Showing papers on "Nanoparticle published in 2000"
IBM1
TL;DR: Thermal annealing converts the internal particle structure from a chemically disordered face- centered cubic phase to the chemically ordered face-centered tetragonal phase and transforms the nanoparticle superlattices into ferromagnetic nanocrystal assemblies that can support high-density magnetization reversal transitions.
Abstract: Synthesis of monodisperse iron-platinum (FePt) nanoparticles by reduction of platinum acetylacetonate and decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers is reported. The FePt particle composition is readily controlled, and the size is tunable from 3- to 10-nanometer diameter with a standard deviation of less than 5%. These nanoparticles self-assemble into three-dimensional superlattices. Thermal annealing converts the internal particle structure from a chemically disordered face-centered cubic phase to the chemically ordered face-centered tetragonal phase and transforms the nanoparticle superlattices into ferromagnetic nanocrystal assemblies. These assemblies are chemically and mechanically robust and can support high-density magnetization reversal transitions.
5,568 citations
TL;DR: In this article, solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤ 5%, are presented.
Abstract: ▪ Abstract Solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤5%, are presented. Preparation of monodisperse samples enables systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close-packed, glassy, and ordered nanocrystal assemblies (superlattices, colloidal crystals, supercrystals). Rigorous structural characterization is critical to understanding the electronic and optical properties of both nanocrystals and their assemblies. At inter-particle separations 5–100 A, dipole-dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. At separations <5 A, exchange interactions cause otherwise insulating ass...
4,116 citations
TL;DR: In this article, the physical origin of surface plasmon absorption in gold nanoparticles with emphasis on the Mie and also the Maxwell-Garnett theory is discussed. And the effects of particle size and shape on the resonance condition are reviewed.
Abstract: Driven by the search for new materials with interesting and unique properties and also by the fundamental question of how atomic and molecular physical behaviour develops with increasing size, the field of nanoparticle research has grown immensely in the last two decades. Partially for these reasons, colloidal solutions of metallic (especially silver and gold) nanoparticles have long fascinated scientists because of their very intense colours. The intense red colour of colloidal gold nanoparticles is due to their surface plasmon absorption. This article describes the physical origin of the surface plasmon absorption in gold nanoparticles with emphasis on the Mie and also the Maxwell-Garnett theory and reviews the effects of particle size and shape on the resonance condition. A better understanding of the relationship between the optical absorption spectrum (in particular, the plasmon resonance) and such particle properties as its dimensions or surrounding environment can prove fruitful for the use of the ...
2,007 citations
TL;DR: In this paper, the authors introduce the fundamentals of TEM and its applications in structural determination of shape-controlled nanocrystals and their assemblies, and demonstrate in situ TEM for characterizing and measuring the thermodynamic, electric, and mechanical properties of individual nanostructures, from which the structure−property relationship can be registered with a specific nanoparticle/structure.
Abstract: The physical and chemical properties of nanophase materials rely on their crystal and surface structures. Transmission electron microscopy (TEM) is a powerful and unique technique for structure characterization. The most important application of TEM is the atomic-resolution real-space imaging of nanoparticles. This article introduces the fundamentals of TEM and its applications in structural determination of shape-controlled nanocrystals and their assemblies. By forming a nanometer size electron probe, TEM is unique in identifying and quantifying the chemical and electronic structure of individual nanocrystals. Electron energy-loss spectroscopy analysis of the solid-state effects and mapping the valence states are even more attractive. In situ TEM is demonstrated for characterizing and measuring the thermodynamic, electric, and mechanical properties of individual nanostructures, from which the structure−property relationship can be registered with a specific nanoparticle/structure.
1,980 citations
TL;DR: A series of experiments and a theoretical model designed to systematically define and evaluate the relative importance of nanoparticle, oligonucleotide, and environmental variables that contribute to the observed sharp melting transitions associated with DNA-linked nanoparticle structures are reported.
Abstract: We report a series of experiments and a theoretical model designed to systematically define and evaluate the relative importance of nanoparticle, oligonucleotide, and environmental variables that contribute to the observed sharp melting transitions associated with DNA-linked nanoparticle structures. These variables include the size of the nanoparticles, the surface density of the oligonucleotides on the nanoparticles, the dielectric constant of the surrounding medium, target concentration, and the position of the nanoparticles with respect to one another within the aggregate. The experimental data may be understood in terms of a thermodynamic model that attributes the sharp melting to a cooperative mechanism that results from two key factors: the presence of multiple DNA linkers between each pair of nanoparticles and a decrease in the melting temperature as DNA strands melt due to a concomitant reduction in local salt concentration. The cooperative melting effect, originating from short-range duplex-to-duplex interactions, is independent of DNA base sequences studied and should be universal for any type of nanostructured probe that is heavily functionalized with oligonucleotides. Understanding the fundamental origins of the melting properties of DNA-linked nanoparticle aggregates (or monolayers) is of paramount importance because these properties directly impact one's ability to formulate high sensitivity and selectivity DNA detection systems and construct materials from these novel nanoparticle materials.
1,420 citations
TL;DR: In this article, a review of inorganic nanoparticles with conducting polymers, giving rise to a host of nanocomposites with interesting physical properties and important application potential are discussed.
Abstract: Inorganic nanoparticles of different nature and size can be combined with the conducting polymers, giving rise to a host of nanocomposites with interesting physical properties and important application potential. Such nanocomposites have been discussed in this review, throwing light on their synthesis techniques, properties, and applications. A large variety of nanoparticles have been chosen in this respect with inclusion techniques utilizing both chemical and electrochemical routes. The nature of the association between the components can be studied from TEM pictures. Depending upon the synthesis techniques and the characteristics of the inorganic materials, ultimate properties of the resulting composite are controlled. In this way, the exceptional colloidal stability of different silica sols have been utilized to form stable PPy-silica and PAn-silica nanocomposite colloids. Similarly the magnetic susceptibility of γ-Fe2O3, the elctrochromic property of WO3, and the catalytic activity of Pd, Pt, etc. met...
1,244 citations
Book•
01 Jan 2000
TL;DR: Theoretical Aspects of Strained-layer Quantum-Well Lasers are discussed in this article, as well as their application in the synthesis and characterization of nanostructured materials.
Abstract: Volume 1: Synthesis and Processing HG Jiang, ML Lau, VL Telkamp, and EJ Lavernia, Synthesis of Nanostructured Coatings by High Velocity Oxygen Fuel Thermal Spraying KE Gonsalves, SP Rangarajan, and J Wang, Chemical Synthesis of Nanostructured Metals, Metal Alloys, and Semiconductors J Costa, Nanoparticles from Low-Pressure and Low-Temperature Plasma CD Johnson, M Noh, H Sellinschegg, R Schneidmiller, and DC Johnson, Kinetic Control of Inorganic Solid State Reactions Resulting from Mechanistic Studies Using Elementally Modulated Reactants EJ Gonzalez and GJ Piermarini, Low Temperature Compaction on Nanosize Powders WH Weinberg, CM Reaves, BZ Nosho, RI Pelzel, and SP denBaars, Strained-layer Heteroepitaxy to Fabricate Self-assembled Semiconductor Islands JJ McClelland, Nanofabrication via Atom Optics KC Kwaitkowski and CM Lukehart, Nanocomposites Prepared by Sol-Gel Methods: Synthesis and Characterization Q Yitai, Chemical Preparation and Characterization of Nanocrystalline Materials DJ Duval and SH Risbud, Semiconductors Quantum Dots-Progress in Processing ITH Chang, Rapid Solidification Processing of Nanocrystalline Metallic Alloys KL Choy, Vapor Processing of Nanostructured Materials Volume 2: Spectroscopy and Theory JM Cowley and JCH Spence, Nanodiffraction M-I Baraton, FT-IR Surface Spectrometry of Nanosized Particles P Milani and CE Bottani, Vibrational Spectroscopy of Mesoscopic Systems RM Taylor II and R Superfine, Advanced Interfaces to Scanning-probe Microscopes R Blick, Microwave Spectroscopy on Quantum Dots E Meyer and R Luthi, Tribological Experiments with Friction Force Microscopy M J Yacaman and JA Ascencia, Electron Microscopy Techniques Applied to Study of Nanostructured Materials and Ancient Materials K Ounadjela and RL Stamps, Mesoscopic Magnetism in Metals DJ Whitehouse, Tools of Nanotechnology: Nanometrology VGasparian, M Ortuno, G Schon, and U Simon, Tunneling Times in Nanostructures SB Sinnott, Theory of Atomic-Scale Friction D Ahn, Theoretical Aspects of Strained-layer Quantum-Well Lasers LR Ram Mohan, I Vurgaftman, and JR Meyer, Wavefunction Engineering: A New Paradigm in Quantum Nanostructure Modeling Volume 3: Electrical Properties J Smolines and G Ploner, Electron Transport and Confining Potentials in Semiconductor Nanostructures MA Reed, JW Sleight, and MR Deshpande, Electron Transport Properties of Quantum Dots U Simon and G Schon, Electrical Properties of Chemically Tailored Nanoparticles and Their Applications in Microelectronics RP Andres, S Datta, DB Janes, CP Kubiak, and R Reifenberger, Design, Fabrication, and Electronic Properties of Self-assembled Molecular Nanostructures TP Sidiki and CM Sotomayor Torres, Silicon-based Nanostructures PV Kamat, K Murakoshi, Y Wada, and S Yanagida, Semiconductor Nanoparticles FM Peeters and J DeBoeck, Hybrid Magnetic-Semiconductor Nanostructures OI Micic and AJ Nozik, Colloidal Quantum Dots of III-V Semiconductors VV Moshchalkov, Y Bruynseraede, L Van Look, MJ Van Bael, Y Bruynseraede, and A Tonomura, Quantization and Confinement Phenomena in Nanostructured Superconductors M Graetzel, Properties and Applications of Nanocrystalline Electronic Junctions S Mitsui, Nanostructured Fabrication Using Electron Beam and Its Applications to Nanometer Devices Volume 4: Optical Properties DD Notle, MR Melloch, Y Ding, M Dinu, KM Kwolek, and I Lahiri, Photorefractive Semiconductor Nanostructures F Gonella and P Mazzoldi, Metal Nanocluster Composite Glasses D Thomas, Porous Silicon W Chen, Fluorescence, Thermoluminescence, and Photostimulated Luminescence of Nanoparticles VM Shalaev, Surface-enhanced Optical Phenomena in Nanostructured Fractal Materials VI Klimov, Linear and Nonlinear Optical Spectroscopy of Semiconductor Nanocrystals S Vijayalakshmi and H Grebel, Nonlinear Optical Properties of Nanostructures SS Li and MZ Tidrow, Quantum Well Infrared Photodetectors W Tan and R Kopelman, Nanoscopic Optical Sensors and Probes Volume 5: Organics, Polymers, and Biological Materials PJ Stang and B Olenyuk, Transition-Metal-Mediated Self-Assembly of Discrete Nanoscopic Species with Well-Defined Shapes and Geometries M Gomez-Lopez and JF Stoddart, Molecular and Supramolecular Nanomachines AC Benniston and PR Mackie, Functional Nanostructures Incorporating Responsive Modules A Archut and F Voegtle, Dendritic Molecules: Historical Developments and Future Applications PM Ajayan, Carbon Nanotubes J Sloan and MLH Green, Encapsulation and Crystallization Behavior of Materials Inside Carbon Nanotubes H Kasai, HS Nalwa, S Okada, H Oikawa, and H Nakanishi, Fabrication and Spectroscopic Characterization of Organic Nanocrystals G Liu, Polymeric Nanostructures B Wessling, Conducting Polymers as Organic Nanometals E Nakache, N Poulain, F Candau, AM Orecchioni, and JM Irache, Biopolymers and Polymers Nanoparticles and Their Biomedical Applications T Bayburt, J Carlson, B Godfrey, M Shank-Retzlaff, and SG Sligar, Structure, Behavior, and Manipulation of Nanostructure Biological Assemblies TM Cooper, Biomimetic Thin Films
964 citations
TL;DR: In this article, the surface of preformed 12-nm-diameter Au nanoparticles is reduced by boiling sodium citrate, producing particles highly uniform in size and shape, and a similar procedure, utilizing the reductant NH2OH at room temperature, produces two populations of particles.
Abstract: New fields of research in chemistry and physics require improved synthetic techniques for colloidal metal particles. This paper reports a generally applicable technique for synthesizing colloidal Au particles of mean diameters between 20 and 100 nm that exhibit improved monodispersity relative to previously published methods. In this approach (called “seeding”) Au3+ is reduced on the surface of preformed 12-nm-diameter Au nanoparticles by introduction of boiling sodium citrate, producing particles highly uniform in size and shape. A similar procedure, utilizing the reductant NH2OH at room temperature, produces two populations of particles; the larger population is even more spherical than citrate-reduced particles of similar size, while the smaller population is very distinctly rod-shaped.
916 citations
TL;DR: Th thin films of hollow MoS2 nanoparticles, deposited by a localized high-pressure arc discharge method, exhibit ultra-low friction and wear in nitrogen and 45% humidity, attribute this ‘dry’ behaviour in humid environments to the presence of curved S–Mo–S planes that prevent oxidation and preserve the layered structure.
Abstract: The tribological properties of solid lubricants such as graphite and the metal dichalcogenides MX2 (where M is molybdenum or tungsten and X is sulphur or selenium) are of technological interest for reducing wear in circumstances where liquid lubricants are impractical, such as in space technology, ultra-high vacuum or automotive transport. These materials are characterized by weak interatomic interactions (van der Waals forces) between their layered structures, allowing easy, low-strength shearing. Although these materials exhibit excellent friction and wear resistance and extended lifetime in vacuum, their tribological properties remain poor in the presence of humidity or oxygen, thereby limiting their technological applications in the Earth's atmosphere. But using MX2 in the form of isolated inorganic fullerene-like hollow nanoparticles similar to carbon fullerenes and nanotubes can improve its performance. Here we show that thin films of hollow MoS2 nanoparticles, deposited by a localized high-pressure arc discharge method, exhibit ultra-low friction (an order of magnitude lower than for sputtered MoS2 thin films) and wear in nitrogen and 45% humidity. We attribute this 'dry' behaviour in humid environments to the presence of curved S-Mo-S planes that prevent oxidation and preserve the layered structure.
770 citations
TL;DR: In this paper, a laser ablation of a metal silver plate in an aqueous solution of sodium dodecyl sulfate, C12H25OSO3Na, was shown to be essentially the same as that of silver nanoparticles chemically prepared in a solution.
Abstract: Silver nanoparticles were produced by laser ablation of a metal silver plate in an aqueous solution of sodium dodecyl sulfate, C12H25OSO3Na. The absorption spectrum of the silver nanoparticles is found to be essentially the same as that of silver nanoparticles chemically prepared in a solution. The size distribution of the nanoparticles measured by an electron microscope shifts to a smaller size with increase in the concentration of sodium dodecyl sulfate and with a decrease in the irradiation laser power. These findings are explained by a scheme that the nanoparticles are formed via rapid formation of an embryonic silver particle and a consecutive slow particle growth in competition with termination of the growth due to SDS coating on the particle.
768 citations
TL;DR: In this article, transition metal oxide nanoparticles have been synthesized sonochemically from metal acetates using X-ray diffraction (XRD), diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM), and BET nitrogen adsorption.
Abstract: Transition metal oxide nanoparticles have been synthesized sonochemically from metal acetates. The metal oxide nanoparticles are characterized using X-ray diffraction (XRD), diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM), and BET nitrogen adsorption. The results of DRS are analyzed in detail, and the band gap energies for CuO, ZnO, and Co3O4 are seen to be 2.18, 3.35, and 2.26 (3.40), respectively. Different particle sizes, morphology, and yields are observed when water and 10% water−N,N-dimethylformamide (DMF) are used as solvents, and the possible mechanisms are discussed.
TL;DR: The presented carrier of colloidal lipid particles with improved payloads and enhanced storage stability was investigated and adds additional benefits to the well-known opportunities of conventional SLN and is suited for topical use.
TL;DR: In this paper, a survey on nano-particles and nanocomposites and the importance of small particle sizes on their optical properties is presented, focusing on results from a laboratory concerning nanocom composites with extremely high or low refractive indices and dichroic nanocomposition and their application in bicolored liquid crystal displays.
Abstract: Upon transmission of visible light through composites comprising of a transparent polymer matrix with embedded particles, the intensity loss by scattering is substantially reduced for particle diameters below 50-100 nm (nanoparticles, nanosized particles). As a consequence, related materials (nanocomposites) have found particular interest in optical studies. The first part of this article deals with a historical survey on nano-particles and nanocomposites and the importance of small particle sizes on their optical properties. The second part focuses on results from our laboratory concerning nanocomposites with extremely high or low refractive indices and dichroic nanocomposites and their application in bicolored liquid crystal displays (LCD). The inorganic colloids required for these studies (lead sulfide, iron sulfides, gold, and silver) were prepared in situ in presence of a polymer or isolated as redispersable metal colloids modified at the surface with a self-assembled monolayer (SAM) of an alkanethiol. The nanocomposites themselves were finally obtained by coprecipitation, spin coating, solvent casting or melt extrusion, with poly(ethylene oxide), gelatin, poly(vinyl alcohol) and polyethylene as matrix polymers.
TL;DR: It was shown that heat denatured HSA nanoparticles possessed the greatest number of amino groups on their surface, and the particle size depended mainly on the amount of desolvating agent added, but not on the amounts of cross-linker or the kind of cross -linking procedure.
TL;DR: In this paper, the nanoparticles were produced by laser ablation of a metal silver plate in aqueous solutions of surfactants, CnH2n+1SO4Na (n = 8, 10, 12, 16).
Abstract: Silver nanoparticles were produced by laser ablation of a metal silver plate in aqueous solutions of surfactants, CnH2n+1SO4Na (n = 8, 10, 12, 16). The nanoparticles thus produced were characterized by electron microscopy and UV−visible absorption spectroscopy. The abundances of the nanoparticles before and after centrifugation were measured as a function of the surfactant concentration. The concentration dependence of the abundance implies that the surfactant coverage and the charge state on the nanoparticle surface are closely related to the stability of the nanoparticles in the solutions. The nanoparticles tend to be aggregated when the coverage is less than unity, while they are very stable when the surface is covered with a double layer of the surfactant molecules.
TL;DR: In this article, the results of X-ray diffraction and electron microscopy characterizations show that the crystalline nanoparticles exhibit an ellipsoidal form with two characteristic dimensions of around 15 and 30 nm.
Abstract: Concentrated colloidal solutions of well-dispersed YVO4:Eu nanoparticles are synthesized by precipitation reactions at room temperature and stabilized by sodium hexametaphosphate. X-ray diffraction and electron microscopy characterizations show that the crystalline nanoparticles exhibit an ellipsoidal form with two characteristic dimensions of around 15 and 30 nm. In comparison with the bulk, a lower luminescence efficiency as well as a higher concentration quenching are observed. These deviations are explained as the variations of some characteristics of the colloidal samples, such as the crystallinity and the surface chemistry. When these parameters are optimized, the quantum yield of the luminescence reaches 38% for the nanoparticles containing a europium concentration of 15%.
TL;DR: In this article, a pulse sonoelectrochemical technique from an aqueous solution of AgNO3 in the presence of nitrilotriacetate N(CH2COOH)3-NTA was used to obtain shape-defined silver nanoparticles with spheres, rods and dendrites.
Abstract: Shaped silver nanoparticles with spheres, rods, and dendrites have been prepared by a pulse sonoelectrochemical technique from an aqueous solution of AgNO3 in the presence of nitrilotriacetate N(CH2COOH)3-NTA. The silver nanoparticles were characterized by using transmission electron microscopy, X-ray diffraction, and absorption spectroscopy. The effects of electrosonic time on particle shape have been discussed. It was found that the concentration of AgNO3 and NTA affects the shape of the nanoparticles.
TL;DR: In this paper, a 3-fold enhancement in photocurrent generation has been achieved upon modification of TiO2 films with Au nanoparticles, which is explained on the basis of improved interfacial charge-transfer kinetics of the TiO 2/Au composite film.
Abstract: TiO2 films cast on conducting glass plates were modified by adsorbing gold nanoparticles (5 nm diameter) from a toluene solution. Selective formation of Au islands and larger particles on the TiO2 surface could be seen from transmission electron micrographs and AFM images. Although the adsorbed Au particles are larger in diameter (50−70 nm), they retain surface plasmon characteristics, similar to those observed for smaller gold nanoparticles in solutions. A 3-fold enhancement in photocurrent generation has been achieved upon modification of TiO2 films with Au nanoparticles. This improved photoelectrochemical performance is explained on the basis of improved interfacial charge-transfer kinetics of the TiO2/Au composite film. Such semiconductor−metal composite films have potential applications in improving the performance of photoelectrochemical solar cells.
TL;DR: In this article, a new method called high-gravity reactive precipitation (HGRP), which means that reactive precipitation takes place in high gravity conditions, is presented for the massive production of nanoparticles.
Abstract: On the basis of the analysis of key engineering factors predominating in a reactive precipitation process, a new method called high-gravity reactive precipitation (HGRP), which means that reactive precipitation takes place in high-gravity conditions, is presented here for the massive production of nanoparticles. A rotating packed-bed reactor was designed to generate acceleration higher than the gravitational acceleration on Earth. The syntheses of nanoparticles of CaCO3, aluminum hydroxide, and SrCO3 were employed to demonstrate the advantages and industrial potentials of this technology, where the typical gas−liquid−solid, gas−liquid, and liquid−liquid multiphase reaction systems were involved. Experimental results show that the mean size of CaCO3 particles can be controlled and adjusted in the range of 17−36 nm through the change of operation conditions such as high-gravity levels, fluid flow rates, and reactant concentrations. Nanofibrils of aluminum hydroxide of 1−10 nm in diameter and 50−300 nm in le...
TL;DR: In this paper, a correlation between the electron spin−orbital angular momentum coupling and the superparamagnetic properties has been established in MgFe2O4 and CoFe 2O4 spinel ferrite nanoparticles The contribution to the magnetic anisotropy from the Fe3+ lattice sites is almost the same in both nanocrystallites as neutron diffraction studies have shown a similar cation distribution in these two types of spinel magnetite nanoparticles.
Abstract: A correlation between the electron spin−orbital angular momentum coupling and the superparamagnetic properties has been established in MgFe2O4 and CoFe2O4 spinel ferrite nanoparticles The contribution to the magnetic anisotropy from the Fe3+ lattice sites is almost the same in both nanocrystallites as neutron diffraction studies have shown a similar cation distribution in these two types of spinel ferrite nanoparticles Due to the strong magnetic couplings from Co2+ lattice sites, the blocking temperature of CoFe2O4 nanoparticles is at least 150 deg higher than the same sized MgFe2O4 nanoparticles Mossbauer spectroscopy studies demonstrate that the magnetic anisotropy of CoFe2O4 nanoparticles is higher than that of the same size MgFe2O4 nanoparticles These studies indicate that the superparamagnetic properties of nanoparticles can be controlled through chemically adjusting the magnetic anisotropy energy
TL;DR: In this article, the surface of 3-mercaptopropyltrimethoxysilane (MPS) modified semiconductor nanocrystals was synthesized in aqueous solutions.
Abstract: CdTe nanocrystals capped with 1-mercapto-2,3-propandiol, CdSe nanocrystals capped with sodium citrate, and core−shell CdSe/CdS nanocrystals capped with sodium citrate were synthesized in aqueous solutions, and their surface was modified by 3-mercaptopropyltrimethoxysilane (MPS) in water−ethanol mixtures. By addition of sodium silicate, “raisin bun”-type composite particles were formed, with either CdTe, CdSe, or CdSe/CdS nanocrystals being homogeneously incorporated as multiple cores into silica spheres of 40−80 nm size, accompanied by some alteration of optical properties of the nanoparticles and, in particular, the reduction of the luminescence quantum yield. Further, growth of larger silica spheres (100−700 nm) can be performed by the Stober technique using either MPS-modified semiconductor nanocrystals or “raisin bun”-type composite particles as seeds, which gives semiconductor-doped silica globules of desirable sizes in the submicrometer range. The composite spheres can be used as building blocks for...
TL;DR: In this article, a colloidal biocatalysts, comprising polystyrene (PS) carrier particles coated with enzyme multilayers, were fabricated via the layer-by-layer self-assembly method.
Abstract: Colloidal biocatalysts, comprising polystyrene (PS) carrier particles coated with enzyme multilayers, were fabricated via the layer-by-layer self-assembly method. Glucose oxidase (GOD), horseradish peroxidase (POD), or preformed enzyme−polyelectrolyte complexes were assembled in alternation with oppositely charged polyelectrolytes onto PS particles. Microelectrophoresis, single-particle light scattering, and transmission electron microscopy confirmed stepwise growth of the multilayer films on the colloid particles. The high surface area enzyme multilayer-coated particles were successfully employed as specific enzyme reactors (i.e., as catalysts). Whereas no loss in activity was observed for the enzymes immobilized directly onto particle surfaces, precomplexing the enzymes with polymer in solution drastically reduced their activity (by up to 70%). The enzymatic activity (per particle) was found to increase with the number of enzyme layers immobilized, irrespective of whether the enzyme was precomplexed. Ho...
TL;DR: In this paper, the authors showed that these MnFe2O4 nanoparticles are truly superparamagnetic and showed that they can have a size distribution as narrow as ∼9%.
Abstract: MnFe2O4 nanoparticles are synthesized by using sodium dodecylbenzenesulfonate (NaDBS) to form water-in-toluene reverse micelles. The nanoparticles are single crystalline, and the average particle size can be controlled from 4 to 15 nm. High- and low-resolution transmission electron microscopy characterization has shown that the nanoparticles can have a size distribution as narrow as ∼9%. Neutron diffraction and magnetic measurements have been conducted on the nanoparticles with a diameter of 7.7 ± 0.7 nm. The results unambiguously prove that these MnFe2O4 nanoparticles are truly superparamagnetic. The synthesis and characterization of these nanoparticles will facilitate the development of MnFe2O4 nanoparticles for the potential applications such as contrast enhancement agents of magnetic resonance imaging and magnetic carriers for site-specific drug delivery.
TL;DR: In this article, the authors used hydrogel nanoparticles that undergo volume phase transitions in response to changes in temperature and pH to assemble colloidal crystal gels with environmentally tunable optical properties.
Abstract: Hydrogel nanoparticles that undergo volume phase transitions in response to changes in temperature and pH have been used to assemble colloidal crystal gels with environmentally tunable optical properties. When monodisperse, ∼210-nm-diameter hydrogel particles are close-packed via centrifugation, the resultant viscous polymer pellet displays a bright iridescence in the visible region of the spectrum. This iridescence can then be modulated via temperature changes, which induce the component nanoparticles to undergo thermo-initiated volume phase transitions. More importantly, these crystals undergo a completely reversible order−disorder transition in response to larger temperature fluctuations; the crystal can be processed in its disordered (solution) state and then reformed to the iridescent crystal spontaneously upon cooling. The preparation and initial characterization of these materials are presented.
TL;DR: In this paper, a simple one-pot route is used to synthesize a uniform, thin shell of titanium dioxide, where the reduction of Ag+ to Ag0 and the controlled polymerization of TiO2 on the surface of silver crystallites take place simultaneously.
Abstract: Silver nanoparticles coated with a uniform, thin shell of titanium dioxide are synthesized via a remarkably simple one-pot route, where the reduction of Ag+ to Ag0 and the controlled polymerization of TiO2 on the surface of silver crystallites take place simultaneously. The prepared dispersions of coated nanoparticles display a surface plasmon band, which is significantly red-shifted with respect to that of bare Ag. High-quality ultrathin films of the core−shell clusters are prepared via layer-by-layer assembly. The nanoparticles are arranged in closely packed layers interlaced with polyelectrolyte producing a stratified core−shell hybrid material with unique structure and catalytic and electron-transport properties.
TL;DR: In this article, ultrasonic irradiation of an aqueous solution of SnCl4 and azodicarbonamide under ambient air was used to synthesize SnO2 semiconductor nanoparticles.
Abstract: SnO2 semiconductor nanoparticles were synthesized by an ultrasonic irradiation of an aqueous solution of SnCl4 and azodicarbonamide under ambient air. These nanoparticles are ∼3−5 nm in size, as calculated using the Debye−Scherrer formula, and as observed by TEM. The SnO2 nanoparticles were also characterized by powder X-ray diffraction (XRD), reflection spectroscopy and FT-IR spectroscopy, transmission electron microscopy (TEM), DSC, and TGA. The band gap was calculated from reflection spectroscopy. Electrochemical tests were performed using the SnO2 nanoparticles as the electrode's materials in nonaqueous Li salt solutions. The results showed promising reversibility, cycle life and high capacity for lithium insertion into the SnO2 nanoparticles.
TL;DR: In this paper, poly(amidoamine) dendrimers were used to obtain stable nanoparticles of gold, platinum, and silver by reduction of their metal salts with NaBH4.
Abstract: Nanoparticles of gold, platinum, and silver were prepared by reduction of their metal salts with NaBH4 in the presence of poly(amidoamine) dendrimers. The dendrimers used were generation 3, 4, and 5 having surface amino group (G3, G4, and G5) as well as generation 3.5, 4.5, and 5.5 having surface carboxyl group (G3.5, G4.5, and G5.5). The metal nanoparticles obtained were characterized by UV−vis spectroscopy and transmission electron microscopy. By using G3−G5, gold nanoparticles in the 1.5−4.0 nm size regime were obtained where their size decreased with increasing concentration of the dendrimers as well as the generation of the dendrimers. Similarly, platinum nanoparticles with a diameter of 2.4−3.0 nm were obtained, and their size was insensitive against the concentration as well as the generation of G3−G5. In the case of silver nanoparticles, very small silver particles using G3.5−G5.5 were obtained. In addition, the dendrimer concentration required for obtaining stable nanoparticles was found to be de...
TL;DR: In this paper, the authors used X-ray powder diffraction measurements and high-resolution transmission electron microscopy to confirm doping and energy transfer in LaPO4Eu and CePO4:Tb.
Abstract: Nanocrystals of LaPO4:Eu and CePO4:Tb with a mean particle size of 5 nm and a narrow size distribution have been prepared by reacting the corresponding metal chlorides, phosphoric acid, and a base at 200 °C in tris(ethylhexyl) phosphate. Highly crystalline material was obtained as confirmed by X-ray powder diffraction measurements and high-resolution transmission electron microscopy. Successful doping with europium was evident from the splitting and the intensity pattern of the luminescence lines. Luminescence lifetime measurements were used to confirm doping and energy transfer in both materials. Colloidal solutions of CePO4:Tb exhibit an overall luminescence quantum yield of 16%.