2009 May.
Artigo em Inglês | MEDLINE | ID: mdl-19452935

RESUMO

High purity ZnO nanowire arrays were synthesized uniformly on a 1.5 cm x 2 cm tin-doped indium oxide (ITO) glass substrate. The ZnO nanowire arrays were formed with a uniform diameter distribution of 30-50 nm and a length of about 5 microm, synthesized via thermal decomposition of zinc acetate at 300 degrees C in air. Analysis by X-ray diffraction and transmission electron microscopy showed that the ZnO nanowires are of single crystal structure with a preferred growth orientation of [001]. A study of the growth mechanism showed that it is a vapor-solid (VS) growth process. The synthesis of these nanowires begins with the processes of dehydration, vaporization, decomposition, and oxidation of the zinc acetate. Next, the ZnO clusters are deposited to form seeds that give rise to selective epitaxial growth of the ZnO nanowires. Optical analysis of ZnO nanowires was performed by UV-visible and fluorescence spectrophotometry, investigating both the photocurrent characteristics and UV photoresponse of the ZnO nanowire photodetectors. A study of optical properties showed that the as-produced ZnO nanowires have great potential as UV photodetectors/sensors.

11.
Nanotechnology ; 18(46): 465607, 2007 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-21730487

RESUMO

Carbon nanotube (CNT)-grafted TiO(2) (CNT/TiO(2)) was synthesized as an electrically conductive catalyst that exhibits redox ability under electrical excitation besides ultraviolet (UV) irradiation. The CNT/TiO(2) material was synthesized by a two-step process. Ni nanoparticles were photodeposited onto TiO(2) first. The Ni nanoparticles then served as seeds for the growth of CNTs using the chemical vapor deposition (CVD) of C(2)H(2). The CNT/TiO(2) nanocomposite exhibits strong oxidation activity toward NO gas molecules via both photocatalysis under UV irradiation and electrocatalysis under a DC voltage of 500 V in dark conditions.

12.
J Phys Chem B ; 110(46): 23242-6, 2006 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-17107172

RESUMO

Platelet graphite nanofibers (PGNFs) were synthesized by in situ thermal decomposition from a mixture containing poly(ethylene glycol) (PEG) serving as the carbon source and nickel chloride (NiCl(2)) serving as the catalytic precursor. The mixture was conducted by thermal treatment under a nitrogen atmosphere at 750 degrees C and results found PGNFs with high purity and a uniform diameter distribution formed without hydrocarbon gases in the process. Observations using field-emission scanning electron microscopy and high-resolution transmission electron microscopy revealed PGNFs with a high degree of graphitization, well-ordered graphene layers, and uniform diameters of 10-20 nm. Thermogravimetry-differential scanning calorimetry-mass spectrometry was employed to study the thermal decomposition phenomena of the mixture (PEG/NiCl(2)) before the thermal process. The analysis clarified the in situ synthesis growth mechanism of PGNFs from the mixture.


Assuntos
Grafite/síntese química , Nanoestruturas/química , Nanotecnologia , Polietilenoglicóis/química , Temperatura Alta , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Nanoestruturas/ultraestrutura , Níquel/química , Termogravimetria
13.
Nanotechnology ; 17(6): 1745-51, 2006 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-26558588

RESUMO

Gd2O3:Eu(3+) and Gd2Ti2O7:Eu(3+) films 10 nm in thickness were individually coated onto silica spheres (particle size of 150-170 nm) using the sol-gel method. The synthesized materials were addressed as Gd2O3:Eu(3+)@SiO2 and Gd2Ti2O7:Eu(3+)@SiO2 phosphors. An x-ray powder diffractometer (XRD), field emission scanning electron microscope (FE-SEM), high-resolution transmission electron microscope (HR-TEM), and photoluminescence spectrophotometer (PL) were employed to characterize the core-shell phosphors. Uniform core-shell phosphor particles were observed using FE-SEM. The XRD and HR-TEM results indicated that the coated-shell layer was well crystallized after sintering at 1000 °C. The Gd2O3:Eu(3+)@SiO2 PL measurement showed a red emission at the main 615 nm wavelength. The Gd2Ti2O7:Eu(3+)@SiO2 phosphor showed an orange-red emission at the 588 and 615 nm wavelengths. In comparison with the Gd2O3:Eu(3+) and Gd2Ti2O7:Eu(3+) bulk material results, the core-shell phosphors maintained the same emission ability as the bulk materials and the novel core-shell phosphors possessed great potential in quantum phosphor applications.

14.
Nanotechnology ; 17(10): 2490-7, 2006 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-21727494

RESUMO

Ultraviolet- and visible-light-responsive titania-based photocatalysts were synthesized and employed in the photocatalytic oxidation of NO(x). Sol-gel processes using tetrabutyl orthotitanate and ethanol under acid catalyzed condition and controlled calcination were performed to synthesize titanium dioxide with a mixed crystal lattice of anatase, brookite and rutile phases. The TiO(2) prepared under calcination at 200 °C exhibited high photocatalytic activity for degradation of NO(x) under both ultraviolet (UV) and visible-light illumination. The experimental results showed that up to 70% removal of NO(x) could be obtained in a continuous flow type reaction system under irradiation with visible light. The calcination temperature has an important influence on the particle size and lattice structure of TiO(2). It is also found that the peculiar mixed-phase structure of TiO(2), evidenced from Raman, x-ray diffractometry (XRD), and UV-vis spectroscopy, was inferred to be an important factor for visible-light absorption and NO(x) removal activity under a wide range of visible-light illumination.

15.
Nanotechnology ; 17(16): 4048-52, 2006 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-21727536

RESUMO

Gd(2)O(3):Eu(3+) nano-wire phosphors embedded in SBA-15 silica templates were synthesized using a combination of the sol-gel method and hydrothermal reactions followed by a sintering process at 1000 °C. The crystal structure of Gd(2)O(3):Eu(3+) was confirmed using x-ray diffraction. Observation using transmission electron microscopy shows that the nano-wire diameters were very uniform in the 7-9 nm range. In comparison with bulk Gd(2)O(3):Eu(3+) materials, we found that the photo-luminescent property of the nano-wire was different. The analysis shows that the main nano-wire emission peaks were at 585, 597, 613 and 620 nm. The CIE value (x = 0.62, y = 0.38) indicates that the nano-wire emitted a pink colour and not red as for the bulk material. The field emission experimental results agreed well with the photo-luminescent analysis results.

16.
Nanotechnology ; 17(18): 4629-34, 2006 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-21727587

RESUMO

Carbon nanofibres (CNFs) exhibiting bamboo-like, hollow fibril morphology were prepared from a mixture of polyethylene glycol (PEG) and iron-based compounds such as Fe(2)(SO(4))(3)·nH(2)O, Fe(NO(3))·9H(2)O or FeO(OH) by a thermal process. These materials were well mixed in distilled water prior to thermal treatment in an air/nitrogen atmosphere. With increasing temperature, the mixture underwent solvent removal, dehydrogenation, thermal decomposition, carbonization and catalytic graphitization to form CNFs. Results show that CNFs can be formed with different PEG/catalyst ratios (100/1-1000/1 by weight) at 750 °C. The catalyst effect is discussed for the formation of bamboo-like CNFs. The diameter of the CNFs was about 30-50 nm while the length was a few micrometres.

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