Bing Zhao

Monolayer graphene/NiO nanosheets with two-dimension structure for supercapacitors

In this paper, graphene oxide (GO) synthesized from the modified Hummer method is used directly to fabricate unique two-dimension graphene/NiO composite material. Nickel ions are adsorbed on both sides of GO based on self-assembly by the electrostatic interactions of two species, forming the monolayer graphene/NiO sheet. The as-prepared composite is characterized using X-ray diffraction (XRD), Raman, SEM, TEM, Energy Dispersive Spectrometer (EDS) analysis and nitrogen adsorption/desorption. The results demonstrate that the NiO nanoparticles (5–7 nm) is uniformly dispersed on the surface of graphene, which greatly increases the surface area of the composite (134.5 m2 g−1). This two-dimensional structure enhances supercapacitive performance with a high specific capacitance of 525 F g−1 at a current density of 200 mA g−1. A capacity retention of 95.4% can be maintained after 1000 cycles, suggesting its promising potential in supercapacitors.

Hierarchical self-assembly of microscale leaf-like CuO on graphene sheets for high-performance electrochemical capacitors

In this paper, a leaf-like porous CuO–graphene nanostructure is synthesized by a hydrothermal method. The as-prepared composite is characterized using XRD, Raman, SEM, TEM and nitrogen adsorption–desorption. The growth mechanism is discussed by monitoring the early growth stages. It is shown that the CuO nanoleaves are formed through oriented attachment of tiny Cu(OH)2 nanowires. Electrochemical characterization demonstrates that the leaf-like CuO–graphene are capable of delivering specific capacitances of 331.9 and 305 F g−1 at current densities of 0.6 and 2 A g−1, respectively. A capacity retention of 95.1% can be maintained after 1000 continuous charge–discharge cycles, which may be attributed to the improvement of electrical contact by graphene and mechanical stability by the layer-by-layer structure. The method provides a facile and straightforward approach to synthesize CuO nanosheets on graphene and may be readily extended to the preparation of other classes of hybrids based on graphene sheets for technological applications.

Insight on fractal assessment strategies for tin dioxide thin films.

Tin oxide is a unique material of widespread technological applications, particularly in the field of environmental functional materials. New strategies of fractal assessment for tin dioxide thin films formed at different substrate temperatures are of fundamental importance in the development of microdevices, such as gas sensors for the detection of environmental pollutants. Here, tin dioxide thin films with interesting fractal features were successfully prepared by pulsed laser deposition techniques under different substrate temperatures. Fractal method has been first applied to the evaluation of this material. The measurements of carbon monoxide gas sensitivity confirmed that the gas sensing behavior is sensitively dependent on fractal dimensions, fractal densities, and average sizes of the fractal clusters. The random tunneling junction network mechanism was proposed to provide a rational explanation for this gas sensing behavior. The formation process of tin dioxide nanocrystals and fractal clusters could be reasonably described by a novel model.

Irradiated Graphene Loaded with SnO2 Quantum Dots for Energy Storage

Tin dioxide (SnO2) and graphene are unique strategic functional materials with widespread technological applications, particularly in the areas of solar batteries, optoelectronic devices, and solid-state gas sensors owing to advances in optical and electronic properties. Versatile strategies for microstructural evolution and related performance of SnO2 and graphene composites are of fundamental importance in the development of electrode materials. Here we report that a novel composite, SnO2 quantum dots (QDs) supported by graphene nanosheets (GNSs), has been prepared successfully by a simple hydrothermal method and electron-beam irradiation (EBI) strategies. Microstructure analysis indicates that the EBI technique can induce the exfoliation of GNSs and increase their interlayer spacing, resulting in the increase of GNS amorphization, disorder, and defects and the removal of partial oxygen-containing functional groups on the surface of GNSs. The investigation of SnO2 nanoparticles supported by GNSs (SnO2/GNSs) reveals that the GNSs are loaded with SnO2 QDs, which are dispersed uniformly on both sides of GNSs. Interestingly, the electrochemical performance of SnO2/GNSs indicates that SnO2 QDs supported by a 210 kGy irradiated GNS shows excellent cycle response, high specific capacity, and high reversible capacity. This novel SnO2/GNS composite has potential practical applications in SnO2 electrode materials during Li(+) insertion/extraction.

Three-Dimensional Interconnected Spherical Graphene Framework/SnS Nanocomposite for Anode Material with Superior Lithium Storage Performance: Complete Reversibility of Li2S

Three-dimensional (3D) interconnected spherical graphene framework-decorated SnS nanoparticles (3D SnS@SG) is synthesized by self-assembly of graphene oxide nanosheets and positively charged polystyrene/SnO2 nanospheres, followed by a controllable in situ sulfidation reaction during calcination. The SnS nanoparticles with diameters of ∼10-30 nm are anchored to the surface of the spherical graphene wall tightly and uniformly. Benefiting from the 3D interconnected spherical graphene framework and subtle SnS nanoparticles, the generated Li2S could keep in close contact with Sn to make possible the in situ conversion reaction SnS + 2Li+ + 2e- ↔ Sn + Li2S. As a result, the 3D SnS@SG as the anode material for lithium ion batteries shows a high initial Coulombic efficiency of 75.3%. Apart from the irreversible capacity loss of 3D spherical graphene, the initial Coulombic efficiency of SnS in the 3D SnS@SG composite is as high as 99.7%, demonstrating the almost complete reversibility of Li2S in this system. Furthermore, it also exhibits an excellent reversible capacity (800 mAh g-1 after 100 cycles at 0.1 C and 527.1 mAh g-1 after 300 cycles at 1 °C) and outstanding rate capability (380 mAh g-1 at 5 °C).

Preparation of TiO2 nanowire gas nanosensor by AFM anode oxidation

Applications of atomic force microscopy (AFM) to the fabrication of chemical nanosensors are presented in this paper. Using AFM cantilever as cathode, the surface of Ti thin film is oxidized to form a few tens of nanometers wide oxidized metal semiconductor wire, which works as a nanowire-based hydrogen sensor. The reaction mechanism is proposed. The AFM observations of fabrication of a TiO2 nanowire are carried out. The sensitive characteristic of such TiO2 nanowires to hydrogen is investigated.

The charge storage characteristics of PZT nanocrystal thin film

Lead zirconate titanate (PZT) films have been extensively investigated for many applications: the nonvolatile memory devices based on their remarkable ferroelectric properties, the microelectromechanical system (MEMS) based on their piezoelectricity as well in sensors as in actuators. In this paper, we inject charges into PZT thin films, and then the charge storage and transportation through PZT thin films were observed by electric force microscopy (EFM). Results were studied and charging mechanisms were proposed.

Facile synthesis of ultrathin, undersized MoS2/graphene for lithium-ion battery anodes

Ultrathin, undersized MoS2/graphene composites are fabricated by a facile acetic acid assisted hydrothermal route and post-annealing. The structure and morphology characterization reveals that the MoS2 nanosheets with ∼5 layers and 130–160 nm in size are decorated on the surface of graphene nanosheets homogeneously and tightly. The effects of acetic acid and N-methyl-pyrrolidone solvent on the microstructures and electrochemical performances of the MoS2/graphene composites are investigated. It is found that the acetic acid could maintain a constant pH and promote hydrolysis of thiourea, and thus many more MoS2 crystals nucleus were formed, while the N-methyl-pyrrolidone could inhibit the aggregation of the as-prepared MoS2 sheets, and therefore few-layered MoS2 sheets with a small size are obtained. Electrochemical tests confirmed that the lithium storage performance of ultrathin, undersized MoS2/graphene is greatly improved compared to that without addition of acetic acid or N-methyl-pyrrolidone solvent. A high reversible capacity of 1229 mA h g−1 is achieved in the initial cycle and is maintained at 942.6 mA h g−1 after 50 cycles at a current density of 100 mA g−1. Even at a current density of 1000 mA g−1, the reversible capacity could be maintained as high as 747 mA h g−1.

Facile fabrication and application of SnO2–ZnO nanocomposites: insight into chain-like frameworks, heterojunctions and quantum dots

Versatile strategies for the heterostructure and related performance of nanocomposites are of fundamental importance in the development of advanced functional materials. Semiconductor oxide materials, such as SnO2 and ZnO, have attracted great interest owing to their potential to combine desirable properties. In this work, a novel SnO2–ZnO heterostructured nanocomposite has been fabricated by a sol–gel method and supercritical fluid drying processes. Nanostructure analysis indicated that the SnO2–ZnO composites show chain-like frameworks with heterojunction features, which were embedded with SnO2 and ZnO quantum dots (QDs). The size distribution of SnO2 and ZnO QDs ranged from 3 to 7 nm, which were uniformly dispersed on SnO2–ZnO chain-like frameworks. The experimental results indicated that the calcination temperature could effectively affect the photocatalytic degradation of SnO2–ZnO nanocomposites. When the calcination temperature increased from 500 to 700 °C, the photocatalytic degradation rate increased as the reaction time increased from 30 to 150 min. The new insight obtained in this study will be beneficial for the practical applications of binary oxide semiconductor composites for the photocatalytic degradation of organic pollutants.

Retracted Article: Facile synthesis of hierarchical Mn3O4 superstructures and efficient catalytic performance

The development of novel materials with excellent performance depends not only on the constituents but also on their remarkable micro/nanostructures. In this work, manganese oxide (Mn3O4) hausmannite structures with a uniform three-dimensional (3D) flower-like hierarchical architecture have been successfully synthesized by a novel chemical route using surfactants as structure-directing agents. Microstructure analysis indicates that the obtained 3D flower-like Mn3O4 superstructure consists of a large number of two-dimensional (2D) Mn3O4 nanosheets, which is different from the reported 3D Mn3O4 hierarchical structures based on zero-dimensional nanoparticles or one-dimensional nanowires and nanorods. This 3D Mn3O4 hierarchical architecture provides us with another type of manganese oxide with different superstructural characteristics, which may have potential practical applications in the catalytic degradation of organic pollutants. The catalytic performance of this hierarchical Mn3O4 superstructure, which was prepared by three different types of structure-directing agents, including cetyltrimethylammonium bromide (CTAB), poly(vinylpyrrolidone) (PVP), and poly(ethylene oxide)-poly(propylene oxide) (P123), was evaluated for the catalytic degradation of organic pollutants, e.g. methylene blue. Interestingly, the hierarchical Mn3O4 superstructure prepared using CTAB as a template showed efficient catalytic degradation. The formation processes and possible growth mechanism of this novel 3D Mn3O4 hierarchical superstructure assembled by 2D Mn3O4 nanosheets are discussed in detail.