Guanghai Li

Origin of the green photoluminescence from zinc sulfide nanobelts

ZnS nanobelts with a pure wurtzite phase have been synthesized by a thermal evaporation method with the assistance of H2S in an Ar atmosphere. Photoluminescence band centered at about 535nm has been observed under excitation in the range of 250–480nm with decay rate as short as 860ps. The origin of this intense photoluminescence is related to elemental sulfur species on the surface of the ZnS nanobelts. This assignment is substantiated by structural analysis by high-resolution electron microscopy, x-ray photoelectron spectroscopy, and photoluminescence and excitation technique. ZnS nanobelts with intense surface photoluminescence could be used as effective green light emitters, humid sensors, and UV light detectors.

Synthesis of mesoporous carbon capsules encapsulated with magnetite nanoparticles and their application in wastewater treatment

Mesoporous carbon capsules encapsulated with Fe3O4 nanoparticles were prepared by the successive coating of a silica layer and a subsequent mesoporous silica/carbon layer on the surface of Fe3O4 nanoparticles followed by chemical etching with NaOH solution. TEM observations show that the as-obtained samples had a rattle-like structure: Fe3O4 nanoparticles were encapsulated in the interior of the mesoporous carbon capsules. The typical nitrogen adsorption/desorption results demonstrate that the specific surface area for the as-prepared samples is up to 1570 m2 g−1, and the total pore volume is about 3.02 cm3 g−1. The porous wall structure of the lateral carbon capsules provides the sufficient spaces that contribute to high adsorption capacities and faster adsorption rates of pollutants molecules in aqueous media. The nanocomposites are superparamagnetic at room temperature with a saturation magnetization of 5.5 emu g−1, which provides the prerequisite for the fast magnetic separation in wastewater treatment application. Water treatment experiments indicated that the as-prepared samples exhibited higher adsorption rates and more effective removal capacity of organic pollutants compared with commercial activated carbon (AC), and their maximum adsorption capabilities for methylene blue (MB), congo red (CR), and phenol reached 608.04, 1656.9 and 108.38 mg g−1, respectively. The multifunctional nanocomposites can be potentially used as absorbents for fast, convenient, and highly efficient removal of pollutants from the wastewater, which will play important roles in the purification or desalination of natural water and industrial effluents.

Competition between ferromagnetic metallic and paramagnetic insulating phases in manganites

La0.67Ca0.33Mn1−xCuxO3 (x=0 and 0.15) epitaxial thin films were grown on the (100) LaAlO3 substrates, and the temperature dependence of their resistivity was measured in magnetic fields up to 12 T by a four-probe technique. We found that the competition between the ferromagnetic metallic (FM) and paramagnetic insulating (PI) phases plays an important role in the observed colossal magnetoresistance (CMR) effect. Based on a scenario that the doped manganites approximately consist of phase-separated FM and PI regions, a simple phenomenological model was proposed to describe the CMR effect. Using this model, we calculated the resistivity as functions of temperature and magnetic field. The model not only qualitatively accounts for some main features related to the CMR effect, but also quantitatively agrees with the experimental observations.

Fabrication and electronic transport properties of Bi nanotube arrays

Bi nanotubes embedded in anodic alumina membranes were fabricated by pulsed electrodeposition. Scanning electron microscope, x-ray diffraction, and high-resolution transmission electron microscope analyses revealed that the Bi nanotubes are highly oriented and single crystalline. Electronic transport measurements proved that there is a metal–semiconductor transition of Bi nanotube arrays with the decrease of the wall thickness of the nanotubes, and this transition depends only on the wall thickness and is independent of the diameter of the nanotubes. The quantum confinement effect is believed to play an important role in determining transport properties. The Bi nanotubes may find applications in thermoelectric nanodevices.

A route to fabricate single crystalline bismuth nanowire arrays with different diameters

Single crystalline bismuth nanowire arrays in anodic alumina membrane have been fabricated by pulsed electrodeposition. The nanowires of different diameters were obtained by changing the electrical parameter of the pulsed electrodeposition using anodic alumina membrane as template with the same pore size. X-ray diffraction and TEM analysis show that the bismuth nanowires are single crystalline with highly preferential orientation, and the diameter of nanowires increases with increasing the relaxation time of pulse. The growth mechanism of nanowires was discussed.

Large-Scale Self-Assembly of 3D Flower-like Hierarchical Ni/Co-LDHs Microspheres for High-Performance Flexible Asymmetric Supercapacitors

In this study, a facile and inexpensive and self-assembled strategy to massively fabricate Ni/Co layered double hydroxides (LDHs) is developed under mild reaction conditions (55 °C). The resulting composite material displays a special three-dimensional hierarchical microsphere structure with well-defined flower-like configuration. The fabrication mechanism can be ascribed to stepwise and regular reaction process of nanoparticles and nanosheets gradually growing to nanopetals and then assembling into flower-like microspheres, based on the systematically investigation of various reaction factors including the Ni:Co feeding ratio, the reaction time and the initial pH-value. Because of its large surface, ultrathin feature and synergetic results of this Ni/Co LDHs nanosheets (20 nm), these Ni/Co-LDHs microspheres deliver an excellent capacitance value about 2228 F·g(-1) (1 A·g(-1)). An all-solid-state flexible asymmetric supercapacitor is designed and assembled by exploiting this Ni/Co-LDHs as the positive materials, which exhibits energy density of 165.51 Wh·kg(1-) at 1.53 KW·kg(1-). It may have vast potential significance in personal wearable equipment. Moreover, this monolithic design provides a promising approach for large scale fabrication of other LDHs materials.

Efficient removal of Cr(VI) from wastewater under sunlight by Fe(II)-doped TiO2 spherical shell

Fe(II)-doped TiO2 spherical shell catalyst was synthesized by one-pot hydrothermal method. The photocatalytic removal of Cr(VI) from plating wastewater under sunlight of the catalyst was demonstrated. It was found that the removal effectiveness of about 99.99% for initial Cr(VI) concentration of 102.3 ppm and 99.01% for 153.4 ppm under 3h sunlight irradiation is realized. The Fe(II) ions serve not only as reducing agents for reducing the Cr(VI) to Cr(III) but also as an intermedium of a two-step reduction, in which the TiO2 photoreduces the Fe(II) ions to Fe atoms firstly, and then the Fe atoms reduce the Cr(VI) to Cr(III). The improved photocatalytic activity of the catalyst is considered due to the synergistic effect of a multi reducing process by Fe(II) doping. The extended optical response and effectively utilization of sunlight of the special spherical-shell-like morphology also contribute to the enhanced photocatalytic activity.

Highly efficient and recyclable triple-shelled Ag@Fe3O4@SiO2@TiO2 photocatalysts for degradation of organic pollutants and reduction of hexavalent chromium ions

Herein, we demonstrate the design and fabrication of the well-defined triple-shelled Ag@Fe3O4@SiO2@TiO2 nanospheres with burr-shaped hierarchical structures, in which the multiple distinct functional components are integrated wonderfully into a single nanostructure. In comparison with commercial TiO2 (P25), pure TiO2 microspheres, Fe3O4@SiO2@TiO2 and annealed Ag@Fe3O4@SiO2@TiO2 nanocomposites, the as-obtained amorphous triple-shelled Ag@Fe3O4@SiO2@TiO2 hierarchical nanospheres exhibit a markedly enhanced visible light or sunlight photocatalytic activity towards the photodegradation of methylene blue and photoreduction of hexavalent chromium ions in wastewater. The outstanding photocatalytic activities of the plasmonic photocatalyst are mainly due to the enhanced light harvesting, reduced transport paths for both mass and charge transport, reduced recombination probability of photogenerated electrons/holes, near field electromagnetic enhancement and efficient scattering from the plasmonic nanostructure, increased surface-to-volume ratio and active sites in three dimensional (3D) hierarchical porous nanostructures, and improved photo/chemical stability. More importantly, the hierarchical nanostructured Ag@Fe3O4@SiO2@TiO2 photocatalysts could be easily collected and separated by applying an external magnetic field and reused at least five times without any appreciable reduction in photocatalytic efficiency. The enhanced photocatalytic activity and excellent chemical stability, in combination with the magnetic recyclability, make these multifunctional nanostructures promising candidates to remediate aquatic contaminants and meet the demands of future environmental issues.

Fabrication and optical absorption of ordered indium oxide nanowire arrays embedded in anodic alumina membranes

Ordered semiconductor In2O3 nanowire arrays embedded in anodic alumina membranes were fabricated by electrodeposition and oxidizing methods. The X-ray diffraction and transmission electron microscopy indicate that the In2O3 nanowires with polycrystalline structure are uniformly assembled into the hexagonally ordered nanochannels of the anodic alumina membranes. The optical absorption band edge of In2O3 nanowires array exhibits a marked red shift with respect to that of the bulk In2O3, and depends on the post-heat treatment temperature. This is attributed to the oxygen vacancy in In2O3 nanowires and the interface interactions between the anodic alumina membranes and the In2O3 nanowires.

Pulsed electrodeposition of single-crystalline Bi2Te3 nanowire arrays

Thermoelectric material Bi2Te3 nanowire arrays have been successfully prepared by pulsed electrochemical deposition into the nanochannels of porous anodic alumina membranes. X-ray diffraction analyses show that the as-synthesized nanowires have a highly preferential orientation. Scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy observations indicate that the high-filling-rate and uniform Bi2Te3 nanowires are single crystalline. Energy dispersive spectrometer analyses indicate that the compositions of the nanowires can be controlled by changing the potentials and the solution concentrations. The electrical resistance measurements indicate that the resistances increase with decreasing temperature and show a typical semiconductor characteristic. The growth mechanism is discussed together with the electrochemical deposition process studies.