Nanostructured CaWO4, CaWO4 : Pb2+ and CaWO4 : Tb3+ particles: polyol-mediated synthesis and luminescent properties

Nano-submicrostructured CaWO4, CaWO4 : Pb2+ and CaWO4 : Tb3+ particles were prepared by polyol method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), thermogravimetry-differential thermal analysis (TG-DTA), photoluminescence (PL), cathodo-luminescence (CL) spectra and PL lifetimes. The results of XRD indicate that the as-prepared samples are well crystallized with the scheelite structure of CaWO4. The FE-SEM images illustrate that CaWO4 and CaWO4 : Pb2+ and CaWO4 : Tb3+ powders are composed of spherical particles with sizes around 260, 290, and 190 nm respectively, which are the aggregates of smaller nanoparticles around 10-20 nm. Under the UV light or electron beam excitation, the CaWO4 powders exhibits a blue emission band with a maximum at about 440 nm. When the CaWO4 particles are doped with Pb2+, the intensity of luminescence is enhanced to some extent and the luminescence band maximum is red shifted to 460 nm. Tb(3+)-doped CaWO4 particles show the characteristic emission of Tb3+ 5D4-7FJ (J = 6 - 3) transitions due to an energy transfer from WO4(2-) groups to Tb3+.     

Nanostructured CaWO4, CaWO4:Eu3+ and CaWO4:Tb3+ particles: sonochemical synthesis and luminescent properties

Nanostructured CaWO4, CaWO4:Eu3+, and CaWO4:Tb3+ phosphor particles were synthesized via a facile sonochemical route. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, low voltage cathodoluminescence spectra, and photoluminescence lifetimes were used to characterize the as-obtained samples. The X-ray diffraction results indicate that the samples are well crystallized with the scheelite structure of CaWO4. The transmission electron microscopy and field emission scanning electron microscopy images illustrate that the powders consist of spherical particles with sizes from 120 to 160 nm, which are the aggregates of even smaller nanoparticles ranging from 10 to 20 nm. Under UV light or electron beam excitation, the CaWO4 powder exhibited a blue emission band with a maximum at 430 nm originating from the WO4/2- groups, while the CaWO4:Eu3+ powder showed red emission dominated by 613 nm ascribed to the 5D0 --> 7F2 of Eu3+, and the CaWO4:Tb3+ powders showed emission at 544 nm, ascribed to the 5D4 --> 7F5 transition of Tb3+. The PL excitation and emission spectra suggest that the energy is transferred from WO4/2- to Eu3+ CaWO4:Eu3+ and to Tb3+ in CaWO4:Tb3+. Moreover, the energy transfer from WO4/2- to Tb3+ in CaWO4:Tb3+ is more efficient than that from WO4/2- to EU3+ in CaWO4:Eu3+. This novel and efficient pathway could open new opportunities for further investigating the novel properties of tungstate materials.     

Hydrothermal synthesis and luminescence properties of hierarchical SrF2 and SrF2:Ln3+ (Ln = Er,Nd, Yb,Eu, Tb) micro/nanocomposite architectures

Highly uniform SrF₂ and SrF₂:Ln³⁺ (Ln = Er, Nd, Yb, Eu, Tb) hierarchical microspheres assembled by 2D nanoplates have been successfully synthesized by a facile and friendly hydrothermal route. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra were used to characterize the samples. The experimental results indicate that reaction time and chelating reagent play a key role in forming the hierarchical microspheres. The formation mechanism was proposed based on the evolution of this morphology as a function of hydrothermal time. The near-infrared luminescence of lanthanide ions (Er, Nd, and Yb) doped SrF₂ microspheres were discussed in detail. In addition, the as-obtained SrF₂:Eu³⁺ sample exhibits orange-red emission centered at 590 nm under excitation at 393 nm, while the SrF₂:Tb³⁺ exhibits a strong green emission at 540 nm. The as-synthesized SrF₂:Ln³⁺ luminescent microspheres might find some potential applications in areas of photoluminescence, telecommunication and laser emission.     

Synthesis of size- and shape-controlled monodisperse PbSe quantum dots via a green approach

Spherical, octahedral, and cubic shaped PbSe quantum dots were successfully synthesized by virtue of a green chemical route, using environmentally friendly N,N-dimethyl-oleoyl amide as the solvent of Se. The process eliminates trioctylphoshine from the synthesis, using oleic acid as capping ligand in the noncoordinating solvent. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopic (EDS), were used to characterized the samples. The crystalline size can be tuned in a range from 8 nm to 16 nm by varing the reaction time or growth temperature. Based on the evidence of TEM images, the mechanism of PbSe quantum dots evolution from spherical to cubic structure has also been discussed. We found that the growth temperature played an important role in the morphology of PbSe quantum dots. This finding will enhance our understanding for the formation mechanism of nanomaterials with special shapes.     

The synthesis and photocatalytic activity of ZnSe microspheres

This paper reports the synthesis of semiconductor ZnSe microspheres composed of nanoparticles via a solvothermal route between the organic molecule selenophene (C(4)H(4) Se) and ZnCl(2) without adding any surfactant. The ZnSe microspheres were characterized by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), specific surface area measurement, and photoluminescence (PL) spectra. A strong and broad blue PL emission at 443 nm in wavelength (～2.79 eV in photon energy) is attributed to the near-band-edge (NBE) emission of ZnSe, while the 530 nm peak is a defect-related (DL) emission. The photocatalytic activity of the as-prepared ZnSe microspheres was evaluated by photodegradation of methyl orange (MO) dye under ultraviolet (UV) light and visible light irradiation. The degradations of MO reach 94% or 95.1%, close to 100%, in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 7 or 10 h under UV irradiation, respectively. Meanwhile the degradations of MO reach 94.3% or 60.6% in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 12 h, respectively. The degradation rate of ZnSe microspheres is twice that of ZnSe commercial powder under UV light irradiation, and three times under visible light irradiation. The degradation process of MO dye on ZnSe microspheres under UV or visible light is also discussed.     

Template-free solvothermal synthesis of hierarchical boehmite hollow microspheres with strong affinity toward organic pollutants in water

Three-dimensional hierarchical boehmite hollow microspheres with a very high yield at low cost were successfully synthesized via a one-pot template-free solvothermal route using aluminum chloride hexahydrate as precursor in a mixed ethanol–water solution with assistance of trisodium citrate. The as-synthesized products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption/desorption techniques. The results show that Cl⁻ and addition amount of trisodium citrate have significant effect on the morphologies of the resultant products, and 6–8 mmol of trisodium citrate is optimal for the synthesis of boehmite hollow microspheres assembled from randomly interconnecting and aligned nanorods with solvothermal time no less than 15 h. A synergistic mediation mechanism of citrate ions and Cl⁻ to form boehmite hollow spheres via self-assembly morphology evolution was proposed based on the experimental results. Interestingly, the typical boehmite hollow microspheres with a surface area of 102 m² g⁻¹, pore volume of 0.37 cm3 g⁻¹, and the average pore size of 14.6 nm show superb adsorption properties for Congo red with maximum capacity of 114.7 mg g⁻¹ which is higher than that of a commercial boehmite. This simple synthetic route is a very promising way for the design and synthesis of new functional hierarchical nanostructured materials with desired adsorptive properties.     

Synthesis of flower-like CuS nanostructured microspheres using poly(ethylene glycol) 200 as solvent

CuS flower-like microspheres with the diameter of about 3-4 microm constructed by nanoflakes with thickness of about 30-40 nm have been successfully synthesized by a simple wet chemical method. In this reaction system, Poly(ethylene glycol) 200 (PEG 200) was used as solvent, CuCl2 2H2O as cuprum source, and thioacetamide (TAA) as sulfur source. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) in detail. The XRD patterns revealed that the products were pure hexagonal phase of CuS. Experiments with various parameters indicated that the reaction temperature and molar ratio of CuCl2 2H2O to thioacetamide had strong effects on the sizes and morphologies of CuS crystals. A possible growth mechanism on the formation of CuS microspheres was proposed. The PEG 200 acted as solvent, complexing agent, and soft template in this synthesis. Furthermore, optical studies of the products including UV-Vis absorption spectrum and photoluminescence spectrum have also been carried out.     

Three-dimensional (3D) sea-urchin-like hierarchical TiO2 microspheres: growth mechanism and highly enhanced photocatalytic activity

Three-dimensional (3D) sea-urchin-like hierarchical TiO₂ microspheres were synthesized by a template-free hydrothermal method. The effects of preparation parameters on the microstructure of 3D sea-urchin-like hierarchical TiO₂ were investigated using scanning electron microscopy (SEM), transmission electron microscopy, X-ray diffractometer, energy-dispersive X-ray spectrometer and Brunauer–Emmett–Teller technologies. The growth mechanism and photocatalytic activity of 3D sea-urchin-like TiO₂ microspheres were discussed. The results of electron microscopy characterizations SEM showed that the microspheres were consisted of numerous one-dimensional (1D) nanorods. A three-step growth model: oxygenated to be 1D nanorods, self-assembly and protonation, was proposed to illustrate the growth mechanism of sea-urchin-like structures. The synthesized 3D sea-urchin-like hierarchical TiO₂ microspheres exhibited a better photocatalytic activity for photodegradation of rhodamine B under sunlight irradiation compared to that of P25, which was attributed to the special 3D hierarchical nanostructure, the increased number of surface active sites and anatase crystal structure.     

Synthesis of crystal MFe2O4 (M = Mg,Cu, Ni) microspheres

A low-temperature solvothermal synthetic method was developed for the large-scale synthesis of uniform-sized ferrite MFe₂O₄ (M = Mg, Cu, Ni) microspheres. The size of the as-prepared ferrite MFe₂O₄ microspheres could be controlled to be diameters 300–800 nm in diameter by adjusting some growth parameters, such as reaction time and concentration. The structures of the as-prepared ferrite MFe₂O₄ microspheres were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX). The magnetic properties of the ferrite MFe₂O₄ microspheres were also investigated.     

微纳分级结构碳酸钙中空微球的可控制备

以CaCl₂和Na₂CO₃为反应原料, 以聚乙烯吡咯烷酮(PVP)和十二烷基磺酸钠(SDSN)为模板剂, 在50℃采用化学沉淀反应, 干燥、煅烧后成功制备了具有微纳分级结构的CaCO₃中空微球。采用扫描电子显微镜、透射电子显微镜和X射线衍射等检测手段对所制备的样品形貌、结构进行了表征, 结果显示：所制备的微纳分级结构CaCO₃中空微球直径为4~6 μm, 壳壁由直径约60 nm的CaCO₃颗粒组成, 壳层厚度约为200 nm, CaCO₃中空微球晶相组成为方解石和球霰石的共混体。同时, 在反应温度为50℃、PVP添加量为0.4 g, SDSN浓度为0.1 mol/L的条件下, 所制备的微纳分级结构CaCO₃中空微球分散性好, 且形貌比较完整。     

Synthesis and characterization of flower-like MoS2 microspheres by a facile hydrothermal route

Flower-like MoS₂ microspheres with high purity were successfully synthesized via a facile hydrothermal route by adding sodium silicate as an additive. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). XRD patterns showed that the MoS₂ microspheres had good crystallinity with well-stacked layered structure. TEM and SEM images showed that the MoS₂ microspheres had uniform sizes with mean diameter about 480 nm and were constructed with MoS₂ sheets with thickness of several nanometers. It was found that the possible precursor H₄SiMo₁₂O₄₀ obtained by sodium silicate reacting with sodium molybdate played a crucial role in the formation of the flower-like MoS₂ microspheres in our experiment. A possible formation mechanism of MoS₂ microspheres was preliminarily presented.     

Synthesis of the Fe3O4@SiO2@SiO2-Tb(PABA)3 luminomagnetic microspheres

In this paper, we describe the synthesis and characterization of a luminomagnetic microspheres with core-shell structures (denoted as Fe3O4@ SiO2 @SiO2-Tb(PABA)3). The luminomagnetic microspheres were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), and photoluminescence spectrophotometer (PL). The SEM observation shows that the microsphere consists of the magnetic core with about 400 nm in average diameter and silica shell doped with terbium complex with an average thickness of about 90 nm. It has a saturation magnetization of 15.8 emu/g and a negligible coercivity at room temperature and exhibits strong green emission peak from 5D4 --> 7F5 transition of Tb3+ ions. The luminomagnetic microspheres with good magnetic response and fluorescence probe property as well as water-dispersibility would have potential medical applications, such as time-resolved fluoroimmunoassay (TR-FIA), fluorescent imaging, and magnetic resonance imaging (MRI).     

Effect of key parameters on the morphology transformation of three-dimensional TiO2 solid microspheres

Three-dimensional (3D) TiO₂ solid microspheres with different morphologies have been synthesized on a large scale by a simple hydrothermal method using titanium tetrachloride (TiCl₄) as the titanium source and ammonium fluoride (NH₄F) as the etchant. X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) studies show that the 3D solid microspheres, with an average diameter from hundreds of nanometers to several micrometers, are composed of numerous anatase TiO₂ particles. In addition, the morphologies of the as-prepared 3D solid microspheres can be controlled by adjusting the dosage of NH₄F and the reaction temperatures. The present study has enlarged the family of 3D solid microspheres, and offers a possible route for the synthesis of other inorganic hierarchical structures.     

Patterning of red, green, and blue luminescent films based on CaWO4:Eu3+, CaWO4:Tb3+, and CaWO4 phosphors via microcontact printing route

The multicolor patterned luminescent films of CaWO(4):Eu(3+) (red), CaWO(4):Tb(3+) (green), and pure CaWO(4) (blue) on quartz substrates were fabricated by the facile and low-cost microcontact printing (μCP) method combining with the Pechini sol-gel route. On the basis of the μCP process, a hydrophobic self-assembled monolayer (SAM) was first created on the hydrophilic surface of quartz substrates by poly(dimethylsiloxane) (PDMS) mold printing, and then, the multicolor patterned luminescent films were selectively deposited on the hydrophilic regions via a spin coating process and heating treatment. The X-ray diffraction, optical microscopy, scanning electron microscopy, and photoluminescence (PL) spectra were used to characterize the structure and fluorescence properties of the corresponding samples. The results demonstrate that the μCP process can be used for patterning the inorganic phosphor materials and have potential for fabricating rare-earth luminescent pixels for the applications of display devices.     

分级介孔结构组成的ZnO微球及光催化性能

以硝酸锌、脲素及酒石酸为反应物, 采用水热法制备碱式碳酸锌前驱体微球, 通过煅烧前驱体制备了介孔氧化锌微球。通过扫描电子显微镜(SEM)可以观察到, 氧化锌微球的直径约为2~4 μm, 由大量厚度约为10 nm的介孔纳米片组装而成。X 射线衍射(XRD)和透射电镜(TEM)结果表明: ZnO微球为六方纤锌矿结构, 并结晶较好。比表面积测试(BET)表明ZnO微球为介孔材料, 孔径为20~50 nm, ZnO微球比表面积约为29.8 m²/g。以亚甲基蓝为目标降解物, 对介孔氧化锌微球进行了光催化降解实验。实验结果表明, 所合成的介孔ZnO微球对亚甲基蓝的光催化性能较好。     

Dy3+掺杂CaWO4荧光粉体的制备及发光性能

采用固相陶瓷方法制备了Dy3+掺杂的CaWO4∶Dyx3+荧光粉体。采用XRD、SEM和FT-IR对制备粉体的微观结构进行了表征;采用荧光分析法研究了制备的荧光体的室温光致发光性能;探讨了掺杂剂Dy3+浓度对CaWO4∶Dyx3+荧光粉体的微结构和光致发光性能的影响。结果表明,制备的CaWO4∶Dyx3+荧光粉体为白钨矿结构,Dy3+的掺入会抑制CaWO4∶Dy3x+晶粒的生长。当Dy3+的掺入量为1%(摩尔分数)时,其在480nm(蓝)和575nm(黄)的发射强度达到最大;随着Dy3+浓度的增加,其特征发射峰(480nm和575nm)强度反而逐渐下降。     

Photocatalytic activities of Mo-doped Bi2WO6 three-dimensional hierarchical microspheres

The Mo-doped Bi₂WO₆ three-dimensional (3D) hierarchical microspheres from nanoplates have been synthesized by a hydrothermal route. The products were characterized in detail by multiform techniques: X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDS), scanning electron microscopy (SEM), and UV-vis absorption spectrum. The results of the photocatalytic degradation of Rhodamine-B (RhB) in aqueous solution showed that molybdenum ions doping greatly improved the photocatalytic efficiency of Bi₂WO₆ 3D hierarchical microspheres. The Mo-doped Bi₂WO₆ microspheres with atomic ratio of Mo-W of 0.05 had the best activity in photodegradation of RhB in aqueous solution under 500 W Xe lamp light irradiation.     

Bio-template route for facile fabrication of Cd(OH)2@yeast hybrid microspheres and their subsequent conversion to mesoporous CdO hollow microspheres

Cadmium oxide (CdO) microspheres with a porous hollow microstructure were prepared by a facile yeast mediated bio-template route. The yeast provides a solid scaffold for the deposition of cadmium hydroxide (Cd(OH)₂) from cadmium acetate and sodium hydroxide solutions to form the hybrid Cd(OH)₂@yeast precursor. Thermal conversions of this at above 500 °C in air have produced hollow CdO microspheres. The products were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), thermal gravimetric and differential thermal analysis (TGA-DTA), and Brunauer-Emmett-Teller (BET) surface analysis respectively. The obtained CdO microspheres have uniform size (length = 2.6 ± 0.4 μm; width = 2.0 ± 0.2 μm) and a well defined, continuous, mesoporous hollow microstructure. The shell is about 250-280 nm in thickness. The mechanism of formation of Cd(OH)₂@yeast precursor and its conversion to CdO hollow microspheres is discussed. In comparison with traditional template-directed method, the present strategy represents a general, economical and environmentally benign route for the formation of metal oxide hollow microspheres. These materials have potential applications in different fields such as encapsulation, drug delivery, efficient catalysis, battery materials and photonic crystals. The method presented can be extended to the synthesis of other inorganic hollow microstructures of different sizes and shapes by pre-selecting suitable bio-templates.     

Ionic liquid assisted hydrothermal synthesis of hollow vesicle-like MoS2 microspheres

The preparation of MoS₂ microspheres with hollow vesicle-like structure was successfully achieved, which used hydrazine solution with (NH₄)₂MoS₄ as the precursor. The reaction process was assisted by a convenient ionic liquid (1-butyl-3-methylimidazolium chloride) with the hydrothermal method at 200 °C for 24 h. X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) techniques were used to characterize the samples. It was shown that the MoS₂ microspheres had uniform spherical morphology with the diameter of 1-2 μm. It was also indicated that the hollow vesicle monomers on the surface of microspheres were structured with multi-layer of MoS₂, whose d spacing was 1.0 nm. A tentative formation mechanism was proposed for the growth process of the MoS₂ microspheres with hollow vesicle-like structure.     

微波辐射作用下制备二氧化锆微球的研究

以氧氯化锆为主要原料,在微波作用下,采用溶胶-凝胶法制备二氧化锆微球,研究不同混合溶剂对二氧化锆微球形貌的影响,通过扫描电镜(SEM)、透视电镜(TEM)、X射线衍射(XRD)等分析手段对微球进行表征。结果表明:制备二氧化锆微球分散性较好,异丙醇与水的混合溶剂直接影响微球的成核及生长。