Morphology-controlled synthesis of ZnS nanostructures via single-source approaches

ZnS nanoparticles of various morphologies, including hollow or solid spherical, and polyhedral shape, were synthesized from single-source precursor Zn(S₂COC₂H₅)₂ without using a surfactant or template. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy. The results indicate that ZnS hollow and solid spheres assembled by nanoparticles can be easily generated by the solution phase thermalysis of Zn(S₂COC₂H₅)₂ at 80 °C using N, N-dimethylformamide (DMF) and ethylene glycol (EG) or water as solvents, respectively, whereas solvothermal process of the same precursor led to ZnS nanoparticles of polyhedral shape with an average size of 120 nm. The optical properties of these ZnS nanostructures were investigated by room-temperature luminescence and UV-vis diffuse reflectance spectra.     

Self-catalytic growth and photoluminescence properties of ZnS nanostructures

Mass production of uniform wurtzite ZnS nanostructures has been achieved by a H₂-assisted thermal evaporation technique. X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) observations show that the ZnS nanostructures consist of nanobelts, nanosheets with a hexagonal wurtzite structure. The as-synthesized nanobelts have a length of several tens of micrometers and a width of several hundreds of nanometers. Self-catalytic vapor-liquid-solid (VLS) growth and vapor-solid (VS) growth are proposed for the formation of the ZnS nanostructures because neither a metal catalyst nor a template was introduced in the synthesis process. Room-temperature photoluminescence measurement indicates that the synthesized ZnS nanostructures have a strong emission band at a wavelength of 443 nm, which may be attributed to the presence of various surface states.     

Facile synthesis of mesoporous core-shell TiO2 nanostructures from TiCl3

The present study reports the synthesis and formation process of mesoporous core-shell TiO₂ nanostructures by employing a glucose-assisted solvothermal process using water-ethanol mixture as solvent and subsequent calcination process at 550 °C for 4 h. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption analysis were used to investigate the structural properties of these nanostructures. By optimizing the preparation conditions, especially the contents of water and ethanol in the mixture solvent, mesoporous core-shell TiO₂ nanostructures were obtained. These mesoporous nanostructures have anatase phase and exhibit the superior photocatalytic activity. This synthesis route is facile due to the usage of stable and low-cost Ti precursor such as TiCl₃ and is thus applicable for large-scale production.     

Large-scale synthesis of hexagonal cone-shaped ZnO nanoparticles with a simple route and their application to photocatalytic degradation

We report the large-scale synthesis of hexagonal cone-shaped ZnO nanoparticles by the esterification between zinc acetate and alcohol. The morphology of the ZnO nanoparticles was investigated by transmission electron microscopy, selected area electron diffraction and scanning electron microscopy measurements. The synthesized ZnO nanoparticles are single-crystalline with hexagonal phase and show a strong UV emission at −378 nm due to the excellent crystallinity of particles. A possible formation mechanism of the hexagonal cone-shape structure is proposed. Furthermore, the as-prepared ZnO particles exhibit high photocatalytic activity for the photocatalytic degradation of Rhodamine B, indicating that the ZnO nanostructure is promising as a semiconductor photocatalyst.     

Biomolecule-assisted synthesis of ZnS nanocorals and open-benzene ring in supercritical carbon dioxide

The nanostructured ZnS of cubic nanocorals and open-benzene ring has been synthesized by the biomolecule-assisted method in mixture of supercritical carbon dioxide and water as reaction medium at 150 °C and 28 MPa. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectrum of sample were characterized. The sodium tripoly phosphate and CO₂ as well as high-pressure condition might be the key factors for formation of the particular morphologies and nanostructures of ZnS. This synthesis method could be employed for preparation of other semiconductor nanomaterials.     

Hematite solid and hollow spindles: Selective synthesis and application in gas sensor and photocatalysis

Hematite solid spindles and hollow spindles have been selectively synthesized by a template-free, economical hydrothermal method, using FeCl₃·6H₂O as the starting materials and NaOH as the homogeneous precipitant. XRD analyses indicated that the products consisted of α-Fe₂O₃. SEM and TEM measurements showed that the morphologies of products were in the shape of solid spindles and hollow spindles, respectively. A possible formation process based on the nucleation-oriented aggregation-recrystallization mechanism is proposed. Moreover, the as-prepared hollow spindle-like α-Fe₂O₃ exhibits a good response and reversibility to some organic gas, such as 2-propanol and acetone. Compared with other hematite nanostructures, the porous hollow hematite spindles show outstanding performance in gas sensing due to their large surface area and porous hollow structure. Because of the unique porous hollow structures of the samples, the photocatalytic property of the spindle-like α-Fe₂O₃ was also investigated.     

Hydrothermal synthesis of magnetic reduced graphene oxide sheets

We demonstrated an environmental friendly and efficient route for preparation of magnetic reduced graphene oxide composite (MN-CCG). Glucose was used as the reducing agent in this one-step hydrothermal method. The reducing process was accompanied by generation of magnetic nanoparticles. The structure and composition of the nanocomposite was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, thermal gravimetric analysis, atomic force microscopy and transmission electron microscopy. It was found that the prepared MN-CCG is highly water suspendable and sensitive to magnetic field.     

Hybrid nanostructures of Au nanocrystals and ZnO nanorods: Layer-by-layer assembly and tunable blue-shift band gap emission

A layer-by-layer assembly technique was developed to synthesize the hybrid nanostructures of Au nanocrystals with diameter of about 5 nm and ZnO nanorods via the electrostatic interaction. In comparison with ZnO nanorods, the Au-ZnO hybrid nanostructures exhibited the broadened and red-shifted surface plasmon band, enhanced band gap emission, and suppressed defect emission due to the strong interfacial coupling between Au and ZnO. Moreover, the band gap emission of the Au-ZnO hybrid nanostructures is controllably blue-shifted with decreasing distance between the Au nanocrystals and ZnO nanorods tuned by the amount of the polyelectrolyte layers due to the exciton and plasmon interactions.     

Fabrication of ZnS/ZnO hierarchical nanostructures by two-step vapor phase method

A simple two-step vapor phase method is presented to fabricate ZnS/ZnO hierarchical nanostructures in bulk quantities. That is ZnS nanobelts were first synthesized and then used as substrate for growth of ZnO nanorod arrays. Investigation results demonstrate that the polar surfaces of ZnS nanobelts could induce a preferred asymmetric growth of ZnO nanorods on the side surfaces. But it is believed that if the local concentration of ZnO was high enough, ZnO nanorods could also grow symmetrically on the top/bottom surface of the ZnS nanobelts. The optical property of the products was also recorded by means of photoluminescence (PL) spectroscopy.     

Cathodoluminescence and its mapping of flower-like ZnO, ZnO/ZnS core-shell and tube-like ZnS nanostructures

The cathodoluminescence (CL) properties including intensity and distribution of the band to band and defect emission of the flower-like ZnO, ZnO/ZnS core-shell and tube-like ZnS nanostructures have been investigated. It is indicated that the Ultraviolet (UV) emission at 380 nm of the flower-like ZnO nanostructures due to the band to band emission is weaker than their yellow emission at 600 nm induced by interstitial oxygen. Moreover, the UV emission of the ZnO nanorods unevenly distributes from the tip to the end. The UV emission on the tip is stronger than that of others due to the waveguide. On the contrary, the yellow emission at 600 nm is uniform. Furthermore, the UV emission of ZnO has been greatly enhanced and the yellow emission has been inhibited by the formation of ZnO/ZnS core-shell nanostructures in the sulfuration process due to the elimination of interstitial oxygen. However, the polycrystalline tube-like ZnS nanostructures shows the uniform and weak defect emission due to S vacancies.     

Facile synthesis of α-MnO2 nanostructures for supercapacitors

Various α-MnO₂ nanostructures have been successfully synthesized by a simple hydrothermal method based on the redox reactions between the MnO₄⁻ and H₂O in mixture containing KMnO₄ and HNO₃. The effect of varying the hydrothermal time to synthesize MnO₂ nanostructures and the forming mechanism of α-MnO₂ nanorods were investigated by using XRD, SEM and TEM. The results revealed an evolvement of morphologies ranging from brushy spherical morphology to nanorods depending upon the hydrothermal time. The surface area of the synthesized nanomaterials varied from 89 to 119 m²/g. Electrochemical properties of the products were evaluated using cyclic voltammetry and galvanostatic charge–discharge studies, and the sample obtained by hydrothermal reaction for 6 h at 120 °C showed maximum capacitance with a value of 152 F/g. In addition, long cycle life and excellent stability of the material were also demonstrated.     

Hydrothermal synthesis and photoluminescence properties of nano-crystalline GdBO3:Eu phosphor

Nano-crystalline GdBO₃:Eu³⁺ was prepared by a hydrothermal method and the effects of some processing variables such as pH, temperature were investigated. The as-synthesized powders were spherical shaped agglomerates of nanoparticles. The luminescent properties were compared with samples synthesized by conventional solid-state reaction method. Both the photoluminescence intensity and chromaticity were improved and a red-shift in the CT band was observed for the hydrothermally synthesized samples. Possible mechanisms of phase formation were investigated and explanations for the changes in optical properties are proposed.     

VO2(B) nanospheres: Hydrothermal synthesis and electrochemical properties

Monodisperse VO₂(B) nanospheres with an average size of 100 nm were synthesized by hydrothermal method. Experiments showed that the surfactant octadecyl-amine played an important role during the formation of the nanospheres, and possible mechanism was suggested. Moreover, the potential uses of VO₂ nanospheres were primarily probed as electrodes for lithium-ion batteries.     

A template-free alcoholthermal route to Ti(Sn)-doped ZnO nanorods

Ti(Sn)-doped single-crystalline ZnO nanorods with an average diameter of 20 nm and length up to nearly 1 μm were synthesized by a facile ultrasonic irradiation-assisted alcoholthermal method without involving any templates. Photoluminescence spectra of the Ti-doped ZnO nanorods were measured at room temperature and three emitting bands, being a violet emission at 400-415 nm, a blue band at 450-470 nm and a green band at around 550 nm, were detected. The emission intensities of the Ti-doped ZnO nanorods enhance gradually with increasing the doping concentrations. As to the Sn-doped ZnO nanorods, the green emission shifts to 540 nm and the emission intensities increase first but decrease later with increasing the doping concentrations.     

Size-dependent blue luminescent CdS nanocrystals synthesized through a single-source molecular precursor route

In this paper, we report on the synthesis of size-dependent blue luminescent CdS nanocrystals by using a new nonhydrolytic single-source molecular method. The size of the synthesized CdS nanocrystals could be easily controlled by adjusting the ratio of reaction sources under inert atmosphere. The studies on the optical properties reveal an obvious size-dependent photoluminescence characteristic of the synthesized nanocrystals.     

A facile method to prepare PbS nanorods

PbS nanorods with an average diameter of about 30 nm have been successfully prepared through a simple polyglycol-assisted route for the first time. The obtained PbS nanorods have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electronic diffraction (SAED). Experiments show that polyglycol plays an important role for the control of the morphology of PbS nanostructures. The preliminary result of the UV-vis absorption spectrum of the PbS nanorods is also presented.     

Fast-grown CdS quantum dots: Single-source precursor approach vs microwave route

A cross-disciplinary protocol of characterization by joint techniques enables one to closely compare chemical and physical properties of CdS quantum dots (QDs) grown by single source precursor methodology (SSPM) or by microwave synthetic route (MWSR). The results are discussed in relation with the synthesis protocols. The QD average sizes, reproducible as a function of the temperatures involved in the growth processes, range complementarily in 2.8–4.5 nm and 4.5–5.2 nm for SSPM and MWSR, respectively. Hexagonal and cubic structures after X-ray diffraction on SSPM and MWSR grown CdS QDs, respectively, are tentatively correlated to a better crystalline quality of the latter with respect to the further ones, suggested by (i) a remarkable stability of the MWSR grown QDs after exposure to air during several days and (ii) no evidence of their fragmentation during mass spectrometry (MS) analyses, after a fair agreement between size dispersities obtained by transmission electron microscopy (TEM) and MS, in contrast with the discrepancy found for the SSPM grown QDs. Correlatively, a better optical quality is suggested for the MWSR grown QDs by the resolution of n > 1 excitonic transitions in their absorption spectra. The QD average sizes obtained by TEM and deduced from MS are in overall agreement. This agreement is improved for the MWSR grown QDs, taking into account a prolate shape of the QDs also observed in the TEM images. For both series of samples, the excitonic responses vs the average sizes are consistent with the commonly admitted empirical energy-size correspondence. A low energy PL band is observed in the case of the SSPM grown QDs. Its decrease in intensity with QD size increase suggests a surface origin tentatively attributed to S vacancies. In the case of the MWSR grown QDs, the absence of this PL is tentatively correlated to an absence of S vacancies and therefore to the stable behavior observed when the QDs are exposed to air.     

Synthesis of flower- and rod-like nickel sulfide nanostructures by an organic-free hydrothermal process

Well-crystalline flower- and rod-like NiS nanostructures have been synthesized by an organic-free hydrothermal process at a low temperature of 200 °C. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were employed to characterize the as-synthesized NiS nanostructures. The effects of temperature and reaction time on the morphology have been also investigated. The two-step flake-cracking mechanism for the formation of flower- and rod-like NiS nanostructures was discussed. The products were also investigated by photoluminescence (PL) spectroscopy.     

Controllable synthesis of hierarchical nanostructures of CaWO4 and SrWO4 via a facile low-temperature route

CaWO₄ and SrWO₄ nanostructures have been synthesized via a simple microemulsion-mediated route. With careful control of the fundamental experimental parameters including the concentration of reactants, the reaction time and the temperature, the products with different morphologies of dumbbell, coral, rod and dendrite have been obtained, respectively. The possible formation mechanism of these unique morphologies has been proposed based on surfactant self-assembly under different experimental conditions. The as-synthesized CaWO₄ samples with various morphologies exhibit different photoluminescence properties. X-ray powder diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and luminescence spectroscopy were used to characterize these products.     

Hydrothermal synthesis and vacuum ultraviolet-excited luminescence properties of novel Dy-doped LaPO4 white light phosphors

Novel LaPO₄:Dy³⁺ white light phosphors with monoclinic system were successfully synthesized by hydrothermal method at 240 °C. The strong absorption at around 147 nm in excitation spectrum was assigned to the host absorption which suggested that the vacuum ultraviolet-excited energy was efficiently transferred from the host to the Dy³⁺ ion. The f-d transition of Dy³⁺ ion was observed locating at 182 nm. Under 147 nm excitation, La_1−xPO₄:xDy³⁺ phosphor exhibited two emission bands locating at 571 nm (yellow) and 478 nm (blue) which corresponded to the hypersensitive transitions ⁴F_9/2-⁶H_13/2 and ⁴F_9/2-⁶H_15/2. It was the two emission bands that lead to the white light.