烷基胺为媒介的铜纳米棒的合成及其生长机制研究

以氯化铜为前躯体,葡糖糖为还原剂,烷基胺(十六胺和十八胺的混合物)为络合剂和表面包覆剂,经过络合反应和溶剂热两步反应首先得到形貌均一、直径约为100 nm的铜纳米颗粒, 随后自发生长为五重孪晶铜纳米棒(仍含有部分颗粒)。实验过程中分别对溶剂热反应1 h、3 h和5 h后的还原产物的形貌特征加以表征,可以推断被还原的铜原子首先均匀成核形成初级铜纳米颗粒,经过奥斯特瓦尔德老化过程生长为五重孪晶的次级铜纳米颗粒,由于孪晶结构具有很高的生长活性,在烷基胺的表面包覆作用下生长为各项异性的铜纳米棒。该方法提供了一种有效的铜纳米棒的制备方法并且降低了一维铜纳米材料的合成成本。     

Synthesis of organic monolayer-stabilized copper nanocrystals in supercritical water

When water is heated and pressurized above the critical point, it becomes a suitable solvent to employ organic capping ligands to control and stabilize the synthesis of nanocrystals. Without alkanethiol ligands, Cu(NO(3))(2) hydrolyzes to form polydisperse copper(II) oxide particles with diameters from 10 to 35 nm. However, in the presence of 1-hexanethiol, X-ray photoelectron spectroscopy, selected area electron diffraction, and transmission electron microscopy reveal the formation of copper nanocrystals approximately 7 nm in diameter. The use of a different precursor, Cu(CH(3)COO)(2), leads to particles with significantly different morphologies. A mechanism is proposed for sterically stabilized nanocrystal growth in supercritical water that describes competing pathways of hydrolysis to large oxidized copper particles versus ligand exchange and arrested growth by thiols to produce small monodisperse Cu nanoparticles.     

Coordinatively induced length control and photoluminescence of W18O49 nanorods

A coordinatively induced length control of W18O49 nanorods has been developed using thermal decomposition of W(CO)6 in octyl ether solutions of single or mixed capping agents, oleic acid (OA), oleic acid/hexadecylamine (HDA), and oleic acid/trioctylphosphine oxide (TOPO). The order of length for nanorods synthesized with different capping agents was OA > OA/HDA > OA/TOPO, which was the opposite of order of their coordinating power. The order of crystalline size (diameter x length) from the TEM image was OA/HDA > OA > OA/TOPO and matched exactly with the order of crystallinity from the XRD pattern. The order of photoluminescence intensity was OA/HDA < OA < OA/TOPO and was the opposite of the order for the crystalline size or crystallinity. The strong coordinating power and steric bulkiness of TOPO is thought to interrupt the growth of the nanorods, the rearrangement of the end face atoms, and the fusion of the lateral faces and, thereby, increase the oxygen defects and the photoluminescence intensity.     

ZnO纳米线形态对其光致发光性能的影响

以多孔氧化铝膜为模板,电化学沉积出Zn纳米线,再通过高温氧化得到ZnO纳米线阵列。通过改变制备多孔氧化铝模板的工艺参数来改变模板纳米孔径,进而改变ZnO纳米线的直径,得到不同形态的ZnO纳米线阵列。应用X射线衍射仪、透射电子显微镜测试技术表征了ZnO纳米线的结构与形貌。结果发现,X射线衍射时会出现随ZnO纳米线直径增大衍射峰增多和增强的现象。采用荧光光谱仪测试样品的光致发光性能,通过Gaussian原理对谱峰的拟合分析了ZnO纳米线形态对其光致发光光谱的影响。结果表明,随着纳米线直径从30nm至60nm依次增大,其结晶性和化学计量比逐渐变好。近紫外区和蓝光区的发射峰随着纳米线直径的增大而蓝移,而纳米线直径为60nm的样品则出现随直径增大而红移的现象。结果可见,直径在55~60nm间的某点将是ZnO纳米线的结构和光致发光性能变化的临界点。     

Effect of aspect ratio of vertically aligned copper nanowires in the presence of cellulose nanofibers on the thermal conductivity of epoxy composites

The composites comprising vertically aligned network of copper nanowires (CuNWs) in the presence of cellulose nanofibers were fabricated by using the freeze‐templating method and the effect of aspect ratio (A/R) of CuNWs on the thermal conductivity of epoxy composites was investigated. The thermal conductivity of epoxy composites increased to 0.79 W m^?1 K^?1 at 1.12 vol% of high A/R CuNWs loading, corresponding to the thermal conductivity enhancement of 365% as compared to the pure epoxy. The thermal conductivity of vertically aligned higher A/R CuNWs/epoxy, which is 38.5% and 51.9% higher than those of the lower A/R CuNWs and the randomly aligned CuNWs, respectively. The application of the epoxy composites in heat dissipation was demonstrated by the temperature changes of composites on a hot plate with the increase of heating time. These results indicate that the thermally conductive composites in this study could be applied for thermal dissipating materials in electronic devices.     

Synthesis of size-controlled and shaped copper nanoparticles

The synthesis of stable, monodisperse, shaped copper nanoparticles has been difficult, partially because of copper's propensity for oxidation. This article reports the findings of an investigation of a synthetic route for the synthesis of size-controllable and potentially shape-controllable molecularly capped copper nanoparticles. The approach involved the manipulation of reaction temperature for the synthesis of copper nanoparticles in organic solvents in the presence of amine and acid capping agents. By manipulating the reaction temperature, this route has been demonstrated for the production of copper nanoparticles ranging from 5 to 25 nm. The size dependence of the melting temperature of copper nanoparticles, especially for surface melting, is believed to play an important role in interparticle coalescence, leading to size growth as the reaction temperature is increased. Control of the reaction temperature and capping molecules has also been demonstrated to produce copper nanoparticles with different shapes such as rods and cubes. The previously proposed combination of the selective formation of a seed precursor and a selective growth direction due to the preferential adsorption of capping agents on certain nanocrystal facets is believed to be responsible for shape formation by kinetically controlling the growth rates of crystal facets. The nanoparticles are characterized using TEM, XRD, and UV-visible techniques. A mechanistic consideration of the size control and shape formation is also discussed.     

双功能聚二甲基硅氧烷/铜纳米线复合薄膜的制备与性能

通过环境友好的葡萄糖模板法和改进的湿化学还原法制备了聚二甲基硅氧烷/铜纳米线(PDMS/CuNWs)复合薄膜, 其采用的“类夹心结构”有效解决了铜在空气中易氧化进而导致电导率大幅度下降的问题, 同时获得了具有优异电磁屏蔽和光热转化性能的双功能轻质柔性复合薄膜. CuNWs面密度为1.6 g/cm²的复合薄膜在重复弯折1000次后性能保持率最高可达99.07％; CuNWs面密度为2.4 g/cm²的复合薄膜在X波段下总电磁屏蔽效能达到30.1 dB, 屏蔽效率达到99.9％; 同时, 在2 W/cm²的近红外光照射下, 复合薄膜在仅加热15 s后其表面温度高达211.2 ℃, 具有十分快速的光热响应和转化效率.     

Effects of the architecture and environment on polymeric molecular assemblies of novel amphiphilic diblock copolynorbornenes with narrow polydispersity via living ring‐opening metathesis polymerization

Diblock copolymers of 5‐(methylphthalimide)bicyclo[2.2.1]hept‐2‐ene (NBMPI) and 1,5‐cyclooctadiene were synthesized by living ring‐opening metathesis polymerization with a well‐defined catalyst {RuCl₂(CHPh)[P(C₆H₁₁)₃]₂}. Unhydrogenated diblock copolymers showed two glass transitions due to poly(NBMPI) and polybutadiene segments, such as two glass‐transition temperatures at ?86.5 and 115.3 °C for poly 1a and ?87.2 and 115.3 °C for poly 1b . However, only one melting temperature could be observed for hydrogenated copolymers, such as 119.8 °C for poly 2a and 121.7 °C for poly 2b . The unhydrogenated diblock copolymer with the longer poly(NBMPI) chain (poly 1a ; temperature at 10% mass loss = 400 °C) exhibited better thermal stability than the one with the shorter poly(NBMPI) chain (poly 1b ; temperature at 10% mass loss = 385 °C). Two kinds of hydrogenated diblock copolymers, poly 2a and poly 2b , exhibited relatively poor solubility but better thermal stability than unhydrogenated diblock copolymers because of the polyethylene segments. Poly[(hydrochloride quaternized 2‐norbornene‐5‐methyleneamine)‐b‐butadiene]‐1 (poly 3a ) was obtained after the hydrolysis and quaternization of poly 1a . Dynamic light scattering measurements indicated that the hydrodynamic diameters of the cationic copolymer (poly 3a ) in water (hydrodynamic diameter = 1580 nm without salt), methanol/water (4/96 v/v; hydrodynamic diameter = 1500 nm without salt), and tetrahydrofuran/water (4/96 v/v; hydrodynamic diameter = 1200 nm without salt) decreased with increasing salt (NaCl) concentration. The effect of temperature on the hydrodynamic diameter of hydrophobically modified poly 3a was also studied. The inflection point of the hydrodynamic diameter of poly 3a was observed at various polymer concentrations around 30 °C. The critical micelle concentration of hydrophobically modified poly 3a was observed at 0.018 g dL^?1. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2901–2911, 2006     

Controlled Synthesis of Water‐Dispersible Faceted Crystalline Copper Nanoparticles and Their Catalytic Properties

We report a solution‐phase synthetic route to copper nanoparticles with controllable size and shape. The synthesis of the nanoparticles is achieved by the reduction of copper(II) salt in aqueous solution with hydrazine under air atmosphere in the presence of poly(acrylic acid) (PAA) as capping agent. The results suggest that the pH plays a key role for the formation of pure copper nanoparticles, whereas the concentration of PAA is important for controlling the size and geometric shape of the nanoparticles. The average size of the copper nanoparticles can be varied from 30 to 80 nm, depending on the concentration of PAA. With a moderate amount of PAA, faceted crystalline copper nanoparticles are obtained. The as‐synthesized copper nanoparticles appear red in color and are stable for weeks, as confirmed by UV/Vis and X‐ray photoemission (XPS) spectroscopy. The faceted crystalline copper nanoparticles serve as an effective catalyst for N‐arylation of heterocycles, such as the C? N coupling reaction between p‐nitrobenzyl chloride and morpholine producing 4‐(4‐nitrophenyl)morpholine in an excellent yield under mild reaction conditions. Furthermore, the nanoparticles are proven to be versatile as they also effectively catalyze the three‐component, one‐pot Mannich reaction between p‐substituted benzaldehyde, aniline, and acetophenone affording a 100 % conversion of the limiting reactant (aniline).     

The Structure‐Controlling Solventless Synthesis and Optical Properties of Uniform Cu2S Nanodisks

Uniform Cu₂S nanodisks have been synthesized from a well‐characterized layered copper thiolate precursor by structure‐controlling solventless thermolysis at 200–220 °C under a N₂ atmosphere. The development from small Cu₂S nanoparticles (diameter ≈3 nm) to nanodisks (diameter 8.3 nm) and then to faceted nanodisks (diameter 27.5 nm, thickness 12.7 nm) is accompanied by a continuous phase transition from metastable orthorhombic to monoclinic Cu₂S, the ripening of small particles by aggregation, and finally the crystallization process. The growth of the nanoproduct is constrained by the crystal structure of the precursor and the in situ‐generated thiol molecules. Such controlled anisotropic growth leads to a nearly constant thickness of faceted nanodisks with different diameters, which has been confirmed by TEM observations and optical absorption measurements.     

金纳米线阵列制备及其光谱特性

利用电化学沉积方法在重离子径迹模板中制备出直径从45 nm到200 nm, 长径比达700的金纳米线阵列, 利用扫描电子显微镜(SEM)和X射线衍射(XRD)对所制备金纳米线的形貌及晶体结构进行分析, 结果表明, 在1.5 V(无参比电极)沉积电压下所制备出的直径为200 nm金纳米线沿[100]晶向具有较好择优取向. 利用紫外-可见光谱(UV-Vis)对镶嵌在透明模板中平行排列的金纳米线阵列光学特性进行研究, 发现金纳米线直径为45 nm时, 其紫外可见光谱在539 nm处有强烈吸收峰, 随着金纳米线直径增加, 吸收峰红移, 当金纳米线直径达到200 nm时, 其吸收峰峰位移至700 nm. 结合金纳米颗粒相关表面等离子体共振吸收效应对实验结果进行了讨论.     

Morphology and size-controlled synthesis of silver nanoparticles in aqueous surfactant polymer solutions

We have employed a number of reducing and capping agents to obtain Ag(0) metallic nanoparticles of various sizes and morphologies. The size and morphology were tuned by selecting reducing and capping agents. Spherical particles of 15 and 43 nm diameter were obtained when 1 wt% aqueous starch solution of AgNO₃ precursor salt was reduced by d(+)-glucose and NaOH, respectively, on heating at 70 °C for 30 min. Smaller size particles obtained in the case of d(+)-glucose reduction has been attributed to the slow reduction rate by mild reducing agent d(+)-glucose compared to strong NaOH. Conducting the reduction at ambient temperature of silver salt in liquid crystalline pluronic P123 and L64 also gave spherical particles of 8 and 24 nm, respectively, without the addition of any separate reducing agent. NaOH reduction of salt in ethylene glycol (11 g)/polyvinyl pyrolidone (PVP; 0.053 g) mixture produced large self-assembled cubes of 520 nm when smaller (26–53 nm) star-shaped sharp-edged structures formed initially aggregated on heating the preparation at 190 °C for 1 h. Increasing the amount of PVP (0.5 g) in ethylene glycol (11 g) and heating at 70 °C for 30 min yielded a mixture of spherical and non-spherical (cubes, hexagons, pentagons, and triangle) particles without the addition of an extra reducing agent. Addition of 5 wt% PVP to 1 wt% aqueous starched solution resulted in the formation of a mixture of spherical and anisotropic structures when solution heated at 70 °C for 1 h. Homogeneous smaller sized (29 nm) cubes were synthesized by NaOH reduction of AgNO₃ in 12.5 wt% of water-soluble polymer poly(methyl vinyl ether) at ambient temperature in 30 min reaction time.     

Experimental and First‐Principles Characterization of Functionalized Magnetic Nanoparticles

Magnetic iron oxide nanoparticles synthesized by coprecipitation and thermal decomposition yield largely monodisperse size distributions. The diameters of the coprecipitated particles measured by X‐ray diffraction and transmission electron microscopy are between approximately 9 and 15 nm, whereas the diameters of thermally decomposed particles are in the range of 8 to 10 nm. Coprecipitated particles are indexed as magnetite‐rich and thermally decomposed particles as maghemite‐rich; however, both methods produce a mixture of magnetite and maghemite. Fourier transform IR spectra reveal that the nanoparticles are coated with at least two layers of oleic acid (OA) surfactant. The inner layer is postulated to be chemically adsorbed on the nanoparticle surface whereas the rest of the OA is physically adsorbed, as indicated by carboxyl O? H stretching modes above 3400 cm^?1. Differential thermal analysis (DTA) results indicate a double‐stepped weight loss process, the lower‐temperature step of which is assigned to condensation due to physically adsorbed or low‐energy bonded OA moieties. Density functional calculations of Fe–O clusters, the inverse spinel cell, and isolated OA, as well as OA in bidentate linkage with ferrous and ferric atoms, suggest that the higher‐temperature DTA stage could be further broken down into two regions: one in which condensation is due ferrous/ferrous– and/or ferrous/ferric–OA and the other due to condensation from ferrous/ferric– and ferric/ferric–OA complexes. The latter appear to form bonds with the OA carbonyl group of energy up to fivefold that of the bond formed by the ferrous/ferrous pairs. Molecular orbital populations indicate that such increased stability of the ferric/ferric pair is due to the contribution of the low‐lying Fe³⁺ t_2g states into four bonding orbitals between ?0.623 and ?0.410 a.u.     

大孔硅胶的制备及其在多糖衍生物手性固定相上的应用

为制备孔径为100 nm的大孔硅胶,考察了热液法和焙烧法对球形硅胶（粒径5 μm,孔径10 nm）的扩孔效果。采用热液法扩孔时,在水溶液中加入22 g/L氟化钠,可以有效增强扩孔效果,在高压釜内160℃加热48 h便可扩孔至100 nm,但孔径不均匀。采用焙烧法扩孔时,通过调节焙烧温度、时间以及复盐LiCl-NaCl的加入量可以方便地控制扩孔速度与效果;在每10 g硅胶中加入1.125 g LiCl·H₂O和0.75 g NaCl,于500℃焙烧3~5 h,可得到100 nm大孔硅胶;该方法简单、高效,扩孔后的硅胶孔径分布均匀,表面形态与商品化的Fuji-1000硅胶相似。将两种扩孔方式得到的硅胶经氨基修饰后,涂覆纤维素-三（3,5-二甲基苯基氨基甲酸酯）制得了相应的手性固定相。结果表明,采用焙烧法扩孔得到的硅胶制备的固定相明显具有较好的分离选择性及分离度。     

Tuning of the Temperature Window for Unit‐Cell and Pore‐Size Enlargement in Face‐Centered‐Cubic Large‐Mesopore Silicas Templated by Swollen Block Copolymer Micelles

The unit‐cell size and pore diameter as functions of temperature are investigated in the syntheses of FDU‐12 silicas with face‐centered cubic structure templated by Pluronic (PEO‐PPO‐PEO) block copolymer micelles swollen by toluene. The temperature range in which the unit‐cell size and pore size strongly increase as temperature decreases is correlated with the critical micelle temperature (CMT) of the surfactant. While Pluronic F127 affords a wide range of unit‐cell parameters (28–51 nm) and pore diameters (16–32 nm), it renders moderately enlarged pore sizes at 25 °C. The use of Pluronic F108 with higher CMT affords FDU‐12 with very large unit‐cell size (～49 nm) and large pore diameter (27 nm) at 23 °C. Large unit‐cell size (40–41 nm) and pore size (22 nm) were obtained even at 25 °C. The application of Pluronics F87 and F88 with much smaller molecular weights and higher CMTs also allows one to synthesize FDU‐12 with quite large unit‐cell parameters and pore sizes at room temperature. The present work demonstrates that one can judiciously select Pluronic surfactants with appropriate CMT to shift the temperature range in which the pore diameter is readily tunable.     

硼酸铝纳米棒的制备、结构及生长机理

以仲丁醇铝和硼酸为原料, 葡萄糖作模板剂, 在水介质中120 ℃形成淡黄色干凝胶, 再于750 ℃焙烧得到尺寸均一的硼酸铝纳米棒. 通过改变仲丁醇铝/硼酸的摩尔比实现了对产物形貌及长径比的控制合成. 采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)对产物结构和形貌进行表征. 结果表明产物为Al4B2O9纳米棒, 直径为15-45 nm, 长度为100-300 nm. 根据表征结果对葡萄糖参与的硼酸铝纳米棒的生长机理进行了探讨. 结果表明, 葡萄糖与硼酸反应产生网状结构的配合物, 同时释放质子, 促使铝源均匀地分散在网格间, 为硼酸铝的生成提供一有利的反应空间. 纳米棒的生长为自催化生长过程, 在750 ℃热处理时沿着(100)面方向生长.     

Controlled Synthesis of Narrow-Dispersed Copper Nanoparticles

A controlled synthesis method for preparing narrow-dispersed copper nanoparticles, using water and ethylene glycol as the reaction media respectively, has been reported. In order to obtain pure-phase copper nanoparticles using water, the reaction time of 8 h is essential. Owing to the reduction property of ethylene glycol, the reaction rate using ethylene glycol is higher. In addition, the amount of reduction agent can reduce largely. Polyvinyl pyrrolidone plays great role on the size of copper particles, and the increasing of polyvinyl pyrrolidone concentration attributes to the smaller dimension particles. The mean diameter is about 4 nm when the concentration of polyvinyl pyrrolidone is 0.5 mmol/L. Polyvinyl pyrrolidone acts as the polymeric capping agents in the reaction, preventing the agglomeration of the copper nanoparticles. When water is the reaction medium, Cu²⁺ complex is reduced to Cu⁺ complex firstly, and the further reduction of Cu⁺ forms the pure copper nanoparticle.     

Polyelectrolyte complexes of poly(methacryloxyethyl trimethylammonium chloride) and poly(ethylene oxide)-block-poly(sodium methacrylate) studied by asymmetrical flow field-flow fractionation and dynamic light scattering

Polyelectrolyte complex (PEC) formation between cationic poly(methacryloxyethyl trimethylammonium chloride) (PMOTAC) and anionic poly(ethylene oxide)-block-poly(sodium methacrylate) (PEO-b-PMANa) was studied by asymmetrical flow field-flow fractionation and dynamic light scattering. The influence of ionic strength and mixing ratios of the charged units of the polyelectrolytes on the complex formation was evaluated. The diffusion coefficients and the hydrodynamic diameter distributions of the free and complexed polyelectrolytes were measured. In the absence of salt, the weight averaged hydrodynamic diameters were 48 and 28 nm for PMOTAC and PEO-b-PMANa, respectively. In the presence of salt, the particles were smaller, with weight averaged hydrodynamic diameters of 44-45 and 8-10 nm, respectively. In salt-free solution, at 1:1 mixing ratio of the charged monomer units of PMOTAC and PEO-b-PMANa, polydisperse particles with diameters of 2000-4000 nm were formed. In the presence of 20, 80, and 160 mM of sodium chloride, the 1:1 complexes were relatively monodisperse particles with weight averaged hydrodynamic diameters of 93, 124, and 120 nm, respectively.     

Growth of silver nanowires from solutions: a cyclic penta-twinned-crystal growth mechanism

Silver nanowires are synthesized by simple reduction of the silver ions with reductants such as glucose, sodium citrate, and sodium hypophosphite, etc., in the absence of the so-called surfactants or capping reagents at the temperature from 80 to 200 degrees C. Regardless of the reductants, the nanowires prepared at a given temperature are uniform in diameters, ranging from 30 to 50 nm at 100 degrees C. Nanoparticles coexist with nanowires in the products with larger diameters (usually larger than 50 nm). We find that all the silver nanowires in the as-prepared products are of cyclic penta-twinned structure, where five crystallites bond by the {111} facets. We propose that the intrinsic factor of the cyclic penta-twinned structure, i.e., the angular mismatch of the five crystallites in forming a gapless rod, controls the size of the nanowires and guides the directional growth of the nanowires with {110} as the active facets. The nanoparticles in the products are aggregates of imperfect penta-twinned crystals, which inhibits them from growing into nanowires and results in larger size. From the structural information of the nanoparticles synthesized at room temperature, we propose that the formation of the cyclic penta-twinned structure is due to the stacking fault and the intrinsic equilibrium structures of the lower energy.     

Template‐Synthesized Copper Nanotubes via Electroless Plating

Template synthesis method of preparing copper nanotubes via electroless plating has been investigated in this paper. The tubular structures were obtained by calcinring copper‐coated carbon nanofibers. The final products were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), and x‐ray diffractometer (XRD). The results show that copper nanotubes can be synthesized by this method. The inner diameter of the prepared copper nanotubes is about 100 nm, and the wall thickness is about 25 nm. In this method, it is convenient to control the dimension or the shape of the obtained copper nanotubes by using different nanofibers as templates.