高效稀土上转换纳米晶体合成

详细介绍了上转换纳米晶体的主要合成方法及其优缺点.共沉淀法具有产率高、易大规模制备等优点,但后续需要煅烧结晶,晶体形貌控制较差.水热/溶剂热法能够制备结晶性良好、尺寸均一的纳米晶体,但其发光性能的可调控性相对较差.热分解法能够获得粒径均一的纳米晶体,但需要使用预先制备的金属前驱体.晶种介导的高温生长法和阳离子交换法均可优化晶体的形貌与功能,易获得尺寸分布均一、光学性能优异的上转换纳米晶体.通过主体材料优化、纳米晶体结构设计和仿真设计指导等方法,可以有效提高纳米晶体的发光效率,优化后合成的纳米晶体在生物成像和疾病诊断中展示出良好的应用前景.

电催化二氧化碳还原用铜基催化剂设计策略

随着全球经济增长,对能源需求不断攀升,进而推动了能源的开发与利用,不可避免导致CO_(2)排放量的持续上升。为有效应对这一环境挑战,电催化CO_(2)还原(CO_(2)RR)技术应运而生,并迅速成为研究热点。该技术不仅可将CO_(2)转换为燃料和化学品,而且有助于实现可再生能源储存。在众多催化剂中,铜基催化剂因其能高效将CO_(2)直接转化为高价值多碳化学品(如乙烯和乙醇)而受到关注。近年来,铜基CO_(2)RR催化剂优化设计进展显著,主要集中在提高催化活性、选择性和稳定性上。重点综述了近年来电催化CO_(2)RR用铜基催化剂的优化设计策略研究进展。从调控催化活性和选择性以及稳定性2方面,分别讨论了晶面工程、合金化处理、铜氧化态调节、催化剂表面功能化和缺陷工程等代表性调控策略的研究进展,探讨了电催化剂的核心参数(组成、微观结构、形貌、尺寸等)对催化剂性能的协同效应。最后对未来电催化CO_(2)RR技术的发展前景进行展望,并分析当前面临的挑战。

Synthesis of γ-Al_2O_3 nanoparticles by chemical precipitation method

Highly pure active γ-Al2O3 nanoparticles were synthesized from aluminum nitrate and ammonium carbonate with a little surfactant by chemical precipitation method. The factors affecting the synthesis process were studied. The properties of γ-Al2O3 nanoparticles were characterized by DTA, XRD, BET, TEM, laser granularity analysis and impurity content analysis. The results show that the amorphous precursor AI（OH）3 sols are produced by using 0.1 mol/L Al（NO3）3·9H2O and 0.16 mol/L （NH4）2CO3·H2O reaction solutions, according to the volume ratio 1.33, adding 0.024%（volume fraction） surfactant PEG600, and reacting at 40℃, 1000 r/min stirring rate for 15min. Then, after stabilizing for 24 h, the precursors were extracted and filtrated by vacuum, washed thoroughly with deionized water and dehydrated ethanol, dried in vacuum at 80℃ for 8h, final calcined at 800℃ for 1h in the air, and high purity active γ-Al2O3 nanoparticles can be prepared with cubic in crystal system, OH^7-FD3M in space group, about 9 nm in crystal grain size, about 20 nm in particle size and uniform size distribution, 131.35 m^2/g in BET specific surface area, 7 - 11 nm in pore diameter, and not lower than 99.93% in purity.

Surfactant-assisted synthesis and magnetic properties of monodispersed manganese ferrite nanocrystals

Monodispersed manganese ferrite （MnFe2O4） nanocrystals could be successfully synthesized in large quantities via a facile synthetic technique based on the pyrolysis of organometallic compound precursor, in which octadecene was used as solvent, and oleic acid and oleylamine were used as capping ligands. MnFe204 nanocrystals were obtained with size in a tunable range of 4- 15 nm and their morphologies could be tuned from spherical to triangle-shaped by varying the surfactants. The phase structure, morphology, and size of the products were characterized in detail by X-ray diffraction （XRD） and transmission electron microscopy （TEM）. Magnetic properties of MnFe2O4 nanocrystals with different morphologies were measured using a superconducting quantum interference device （SQUID）. Both monodisperse MnFe204 nanocrystals with spherical and triangle-shapes are superparamagnetic at room temperature while ferromagnetic at 2 K. The pyrolysis method may provide an effective route to synthesize other spinel ferrites or metal oxides nanocrystals.

Monodisperse Upconversion NaYF4 Nanocrystals： Syntheses and Bioapplications

A facile strategy using cheap and readily available precursors has been successfully developed for the synthesis of rare-earth doped hexagonal phase NaYF4 nanocrystals with uniform shape and small particle size as well as strong photoluminescence. Due to their optical properties and good biocornpatibility, these multicolor nanocrystals were successfully used as a bio-tag for cancer cell imaging. This novel synthetic method should also be capable of extension to the synthesis of other fluoride nanocrystals such as YF3 and LaF3.

Synthesis and characterization of water-soluble magnetite nanocrystals via one-step sol-gel pathway

Water-soluble magnetite nanocrystals have been prepared by one-step non-alkoxide sol-gel method.The magnetic properties of magnetite nanocrystals obtained are size dependent.The experimental results also reveal that 2-pyrrolidone not only serves as solvent,but also involves surface coordination which renders the magnetite nanoparticles water-soluble and colloidal solution stable.Although the current synthetic approach is a small modification to the non-alkoxide sol-gel method,it allows us to directly obtain high-quality water-soluble magnetic nanocrystals.In addition,we realize that this method could be easily extended to preparation of many other transition and main group metal oxide water-soluble nanocrystals only from simple metal ion salts.

Synthesis of Monodisperse CexZr1-xO2 Nanocrystals and the Size-Dependent Enhancement of Their Properties

Monodisperse CexZr1-xO2 nanocrystals have been synthesized using a simple two-phase approach; adjusting the ratio of precursors used, amount of capping agent used, reaction time and temperature affords precise control over their composition, structure and size. Size-dependent enhancement of oxygen-storage capacity and kinetics of oxygen storage and release were observed. Systematic studies were conducted in order to understand the size-dependent enhancement of these properties. This work provides important insights into the synthesis and fundamental understanding of multi-component nanocrystals with a large variety of applications.

Synthesis of NiFe_2O_4 nanoparticles by a low temperature microwave-assisted ball milling technique

Nanocrystalline NiFe2O4 particles with mean size of about 20 nm were directly synthesized by a novel microwave-assisted ball-milling approach, using basic nickel carbonate and iron powders as the raw materials. The results showed that an interme- diate product Fe2Ni2（OH）sCO3 · 2H2O was formed by milling NiCO3 · 2Ni（OH）2· 4H2O and Fe powders with microwave assis- tance, then this intermediate product further reacted to form NiFe2O4 nanocrystals. On the other hand, by using NiO and Fe2O3 as the raw materials, NiFe2O4 could not be able to form. NiFe2O4 nanocrystals could be directly synthesized without post-sintering by this process. This makes it a new promising approach for ferrite nanoparticle, which is simple and environ- mentally friendly.

Synthesis of Pd Nanocrystals Enclosed by {100} Facets and with Sizes 〈10 nm for Application in CO Oxidation

The catalytic activity of noble-metal nanocrystals is mainly determined by their sizes and the facets exposed on the surface. For single crystals, it has been demonstrated that the Pd（100） surface is catalytically more active than both Pd（110） and Pd（111） surfaces for the CO oxidation reaction. Here we report the synthesis of Pd nanocrystals enclosed by {100} facets with controllable sizes in the range of 6-18 nm by manipulating the rate of reduction of the precursor. UV-vis spectroscopy studies indicate that the rate of reduction of Na2PdC14 can be controlled by adjusting the concentrations of Br- and C1- ions added to the reaction mixture. Pd nanocrystals with different sizes were immobilized on ZnO nanowires and evaluated as catalysts for CO oxidation. We found that the activity of this catalytic system for CO oxidation showed a strong dependence on the nanocrystal size. When the size of the Pd nanocrystals was reduced from 18 nm to 6 nm, the maximum conversion rate was significantly enhanced by a factor of -10 and the corresponding maximum conversion temperature was lowered by -80℃.

Effective Approach for the Synthesis of Monodisperse Magnetic Nanocrystals and M-Fe3O4 （M = Ag, Au, Pt, Pd） Heterostructures

Monodisperse and size-tunable magnetic iron oxide nanoparticles （NPs） have been synthesized by thermal decomposition of an iron oleate complex at 310 ℃ in the presence of oleylamine and oleic acid. The diameters of the as-synthesized iron oxide NPs decrease with increasing concentrations of iron oleate complex and oleic acid/oleylamine. In addition, the size-dependent crystallinity and magnetic properties of iron oxide NPs are presented. It is found that larger iron oxide NPs have a higher degree of crystallinity and saturation magnetization. More importantly, various M-iron oxide heterostructures （M = Au, Ag, Pt, Pd） have been successfully fabricated by using the same synthesis procedure. The iron oxide NPs are grown over the pre-made metal seeds through a seed-mediated growth process. The physicochemical properties of Au-Fe3O4 heterostructures have been characterized by X-ray diffraction （XRD）, superconducting quantum interference device （SQUID） magnetometry and UV-vis spectroscopy. The as-synthesized Au-Fe3O4 heterostructures show a red-shift in surface plasmon resonance peak compared with Au NPs and similar magnetic properties to Fe3O4 NPs. The heterojunction effects present in such nanostructures offer the opportunity to tune the irphysicochemical properties. Therefore, this synthesis process can be regarded as an efficient way to fabricate a series of heterostructures for a variety of applications.

Sodium lanthanide fluoride core-shell nanocrystals： A general perspective on epitaxial shell growth

Understanding the structural characteristics and growth mechanism（s） are essen-tial for generating core-shell nano-heterostructures with distinctive properties. Especially in lanthanide-based nanocrystals, rational design of the core-shell composition can be utilized to enhance/tune the optical properties of the final nanostructure, or can be used to integrate multiple functional applications （e.g., luminescent/magnetic）. In this article, we review the progress in our current understanding of the epitaxial shell growth in sodium lanthanide fluoride （NaLnF4） nanocrystals. In order to understand epitaxial shell growth the core nanocrystals have to be uniform, and to date the synthesis of high quality near uniform size/shape dispersion controlled synthesis of lanthanide-based nanocrystals has been achieved mainly with this class of nanocrystals. The progress in core-shell synthesis and the epitaxial shell growth mechanism in this class of nanocrystals （NaLnF4） are reviewed, and a general perspective is provided on the core-shell morphology based on different characterization techniques. While there has been tremendous progress in studying the impact of core-shell structures in various functional applications, this review also highlights, in our view, the still limited understanding of ways to control the core-shell morphology and it emphasizes some important, unanswered questions that remain to be addressed to maximize their performance.

Thorium/uranium mixed oxide nanocrystals： Synthesis, structural characterization and magnetic properties

One of the primary aims of the actinide community within nanoscience is to develop a good understanding similar to what is currently the case for stable elements. As a consequence, efficient, reliable and versatile synthesis techniques dedicated to the formation of new actinide-based nano-objects （e.g., nanocrystals） are necessary. Hence, a ＂library＂ dedicated to the preparation of various actinidebased nanoscale building blocks is currently being developed. Nanoscale building blocks with tunable sizes, shapes and compositions are of prime importance. So far, the non-aqueous synthesis method in highly coordinating organic media is the only approach which has demonstrated the capability to provide size and shape control of actinide-based nanocrystals （both for thorium and uranium, and recently extended to neptunium and plutonium）. In this paper, we demonstrate that the non-aqueous approach is also well adapted to control the chemical composition of the nanocrystals obtained when mixing two different actinides. Indeed, the controlled hot co-injection of thorium acetylacetonate and uranyl acetate （together with additional capping agents） into benzyl ether can be used to synthesize thorium/uranium mixed oxide nanocrystals covering the full compositional spectrum. Additionally, we found that both size and shape are modified as a function of the thorium：uranium ratio. Finally, the magnetic properties of the different thorium/uranium mixed oxide nanocrystals were investigated. Contrary to several reports, we did not observe any ferromagnetic behavior. As a consequence, ferromagnetism cannot be described as a universal feature of nanocrystals of non-magnetic oxides as recently claimed in the literature.

Shape-controlled syntheses of rhodium nanocrystals for the enhancement of their catalytic properties

Rhodium （Rh） is a critical component of many catalysts for a variety of chemical transformation processes. Controlling the shape of Rh nanocrystals offers an effective route to the optimization of their catalytic performance owing to a close correlation between the catalytic activity/selectivity and the surface atomic structure. It also helps to substantially reduce the loading amount and thus achieve a sustainable use of this scarce and precious metal. In this review article, we focus on recent progress in the shape-controlled synthesis of Rh nanocrystals with the goal of enhandng their catalytic properties. Both traditional and newly- developed synthetic strategies and growth mechanisms will be discussed, including those based on the use of surface capping agents, manipulation of reduction kinetics, control of surface diffusion rate, management of oxidation etching, and electrochemical alteration. We also use two examples to highlight the unique opportunities offered by shape-controlled synthesis for enhancing the use of this metal in catalytic applications. The strategies can also be extended to other precious metals in an effort to advance the production of cost-effective catalysts.

Sodium carbonate-assisted synthesis of hierarchically porous single-crystalline nanosized zeolites

Hierarchically porous single-crystalline nanosized zeolites as heterogeneous catalysts show great poten- tial in fine chemistry because they offer more rich hierarchically porous channels for the mass transfer and molecular diffusion. However, the synthesis of hierarchically porous nanosized zeolites generally requires the assistance of templates acting as the mesoporogens, which limits its popularity. Herein, we report a one-pot and template-free synthesis of hierarchically porous single-crystalline nanosized zeolite beta only by introducing sodium carbonate in precursor solution. The resulted sample features the extraordinary properties, including the uniform nanocrystal （200-300 nm）, high pore volume （0.65 cm3g 1） and the hierarchical pore-size distribution （e.g., 2-8 and 90-150 nm）. After slicing pro- cessing, it is interestingly found that a large number of interconnected mesopores penetrate throughout whole material, which enables the hierarchically porous nanosized zeolite beta remarkably superior cat- alytic activity than the conventional zeolite beta in condensation of henzaldehyde with ethanol at room temperature. More importantly, this one-pot sodium carbonate-assisted synthetic strategy is highly ver- satile, which has also been successfully developed to synthesize hierarchically porous nanosized single- crystalline zeolites ZSM-5 and TS.