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The transport phenomena of dust particles have been widely observed in fusion plasmas. In this article, we report the observations of dust fragmentations in the Experimental Advanced Superconducting Tokamak (EAST). A dust particle splits into two daughter particles and their motions are recorded before and after the breakup with a fast video camera. The trajectories of the daughter particles in the experiment are consistent with equation-of-motion simulations. The stability of a rotating charged particle in the plasma is briefly discussed.
The size-dependent optical properties of CdSe nanoparticles are desirable in bio-imaging and cell sorting applications because of their tunable photoluminescence in the visible range. Previous studies have already suggested that CdSe QDs could be utilized for pathogen detection by using suitable capping agents to make it biocompatible; however, systematic works on the effect of crystallite size and composition of the nanocrystals are scarce. The present research will be focused on the effect of CdSe crystal size and composition (pure and doped systems) to systematically evaluate its applicability in detecting pathogens, like Escherichia coli (E. coli). Highly luminescent water-soluble CdSe QDs were firstly synthesized in the aqueous phase, in the presence of thioglycolic acid (TGA) as a capping agent. CdSe/TGA molar ratios, reaction temperature, time, and pH were evaluated in order to optimizer the QDs optical properties. X-Ray diffraction (XRD) measurements confirmed the formation of CdSe exhibiting hexagonal structure with an estimated averaged crystallite size in the 4-6 nm range. Transmission electron microscopy (TEM) analyses evidenced the formation of CdSe nanocrystals with particle sizes between 3-5 nm. UV-Vis measurements showed a strong exciton peak between 390-400 nm with an estimated band gap of 2.64 eV (bulk: 1.74 eV); additionally, a strong fluorescence peak was observed between 500-550 nm using an excitation wavelength of 400 nm. Fourier Transform Infrared Spectroscopy (FT-IR) analyses suggested the actual functionalization of the CdSe surface with TGA functional groups. Preliminary results of the CdSe/TGA coupling with the selected bacteria, E. coli, are presented and discussed.
Medical research has demonstrated the importance of the utilization of stable, fluorescent nanoprobes. The present work addresses the applicability of biocompatible and fluorescent ZnO nanoparticles as probes for detection of pathogens with the aim of achieving extremely low detection limits. For this purpose, ZnO surface must be functionalized for its subsequent interaction with bacterial cellular membrane (coupling), which will allow the corresponding detection and quantification. Herein we will discuss the aqueous synthesis of stable, water soluble and biologically compatible ZnO nanoparticles (NPss) capped with L-glutathione (GSH). The understanding of the interactions between GSH molecules and surface atoms in ZnO QDs became critical to foster the applicability of this nanomaterial in the biomedical and bioengineering fields. In this regard, the GSH/ZnO molar ratios, reaction temperature (40°C and 60°C), time and pH (6-9) became crucial factors to attain suitable tuning of the QDs properties. ZnO/GSH synthesized QDs were characterized by Transmission Electron Microscopy, X-Ray Diffraction, FT-IR, UV-Vis and photoluminescence (PL) spectroscopy. The QDs shape was spherical with a particle size between 80-100nm. The synthesis of ZnO/GSH under different experimental conditions and the corresponding coupling with E. Coli species, are presented and discussed.
The temperature induced structural transformations in physical mixtures of 1nm palladium and ultrafine (∼0.5nm) copper nanoparticles supported on carbon were studied using in-situ real time synchrotron based x-ray diffraction. These nanoparticles were subjected to two-step thermal annealing from 25°C to 700°C. The Pd and Cu nanoparticles were found to coalesce forming alloy nanoparticles that subsequently undergo a structural phase transformation from ordered B2 to disordered fcc. The random alloy formed at the end of the thermal treatments was found to be copper-rich.
This paper describes a kinetic study of the mediator-template assembly of gold nanoparticles in solutions based on the spectrophotometric measurement of the surface plasmon resonance optical property. Gold nanoparticles of ∼5 nm diameter encapsulated with tetraoctylammonium bromide shells were studied as a model system. The core-shell nanoparticles were assembled into 3D spherical assemblies via a mediator-template assembly route in which a thioether-based multidentate ligand functions as a mediator and the tetraoctylammonium shell molecules function as a templating agent. In this report, the results were compared with those obtained for the assembly of gold nanoparticles in several different systems with features similar to the mediator-template assembly. The findings further provided further insights into understanding the kinetic factors governing the assembly of nanoparticles, and have important implications to the design and control of the nanostructures for sensory and catalytic applications.
The understanding of the surface properties of metal nanoparticles is essential for exploiting their unique catalytic properties. This paper reports findings of the preparation of silica-supported Pt and Au nanoparticles and the FTIR characterization of CO adsorption on the supported nanoparticles. The nanoparticles were prepared by both a traditional impregnation method and molecular-capping based synthesis method. By comparing the spectroscopic characteristics of CO adsorption on these catalysts, similarities and differences in CO stretching bands have been identified. The findings are significant because important insights have been gained into the surface binding properties of Au and Pt nanoparticle catalysts.
This paper reports findings of an investigation of the synthesis of monolayer-capped iron oxide and core (iron oxide)-shell (gold) nanocomposite and their assembly towards thin films as sensing materials. Pre-synthesized and size-defined iron oxide nanoparticles were used as seeding materials for the reduction of gold precursors, which was shown to be effective for coating the iron oxide cores with gold shells (Fe oxide@Au). The unique aspect of our synthesis is the formation of Fe oxide@Au core-shell nanoparticles with controllable surface properties. By controlling the reaction temperatures and manipulating the capping agent properties and solution compositions, the size, shape, composition, and monodispersity can be tailored. The core-shell nanoparticles were shown to form molecularly-mediated thin film assemblies using molecular mediators. The sensing properties of the nanostructures on piezoelectric devices were examined for the detection of volatile organic compounds. The preliminary results have provided important insights into the design of core-shell nanocomposites as sensing materials.
The ability to control composition and size in the synthesis of bimetallic nanoparticles is important for the exploitation of the bimetallic catalytic properties. This paper reports recent findings of an investigation of the synthesis of gold-platinum (AuPt) bimetallic nanoparticles in aqueous solution via reduction of AuCl4− and PtCl42− using a combination of reducing and capping agents. In addition to characterization of the morphological properties of the AuPt nanoparticles using TEM and XRD, the electrocatalytic activity of the carbon-supported AuPt nanoparticle catalysts was also examined for oxygen reduction reaction (ORR) using the rotating disk electrode (RDE) technique. The findings have implications to the design of bimetallic nanoparticle catalysts for fuel cell reactions.
This paper reports the preliminary results of an investigation of the synthesis of monolayer-capped GaAs nanoparticles using different surface capping molecules. Our approach focuses on the surface encapsulation using alkanethiolates. The organic shell can effectively block the aggregation during nanoparticle synthesis, providing molecular-level control of the core-shell structure. The results have demonstrated the effect of surface alkanethiolate modification on the interparticle spatial properties and particle sizes, which upon further refinement could lead to the ability in controlling the size of GaAs nanoparticles.
This paper describes the results of an investigation of modified synthetic protocols to produce monodispersed magnetic ferrite nanoparticles, γ-Fe2O3 and Fe3O4, and their magnetic properties. The synthesis involved thermal decomposition of organometallic precursors followed by oxidation or reduction. In the synthesis of γ-Fe2O3, iron pentacarbonyl was used as the precursor and trimethylamine oxide as the oxidant. In the synthesis of Fe3O4, iron (III) acetylacetonate was reduced by 1, 2-hexadecanediol. The particle sizes ranged from 5–15 nm with high monodispersity. Results from TEM, XPS, and SQUID characterizations of these iron oxide nanoparticles are discussed.
Nanostructured thin films were assembled on interdigited microelectrode (IME) arrays as sensitive interfacial materials of an electrochemical detector, which can be integrated into microfluidic sensor devices. The goal is to produce sensor devices at extremes of miniaturization. The IME were created on glass wafers using conventional lithographic techniques. Open channels were etched on quartz or glass, and covered by PDMS materials, which were created using soft-lithography. The capability of chemical recognition was provided by the ligand framework structures of the nanostructured thin films on the electrode surface. A model system for such nanostructures involved the use of monolayer-capped gold nanoparticles of ∼2 nm core sizes which were assembled by carboxylic acid functionalized alkyl thiol linkers. The detection of dopamine was studied as a redox probe to test the feasibility of the microfluidic device. Results of cyclic voltammetric and chronoamperometric experiments are presented. Implications of the findings to the development of sensitive, selective, rapid and portable microanalytical devices for chemical/biological sensing are also discussed.
The application of molecularly-capped gold nanoparticles (1–5 nm) in catalysis (e.g., electrocatalytic oxidation of CO and methanol) requires a thorough understanding of the surface composition and structural properties. Gold nanoparticles consisting of metallic or alloy cores and organic encapsulating shells serve as an intriguing model system. One of the challenges for the catalytic application is the ability to manipulate the core and the shell properties in controllable ways. There is a need to understand the relative core-shell composition and the ability to remove the shell component under thermal treatment conditions. In this paper, we report results of a thermogravimetric analysis of the alkanethiolate monolayer-capped gold nanoparticles. This investigation is aimed at enhancing our understanding of the relative core-shell composition and thermal profiles.
This paper describes the results of an investigation of the structure and composition of core-shell gold and alloy nanoparticles as catalytically active nanomaterials for potential fuel cell catalysis. Centered on the electrocatalytic methanol oxidation, we show three sets of results based on electrochemical, surface, and composition characterizations. First, electrochemical studies have revealed that the nanostructured catalysts are active towards the electrooxidation of methanol and carbon monoxide. Second, X-ray photoelectron spectroscopy (XPS) data have shown that the organic encapsulating shells can be effectively removed electrochemically or thermally, which involves the formation of oxides on the nanocrystals. Thirdly, direct current plasma - atomic emission spectrometry (DCP-AES) has revealed insights for the correlation of the composition of alloy nanoparticles with the catalytic activities. Implications of these results to the design of nanostructured catalysts will also be discussed.
This paper reports a study on the assembly of gold nanoparticles via a tetradentate organosulfur ligand, tetra[(methylthio)methyl] silane. We have characterized the evolution of the assembly from individual nanoparticles to spheres (30 ∼ 160 nm) of linked nanoparticles using UV-Visible, TEM, and AFM techniques. We have also demonstrated that the assemblies could be effectively disassembled via manipulating the ligand chemistry. Intriguing assembly-substrate interactions were observed, which could be related to interfacial hydrophobicity. Implications of these findings to the development of abilities in interfacial manipulation of the nanostructures are also discussed.
Thin films derived from nanocrystal cores and functionalized linkers provide large surface-to-volume ratio and three-dimensional ligand framework. This paper describes the results of an investigation of the interfacial ion fluxes associated with redox reactivity and structural properties of such films using cyclic voltammetry, electrochemical quartz-crystal nanobalance, surface infrared reflection spectroscopy, and X-ray photoelectron spectroscopy. Films from gold nanocrystals of 2 nm core sizes and 11-mercaptoundecanoic acid were studied as a model system. First, the film coated on electrode surface displays redox-like voltammetric waves characteristic of the deprotonation-reprotonation of the carboxylic acid groups in the nanostructured network. This process is accompanied by mass changes. Secondly, the film exhibits capability for the complexation of copper ions via the nanostructured carboxylate framework. This process is also accompanied by interfacial fluxes of electrolyte cations across the electrode | film | electrolyte interface which compensate electrostatically the fixed negative charges in the reduction process.
This paper reports results of the characterizations of nanoparticle assembly formed via spontaneous core-shell and shell-shell reactivities at thiolate-capped gold nanoparticles. Gold nanoparticles of two different core sizes and thiols with carboxylic acid terminals are exploited as a model system. The reactivities involve covalent Au-thiolate bonding and non-covalent hydrogen-bonding with anisotropic linking character. We employed infrared reflection spectroscopy (IRS), atomic force microscopy (AFM) and transmission electron microscopy (TEM) for the characterizations. While IRS provides structural assessment, TEM and AFM imaging measurements probe the morphological properties.
Nanostructured thin films were assembled as metal-responsive electrode materials from monolayer-capped gold nanoparticles (2 nm) and carboxylic acid functionalized alkyl thiol linkers via an exchange-crosslinking-precipitation reaction pathway. The network assemblies have open frameworks in which void space forms channels or chambers with the nanometer sized cores defining its size and the shell structures defining its chemical specificity. Such nanostructures were investigated as responsive materials for the detection of metal ion fluxes. Cyclic voltammetry, in-situ electrochemical quartz-crystal nanobalance, and surface infrared reflection spectroscopy techniques were used to characterize the interfacial redox reactivity and mass fluxes at the nanostructured electrode materials. The system showed remarkable reversible mass loading arising from incorporation of ionic species into the film. The diagnostic stretching bands of the carboxylic and carboxylate groups at the shell allowed the identification and assessment of the interfacial carboxylate-metal ion reactivity.
This paper reports the result of a study of organic-inorganic network assembles as chemically sensitive interfacial materials. Core-shell gold nanoparticles of a 5 nm size and organic linkers such as 1,9-nonanedithiol and 1,5-pentadithiol are utilized as building blocks for constructing network assembles on planar substrates. To explore the responsive properties of such materials to volatile organic compounds, we utilized interdigitated microelectrodes as transducer. The responses at these nanostructured interfaces are demonstrated to be dependent on the chain length of the linking molecules. The difference of molecular interactions at the nanostructured interface has a significant impact to the response profile and sensitivity. The implications of the findings to the delineation of design parameters for constructing organic-inorganic network assemblies as chemically-sensitive interfacial materials are also discussed.
The structural, electrical and electrochemical properties of nanoparticle thin films derived by a one-step exchange-crosslinking-precipitation route were characterized by microscopic, spectroscopic and electrochemical techniques. Thiolate-encapsulated gold nanocrystals of 2-nm and 5-nm core sizes and alkyldithiol crosslinkers were studied as a model system. The mixing of the two components in solutions allowed sequential exchanging, crosslinking and precipitation of dithiol-crosslinked nanocrystal thin films. The films were specularly reflecting and electronically continuous, and have potential applications in catalysis and molecular recognition.
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