Ultrasmall Metal Research Articles

Ultra-small Palladium Nanoparticle Decorated Carbon Nanotubes: Conductivity and Reactivity.

Carbon nanotubes decorated with ultra-small metal nanoparticles are of great value in catalysis. We report that individual multiwalled carbon nanotubes decorated with ultra-small palladium nanoparticles can be detected by using the nano-impacts method. The high conductivity and reactivity of each decorated carbon nanotube is directly evidenced; this is achieved through studying the proton-reduction reaction for the underpotential deposition of hydrogen onto the nanoparticles decorated on the carbon nanotube walls. The reductive spikes from current amplification are analyzed to estimate the approximate length of the decorated carbon nanotubes, revealing that the decorated carbon nanotubes are electroactive along its entire length of several micrometers.

Ultrasmall metal oxide nanoparticles anchored on three-dimensional hierarchical porous gaphene-like networks as anode for high-performance lithium ion batteries

A rational design of well-dispersed and high-level ultrasmall metal oxide (MOx, M=Sn or Fe) nanoparticles anchored on 3D hierarchical porous graphene-like (HPG) networks and fabrication via a simple hydrothermal process have been achieved for the first time. By taking the advantages of the 3D HPG composites like that the well-dispersed MOx nanoparticles in ultrasmall size with the high mass loadings (more than 70%) on conductive 3D HPG substrates provide abundant active sites for Li ion insertion and good conductivity and short diffusion length for Li ions, which are beneficial for high capacity and rate capability. Meanwhile, 3D HPG can hold the ultrasmall MOx nanoparticles tightly by the pores, which avoids serious volume change and agglomeration of the ultrasmall MOx nanoparticles caused by lithium insertion/extraction. This ensures the material high capacity and cycling stability. The as-prepared SnO2-3D HPG and Fe2O3-3D HPG electrodes exhibit high reversible capacity of 986mAhg−1 and 907mAhg−1 after 100 cycles at 100mAg−1, respectively. In addition, the two electrodes exhibit excellent cycling performance at various rates and superior rate performance at 10Ag−1 and a long lifetime of 1000 cycles with nearly 90% capacity retention. Such high performance is superior to those reported recently. It is a chance to extend this present synthesis method to prepare other electrode materials with high electron/Li ion transfer kinetics for practical and large-scale applications in electrochemical fields.

General method to synthesize ultrasmall metal oxide nanoparticle suspensions for hole contact layers in organic photovoltaic devices

Abstract

One-pot fabrication of yolk-shell nanospheres with ultra-small Au nanoparticles for catalysis.

We report a "one-pot" method for the direct synthesis of an organosilica shell/silica core nanoreactor confined with ultra-small metal (Au, Pd, and Ru) nanoparticles. The nano-reactor confined with Au nanoparticles showed high activity towards styrene oxidation using O2 as the oxidant under 1 atm pressure and could be stably recycled without deterioration of both conversion and selectivity. The strategy could be adapted onto other nanostructures with little modification to obtain yolk-shell nanoreactors for catalysis application.

Bio-NCs--the marriage of ultrasmall metal nanoclusters with biomolecules.

Ultrasmall metal nanoclusters (NCs) have attracted increasing attention due to their fascinating physicochemical properties. Today, functional metal NCs are finding growing acceptance in biomedical applications. To achieve a better performance in biomedical applications, metal NCs can be interfaced with biomolecules, such as proteins, peptides, and DNA, to form a new class of biomolecule-NC composites (or bio-NCs in short), which typically show synergistic or novel physicochemical and physiological properties. This feature article focuses on the recent studies emerging at the interface of metal NCs and biomolecules, where the interactions could impart unique physicochemical properties to the metal NCs, as well as mutually regulate biological functions of the bio-NCs. In this article, we first provide a broad overview of key concepts and developments in the novel biomolecule-directed synthesis of metal NCs. A special focus is placed on the key roles of biomolecules in metal NC synthesis. In the second part, we describe how the encapsulated metal NCs affect the structure and function of biomolecules. Followed by that, we discuss several unique synergistic effects observed in the bio-NCs, and illustrate them with examples highlighting their potential biomedical applications. Continued interdisciplinary efforts are required to build up in-depth knowledge about the interfacial chemistry and biology of bio-NCs, which could further pave their ways toward biomedical applications.

Study of carbon and carbon–metal particulates in a canola methyl ester air-flame

In this study we show that the interaction of a solid metal in the form of wire in the post flame region formed using a biodiesel or fatty acid methyl ester (FAME) fuel (an oxygenated compound) can contribute significantly to the oxidation of the probe’s surface resulting in the deposition of metallic nanoparticles and carbon particulates with complex structural morphologies. The FAME used for forming the flame was canola methyl ester (CME). The interaction of the solid support within a flame medium formed using CME resulted in the formation of a distinct material deposition layer covering the surface of the probe. The formed layer was found to consist of clusters composed of aggregates of primary particles with a nearly spherical shape. The aggregates are composed of primary particles of carbon and of metallic characteristics. Other unique features include carbon networks containing numerous encapsulated ultra-small metal particles (<2.0nm in diameter), elongated carbon nanofibers, metallic nanorods, and carbon–metal composites. High resolution transmission electron microscopy analysis reveals that the metal nanoparticles have a high degree of crystallinity. It is observed that the time and flame height parameters of the probe–flame interaction are important factors for varying the morphological characteristics of the deposits. Residence times ranging from 40s to 5min established a strong correlation to deposit morphology. Energy dispersive X-ray (EDX) analysis of material samples on the formed layers reveals the presence of carbon, iron, nickel, chromium and oxygen. The introduction of a probe with similar characteristics in the post flame region formed with No. 2 diesel fuel and air resulted in a thicker material layer covering the surface of the probe. Electron microscopy and EDX analysis showed that the deposits are composed mostly of carbon clusters and no metal content or other complex form of carbon morphology were detected.

Coalescence of Atomically Precise Clusters on Graphenic Surfaces

The interaction of ultrasmall metal clusters with surfaces of graphene is important for developing promising future applications of graphenic materials. In the experiment, chemically synthesized reduced graphene oxide (RGO) in water was mixed with Au25SR18 (where SR, SCH2CH2Ph, is a ligand protecting the cluster core) in tetrahydrofuran, and a completely new cluster, larger in mass, was formed at the liquid–liquid interface. Matrix assisted laser desorption ionization mass spectrometry of the product attached to RGO show that the peak due to Au25SR18 disappears gradually upon reaction and a single sharp peak referred to here as “135 ± 1 kDa cluster” appears. The composition of the new cluster is very close to the well-known magic cluster, Au144SR60 while the peak maximum is at Au135SR57. The formation of 35 ± 1 kDa cluster from the parent Au25 is proposed to be governed by the trapping of smaller clusters in a deep potential well generated at the graphene surface. We theoretically model the active role of...

Assembly of Nanoions via Electrostatic Interactions: Ion-Like Behavior of Charged Noble Metal Nanoclusters

The assembly of ultrasmall metal nanoclusters (NCs) is of interest to both basic and applied research as it facilitates the determination of cluster structures and the customization of cluster physicochemical properties. Here we present a facile and general approach to assemble noble metal NCs by selectively inducing electrostatic interactions between negatively-charged metal NCs and divalent cations. The charged metal NCs, which have well-defined sizes, charges and structures; and behave similarly to multivalent anions, can be considered as nanoions. These nanoions exhibit step-like assembly behavior when interacting with the counter cations – assembly only occurs when the solubility product (Ksp) between the carboxylate ions on the NC surface and the divalent cations is exceeded. The assembly here is distinctively different from the random aggregation of colloidal particles by counter ions. The nanoions would assemble into fractal-like monodisperse spherical particles with a high order of regularity that mimic the assembly of ionic crystals.

Surfactant-Free, Stable Noble Metal–Graphene Nanocomposite as High Performance Electrocatalyst

Preparation of a noble metal–graphene nanocomposite (MGN)-based clean and stable catalyst with uniform distribution of ultrafine nanoparticles can greatly improve the performance of fuel cells. Here, we show that surfactant-free MGNs for different noble metals can be prepared for high-performance fuel cell catalysis by the reaction of respective ultrasmall colloidal metal oxide/hydroxides with partially reduced colloidal graphene oxide. The resultant MGN is composed of highly dispersed M–M+n based nanoparticles of ultrasmall size and produces a strong and stable catalytic current for ethanol and formic acid oxidation.

Ultrasmall metal nanoclusters for bio‐related applications

The study of ultrasmall metal nanoclusters (NCs, ranging from subnanometer to ca 2 nm) is evidently a quickly evolving field in current nanoscience and nanotechnology research. Metal NCs, typically composed of several to hundreds of metal atoms, have attracted great interest in recent years owing to their unique properties including ultrasmall size and enhanced photoluminescence, together with other properties such as excellent photostability, low toxicity, and good biocompatibility desired for biological applications. This review summarizes recent advances in the field of bio-related applications of metal NCs materials. We highlight the applications of metal NCs for biosensor development, fluorescent biological imaging, and biomedical research, and finally discuss briefly some current challenges and future work.

Competition between surface screening and size quantization for surface plasmons in nanoparticles

We present a theoretical model for analyzing the size dependence of the surface plasmon resonance of metallic nanospheres in a range of sizes down to a single nanometer. Within this model, we explicitly show how different microscopic mechanisms, namely quantization due to size (quantum size effect (QSE)) and dynamical surface screening, affect the energy of the surface plasmon. We demonstrate that the latter mechanism, which can move the surface plasma energy both toward the red or the blue, can be comparable to or even stronger than QSE. Thus, depending on material parameters, QSE may only be observed for ultra-small metal nanoparticles much closer to 1 nm in size than to 10 nm. Results presented herein are in quantitative agreement with recent published experimental results for Ag and Au.

Beyond gold: rediscovering tetrakis-(hydroxymethyl)-phosphonium chloride (THPC) as an effective agent for the synthesis of ultra-small noble metal nanoparticles and Pt-containing nanoalloys

The use of tetrakis-(hydroxymethyl)-phosphonium chloride (THPC) as simultaneous reducing agent and stabilizing ligand has been extended to the single-step synthesis at room temperature of a wide variety of monometallic nanoparticles and bi-/tri- metallic nanoalloys containing noble metals with potential application in catalysis. The colloidal suspensions exhibit mean diameters below 4 nm with narrow size distributions and high stability in aqueous solution for long periods of time.

Design of an ultrasmall Au nanocluster–CeO2 mesoporous nanocomposite catalyst for nitrobenzene reduction

In this work we are inspired to explore gold nanoclusters supported on mesoporous CeO2 nanospheres as nanocatalysts for the reduction of nitrobenzene. Ultrasmall Au nanoclusters (NCs) and mesoporous CeO2 nanospheres were readily synthesized and well characterized. Due to their ultrasmall size, the as-prepared Au clusters can be easily absorbed into the mesopores of the mesoporous CeO2 nanospheres. Owing to the unique mesoporous structure of the CeO2 support, Au nanoclusters in the Au@CeO2 may effectively prevent the aggregation which usually results in a rapid decay of the catalytic activity. It is notable that the ultrasmall gold nanoclusters possess uniform size distribution and good dispersibility on the mesoporous CeO2 supports. Compared to other catalyst systems with different oxide supports, the as-prepared Au nanocluster-CeO2 nanocomposite nanocatalysts showed efficient catalytic performance in transforming nitrobenzene into azoxybenzene. In addition, a plausible mechanism was deeply investigated to explain the transforming process. Au@CeO2 exhibited efficient catalytic activity for reduction of nitrobenzene. This strategy may be easily extended to fabricate many other heterogeneous catalysts including ultrasmall metal nanoclusters and mesoporous oxides.

Photohole-oxidation-assisted anchoring of ultra-small Ru clusters onto TiO2 with excellent catalytic activity and stability

Ultra-small metal clusters with good activity and stability are of great significance for their practical applications in catalysis and materials science. Here we report a photohole-oxidation-assisted approach for anchoring ultra-small Ru clusters (∼1.5 nm) with an extremely high density (∼1017 m−2) onto TiO2 support. The resulting clusters have good thermal stability and exhibit excellent long-term catalytic activity for the hydrogenation of CO2 to methane (methanation). The anchoring process involves the oxidation of Ru3+ in solution by photogenerated holes on the TiO2 surface to give tiny RuO2 species (<0.8 nm) immobilized on the surface, followed by a H2 reduction step to produce Ru0 clusters. Aberration-corrected high-resolution transmission electron microscopy (Cs-HRTEM) observations identify the Ru–Ru bond length contraction at the metal surface (relative to the interior of the particle) as well as bond length changes in the defect region at the metal–support interface. Density functional theory (DFT) calculations further demonstrate that the ultra-small Ru clusters are well stabilized and tightly anchored onto the TiO2 substrate via Ru–O covalent bonding in the defect region of the metal–support interface. The high-dispersion of ultra-small Ru clusters as well as the strong chemical bonding at the interface account for their surprisingly high catalytic reactivity and excellent thermal/reaction stability. This synthetic method may open up a new way to fabricate thermally stable ultra-small metal clusters for practical industrial applications in catalysis.

There and Back Again: The Unique Nature of Copper in Ambient Pressure Dried-Silica Aerogels

We have previously reported the formation of framework single-site copper in silica ambient-pressure-dried (APD) aerogels and xerogels, for which the metal (2–11 wt %) was added during the sol–gel stage (Kristiansen, T.; Mathisen, K.; Einarsrud, M.-A.; Bjorgen, M.; Nicholson, D. G. J. Phys. Chem. C2011, 115, 19260–19268). We here present a fundamental study on the formation of ultrasmall metal nanoclusters in hydrogen and complete restoration of the initial surroundings in nitric oxide/oxygen, using in situ X-ray absorption spectroscopy (XAS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). We coupled density functional theory (DFT) with the Cu–Cu shell multiplicities and distances from extended X-ray absorption fine structure (EXAFS) to investigate the dimensions and structure dynamics of the copper nanoclusters. Their average cluster size did not exceed dimensions above 1.6 nm in either gel system up to 450 °C in hydrogen; however, a significant drop in the first Cu–Cu s...

The impacts of nanotechnology on catalysis by precious metal nanoparticles

AbstractThis review article focuses on the impacts of recent advances in solution phase precious metal nanoparticles on heterogeneous catalysis. Conventional nanometal catalysts suffer from size polydispersity. The advent of nanotechnology has significantly advanced the techniques for preparing uniform nanoparticles, especially in solution phase synthesis of precious metal nanoparticles with excellent control over size, shape, composition and morphology, which have opened up new opportunities for catalysis. This review summarizes some recent catalytic research by using well-defined nanoparticles, including shape-controlled nanoparticles, high index-faceted polyhedral nanocrystals, nanostructures of different morphology (e.g., core-shell, hollow, etc.), bi- and multi-metallic nanoparticles, as well as atomically precise nanoclusters. Such well-defined nanocatalysts provide many exciting opportunities, such as identifying the types of active surface atoms (e.g., corner and edge atoms) in catalysis, the effect of surface facets on catalytic performance, and obtaining insight into the effects of size-induced electron energy quantization in ultra-small metal nanoparticles on catalysis. With well-defined metal nanocatalysts, many fundamentally important issues are expected to be understood much deeper in future research, such as the nature of the catalytic active sites, the metal-support interactions, the effect of surface atom arrangement, and the atomic origins of the structure-activity and the structure-selectivity relationships.

Synthesis and Dispersion of Ultra-Small Binary and Ternary Metal Oxide Nanoparticles for Dielectric Thin Films

ABSTRACTFabrication of dielectric thin films using dispersions of ultra-small ZrO2and BaTiO3nanoparticles with a low-temperature processing is reported. Highly crystalline and monodisperse cubic-ZrO2and tetragonal-BaTiO3nanoparticles were synthesized using non-aqueous approach. Post synthesis, nanoparticle dispersions were realized through chemical modification of their surface. The obtained dispersions were then employed for the fabrication of homogeneous and densely-packed dielectric thin films, verified through scanning electron microscopy.

Study on optical properties of aggregated ultra-small metal nanoparticles

We study the optical properties of dimer and septamer aggregates (in forms of being separated or merged) of ultra-small silver nanoparticles (a few nanometers in diameter) by calculating their extinction spectra and optical field distributions using the discrete dipole approximation method. Characteristics of their extinction spectra are identified due to different resonance modes dependent on the incidence states of light. Specifically, as polarization of the incidence light is perpendicular to the center-to-center lines of the nanoparticles, interaction of neighboring nanoparticles is in the “repulsive coupling mode”, which results in blue-shift of the resonance peak with decrease of the nanoparticle interspacing. While, whenever there is a projection of the polarization of incident light on the center-to-center lines of the nanoparticles, the “attractive coupling mode” between the nanoparticles dominates in their resonant interaction, which results in red-shift of the resonance peak with decrease of the nanoparticle interspacing. It is also shown that optical interaction of the ultra-small nanoparticles is only effective when their interspacings are approximately less than 15 nm, and particularly prominent when Coulomb interactions of the electronic charges of plasmons are active within a few nanometers.

?Longitudinal Water Proton Relaxivities of Ultra Small 3d and 4f Transition Metal Oxide Nanoparticles

We report the longitudinal water proton relaxivities (r1) of several 3d and 3f transition metal oxide nanoparticles. These include ultrasmall iron oxide, manganese oxide, europium oxide, gadolinium oxide, and dysprosium oxide nanoparticles. The nanoparticles ranged from 1.0 to 3.0 nm in diameter. Ultrasmall metal oxide nanoparticles with metal ions of high and pure S-state electron magnetic moments showed high r1 relaxivities. The measured relaxivities indicate that ultrasmall gadolinium oxide nanoparticles with a high r1 relaxivity of 12.6 mM −1s−1 may be suitable for use as a sensitive T1 MRI contrast agent.

Nanopore/electrode structures for single-molecule biosensing

Biological and solid-state nanopores have recently attracted much interest as ultrafast DNA fragment sizing and sequencing devices. Their potential however goes far beyond DNA sequencing. In particular, nanopores offer perspectives of single-molecule (bio)sensing at physiologically relevant concentrations, which is key for studying protein/protein or protein/DNA interactions. Integration of electrode structures into solid-state nanopore devices moreover enables control and fast switching of the pore properties, e.g. for active control of biopolymer transport through the nanopore. We present some of recent work in this area, namely the fabrication and characterization of nanopore/electrode architectures for single-(bio)molecule sensing. Specifically, we introduce a new technique to fabricate ultra-small metal nanopores with diameters smaller than 20 nm based on ion current feedback (ICF) controlled electrodeposition. It offers precise control of the pore conductance, is easily multiplexed, and can be extended to a wide range of different metals.