Yundan Liu

Upconversion-P25-graphene composite as an advanced sunlight driven photocatalytic hybrid material

Herein, a new nanocomposite consisting of up-conversion (UC) material (YF3:Yb3+,Tm3+), TiO2 (P25) and graphene (GR) has been prepared and shown to be an advanced sunlight activated photocatalyst. During the facile hydrothermal method, the reduction of graphene oxide and loading of YF3:Yb3+,Tm3+ and P25 were achieved simultaneously, and the functionalities of each part were integrated together. The as-prepared ternary UC–P25–GR nanocomposite photocatalyst exhibited great adsorptivity of dyes, a significantly extended light absorption range, efficient charge separation properties and superior durability. Indeed, the photocatalytic activity of this novel ternary nanocomposite under sunlight was improved compared with those of P25–GR nanocomposites and bare P25. Overall, this work could provide new insights into the fabrication of ternary composites as high performance photocatalysts and facilitate their application in environmental protection issues.

Large-scale production of ultrathin topological insulator bismuth telluride nanosheets by a hydrothermal intercalation and exfoliation route

A convenient hydrothermal intercalation/exfoliation method for large-scale manufacturing of bismuth telluride (Bi2Te3) nanosheets is reported here. Lithium cations can be intercalated between the layers of Bi2Te3 using the reducing power of ethylene glycol in the common hydrothermal process, and high quality Bi2Te3 nanosheets with thickness down to only 3–4 nm are obtained by removing lithium in the following exfoliating process. Scanning electron microscopy, transmission electron microscopy and Raman spectrum characterizations confirm that the high yield of Bi2Te3 nanosheets with good quality were successfully achieved and the sizes of the immense nanosheets reached 200 nm width and 1 μm length. This hydrothermal intercalation/exfoliation method is general, as it has been extended to other layered materials, such as Bi2Se3 and MoS2. Our results suggest a simple route for the large-scale production of thin and flat Bi2Te3 nanosheets, which may be beneficial to further electronic and spintronics applications.

An architectured TiO2 nanosheet with discrete integrated nanocrystalline subunits and its application in lithium batteries

An anatase TiO2 nanosheet with discrete integrated subunits was successfully synthesized via a rapid annealing treatment, which could be classified as non-equilibrium conditions on an as-prepared hydrogen titanate nanosheet. This unique TiO2 nano-object is uniform in length and width as a “sheet-like” shape which is integrated with numerous discrete nanocrystalline subunits. In contrast with the internal architecture of the TiO2 nanosheets produced under equilibrium and non-equilibrium conditions, the local structure collapse transformation mechanism from the hydrogen titanate nanosheet to the anatase TiO2 nanosheet with internal architecture is discussed. This unique anatase nano-object electrode exhibits high reversible lithium ion storage capacities and superior cyclic capacity retention at a high current rate. Such enhanced lithium storage performance could be attributed to the discrete subunits aggregation allowing efficient Li+ ion diffusion and the interior anisotropy in the nanosheet can be more effective to buffer the volume variation during the lithium insertion/desertion cycle.

Photoresponse properties of large-area MoS2 atomic layer synthesized by vapor phase deposition

Photoresponse properties of a large area MoS2 atomic layer synthesized by vapor phase deposition method without any catalyst are studied. Scanning electron microscopy, atomic force microscopy, Raman spectrum, and photoluminescence spectrum characterizations confirm that the two-dimensional microstructures of MoS2 atomic layer are of high quality. Photoelectrical results indicate that the as-prepared MoS2 devices have an excellent sensitivity and a good reproducibility as a photodetector, which is proposed to be ascribed to the potential-assisted charge separation mechanism.

Electrostatic properties of few-layer MoS2 films

Two-dimensional MoS2-based materials are considered to be one of the most attractive materials for next-generation nanoelectronics. The electrostatic properties are important in designing and understanding the performance of MoS2-based devices. By using Kelvin probe force microscopy, we show that few-layer MoS2 sheets exhibit uniform surface potential and charge distributions on their surfaces but have relatively lower surface potentials on the edges, folded areas as well as defect grain boundaries.

Ambipolar charge injection and transport of few-layer topological insulator Bi2Te3 and Bi2Se3 nanoplates

We report the electrostatic properties of few-layer Bi2Te3 and Bi2Se3 nanoplates (NPs) grown on 300 nm SiO2/Si substrate. Electrons and holes are locally injected in Bi2Te3 and Bi2Se3 nanoplates by the apex of an atomic force microscope tip. Both carriers are delocalized uniformly over the whole nanoplate. The electrostatic property of topological insulator Bi2Te3 and Bi2Se3 nanoplates after charge injection is characterized by Kelvin probe force microscopy under ambient environment and exhibits an ambipolar surface potential behavior. These results provide insight into the electronic properties of topological insulators at the nanometer scale.

Electrochemically reduced graphene oxide with porous structure as a binder-free electrode for high-rate supercapacitors

A binder-free electrode is prepared by directly depositing electrochemically reduced graphene oxide (ERGO) on the metal current collector. Fourier transform infrared spectroscopy and Raman spectrum have been used to demonstrate the effective reduction of graphene oxide on the electrode, and the porous structure of the ERGO film was further characterized by scanning electron microscopy. The electrochemical properties of ERGO were investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). Electrochemical measurements showed that the binder-free ERGO electrode had high specific capacity, good cycle stability, as well as excellent high-rate capability. The specific capacitance of the constructed electrode was 131.6 F g−1 at a scan rate of 10 mV s−1 and maintained 66.9% of the initial value when the scan rate was increased up to 1000 mV s−1. Owing to its favorable electrochemical performance, this binder-free ERGO electrode with porous structure has great potential in future commercial electrochemical supercapacitors.

Growth and surface potential characterization of Bi2Te3 nanoplates

Topological insulator Bi2Te3 nanoplates with hexagonal, triangular and truncated triangular nanostructures have been fabricated with thickness of ∼10 nm by vacuum vapor phase deposition method. The possible formation mechanism of Bi2Te3 nanoplates with different nanostructures has been proposed. We have examined the surface potentials of Bi2Te3 nanoplates using Kelvin probe force microscopy. The surface potential of Bi2Te3 nanoplates is determined to be about 482 mV on the SiO2/Si substrate, 88 mV and -112 mV on the n-doped and p-doped Si (111) substrates, respectively. The surface potential information provides insight into understanding electronic properties of Bi2Te3 nanoplates, which may open a new door to the exploration of the topological insulators.

Hydrothermal exfoliated molybdenum disulfide nanosheets as anode material for lithium ion batteries

Abstract Ultrathin MoS 2 nanosheets were prepared in high yield using a facile and effective hydrothermal intercalation and exfoliation route. The products were characterized in detail using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The results show that the high yield of MoS 2 nanosheets with good quality was successfully achieved and the dimensions of the immense nanosheets reached 1 μm–2 μm. As anode material for Li-ion batteries, the as-prepared MoS 2 nanosheets electrodes exhibited a good initial capacity of 1190 mAh·g −1 and excellent cyclic stability at constant current density of 50 mA·g −1 . After 50 cycles, it still delivered reversibly sustained high capacities of 750 mAh·g −1 .

One-step hydrothermal fabrication and enhancement of the photocatalytic performance of CdMoO4/CdS hybrid materials

A series of CdMoO4/CdS hybrid composites were synthesized via a one-step hydrothermal method. The products were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman and UV-vis diffuse reflection spectroscopy. The photocatalytic activities of the CdMoO4/CdS hybrid materials compared with CdMoO4 microspheres and dendritic CdS nanostructures were evaluated by rhodamine B (RhB) decomposition under sunlight irradiation. The results revealed that the as-prepared CdMoO4/CdS hybrid composites showed superior photocatalytic activities for the degradation of RhB under sunlight irradiation, especially compared with dendritic CdS decorated with 22% CdMoO4 microspheres. The superior photodegradation performance of the as-prepared CdMoO4/CdS hybrid composites can be ascribed to the presence of CdMoO4 as an electron acceptor which improves the effective charge separation in CdS.