NaTaO3及NaTaO3∶Bi3+光催化剂的光致发光光谱研究

采用光致发光光谱技术对一系列不同条件下制备的NaTaO3及不同掺杂量的NaTaO3∶Bi3+进行了研究. 结果表明, NaTaO3的发光性质与其制备条件密切相关: 在钠离子不足的条件下合成的样品, 其发光带主要位于515和745 nm左右; 而在钠离子充足条件下合成的样品, 其发光带位于460 nm左右, 随着n(Na)/n(Ta)的降低, 发光带向长波长方向移动; 掺入Bi3+之后, 其发光峰由515 nm移至455 nm, 随着Bi3+掺入量的增加, 455 nm的发光带强度减弱. 515 nm的发光带与替位缺陷TaNa....相关; 745 nm的发光带与VNa`缺陷相关; 而460 nm的发光带与本征TaO6基团相关. 将Bi3+掺入到钽酸钠样品, TaNa....由BiNa..替代, 相应的发光带向高的n(Na)/n(Ta)方向移动, 从而呈现出本征TaO6基团的发光带.     

Controlling internal nanostructures of porous microspheres prepared via electrospraying

The focus of this work is to control and study internal nanostructures of electrosprayed polymer microspheres. In order to make the study easy, the microspheres were cut, and scanning electron microscopy coupled with image analysis software was employed to evaluate the size distributions and the internal nanostructures of microspheres. According to the observation and analysis results, three types of polyethersulfone porous microspheres (perfect sphere-shaped, red blood cell-shaped, and Chinese lantern-shaped) with a diameter ranging from 3 to 20 μm were prepared via electrospraying technology. By controlling the process parameters, the porous microspheres with three kinds of internal nanostructures, namely, macrovoid internal nanostructure, sponge-pore internal nanostructure, and parallel internal macrovoid nanostructure were produced. The results demonstrate that the presence of some additive, such as polyethylene glycol and polyvinyl alcohol, can control the internal nanostructures of the electrosprayed microspheres effectively. The possible mechanism for the formation of internal nanostructures was also proposed.     

Facile synthesis of ultrasmall GdF3 nanowires via an oriented attachment growth and their luminescence properties

Ultrasmall nanowires of rare-earth fluoride were prepared via an oriented attachment growth for the first time, and the formation process and the role of the capping ligand were discussed. Furthermore, as a luminescence host, they showed higher emitting intensity with Eu(3+) doping.     

Synthesis of quantum-sized cubic ZnS nanorods by the oriented attachment mechanism

Quantum-sized ZnS nanocrystals with quasi-spherical and rod shapes were synthesized by the aging reaction mixtures containing diethylzinc, sulfur, and amine. Uniform-sized ZnS nanorods with the average dimension of 5 nm x 21 nm, along with a small fraction of 5 nm-sized quasi-spherical nanocrystals, were synthesized by adding diethylzinc to a solution containing sulfur and hexadecylamine at 125 degrees C, followed by aging at 300 degrees C. Subsequent secondary aging of the nanocrystals in oleylamine at 60 degrees C for 24 h produced nearly pure nanorods. Structural characterizations showed that these nanorods had a cubic zinc blende structure, whereas the fabrication of nanorods with this structure has been known to be difficult to achieve via colloidal chemical synthetic routes. High-resolution TEM images and reaction studies demonstrated that these nanorods are formed from the oriented attachment of quasi-spherical nanocrystals. Monodisperse 5 nm-sized quasi-spherical ZnS nanocrystals were separately synthesized by adding diethylzinc to sulfur dissolved in a mixture of hexadecylamine and 1-octadecene at 45 degrees C, followed by aging at 300 degrees C. When oleic acid was substituted for hexadecylamine and all other procedures were unchanged, we obtained 10 nm-sized quasi-spherical ZnS nanocrystals, but with broad particle size distribution. These two different-sized quasi-spherical ZnS nanocrystals showed different proportions of zinc blende and wurtzite crystal structures. The UV absorption spectra and photoluminescence excitation spectra of the 5 nm ZnS quasi-spherical nanocrystals and of the nanorods showed a blue-shift from the bulk band-gap, thus showing a quantum confinement effect. The photoluminescence spectra of the ZnS nanorods and quasi-spherical nanocrystals showed a well-defined excitonic emission feature and size- and shape-dependent quantum confinement effects.     

Role of the oriented attachment mechanism in the phase transformation of oxide nanocrystals

"Bottom-up" methods to obtain nanocrystals usually result in metastable phases, even in processes carried out at room temperature or under soft annealing conditions. However, stable phases, often associated with anisotropic shapes, are obtained in only a few special cases. In this paper we report on the synthesis of two well-studied oxides-titanium and zirconium oxide-in the nanometric range, by a novel route based on the decomposition of peroxide complexes of the two metals under hydrothermal soft conditions, obtaining metastable and stable phases in both cases through transformation. High-resolution transmission electron microscopy analysis reveals the existence of typical defects relating to growth by the oriented attachment mechanism in the stable crystals. The results suggest that the mechanism is associated to the phase transformation of these structures.     

Structure controlling and adsorption application of polyethersulfone porous microspheres prepared via electrospraying

The focus of this work is to control the structure of electrosprayed polymer microspheres and then study the effect of different structures on the microspheres＇ adsorption properties. Scanning electron microscopy （SEM） coupled with image analysis software was employed to evaluate the size distributions and the structure of microspheres. According to the observation and analysis results, two types of polyethersulfone （PES） porous microspheres （perfect sphere-shaped and collapsed） were prepared via electrospraying technology by adjusting the solvent and polymer molecular weight. The porous PES microspheres can remove bisphenol A （BPA） from its aqueous solution effectively. Compared with collapsed microspheres, the rough microspheres had much higher specific surface area and better mobility in the BPA aqueous solution, so it showed a better adsorption capacity than that of collapsed microspheres. The solvent evaporation rate and the occurrence rate of phase separation significantly affect the structure and morphology of microspheres.     

A kinetic model to describe nanocrystal growth by the oriented attachment mechanism.

The classical model of particle coagulation on colloids is revisited to evaluate its applicability on the oriented attachment of nanoparticles. The proposed model describes well the growth behavior of dispersed nanoparticles during the initial stages of nanoparticle synthesis and during growth induced by hydrothermal treatments. Moreover, a general model, which combines coarsening (i.e., Ostwald ripening) and oriented attachment effects, is proposed as an alternative to explain deviations between experimental results and existing theoretical models.     

Assembly of oriented zeolite monolayers and thin films on polymeric surfaces via hydrogen bonding

The b-oriented monolayers of microsized silicalite-1 crystals have been manually assembled on glass plate supported poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), chitosan, and poly(methyl methacrylate) (PMMA) thin films via hydrogen bonding with much enhanced binding strength and satisfactory degrees of coverage and close packing. The exerted pressure and rubbing time in the manual assembly do not affect the binding strength of the silicalite-1 monolayer on the glass plate supported polymeric film. This manual assembly has been further applied to fabricate zeolite monolayers on commercially available Plexiglas surfaces and b-oriented multilayered films of silicalite-1 crystals on glass plates. The assembly method established in this study provides a feasible way to produce zeolite monolayers on polymer-modified solid substrates and Plexiglas and to fabricate zeolite-polymer composite membranes by means of the layer-by-layer technique.     

Hydrothermal synthesis and photocatalytic property of porous CuO hollow microspheres via PS latex as templates

Porous copper oxide (CuO) hollow microspheres have been fabricated through a simple hydrothermal method using PS latex as templates. The as-obtained samples were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). The influences of the mole ratio of Ethylenediamine (C₂H₈N₂) and copper acetate (Cu(Ac)₂·H₂O), hydrothermal temperature and time on the size and morphologies of the final products have been investigated. The possible formation mechanism of porous CuO hollow microspheres has been proposed and the specific surface area of the hollow microspheres with 81.71 m²/g is measured by BET method. The band gap value calculated from a UV–vis absorption spectrum of porous CuO hollow microspheres is 2.71 eV. The as-synthesized product exhibits high photocatalytic activity during the photodegradation of an organic dyestuff, rhodamine B (RhB), under UV-light illumination.     

Synthesis of silver nanoplates by two-dimensional oriented attachment

Synthesis of silver nanoplates was studied in the modified polyol method, where the nucleation and seed stage occurred in a poly(ethylene glycol) (PEG)-water mixture solution, and the growth stage happened in the PEG environment. The morphological evolution of nanoplates was characterized using UV, SEM, and TEM. Interestingly, plane nanostructures with unusual jagged edges were finally formed in our modified polyol method. Using TEM, we observed the medium state of fusion between two nanoplates, resulting in generating unusual jagged edges. Therefore, a novel two-dimensional oriented attachment occurred in our modified polyol method, which involves smaller nanoplates as the building blocks. Further control experiments showed that the presence of water could break this kinetic preferred reactivity, leading to the formation of nanoparticles.     

The evolvement of pits and dislocations on TiO2-B nanowires via oriented attachment growth

TiO₂-B nanowires were synthesized by an ion exchanging-thermal treatment. The unique morphology of pits and dislocations interspersed on TiO₂-B nanowires were firstly characterized and studied by high-resolution transmission electron microscopy (HRTEM). Oriented attachment is suggested as an important growth mechanism in the evolvement of pits and dislocations on TiO₂-B nanowires. Lattice shears and fractures were originally formed during the ion exchanging process of the sodium titanate nanowires, which resulted in the formation of primary crystalline units and vacancies in the layered hydrogen titanate nanowires. Then the (110) lattice planes of TiO₂-B grown in [110] direction is faster than the other lattice planes, which caused the exhibition of long dislocations on TiO₂-B nanowires. The enlargement of the vacancies, which was caused by the rearrangement of primary crystalline units, should be the reason of the formation of pits. Additionally, the transformation from TiO₂-B to anatase could be also elucidated by oriented attachment mechanism.     

Preparation of a colloidal array of NaTaO3 nanoparticles via a confined space synthesis route and its photocatalytic application

The confined space synthesis method has been applied to the preparation of sodium tantalate (NaTaO(3)); hydrothermal reaction of NaOH and Ta(2)O(5) was carried out in the pores of a three-dimensional mesoporous carbon, which was replicated by the colloidal array of silica nanospheres (SNSs) 20 nm in size. This approach led to the formation of a colloidal array of NaTaO(3) nanoparticles 20 nm in size with a surface area of 34 m(2) g(-1). The photocatalytic performance of the colloidal array of NaTaO(3) nanoparticles for overall water splitting under UV irradiation (λ > 200 nm) was evaluated after loading a NiO cocatalyst onto NaTaO(3) samples. The NiO-loaded NaTaO(3) nanoparticles showed photocatalytic activity for overall water splitting more than three times as high as non-structured bulk NaTaO(3) particles.     

Bandgap engineering of SrTiO3/NaTaO3 heterojunction for visible light photocatalysis

Hybrid density functional of HSE06 has been adopted to investigate the geometry and electronic properties of SrTiO₃/NaTaO₃ heterostructures in contrast with the cubic SrTiO₃ and cubic NaTaO₃. The SrTiO₃/NaTaO₃ heterostructures with varied monolayers of SrTiO₃ and NaTaO₃ units are constructed, and all the heterojunction systems have the smaller bandgaps as compared with those of pure SrTiO₃ and NaTaO₃. For the (SrTiO₃)_m/(NaTaO₃)_n (m + n = 10) systems, the bandgap decreases in the order of m = 1, 2, 3, 4, 5, while the bandgap increases in the order of m = 5, 6, 7, 8, 9. We also investigate the (SrTiO₃)_m/(NaTaO₃)_m systems (m = 1, 2, 3, 4, 5, 6, 7), and the calculated results suggest that the (SrTiO₃)₆/(NaTaO₃)₆ system has the smallest bandgap of 2.58 eV in our considered systems. This study indicates the development of SrTiO₃/NaTaO₃ heterojunction is a promising way to improve the photocatalytic activities of SrTiO₃ and NaTaO₃.     

Synthesis and applications of porous spg (shirasu porous glass) microspheres

Fairly uniform porous microspheres of poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) were synthesized using a particular microporous glass membrane (SPG). Average diameters of these spheres are from 2.5 to 38 μm with the coefficient of variation (CV) around 10%. A maximum specific surface area of 370 m² /g was achieved. Uniform dispersion of MMA droplets was successfully prepared only when the swelling process reported by Higuchi and Misra was adopted. Two potential applications, one as a packing material for column chromatography, and the other as a carrier of enzyme immobilization, were demonstrated.     

Construction of 3D hierarchical SnO2 microspheres from porous nanosheets towards NO decomposition

Three-dimensional (3D) hierarchical architectures are currently attracting worldwide interest owing to their fascinating morphology-dependent properties and potential applications. Herein we constructed SnO₂ microspheres with 3D hierarchical flower-like architectures self-assembled with porous SnS₂ nanosheets by a facile hydrothermal method with subsequent calcination. The chemical and physical properties as well as photocatalytic application of SnO₂ microspheres were investigated. The size and morphology were examined with scanning electron microscopy and transmission electron microscopy. The phase and crystalline structure were determined with powder X-ray diffraction. The UV–Vis absorption property was determined with UV–Vis diffuse reflectance. The photocatalytic activities were evaluated with nitrogen monoxide (NO) decomposition under UV–Vis light irradiation. The effects of calcination temperature on morphology and NO decomposition were also studied.     

Preparation of PLGA microspheres with different porous morphologies

Poly(D,L-lactide-co-glycolide)(PLGA) microspheres were prepared by emulsion solvent evaporation method. The influences of inner aqueous phase, organic solvent, PLGA concentration on the morphology of microspheres were studied. The results showed that addition of porogen or surfactants to the inner aqueous phase, types of organic solvents and polymer concentration affected greatly the microsphere morphology. When dichloromethane was adopted as organic solvent, microspheres with porous structure were produced. When ethyl acetate served as organic solvent, two different morphologies were obtained. One was hollow microspheres with thin porous shell under a lower PLGA concentration, another was erythrocyte-like microspheres under a higher PLGA concentration. Three types of microspheres including porous, hollow core with thin porous shell(denoted by hollow in brief) and solid structures were finally selected for in vitro drug release tests. Bovine serum albumin(BSA) was chosen as model drug and encapsulated within the microspheres. The BSA encapsulation efficiency of porous, hollow and solid microspheres was respectively 90.4%, 79.8% and 0. And the ultimate accumulative release was respectively 74.5%, 58.9% and 0. The release rate of porous microspheres was much slower than that of hollow microspheres. The experiment results indicated that microspheres with different porous structures showed great potentials in controlling drug release behavior.     

Designing PbSe nanowires and nanorings through oriented attachment of nanoparticles

Single-crystal PbSe nanowires are synthesized in solution through oriented attachment of nanocrystal building blocks. Reaction temperatures of 190-250 degrees C and multicomponent surfactant mixtures result in a nearly defect-free crystal lattice and high uniformity of nanowire diameter along the entire length. The wires' dimensions are tuned by tailoring reaction conditions in a range from approximately 4 to approximately 20 nm in diameter with wire lengths up to approximately 30 microm. PbSe nanocrystals bind to each other on either {100}, {110}, or {111} faces, depending on the surfactant molecules present in the reaction solution. While PbSe nanocrystals have the centrosymmetric rocksalt lattice, they can lack central symmetry due to a noncentrosymmetric arrangement of Pb- and Se-terminated {111} facets and possess dipole driving one-dimensional oriented attachment of nanocrystals to form nanowires. In addition to straight nanowires, zigzag, helical, branched, and tapered nanowires as well as single-crystal nanorings can be controllably prepared in one-pot reactions by careful adjustment of the reaction conditions.     

Evolution of single crystalline dendrites from nanoparticles through oriented attachment

Single crystalline PbMoO4 dendrites were prepared by a simple hydrothermal method in the presence of surfactants. The formation and evolution of these dendrites was investigated by transmission electron microscopy, and the results clearly showed that the dendritic structure was achieved through oriented attachment of nanoparticles along crystallographically specific direction while the traditional Ostwald ripening mechanism also acted to form the initial particles before attachment and smooth the morphology of the dendrites after attachment.