Synthesis of atomically ordered AuCu and AuCu(3) nanocrystals from bimetallic nanoparticle precursors

A new multistep approach was developed to synthesize atomically ordered intermetallic nanocrystals, using AuCu and AuCu(3) as model systems. Bimetallic nanoparticle aggregates are used as precursors to atomically ordered nanocrystals, both to precisely define the stoichiometry of the final product and to ensure that atomic-scale diffusion distances lower the reaction temperatures to prevent sintering. In a typical synthesis, PVP-stabilized Au-Cu nanoparticle aggregates synthesized by borohydride reduction are collected by centrifugation and annealed in powder form. At temperatures below 175 degrees C, diffusion of Cu into Au occurs, and the atomically disordered solid solution Cu(x)Au(1)(-)(x) exists. For AuCu, nucleation occurs by 200 degrees C, and atomically ordered AuCu exists between 200 and 400 degrees C. For AuCu(3), an AuCu intermediate nucleates at 200 degrees C, and further diffusion of Cu into the AuCu intermediate at 300 degrees C nucleates AuCu(3). Atomically ordered AuCu and AuCu(3) nanocrystals can be redispersed as discrete colloids in solution after annealing between 200 and 300 degrees C.     

Low-temperature polyol synthesis of AuCuSn2 and AuNiSn2: using solution chemistry to access ternary intermetallic compounds as nanocrystals

Ternary intermetallic compounds, which possess a wide variety of important properties with both academic and technological relevance, are typically synthesized using traditional high-temperature methods. Here, we demonstrate that the polyol method, which is used extensively to synthesize nanocrystals and nanocrystalline powders of metals and simple binary compounds, serves as an effective low-temperature exploratory medium for synthesizing new ordered ternary intermetallics as nanocrystals. Accordingly, we describe the synthesis and structural characterization of AuCuSn2 and AuNiSn2, which adopt an ordered NiAs-type superstructure that is not observed using equilibrium synthetic methods. AuCuSn2 forms in solution of 120 degrees C as well-formed nanocrystals, and the ordered phase is stable up to 450 degrees C. AuNiSn2 behaves similarly to AuCuSn2.     

Low-temperature solution synthesis of the non-equilibrium ordered intermetallic compounds Au3Fe, Au3Co, and Au3Ni as nanocrystals

Alloys and intermetallic compounds of Au with the 3d transition metals Fe, Co, and Ni are nonequilibrium phases that have many useful potential applications as catalytic, magnetic, optic, and multifunctional magneto-optic materials. However, the atomically ordered Au-M (M = Fe, Co, Ni) intermetallics are particularly elusive from a synthetic standpoint. Here we report the low-temperature solution synthesis of the L12 (Cu3Au-type) intermetallic compounds Au3Fe, Au3Co, and Au3Ni using n-butyllithium as a reducing agent. Reaction pathway studies for the Au3Co system indicate that Au nucleates first, followed by Co incorporation to form the intermetallic. The nonequilibrium intermetallic nanocrystals have been characterized by powder XRD, TEM, EDS, selected area electron diffraction, and nanobeam electron diffraction, which collectively confirm the compositions and superlattice structures.     

Galvanic replacement reactions of active-metal nanoparticles

We present a systemic investigation of a galvanic replacement technique in which active-metal nanoparticles are used as sacrificial seeds. We found that different nanostructures can be controllably synthesized by varying the type of more noble-metal ions and liquid medium. Specifically, nano-heterostructures of noble metal (Ag, Au) or Cu nanocrystals on active-metal (Mg, Zn) cores were obtained by the reaction of active-metal nanoparticles with more noble-metal ions in ethanol; Ag nanocrystal arrays were produced by the reaction of active-metal nanoparticles with Ag(+) ions in water; spongy Au nanospheres were generated by the reaction of active-metal nanoparticles with AuCl(4)(-) ions in water; and SnO(2) nanoparticles were prepared when Sn(2+) were used as the oxidant ions. The key factors determining the product morphology are shown to be the reactivity of the liquid medium and the nature of the oxidant-reductant couple, whereas Mg and Zn nanoparticles played similar roles in achieving various nanostructures. When microsized Mg and Zn particles were used as seeds in similar reactions, the products were mainly noble-metal dendrites. The new approach proposed in this study expands the capability of the conventional nanoscale galvanic replacement method and provides new avenues to various structures, which are expected to have many potential applications in catalysis, optoelectronics, and biomedicine.     

Synthesis of Cu3Sn Alloy Nanocrystals through Sequential Reduction Induced by Gradual Increase of the Reaction Temperature

Cu₃Sn alloy nanocrystals are synthesized by sequential reduction of Cu and Sn precursors through a gradual increase of the reaction temperature. By transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDS), UV/Vis spectroscopy, and X‐ray diffraction (XRD) analyses, the alloy formation mechanism of Cu₃Sn nanocrystals has been studied. The incremental increase of the reaction temperature sequentially induces the reduction of Sn, the diffusion of Sn into the preformed Cu nanocrystals, resulting in the intermediate phase of Cu–Sn alloy nanocrystals, and then the formation of Cu₃Sn alloy nanocrystals. We anticipate that the synthesis of Cu₃Sn alloy nanocrystals encourages studies toward the synthesis of various alloy nanomaterials.     

【撤稿】Au纳米颗粒二维超晶格结构的稳定性

We synthesized 5.5 nm Au nanocrystals coated by dodecanethiol (C₁₂SH₂₆) by reverse micelle method. The Au nanocrystals are multiply twinned particles (MTP), which are mainly characterized by decahedral and icosahedral structures. The 2D hexagonal network self-organizationa of Au nanocrystals are realized on both amorphous carbon (AC) and highly oriented pyrolitic graphite (HOPG) surfaces. The stability of 2D superlattices of Au nanocrystals in vacuum has been systematically surveyed, and it is found that large single triangular nanocrystals have been formed after 75 days due to the coalescence among the neighboring nanoparticles and the rearrangement of the atomics. When the Au nanocrystals in 2D organizations are annealed in air (573 K, 15 min), higher ordered 2D self-assemblies are stable, whereas worm-like coalesced nanoparticles form in those less ordered organizations. This demonstrates that the thermal stability of 2D self-assemblies is determined by the level of nanocrystals ordering.     

Reacting the unreactive: a toolbox of low-temperature solution-mediated reactions for the facile interconversion of nanocrystalline intermetallic compounds

Metallurgical materials, including intermetallic compounds, are notoriously inert toward low-temperature reactivity. However, as nanocrystals, their reactivity is significantly enhanced. Here we show that intermetallic PtSn and AuCu nanocrystals can be converted, in solution at low temperatures, into derivative intermetallics. For example, PtSn can be converted into PtSn2 and Pt3Sn by reaction with SnCl2 and K2PtCl6, respectively. The reactions are also reversible, for example, the sequences PtSn --> PtSn2 --> PtSn and PtSn --> Pt3Sn --> PtSn are all readily achievable. The strategy also allows nanocrystalline AuCu to be successfully converted into AuCu3 via reaction with Cu(C2H3O2)2.H2O, suggesting that this approach may be general.     

ZnO纳米管有序阵列与Cu2O纳米晶核壳结构的光电化学性能及全固态纳米结构太阳电池研究简

采用电化学方法在铟锡氧化物(ITO)导电玻璃基底上制备了高度有序的ZnO纳米管阵列,然后在ZnO纳米管阵列上电化学沉积Cu2O纳米晶颗粒,获得了一维有序Cu2O/ZnO核壳式纳米阵列结构,通过控制Cu2O纳米晶的沉积电量得到不同厚度的Cu2O壳层,并对该核壳式纳米阵列的形貌和结构进行了分析. 以Cu2O/ZnO一维核壳式纳米阵列结构为光电极组装全固态纳米结构太阳电池,研究了Cu2O壳层厚度对光电极光吸收性能、光电性能以及组装电池光伏性能的影响,优化了电池中对电极材料的喷金厚度. 结果表明,以Cu2O沉积电量为1.5 C的Cu2O/ZnO为光活性层,以4 mA电流下真空镀金20~25 min的铜基底为对电极组装的简易太阳电池最高可获得0.013%的光电转换效率.     

Bimetallic Pd/Sn-based Nanoparticles and their Catalytic Properties in the Semihydrogenation of Diphenylacetylene

Multimetallic nanoparticles often enhance the catalytic performance of their monometallic counterparts by increasing reaction rates, catalyst selectivity, and/or stability. A prerequisite for understanding structure- and composition-associated properties, however, is the careful design of multimetallic nanoparticles with various structures and compositions. Here, bimetallic Pd/Sn-based nanoparticles are prepared with a tunable composition and structure exploiting ionic liquids (ILs) as reaction medium (i. e., methyltrioctylammonium bis(trifluoromethylsulfonyl)imide). The nanoparticles are obtained in a one-pot synthetic procedure by reducing the metal salt precursors with triethylborohydride in the IL. The results show that the reaction parameters, in particular the nature and ratio of the Pd²⁺/Sn²⁺ precursors as well as the reaction temperature, influence NP formation and composition. X-ray diffraction with Rietveld analysis and transmission electron microscopy are employed to determine NP size and phase composition. Under optimized reaction conditions Pd₂Sn or PdSn nanocrystals are formed as single-phase products after introducing an additional annealing step at 200 °C. Nanocrystals with intermetallic composition reveal enhanced catalytic properties in the semihydrogenation of diphenylacetylene which was used as a model reaction.     

Enhancement of the stability and reaction rate by thenoyl and CF3 groups in the formation of gold nanocrystals using β-diketones

We describe a synthetic route for the high yield production of Au nanomaterials via a simple one step reduction process. Thenoyltrifluoroacetone was used as a reducing and stabilizing agent as well for the synthesis of gold nanoparticles. The reaction rate for the formation of Au nanoparticles using thenoyltrifluoroacetone was much faster than that of any other β-diketones such as acetylacetone. By simply varying the reaction temperature and the concentration, the shape and size of the resulting Au nanocrystals were easily controlled. The colloidal state of the Au nanocrystals in water lasts several weeks without any spectral changes.     

A facile method for gold decoration of Te@CdTe nanorods in aqueous solution

Colloidal synthesis of metal-semiconductor hybrid nanostructures is mainly achieved in organic solution. In some applications of hybrid nanoparticles relevant in aqueous media, phase transfer of hydrophobic metal-semiconductor hybrid nanostructures is essential. In this work, we present a simple method for direct synthesis of water-soluble gold (Au) decorated Te@CdTe hybrid nanorods (NRs) at room temperature by using aqueous Te@CdTe NRs as templates, which were preformed by using CdTe nanocrystals (NCs) as precursor in the presence of hydrazine hydrate (N(2)H(4)). Our results showed that NRs were decorated with Au islands both on tips and along the surface of the NRs. The size and density of Au islands can be controlled by varying the amount of Au precursor (mixture of HAuCl(4) and thioglycolic acid (TGA)) and TGA/HAuCl(4) ratio. A possible growth mechanism for the Au decoration of Te@CdTe NRs is concluded as three steps: (1) the formation of AuTe(1.7) via the substitution reaction of Cd(2+) by Au(3+), (2) adsorption of Au-TGA complex onto the preformed AuTe(1.7) anchors and following reduction by CdTe and N(2)H(4), leading to the formation of small Au NCs, (3) Au NCs grow to bigger ones, followed by reduction of more Au precursor by N(2)H(4).     

银金硫三元团簇的形成与光过程的硫金敏化

采用激光烧蚀银金硫混合物样品产生团簇离子,用飞行时间质谱仪检测的方法研究了银金硫三元团簇离子的形成。研究表明,银硫二元团簇、金硫二元团簇和银金硫三元团簇同时生成,主要系列有(Ag~2~n~+~1S~n~-~1)^+、(Ag~2~n~-~1S~n)^-、(Ag~2~nAuS~n)^+和(Ag~2~nAuS~n~+~1)^-。将其与感光乳剂中的金硫敏化中心相关联,指出正离子团簇和负离子团簇分别在曝光过程中起着光电子陷阱和正空穴陷阱的作用。     

铂基金属间化合物纳米晶的最新进展:可控合成与电催化应用

铂基金属间化合物纳米晶因其高度有序的结构特点,优异的抗氧化及耐腐蚀性能,作为电极材料被广泛应用于各类电催化反应,目前已有的PtCo金属间化合物纳米晶在燃料电池阴极反应(氧还原反应)中的活性和稳定性均达到了美国能源部(DOE) 2020年的目标。为了进一步提高金属间化合物纳米晶的电催化性能,需要对影响纳米晶电催化性能的因素进行深入研究。本文综述了铂基金属间化合物纳米晶的研究现状,着重介绍了铂基金属间化合物的可控合成策略及其在电催化领域的最新研究进展,分析总结了该领域存在的问题,并展望了其未来发展方向。     

Synthesis and shape control of CuInS(2) nanoparticles

Cu(2)S-CuInS(2) hybrid nanostructures as well as pure CuInS(2) (CIS) nanocrystals were synthesized by methods of colloidal chemistry. The structure, the shape and the composition of these nanomaterials were investigated with transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). By changing the reaction conditions, CuInS(2) nanorods with different aspect ratio, dimeric nanorods as well as hexagonal discs and P-shaped particles could be synthesized. Under our reaction conditions, CIS nanoparticles crystallize in the hexagonal wurtzite structure, as confirmed by Rietveld analysis of the X-ray diffraction patterns. The formation of Cu(2)S-CuInS(2) hybrid nanostructures turned out to be an essential intermediate step in the growth of CIS nanoparticles, the copper sulphide part of the hybrid material playing an important role in the shape control of the CIS nanocrystals. By a treatment of Cu(2)S-CuInS(2) with 1,10-phenanthroline, Cu(2)S parts of the hybrid nanostructures could be removed, and pure CIS nanoparticles with shapes not accessible with other methods can be obtained. Our synthetic procedure turned out to be suitable to synthesize also other compounds, like CuInS(2)-ZnS alloys, and to modify, in this way, the optical properties of the nanocrystals.     

高载量PtNi金属间化合物的氧还原电催化性能

采用改进的多元醇法制备了PtNi(原子比1∶1)质量分数为60%的高金属载量碳载PtNi合金(PtNi/C), 通过在450 ℃下退火处理获得了碳载PtNi金属间化合物氧还原电催化剂. 该催化剂对氧还原的质量比活性和面积比活性分别是商业化Pt/C(JM Pt/C)催化剂的1.66和2.3倍; 并且加速耐久性测试后PtNi金属间化合物催化剂的质量比活性仍与Pt/C的初始性能相当, 耐久性得到了大幅提升. PtNi/C金属间化合物催化剂氧还原活性和稳定性的提高归因于PtNi的有序原子排布结构及催化剂表面零价金属含量的提高.     

Deposition of gold nanoparticles on silica spheres by electroless metal plating technique

A previously proposed method for metal deposition with silver [Kobayashi et al., Chem. Mater. 13 (2001) 1630] was extended to uniform deposition of gold nanoparticles on submicrometer-sized silica spheres. The present method consisted of three steps: (1) the adsorption of Sn(2+) ions took place on surface of silica particles, (2) Ag(+) ions added were reduced and simultaneously adsorbed to the surface, while Sn(2+) was oxidized to Sn(4+), and (3) Au(+) ions added were reduced and deposited on the Ag surface. TEM observation, X-ray diffractometry, and UV-vis absorption spectroscopy revealed that gold metal nanoparticles with an average particle size of 13 nm and a crystal size of 5.1 nm were formed on the silica spheres with a size of 273 nm at an Au concentration of 0.77 M.     

Ca6Cu2Sn7: novel 3D open framework with unusual Sn4 tetramers

The new ternary polar intermetallic phase, Ca6Cu2Sn7, has been synthesized by the solid-state reaction of the stoichiometric mixture of the pure elements in welded Ta tubes at high temperature. Its structure was established by single-crystal X-ray diffraction studies. Ca6Cu2Sn7 crystallizes in the monoclinic space group C2/m (No. 12) with cell parameters of a=14.257(7), b=4.564(2), and c=12.376(7) A, beta=93.979(6) degrees, V=803.3(7) A3, and Z=2. The structure of Ca6Cu2Sn7 belongs to a new structure type and features a 3D anionic open-framework composed of [Cu2Sn3] layers interconnected by unusual Sn4 tetramers, forming large tunnels along the b axis which are composed of Cu4Sn12 16-membered rings. The calcium atoms are located in these large tunnels. Ca6Cu2Sn7 is metallic and exhibits temperature-independent paramagnetism.     

Wet chemical synthesis and a combined X-ray and Mössbauer study of the formation of FeSb2 nanoparticles

Understanding how solids form is a challenging task, and few strategies allow for elucidation of reaction pathways that are useful for designing the synthesis of solids. Here, we report a powerful solution-mediated approach for formation of nanocrystals of the thermoelectrically promising FeSb(2) that uses activated metal nanoparticles as precursors. The small particle size of the reactants ensures minimum diffusion paths, low activation barriers, and low reaction temperatures, thereby eliminating solid-solid diffusion as the rate-limiting step in conventional bulk-scale solid-state synthesis. A time- and temperature-dependent study of formation of nanoparticular FeSb(2) by X-ray powder diffraction and iron-57 M?ssbauer spectroscopy showed the incipient formation of the binary phase in the temperature range of 200-250 °C.     

Intermetallic phase formation in electrochemical alloy deposition

Three examples of the electrochemical deposition of intermetallic phases are shown. Electrodeposition of the single-phase -brass superlattice at underpotentials of Zn in Cu-Zn alloy plating is explained by an accumulative underpotential deposition (UPD) mechanism. Growth of the Cu-Sn intermetallic phase layer in the contact immersion deposition of Sn onto Cu is accounted for by a UPD/vertical solid-state diffusion mechanism. Ag₃Sn formation in the Sn/Ag-nanoparticle composite plating is illustrated by atomic site exchange at the interface between the deposited Sn matrix and the occluded Ag nanoparticles.     

Upconversion emission enhancement of Gd3+ ions induced by surface plasmon field in Au@NaYF4 nanostructures codoped with Gd(3+)-Yb(3+)-Tm(3+) ions

Au nanoparticles (NPs) attached β-NaYF(4) nanocrystals codoped with Gd(3+)-Yb(3+)-Tm(3+) were synthesized by a facial solution method. The UV-vis-near-infrared absorption spectrum shows typical surface plasmon resonance band of Au NPs in addition to the characteristic absorption peaks of Yb(3+) ion. X-ray diffraction and selected area electron diffraction results indicate the existence of Au NPs. The transmission electron microscopic image reveals the formation of Au@NaYF(4) nanostructures. Enhanced ultraviolet (UV) upconversion luminescence (UCL) was observed in the nanostructures under the excitation of 980-nm infrared laser. The largest enhancement factor was obtained as 76 for the (6)I(J)→(8)S(7/2) emission of Gd(3+) ions, which was much larger than those emission enhancement factors of Tm(3+). It is for the first time to our knowledge that the emission enhancement of Gd(3+) ions was obtained. Local field enhancement induced by Au NPs was found to be responsible for the UCL enhancement, which is the further experimental evidence of local field enhancement theory. Magnetic measurements of the Au@NaYF(4) nanostructure indicated it would have potential application in magnetic resonance imaging.