溶剂热法制备硒化铅亚微米八面体

在聚乙烯吡咯烷酮K30(PVP)存在下,采用溶剂热法成功地合成出立方相硒化铅(PbSe)纳米晶。分别用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对样品的形貌和晶体结构进行了表征分析。SEM结果表明样品为大量的尺寸均一的八面体形状的纳米晶,经XRD分析证明,八面体状的纳米晶是立方相PbSe。进一步考察了反应时间对样品形貌的影响,并分析了PbSe亚微米八面体的生长机制。     

Epitaxial overgrowth of platinum on palladium nanocrystals

This paper describes a systematic study on the epitaxial overgrowth of Pt on well-defined Pd nanocrystals with different shapes (and exposed facets), including regular octahedrons, truncated octahedrons, and cubes. Two different reducing agents, i.e., citric acid and L-ascorbic acid, were evaluated and compared for the reduction of K?PtCl? in an aqueous solution in the presence of Pd nanocrystal seeds. When citric acid was used as a reducing agent, conformal overgrowth of octahedral Pt shells on regular and truncated octahedrons of Pd led to the formation of Pd-Pt core-shell octahedrons, while non-conformal overgrowth of Pt on cubic Pd seeds resulted in the formation of an incomplete octahedral Pt shell. On the contrary, localized overgrowth of Pt branches was observed when L-ascorbic acid was used as a reducing agent regardless of the facets expressed on the surface of Pd nanocrystal seeds. This work shows that both the binding affinity of a reducing agent to the Pt surface and the reduction kinetics for a Pt precursor play important roles in determining the mode of Pt overgrowth on Pd nanocrystal surface.     

Phase Controlled Monodispersed CdS Nanocrystals Synthesized in Polymer Solution Using Microwave Irradiation

Cadmium sulfide (CdS) nanocrystals were synthesized in aqueous solution of polyvinyl pyrrolidone (PVP) via the simple and rapid microwave irradiation method. It is revealed that sulfur source is a key factor in controlling the phase formation of the resulting nanocrystals. The hexagonal and cubic structure of CdS nanocrystals could be obtained with varying sulfur sources of thioacetamide and sodium sulphide respectively. The interaction mechanism of PVP with precursor ions of cadmium and sulfur sources in the preparation process was proposed. It is found that PVP compounded the CdS nanoparticles and protected them from agglomerating. With increasing of PVP concentration, the average particle size of CdS nanocrystals increased and subsequently their optical band gap decreased. At the appropriate dosage of PVP, well isolated nanoparticles with relatively narrow size distribution were obtained for both sulfur sources. Moreover the stability of CdS nanoparticles enhanced after coating with polymer.     

Reduction of aromatic nitro compounds on Pd colloids prepared by γ-irradiation

Poly(vinylpyrrolidone) (PVP), stabilized Pd colloids were successfully prepared by γ-irradiation in aqueous solution without additional reducing agent. The ‘clean’ Pd colloid was used as catalysts for the reduction of 2-, 3-, 4-nitrophenol, 2,4,6-trinitrotoluene, and 4-nitrobenzo-15-crown in aqueous solution at room temperature. The reduction process was monitored by UV–Visible spectroscopy.     

Fabrication of nanometer-to-micron sized Cu2O single crystals by electrodeposition

Nanometer-to-micron sized cuprous oxide (Cu₂O) single crystals were fabricated on Au/Pd sputter-coated silicon wafer and stainless steel cathode substrates by electrodeposition in CuSO₄ at pH 4.0 at room temperature (25 °C) with no additives. The Cu₂O crystals were generally of an octahedral shape with sizes ranging from 100 nm to 400 nm on Si wafer, and 1 μm to 3 μm on stainless steel substrates respectively. Very small crystals of a spherical shape were also observed under low applied voltage. Transient crystal shapes observed on the cathode near the electrolyte surface suggest that growth slows down once {1 1 1} free surfaces are formed, and this explains the robust observation of the octahedral crystal shape. The effect of electrodeposition parameters such as deposition voltage and deposition time on the size of the crystals and their coverage on the substrates was investigated. Apart from the cathode, similar octahedral Cu₂O nanocrystals were also found to deposit on the Cu anode used. This work provides a method to fabricate Cu₂O crystals on both electrodes in a single step.     

表面活性剂调节高矫顽力FePt纳米颗粒的合成

在表面活性剂聚乙烯吡咯烷酮(PVP)存在的体系中,通过NaBH4还原前驱体Fe(acac)3和H2PtCl6·6H2O,制备出了单分散的尺寸在3.0 nm左右的FePt纳米颗粒。XRD和TEM表征结果显示,表面活性剂PVP的用量影响FePt纳米颗粒相变,但对颗粒的尺寸无明显作用。由此推测,PVP对FePt纳米颗粒的相变起"催化"作用,适量的PVP诱导纳米颗粒的相变,可以通过改变表面活性剂的用量来调节FePt纳米颗粒的磁性能,当表面活性剂PVP单体与FePt前驱体的摩尔比(PVP/FePt)为7时,制得的FePt纳米颗粒经过500℃保温30 min热处理后,矫顽力高达5.2 kOe。     

Acetophenone Hydrogenation on Polymer–Palladium Catalysts. The Effect of Polymer Matrix

Catalytic properties of Pd supported on two polymers of similar basicity but different electrical properties, a π-conjugated conducting-polypyrrole (PPY) and the electro-inactive poly(4-vinylpyridine) (PVP) have been studied in the hydrogenation of acetophenone (ACT) and compared with that of γ-Al₂O₃ supported Pd. Experimental evidences provided by several techniques: X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission electron (TEM) microscopy, X-ray diffraction (XRD) and temperature programmed desorption (TPD) of hydrogen show that both polymers PVP and PPY exhibited ability to stabilize finely dispersed palladium nanoparticles, better this ability is offered by electro-inactive PVP. Palladium nanoparticles within a narrow range of size 2–20nm as well as very high surface concentration of Pd (22.2at %) in agglomerates were established in the latter polymer supported catalysts. Distinctly lower surface concentration of Pd (1.8at %) and crystalline Pd particles of dimension within a wide range, from 5nm up to ca. 1500nm appeared in the matrix of electroactive polymer – PPY. The hydrogenation of ACT to ethylbenzene (ETB) via 1-phenylethanol (ACP) (as the intermediate) proceeded over all studied catalysts. The effects of solvents, Pd content, ACT concentration and the additives of ACP, ETB were also studied. The catalytic properties of Pd/PPY in terms of activity and selectivity significantly differ from those of Pd/PVP and Pd/Al₂O₃. Both latter catalysts offered high activity and selectivity in the C=O in ACT to C–OH reduction. Definitely lower activity and higher tendency towards the hydrogenolysis of C–OH in ACP reflected Pd/PPY catalysts. Such unprofitable properties of Pd/PPY can be attributed to relatively strong adsorption of all organic reactant ACT, ACP, ETB. A competition of the ACP and ETB with the ACT occurred only in the case of Pdcentres created in the electroactive polymer, whereas Pd sites dispersed in the electro-inactive PVP similarly as the ones in Al₂O₃ exhibited definitely more substrate – ACT specific character.     

纳米晶生长习性机理--负离子配位多面体生长基元模型的应用

用负离子配位多面体生长基元理论模型讨论了CdS纳米晶的取向连生和用十二烷硫醇阻止连生的机理,以及立方GaP与立方BN,立疗CdS与六方CdS形成核一壳结构的异质同构和同质异构实际范例。用[Ti-O6]^8-八面体相互联结后形成各种不同维度的生长基元的论点解释厂TiO2晶粒的结晶习性及形貌特征。     

Investigation on the role of the molecular weight of polyvinyl pyrrolidone in the shape control of high-yield silver nanospheres and nanowires

Serving as shape control agent, polyvinyl pyrrolidone (PVP) has been widely used in chemical synthesis of metal nanoparticles. However, the role of molecular weight (MW) of PVP has been rarely concerned. In this study, we show a facile method to control the shapes of silver nanocrystals using PVP with different MWs. PVP_MW=8,000, PVP_MW=29,000, PVP_MW=40,000, and PVP_MW=1,300,000 are compared in the present study. Surprisingly, high-yield silver rodlike nanostructures, nanospheres, and nanowires can be obtained under the same growth environment and reactant concentrations by simply changing the MW of PVP. The mechanism studies of the role of PVP with different MWs in the growth process were carried out systemically using the morphology and spectroscopic measurement, FT-IR spectrum analysis, and seed crystallization monitoring. The results indicate that the MW of PVP plays a determinant role in the morphology and optical property control of the silver nanocrystals. Meantime, the concentration of PVP was found to be an assistant factor to further improve the shape and the yield of the synthesized nanocrystals.     

Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by bis(benzonitrile)dichloropalladium in the presence of polyvinylpyrrolidone

Pd(PhCN)₂Cl₂ [bis(benzonitrile)dichloropalladium] were investigated in the presence of polyvinylpyrrolidone (PVP) as a polymer support for the direct synthesis of diphenyl carbonate (DPC) by the oxidative carbonylation of phenol using carbon monoxide (CO) and air. Pd(PhCN)₂Cl₂ was found to be more efficient than the conventional PdBr₂ system, and its efficiency was accelerated in the presence of high molecular weight PVP with M_w=360,000 and 1,300,000. The best efficiency of Pd(PhCN)₂Cl₂/Mn(TMHD)₃ [tris(2,2,6,6-tetramethyl-3,5-heptanedionato)manganese]/(Ph₃P)₂NBr [bis(triphenylphosphoranylidene)ammonium bromide] system was obtained by using 0.241 mmol of PVP with M_w=360,000 where TOF (turnover frequency) reached 11.31 (mol-DPC/mol-Pd h, Pd/Mn/Br/phenol=1/2/20/2667; CO 0.50 MPa; air 0.25 MPa, 100°C, 3 h).     

Heterogeneous hydrogenation of nitrobenzenes over recyclable Pd(0) nanoparticle catalysts stabilized by polyphenol-grafted collagen fibers

A novel heterogeneous palladium (Pd) nanoparticle catalyst stabilized by collagen fibers (CF) was synthesized. Epigallocatechin-3-gallate (EGCG), a typical natural polyphenol, was grafted onto the CF surface to improve the stabilization and immobilization of Pd(0) nanoparticles. The main physical and chemical properties of the catalyst were characterized by means of Scanning Electron Microscopy, Fourier Transform-Infrared Spectroscopy, X-ray Photoelectron Spectroscopy, X-ray Diffraction and Transmission Electron Microscopy. This catalyst is in an ordered fibrous state with high flexibility. The Pd(0) nanoparticles with diameters of 3–4 nm are homogeneously dispersed onto the outer surfaces of CF, and they are stabilized by the coordinative interactions between the surface Pd atoms of nanoparticle and the surrounding oxygen and nitrogen atoms of the EGCG-grafted CF. These stabilized Pd(0) nanoparticles were found to be active and selective catalysts for nitrobenzene and its derivatives, directly hydrogenating to the correspondingly reductive anilines under mild conditions. Both Pd particle size and activity of the catalyst showed a marked dependence on the grafting degree of EGCG on CF. These catalysts can be easily recovered, reused multiple times, and stored for two months in air while maintaining high catalytic efficiencies. All these facts suggest that the EGCG-grafted CF can be used as an effective stabilizer for the preparation of Pd(0) nanoparticle catalysts.     

Air‐Stable and Highly Active Dendritic Phosphine Oxide‐ Stabilized Palladium Nanoparticles: Preparation,Characterization and Applications in the Carbon‐Carbon Bond Formation and Hydrogenation Reactions

Dendrimer‐stabilized palladium nanoparticles were formed in the reduction of palldium bis(acetylacetonate) [Pd(acac)₂] in the presence of phosphine dendrimer ligands using hydrogen in tetrahydrofuran. The resulting Pd nanoparticles were characterized by TEM, ³¹P NMR and ³¹P MAS NMR. The results indicated that the dendritic phosphine ligands were oxidized to phosphine oxides. These dendrimer‐stabilized Pd nanoparticles were demonstrated to be efficient catalysts for Suzuki and Stille coupling reactions and hydrogenations. The dendritic wedges served as a stabilizer for keeping the nanoparticles from aggregating, and as a vehicle for facilitating the separation and/or the recycling of the Pd catalyst. In the case of the Suzuki coupling reaction, these Pd nanoparticles exhibited high catalytic efficiency (TON up to 65,000) and air stability as compared with the commonly used homogeneous catalyst tetrakis(triphenylphosphine)palladium [Pd(PPh₃)₄]. In addition, the results obtained from the bulky dendritic substrate suggest that the Pd nanoparticles might act as reservoir of catalytically active species, and that the reaction is actually catalyzed by the soluble Pd(0) and/or Pd(II) species leached from the nanoparticle surface.     

A convenient method for preparing shape-controlled nanocrystalline Cu2O in a polyol or water/polyol system

A facile method capable of preparing well-dispersed Cu₂O nanocrystals with controllable shapes, such as rods, needles to other irregular shapes, has been developed. The different shapes of Cu₂O nanocrystals can be obtained simply by adjusting the composition of the reaction system. For example, if small amounts of poly(vinyl pyrrolidone) (PVP) was added in a mixture of Cu(NO₃)₂ and ethylene glycol, the needle-shaped nanocrystals could be formed. Interestingly further addition of small amounts of water in above system enabled us to obtain Cu₂O nanorods. Moreover the ratio of water/EG and the species of stabilizers played a crucial role in fine tuning the structure and size of as-prepared Cu₂O nanocrystals.     

Layers of Metal Nanoparticles on Semiconductors Deposited by Electrophoresis from Solutions with Reverse Micelles

Pd nanoparticles were prepared with reverse micelles of water/AOT/isooctane solution and deposited onto silicon or InP substrates by electrophoresis. A large change of capacitance-voltage characteristics of mercury contacts on a semiconductor was found after Pd deposition. This change could be modified when the Pd deposition is followed by a partial removal of the deposited AOT. The deposited Pd nanoparticles were investigated by optical mictroscopy, SIMS and SEM. Finally, Schottky diodes with barrier height as high as 1.07 eV were prepared by deposition of Pd nanoparticles on n-type InP and by a partial removal of superfluous AOT. These diodes are prospective structures for further testing as hydrogen sensors.     

Hydrogenation activity and selectivity behavior of supported palladium nanoparticles

Enhancement in activity and selectivity of catalytic hydrogenation using supported nanosize palladium catalyst has been investigated. Pd/C catalyst prepared in the presence of polyvinyl pyrrolidone (PVP) as a stabilizer gave Pd particle size in a narrow range of 3–5 nm. While, evaluating for hydrogenation of 2-butyne-1,4-diol, the rate enhancement was found to be 10 times higher as compared to the conventional (bulk) Pd catalysts. A proper choice of stabilizer (PVP) giving small particle size as well as highly dispersed nature of nano particles were the major factors for such a dramatic enhancement of activity.     

Synthesis of Colloidal Cobalt Nanoparticles with Controlled Size and Shapes

A method of producing high quality magnetic colloidal dispersions by the rapid pyrolysis of cobalt carbonyl in an inert atmosphere was employed to produce monodispersed, stabilized, defect-free -cobalt nanocrystals with spherical shapes and sizes ranging from 3 to 17 nm, as well as cubic and rod-like shaped particles. The size distribution and the shape of the nanocrystals were controlled by varying the surfactant composition (oleic acid, phosphonic oxides and acids), its concentration and the reaction temperature. These particles have been observed to produce 2D self-assemblies when evaporated at low rates in a controlled atmosphere. A combination of X-ray powder diffraction; transmission electron microscopy; and SQUID magnetometry has been used to characterize both the dispersed nanocrystals and the assembled superlattices.     

Synthesis and crystal structure of bis(morpholino dithiocarbamato) Cd(II) complex and its use as precursor for CdS quantum dots using different capping agents

ABSTRACT

Cadmium(II) morpholine dithiocarbamate complex [Cd(morphdtc)₂] was synthesized and characterized by single crystal X-ray crystallography. The molecular structure of the complex showed Cd(II) ion in a distorted 4?+?2 octahedral geometry, in which the two morpholine dithiocarbamates act as bidentate chelating and the central Cd ion bond the sulfur atoms of adjacent morpholine acting as bridging ligands to form centrosymmetric five coordinate dimeric molecules. The Cd(II) complex was thermolysed at 180°C to prepare CdS nanoparticles using three different capping agents. The pXRD patterns revealed a mixture of hexagonal and cubic crystalline phases of CdS nanocrystals. TEM images revealed semi-spherical and spherical nanoparticles, with the size range of 4.50–5.70?nm for OLM-CdS, 3.33–5.96?nm for HDA-CdS, and 3.00–5.83?nm for ODA-CdS. The particle size distribution of the CdS nanocrystallite is within the range 1.06?nm (SD?±?0.73) for OLM-CdS, 0.68?nm, (SD?±0.73) for HDA-CdS and 1.18?nm, (SD?±?0.60) for ODA-CdS. The lattice fringes showed that the particles are almost in the same environment with the interplanar of 0.32?nm for OLM-CdS, 0.34?nm for HDA-CdS, and 0.32?nm ODA-CdS. The band gaps energy were confirmed to be 1.59?eV for OLM-CdS, 1.65?eV for HDA-CdS, and 1.62?eV for ODA-CdS nanoparticles, respectively.     

Instant precipitation of KMgF3:Ni2+ nanocrystals with broad emission (1.3‐2.2 μm) for potential combustion gas sensors

Optical gas sensors present fundamental and industrial importance considering their broad applications. Challenges remain to obtain new photonic materials with broadband emission covering the absorption spectrum of typical combustion gases. Here, broadband near‐infrared (NIR) photoluminescence (PL) spanning the wide absorption spectrum of typical combustion products is realized through instant precipitation of stable cubic perovskite KMgF₃:Ni²⁺ nanocrystals inside an aluminosilicate glass matrix after melt‐quenching. Excited by an 808 nm laser diode, NIR luminescence with a peak centered at ~1624 nm and a bandwidth (FWHM) greater than 315 nm is observed, originating from ³T_2g(³F) → ³A_2g(³F) electronic transition of octahedral coordinated Ni²⁺ in KMgF₃ GC. Controlled precipitation of these perovskite crystals from a supercooled aluminosilicate melt enables immediate encapsulation and, hence, stabilization in an inorganic glass phase. While the precipitation temperature has only a small effect on crystallite size, it controls the redox state of the melt and the degree of dopant incorporation into the crystalline phase so that PL performance can be optimized. Spontaneous crystallization of perovskite nanocrystals inside glass may offer a new way to stabilize these novel nanocrystals. Moreover, spontaneous crystallization can be attractive in the control of activator partitioning and in the fabrication of composite fiber devices with high transparency and emission gain. In the present case, this offers a potential platform for broadly tunable gain media, for example, for combustion gas sensing.     

Improvement of electrochemical performance of tin dioxide negative electrode materials upon cobalt substitution

The cobalt-substituted tin dioxide nanocrystals were synthesized by the one-pot hydrothermal method. According to the powder X-ray diffraction and elemental analyses, the cobalt ions were successfully substituted into the rutile lattice of the SnO₂ phase, which consequently resulted in an increase in the volume of the unit cell. Electron microscopy revealed that with an increase in the content of the substituted cobalt ions, the particle size of the SnO₂ nanocrystals becomes smaller. In addition, the X-ray absorption spectroscopy clearly demonstrated that the substituent cobalt ions were stabilized in a divalent oxidation state in a distorted octahedral symmetry, while the tin ions were in a tetravalent oxidation state. The electrochemical measurements revealed that the substitution of Sn with Co significantly enhanced the negative electrode performance of tin dioxide nanocrystals at optimal Co content. The present study clearly demonstrated that a partial substitution of cobalt in the SnO₂ phase can provide an effective way of optimizing the electrochemical properties of the tin dioxide nanocrystals.     

Palladium Catalytic Species Containing Chiral Phosphites: Towards a Discrimination between Molecular and Colloidal Catalysts

Palladium nanoparticles ( Pd1 – Pd3 ) stabilized by chiral diphosphite ligands ( 1 – 3 ), were synthesized and tested as catalysts for the allylic alkylation reaction, using different substrates (rac‐ I , rac‐ III and rac‐ V ). Carbohydrate ligands ( 1 and 2 ), only differing in the C‐3 configuration, led to a remarkable difference in stability of the corresponding nanoparticles: while Pd1 is a robust catalyst, Pd2 decomposes into molecular species. In addition, the high enantioselective systems, Pd1 and Pd3 , are only active for a substrate containing phenyl groups. Concerning the catalytic behaviour of the corresponding molecular systems, palladium complexes coordinated to ligands 1 or 3 , gave excellent asymmetric inductions, but an analogous catalyst accommodating ligand 2 , was not found selective.