Nm In Edge Length Research Articles

Synthesis of Small-Sized Freestanding Co3O4 Nanosheets with Improved Activity for H2O2 Sensing and Oxygen Evolution

Small-sized freestanding Co3O4 nanosheets have been successfully synthesized on conductive substrate via a novel and simple electrochemical-based strategy. The as-synthesized sheets have a small size of 30 ± 10 nm in edge length and about 10 ± 5 nm in thickness with most sheets lying perpendicular to the substrate. The combined properties of products such as small size, two-dimension shape and freestanding pose could lead to integrative advantages of high surface-to-volume ratio, the maximized exposed surfaces without particles aggregation, strong affinity and good conductivity. As for electrochemical tests, the as-synthesized Co3O4 nanosheets show an improved sensitivity of ∼0.56 A M−1 cm−2 with lower detection limit of 1 μM at concentration range of 0–1.8 mM for H2O2 sensing, and also exhibit good performance for oxygen evolution with low evolution over-potential, high catalytic efficiency and durable stability.

Synthesis of nano-cubic ZnSn(OH)3 based on stannate reaction with liquid laser ablation-induced ZnO below room temperature

A environmental-friendly and simple method is developed to fabricate the nanostructured zinc hydroxystannate [ZnSn(OH)6, ZHS] based on laser ablation of Zn target in water and subsequent stannate reaction at a low temperature (5 °C) without any surfactants. The ZHS nanocubes with about 155 nm in edge length have been successfully produced. Such ZHS nanocubes are single crystalline with perovskite structure and enclosed by six external faces of {001} planes. They are unchanged in the shape after subsequent annealing at temperatures up to 800 °C. The amorphous nano-cubic zinc stannate (ZnSnO3), a multifunctional material, is thus produced by thermal decomposition of the pre-formed ZHS at 300–400 °C. Further experiments have revealed that the low reaction temperature and the laser ablation-induced ZnO colloids are crucial to formation of the ZHS nanocubes. This study is important to understand in detail the growth mechanism of the ZHS crystals, and also provides a green, simple and low-cost synthesis method for nanostructured ZHS and its decomposition products (ZnSnO3, Zn2SnO4 and SnO2, etc.).

Size-dependent transformation from Ag templates to Au–Ag nanoshells via galvanic replacement reaction in organic medium

The transformation from Ag templates to Au–Ag nanoshells via galvanic replacement reaction with HAuCl4 was systematically studied in an organic medium in the presence of oleylamine. Decahedral (~43 nm in size) and triangular prism (~53 nm in edge length) Ag templates transformed into equiaxed and triangular prismatic Au–Ag nanoshells, respectively. The first step involved structural and morphological changes from Ag templates to Au–Ag nanoshells with an interior cavity. In the second step, the growth of the shells continued through the deposition of Au. The shell thickness increased from ~5 to ~10 nm for the equiaxed Au–Ag nanoshells (~39-nm interior cavity) and ~5 to ~8 nm for the triangular prismatic Au–Ag nanoshells (~52-nm interior edge length). Oleylamine not only served as a surfactant but also removed AgCl precipitates and reduced HAuCl4. For the nanoshells derived from the ~20-nm Ag decahedrons, further reaction in excess HAuCl4 collapsed the nanoshells into Au-rich solid fragments. However, the nanoshells derived from the ~43-nm Ag decahedrons, the nanoshell structure not only persisted in excess HAuCl4, but its shell thickness also increased. The size-dependent transformation of these nanoshells is discussed.

A Mechanistic Study on the Nucleation and Growth of Au on Pd Seeds with a Cubic or Octahedral Shape

AbstractThis article reports a systematic study on the seed‐mediated growth of Pd–Au bimetallic nanocrystals with a variety of controlled morphologies. The key to the success of this synthesis is to manipulate the reaction kinetics by controlling a set of experimental parameters, which include the amount of ascorbic acid used as a reductant, the amount of HAuCl4 as a precursor to elemental Au, the reaction temperature, and the type of seeds employed. Starting from Pd nanocubes of 18 nm in edge length, Pd–Au bimetallic nanocrystals with a number of morphologies, which includes hybrid dimers, core–shell nanocubes with flat faces, and core–shell nanocubes with concave faces could all be obtained by simply speeding up the reduction of HAuCl4. The same synthesis and control could also be extended to seeds based on Pd octahedrons. For the first time, it was possible to generate Pd@Au core–shell nanocubes and octahedrons with concave faces. The Pd@Au core–shell nanocubes with concave faces exhibited enhanced activity in catalyzing the oxidization of ascorbic acid relative to their counterparts with flat faces or the cubic Pd seeds.

Sonochemical Synthesis of Ag/AgCl Nanocubes and Their Efficient Visible‐Light‐Driven Photocatalytic Performance

A novel one-step sonochemical approach to synthesize a plasmonic photocatalyst of AgCl nanocubes (ca. 115 nm in edge length) with a small amount of Ag metal species is presented. The nanoscale Ag/AgCl hybrid photocatalysts with cubic morphology are readily formed under ambient ultrasonic conditions and neither external heat treatment nor reducing agents are required. The size of the Ag/AgCl photocatalysts could be controlled by changing the concentrations of Ag(+) ions and polyvinylpyrrolidone molecules in precursor solutions. The compositions, microstructures, influencing factors, and possible growth mechanism of the Ag/AgCl hybrid nanocubes were systematically investigated. The Ag/AgCl photocatalysts show excellent photocatalytic performance for degradation of various dye molecules under visible light.

Organic-Assisted Nano-Sized Antimony Telluride Prepared by Co-Precipitation Reductive Route

Nano-sized antimony telluride is of much interest for improving the thermoelectric figure of merit. In the present work, organic-assisted antimony telluride nanorods were successfully fabricated by a simple hydrothermal method. The products were characterized by means of X-ray diffraction, scanning electron microscope, and transmission electron microscope. The results show that the typical antimony telluride synthesized by co-precipitation reductive route is rodlike in shape with about 35 nm in thickness and 300 nm in edge length.

Erratum to: Tunable Nanostructures as Photothermal Theranostic Agents

Figure captions 1 through 17 and 19 point to the wrong references. The corrected references and author permissions are listed below. Figure 1. Near-infrared light (650–900 nm) is of particular interest in biological applications as it is minimally absorbed by biological chromophores and water. Reprinted by permission from Macmillan Publishers Ltd, Weissleder et al. Copyright 2001. Figure 2. (a) UV–Vis–NIR absorption spectra of nine HGN samples with varying diameters and wall thicknesses. (b) Image showing the color range of HGN solutions. The vial on the far left contains solid gold nanoparticles, the rest are HNGs with varying diameters and wall thicknesses. Reprinted with permission from Schwartzberg et al. Copyright 2006 American Chemical Society. Figure 3. Calcein AM staining indicated that cancerous cells remained viable (evidenced by green fluorescent signal) when exposed to 1 mW laser power, regardless of nanoparticle presence. At 50 mW laser output a red fluorescent EthD-1 signal indicative of membrane damage was observed in cells exposed to anti-HER2 functionalized GGS NPs only where the laser was applied. Laser exposure alone was harmless to cells, as was laser exposure combined with nonspecifically targeted nanoparticles. Scale bar = 250 lm. Reprinted with permission from Day et al. Figure 4. Kaplan–Meier survival of mice following treatment with GGS NPs and laser irradiation. There is a statistically significant increase in survival with 48 h accumulation compared to 24 h accumulation for the GGS NP treated mice and no difference for 48 h GGS NP treated mice as compared to gold silica nanoshell treated mice. Reprinted by permission from Gobin et al. Figure 5. (a) The extinction (Cext), absorption (Cabs), and scattering (Csca) cross-sections (note that Cext = Cabs + Csca) calculated using the DDA method for a gold nanocage of 45 nm in edge length and 3.5 nm in wall thickness, and with the geometry depicted in the inset in (d). The alloy composition of the nanocages is Au3Ag. (b) SEM images of Ag nanocubes prepared by sulfide-mediated polyol synthesis. The inset shows TEM image of the Ag nanocubes. (c) Normalized Vis–NIR extinction spectra recorded from aqueous suspensions of nanostructures after titrating Ag nanocubes with different amounts of a HAuCl4 aqueous solution. Note that the spectrum in red is corresponding to the Au nanocages shown in (d). (d) SEM image of Au nanocages prepared by refluxing an aqueous solution containing both silver nanocubes and HAuCl4. The inset shows a TEM image of the Au nanocages. Reprinted with permission from Chen et al. Copyright 2007 American Chemical Society. Figure 6. SK-BR-3 breast cancer cells that were treated with immuno gold nanocages and then irradiated by 810-nm laser at a power density of 1.5 W/cm for 5 min showed a well-defined circular zone of dead cells as revealed by: (a) calcein AM assay (where green fluorescence indicates the cells were live), and (b) EthD-1 assay (where red fluorescence indicates the cells were dead). In the control experiment, cells irradiated under the same conditions but without immuno gold nanocage treatment maintained viability, as indicated by (c) calcein fluorescence assay, and (d) the lack of intracellular EthD-1 uptake. Modified with permission from Chen et al. Copyright 2007 American Chemical Society. Figure 7. (a) Photograph of a tumor-bearing mouse under the photothermal treatment. 100 lL of PEGylated nanocages at a concentration of 9 9 10 particles/mL or saline was administrated intravenously through the tail vein as indicated by an arrow. After the nanocages had been cleared from the circulation (72 h after injection), the tumor on the right frank was irradiated by the diode laser at 0.7 W/cm with a beam Address correspondence to Rebekah A. Drezek, Department of Bioengineering, Rice University, 6100 Main Street, Houston, TX 77005, USA. Electronic mail: jky1@rice.edu, joekyoung@gmail. com, lizfig@rice.edu, drezek@rice.edu The online version of the original article can be found under doi: 10.1007/s10439-011-0472-5. Annals of Biomedical Engineering, Vol. 40, No. 5, May 2012 ( 2012) pp. 1206–1208 DOI: 10.1007/s10439-012-0535-2

Quantitative Analysis of the Role Played by Poly(vinylpyrrolidone) in Seed-Mediated Growth of Ag Nanocrystals

This article presents a quantitative analysis of the role played by poly(vinylpyrrolidone) (PVP) in seed-mediated growth of Ag nanocrystals. Starting from Ag nanocubes encased by {100} facets as the seeds, the resultant nanocrystals could take different shapes depending on the concentration of PVP in the solution. If the concentration was above a critical value, the seeds simply grew into larger cubes still enclosed by {100} facets. When the concentration fell below a critical value, the seeds would evolve into cuboctahedrons enclosed by a mix of {100} and {111} facets and eventually octahedrons completely covered by {111} facets. We derived the coverage density of PVP on Ag(100) surface by combining the results from two measurements: (i) cubic seeds were followed to grow at a fixed initial concentration of PVP to find out when {111} facets started to appear on the surface, and (ii) cubic seeds were allowed to grow at reduced initial concentrations of PVP to see at which concentration {111} facets started to appear from the very beginning. We could calculate the coverage density of PVP from the differences in PVP concentration and the total surface area of Ag nanocubes between these two samples. The coverage density was found to be 140 and 30 repeating units per nm(2) for PVP of 55,000 and 10,000 g/mol in molecular weight, respectively, for cubic seeds of 40 nm in edge length. These values dropped slightly to 100 and 20 repeating units per nm(2), respectively, when 100 nm Ag cubes were used as the seeds.

Preparation of Silver Nanoplates and Application in PCB Ink-Jet

Compared with traditional etch processing, inkjet technology has the features of simpler workmanship, less resources-utilizing, lower cost and environmentally friendly adaptation, which is sure to be another innovation of printed circuit board(PCB) technology. In this paper, size and shape controlled silver nanoparticles have been synthesized，which was used as conductive medium in ink-jet inks. Then it was printed into conductive lines on epoxy resin by a drop-on-demand inkjet printer. PVP was used as a polymeric stabilizer providing both electrostatic and steric stabilization. Ag2C2O4 was used to prepared spherical nano-silver. In the preparation of flake-like silver powders, the fully inorganic phase system contains AgNO3 as a silver precursor, DMF as a as a media dissolving silver salt, and PVP as a reducing reagent. The morphologies and structures of the nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was shown that the sample is silver with cubic asymmetry from the pattern of XRD. TEM images indicated that the size of spherical nano-particles was no more than 20 nm. But the small triangular nanoplates, with rather narrow size distribution, were in the range from 20nm up to 60 nm in edge length. The electrical conductivity was also measured by the four-probe tested method after calcined on the substrates. It was shown that the conductivity was 25S/cm when adding the spherical powders and the nano-silver ink has been successfully designed for inkjet printing.

Fabrication of octahedral carbon nanocages via an in-situ template approach

Octahedral carbon nanocages have been prepared by pyrolysis of ethanol at 700 °C in the existence of basic magnesium carbonate. The as-prepared carbon nanocages with high geometric symmetry are ~ 300–500 nm in edge length, and the edges and corners are clearly demarcated. It is found that the ethanol molecules provide the carbon nanocages with active carbon atoms, and the in-situ formed magnesium oxide nanocrystals, coming from the thermal decomposition of basic magnesium carbonate, serve as hard templates for the formation of octahedral carbon nanocages. On the basis of comparative experiments, a possible growth mechanism is proposed to explain the formation of octahedral carbon nanocages.

Structure Sensitivity of Alkynol Hydrogenation on Shape- and Size-Controlled Palladium Nanocrystals: Which Sites Are Most Active and Selective?

The activity and selectivity of structure-sensitive reactions are strongly correlated with the shape and size of the nanocrystals present in a catalyst. This correlation can be exploited for rational catalyst design, especially if each type of surface atom displays a different behavior, to attain the highest activity and selectivity. In this work, uniform Pd nanocrystals with cubic (in two different sizes), octahedral, and cuboctahedral shapes were synthesized through a solution-phase method with poly(vinyl pyrrolidone) (PVP) serving as a stabilizer and then tested in the hydrogenation of 2-methyl-3-butyn-2-ol (MBY). The observed activity and selectivity suggested that two types of active sites were involved in the catalysis--those on the planes and at edges--which differ in their coordination numbers. Specifically, semihydrogenation of MBY to 2-methyl-3-buten-2-ol (MBE) occurred preferentially at the plane sites regardless of their crystallographic orientation, Pd(111) and/or Pd(100), whereas overhydrogenation occurred mainly at the edge sites. The experimental data can be fit with a kinetic modeling based on a two-site Langmuir-Hinshelwood mechanism. By considering surface statistics for nanocrystals with different shapes and sizes, the optimal catalyst in terms of productivity of the target product MBE was predicted to be cubes of roughly 3-5 nm in edge length. This study is an attempt to close the material and pressure gaps between model single-crystal surfaces tested under ultra-high-vacuum conditions and real catalytic systems, providing a powerful tool for rational catalyst design.

Refractive Index Sensitivities of Noble Metal Nanocrystals: The Effects of Multipolar Plasmon Resonances and the Metal Type

The refractive index change-based plasmonic sensing with noble metal nanocrystals has been demonstrated unambiguously in a number of studies. The refractive index sensitivity and figure of merit of noble metal nanocrystals are two key parameters for this type of plasmonic sensing. Here, we report our studies of the effects of multipolar plasmon resonances and the metal type on the refractive index sensitivity and figure of merit of noble metal nanocrystals. Ag nanocubes of 84 nm in edge length are found to exhibit well-defined dipolar, quadrupolar, and octupolar resonances. The dipolar resonance has the highest index sensitivity of 336 nm/RIU (refractive index unit), while the quadrupolar resonance possesses the largest figure of merit of 4.55. A comparison between the Ag and Au nanocubes that have comparable particle sizes and dipolar plasmon resonances in a similar spectral region shows that the index sensitivity of the Ag nanocubes is about twice that of the Au nanocubes. The effect of the metal type on the index sensitivity is further confirmed by coating a Ag shell around Au nanorods, where the index sensitivity of the Au−Ag core−shell nanobars is determined to be larger than that of the uncoated Au nanorods that have a longitudinal dipolar plasmon wavelength close to that of the core−shell nanobars. The experimentally observed overall trend in the index sensitivity is also in agreement with that revealed by electrodynamic calculations.

Size-control synthesis of structure deficient truncated octahedral Fe3−δO4 nanoparticles: high magnetization magnetites as effective hepatic contrast agents

This study reports the size-controlled synthesis of truncated octahedral Fe3−δO4 nanoparticles varying from 5 to 22 nm in edge length. Size-dependent XRD spectra show that the iron oxide gradually shifted from magnetite toward maghemite as the size decreased. The nonstoichiometric Fe3−δO4 was expressed the resulting iron oxide nanoparticles. The smaller particle size resulted in larger δ value. The size dependence of the XRD, magnetization, and Raman measurements indicate that the 22 nm-sized particles formed magnetite nanoparticles. The saturation magnetization increased linearly as the particle size increased, eventually reaching 94 emu/g, which is comparable to bulk magnetite (92 emu/g). The magnetic behavior of Fe3−δO4 nanoparticles exhibited a transition from superparamagnetism to ferromagnetism when the particles reached 22 nm in size. The XRD, electron diffraction analysis, fast Fourier transform filtering analysis, and Ar ion beam etching results in this study indicate that the presence of metallic iron in the 22 nm-sized magnetite nanoparticles was responsible for their high magnetization. The high magnetization of the 22 nm-sized magnetite was achieved by different surface modification strategies using surfactant (CTAB) and a polymer (PSMA), generating hydrophilic properties. The chosen PSMA-coated magnetites have an r2 relaxivity larger than 200 mM−1 s−1, whereas the commercial Resovist hepatic agent achieves only 91 mM−1 s−1. In an effort to develop highly effective hepatic contrast agents, the PSMA-coated magnetite was injected into BALB/C mice to evaluate the T2* relaxation and image contrast. Results show a greater signal reduction in the liver than Resovist agent. The biodistribution profile of these iron oxide nanoparticles shows significant liver uptake, which is consistent with MRI observations.

The Role of Oxygen in Synthesizing Monodisperse Silver Nanocubes

In this work, we report on silver nanocubes prepared by using the conventional polyol synthesis in the presence of hydrochloric acid and oxygen. We found that by controlling the headspace oxygen concentration in the sample vial at a temperature of 140°C, monodisperse silver nanocubes of 100–115 nm in edge length were produced. A specific headspace oxygen concentration along with the chloride ions promoted the oxidative etching of twinned particles so that only single crystal cubes were produced. At lower oxygen concentrations, nanorods and wires were obtained whereas at very high concentrations all the particles were completely etched away resulting in a solution with no nanoparticles. Electron diffraction and X-ray diffraction analysis was employed to study the structural characterization. Scanning electron microscopy was used to examine the morphology of the silver nanoparticles.

Facile synthesis of Ag nanocubes of 30 to 70 nm in edge length with CF(3)COOAg as a precursor.

This paper describes a new protocol to synthesize Ag nanocubes of 30 to 70 nm in edge length with the use of CF(3)COOAg as a precursor to elemental silver. By adding a trace amount of NaSH and HCl to the polyol synthesis, Ag nanocubes were obtained with good quality, high reproducibility, and on a scale up to 0.19 g per batch for the 70 nm Ag nanocubes. The Ag nanocubes were found to grow in size at a controllable pace over the course of synthesis. The linear relationship between the edge length of the Ag nanocubes and the position of localized surface plasmon resonance (LSPR) peak provides a simple method for finely tuning and controlling the size of the Ag nanocubes by monitoring the UV/Vis spectra of the reaction at different times.

Controlling the Shapes of Silver Nanocrystals with Different Capping Agents

This paper provides direct evidence to support the role of a capping agent in controlling the evolution of Ag seeds into nanocrystals with different shapes. Starting with single-crystal seeds (spherical or cubic in shape), we could selectively obtain Ag octahedrons enclosed by {111} facets and nanocubes/nanobars enclosed by {100} facets by adding sodium citrate (Na(3)CA) and poly(vinyl pyrrolidone) (PVP), respectively, as a capping agent while all other parameters were kept the same. This research not only offers new insights into the role played by a capping agent in shape-controlled synthesis but also provides, for the first time, Ag octahedrons as small as 40 nm in edge length for optical and spectroscopic studies.

Growth Factors for Silver Nanoplates Formed in a Simple Solvothermal Process

We synthesized both big and ultra-small silver nanoplates through a simple solvothermal process in a common autoclave. Using this approach, we achieved the reduction of silver nitrate in DMF or ethanol in the presence of PVP as a capping agent. The reduction capacity of PVP was also investigated. Growth factors such as the concentration of silver precursor, quantity of capping agent, reaction time, and temperature have been shown to play important roles in the formation of different sizes and shapes of silver nanoplates. The big plates, over 100 nm in edge length, were found mainly in the shape of a connected triangular. Single triangle plates, truncated triangular plates, and hexangular plates were also found under different reaction conditions. The ultra-small silver nanoplates, 20-100 nm in edge length, were successfully extracted from the solution under different centrifugation conditions. The UV-vis spectrum exhibited intense in-plane dipole absorption peaks varying from 470-630 nm, as reflected by the gradual color change of the solution from orange to red, and finally to blue.

A rapid phase transfer method for nanoparticles using alkylamine stabilizers

Phase transfer of noble metal nanoparticles (NPs) (>20 nm) from aqueous to organic media is a challenge in colloidal science. We have developed a rapid and simple phase transfer method with alkylamine as the surfactant, through which gold (106 nm in diameter) and silver NPs (118 nm in edge length) can be transferred from aqueous to organic phases. Three alkylamines with different chain-lengths (NH 2–(CH 2) n−1 –CH 3, n = 12, 16 and 18) were compared, and octadecylamine (ODA) was the most efficient. The ODA–NP complex rapidly formed as a result of shaking the mixture of ODA (in ethanol) and NPs (in water). After 20 s, the complex separated from the liquid phase because of their hydrophobicity. The undissolved ODA–NP complex could be redispersed into organic solvents, such as chloroform. Ultraviolet–visible (UV–vis) spectroscopy and transmission electron microscopy (TEM) results show that the metal NPs are still monodisperse having been transferred into organic solvents. The whole process of the phase transfer of NPs from aqueous to organic media can be made to happen in less than 1 min.

The fabrication of ordered arrays of exchange biasedNi/FeF2 nanostructures

The fabrication of ordered arrays of exchange biasedNi/FeF2 nanostructures by focused ion beam lithography is reported. High qualitynano-elements, with controlled removal depth and no significant re-deposition,were carved using small ion beam currents (30 pA), moderate dwell times (1 µs) and repeated passages over the same area. Two types of nanostructureswere fabricated: square arrays of circular dots with diameters from125 ± 8 to500 ± 12 nm and periodicitiesranging from 200 ± 8 to1000 ± 12 nm, and square arraysof square antidots (207 ± 8 nm in edge length) with periodicities ranging from300 ± 8 to1200 ± 12 nm. The arrays were characterized using scanning ion and electron microscopy, and atomicforce microscopy. The effect of the patterning on the exchange bias field (i.e., the shift inthe hysteresis loop of ferromagnetic Ni due to proximity to antiferromagneticFeF2) was studied using magneto-transport measurements. These high quality nanostructuresoffer a unique method to address some of the open questions regarding the microscopicorigin of exchange bias. This is not only of major relevance in the fabrication andminiaturization of magnetic devices but it is also one of the important proximityphenomena in nanoscience and materials science.

Controllable Synthesis of PbSe Nanostructures and Growth Mechanisms

Octopod-like PbSe structures with eight symmetric arms of 1.0−3.0 µm in length have been hydrothermally synthesized without any surfactant. Keeping the other conditions the same, only by changing the molar ratio of NaOH/Pb(NO3)2 from 40 to 5, quasi-spherical nanoparticles were obtained. As poly(vinyl pyrrolidone) (PVP) was added, single-crystal PbSe nanosheets of 20−60 nm in thickness and 0.5−5.0 µm in-plane sizes can be formed. Similarly, by changing the molar ratio of NaOH/Pb(NO3)2 from 40 to 5, the nanocubes of ∼70 nm in edge length were formed. The possible growth mechanisms for the nanosheets and octopod-like structures of PbSe are discussed on the basis of transmission electron microscopy and scanning electron microscopy analysis from the time-dependent experiments.