In this paper, the Fe/Ni microparticles are synthesized by two reactions which directly utilize H2 to reduce NiO and Fe3O4 microspheres. X-ray diffraction and transmission electron microscopy show that the as-synthesized Fe/Ni microparticles possess a body/face-centered cubic crystalline structure and core/shell morphology. The magnetic hysteresis loops show that the as-fabricated core/shell Fe/Ni microparticles have a high saturation magnetization (132.8 emu g−1) at 305 K. The as-prepared Ni/Fe microparticles are used to remove Cr(VI) via a coupled adsorption/reduction process. The introduction of nickel not only controls the iron passivation but also advances efficient flow of electron transfer between iron and Cr(VI), thus efficient reduction of Cr(VI) to Cr(III). The excellent products with both high saturation magnetization and Cr(VI) adsorption capacity can be used as candidates for environmental remediation materials.

•Bismuth sulfide nanowires are prepared by hydrothermal method without any surfactant.•The RT ethanol gas sensitivity of Bi2S3 nanowires is investigated by SPV technique.•Sensitivity and selectivity curve of Bi2S3 NWs are measured and good gas sensing performance appear.A facile and effective procedure for the synthesis of bismuth sulfide (Bi2S3) nanowires is reported in which thiourea is used as source of sulfur ions and precisely controlled to release sulfur ions for the formation of Bi2S3 nanowires without any surfactant and template. The as-synthesized products are characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, and UV–vis absorption, respectively. The results indicated the as-fabricated specimens are high purity and single-crystal Bi2S3 nanowires with a diameter range from 50 to 100 nm. For a comparative study, both ethanol gas responses of Bi2S3 nanowires and conventional powders are investigated by means of the surface photovoltage technique at different temperatures. Unexpectedly, at room temperature, the as-obtained results demonstrate the response of Bi2S3 nanowires is 2 times higher than that of Bi2S3 conventional powders even if the concentration of ethanol is down to 10 ppm, showing a superior response to ethanol vapors and good stability, which indicates potential applications for room-temperature nanosensors, including ethanol alarms, ethanol flowmeters, and ethanol detectors.

Cubic phase (zinc-blende) GaN (referred to as c-GaN)-based phosphor-free white light emitting diodes (LEDs) can exhibit superior characteristics and ultrahigh efficiency compared with conventional hexagonal phase (wurtzite) GaN (referred as h-GaN)-based examples. However, one notorious issue is low quality of c-GaN due to thermodynamical instability of cubic phase, epilayer-substrate chemical incompatibility, and large lattice-mismatch during epitaxial deposition, giving rise to insufficient light emission efficiency. Therefore, improving the quality of c-GaN is a key step towards high performance white LEDs. Here, we report the growth of high quality single crystalline GaN microcubes (MCs) with pure zinc-blende phase for large scale production by the chemical vapor deposition method. From the GaN MCs, high-performance yellow luminescence (YL) is observed by different temperature photoluminescence spectra and the possible origin of the YL band is investigated. Furthermore, the fabricated phosphor-free single homojunction based on individual GaN MCs showed a diode nonlinear rectification behavior and the electroluminescence exhibited white emission when the operating voltage is 12 V. At room temperature, due to the reduction of threading dislocation density and the absence of piezoelectric polarization of the zinc-blend phase GaN, the device can exhibit an internal quantum efficiency of ∼99.2% and virtually no efficiency droop as the injection current increases. The device also exhibits an output power of ∼4.4 mW at a typical operating current of 20 mA, which is approximately 50% stronger than that of conventional h-GaN homojunction LEDs.

Superparamagnetic Fe3O4 nanocrystals anchored on multiwalled carbon nanotubes (MWCNTs) were fabricated via a straightforward co-precipitating technique which nicely integrates the magnetic and dielectric components into a synergistic microwave absorber. A complex permeability analysis indicates that the resonance frequency of Fe3O4/MWCNTs heterostructures appears at 9.1 GHz relying on superparamagnetic relaxation, which is much higher than that of conventional Fe3O4 ferromagnetic particles. As a result of the blue-shift of the resonance frequency, the Fe3O4/MWCNTs nanocomposites exhibit remarkably improved microwave absorption performances in a high frequency range (Ku-band). Moreover, combing the synergistic effect between ultra small Fe3O4 nanocrystals and MWCNTs, the Fe3O4/MWCNTs hybrids exhibit a bandwidth of frequency less than −20 dB, almost covering the whole 2–18 GHz range by adjusting the absorber thickness. The results provide a new approach to enhance the resonance frequency break of the Snoek limit, which significantly optimizes microwave absorption ability for high frequency applications.

High-yield purity chain-like one-dimensional nanostructures consisting of single crystal Fe nanoparticles have been produced by using solution dispersion approach. Room temperature magnetic measurement shows that the as-fabricated Fe nanochains are ferromagnetic with a high saturation magnetization (203 emu/g) whereas the nanoparticles are single magnetic domains, which indicate that the as-synthesized products have superparamagnetism behavior with the saturation magnetization of about 28 emu/g. Maybe this results from the directional alignment of the nanoparticles. The excellent characteristic may have led to the potential applications in spin filtering, high density magnetic recording, and nanosensors.

Using a facile vapor–solid route, double helical, organic, small molecular microfibril, i.e. 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was synthesized, which was based on the spontaneous twisting of supramolecular microtubes. The average diameter of the resulting helical structures was about 200 nm and the overall length was of several micrometers. The helical microfibrils, which were obtained by coiling the multilayer microtubes from the inner to the outer molecular layers, tend to release their internal rotation stress to exhibit the most stable morphology as indicated by a series of characterizations. The change in van der Waals force, together with the surface free energy among the adjacent microtubes molecular layers, were the driving forces to induce the formation of a helical structure. The obtained results present an extremely facile strategy for the fabrication of small molecular, double helical microfibrils with morphological transformation.

•Vertically aligned single-crystal ZnS nanotubes with hexagonal cross-section.•The process of preparation is simple and environmentally friendly.•Excellent optical property superior to ZnS NWs reported previously.•ZnS is of high-yield and inexpensive.Without the presence of any catalysts or templates, single-crystal zinc sulfide (ZnS) nanotubes have been successfully synthesized in bulk quantity by a facile and controllable process based on thermal evaporation of ZnS powders. X-ray diffraction (XRD), energy dispersed X-ray spectrometry (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were used to characterize the products. The results indicate that the synthesized ZnS nanotubes are single-crystalline with hexagonal cross-sections. The diameters of the ZnS nanotubes vary from 200 to 700 nm and lengths are about several micrometers. The growth of ZnS nanotubes is controlled by the conventional rolling mechanism. And the room temperature photoluminescence (PL) indicated a stable and strong green emission centered at about 542 nm, which may result from nanotube effects.

In this work, we successfully synthesized nearly monodisperse ZnO, In2O3, CoO, and Fe3O4 nanocrystals by using a universal route. The designed synthetic route is a two-step chemical process, based on the hot reduction of metal oleate ((C18H33O2)xM, M=Zn, In, Co, Fe) with metal sodium in liquid paraffin followed by the rapid oxidation of the resulting products. During the reaction, the byproduct sodium oleate is used as the capped surfactant. XRD and XPS results display that the as-obtained products are ZnO, In2O3, CoO, and Fe3O4 rather than metal/metal oxides core/shell nanocomposites. TEM images of these products show that they are nearly monodisperse nanoparticles with relatively uniform size distribution. On the basis of our experimental results, the possible formation mechanism for nearly monodisperse MxOy nanocrystals was proposed. In our performance tests, ZnO and In2O3 nanocrystals display good optical behavior, while CoO and Fe3O4 nanocrystals show good ferromagnetism and superparamagnetism behavior at room temperature, respectively.

We present successful fabrication of single n-ZnO/p-AlGaN heterojunction nanowires with excellent optoelectronic properties. Because of the formation of high-quality interfacial structure, heterojunction nanowire showed a diodelike rectification behavior and an electroluminescence (EL) ultraviolet (UV) emission centered at 394 nm from a single nanowire was observed when the injection current is 4 μA due to high exciton efficiency in the interfacial layer between ZnO and AlGaN. With the increase of the applied current, the EL peak at 5 μA becomes weaker revealing an optimal injection current of less than 5 μA. These results are expected to open up new application possibilities in nanoscale UV light-emitting devices based on single ZnO heterostructure.

Well-dispersed magnetic-based silver composite microspheres (Fe3O4@SiO2@Ag) with a nanosheet-assembled shell structure were synthesized at room temperature, where sonicating and mechanical stirring techniques were both employed and played important roles during the silver shell growth process. The results show that the nanosheet-assembled silver shell could be obtained and controlled by adjusting the concentration of citrate ions as a morphology directing-reagent. The gaps in or between cross-linked nanosheets in the shell of the composite microspheres were proposed to provide sufficient “hot spots” when they were used as a SERS substrate. The SERS measurements exhibit clear enhancement signals by using R6G as a probe molecule, and even at concentrations as low as 10−14 M, all enhancement peaks could be observed clearly. The film assembled from the composite microspheres exhibited good reproducibility across the entire area. Additionally, the magnetic Fe3O4@SiO2@Ag microspheres can be separated from solution rapidly, which shortened the detection time. Considering their excellent SERS performance, this kind of composite microsphere, which has both a SERS active shell and a magnetically separable core, would be very useful as an effective SERS substrate for detecting organic pollutants in solution.

Unlike the previous ferrites (MFe2O4; M = Fe, Co, Zn, and Mn) solid nanospheres/nanoparticles, which were prepared by polluted solvothermal (glycol) approaches, here controllable monodisperse porous ferrites hollow nanospheres are promptly synthesized by a nontemplate hydrothermal method which has introduced an addition agent, polyacrylamide. The hollow nanospheres with different size can be prepared by varying the synthetic compositions. Scanning/transmission micros-graphs show the outside diameters of ferrite nanospheres are 180–380 nm and the shell thicknesses of that are only 20–45 nm, which could be adjusted by controlling CH3COONa concentration. X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectroscopy, scanning electron (SEM) and transmission electron (TEM) microscopy, energy-dispersive spectrometer (EDS), the measurement of N2 adsorption–desorption isotherms and Brunauer–Emmett–Teller (BET) surface area, and superconducting quantum interference device (SQID) magnetometer were adopted to analyze their phase composition, morphology, porosity, and magnetic properties, respectively. The results of controlled experiments show that citrate and polyacrylamide are vital for the phase purities and morphology of ferrites. In particular, the as-obtained samples exhibit a large adsorption capacity for the toxic solution containing As(V) and Cr(VI) ions, and the calculated result of the maximum adsorption capacity is 340 mg/g based on Langmuir model, which shows excellent As(V) and Cr(VI) ions uptake capacity in contrast to other solid nanosphere materials.Keywords: absorption; As(V) and Cr(VI) ions; ferrites; hollow nanospheres; mesoporous;

Understanding the factors that influence the growth and final shape of semiconductor tellurium microstructures is important for controlling their properties. However, relative to their single-crystalline nanostructures, the growth of complex structures that are ideally composed of nanostructures arranged in a particular way can be difficult to control. Here, we developed a facile solvothermal method and successfully completed the controlled synthesis of Te particles with distinctive morphologies, including flower-like, ball-flower, nestlike, and sheetlike structures. These structures, self-assembled from nanorods and nanosheets, are systematically studied by adjusting the reaction parameters, such as the amount of NaOH, the volume ratio of EG/EN, the amount of PVP, and the reaction time. Results reveal that the morphology of Te microstructures can be easily controlled by simply altering the reaction conditions and that NaOH plays a crucial role in the final morphology of Te products. The growth mechanisms and morphology control of hierarchical Te microstructures are proposed and discussed. This is the first time to report the preparation of complex hierarchical Te microstructures through a simple solution route. This simple solution approach to fabricate hierarchical Te superstructures with controllable morphologies can be easily scaled up and potentially extended to the hierarchical assembly of building blocks of other semiconductors.

The heterojunction between n-GaN nanowires (NWs) and p-cuprous oxide (Cu2O) (111) is fabricated vertically by thermal evaporation of GaN conventional powders without using any catalyst or template. The high-quality NW/Cu2O heterostructure is confirmed by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electronic diffraction, and energy-dispersive spectroscopy measurements. Diameters of these NWs range from 200 to 400 nm and their lengths arrive at several micrometers. In addition, the room-temperature photoluminescence properties of prepared products have been investigated. The results show that a strong sharp excitonic emission reveals excellent optical property superior to state-of-the-art GaN NWs on silicon or diamond substrates underlining a promising efficient ultraviolet (UV) optoelectronic device based on GaN/Cu2O heterojunction.Highlights► High-quality heterojunction of n-GaN/p-Cu2O nanowires is fabricated vertically by physical vapor deposition. ► The process of preparation is a simple and an environmentally friendly one. ► In photoluminescence, a strong sharp excitonic emission reveals excellent optical property superior to GaN NWs on silicon or diamond substrates reported previously. ► Copper is more abundant and less expensive than diamond to use for investigation and yield optoelectronic devices.

Uniform silver hollow microcubes assembled by nanosheets have been synthesized by using Cu2O cubes as chemical template at room temperature. In the reaction system, the Ag+ ions were reduced by Cu+ ions released from Cu2O cubes, meanwhile the morphology of silver growth units were controlled by trisodium citrate in the form of nanosheets around the template during the reaction. It was found that the concentrations of acid, citrate ions and AgNO3 were critical to the formation of perfect nanosheet-assembled hollow microcubes. According to the experiment results, an interface redox growth mechanism of nanosheet-assembled Ag hollow microcubes was proposed. Since the obtained Ag hollow cubes are composed of Ag nanosheets, the hierarchical shells are bestrewed with pores or gaps which created abundant active “hot spots” for highly sensitive surface enhanced Raman scattering (SERS) detection. The SERS experiments using rhodamine 6G (R6G) as probing molecules showed that the pack density and porous structure of the shell in the final products strongly affected the SERS signals. The product with higher porous shell structure exhibited stronger SERS signals than others, indicating the rough Ag hollow microcubes could act as excellent substrates for ultrasensitive detection.

Uniform orange-like Fe3O4/polypyrrole (PPy) composite microspheres have been synthesized using Fe3O4 microspheres as a chemical template under sonication. In the orange-like Fe3O4/PPy composite microspheres, the Fe3O4 particles played the role of “seeds” while the PPy was the “pulp and peel”. A growth mechanism for the orange-like Fe3O4/PPy composite microspheres was proposed in which partial pyrrole monomers are immersed into the gaps of Fe3O4 microspheres under sonication, meanwhile Fe3+ ions released from Fe3O4 microspheres in an acidic environment initiated the polymerization of pyrrole monomers in the interior or around the Fe3O4 microspheres, finally forming an orange-like structure. When used as an absorbent of Cr(VI) ions, the as-obtained Fe3O4/PPy microspheres showed strong adsorption capability with an adsorption capacity of about 209.2 mg g−1, which is mainly attributed to the PPy “pulp and peel”. Furthermore, the magnetic Fe3O4 “seeds” in composite microspheres make them easy to separate from wastewater by magnetic separation.

In this study, we report the preparation of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) micro/nanotubes (M/NTs) by a simple physical vapor deposition (PVD) process, and it was found that tubular structures with a diameter from 300 nm to 5 μm and lengths up to tens of micrometres were obtained on a glass substrate at a deposition temperature of 350–400 °C. Detailed studies revealed that PTCDA M/NTs were formed via curling and seaming of a 2D lamellar structure constructed by virtue of the cooperation of some noncovalent interactions such as π–π interactions and H-bonds, and it was a temperature-activated process. Devices based on single PTCDA microtubes with different diameters exhibited resistance decreased by 2 orders of magnitude in reducing hydrazine vapor (even for such a low concentration as 5 ppm). Such a successful application of the PVD process to simple organic molecules and highly efficient performance in devices are expected to provide great opportunities for the formation of diverse functional organic hollow nanostructures.

High saturation magnetization monodisperse Fe3O4 hollow microspheres (109.48 emu/g) with superparamagnetic property at room temperature are promptly synthesized by a one-step solvothermal process with the presence of sodium dodecylbenzenesulfonate as an additive. The as-synthesized products possess superparamagnetism, large cavity, high water solubility, and saturation magnetization at room temperature. In particular, these hollow microspheres exhibit both of a rather short separation time from industry wastewater and a high adsorption capacity about 180 mg/g at high Cr(VI) concentrations, which is much better than those of reported magnetite solid nanoparticles. In addition, the X-ray photoelectron spectra (XPS) show that the uptake of Cr(VI) into the spheres was mainly governed by a physicochemical process. The micelle-assisted Ostwald ripening process was proposed to explain the rapid formation of hollow structures by a series of control experiments. The as-manufactured products with the two advantages mentioned above serve as ideal candidates for environmental remediation materials.Keywords: adsorption; fast chromium removal; high saturation magnetization; magnetite; superparamagnetism; water treatment;

In this paper, ZnxCd1 − xS nanocrystals (NCs) were directly immobilized on graphene nanoribbons (NRs) by a facile one-step reaction. During the reaction, the formation of NCs and the reduction of graphene oxide to graphene NRs occurred simultaneously and the value of x could be adjusted by controlling the molar ratio of Zn and Cd precursors. The facts were confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR). Moreover, Ultraviolet–visible (UV–vis) absorption spectroscopy data indicate that the absorbance of the nanocomposites can be successfully tuned from 319 to 583 nm, making them a great promise for wide potential applications in optoelectronics.Highlights► The tunable optical properties of the graphene-ZnxCd1 − xS were observed. ► The formation of alloyed ZnxCd1 − xS nanocrystals was evidenced by XRD and HRTEM. ► The reduction of graphene oxide was observed by UV–vis and IR spectra.

Based on physical vapor deposition (PVD) in the absence of any template and catalyst, β-Zn4Sb3 nanowires (NWs) have firstly been synthesized under controlled conditions. Composition, morphology, structure, and thermoelectric property of the fabricated β-Zn4Sb3 products are characterized by different instruments. Moreover, room temperature Hall effects are conducted to study the electric transport property of the as-annealed β-Zn4Sb3 NWs and synthesized powders. In particular, the as-obtained results reveal that the as-annealed β-Zn4Sb3 NWs possess a high dimensionless figure of merit (ZT, 1.59) at 675 K. It is much higher than that of all bulk β-Zn4Sb3 materials (no more than 1.3), which has potential applications for thermoelectric nanodevices.Highlights► For the first time, good quality and homogeneous β-Zn4Sb3 nanowires have been synthesized by physical vapor deposition without any template and catalyst. ► The process of preparation is a simple and an environmentally friendly one. ► High-performance thermoelectric properties (for example, ZT is 1.59 at 675 K) appear in the as-annealed β-Zn4Sb3 nanowires.

ZnTe microspheres with an average diameter of 600 nm are fabricated by a facile solvothermal method for the first time where each microsphere is composed of primary nanoparticles with a diameter of about 30 nm. In addition, photoelectric effect of a single ZnTe microsphere is studied by photo-assisted conductive atomic force microscopy. Both of I–V curves from the single ZnTe microsphere indicate that its light current has a steep increase under ultraviolet (UV) light and arrives up to 99.97 nA whereas the dark current is 3.37 nA. The enhancement of light current comes mainly from a significant photoelectron increasing, which will make such materials attractive in many applications such as solar cells, photocatalysts, etc.Highlights► For the first time, ZnTe microspheres are successfully fabricated by solvothermal. ► Light current of single microsphere has a steep increase under ultraviolet light. ► The single ZnTe microspheres are expected to be applications in solar cells. ► The solvothermal used here is a facile, effective, reproducible method.

Sphere-like hierarchical bismuth oxyiodides (BiOIs) were synthesized by using polyvinylpyrrolidone (PVP) assisted solvothermal synthesis approach, and characterized by X-ray diffraction/photoelectron spectroscopy and scanning/transmitting electron microscopy. The prepared hierarchical microspheres (HMs) possess a tetragonal phase and are composed of primary plate-like nanostructures with a thickness of several tens nanometers. Visible light photocatalytic activities (VLPAs) of BiOI HMs on the degradation of methyl orange (MO) were studied at room temperature. Twenty minutes later, VLPAs of the HMs reached up to about 80% whereas those of the corresponding conventional powders (CPs) were less than 20%. The high VLPAs of the HMs would have a potential photocatalytic application in environmental purification.Highlights► Bismuth oxyiodides were obtained by using PVP assisted solvothermal synthesis. ► Sphere-like hierarchical bismuth oxyiodides (BiOIs) have homogeneous size. ► Homogeneous BiOI spheres have high visible light photocatalytic activities.

The straight single crystal silver telluride nanowires with the diameter of about 200 nm and length up to micrometers of decades have been prepared by the hydrothermal process without any template or any surfactant. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectrum, transmission electron microscopy (TEM) and high-resolution TEM reveal that the as-synthesized products are high purity and well-crystallized. The reversible structural phase transition from the low-temperature monoclinic structure to the high-temperature face-centered cubic structure was observed by differential scanning calorimetry. In particular, the electrical properties of individual Ag2Te nanowires were investigated by the voltammetric technique for the first time and I–V curves were clearly nonlinear and symmetrical with respect to both axes. Furthermore, the drastic reduction in electrical current around the phase transition temperature in the single nanowire is discovered, paving further studies for fabrication of one-dimensional nanoscale devices.

Based on chemical vapor deposition (CVD) in the absence of any template and catalyst, large-scale oriented vertical FeSe nanorod (NR) array (NRA) has been produced. Electron microscopy shows a typical diameter and length of single FeSe NRs are ~ 200 and 600 nm, respectively and electron/X-ray diffraction confirms the single-crystal α-phase. Magnetic measurements reveal these NRAs are superconducting with an onset Tc above 16 K, which is much higher than Tc of counterpart bulk sample (~ 8 K). Superconducting FeSe NRAs with the Tc may open up new possibilities for the fundamental understanding of the effect of dimensionality.

A systematic study was conducted on the fabrication, structural characterization, and magnetic properties of MgB2 wire-like nanostructures with C doping between 0% and 20%. Based on chemical vapor deposition technique, non/C-doped MgB2 nanowires (NWs) with an average diameter of 60 nm and length up to several micrometers were produced by homemade MgB2 nanotubes, the mixture gases (Ar + CH4 + H2), and Ni catalyst. Electron and X-ray diffraction confirm that the as-synthesized non/C-doped MgB2 NWs are single crystalline with primitive hexagonal lattice structure. DC magnetization measurements indicate a high superconducting transition temperature (39 K) for nondoping MgB2 NWs and that on increasing the carbon content the transition broadens and shifts toward lower temperatures. The technique is an attractive synthetic method since its flexibility allows for optimization of the doping synthesis. In particular, a comprehensive investigation of influence of NW doping on superconductivity is reported for the first time.

The search for above room temperature ferromagnetism in dilute magnetic semiconductors has been intense in recent year. Arrays of perpendicular ferromagnetic nanowire/rods have recently attracted considerable interest for their potential use in many areas of advanced nanotechnology. We report a simple low-temperature chemical vapor deposition (CVD) to create self-assembled comb-like Ni-/undoped ZnO nanostructure arrays. The phases, compositions, and physical properties of the studied samples were analyzed by different techniques, including high-resolution X-ray diffraction/photoelectron spectroscopy/transmission electron microscopy, photoluminescence, and MPMS. In particular, the Ni-doped ZnO nanocombs (NCs) with ferromagnetic and superparamagnetic properties have been observed whereas undoped ZnO NCs disappear. The corresponding ferromagnetic source mechanism is discussed, in which defects such as O vacancies would play an important role.

Based on a low-temperature route, monodispersed CoFe2O4 microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural and magnetic characteristics of the as-prepared MSs were characterized by X-ray diffraction/photoelectron spectroscopy, scanning/transmitting electron microscopy, and vibrating sample magnetometer. The results indicate that the diameters of CoFe2O4 MSs with narrow size distribution can be tuned from over 200 to ~330 nm. Magnetic measurements reveal these MSs exhibit superparamagnetic behavior at room temperature with high saturation magnetization. Furthermore, the mechanism of formation of the monodispersed CoFe2O4 MSs was discussed on the basis of time-dependent experiments, in which hydrophilic PVP plays a crucial role.

Large-scale single crystalline MgB2 tubelike nanostructures were successfully prepared by thermal evaporation of MgB2 particles precursors without involvement of template or patterned catalyst. The inner diameter, outer diameter and length of the as-fabricated single MgB2 nanotube (NT) are respectively about 30 nm, 90 nm and several tens of microns. Existence of superconductivity within the products is confirmed by AC and DC magnetic susceptibility at low temperatures. The work represents the achievement to produce the bulk superconductivity with the hollow-structured morphology. Synthesis of MgB2 NTs with bulk superconductivity may open up new possibilities for the fundamental understanding of the effect of dimensionality on superconductivity.

Well-aligned single-crystalline wurzite zinc oxide (ZnO) nanowire arrays were successfully fabricated on a Si substrate by a simple physical vapor-deposition (PVD) method at a relatively low temperature of about 500°C. The as-fabricated nanowires were preferentially arranged along the [001] direction of ZnO. The photoluminescence spectrum of ZnO nanowire arrays showed two emission bands: a strong green emission at around 500 nm and a weak ultraviolet emission at 380 nm. The strong green light emission was related to the existence of the oxygen vacancies in ZnO crystals. Corresponding growth mechanism of the ZnO nanowires was briefly discussed.

High-density hierarchical brush-like nanostructures of Ce-doped ZnO are first synthesized by a two-step approach (sol–gel and chemical vapor deposition). This novel structure, called nanobrush, is a new member in the family of hexagonal crystal ZnO nanostructures, which is composed of two parts: a micron-sized prism-like base and nano-sized vertical nanorod arrays. The nanobrush is enclosed by the (0001) and {011¯0} facets and grows towards the [0001] direction. Room-temperature photoluminescence (RTPL) spectra show a weak UV emission but a strong broad green emission.

Single crystalline Fe-doped ZnO nanocantilever arrays have been synthesized by thermal evaporating amorphous Zn-Fe-C-O composite powder. The characterizations of composition, structure and phonon spectrum properties of the nanocantilevers have been performed. Arrays of uniform, perfectly aligned and single-crystal nanowires have been observed by electron microscopy. The results of the X-ray photo-electric spectra and the Raman spectrum provide the evidence that Fe is incorporated into the ZnO lattice at Zn site. Abnormally, the room temperature UV emission band of Fe-doped ZnO nanocantilevers disappears and the green one has a large red-shift, and the intensity of the green emission is strongly quenched because the Fe3+ enters the ZnO crystal lattice.

•MoS2 nanobelts grown on (AlGa)N and ZnO were synthesized by chemical vapor deposition.•The MoS2 nanobelts arrays grown on (AlGa)N were straight, pure and well-crystallized.•Enhanced photoluminescence of MoS2/(AlGa)N was observed.As important two-dimensional nanostructures, MoS2 nanobelts grown on (AlGa)N and ZnO substrates, respectively, are facilely and economically fabricated by one-step chemical vapor deposition without using any catalyst. The characterizations for morphologies, compositions, and optical properties are performed by scanning electron microscopy (SEM), energy dispersed X-ray spectrometry (EDS), and photoluminescence spectroscopy (PL). SEM confirms that MoS2 nanobelts grown on (AlGa)N substrates compared with ones grown on ZnO substrates have higher quality although EDS shows that both of the nanobelt arrays are composed of the same constituents, that is, pure MoS2. In addition, the room-temperature optical properties show that MoS2 nanobelts on (AlGa)N substrates possess excellent photoluminescence superior to ones on ZnO substrates.

In this study, we report the preparation of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) micro/nanotubes (M/NTs) by a simple physical vapor deposition (PVD) process, and it was found that tubular structures with a diameter from 300 nm to 5 μm and lengths up to tens of micrometres were obtained on a glass substrate at a deposition temperature of 350–400 °C. Detailed studies revealed that PTCDA M/NTs were formed via curling and seaming of a 2D lamellar structure constructed by virtue of the cooperation of some noncovalent interactions such as π–π interactions and H-bonds, and it was a temperature-activated process. Devices based on single PTCDA microtubes with different diameters exhibited resistance decreased by 2 orders of magnitude in reducing hydrazine vapor (even for such a low concentration as 5 ppm). Such a successful application of the PVD process to simple organic molecules and highly efficient performance in devices are expected to provide great opportunities for the formation of diverse functional organic hollow nanostructures.

Cubic phase (zinc-blende) GaN (referred to as c-GaN)-based phosphor-free white light emitting diodes (LEDs) can exhibit superior characteristics and ultrahigh efficiency compared with conventional hexagonal phase (wurtzite) GaN (referred as h-GaN)-based examples. However, one notorious issue is low quality of c-GaN due to thermodynamical instability of cubic phase, epilayer-substrate chemical incompatibility, and large lattice-mismatch during epitaxial deposition, giving rise to insufficient light emission efficiency. Therefore, improving the quality of c-GaN is a key step towards high performance white LEDs. Here, we report the growth of high quality single crystalline GaN microcubes (MCs) with pure zinc-blende phase for large scale production by the chemical vapor deposition method. From the GaN MCs, high-performance yellow luminescence (YL) is observed by different temperature photoluminescence spectra and the possible origin of the YL band is investigated. Furthermore, the fabricated phosphor-free single homojunction based on individual GaN MCs showed a diode nonlinear rectification behavior and the electroluminescence exhibited white emission when the operating voltage is 12 V. At room temperature, due to the reduction of threading dislocation density and the absence of piezoelectric polarization of the zinc-blend phase GaN, the device can exhibit an internal quantum efficiency of ∼99.2% and virtually no efficiency droop as the injection current increases. The device also exhibits an output power of ∼4.4 mW at a typical operating current of 20 mA, which is approximately 50% stronger than that of conventional h-GaN homojunction LEDs.

Using a facile vapor–solid route, double helical, organic, small molecular microfibril, i.e. 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was synthesized, which was based on the spontaneous twisting of supramolecular microtubes. The average diameter of the resulting helical structures was about 200 nm and the overall length was of several micrometers. The helical microfibrils, which were obtained by coiling the multilayer microtubes from the inner to the outer molecular layers, tend to release their internal rotation stress to exhibit the most stable morphology as indicated by a series of characterizations. The change in van der Waals force, together with the surface free energy among the adjacent microtubes molecular layers, were the driving forces to induce the formation of a helical structure. The obtained results present an extremely facile strategy for the fabrication of small molecular, double helical microfibrils with morphological transformation.

Well-dispersed magnetic-based silver composite microspheres (Fe3O4@SiO2@Ag) with a nanosheet-assembled shell structure were synthesized at room temperature, where sonicating and mechanical stirring techniques were both employed and played important roles during the silver shell growth process. The results show that the nanosheet-assembled silver shell could be obtained and controlled by adjusting the concentration of citrate ions as a morphology directing-reagent. The gaps in or between cross-linked nanosheets in the shell of the composite microspheres were proposed to provide sufficient “hot spots” when they were used as a SERS substrate. The SERS measurements exhibit clear enhancement signals by using R6G as a probe molecule, and even at concentrations as low as 10−14 M, all enhancement peaks could be observed clearly. The film assembled from the composite microspheres exhibited good reproducibility across the entire area. Additionally, the magnetic Fe3O4@SiO2@Ag microspheres can be separated from solution rapidly, which shortened the detection time. Considering their excellent SERS performance, this kind of composite microsphere, which has both a SERS active shell and a magnetically separable core, would be very useful as an effective SERS substrate for detecting organic pollutants in solution.

Uniform orange-like Fe3O4/polypyrrole (PPy) composite microspheres have been synthesized using Fe3O4 microspheres as a chemical template under sonication. In the orange-like Fe3O4/PPy composite microspheres, the Fe3O4 particles played the role of “seeds” while the PPy was the “pulp and peel”. A growth mechanism for the orange-like Fe3O4/PPy composite microspheres was proposed in which partial pyrrole monomers are immersed into the gaps of Fe3O4 microspheres under sonication, meanwhile Fe3+ ions released from Fe3O4 microspheres in an acidic environment initiated the polymerization of pyrrole monomers in the interior or around the Fe3O4 microspheres, finally forming an orange-like structure. When used as an absorbent of Cr(VI) ions, the as-obtained Fe3O4/PPy microspheres showed strong adsorption capability with an adsorption capacity of about 209.2 mg g−1, which is mainly attributed to the PPy “pulp and peel”. Furthermore, the magnetic Fe3O4 “seeds” in composite microspheres make them easy to separate from wastewater by magnetic separation.