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Chemosphere 05/2013; · 3.21 Impact Factor
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ABSTRACT: To elucidate the environmental fate of tetracycline (TC), we reported the light-source-dependent dual effects of humic acid (HA) and NO3(-) on TC photolysis. TC photolysis rate was highly pH- and concentration-dependent, and was especially enhanced at higher pH and lower initial TC concentrations. Under UV-254 and UV-365 irradiation, HA inhibited TC photolysis through competitive photoabsorption or reactive oxygen species (ROS) quenching with TC; under solar and xenon lamp irradiation, TC photolysis was enhanced at low HA concentration due to its photosensitization, whereas was suppressed at high HA concentration due to competitive photoabsorption or ROS quenching with TC. Similarly, the effect of NO3(-) on TC photolysis varied with light irradiation conditions. Even under the same light irradiation conditions, the effects of HA or NO3(-) on TC photolysis varied with their concentrations. The electron spin resonance spectrometer and ROS scavenger experiments demonstrated that TC photolysis was involved in O2(-)-mediated self-sensitized photolysis. The photolysis pathways were involved in hydroxylation and loss of some groups. More toxic intermediates than TC were generated under different light irradiation conditions. These results can provide insight into the potential fate and transformation of TC in surficial waters.
Chemosphere 04/2013; · 3.21 Impact Factor
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ABSTRACT: A self-limiting growth process based on the interface-controlled reaction of molten boron oxide (B2 O3 ) with ammonia (NH3 ) is demonstrated for the facile and lost-cost synthesis of ultrathin (20-30 nm) crystalline hexagonal boron nitride (h-BN) films over large areas. The as-grown h-BN films are of high quality, being densely continuous, uniform and smooth, and highly transparent over a broad wavelength range.
Small 03/2013; · 8.35 Impact Factor
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Kaihui Liu,
Xiaoping Hong,
Muhong Wu,
Fajun Xiao, Wenlong Wang,
Xuedong Bai,
Joel W Ager,
Shaul Aloni,
Alex Zettl,
Enge Wang,
Feng Wang
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ABSTRACT: Van der Waals-coupled materials, ranging from multilayers of graphene and MoS(2) to superlattices of nanoparticles, exhibit rich emerging behaviour owing to quantum coupling between individual nanoscale constituents. Double-walled carbon nanotubes provide a model system for studying such quantum coupling mediated by van der Waals interactions, because each constituent single-walled nanotube can have distinctly different physical structures and electronic properties. Here we systematically investigate quantum-coupled radial-breathing mode oscillations in chirality-defined double-walled nanotubes by combining simultaneous structural, electronic and vibrational characterizations on the same individual nanotubes. We show that these radial-breathing oscillations are collective modes characterized by concerted inner- and outer-wall motions, and determine quantitatively the tube-dependent van der Waals potential governing their vibration frequencies. We also observe strong quantum interference between Raman scattering from the inner- and outer-wall excitation pathways, the relative phase of which reveals chirality-dependent excited-state potential energy surface displacement in different nanotubes.
Nature Communications 01/2013; 4:1375. · 7.40 Impact Factor
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ABSTRACT: Carbon nanomaterials, including the one-dimensional (1-D) carbon nanotube (CNT) and two-dimensional (2-D) graphene, are heralded
as ideal candidates for next generation nanoelectronics. An essential component for the development of advanced nanoelectronics
devices is processing-compatible oxide. Here, in analogy to the widespread use of silicon dioxide (SiO2) in silicon microelectronic industry, we report the proof-of-principle use of graphite oxide (GO) as a gate dielectrics for
CNT field-effect transistor (FET) via a fast and simple solution-based processing in the ambient condition. The exceptional
transistor characteristics, including low operation voltage (2 V), high carrier mobility (950 cm2/V−1 s−1), and the negligible gate hysteresis, suggest a potential route to the future all-carbon nanoelectronics.
Keywordscarbon-based nanoelectronics-graphene oxide-gate dielectrics
Science China: Physics, Mechanics and Astronomy 04/2012; 53(5):828-833. · 0.78 Impact Factor
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Kaihui Liu,
Jack Deslippe,
Fajun Xiao,
Rodrigo B Capaz,
Xiaoping Hong,
Shaul Aloni,
Alex Zettl, Wenlong Wang,
Xuedong Bai,
Steven G Louie,
Enge Wang,
Feng Wang
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ABSTRACT: Electron-electron interactions are significantly enhanced in one-dimensional systems, and single-walled carbon nanotubes provide a unique opportunity for studying such interactions and the related many-body effects in one dimension. However, single-walled nanotubes can have a wide range of diameters and hundreds of different structures, each defined by its chiral index (n,m), where n and m are integers that can have values from zero up to 30 or more. Moreover, one-third of these structures are metals and two-thirds are semiconductors, and they display optical resonances at many different frequencies. Systematic studies of many-body effects in nanotubes would therefore benefit from the availability of a technique for identifying the chiral index of a nanotube based on a measurement of its optical resonances, and vice versa. Here, we report the establishment of a structure-property 'atlas' for nanotube optical transitions based on simultaneous electron diffraction measurements of the chiral index and Rayleigh scattering measurements of the optical resonances of 206 different single-walled nanotube structures. The nanotubes, which were suspended across open slit structures on silicon substrates, had diameters in the range 1.3-4.7 nm. We also use this atlas as a starting point for a systematic study of many-body effects in the excited states of single-walled nanotubes. We find that electron-electron interactions shift the optical resonance energies by the same amount for both metallic and semiconducting nanotubes, and that this shift (which corresponds to an effective Fermi velocity renormalization) increases monotonically with nanotube diameter. This behaviour arises from two sources: an intriguing cancellation of long-range electron-electron interaction effects, and the dependence of short-range electron-electron interactions on diameter.
Nature Nanotechnology 04/2012; 7(5):325-9. · 27.27 Impact Factor
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ABSTRACT: Piezotronics is a new field integrating piezoelectric effect into nanoelectronics, which has attracted much attention for the fundamental research and potential applications. In this paper, the piezotronic effect of zinc oxide (ZnO) nanowires, including the response of the electrical transport and photoconducting behaviors on the nanowire bending, has been investigated by in situ transmission electron microscopy (TEM), where the crystal structure of ZnO nanowires were simultaneously imaged. Serials of consecutively recorded current-voltage (I-V) curves along with an increase of nanowire bending show the striking effect of bending on their electrical behavior. With increasing the nanowire bending, the photocurrent of ZnO nanowire under ultraviolet illumination (UV) drops dramatically and the photo response time becomes much shorter. In addition, the dynamic nanomechanics of ZnO nanowires were studied inside TEM. These phenomena could be attributed to the piezoelectric effect of ZnO nanowires, and they suggest the potential applications of ZnO nanowires on piezotronic devices.
Advanced Materials 04/2012; 24(34):4676-82. · 13.88 Impact Factor
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ABSTRACT: We have developed an efficient chemical exfoliation approach for the high-throughput synthesis of solution-processable, high-quality graphene sheets that are noncovalently functionalized by alkylamine. Purely coherent nonlinear optical response of these graphene sheets has been investigated, using near-infrared, visible, and ultraviolet continous wave and ultrafast laser beams. Spatial self-phase modulation has been unambiguously observed in the solution dispersions. Our results suggest that this coherent light scattering is due to a broadband, ultrafast, and remarkably huge third-order optical nonlinearity χ(3), which is a manifestation of the graphene's cone-shaped large-energy-scale band structure. Our experimental findings endow graphene new potentials in nonlinear optical applications.
Nano Letters 11/2011; 11(12):5159-64. · 13.20 Impact Factor
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ABSTRACT: We present an innovative wet-chemistry-assisted nanotube-substitution reaction approach for the highly efficient synthesis of boron- and nitrogen-codoped single-walled carbon nanotubes (B(x)C(y)N(z)-SWNTs) in bulk quantities. The as-synthesized ternary system B(x)C(y)N(z)-SWNTs are of high purity and quality and have fairly homogeneous B and N dopant concentrations. Electrical transport measurements on SWNT-network thin-film transistors revealed that the B(x)C(y)N(z)-SWNTs were composed primarily of the semiconducting nanotubes, in contrast to the starting pristine C-SWNTs, which consisted of a heterogeneous mixture of both semiconducting and metallic types.
Journal of the American Chemical Society 08/2011; 133(34):13216-9. · 9.91 Impact Factor
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ABSTRACT: Photolysis of Enro in water was investigated under simulated sunlight irradiation using a Xenon lamp. The results showed that Enro photolysis followed apparent first-order kinetics. Increasing Enro concentration from 5.0 to 40.0 mg L⁻¹ led to the decrease of the photolysis rate constant from 1.6 × 10⁻² to 3.0 × 10⁻³ min⁻¹. Compared with the acidic and basic conditions, the photolysis rate was faster at neutral condition. Both of nitrate and humic acid can markedly decrease the photolysis rate of Enro because they can competitively absorb photons with Enro. The electron spin resonance and reactive oxygen species scavenging experiments indicated that Enro underwent self-sensitized photooxidation via OH and ¹O₂. After irradiation for 90 min, only 13.1% reduction of TOC occurred in spite of fast photolysis of 58.9% of Enro, indicating that Enro was transformed into intermediates without complete mineralization. The photolysis of Enro involved three main pathways: decarboxylation, defluorination, and piperazinyl N⁴-dealkylation. The bioluminescence inhibition rate using Vibrio fischeri increased to 67.2% at 60 min and then decreased to 56.9% at 90 min, indicative of the generation of some more toxic intermediates than Enro and then the degradation of the intermediates. The results will help us understand fundamental mechanisms of Enro photolysis and provide insight into the potential fate and transformation of Enro in surface waters.
Chemosphere 07/2011; 85(5):892-7. · 3.21 Impact Factor
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ABSTRACT: A suspended graphene oxide device is fabricated and investigated using a transmission electron microscope (TEM) scanning tunneling microscope (STM) setup. A detailed study of step-by-step reduction of an individual graphene oxide sheet under current flow and Joule heating in tandem with conductivity measurements, atomic structure imaging, chemical composition, and bonding alternations tracing is performed. As monitored by electron energy loss spectroscopy, the oxygen content is tuned from that peculiar to a pristine graphene oxide (i.e., 23.8 at %) to oxygen-free pure graphene. Six orders of magnitude conductance rise is observed during this process with the final conductivity reaching 1.5 × 10(5) S/m. Quantification of plasma energy losses of the starting graphene oxide shows that ∼40% of the oxygen atoms are in the form of epoxy, and ∼60% oxygen atoms are in the form of hydroxyl. The total portion of sp(3) bonds in pristine graphene oxide is estimated to be ∼45%. The epoxy groups show a larger influence on the conductivity of graphene oxide than hydroxyl ones. Through analyzing consecutive plasma-loss energy spectra under gradual graphene oxide to graphene transformation, it is found that the oxygen atoms in epoxy groups decompose prior to those in hydroxyl groups.
ACS Nano 05/2011; 5(6):4401-6. · 10.77 Impact Factor
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ABSTRACT: Complex nanostructures such as branched semiconductor nanotetrapods are promising building blocks for next-generation nanoelectronics. Here we report on the electrical transport properties of individual CdS tetrapods in a field effect transistor (FET) configuration with a ferroelectric Ba(0.7)Sr(0.3)TiO(3) film as high-k, switchable gate dielectric. A cryogenic four-probe scanning tunneling microscopy (STM) is used to probe the electrical transport through individual nanotetrapods at different temperatures. A p-type field effect is observed at room temperature, owing to the enhanced gate capacitance coupling. And the reversible remnant polarization of the ferroelectric gate dielectric leads to a well-defined nonvolatile memory effect. The field effect is shown to originate from the channel tuning in the arm/core/arm junctions of nanotetrapods. At low temperature (8.5 K), the nanotetrapod devices exhibit a ferroelectric-modulated single-electron transistor (SET) behavior. The results illustrate how the characteristics of a ferroelectric such as switchable polarization and high dielectric constant can be exploited to control the functionality of individual three-dimensional nanoarchitectures.
Nano Letters 05/2011; 11(5):1913-8. · 13.20 Impact Factor
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ABSTRACT: Radial breathing mode (RBM) oscillation is the most characteristic vibration mode in carbon nanotubes. Here we investigate the intrinsic behavior of RBM oscillations of structurally defined single-walled carbon nanotubes (SWNTs) by combining Raman-scattering and electron-diffraction techniques on the same suspended nanotubes. The independent determination of RBM frequencies and nanotube structures allows us to establish conclusively the perfect linear relation between RBM frequencies and inverse nanotube diameters, which has been long speculated to hold in pristine SWNTs. Understanding the intrinsic diameter dependence of SWNT RBM oscillation not only is crucial for reliable Raman characterization of carbon nanotubes, but also enables quantitative probing of SWNT-environment interactions through the RBM oscillation frequency shift.
Phys. Rev. B. 03/2011; 83(11).
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Advanced Materials 03/2011; 23(10):1246-51. · 13.88 Impact Factor
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ABSTRACT: The micron grade multi-metal oxide bismuth silicate (Bi12SiO20, BSO) was prepared by the chemical solution decomposition technique. Photocatalytic degradation of pentachlorophenol (PCP) was investigated in the presence of BSO under xenon lamp irradiation. The reaction kinetics followed pseudo first-order and the degradation ratio achieved 99.1% after 120 min at an initial PCP concentration of 2.0 mg/L. The pH decreased from 6.2 to 4.6 and the dechlorination ratio was 68.4% after 120 min at an initial PCP concentration of 8.0 mg/L. The results of electron spin resonance showed that superoxide radical (O2*-) was largely responsible for the photocatalytic degradation of PCP. Interestingly, this result was different from that of previous photocatalytic reactions where valence band holes or hydroxyl radicals played the role of major oxidants. Some aromatic compounds and aliphatic carboxylic acids were determined by GC/MS as the reaction intermediates, which indicated that O2*- can attack the bond between the carbon and chlorine atoms to form less chlorinated aromatic compounds. The aromatic compounds were further oxidized by O2*- to generate aliphatic carboxylic acids which can be finally mineralized to CO2 and H2O.
Journal of Environmental Sciences 01/2011; 23(11):1911-8. · 1.66 Impact Factor
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ABSTRACT: Oxide materials with resistance hysteresis are very promising for next generation memory devices. However, the microscopic dynamic process of the resistance change is still elusive. Here, we use in situ transmission electron microscopy method to study the role of oxygen vacancies for the resistance switching effect in cerium oxides. The structure change during oxygen vacancy migration in CeO(2) induced by electric field was in situ imaged inside high-resolution transmission electron microscope, which gives a direct evidence for oxygen migration mechanism for the microscopic origin of resistance change effect in CeO(2). Our results have implications for understanding the nature of resistance change in metal oxides with mixed valence cations, such as fluorite, rutile and perovskite oxides.
Micron 06/2010; 41(4):301-5. · 1.53 Impact Factor
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ABSTRACT: The switching behaviors of ionic/electronic mixed conductor-based solid electrolyte nonvolatile memories have been attributed to repetitive formation and breakage of the conductive pathways inside a solid electrolyte. However, direct evidence of such pathway existence and their formations has never been provided. Herein, we reproduced the switching behavior of a Ag/Ag(2)S/W sandwich structure inside a high-resolution transmission electron microscope equipped with a scanning tunneling microscope unit. The on/off current ratio of 5 orders of magnitude was documented. The in situ formation and breakage of a nanoscale conductive channel were ultimately verified in real time and under atomic resolution. We found that a conducting Ag(2)S argentite phase and a Ag nanocrystal together formed the ionic and electronic conductive channel. The preferential atomic sites for Ag nanocrystal growth within the argentite phase were finally clarified.
ACS Nano 05/2010; 4(5):2515-22. · 10.77 Impact Factor
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ABSTRACT: Cerium oxides have attracted much attention because of their uses in three-way catalysts and other catalyst applications. The redox reaction of cerium oxides, as the basis of their use as catalysts, usually takes place at high temperature (>600 K) and/or low oxygen partial pressure. There have been continuous efforts to lower the operating temperatures of cerium oxide further to improve the performance of the catalysts and reduce pollution under the cold-start condition. Here, we report a direct atomic-scale observation of a redox process in cerium oxides driven by an electrical field at ambient temperature. The dynamic changes taking place during the electrically driven redox reaction were imaged by in situ high-resolution transmission electron microscopy, where reversible phase transformations due to the migration of oxygen vacancies have been reproducibly achieved. These results could lead to the low-temperature operation of catalysts for the purification of automobile emissions of pollutants, oxygen generation, and intermediate-temperature solid oxide fuel cells.
Journal of the American Chemical Society 03/2010; 132(12):4197-201. · 9.91 Impact Factor
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ABSTRACT: The higher-order harmonic resonances, including second and third harmonic modes, were induced by applying alternative current signals inside a high-resolution transmission electron microscope (HRTEM), which have been used to study the mechanical properties of individual cadmium sulphide (CdS) nanowires. Young's moduli (E) and mechanical quality factors (Q) of individual CdS nanowires with diameters in the range of 50-350 nm were measured with the assistance of the mechanical resonances. The results indicate that the smooth nanowires have larger E and Q in comparison with the rough nanowires, and for the rough nanowires, E and Q increase with increasing diameters. The morphology- and size-dependent mechanical properties of CdS nanowires are directly correlated with their structure, as imaged by in situ TEM.
Journal of electron microscopy 02/2010; 59(4):285-9. · 1.31 Impact Factor
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ABSTRACT: We report a method for the determination of the chiral indices of large-indexed carbon nanotubes by electron diffraction. By the use of this method, the index assignment errors, originating from the tilt of a nanotube with respect to the incident electron beam, can be directly specified. As an example, the chiral indices of a double-walled nanotubes with index up to 80 and under a high tilt angle of as large as 20° have been accurately identified. Only the data of the maximum peaks of the diffraction layer lines are required in the study, which makes the chiral index determination much easier based on the common diffraction patterns.
Journal of Physics D Applied Physics 06/2009; 42(12):125412. · 2.54 Impact Factor
