A facile strategy was designed for the fabrication of Fe3O4-nanoparticle-decorated TiO2 nanofiber hierarchical heterostructures (FTHs) by combining the versatility of the electrospinning technique and the hydrothermal growth method. The hierarchical architecture of Fe3O4 nanoparticles decorated on TiO2 nanofibers enables the successful integration of the binary composite into batteries to address structural stability and low capacity. In the resulting unique architecture of FTHs, the 1D heterostructures relieve the strain caused by severe volume changes of Fe3O4 during numerous charge-discharge cycles, and thus suppress the degradation of the electrode material. As a result, FTHs show excellent performance including higher reversible capacity, excellent cycle life, and good rate performance over a wide temperature range owing to the synergistic effect of the binary composition of TiO2 and Fe3O4 and the unique features of the hierarchical nanofibers.
Yolk/shell nanoparticles (NPs), which integrate functional cores (likes Fe3O4) and an inert SiO2 shell, are very important for applications in fields such as biomedicine and catalysis. An acidic medium is an excellent etchant to achieve hollow SiO2 but harmful to most functional cores. Reported here is a method for preparing sub-100 nm yolk/shell Fe3O4@SiO2 NPs by a mild acidic etching strategy. Our results demonstrate that establishment of a dissolution–diffusion equilibrium of silica is essential for achieving yolk/shell Fe3O4@SiO2 NPs. A uniform increase in the silica compactness from the inside to the outside and an appropriate pH value of the etchant are the main factors controlling the thickness and cavity of the SiO2 shell. Under our “standard etching code”, the acid-sensitive Fe3O4 core can be perfectly preserved and the SiO2 shell can be selectively etched away. The mechanism of regulation of SiO2 etching and acidic etching was investigated.
Iron oxides have attracted considerable interest as abundant materials for high-capacity Li-ion battery anodes. However, their fast capacity fading owing to poorly controlled reversibility of the conversion reactions greatly hinders their application. Here, a sandwich-structured nanocomposite of N-doped graphene and nearly monodisperse Fe3O4 nanoparticles were developed as high-performance Li-ion battery anode. N-doped graphene serves as a conducting framework for the self-assembled structure and controls Fe3O4 nucleation through the interaction of N dopants, surfactant molecules, and iron precursors. Fe3O4 nanoparticles were well dispersed with a uniform diameter of ~15 nm. The unique sandwich structure enables good electron conductivity and Li-ion accessibility and accommodates a large volume change. Hence, it delivers good cycling reversibility and rate performance with a capacity of ~1,227 mA·h·g–1 and 96.8% capacity retention over 1,000 cycles at a current density of 3 A·g–1. Our work provides an ideal structure design for conversion anodes or other electrode materials requiring a large volume change.
The assembly of hybrid nanomaterials has opened up a new direction for the construction of high-performance anodes for lithium-ion batteries (LIBs). In this work, we present a straightforward, eco-friendly, one-step hydrothermal protocol for the synthesis of a new type of Fe2O3-SnO2/graphene hybrid, in which zero-dimensional (0D) SnO2 nanoparticles with an average diameter of 8 nm and one-dimensional (1D) Fe2O3 nanorods with a length of ~150 nm are homogeneously attached onto two-dimensional (2D) reduced graphene oxide nanosheets, generating a unique point-line-plane (0D-1D-2D) architecture. The achieved Fe2O3-SnO2/graphene exhibits a well-defined morphology, a uniform size, and good monodispersity. As anode materials for LIBs, the hybrids exhibit a remarkable reversible capacity of 1,530 mA·g?1 at a current density of 100 mA·g?1 after 200 cycles, as well as a high rate capability of 615 mAh·g?1 at 2,000 mA·g?1. Detailed characterizations reveal that the superior lithium-storage capacity and good cycle stability of the hybrids arise from their peculiar hybrid nanostructure and conductive graphene matrix, as well as the synergistic interaction among the components.
CO oxidation has been performed on Co3O4 nanobelts and nanocubes as model catalysts. The Co3O4 nanobelts which have a predominance of exposed {011} planes are more active than Co3O4 nanocubes with exposed {001} planes. Temperature programmed reduction of CO shows that Co3O4 nanobelts have stronger reducing properties than Co3O4 nanocubes. The essence of shape and crystal plane effect is revealed by the fact that turnover frequency of Co3+ sites of {011} planes on Co3O4 nanobelts is far higher than that of {001} planes on Co3O4 nanocubes.
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We have demonstrated the improved performance of oxygen evolution reactions (OER) using Au/nickel phosphide (Ni12P5) core/shell nanoparticles (NPs) under basic conditions. NPs with a Ni12P5 shell and a Au core, both of which have well-defined crystal structures, have been prepared using solution-based synthetic routes. Compared with pure Ni12P5 NPs and Au-Ni12P5 oligomer-like NPs, the core/shell crystalline structure with Au shows an improved OER activity. It affords a current density of 10 mA/cm2 at a small overpotential of 0.34 V, in 1 M KOH aqueous solution at room temperature. This enhanced OER activity may relate to the strong structural and effective electronic coupling between the single-crystal core and the shell.
Superexchange effects play an important role in the determination of crystal structures; however, there has been much less reported on how they determine the stability of clusters. Using evolutionary search strategies and DFT+U (density functional theory with the Hubbard U correction) calculations, we investigate the global minimum-energy structures of Fe12On clusters. Among predicted Fe12On clusters, a cage-shaped Fe12O12 cluster with unexpected stability was observed. In addition, the bare Fe12O12 cluster is shown to possess an extremely large energy gap (2.00 eV), which is greater than that of C60, Au20 and Al13?clusters. Using a Heisenberg model, we traced the origin of the unexpected stability of the bare Fe12O12 cluster to magnetic competition between the nearest-neighbor exchange constant J1 and the next-nearest neighbor exchange constant J2 that was induced by the superexchange interactions. The bare Fe12O12 cluster is thus a unique molecule that is stable and chemically inert.
The efficient catalytic oxidation of water to dioxygen is envisioned to play an important role in solar fuel production and artificial photosynthetic systems. Despite tremendous efforts, the development of oxygen evolution reaction (OER) catalysts with high activity and low cost under mild conditions remains a great challenge. In this work, we develop a hybrid consisting of Co3O4 nanocrystals supported on single-walled carbon nanotubes (SWNTs) via a simple self-assembly approach. A Co3O4/SWNTs hybrid electrode for the OER exhibits much enhanced catalytic activity as well as superior stability under neutral and alkaline conditions compared with bare Co3O4, which only performs well in alkaline solution. Moreover, the turnover frequency for the OER exhibited by Co3O4/SWNTs in neutral water is higher than for bare Co3O4 catalysts. Synergetic chemical coupling effects between Co3O4 nanocrystals and SWNTs, revealed by the synchrotron X-ray absorption near edge structure (XANES) technique, can be regarded as contributing to the activity, cycling stability and stable operation under neutral conditions. Use of the SWNTs as an immobilization matrix substantially increases the active electrode surface area, enhances the durability of catalysts under neutral conditions and improves the electronic coupling between Co redox-active sites of Co3O4 and the electrode surface. 相似文献
The evolution of the film thickness and plasmonic properties for sputtered deposited Au nanoparticles on SiO2 layers have been monitored in real time using in situ spectroscopic ellipsometry in the photon energy range 0.75–4.1 eV. The spectroscopic ellipsometry data were analyzed with an optical model in which the optical constants for the Au nanoparticles were parameterized by B-splines which simultaneously provide an accurate determination of an effective thickness and an effective dielectric function. The effective thickness is interpreted with support of transmission and scanning electron microscopy and Rutherford backscattering measurements. Further parameterization of the optical constants by physical oscillators in the isolated spherical particle region allows the microstructural parameters such as size and Au fraction to be extracted. Real time in situ monitoring allows the growth of nanoparticles from the nucleation phase to near percolation to be followed, and there is a red-shift of the plasmon resonance absorption peak as the nanoparticles increase in size and their interaction becomes stronger. 相似文献
The geometric size and distribution of magnetic nanoparticles are critical to the morphology of graphene (GN) nanocomposites, and thus they can affect the capacity and cycling performance when these composites are used as anode materials in lithium-ion batteries (LiBs). In this work, Fe3O4 nanorods were deposited onto fully extended nitrogen-doped GN sheets from a binary precursor in two steps, a hydrothermal process and an annealing process. This route effectively tuned the Fe3O4 nanorod size distribution and prevented their aggregation. The transformation of the binary precursor was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). XPS analysis indicated the presence of N-doped GN sheets, and that the magnetic nanocrystals were anchored and uniformly distributed on the surface of the flattened N-doped GN sheets. As a high performance anode material, the structure was beneficial for electron transport and exchange, resulting in a large reversible capacity of 929 mA·h·g–1, high-rate capability, improved cycling stability, and higher electrical conductivity. Not only does the result provide a strategy for extending GN composites for use as LiB anode materials, but it also offers a route for the preparation of other oxide nanorods from binary precursors.
Systemic thrombolysis with intravenous tissue plasminogen activator (tPA) remains the only proven treatment that is effective in improving the clinical outcome of patients with acute ischemic stroke. However, thrombolytic therapy has some major limitations such as hemorrhage, neurotoxicity, and the short time window for the treatment. In this study, we designed iron oxide (Fe3O4) nanorods loaded with 6% tPA, which could be released within ~30 min. The Fe3O4 nanorods could be targeted to blood clots under magnetic guidance. In addition, the release of tPA could be significantly increased using an external rotating magnetic field, which subsequently resulted in a great improvement in the thrombolytic efficiency. Systematic and quantitative studies revealed the fundamental physical processes involved in the enhanced thrombolysis, while the in vitro thrombolysis assay showed that the proposed strategy could improve thrombolysis and recanalization rates and reduce the risk of tPA-mediated hemorrhage in vivo. Such a strategy will be very useful for the treatment of ischemic stroke and other deadly thrombotic diseases such as myocardial infarction and pulmonary embolism in clinical settings.
Uniform colloidal Bi2S3 nanodots and nanorods with different sizes have been prepared in a controllable manner via a hot injection method. X-ray
diffraction (XRD) results show that the resulting nanocrystals have an orthorhombic structure. Both the diameter and length
of the nanorods increase with increasing concentration of the precursors. All of the prepared Bi2S3 nanostructures show high efficiency in the photodegradation of rhodamine B, especially in the case of small sized nanodots—which
is possibly due to their high surface area. The dynamics of the photocatalysis is also discussed.
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Various sizes and shapes of Mn3O4 nanocrystals have been prepared in a one-pot synthesis in extremely dilute solution by soft template self-assembly. To better
control size and shape, the effects of varying the growth time, reaction temperature, surfactant, and manganese source were
examined. The average size of octahedral Mn3O4 crystallites was found to be related to the reaction time, while higher reaction temperature (150 °C) and the use of a cetyltrimethylammonium
bromide/poly(vinylpyrrolidone) (CTAB/PVP) mixture allowed construction of a better-defined octahedral morphologies. When PVP
or poly(ethylene oxide)-poly(propylene oxide) (P123) was used as template, large-scale agglomeration resulting in loss of
the octahedral morphology occurred and crystallites with a quasi-spherical shape were obtained. The nano-octahedral crystallites
were shown to be an efficient catalyst for the oxidation of methylene blue.
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The rational design of earth-abundant catalysts with excellent water splitting activities is important to obtain clean fuels for sustainable energy devices. In this study, mixed transition metal oxide nanoparticles encapsulated in nitrogendoped carbon (denoted as AB2O4@NC) were developed using a one-pot protocol, wherein a metal–organic complex was adopted as the precursor. As a proof of concept, MnCo2O4@NC was used as an electrocatalyst for water oxidation, and demonstrated an outstanding electrocatalytic activity with low overpotential to achieve a current density of 10 mA·cm?1 (η10 = 287 mV), small Tafel slope (55 mV·dec?1), and high stability (96% retention after 20 h). The excellent electrochemical performance benefited from the synergistic effects of the MnCo2O4 nanoparticles and nitrogen-doped carbon, as well as the assembled mesoporous nanowire structure. Finally, a highly stable all-solid-state supercapacitor based on MnCo2O4@NC was demonstrated (1.5% decay after 10,000 cycles).
The size and density of Ag nanoparticles on n-layer MoS2 exhibit thicknessdependent behavior. The size and density of these particles increased and decreased, respectively, with increasing layer number (n) of n-layer MoS2. Furthermore, the surface-enhanced Raman scattering (SERS) of Ag on this substrate was observed. The enhancement factor of this scattering varied with the thickness of MoS2. The mechanisms governing the aforementioned thickness dependences are proposed and discussed.
Nanomaterials with electrochemical activity are always suffering from aggregations, particularly during the high-temperature synthesis processes, which will lead to decreased energy-storage performance. Here, hierarchically structured lithium titanate/nitrogen-doped porous graphene fiber nanocomposites were synthesized by using confined growth of Li4Ti5O12 (LTO) nanoparticles in nitrogen-doped mesoporous graphene fibers (NPGF). NPGFs with uniform pore structure are used as templates for hosting LTO precursors, followed by high-temperature treatment at 800 °C under argon (Ar). LTO nanoparticles with size of several nanometers are successfully synthesized in the mesopores of NPGFs, forming nanostructured LTO/NPGF composite fibers. As an anode material for lithium-ion batteries, such nanocomposite architecture offers effective electron and ion transport, and robust structure. Such nanocomposites in the electrodes delivered a high reversible capacity (164 mAh·g–1 at 0.3 C), excellent rate capability (102 mAh·g–1 at 10 C), and long cycling stability.
A novel pure cubic-phase pyrochlore structure tin(II) antimonate nanophotocatalyst, stoichiometric Sn2Sb2O7, has been prepared by a modified ion-exchange process using an antimonic acid precursor, and employed in visible-light-driven photocatalytic H2 evolution for the first time. The physicochemical properties (crystal phase, chemical composition and state, textural properties, and optical properties) of the material were investigated by different instrumental techniques. Compared with the antimonic acid precursor, the as-prepared Sn2Sb2O7 had a narrower bandgap, smaller crystal size, and larger BET surface area. The as-prepared Sn2Sb2O7 was validated as a promising candidate for visible-light-driven photocatalytic H2 evolution with a constant rate of 40.10 μmol·h−1·gcat−1. 相似文献
Ultrasmall γ-Fe2O3 nanodots (～ 3.4 nm) were homogeneously encapsulated in interlinked porous N-doped carbon nanofibers (labeled as Fe2O3@C) at a considerable loading (～ 51 wt.%) via an electrospinning technique. Moreover, the size and content of Fe2O3 could be controlled by adjusting the synthesis conditions. The obtained Fe2O3@C that functioned as a self-standing membrane was used directly as a binder- and current collector-free anode for sodium-ion batteries, displaying fascinating electrochemical performance in terms of the exceptional rate capability (529 mA·h·g–1 at 100 mA·g–1 compared with 215 mA·h·g–1 at 10,000 mA·g–1) and unprecedented cyclic stability (98.3% capacity retention over 1,000 cycles). Furthermore, the Na-ion full cell constructed with the Fe2O3@C anode and a P2-Na2/3Ni1/3Mn2/3O2 cathode also exhibited notable durability with 97.2% capacity retention after 300 cycles. This outstanding performance is attributed to the distinctive three-dimensional network structure of the very-fine Fe2O3 nanoparticles uniformly embedded in the interconnected porous N-doped carbon nanofibers that effectively facilitated electronic/ionic transport and prevented active materials pulverization/aggregation caused by volume change upon prolonged cycling. The simple and scalable preparation route, as well as the excellent electrochemical performance, endows the Fe2O3@C nanofibers with great prospects as high-rate and long-life Na-storage anode materials.
Multi-shelled CoFe2O4 hollow microspheres with a tunable number of layers (1–4) were successfully synthesized via a facile one-step method using cyclodextrin as a template, followed by calcination. The structural features, including the shell number and shell porosity, were controlled by adjusting the synthesis parameters to produce hollow spheres with excellent capacity and durability. This is a straightforward and general strategy for fabricating metal oxide or bimetallic metal oxide hollow microspheres with a tunable number of shells.
Approximately 15 nm thick nitrogen-doped lanthanum titanate (La2Ti2O7) nanosheets with a single-crystalline perovskite structure have been prepared by hydrothermal processing and subsequent heat
treatment in NH3 at 600 °C. Doping nitrogen into the La2Ti2O7 nanosheets results in the narrowing of the band gap, extending the light absorption into the visible light region (∼495 nm).
The nitrogen-doped La2Ti2O7 nanosheets not only show significant visible light photocatalytic activity toward the decomposition of methyl orange but
also exhibit enhanced the ultraviolet light photocatalytic activity. The enhancement of photocatalytic activity originates
from the narrowing of the band gap of La2Ti2O7 nanosheets. The results obtained show that the desirable route to extend the photocatalytic activity of a semiconductor from
the ultraviolet to the visible light region is to narrow the band gap rather than to create localized mid-gap states.
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