Phase transfer of silver nanoparticles from aqueous to organic solutions using fatty amine molecules

We demonstrate the phase transfer of silver nanoparticles synthesized in an aqueous medium into hexane containing the cationic surfactant octadecylamine (ODA). During vigorous shaking of the biphasic mixture, rapid phase transfer of the silver nanoparticles into the organic phase was observed. The phase transfer of the silver nanoparticles arises due to coupling of the silver nanoparticles with the ODA molecules present in organic phase via either coordination bond formation or weak covalent interaction. This process renders the nanoparticles sufficiently hydrophobic and dispersible in the organic phase. The ODA-stabilized silver nanoparticles could be separated out from the organic phase in the form of a powder and are readily redispersible in different organic solvents. The nature of binding of the ODA molecules to the silver nanoparticle surface was characterized using UV-vis spectroscopy, thermogravimetry, transmission electron microscopy, nuclear magnetic resonance spectroscopy, X-ray photoemission spectroscopy, and Fourier transform infrared spectroscopy.     

Recycling nanoparticles stabilized in water-in-CO2 microemulsions for catalytic hydrogenations

Catalytic hydrogenations of olefins took place effectively in supercritical CO2 with Pd0 nanoparticles dispersed in the fluid phase using a water-in-CO2 microemulsion consisting of water, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as a surfactant, and 1-octanol as a cosolvent. The hydrogenated products dissolved in supercritical CO2 can be separated from the octanol solution containing AOT microemulsions with Pd0 nanoparticles by phase separation (upper phase, supercritical CO2 with hydrogenated products; lower phase, 1-octanol containing AOT microemulsions with Pd0 nanoparticles) accompanied by reduction of CO2 pressure. After collecting the hydrogenated products by flowing the upper CO2 phase to a collection vessel, the Pd0 nanoparticles remaining in the lower phase can be redispersed into supercritical CO2 by pressurizing the system to a pressure where a homogeneous phase is attained. The redispersed nanoparticles can be reused as catalysts for the next runs of the hydrogenations. Triphenylethylene was hydrogenated to 1,1,2-triphenylethane at conversions of 100% (1st-3rd runs), >99% (4th run), and >96% (5th run) using the recycled Pd0 nanoparticles. The feasibility of using other organic solvents as cosolvents is also studied in the present paper.     

In situ synthesis of gold and silver nanoparticles by using redox-active amphiphiles and their phase transfer to organic solvents

An in situ reduction approach to synthesizing gold and silver nanoparticles by using a series of newly designed, redox-active amphiphiles at basic pH is described. These amphiphiles are the conjugates of a fatty acid (e.g., oleic acid, stearic acid, and lauric acid) and a redox-active amino acid (e.g., tryptophan or tyrosine). The amphiphile-coated nanoparticles are then efficiently transferred from water to different nonpolar organic media (such as benzene, toluene, xylene, cyclohexane, and hexane) simply by acid treatment. The phase-transfer process was monitored by UV/visible spectroscopy and transmission electron microscopy, and the results showed that the average particle size and size distribution remain almost unchanged after transferring to the organic media. The anchoring of the amphiphile to the nanoparticle surface was confirmed by FTIR spectroscopy and thermogravimetric analysis. A mechanism is proposed to describe the stability of colloidal Au and Ag nanoparticles formed in situ and their phase transfer to organic solvents. The presence of the amphiphile increases the thermal stability of the colloidal gold nanoparticle conjugates in organic solvents.     

Formation of silver nanoparticles from a complex of Ag(I) with 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]acetic acid in organic solvents

Specific features of the formation of silver nanoparticles upon the decomposition of the complex of Ag(I) with 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]acetic acid in organic solvents characterized by large donor numbers (27–34) are studied. It is established that the stability of prepared organosols depends to a significant extent on the nature of a dispersion medium and the presence of water and oxygen in this medium. The Ag(I) complex is a solid precursor for the preparation of silver nanoparticles.     

Facile fabrication of amphiphilic gold nanoparticles with V-shaped brushes from block copolymers with a trithiocarbonate group as the junction

Amphiphilic gold nanoparticles grafted with V-shaped brushes (Au-V-brushes) were prepared by grafting a polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer with a trithiocarbonate group as the junction to the Au surface. The obtained Au-V-brushes were subjected to solubility test and UV-vis, FT-IR, TEM and DLS characterizations. It is found that the Au-V-brushes are soluble in both water and organic solvents. In the common solvent DMF, the size of the Au-V-brushes is about 17 nm, whereas in selective solvents (toluene and water) aggregates of 70-90 nm are formed. Phase transfer of the Au-V-brushes from the water phase into the toluene phase occurs upon addition of Na(2)SO(4) into water and the Au-V-brushes can also transfer from the toluene phase to the interface of toluene and water phases after addition of citric acid in the water phase.     

Phase transfer of oleic acid capped Ni(core)Ag(shell) nanoparticles assisted by the flexibility of oleic acid on the surface of silver

The phase transfer protocols in vogue for the oleic acid capped silver nanoparticles, viz., salt-induced precipitation and redispersion or phosphoric acid-induced method, are examined and compared thoroughly. A comprehensive evaluation with respect to the mechanistic aspects involved is made and the merits and demerits of the different procedures are delineated. It is found that the salt-induced precipitation and redispersion is more versatile in that the precipitate can actually be redispersed in both aqueous and organic media. However, in terms of mechanism both the routes seem to be very similar wherein the orientational change of oleic acid on the silver surface in the two different environments-organic and aqueous-plays a crucial role in the adaptability of the system to the different environments. Subsequently, this change of orientation of oleic acid on silver surface in aqueous and organic media has been utilized to phase transfer Ni-based nanoparticulate systems. The nascent oleic acid-capped Ni nanoparticles, which were synthesized by a foam-based protocol, were dispersible in water but not in nonpolar organic media such as cyclohexane or toluene. Then, just by coating a thin shell of silver on them we could achieve complete phase transfer of the Ni(core)Ag(shell) from aqueous to organic media following similar procedures used for oleic acid-capped silver nanoparticles. Here, the phase transfer seems to be facilitated by the orientational flexibility of oleic acid on the silver surface as opposed to other metal surfaces as evidenced from the infrared and thermogravimetric analyses of oleic acid-capped Ni and Ni(core)Ag(shell) nanoparticles. This orientation-assisted phase transfer method could be generalized and can be adapted to other systems where, if the nascent nanoparticles cannot be phase transferred as is, they can be coated by a silver shell and oleic acid making them suitable for dispersion in both aqueous and organic media.     

烷基胺作为络合剂制备亲油性纳米银

在烷基胺/油酸/水混合体系中制备出表面包裹的亲油性纳米银颗粒,体系中的烷基胺作为络合剂和稳定剂起到使Ag离子水溶液与油酸互溶的作用,在还原过程中均匀释放出Ag离子,使Ag表面被油酸包裹具有亲油性。在相同反应条件下,分别以环己胺、正丁胺、三乙胺作为络合剂,考察了不同结构的胺对纳米Ag的形成过程以及对纳米Ag的表面性质和形貌的影响,并考察了所得纳米Ag颗粒的热稳定性。结果表明,相同反应条件下,正丁胺和三乙胺比环己胺更适于作为络合剂和稳定剂来制备油酸包裹的亲油性纳米Ag,所制备的纳米Ag颗粒在烷烃等中具有较好的热稳定性。     

溶剂对反胶束法合成CdS纳米粒子粒径的影响

以磺基琥珀酸二辛酯钠盐(AOT)为保护剂,利用反胶束法在不同烷烃溶液中合成了CdS纳米粒子.采用紫外-可见光谱、透射电子显微镜、荧光光谱法对其进行表征.研究表明:在不同烷烃溶液中合成的CdS纳米粒子,其粒子大小和荧光强度都随溶剂而改变.     

溶致液晶中金属纳米粒子的掺杂及其作用机制研究

在用琥珀酸二异辛酯磺酸钠(AOT)构建的具有长程有序结构的层状溶致液晶内, 用不同方式导入预制的亲油或亲水贵金属纳米粒子, 可得到纳米粒子分布在不同介观空间内的无机/有机杂合体. 依据小角X射线散射和偏光显微镜结果, 通过分析掺杂纳米粒子与液晶模板的相互作用, 对掺杂前后体系结构的变化及制得杂合体的稳定性进行了表征. 结果表明, 除考虑掺杂粒子与层状模板空间的匹配外, 体系中静电斥力、范德华引力和Helfrich涨落力之间的平衡是维持液晶结构稳定的基本条件.     

The aerosol OT+n-butanol+n-heptane+water system: phase behavior, structure characterization, and application to Pt70Fe30 nanoparticle synthesis

A phase diagram of the pseudo-ternary Aerosol OT (AOT)+n-butanol/n-heptane/water system, at a mass ratio of AOT/n-butanol=2, is presented. Conductivity measurements showed that within the vast one-phase microemulsion region observed, the structural transition from water-in-oil to oil-in-water microemulsion occurs continuously without phase separation. This pseudo-ternary system was applied to the synthesis of carbon-supported Pt70Fe30 nanoparticles, and it was found that nanoparticles prepared in microemulsions containing n-butanol have more Fe than those prepared in ternary microemulsions of AOT/n-heptane/water under similar conditions. It was verified that introducing n-butanol as a cosurfactant into the AOT/n-heptane/water system lead to complete reduction of the Fe ions that allowed obtaining alloyed PtFe nanoparticles with the desired composition, without the need of preparing functionalized surfactants and/or the use of inert atmosphere.     

Synthesis of pure colloidal silver nanoparticles with high electroconductivity for printed electronic circuits: the effect of amines on their formation in aqueous media

This paper describes a practical and convenient method to prepare stable colloidal silver nanoparticles for use in printed electronic circuits. The method uses a dispersant and two kinds of reducing agents including 2-(dimethylamino) ethanol (DMAE), which play important roles in the reduction of silver ions in an aqueous medium. The effect of DMAE and dispersant, as well as the factors affecting particle size and morphology are investigated. In the formation of the silver nanoparticles, reduction occurs rapidly at room temperature and the silver particles can be separated easily from the mixture in a short time. In addition, organic solvents are not used. Pure, small and relatively uniform particles with a diameter less than 10 nm can be obtained that exhibit high electroconductivity. The silver nanoparticles are stable, and can be isolated as a dried powder that can be fully redispersed in deionized water. This method of producing colloidal silver nanoparticles will find practical use in electronics applications.     

Size-dependent carrier dynamics in CdS nanoparticles by femtosecond visible-pump/IR-probe measurements

Ultrafast photoexcited carrier dynamics in CdS nanoparticles prepared by an AOT/n-heptane reversed micelle system were investigated by a femtosecond visible-pump/mid-IR probe technique. A mid-IR probe beam was found to mainly probe the ultrafast dynamics of photoexcited electrons in the conduction band. Dispersions of CdS nanoparticles with 8 different mean diameters from 2.9 to 4.1 nm were prepared by tuning the mole ratio between water and AOT (W = [H(2)O]/[AOT]) in the reversed micelle systems. The excited state lifetime strongly depended on the mean size of CdS nanoparticles with a maximum around a mean diameter of 3.5 nm. This result was explained by considering the balance between the carrier recombination rates via surface states and those via interior states. The relationship between the excited state lifetime and the size of CdS nanoparticles was drastically changed when the surface was terminated by thiol molecules.     

Solid-liquid-liquid extraction as an approach to the sensitive detection of a hydrophobic pollutant through surface-enhanced Raman spectroscopy

Surface-enhanced Raman scattering (SERS) spectra of thiram (tetramethylthiuram disulfide), a dimethyl dithiocarbamate fungicide, were recorded after the adsorption on plasmonic silver nanowires from a system of water, organic solvent and nanoparticles. As organic solvents dichloromethane and 1-octanol were involved. A method for measuring the adsorption constant of thiram as a model molecule to the silver surface by studying its partition phenomena in a binary solvent system is presented. The method is based on the extraction of a hydrophobic molecule from an organic solvent by an aqueous suspension of silver anisotropic nanoparticles. The obtained results demonstrate the effectiveness of SERS methodology for the sensitive analysis of compounds with low aqueous solubility, and a reliable SERS spectrum of thiram was obtained with excellent signal/noise ratio at low concentrations. In addition, for vibrational assignments, Density Functional Theory (DFT) was used for the simulation of the Raman and SERS spectra of thiram and its complexes with silver considering the following two models: a single silver atom and an Ag₂₀ cluster.     

Effects of High Pressure on the Surface Plasmon Resonance of Copper and Silver Nanocrystals

We used a diamond anvil cell(DAC) to control the deformation of synthesized copper nanorods and silver nanoparticles. And we measured the surface plasmon resonance of copper nanorods and silver nanoparticles, which exhibit redshifts or blueshifts. The surface plasmon resonance shows an abnormal blue shift for both copper nanorods and silver nanoparticles. The solvents of copper nanorods and silver nanoparticles are n-hexane and water, where the pressure loads include quasi-hydrostatic and non-hydrostatic.     

Small-sized silver nanoparticles for studies of biological effects

The influence of the hydration extent, AOT and silver ion concentration on average particle size and size distribution in micellar solution of silver nanoparticles obtained by biochemical synthesis was investigated. Formation and stability of nanoparticles were controlled by measurements of optical absorption spectra. Particle sizes were determined by transmission electron microscopy. Combinations of varied parameters have been found, making it possible to prepare three micellar solutions of spherical silver nanoparticles with a different average size in the range 4.6–10.5 nm and narrow size distribution (the standard deviation does not exceed 2.5 nm). For the water dispersions prepared from such solutions by the specially developed procedure, possible applications for studies of size effects in the biological action of nanoparticles are also discussed.     

Polymeric Nanoparticles Stabilized by Surfactants: Kinetic Studies

A kinetic study was carried out to monitor the time-dependent formation of surfactant-stabilized polymeric nanoparticles prepared by controlled phase separation. The nanoparticles were made of poly(methylmethacrylate) or polystyrene and several ionic and nonionic surfactants. The dispersion was prepared by fast mixing a solution of the polymers in organic solvents with a solution of a surfactant in water. We observed the formation of well-defined nanoparticles measured by time-resolved small-angle x-ray scattering (TR-SAXS). Our results suggest that the kinetics for the formation of nanoparticles comprising ionic surfactants is much faster (in the range of milliseconds) than that for nanoparticles comprising nonionic surfactants (on the time scales of several seconds). We were able to observe the transformation of particle surface from transient structure to hard sphere one in real time. Some systems manifest a plethora of structural changes that demands further experimental research.     

琥珀酸二异辛酯磺酸钠微乳体系中纳米银的制备及其连续相的影响

在琥珀酸二异辛酯磺酸钠(AOT)为表面活性剂、环己烷为连续相形成的微乳体系中, 利用水合肼还原AgNO₃制备了分散性良好的纳米银. 利用紫外-可见(UV-Vis)光谱和透射电镜(TEM)对所得产物进行了表征, TEM显微图像表明形成粒子为球形结构, 平均粒径为5.10 nm, 标准偏差为2.84 nm. 分别利用正己烷、正庚烷、正辛烷、环己烷和十二烷等作连续介质, 研究了微乳液中连续相对纳米银形成的影响. 随着正烷烃碳链长度的增加, 微乳液中胶束之间的交换速率增大, 形成粒子的平均粒径逐渐减小. 十二烷形成的微乳体系制备的纳米银溶胶具有最宽的共振吸收峰, 所得的纳米银粒子平均粒径最小. 环己烷形成的微乳液中反胶束具有特殊的界面强度, 导致纳米银晶核的形成速率过低, 纳米银晶粒的生长不完全.     

油溶性Ag纳米微粒的制备及表征

Surface modified silver nano particles were synthesized in a mixture solvent of water-alcohol with Pyridinium di-n-octadecyldithio phosphate(PyDDP) as a modification agent. Themorphology and structure of DDP-coated Ag (Ag-DDP) nanoparticles were characterized using X-ray powder diffraction(XRD), Transmission electron microscopy(TEM), Fourier transform infrared spectrum (FT-IR) and Thermo gravimetric analysis(TGA). Anti wear properties of Ag-DDP nano particles were tested using a four-ball tribological testing machine. The disperse properties of Ag-DDP nanoparticles were evaluated in solvents such as chloroform, benzen, toluene, liquid paraffin, distilled water and ethanol. The results show that Ag-DDP nanoparticles disperse in organic solvents, but they don’t disperse in water or ethanol. The good disperse properties in organic solvents enable Ag-DDP nanoparticles to be used as oil additives. The XRD pattern of Ag-DDP nanoparticles indicates that they have fcc crystal structure, and the modification layer can prevent the oxidation of Ag nanocores. TEM graphs show that Ag-DDP nanoparticles have a homogeneous grain distribution; the average diameter is about 15nm. FT-IR and TGA curves indicate that the existence of modification layer can prevent the adsorption of water on the surface of nanoparticles. Tribological tests show that Ag-DDP nanoparticles have good anti-wear properties in liquid paraffin, and they can improve the applied load of base oil.     

Thiol-frozen shape evolution of triangular silver nanoplates

The structural and optical stability of nanoparticles directly influences their applications. The shape evolution of silver nanoplates synthesized in the presence of bis(2-ethylhexyl) sulfosuccinate (AOT) could be effectively frozen using thiols in aqueous solution. These thiols (e.g., 1-hexanethiol, 1-octanethiol, 1-dodecanethiol, and 1-hexadecanethiol) exhibit stronger surface affinity on the silver crystalline surfaces. This is evidenced from both the unchanged shape/size of nanoplates and their unshifted plasmon resonances in optical absorption. To quantitatively explain the thiol-frozen shape evolution mechanism of silver nanoplates at molecular scale, molecular dynamics simulation was performed. The results show that these thiols exhibit larger interaction energies than AOT molecules on the silver atomic surfaces and hence freeze the shape evolution of silver nanoparticles. This thiol-frozen strategy would not only be useful for stabilizing nanoparticles but would also allow the introduction of a wide range of surface chemical functionalities to the nanoparticles for potential applications in nanosensors.