Sterically stabilized polypyrrole–palladium nanocomposite particles synthesized by aqueous chemical oxidative dispersion polymerization

Aqueous chemical oxidative dispersion polymerizations of pyrrole using PdCl₂ oxidant were conducted using water-soluble polymeric colloidal stabilizers in order to synthesize polypyrrole–palladium (PPy–Pd) nanocomposite particles in one step. PPy–Pd nanocomposite particles with number average diameters of approximately 30 nm were successfully obtained as colloidally stable aqueous dispersions, which were stable at least for 7 months, using poly(4-lithium styrene sulfonic acid) colloidal stabilizer. The resulting nanocomposite particles were extensively characterized with respect to particle size, size distribution, colloidal stability, nanomorphology, surface/bulk chemical compositions, and conductivity. X-ray photoelectron spectroscopy indicated the existence of poly(styrene sulfonic acid) colloidal stabilizer on the surface of the nanocomposite particles. Transmission electron microscopy studies confirmed that nanometer-sized Pd nanoparticles were distributed in the PPy matrix.     

负电性纳米银的制备及性质研究

制备了一种表面带负电的胶态纳米银,用透射电镜、吸收光谱、 SERS谱对该纳米银进行了研究.发现纳米银的粒径分布均匀,平均粒径为11 nm,吸收峰为422 nm,常温下放置7个月仍具有较强的SERS活性.当阴离子型分子吲哚丁酸、阳离子型分子碱性品红、亚甲兰及中性分子邻菲罗邻分别吸附在其上时,观察到阳离子型分子碱性品红和亚甲兰及中性分子邻菲罗邻的SERS谱,而阴离子型分子吲哚丁酸则无SERS谱出现.     

胶体铜催化丙烯腈水合的高选择性及其活性中心结构的研究

研究了胶体铜催化丙烯腈水合制丙烯酰胺的高选择性与活性中心结构的关系. 在聚乙烯吡咯烷酮(PVP)保护下, 用肼和氢氧化钠混合液还原CuCl2制得胶体铜, 用其催化丙烯腈水合反应, 选择性达到100％, 产生高选择性的原因如下: (1) 胶体铜的活性中心不是胶粒表面的点缺陷, 而是胶体铜颗粒表面的位错端点. (2) 由于胶体铜具有高硬度和高强度的力学特性, 保证了活性中心结构的稳定性; 胶体铜颗粒的平均粒径(45 nm)超过晶粒的特征长度, 进一步保证了活性中心的稳定性.     

Fe_3O_4/P(NaUA-St-BA)核-壳纳米磁性复合粒子的合成与表征

以表面包敷有反应型的表面活性剂NaUA(十一烯酸钠)的Fe3O4磁性胶体粒子为种子,运用无皂乳液聚合方法原位制备出Fe3O4P(NaUAStBA)核壳纳米磁性复合粒子.Fe3O4磁性胶体粒子的粒径为10nm左右.IR和TG结果分析表明,苯乙烯、丙烯酸酯和NaUA在Fe3O4粒子的表面发生了聚合反应,形成P(NaUAStBA);TEM和激光粒度分析仪测试结果显示,Fe3O4P(NaUAStBA)复合粒子具有核壳结构而且粒子分布均匀、平均粒径60nm;TG测试的结果表明,NaUA在Fe3O4粒子的包覆率为13.83%,P(NaUAStBA)共聚物的包覆率71.85%;振动样品磁强仪(VSM)测试的磁滞回线则表明由无皂乳液聚合得到的Fe3O4P(NaUAStBA)复合粒子具有超顺磁性,可避免磁性微球在磁场中的团聚.另外,合成的磁性胶乳可稳定存放数月.     

PREPARATION AND CHARACTERIZATION OF PVA COATED MAGNETIC NANOPARTICLES*

Polyvinyl alcohol coated magnetic particles (PVA ferrofluids) have been synthesized by chemical co-precipitationof Fe(Ⅱ)/Fe(Ⅲ) salts in 1.5 mol/L NH_4OH solution at 70℃ in the presence of PVA. The resultant colloidal particles havecore-shell structures, in which the iron oxide crystallites form the cores and PVA chains form the shells. The hydrodynamicdiameter of the colloidal particles is in the range of 108 to 155 nm, which increases with increasing PVA concentration from5 wt% to 20 wt%. The size of the magnetic cores is ca. 5～10 nm, which is relatively independent of PVA concentration.Under transmission electron microscopic (TEM) examination, the magnetic cores exhibit somewhat irregular shapes varyingfrom spherical, oval, to cubic. Magnetometry measurement revealed that the PVA coated magnetic particles aresuperparamagnetic. The saturation magnetization of 5 wt% and 20 wt% PVA ferrofluids at 300 K is 54 and 49 emu/g.respectively. All the PVA ferrofluids exhibited excellent colloidal stability in pure water and phosphate buffer saline (PBS,pH=7.4). The ferrofluids can remain stable in above solutions for more than three months at 4℃.     

Continuous production of water dispersible carbon-iron nanocomposites by laser pyrolysis: application as MRI contrasts

Carbon encapsulated iron/iron-oxide nanoparticles were obtained using laser pyrolysis method. The powders were processed to produce stable and biocompatible colloidal aqueous dispersions. The synthesis method consisted in the laser decomposition of an aerosol of ferrocene solution in toluene. This process generated, in a continuous way and in a single step, a nanocomposite formed by amorphous carbon nanoparticles of 50-100 nm size in which isolated iron based nanoparticles of 3-10 nm size are located. The effect of using different carriers and additives was explored in order to improve the efficiency of the process. The samples after purification by solid-liquid extraction with toluene, were oxidised in concentrated nitric acid solution of sodium chlorate, washed and finally ultrasonically dispersed in 1 mM tri-sodium citrate solutions. The dispersions obtained have hydrodynamic particle size less than 150 nm and are stable in the pH range of 2-11. Finally the shortening of the transversal relaxation time of water protons produced by the dispersed particles was studied in order to test the feasibility of these systems to be traced by magnetic resonance imaging techniques.     

Control of the morphology and particle size of boehmite nanoparticles synthesized under hydrothermal conditions

The spontaneous nucleation under hydrothermal conditions often leads to aggregation of crystallizing particles, which is an undesired phenomenon when the goal is the preparation of nanocrystals with narrow particle size distribution. The present paper reports on the synthesis of boehmite nanocrystals under hydrothermal conditions. An aqueous aluminum chloride salt solution was first prepared, and the pH was increased to 11 using a 5 M sodium hydroxide solution. The hydrothermal treatment was performed at 160 degrees C for different periods of time. The system yielded relatively small (15-40 nm) boehmite crystallites aggregated into larger (160 nm) particles. To avoid the aggregation, a biocompatible polymer, sodium polyacrylate (NaPa) 2100, was employed as a size-/morphology-controlling agent. Thus, stable colloidal suspensions of rounded boehmite nanoparticles having a size between 15 and 40 nm were obtained at 160 degrees C for 24 h. Further, the effect of synthesis time on the morphological features of boehmite synthesized in such a NaPa-containing system was investigated. The increase of the synthesis time from 24 to 168 h resulted in the formation of very long boehmite fibers (1000-2000 nm) with an average diameter of about 10 nm. The boehmite samples were characterized by XRD, DLS, TEM, IR, N2 adsorption, and zeta potential measurements. The colloidal stability of the obtained suspension was also studied.     

Improvement of physicochemical properties of N-4472. Part III. VC/N-4472 complex formation and self-association in aqueous solution

To improve the aqueous solubility of a poorly water-soluble drug, N-[2-(3,5-di-tert-butyl-4-hydroxyphenethyl)-4,6-difluorophenyl]-N'-[4-(N-benzylpiperidyl)]urea (N-4472), organic acid/N-4472 evaporates were prepared by using succinic acid, L-tartaric acid, citric acid and L-ascorbic acid (VC). Among these evaporates, only the VC/N-4472 evaporate at a molar ratio of more than 2 (VC/N-4472) formed stable colloidal particles (with a mean particle size 相似文献   

Selective dissolution of the silver component in colloidal Au and Ag multilayers: a facile way to prepare nanoporous gold film materials

Colloidal Au/Ag multilayer films were prepared by alternate assembly of Au nanoparticles with a size of 5 +/- 1.2 nm and Ag nanoparticles with a size of 10 +/- 2.4 nm by using 1,5-pentanedithiol as cross-linker. Nanoporous gold films with a ligament size of 26.7 +/- 4.6 nm were then prepared by selective dissolution of sacrificial templates of silver particles in colloidal Au/Ag multilayers. The complete dissolution of Ag particles in colloidal Au/Ag multilayers in a mixture solution of 3.0 mM HAuCl(4) and 3 M NaCl took place at room temperature without damage of the colloidal Au film. This method to prepare nanoporous gold films was further extended to the preparation of nanoporous gold nanotubes by depositing colloidal Au/Ag film on the inner wall of anodic aluminum oxides (AAO) followed by dissolution of colloidal Ag and removal of AAO templates.     

Effects of sonication on the size and crystallinity of stable zwitterionic organic nanoparticles formed by reprecipitation in water

Nanoparticles of a novel organic zwitterionic Meisenheimer complex, N',N' ',N' '-tri(isopropyl)-4-oxo-6-(isopropyliminio)-2-s-(2H)triazinespiro-1'-2',4',6'-trinitrocyclohexadienylide, were synthesized by reprecipitation in water under different conditions. While reprecipitation alone resulted in a suspension of amorphous particles that fell out of solution within hours, sonication for different periods of time resulted in the formation of crystalline particles that were stable in solution over the course of weeks. The disk-shaped particles had an average diameter of 140 nm and a thickness of 70 nm. Comparison of the optical spectroscopy of these particles with the monomer indicates that they possess delocalized excitonic states and enhanced radiative decay rates. The use of zwitterionic molecules in conjunction with sonication provides a way to exert some level of control over particle size and morphology, as well as increased colloidal stability.     

Modified reverse microemulsion synthesis for iron oxide/silica core–shell colloidal particles

Iron oxide/silica core–shell colloidal particles were prepared by basic reverse microemulsion (RM) method and two modified RM methods. By basic RM method, maximum particle size obtained was mere 40 nm. For building photonic crystals working in the visible range, the colloidal particles must be larger than 100 nm. Thus two modified RM methods were used. By alcohol modified RM method, short chain alcohols were used as co-surfactant. The particle size rose to near 100 nm, but the core–shell structure was comparatively poor. By emulsifier pair modified RM method, the particle size leapt to over 200 nm and a narrow growth window was found favorable to enhance the stability and rigidity of the surfactants layers. The core–shell mechanism was also discussed and a new four-step mechanism was proposed.     

Soluble colloidal manganese dioxide: Formation, identification and prospects of application

Soluble colloidal MnO₂ was prepared by the reduction of KMnO₄ by three reducing agents as MnSO₄, Na₂S₂O₃ and HCOOH in neutral aqueous solutions at 25°C. Under suitable conditions, these solutions were dark brown in color and found to remain stable and transparent for several weeks. The obtained colloid was characterized by spectrophotometric and coagulation methods. The spectral behavior of soluble colloidal MnO₂ was studied. The λ_max was 390 nm when MnO₂ was prepared by the reduction of KMnO₄ by MnSO₄. Both the λ_max and the molar extinction coefficient depended on the method of preparation of colloidal MnO₂. The formation of MnO₂ was confirmed by the determination of the oxidation state of Mn-species in MnO₂. The behavior of as-prepared colloidal solution obeys Beer Lambert law, if the concentrations of the colloidal particles are assumed to be equal to [MNO ₄ ^? ]₀. Both spectral analysis and that using Rayleigh’s law confirmed the existence of colloidal MnO₂. The observed coagulating efficiency depends not only on the concentration of electrolyte but also on the charge carried by the cation of the electrolyte. Stability of the colloidal particles in the aqueous solutions is determined by the negative charge on the surface of the colloidal particles.     

Polymer-Protected Bimetallic Clusters. Preparation and Application to Catalysis

Colloidal dispersions of polymer-protected Pd/Pt and Pd/Au bimetallic clusters were prepared by reduction of an alcoholic solution of PdCl₂ and H₂PtCl₆ or HAuCl₄ in the presence of poly(N-vinyl-2-pyrrolidone). The reduction can be carried out by refluxing in alcohol or by irradiation with visible light. The dispersions of the bimetallic clusters obtained are stable for months at room temperature and have from dark brown to brownish red color. Transmission electron micrographs show that the bimetallic clusters are composed of well-dispersed ultrafine particles of uniform size, about 1.5 nm for Pd-Pd and 3.4 nm for Pd-Au in diameter. The catalytic activity of the bimetallic clusters depends on the metal composition. In the case of the partial hydrogenation of 1, 3-cyclooctadiene, the activity went through a maximum when the alloy composition reached about 80% Pd and 20% Pt, or 60% Pd and 40% Au.     

Formation of the bimodal ensemble of silver nanoparticles in polymer solutions

Silver nanoparticles synthesized in polymer solutions are studied by spectroscopy (in near ultraviolet, visible, and infrared spectral regions) and high-resolution transmission electron microscopy. It is established that the ensemble with bimodal particle size distribution is formed from initially polydisperse nanoparticle ensemble in methylhydroxy ethyl cellulose solution. In contrast to the classical scheme of the ripening of colloidal dispersions, the number of small particles increases with time in the studied system; moreover, particles with a size of about 2 nm turned out to be stable. The large particles grow with time and their concentration drops.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 87–93. Original Russian Text Copyright © 2005 by Serebryakova, Uryupina, Roldughin.     

Synthesis of highly active visible-light-driven colloidal silver orthophosphate

The present study deals with the synthesis of highly uniform and spherical visible-light-driven colloidal silver phosphate (Ag₃PO₄) with the size of ～200 nm. These colloidal particles showed excellent photocatalytic activity for the removal of different dyes and pesticide under sunlight-type excitation. The photocatalytic activity of these particles, obtained by colloidal method, was found to be much higher than silver phosphate obtained by precipitation method, or titanium dioxide, or zinc oxide under identical conditions. The effect of catalyst amount and recyclability on the photocatalytic response of Ag₃PO₄ was also investigated.     

黄曲霉毒素B1抗体和纳米金颗粒的相互作用机理

研究了纳米金标黄曲霉毒素B1单克隆抗体(McAb)探针的制备及其标记机理, 确定了稳定标记5种不同粒径金溶胶(10.7~67.4 nm)所需McAb的最适质量浓度, 分别为0.07, 0.051, 0.033, 0.019, 0.012 mg/mL, 作用时间为5 min, pH为7.4. 对金标探针复合物进行透射电镜、红外光谱和免疫反应性鉴定的结果表明, 与未标记抗体相比, 抗体探针的免疫亲和常数、效价和常温贮藏稳定性得到了明显提高. 通过荧光光谱和圆二色谱研究纳米金与AFB1单抗McAb的相互作用机理, 发现纳米金对McAb产生静态猝灭, 猝灭的速率常数随着温度升高而降低. 确定了结合位点数和结合常数. 结果显示, 表明McAb的色氨酸残基与纳米金颗粒之间发生了Förster偶极-偶极无辐射能量转移. 初步确定反应前后McAb构象组成发生了变化是McAb探针亲和力和稳定性提高的原因.     

Impact of initiators in preparing magnetic polymer particles by miniemulsion polymerization

Sub-micron sized polystyrene particles containing magnetite more than 30 wt.% were prepared by miniemulsion polymerization with commercially available ferricolloid. The effects of some water-soluble initiators and/or oil-soluble initiators on the particles characteristics, such as the size, morphology, magnetic properties and colloidal stability, were studied. The size of monomer droplets/polymer particles increased from 60 to 300 nm during polymerization, keeping magnetic in core when potassium persulfate (KPS) or ammonium persulfate (APS) was used as the sole initiator. These particles were easily separated from the medium within short time scale in external magnetic field, while such characteristics were controlled by the amount of persulfate used for the polymerization. In contrast, when 2,2′-azobis isobutyronitrile (AIBN) was used as the initiator, the size of droplets/particles was retained to be 90 nm at the most and magnetite nanoparticles located at the surface of polystyrene particles, which were so colloidally stable that they were not separated in external magnetic field. The above-mentioned effect of initiators on particle size in persulfate system was likely originated from the decrease of pH value and the increase of ionic strength, which induced the fusion of droplets/particles containing magnetite. Mixed-initiators system resulted in intermediate characteristics, compared with each initiator system. The location of magnetite in the particle seems to depend on where initiation/polymerization occurred in each initiator system.     

New aspects of gold nanorod formation via seed-mediated method

Gold nanorods (AuNRs) were obtained via a wet chemistry technique, in aqueous medium, employing crystallisation seeds. The kinetics of formation, the aspect ratio, and the selectivity of the particles were evaluated according to the parameters of synthesis: the growth-driving agent, seed, and gold precursor concentrations. In 2–4 h, the rod particles attained the expected size and shape under kinetic control, and were stable for at least 2 days. In order to obtain good quality AuNRs in good yields, without enrichment, we suggest keeping the growth-driving agent/gold molar ratio, the Au^I/seed ratio, and the concentration of the reagents in the final solution within specific ranges. For example, even if good molar ratios between the reagents are maintained, relatively highly concentrated reaction solutions lead to AuNRs with lower aspect ratios. The main properties of the prepared colloidal systems and the nanoparticles were evaluated by UV–vis spectroscopy and transmission electron microscopy, respectively.     

Delamination of surfactant-intercalated brucite-like hydroxy salts of cobalt and copper and solvothermal decomposition of the resultant colloidal dispersions

Surfactant anion intercalated hydroxy salts of copper and cobalt of the formula M(OH)2- x (surf)x.mH2O [M = Cu, Co; surf = dodecyl sulfate, dodecyl benzene sulfonate, and x = 0.5 for Cu and 0.67 for Co] delaminate readily in 1-butanol to give translucent colloidal dispersions that are stable for months. The extent of delamination and the colloidal dispersion observed in these solids is higher than what had been observed for layered double hydroxides. The dispersions yield the corresponding nanoparticulate oxides on solvothermal decomposition. While the copper hydroxy salt forms approximately 300 nm dendrimer-like CuO nanostructures comprising nanorods of approximately 10 nm diameter, the cobalt analogue forms approximately 20 nm superparamagnetic particles of Co3O4.     

Absorption spectra of large colloidal silver particles in aqueous solution

Calculations of the optical absorption spectra of spherical particles of silver with a radius (r) of 10 to 80 nm in water were performed. The single intense absorption band for small particles (r=10 nm) with a maximum at about 395 nm is gradually broadened and shifted to the long-wave region with an increase in the particle size (to 435 nm atr=40 nm). In the case of large particles, the band splits into several components absorbing light in the visible spectral region. The results are in good agreement with the optical characteristics of colloidal solutions of silver obtained upon radiochemical reduction of Ag⁺ ions in aqueous solution. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 201–203, January, 1997.