Synthesis and steric stabilization of silver nanoparticles in neat carbon dioxide solvent using fluorine-free compounds

The adjustable solvent properties, vanishingly low surface tensions, and environmentally green characteristics of supercritical carbon dioxide present certain advantages in nanoparticles synthesis and processing. Unfortunately, most current techniques employed to synthesize and disperse nanoparticles in carbon dioxide use environmentally persistent fluorinated compounds as metal precursors and/or stabilizing ligands. This paper illustrates a one-step process for synthesis and stabilization of silver nanoparticles in carbon dioxide using only fluorine-free compounds. Isostearic acid coated silver nanoaparticles were formed and stably dispersed through arrested precipitation. Silver bis(3,5,5-trimethyl-1-hexyl)sulfosuccinate (Ag-AOT-TMH) was reduced in the presence of isostearic acid as a capping ligand in carbon dioxide solvent to form silver nanoparticles. The addition of cyclohexane as cosolvent or an increase in carbon dioxide solvent density enhances the dispersibility of the particles due to an increase in solvent strength. The dispersibility of the isostearic acid capped silver nanoparticles diminished with time until a stable dispersion was achieved due to the precipitation of a fraction of particle sizes too large to be stabilized by the solvent medium, thereby leaving a smaller size fraction of nanoparticles stably dispersed in the CO2 mixtures. This paper presents the one-step synthesis and stabilization of metallic nanoparticles in neat carbon dioxide without the aid of any fluorinated compounds.     

Stability, rheological, magnetorheological and volumetric characterizations of polymer based magnetic nanofluids

The Fe₃O₄ nanoparticles and Fe₃O₄ nanoparticles coated with oleic acid have been dispersed in base fluid of poly(ethylene glycol) (PEG). Stability and particle size distribution of these nanofluids have been studied by result analysis of UV–Vis spectroscopy, zeta potential and dynamic light scattering. Blue shift of UV–Vis spectra has been related to quantum effects such as band gap enlargement with particle size decreasing and also to effect of oleic acid on the ultraviolet wavelength. Flow behavior and suspension structure of Fe₃O₄ nanoparticles dispersed in PEG have been determined by rheological properties. Viscosity values of Fe₃O₄-PEG nanofluid as a function of temperature have also been investigated. The chain-like structure of Fe₃O₄ nanoparticles coated with oleic acid in base fluid of PEG has been verified by measuring the magnetorheological properties. The effect of temperature on magnetorheological properties of Fe₃O₄ nanoparticles coated with oleic acid has also been investigated in base fluid of PEG. The volumetric properties of Fe₃O₄-PEG and Fe₃O₄ coated with oleic acid–PEG nanofluids and PEG–oleic acid solution have also been measured at different temperatures to specify the suspension structure and also interactions of Fe₃O₄, PEG and oleic acid molecules.     

Modifications of poly(methyl-3-propylthiol)siloxane to give stationary phases for open tubular supercritical fluid chromatography

Summary Poly(methyl-3-propylthiol)siloxane has been evaluated for use as stationary phase in open tubular columns for gas and supercritical fluid chromatography. Immobilization of the stationary phase was achieved by crosslinking with 2,4,6-trichloro-1,3,5-triazine. The poly(methyl-3-propylthiol)siloxane stationary phase film was in situ oxidized to the disulphide and sulphonic acid forms and both have been evaluated for use in supercritical fluid chromatography. Good selectivity towards polar polycyclic aromatic compounds has been shown. All the modified forms of the stationary phase were loaded with silver ions and were evaluated with regard to ligand exchange chromatography using supercritical fluid carbon dioxide as a mobile phase. The utility of the stationary phase, having sulphonic acid groups loaded with silver ions, has been demonstrated by separation of fatty acid methyl esters according to their unsaturation.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Specific features of polyol synthesis of silver nanoparticles with the use of solid carboxylates as precursors

Electron microscopy, X-ray diffraction, and chromatography-mass spectrometry have been employed to investigate the reduction of solid silver caprylate in ethylene glycol with the formation of silver nanoparticles. The structural characteristics of silver nanoparticles have been studied as depending on the conditions of their synthesis, including temperature, reduction time, and silver salt concentration. It has been found that, in the studied range of parameters under the conditions, when solid silver caprylate is dispersed in ethylene glycol, the characteristics of resulting nanoparticles are almost independent of the synthesis temperature. This peculiarity is related to the fact that the formation and growth of nanoparticles occur on the surface of silver salt crystals and are accompanied by gradual dissolution thereof. In this system, ethylene glycol plays the roles of a reductant and a solvent for liquid reaction products.     

Electrocatalytic dechlorination of chloroacetic acids by silver nanoparticles modified glassy carbon electrode

A simple potentiostatic method was employed to prepare silver nanoparticles deposited on glassy carbon electrode. The silver nanoparticles exhibit extraordinary electrocatalytic activities toward the reduction process of chloroacetic acids. The electrochemical behavior of trichloroacetic acid, dichloroacetic acid, and monochloroacetic acid has been investigated by cyclic voltammetry at the silver nanoparticles-modified glassy carbon electrode in 0.1 M LiClO₄ solution; each compound exhibits a series of reduction peaks which represent sequential dechlorination steps up to acetic acid. The electrocatalytic dechlorination mechanism for chloroacetic acids was also discussed in this work.     

Reactivity of palladium nanoparticles supported on a microemulsion-based organogel network in supercritical carbon dioxide

Palladium (Pd) nanoparticles were prepared using the phase transfer method and coated with alkylamines as stabilizing agents stably dispersed in nonpolar solvents. Spherical Pd nanoparticles with an average diameter of 4 nm and a relatively narrow size distribution were obtained using hexylamine or dodecylamine, and they were successfully incorporated in microemulsion-based gelatin organogel (OG); also, an OG network containing Pd nanoparticles was prepared via drying. For the Mizoroki-Heck cross-coupling reaction of iodobenzene with methyl acrylate in supercritical carbon dioxide, the Pd nanoparticles in the OG network exhibited much higher reactivity than those in powder state. Preparation conditions of OG (e.g., gelatin concentration) affected the apparent reactivity of the supported Pd nanoparticles. The Pd nanoparticles in the OG network with high gelatin concentration were recycled with no appreciable change of reactivity. In contrast, the reactivity of the Pd nanoparticles with low gelatin concentration decreased during recycling.     

The Effect of a Magnetic Field on a RAPET (Reaction under Autogenic Pressure at Elevated Temperature) of MoO(OMe)(4): Fabrication of MoO(2) Nanoparticles Coated with Carbon or Separated MoO(2) and Carbon Particles

In this article, we present results of the RAPET dissociation of MoO(OMe)4 at 700 degrees C in a closed Swagelok cell. The reaction produces molybdenum dioxide nanoparticles (20 nm) coated with carbon (20 nm). We have also carried out the same reaction under an applied magnetic field of 10 T. This reaction yielded different products. It produces a mixture of comparatively larger (50 nm) molybdenum dioxide nanoparticles and separated uncoated carbon particles (20-30 nm).     

Electrophoretic motion of a nanorod along the axis of a nanopore under a salt gradient

Wood-based activated carbon was modified by deposition of silver using Tollens method. Adsorbents with various contents of silver were used to study NO(2) and NO (the product of NO(2) reduction by carbon) retention. The surface of the initial and exhausted materials was characterized using adsorption of nitrogen, XRD, SEM/EDX, FTIR and TA. The results indicated that with an increasing content of silver on the surface the capacities to retain NO(2) and NO increase until the plateau is reached. The performance depends on the dispersion of nanoparticles and their chemistry. Highly dispersed small silver metal particles promote formation of chelates with NO(2) and/or with NO. An excess of Tollens reagent results in formation of larger silver crystals and silver oxide nanoparticles. If sufficiently dispersed, they also enhance the retention of NO(2) via formation of nitrates deposited in the pore system. The surface of the carbon matrix is also active in NO(2) retention, providing the small pores and edges of graphene layers, where the reductions of NO(2)/oxidation of carbon take place.     

The adsorption behavior of p-hydroxybenzoic acid on a silver-coated filter paper by surface enhanced Raman scattering

On dried filter paper coated with silver nanoparticles, surface-enhanced Raman scattering (SERS) spectra of p-hydroxybenzoic acid (PHBA) were studied, and high-quality SERS spectra were obtained, indicating that the silver-coated filter paper is a highly SERS-active substrate. The analysis showed that the adsorption behavior of PHBA molecules on silver nanoparticles coated on filter paper was different from that in silver aqueous colloids. On the filter paper, it was found that the SERS spectra of PHBA changed with the proportion of PHBA molecules and silver nanoparticles, indicating that the adsorption behavior of PHBA molecules changed with the proportion. The probable reasons are given.     

Structure and photocatalytic properties of materials based on titanium dioxide and silver nanoparticles

Phase composition and structure of mesostructured materials, titanium dioxide and titanium dioxide modified with silver nanoparticles, have been studied by X-ray diffraction analysis. Introduction of Ag(I) ions into the initial composition and variation of the annealing temperature over the 500–950°C range allows controlling the anatase to rutile crystal phase ratio in the samples. The photocatalytic activity of TiO₂ and TiO₂/Ag samples has been demonstrated using the methyl orange degradation reaction. The catalytic properties of the materials have been found to depend on the anatase to rutile phase ratio and on the presence of silver nanoparticles.     

In Situ Treatment of Thermal RF Plasma Processed Nanopowders to Control their Agglomeration and Dispersability

Titanium carbonitride nanoparticles have been produced in an inductively coupled thermal plasma and subsequently modified using a surfactant that has been deposited in situ on their surface in-flight. The surfactant was injected in the reactor while the nanoparticles are still dispersed in the gas phase, allowing the coating of primary particles instead of the corresponding agglomerates. In contrast to naked TiCN nanoparticles, the surfactant coated particles could be readily dispersed in water with a short ultrasonic treatment and built up no large agglomerates as proved by Photon Correlation Spectroscopy measurements. The investigated surfactants seem, however, to undergo a chemical modification and/or a thermal degradation at the surface of the TiCN nanoparticles.     

微乳液中单分散银纳米颗粒的制备及抗磨性能

采用水/液体石蜡/Span 80-Tween 80/正丁醇微乳液体系, 制备了具有良好单分散性的Ag纳米颗粒. 通过X射线粉末衍射仪、透射电子显微镜、傅立叶变换红外光谱仪和热分析仪表征了Ag纳米颗粒的结构、形貌、粒径大小及分布、表面键合性质和热性能. 结果表明, 所制备的Ag纳米颗粒具有立方晶型结构, m(Span 80)∶m(Tween 80)=7∶3时, 粒径分布呈单分散性, 平均粒径约为6 nm. 在四球长时抗磨损试验机上考察了分散于液体石蜡中Ag纳米颗粒的抗磨性能. 实验结果表明, Ag纳米颗粒具有良好的抗磨性, 且能显著提高基础油的承载能力.     

Size crystallographic effects for silver and gold nanoparticles dispersed in a biopolymer matrix

Crystallographic size effects occurring during the formation of zero-valence silver and gold nanoparticles dispersed in a biopolymer polysaccharide matrix (arabinogalactan) have been studied by means of X-ray diffraction analysis. The average size of the nanoparticles has been found to increase with the increase in the metal content in the nanocomposite. Stabilization of the nanoparticles by the polymer matrix is accompanied by the decrease in the unit cell parameter of the metal correlated with the decrease in the coherent scattering length.     

MoS_3 loaded TiO_2 nanoplates for photocatalytic water and carbon dioxide reduction

Photocatalytic water splitting and carbon dioxide reduction provide us clean and sustainable energy resources. The carbon dioxide reduction is also the redemption of the greenhouse effect. MoS_3/TiO_2 photocatalysts based on TiO_2 nanoplates have been synthesized via a hydrothermal acidification route for water and carbon dioxide reduction reactions. This facile approach generates well dispersed Mo S3 with low crystallinity on the surface of TiO_2 nanoplates. The as-synthesized MoS_3/TiO_2 photocatalyst showed considerable activity for both water reduction and carbon dioxide reduction. The thermal treatment effects of TiO_2 , the loading percentage of MoS_3 and the crystalline phase of TiO_2 have been investigated towards the photocatalytic performance. TiO_2 nanoplate synthesized through hydrothermal reaction with the presence of HF acid is an ideal semiconductor material for the loading of MoS_3 for photocatalytic water and carbon dioxide reduction simultaneously in EDTA sacrificial solution.     

Polymer particles with dendrimer@SiO2-Ag hierarchical shell and their application in catalytic column

Polymer particles with dendrimer@SiO₂–Ag hierarchical shell were prepared, and their application in the catalytic column for the reduction of 4-nitrophenol (4-NP) was also investigated. The PS microspheres with the carboxyl group were used as the supports for the immobilization of dendrimer@SiO₂–Ag shell. The polyamidoamine (PAMAM) dendrimer was grafted on the surface of PS microsphere through repetitive Michael addition reaction of methyl acrylate (MA) and amidation of the obtained esters with a large excess of ethylenediamine (EDA) successively. The silver nanoparticles formed inside the PAMAM shell. Then, the silver nanoparticles, which were used as center of nucleation, were coated with SiO₂ shell through improved Stöber method. Moreover, the more silver nanoparticles were dispersed on the surface of SiO₂ shell. The contents of silver element were measured using inductively coupled plasma (ICP-MS). The obtained PS@PAMAM@SiO₂–Ag nanoparticles were packed in stainless steel column, which has been used effectively for the catalytic reduction of 4-NP. Under column pressures, the rigid SiO₂ shell plays a better role in immobilization of silver nanoparticles than the soft PAMAM shell. This technique for packing catalytic nanoparticles in column improves the efficiency of application with metal catalysts as well as reduces the tedious separation processes in catalytic reaction.     

Metallic nanoparticle production utilizing a supercritical carbon dioxide flow process

Metallic nanoparticles of palladium and silver ranging in size from 1 to 15 nm were produced entirely within carbon dioxide by spraying a carbon dioxide carrier solution containing CO2-soluble metal precursors into a CO2 receiving solution containing a reducing agent (NaBH(OAc)3 or H2) and fluorocarbon thiol stabilizing ligands. The process uses the benign solvent CO2 while also allowing for the production of nanoparticles with a limited number of chemical components. Particles were characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS).     

Isolation and characterization of fluorescent nanoparticles from pristine and oxidized electric arc-produced single-walled carbon nanotubes

Fluorescent nanoparticles were isolated from both pristine and nitric acid-oxidized commercially available carbon nanotubes that had been produced by an electric arc method. The pristine and oxidized carbon nanotube-derived fluorescent nanoparticles exhibited a molecular-weight-dependent photoluminescence in the violet-blue and blue to yellowish-green ranges, respectively. The molecular weight dependency of the photoluminescence was strongly related to the specific supplier. We analyzed the composition and morphology of the fluorescent nanoparticles derived from pristine and oxidized nanotubes from one supplier. We found that the isolated fluorescent materials were mainly composed of calcium and zinc. Moreover, the pristine carbon nanotube-derived fluorescent nanoparticles were hydrophobic and had a narrow distribution of maximal lateral dimension. In contrast, the oxidized carbon nanotube-derived fluorescent nanoparticles were superficially oxidized and/or coated by a thin carbon layer, had the ability to aggregate when dispersed in water, and exhibited a broader distribution of maximal lateral dimension.     

表面羧基化Fe3O4磁性纳米粒子的快捷制备及表征

亲水性磁性纳米颗粒在生物科学领域有着广泛应用,本研究提出了一种快速对磁性纳米粒子表面进行羧基化的方法. 首先使用氯化铁和氯化亚铁为原料, 以油酸为表面活性剂, 通过共沉淀法制得油酸包覆的亲油性磁性纳米粒子, 然后用高锰酸钾进行原位氧化, 将覆盖在粒子表面的油酸中的C＝C键氧化成-COOH, 从而得到单层羧基功能化的亲水性磁性纳米粒子. 利用透射电镜(TEM)、X射线衍射(XRD)、傅利叶红外光谱仪(FT-IR)、热重分析仪(TGA)、振动样品磁强计(VSM)、Zeta电位分析仪等对其进行表征. 结果表明磁性纳米粒子表面被成功羧基化,粒子的平均直径约为9 nm,饱和磁化值为64.5 emu/g,剩磁和矫顽力近似为零,具有典型的超顺磁性. 羧基化磁性纳米粒子可在pH7-10的水溶液中形成稳定分散的磁流体,保存6周无沉淀出现.     

Study of the surface chemistry and morphology of single walled carbon nanotube-magnetite composites

The study of the morphologies of the single walled carbon nanotube (SWCNT), magnetite nanoparticles (MNP), and the composite based on them was carried with combined X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). These techniques together with thermogravimetric analyses (TGA) and diffuse reflectance infrared transform spectroscopy (DRIFTS) confirmed the production of pure single phases, and that the composite material consisted of MNP attached to the outer surface of the SWCNT. The Mössbauer spectroscopy (MS) research showed the presence of a large quantity of Lewis acid sites in the highly dispersed magnetite particles supported on the SWCNT outer surface. The DRIFTS carbon dioxide adsorption study of the composites revealed significant adsorption of carbon dioxide, fundamentally in the Lewis acid sites. Then, the Lewis acid sites were observed to be catalytically active. Further, the electron exchange between the Lewis acid sites and the basic or amphoteric adsorbed molecules could influence the magnetic properties of the magnetite. Consequently, together with this first ever use of MS in the study of Lewis acid sites, this investigation revealed the potential of the composites for catalytic and sensors applications.     

Functional polymer nanocomposites containing triazole and carboxyl groups

New water-soluble functional polymer nanocomposites with nanoparticles of metallic silver in a matrix of 1-vinyl-1,2,4-triazole copolymers with crotonic acid have been synthesized. The resulting nanocomposites contain isolated silver nanoparticles 2–12 nm in diameter, preferably spherical in shape, and uniformly distributed in the polymer matrix. ATR IR spectroscopy has revealed that the nanoparticles affect the state of the carboxyl groups in the polymer matrix. It has been found that the size of zero-valent silver nanoparticles depends on the ratio of monomer units in the polymer matrix. The thermo-oxidative stabilities of the synthesized copolymers and polymer nanocomposites produced on their basis have been examined.