Yanhuai Ding

A green approach to the synthesis of reduced graphene oxide nanosheets under UV irradiation

We present a totally green approach towards the synthesis and stabilization of aqueous graphene dispersions through UV-irradiated reduction of exfoliated graphene oxide (GO). Polyvinyl pyrrolidone (PVP) is used to enhance the dispersibility of reduced graphene oxide (RGO) by one-step functionalization. The proposed method is low cost and easy without using any photocatalysts or reducing agents, which can open up a new possibility for green preparation of stable RGO dispersions in large-scale production.

Preparation of PVdF-based electrospun membranes and their application as separators

Abstract A one-step method preparing of poly(vinylidene fluoride)-based electrospun membranes (PEMs) containing TiO2 has been developed. The effect of TiO2 on the morphology, degree of crystallization and electrochemical behavior of PEMs was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and electrochemical measurements. The PEMs containing TiO2 show improved ionic conductivity and cycling performance compared with pure PEMs.

Co-precipitation synthesis and electrochemical properties of graphene supported LiMn1/3Ni1/3Co1/3O2 cathode materials for lithium-ion batteries

Nanostructured graphene supported LiMn1/3Ni1/3Co1/3O2 has been prepared by the co-precipitation method and used as the cathode material for lithium-ion batteries. The structure and morphology of the composite were examined using atomic force microscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and x-ray diffraction. The composite cathodes made of graphene nanosheet supported LiMn1/3Ni1/3Co1/3O2 showed superior electrochemical performance and increased capacity compared to raw LiMn1/3Ni1/3Co1/3O2 electrodes. The outstanding electrochemical behavior of graphene supported LiMn1/3Ni1/3Co1/3O2 was ascribed to the increased electrical conductivity and high structural stability resulting from the addition of graphene.

Nanoscale mechanical characterization of PMMA by AFM nanoindentation: a theoretical study on the time-dependent viscoelastic recovery

Temperature-dependent indent recovery of polymethyl methacrylate is depicted by atomic force microscopy. The viscoelastic indent recovery is predicted by a numerical model based on the Boussinesq elastic theory. From the perspective of an elastic solution, viscoelastic solution for stress and displacement field is constructed through the analysis of the elasticity–viscoelasticity corresponding theory. The findings also illustrate the effect of loading condition, elastic modulus, and viscosity on the viscoelastic recovery rate.

A new two-dimensional TeSe 2 semiconductor: indirect to direct band-gap transitions

A novel two-dimensional (2D) TeSe2 structure with high stability is predicted based on the first-principles calculations. As a semiconductor, the results disclose that the monolayer TeSe2 has a wide-band gap of 2.392 eV. Interestingly, the indirect-band structure of the monolayer TeSe2 transforms into a direct-band structure under the wide biaxial strain (0.02–0.12). The lower hole effective mass than monolayer black phosphorus portends a high carrier mobility in TeSe2 sheet. The optical properties and phonon modes of the few-layered TeSe2 were characterized. The few-layer TeSe2 shows a strong optical anisotropy. Specially, the calculated results demonstrate that the multilayer TeSe2 has a wide range of absorption wavelength. Our result reveals that TeSe2 as a novel 2D crystal possesses great potential applications in nanoscale devices, such as high-speed ultrathin transistors, nanomechanics sensors, acousto-optic deflectors working in the UV-vis red region and optoelectronic devices.摘要本文基于第一性原理计算预测了一种新颖的二维稳定结构TeSe2, 结果显示单层TeSe2是一种半导体材料, 其带隙值为2.392 eV. 有趣的是单层TeSe2的间接能带在宽范围的双向负应变(0.02~0.12)作用下转变为直接能带. 比单层黑磷烯更小的有效空穴电子质量预示了TeSe2具有更高的载流子迁移速率. 此外, 对不同厚度TeSe2的声子模及光学性质也进行了计算, 结果显示不同厚度的TeSe2具有较强的光学各向异性, 尤其是多层TeSe2具有更宽的吸收波长. 这些结果表明, TeSe2作为一种新颖的二维结构在纳米器件领域具有巨大的应用潜力, 如高速超薄晶体管, 纳米力学传感器, 紫外–可见红光区声光偏振器及光电子器件等.

Mechanical properties of a single SnO 2 fiber prepared from the electrospinning method

Uniform SnO2 fibers were prepared from the electrospinning method in this paper. The mechanical properties of a single SnO2 fiber were characterized by three-point bending experiments with atomic force microscopy. Finite element method was employed to simulate the shape of the SnO2 fiber during the bending process. The elastic modulus of SnO2 fibers increased with the calcined temperature. A high elastic modulus of 72.59 GPa was obtained with a diameter of 160 nm. The results indicate that atomic force microscopy tips penetrated the surfaces under maximum loading.Graphical abstractThe force-displacement curve from simulation is in accordance with the results from experiments by using AFM and theoretical calculation. The equivalent strain nephogram indicates that the maximal strain is about 0.0143 at the midpoint of the fiber.

Intrinsic structure and friction properties of graphene and graphene oxide nanosheets studied by scanning probe microscopy

In this paper, atomic structure of single-layered graphene oxide (GO) and chemically reduced graphene oxide (CRGO) nanosheets was investigated using atomic force microscopy and scanning tunneling microscopy (AFM and STM). Furthermore, friction properties of the graphene and GO nanosheets were studied by frictional force microscopy (FFM). STM imaging provided direct evidence and the morphology was influenced by oxygen-containing groups and defects. The atomic scale structural disorder in a hexagonal two-dimensional network of carbon atoms changes the surface condition, which also caused the frictional property variations of the samples.

Compressive mechanical properties of porous GO materials prepared from freeze-drying method

In this paper porous graphene oxide (GO) foams were prepared from freeze-drying method. Compressive mechanical properties of GO foams with different density were investigated by uniaxial compression experiments and finite element (FE) simulation. GO foam exhibited excellent elasticity, which recovered to its original length even after 300 cycles. The structural evolution during the compression was revealed by FE simulation.

Carbon innercoated ordered porous TiO2 as anode materials for lithium-ion batteries

Carbon innercoated ordered porous TiO2 were prepared by anodic oxidation of pure titanium sheets, followed by in situ decomposition of glucose in the TiO2. Structure, morphology, and electrochemical properties of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and a variety of electrochemical testing techniques. Initial discharge capacity and cycling performance of ordered porous TiO2 were improved dramatically by the inner carbon coating. Migration of Li ions and electrons in the carbon layer was beneficial to suppress the charge transfer resistance of TiO2 electrode, which resulted in significant improvement in electrochemical performances.

Preparation and electrochemical properties of LiFePO4/graphene composites from tailoring graphene oxides

LiFePO4/graphene composites have been prepared by using tailoring graphene oxide (GO) nanosheets as precursors. The structure and electrochemical properties of the composites were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman microscopy, and a variety of electrochemical testing techniques. The decrease in graphene size reduces the contact resistance between activated materials, and enhances the lithium-ion transport in LiFePO4/graphene composites. With low weight fractions of small-size graphene sheets, the composites show better electrochemical performance than those with large size graphene sheets.