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Showing papers by "Nanyang Technological University published in 2012"


Journal ArticleDOI
01 Apr 2012
TL;DR: ELM provides a unified learning platform with a widespread type of feature mappings and can be applied in regression and multiclass classification applications directly and in theory, ELM can approximate any target continuous function and classify any disjoint regions.
Abstract: Due to the simplicity of their implementations, least square support vector machine (LS-SVM) and proximal support vector machine (PSVM) have been widely used in binary classification applications. The conventional LS-SVM and PSVM cannot be used in regression and multiclass classification applications directly, although variants of LS-SVM and PSVM have been proposed to handle such cases. This paper shows that both LS-SVM and PSVM can be simplified further and a unified learning framework of LS-SVM, PSVM, and other regularization algorithms referred to extreme learning machine (ELM) can be built. ELM works for the “generalized” single-hidden-layer feedforward networks (SLFNs), but the hidden layer (or called feature mapping) in ELM need not be tuned. Such SLFNs include but are not limited to SVM, polynomial network, and the conventional feedforward neural networks. This paper shows the following: 1) ELM provides a unified learning platform with a widespread type of feature mappings and can be applied in regression and multiclass classification applications directly; 2) from the optimization method point of view, ELM has milder optimization constraints compared to LS-SVM and PSVM; 3) in theory, compared to ELM, LS-SVM and PSVM achieve suboptimal solutions and require higher computational complexity; and 4) in theory, ELM can approximate any target continuous function and classify any disjoint regions. As verified by the simulation results, ELM tends to have better scalability and achieve similar (for regression and binary class cases) or much better (for multiclass cases) generalization performance at much faster learning speed (up to thousands times) than traditional SVM and LS-SVM.

4,835 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that only the Raman frequencies of E 1 and A 1g peaks vary monotonously with the layer number of ultrathin Molybdenum disulfi de (MoS 2 ).
Abstract: Molybdenum disulfi de (MoS 2 ) is systematically studied using Raman spectroscopy with ultraviolet and visible laser lines. It is shown that only the Raman frequencies of E 1 and A1g peaks vary monotonously with the layer number of ultrathin MoS 2 fl akes, while intensities or widths of the peaks vary arbitrarily. The coupling between electronic transitions and phonons are found to become weaker when the layer number of MoS 2 decreases, attributed to the increased electronic transition energies or elongated intralayer atomic bonds in ultrathin MoS 2 . The asymmetric Raman peak at 454 cm − 1 , which has been regarded as the overtone of longitudinal optical M phonons in bulk MoS 2 , is actually a combinational band involving a longitudinal acoustic mode (LA(M)) and an optical mode ( A2u ). Our fi ndings suggest a clear evolution of the coupling between electronic transition and phonon when MoS 2 is scaled down from three- to two-dimensional geometry.

3,375 citations


Journal ArticleDOI
TL;DR: A critical review of the synthesis methods for graphene and its derivatives as well as their properties and the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, and Raman enhancement are described.
Abstract: Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

3,340 citations


Journal ArticleDOI
24 Jan 2012-ACS Nano
TL;DR: The unique characteristics of incident-light control, prompt photoswitching, and good photoresponsivity from the MoS(2) phototransistor pave an avenue to develop the single-layer semiconducting materials for multifunctional optoelectronic device applications in the future.
Abstract: A new phototransistor based on the mechanically exfoliated single-layer MoS2 nanosheet is fabricated, and its light-induced electric properties are investigated in detail. Photocurrent generated from the phototransistor is solely determined by the illuminated optical power at a constant drain or gate voltage. The switching behavior of photocurrent generation and annihilation can be completely finished within ca. 50 ms, and it shows good stability. Especially, the single-layer MoS2 phototransistor exhibits a better photoresponsivity as compared with the graphene-based device. The unique characteristics of incident-light control, prompt photoswitching, and good photoresponsivity from the MoS2 phototransistor pave an avenue to develop the single-layer semiconducting materials for multifunctional optoelectronic device applications in the future.

3,033 citations


Journal ArticleDOI
TL;DR: Recent advances in strategies for advanced metal oxide-based hybrid nanostructure design are reviewed, with the focus on the binder-free film/array electrodes that can provide larger electrochemically active surface area, faster electron transport and superior ion diffusion, thus leading to substantially improved cycling and rate performance.
Abstract: Metal oxide nanostructures are promising electrode materials for lithium-ion batteries and supercapacitors because of their high specific capacity/capacitance, typically 2-3 times higher than that of the carbon/graphite-based materials. However, their cycling stability and rate performance still can not meet the requirements of practical applications. It is therefore urgent to improve their overall device performance, which depends on not only the development of advanced electrode materials but also in a large part "how to design superior electrode architectures". In the article, we will review recent advances in strategies for advanced metal oxide-based hybrid nanostructure design, with the focus on the binder-free film/array electrodes. These binder-free electrodes, with the integration of unique merits of each component, can provide larger electrochemically active surface area, faster electron transport and superior ion diffusion, thus leading to substantially improved cycling and rate performance. Several recently emerged concepts of using ordered nanostructure arrays, synergetic core-shell structures, nanostructured current collectors, and flexible paper/textile electrodes will be highlighted, pointing out advantages and challenges where appropriate. Some future electrode design trends and directions are also discussed.

2,176 citations


Journal ArticleDOI
TL;DR: In this article, two different ways to fabricate nitrogen-doped graphene (N-graphene) and demonstrate its use as a metal-free catalyst to study the catalytic active center for the oxygen reduction reaction (ORR).
Abstract: We present two different ways to fabricate nitrogen-doped graphene (N-graphene) and demonstrate its use as a metal-free catalyst to study the catalytic active center for the oxygen reduction reaction (ORR). N-graphene was produced by annealing of graphene oxide (G-O) under ammonia or by annealing of a N-containing polymer/reduced graphene oxide (RG-O) composite (polyaniline/RG-O or polypyrrole/RG-O). The effects of the N precursors and annealing temperature on the performance of the catalyst were investigated. The bonding state of the N atom was found to have a significant effect on the selectivity and catalytic activity for ORR. Annealing of G-O with ammonia preferentially formed graphitic N and pyridinic N centers, while annealing of polyaniline/RG-O and polypyrrole/RG-O tended to generate pyridinic and pyrrolic N moieties, respectively. Most importantly, the electrocatalytic activity of the catalyst was found to be dependent on the graphitic N content which determined the limiting current density, while the pyridinic N content improved the onset potential for ORR. However, the total N content in the graphene-based non-precious metal catalyst does not play an important role in the ORR process.

2,008 citations


Journal ArticleDOI
TL;DR: It is reported that the high-temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS(2) thin layers with superior electrical performance on insulating substrates.
Abstract: The two-dimensional layer of molybdenum disulfide (MoS2) has recently attracted much interest due to its direct-gap property and potential applications in optoelectronics and energy harvesting. However, the synthetic approach to obtain high-quality and large-area MoS2 atomic thin layers is still rare. Here we report that the high-temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS2 thin layers with superior electrical performance on insulating substrates. Spectroscopic and microscopic results reveal that the synthesized MoS2 sheets are highly crystalline. The electron mobility of the bottom-gate transistor devices made of the synthesized MoS2 layer is comparable with those of the micromechanically exfoliated thin sheets from MoS2 crystals. This synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS2 films are transferable to arbitrary substrates, providing gr...

1,734 citations


Journal ArticleDOI
TL;DR: A controlled encapsulation strategy is reported that enables surfactant-capped nanostructured objects of various sizes, shapes and compositions to be enshrouded by a zeolitic imidazolate framework (ZIF-8).
Abstract: Microporous metal–organic frameworks (MOFs) that display permanent porosity show great promise for a myriad of purposes. The potential applications of MOFs can be developed further and extended by encapsulating various functional species (for example, nanoparticles) within the frameworks. However, despite increasing numbers of reports of nanoparticle/MOF composites, simultaneously to control the size, composition, dispersed nature, spatial distribution and confinement of the incorporated nanoparticles within MOF matrices remains a significant challenge. Here, we report a controlled encapsulation strategy that enables surfactant-capped nanostructured objects of various sizes, shapes and compositions to be enshrouded by a zeolitic imidazolate framework (ZIF-8). The incorporated nanoparticles are well dispersed and fully confined within the ZIF-8 crystals. This strategy also allows the controlled incorporation of multiple nanoparticles within each ZIF-8 crystallite. The as-prepared nanoparticle/ZIF-8 composites exhibit active (catalytic, magnetic and optical) properties that derive from the nanoparticles as well as molecular sieving and orientation effects that originate from the framework material.

1,714 citations


Proceedings ArticleDOI
16 Jun 2012
TL;DR: An actionlet ensemble model is learnt to represent each action and to capture the intra-class variance, and novel features that are suitable for depth data are proposed.
Abstract: Human action recognition is an important yet challenging task. The recently developed commodity depth sensors open up new possibilities of dealing with this problem but also present some unique challenges. The depth maps captured by the depth cameras are very noisy and the 3D positions of the tracked joints may be completely wrong if serious occlusions occur, which increases the intra-class variations in the actions. In this paper, an actionlet ensemble model is learnt to represent each action and to capture the intra-class variance. In addition, novel features that are suitable for depth data are proposed. They are robust to noise, invariant to translational and temporal misalignments, and capable of characterizing both the human motion and the human-object interactions. The proposed approach is evaluated on two challenging action recognition datasets captured by commodity depth cameras, and another dataset captured by a MoCap system. The experimental evaluations show that the proposed approach achieves superior performance to the state of the art algorithms.

1,578 citations


Journal ArticleDOI
TL;DR: This article critically and comprehensively reviews the emerging graphene-based electrochemical sensors, electronic sensors, optical sensors, and nanopore sensors for biological or chemical detection and emphasizes on the underlying detection (or signal transduction) mechanisms.
Abstract: Owing to their extraordinary electrical, chemical, optical, mechanical and structural properties, graphene and its derivatives have stimulated exploding interests in their sensor applications ever since the first isolation of free-standing graphene sheets in year 2004. This article critically and comprehensively reviews the emerging graphene-based electrochemical sensors, electronic sensors, optical sensors, and nanopore sensors for biological or chemical detection. We emphasize on the underlying detection (or signal transduction) mechanisms, the unique roles and advantages of the used graphene materials. Properties and preparations of different graphene materials, their functionalizations are also comparatively discussed in view of sensor development. Finally, the perspective and current challenges of graphene sensors are outlined (312 references).

1,536 citations


Journal ArticleDOI
TL;DR: In this article, a facile two-step method is developed for large-scale growth of ultrathin mesoporous nickel cobaltite (NiCo2O4) nanosheets on conductive nickel foam with robust adhesion as a high-performance electrode for electrochemical capacitors.
Abstract: A facile two-step method is developed for large-scale growth of ultrathin mesoporous nickel cobaltite (NiCo2O4) nanosheets on conductive nickel foam with robust adhesion as a high-performance electrode for electrochemical capacitors. The synthesis involves the co-electrodeposition of a bimetallic (Ni, Co) hydroxide precursor on a Ni foam support and subsequent thermal transformation to spinel mesoporous NiCo2O4. The as-prepared ultrathin NiCo2O4 nanosheets with the thickness of a few nanometers possess many interparticle mesopores with a size range from 2 to 5 nm. The nickel foam supported ultrathin mesoporous NiCo2O4 nanosheets promise fast electron and ion transport, large electroactive surface area, and excellent structural stability. As a result, superior pseudocapacitive performance is achieved with an ultrahigh specific capacitance of 1450 F g−1, even at a very high current density of 20 A g−1, and excellent cycling performance at high rates, suggesting its promising application as an efficient electrode for electrochemical capacitors.

Journal ArticleDOI
23 Mar 2012-ACS Nano
TL;DR: The 3D graphene/Co(3)O(4) composite was used as the monolithic free-standing electrode for supercapacitor application and for enzymeless electrochemical detection of glucose and it is demonstrated that it is capable of delivering high specific capacitance and detecting glucose with a ultrahigh sensitivity.
Abstract: Using a simple hydrothermal procedure, cobalt oxide (Co3O4) nanowires were in situ synthesized on three-dimensional (3D) graphene foam grown by chemical vapor deposition. The structure and morphology of the resulting 3D graphene/Co3O4 composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The 3D graphene/Co3O4 composite was used as the monolithic free-standing electrode for supercapacitor application and for enzymeless electrochemical detection of glucose. We demonstrate that it is capable of delivering high specific capacitance of ∼1100 F g–1 at a current density of 10 A g–1 with excellent cycling stability, and it can detect glucose with a ultrahigh sensitivity of 3.39 mA mM–1 cm–2 and a remarkable lower detection limit of <25 nM (S/N = 8.5).

Journal ArticleDOI
09 Jan 2012-Small
TL;DR: Although the single-layer MoS(2) device shows a rapid response after exposure to NO, the current was found to be unstable, and these FET devices can be used as gas sensors to detect nitrous oxide.
Abstract: Single- and multilayer MoS(2) films are deposited onto Si/SiO(2) using the mechanical exfoliation technique. The films were then used for the fabrication of field-effect transistors (FETs). These FET devices can be used as gas sensors to detect nitrous oxide (NO). Although the single-layer MoS(2) device shows a rapid response after exposure to NO, the current was found to be unstable. The two-, three-, and four-layer MoS(2) devices show both stable and sensitive responses to NO down to a concentration of 0.8 ppm.

Journal ArticleDOI
TL;DR: The recent research activities in the synthesis of metal oxide hollow nanostructures with controlled shape, size, composition, and structural complexity, as well as their applications in LIBs are summarized.
Abstract: Metal oxide hollow structures have received great attention because of their many promising applications in a wide range of fields. As electrode materials for lithium-ion batteries (LIBs), metal oxide hollow structures provide high specific capacity, superior rate capability, and improved cycling performance. In this Research News, we summarize the recent research activities in the synthesis of metal oxide hollow nanostructures with controlled shape, size,composition, and structural complexity, as well as their applications in LIBs. By focusing on hollow structures of some binary metal oxides (such as SnO 2 ,TiO 2 , Fe 2 O 3 , Co 3 O 4 ) and complex metal oxides, we seek to provide some rational understanding on the effect of nanostructure engineering on the electrochemical performance of the active materials. It is thus anticipated that this article will shed some light on the development of advanced electrode materials for next-generation LIBs.

Journal ArticleDOI
TL;DR: In this paper, a review of the recent developments in forward osmosis (FO) focusing on the opportunities and challenges is presented, as well as a clear outline for FO-concerned researchers.

Journal ArticleDOI
TL;DR: In this paper, the authors explain the challenges associated with the Heckman (1979) procedure to control for selection bias, assess the quality of its application in accounting research, and offer guidance for better implementation of selection models.
Abstract: This study explains the challenges associated with the Heckman (1979) procedure to control for selection bias, assesses the quality of its application in accounting research, and offers guidance for better implementation of selection models. A survey of 75 recent accounting articles in leading journals reveals that many researchers implement the technique in a mechanical way with relatively little appreciation of important econometric issues and problems surrounding its use. Using empirical examples motivated by prior research, we illustrate that selection models are fragile and can yield quite literally any possible outcome in response to fairly minor changes in model specification. We conclude with guidance on how researchers can better implement selection models that will provide more convincing evidence on potential selection bias, including the need to justify model specifications and careful sensitivity analyses with respect to robustness and multicollinearity. Data Availability: Data used...


Journal ArticleDOI
TL;DR: This feature article aims to stress the importance of proper nanostructuring and advanced compositing that would result in improved physicochemical properties of metal oxides, thus making them promising negative electrodes for next-generation LIBs.
Abstract: The search for new electrode materials for lithium-ion batteries (LIBs) has been an important way to satisfy the ever-growing demands for better performance with higher energy/power densities, improved safety and longer cycle life. Nanostructured metal oxides exhibit good electrochemical properties, and they are regarded as promising anode materials for high-performance LIBs. In this feature article, we will focus on three different categories of metal oxides with distinct lithium storage mechanisms: tin dioxide (SnO2), which utilizes alloying/dealloying processes to reversibly store/release lithium ions during charge/discharge; titanium dioxide (TiO2), where lithium ions are inserted/deinserted into/out of the TiO2 crystal framework; and transition metal oxides including iron oxide and cobalt oxide, which react with lithium ions via an unusual conversion reaction. For all three systems, we will emphasize that creating nanomaterials with unique structures could effectively improve the lithium storage properties of these metal oxides. We will also highlight that the lithium storage capability can be further enhanced through designing advanced nanocomposite materials containing metal oxides and other carbonaceous supports. By providing such a rather systematic survey, we aim to stress the importance of proper nanostructuring and advanced compositing that would result in improved physicochemical properties of metal oxides, thus making them promising negative electrodes for next-generation LIBs.

Journal ArticleDOI
TL;DR: Results from structural equation modeling (SEM) analysis revealed that respondents who were driven by gratifications of information seeking, socializing, entertainment, status seeking, and status seeking were more likely to share news in social media platforms.

Journal ArticleDOI
04 May 2012-ACS Nano
TL;DR: The growth approach offers a new technique for the design and synthesis of transition metal oxide or hydroxide hierarchical nanoarrays that are promising for electrochemical energy storage, catalysis, and gas sensing applications.
Abstract: The high performance of a pseudocapacitor electrode relies largely on a scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials We present a powerful two-step solution-based method for the fabrication of transition metal oxide core/shell nanostructure arrays on various conductive substrates Demonstrated examples include Co3O4 or ZnO nanowire core and NiO nanoflake shells with a hierarchical and porous morphology The “oriented attachment” and “self-assembly” crystal growth mechanisms are proposed to explain the formation of the NiO nanoflake shell Supercapacitor electrodes based on the Co3O4/NiO nanowire arrays on 3D macroporous nickel foam are thoroughly characterized The electrodes exhibit a high specific capacitance of 853 F/g at 2 A/g after 6000 cycles and an excellent cycling stability, owing to the unique porous core/shell nanowire array architecture, and a rational combination of two electrochemically active materials Our growth approach offers a new techniqu

Journal ArticleDOI
TL;DR: Fe(2)O(3) microboxes with hierarchically structured shells have been synthesized simply by annealing Prussian blue microcubes and demonstrated a scalable synthesis of anisotropic hollow structures with various shell architectures.
Abstract: Fe2O3 microboxes with hierarchically structured shells have been synthesized simply by annealing Prussian blue (PB) microcubes. By utilizing simultaneous oxidative decomposition of PB microcubes and crystal growth of iron oxide shells, we have demonstrated a scalable synthesis of anisotropic hollow structures with various shell architectures. When evaluated as an anode material for lithium ion batteries, the Fe2O3 microboxes with a well-defined hollow structure and hierarchical shell manifested high specific capacity (∼950 mA h g–1 at 200 mA g–1) and excellent cycling performance.

Journal ArticleDOI
TL;DR: A brief review on the current progress in stimuli-responsive shape memory materials can be found in this article, where the focus is on twofold, namely newly observed ones, and novel applications with great potential at present and in near future.

Journal ArticleDOI
08 Oct 2012-Small
TL;DR: This flexible transistor array can be used as a highly sensitive gas sensor with excellent reproducibility and functionalization of the MoS(2) thin film with Pt nanoparticles further increases the sensitivity by up to ∼3 times.
Abstract: By combining two kinds of solution-processable two-dimensional materials, a flexible transistor array is fabricated in which MoS2 thin film is used as the active channel and reduced graphene oxide (rGO) film is used as the drain and source electrodes. The simple device configuration and the 1.5 mm-long MoS2 channel ensure highly reproducible device fabrication and operation. This flexible transistor array can be used as a highly sensitive gas sensor with excellent reproducibility. Compared to using rGO thin film as the active channel, this new gas sensor exhibits much higher sensitivity. Moreover, functionalization of the MoS2 thin film with Pt nanoparticles further increases the sensitivity by up to ∼3 times. The successful incorporation of a MoS2 thin-film into the electronic sensor promises its potential application in various electronic devices.

Journal ArticleDOI
TL;DR: This optimised polymer semiconductor represents a significant progress in semiconductor development, dispelling prevalent skepticism surrounding practical usability of organic semiconductors for high-performance microelectronic devices, opening up application opportunities hitherto functionally or economically inaccessible with silicon technologies, and providing an excellent structural framework for fundamental studies of charge transport in organic systems.
Abstract: Microelectronic circuits/arrays produced via high-speed printing instead of traditional photolithographic processes offer an appealing approach to creating the long-sought after, low-cost, large-area flexible electronics. Foremost among critical enablers to propel this paradigm shift in manufacturing is a stable, solution-processable, high-performance semiconductor for printing functionally capable thin-film transistors — fundamental building blocks of microelectronics. We report herein the processing and optimisation of solution-processable polymer semiconductors for thin-film transistors, demonstrating very high field-effect mobility, high on/off ratio, and excellent shelf-life and operating stabilities under ambient conditions. Exceptionally high-gain inverters and functional ring oscillator devices on flexible substrates have been demonstrated. This optimised polymer semiconductor represents a significant progress in semiconductor development, dispelling prevalent skepticism surrounding practical usability of organic semiconductors for high-performance microelectronic devices, opening up application opportunities hitherto functionally or economically inaccessible with silicon technologies, and providing an excellent structural framework for fundamental studies of charge transport in organic systems.

Journal ArticleDOI
TL;DR: In this Review, the importance of graphene-based electrodes, their fabrication techniques, and application areas are discussed.
Abstract: Graphene, the thinnest two dimensional carbon material, has become the subject of intensive investigation in various research fields because of its remarkable electronic, mechanical, optical and thermal properties. Graphene-based electrodes, fabricated from mechanically cleaved graphene, chemical vapor deposition (CVD) grown graphene, or massively produced graphene derivatives from bulk graphite, have been applied in a broad range of applications, such as in light emitting diodes, touch screens, field-effect transistors, solar cells, supercapacitors, batteries, and sensors. In this Review, after a short introduction to the properties and synthetic methods of graphene and its derivatives, we will discuss the importance of graphene-based electrodes, their fabrication techniques, and application areas.

Journal ArticleDOI
TL;DR: Quantitative results show that the optimal size of BESS exists and differs for both the grid-connected and islanded MGs in this paper.
Abstract: This paper presents a new method based on the cost-benefit analysis for optimal sizing of an energy storage system in a microgrid (MG). The unit commitment problem with spinning reserve for MG is considered in this method. Time series and feed-forward neural network techniques are used for forecasting the wind speed and solar radiations respectively and the forecasting errors are also considered in this paper. Two mathematical models have been built for both the islanded and grid-connected modes of MGs. The main problem is formulated as a mixed linear integer problem (MLIP), which is solved in AMPL (A Modeling Language for Mathematical Programming). The effectiveness of the approach is validated by case studies where the optimal system energy storage ratings for the islanded and grid-connected MGs are determined. Quantitative results show that the optimal size of BESS exists and differs for both the grid-connected and islanded MGs in this paper.

Journal ArticleDOI
TL;DR: In this article, an advanced electrode for high-performance electrochemical capacitors has been designed by growing ultrathin mesoporous Co3O4 nanosheet arrays on the Ni foam support.
Abstract: An advanced electrode for high-performance electrochemical capacitors has been designed by growing ultrathin mesoporous Co3O4 nanosheet arrays on the Ni foam support. This unique 3D electrode manifests exceptional supercapacitive performance with ultrahigh specific capacitance at high current densities and excellent cycling stability.

Journal ArticleDOI
TL;DR: Preparation of freestanding multilayered graphene fi lms by vacuum-assisted fi ltration based on the effective prevention of graphene intersheet restacking and the formation of a 3D graphene hydrogel by a hydrothermal method are reported.
Abstract: For instance, freestanding graphene macroscopic structures have shown unique catalytic, electrochemical, and mechanical properties together with potential applications in chemical fi lters and electrodes for energy storage devices. [ 6–8 , 11 , 30 ] However, in most cases, during the process of assembling nanometerscale building blocks into macroscopic paper-like structures, the large accessible surface area of 2D graphene sheets is lost. The reason for this is that the individual graphene sheets tend to irreversibly aggregate and restack owing to the strong π π stacking and van der Waals force between the planar basal planes of graphene sheets. This reduces the potential applications of graphene materials in electrochemical electrodes, composite materials, and so on. [ 20 ] Therefore, preventing aggregation of graphene sheets in the macroscopic structures, such that the properties of the individual graphene sheets are not compromised, is a critical challenge in constructing functional graphene-based macroscopic structures. Currently, a number of strategies for preventing aggregation have been developed, which include adding spacers (e.g., surfactants, nanoparticles, polymers), [ 27–36 ] template-assisted growth, [ 37 ] and crumpling the graphene sheets. [ 18 , 38 ] Alternatively, several groups have reported the formation of freestanding 3D graphene-based macroscopic structures without the assistance of any spacers or templates. [ 7 , 39,40 ] For instance, Li and coworkers reported the preparation of freestanding multilayered graphene fi lms by vacuum-assisted fi ltration based on the effective prevention of graphene intersheet restacking. [ 7 ] Shi and coworkers demonstrated the formation of a 3D graphene hydrogel by a hydrothermal method. [ 39 ] However, preparing freestanding and fl exible graphene fi lms with large accessible surface area but

Journal ArticleDOI
TL;DR: In this paper, carbon nanocomposites are prepared by confining sulfur in double-shelled hollow carbon spheres, which are obtained from SnO2 hollow spheres dispersed in aqueous glucose solution.
Abstract: New sulfur—carbon nanocomposites are prepared by confining sulfur in double-shelled hollow carbon spheres, which are obtained from SnO2 hollow spheres dispersed in aqueous glucose solution (autoclave, 180 °C, 4 h).

Journal ArticleDOI
TL;DR: In this article, a hierarchical nanostructures composed of carbon coated α-Fe2O3 hollow nanohorns on carbon nanotube (CNT) backbones have been constructed by direct growth and thermal transformation of β-FeOOH nanospindles on CNTs, followed by carbon nanocoating.
Abstract: Novel hierarchical nanostructures composed of carbon coated α-Fe2O3 hollow nanohorns on carbon nanotube (CNT) backbones have been constructed by direct growth and thermal transformation of β-FeOOH nanospindles on CNTs, followed by carbon nanocoating. When evaluated as a potential anode material for lithium-ion batteries, such hierarchical structures exhibit superior lithium storage capabilities by virtue of their advantageous structural features.