Chongyun Liang

Ultrathin BaTiO3 Nanowires with High Aspect Ratio: A Simple One-Step Hydrothermal Synthesis and Their Strong Microwave Absorption

In this paper, we report the facile synthesis of ultrathin barium titanate (BaTiO3) nanowires with gram-level yield via a simple one-step hydrothermal treatment. Our BaTiO3 nanowires have unique features: single crystalline, uniform size distribution and ultra high aspect ratio. The synergistic effects including both Ostwald ripening and cation exchange reaction are responsible for the growth of the ultrathin BaTiO3 nanowires. The microwave absorption capability of the ultrathin BaTiO3 nanowires is improved compared to that of BaTiO3 nanotorus,1 with a maximum reflection loss as high as -24.6 dB at 9.04 GHz and an absorption bandwidth of 2.4 GHz (<-10 dB). Our method has some novel advantages: simple, facile, low cost and high synthesis yield, which might be developed to prepare other ferroelectric nanostructures. The strong microwave absorption property of the ultrathin BaTiO3 nanowires indicates that these nanowires could be used as promising materials for microwave-absorption and stealth camouflage techniques.

Hierarchical hollow Li4Ti5O12 urchin-like microspheres with ultra-high specific surface area for high rate lithium ion batteries

Large specific surface area is critical for Li4Ti5O12 to achieve good rate capacity and cycling stability, since it can increase the contact area between electrolyte/electrode and shorten the transport paths for electrons and lithium ions. In this study, hierarchical hollow Li4Ti5O12 urchin-like microspheres with ultra-high specific surface area of over 140 m2·g−1 and diameter more than 500 nm have been successfully synthesized by combining the versatile sol-gel process and a hydrothermal reaction, and exhibit excellent electrochemical performance with a high specific capacity of 120 mA·h·g−1 at 20 C and long cycling stability of < 2% decay after 100 cycles. Ex situ electron energy loss spectroscopy (EELS) analysis of Li4Ti5O12 microspheres at different charge-discharge stages indicates that only a fraction of the Ti4+ ions are reduced to Ti3+ and a phase transformation occurs whereby the spinel phase Li4Ti5O12 is converted into the rock-salt phase Li7Ti5O12. Even after 100 cycles, the oxidation-reduction reaction between Ti3+ and Ti4+ can be carried out much more effectively on the surface of Li4Ti5O12 nanosheets than on commercially available Li4Ti5O12 particles. All the results suggest that these Li4Ti5O12 microspheres may be attractive candidate anode materials for lithium ion batteries.

A facile phase transformation method for the preparation of 3D flower-like β-Ni(OH)2/GO/CNTs composite with excellent supercapacitor performance

3D flower-like β-Ni(OH)2/GO/CNTs composite was prepared via a facile phase transformation method with a high specific capacitance of ∼1815 F g−1 (nearly 96% of its theoretical pseudocapacitance) at 2 A g−1 and a good cycling performance of ∼97% capacitance retention after 2000 cycles at 10 A g−1. The morphology of β-Ni(OH)2 undergoes successive changes that could be controlled by adjusting the reaction time.

Ultrathin β-Ni(OH)2 nanoplates vertically grown on nickel-coated carbon nanotubes as high-performance pseudocapacitor electrode materials.

Various metal hydroxides/oxides grown on conductive substrates such as nickel foam have been reported and studied as supercapacitor electrode materials. However, the capacitances of these electrodes are extremely limited because of the low content of active materials grown on the limited surface of nickel foam. To achieve high capacitance, we use nickel-coated carbon nanotubes (Ni-CNTs) as the conductive substrate for the growth of β-Ni(OH)2. By a facile chemical method, ultrathin β-Ni(OH)2 nanoplates are vertically grown on the surface of Ni-CNTs. The density, thickness, and content of β-Ni(OH)2 can be easily controlled by modulating the ratio of NiCl2·6H2O to Ni-CNTs. This hierarchical nanostructure can provide remarkable synergistic effects: facilitate electron and ion transport and accelerate the reversible redox reactions. As-prepared Ni-CNTs@β-Ni(OH)2 composites exhibit high specific capacitances (∼1807 F g(-1) at 2 A g(-1), based on the mass of β-Ni(OH)2; ∼1283 F g(-1) at 2 A g(-1), based on the mass of composite), good rate capabilities, and excellent cycling stabilities. This strategy has potential for large-scale production and can be applied to the preparation of other hierarchical nanostructured metal hydroxide/oxide composites.

Porous Au–Ag Alloy Particles Inlaid AgCl Membranes As Versatile Plasmonic Catalytic Interfaces with Simultaneous, in Situ SERS Monitoring

We present a novel porous Au-Ag alloy particles inlaid AgCl membrane as plasmonic catalytic interfaces with real-time, in situ surface-enhanced Raman spectroscopy (SERS) monitoring. The Au-Ag alloy particles inlaid AgCl membranes were obtained via a facile two-step, air-exposed, and room-temperature immersion reaction with appropriate annealing process. Owing to the designed integration of semiconductor component AgCl and noble metal Au-Ag particles, both the catalytic reduction and visible-light-driven photocatalytic activities toward organic contaminants were attained. Specifically, the efficiencies of about 94% of 4-nitrophenol (4-NP, 5 × 10(-5) M) reduction after 8 min of reaction, and degradation of rhodamine 6G (R6G, 10(-5) M) after 12 min of visible light irradiation were demonstrated. Moreover, efficiencies of above 85% of conversion of 4-NP to 4-aminophenol (4-AP) and 90% of R6G degradation were achieved as well after 6 cycles of reactions, by which robust recyclability was confirmed. Further, with distinct SERS signals generated simultaneously from the surfaces of Au-Ag particles under laser excitation, in situ SERS monitoring of the process of catalytic reactions with superior sensitivity and linearity has been realized. Overall, the capability of the Au-Ag particles inlaid AgCl membranes to provide SERS monitored catalytic and visible-light-driven photocatalytic conversion of organic pollutants, along with their mild and cost-effective fabrication method, would make sense for in-depth understanding of the mechanisms of (photo)catalytic reactions, and also future development of potable, multifunctional and integrated catalytic and sensing devices.

Uniform wurtzite MnSe nanocrystals with surface-dependent magnetic behavior

AbstractManganese selenide (MnSe) possesses unique magnetic properties as an important magnetic semiconductor, but the synthesis and properties of MnSe nanocrystals are less developed compared to other semiconductor nanocrystals because of the inability to obtain high-quality MnSe, especially in the metastable wurtzite structure. Here, we have successfully fabricated wurtzite MnSe nanocrystals via a colloidal approach which affords uniform crystal sizes and tailored shapes. The selective binding strength of the amine surfactant is the determining factor in shape-control and shape-evolution. Bullet-shapes could be transformed into shuttle-shapes if part of the oleylamine in the reaction solution was replaced by trioctylamine, and tetrapod-shaped nanocrystals could be formed in trioctylamine systems. The three-dimensional (3D) structure of the bullet-shaped nanorods has been demonstrated by the advanced transmission electron microscope (TEM) 3D-tomography technology. High-resolution TEM (HRTEM) and electron energy-loss spectroscopy (EELS) show that planar-defect structures such as stacking faults and twinning along the [001] direction arise during the growth of bullet-shapes. On the basis of careful HRTEM observations, we propose a “quadra-twin core” growth mechanism for the formation of wurtzite MnSe nanotetrapods. Furthermore, the wurtzite MnSe nanocrystals show lowtemperature surface spin-glass behavior due to their noncompensated surface spins and the blocking temperatures increase from 8.4 K to 18.5 K with increasing surface area/volume ratio of the nanocrystals. Our results provide a systematic study of wurtzite MnSe nanocrystals.

Inheritance of Crystallographic Orientation during Lithiation/Delithiation Processes of Single-Crystal α-Fe2O3 Nanocubes in Lithium-Ion Batteries

Iron oxides are very promising anode materials based on conversion reactions for lithium-ion batteries (LIBs). During conversion processes, the crystal structure and composition of the electrode material are drastically changed. Surprisingly, in our study, inheritance of a crystallographic orientation was found during lithiation/delithiation processes of single-crystal α-Fe2O3 nanocubes by ex situ transmission electron microscopy. Single-crystal α-Fe2O3 was first transformed into numerous Fe nanograins embedded in a Li2O matrix, and then the conversion between Fe and FeO nanograins became the main reversible electrochemical reaction for energy storage. Interestingly, these Fe/FeO nanograins had almost the same crystallographic orientation, indicating that the lithiated/delithiated products can inherit the crystallographic orientation of single-crystal α-Fe2O3. This finding is important for understanding the detailed electrochemical conversion processes of iron oxides, and this feature may also exist during lithiation/delithiation processes of other transition-metal oxides.

Controllable synthesis of elongated hexagonal bipyramid shaped La(OH)3 nanorods and the distribution of electric property by off-axis electron holography

Rare earth oxides/hydroxides are important emerging materials owing to their unique properties. Shape-controlled synthesis of elongated hexagonal bipyramid shaped La(OH)3 nanorods with different aspect ratios and trigram-shaped LaCO3OH nanosheets was systematically carried out by controlling the reaction conditions. Hydrazine and polyvinylpyrrolidone (PVP) surfactants used in synthesis are assumed to play a key “dual-template” role in determining the aspect ratio and shape of the resulting nanostructures. Elongated hexagonal bipyramid shaped La(OH)3 nanorods were found to grow along the preferred orientation [0001]. Six equivalent crystallographic facets,

Synthesis of Au and Au–CuO cubic microcages via an in situ sacrificial template approach

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