Nucleation Of Metal Nanoparticles Research Articles

Continuous nucleation of metallic nanoparticles via photocatalytic reduction.

Whether in organic synthesis or solar energy conversion, light can be a powerful reagent in chemical reactions and introduce new opportunities for synthetic control including duration, intensity, interval, and energy of irradiation. Here, we report the use of a molecular photosensitizer as a reducing agent in metallic nanoparticle syntheses. Using this approach, we report three key findings. (1) Nanoparticles produced by photocatalytic reduction form via a continuous nucleation mechanism, as opposed to burst and burst-like nucleation processes typically observed in metal nanoparticle syntheses. (2) Because nucleation is continuous, as long as the solution is irradiated (and there remains excess reagents in solution), nanoparticle nucleation can be turned on and off by controlling the timing and duration of irradiation, with no observable particle growth. (3) This synthetic method extends to the formation of bimetallic nanoparticles, which we show also form via a continuous nucleation pathway, and follow predicted patterns of metal incorporation as a function of the magnitude of the difference between the reduction potentials of the two metals. Taken together, these results establish a versatile synthetic method for the formation of multimetallic nanoparticles using visible light.

(High-Temperature Energy, Materials, & Processes Division Outstanding Achievement Award Address) Mechanisms of Oxide Exsolution and Electrode Applications in Solid Oxide Cells

Solid oxide cell fuel electrodes based on perovskite oxides are desirable to avoid problems with Ni-based anodes, including coking in hydrocarbon fuels and degradation due to fuel impurities or redox cycling. However, oxide anode electrochemical performance is often lacking, limited by surface processes such as the dissociative adsorption of hydrogen. One way to improve such anodes is by the addition of a reducible cation in the oxide formulation, resulting in cation exsolution and nucleation of metallic nanoparticles on oxide surfaces during cell startup and operation. For example, substitution of small amounts of Ni or Ru on the B-site of Sr(Ti,Fe)O3 results in the formation of Ni-Fe or Ru-Fe nanoparticles, respectively, during exposure of the electrode to fuel during cell operation. This talk will examine the microstructural evolution of these exsolution anodes, making use of in situ x-ray diffraction measurements to detect formation of exsolved metal alloys and oxide phase changes. Exsolved metal nanoparticles enhance electrochemical performance, usually by promoting hydrogen dissociation on electrode surfaces. Changes in perovskite stoichiometry resulting from B-site exsolution can also impact the phase stability of the oxide, in some cases resulting in the formation of Ruddlesden-Popper phases that deleteriously affect electrochemical performance. The application of exsolution in fuel electrodes in novel thin-electrolyte oxygen-electrode-supported cells is discussed; the results indicate that performance in H2/H2O fuel is superior to Ni-YSZ in both electrolysis and fuel cell modes. Electrochemical characteristics of the exsolution electrodes are especially superior to Ni-YSZ when operated in CO/CO2 fuel.

Hollow mesoporous silica capsules loaded with copper, silver, and zinc oxide nanoclusters for sustained antibacterial efficacy

AbstractIntensive and overuse of antibiotics during the last years has triggered a distinct rise in antibiotic resistance worldwide. In addition to the newly developed antimicrobials, there is a high demand for alternative treatment options against persistent bacterial infections. The biocidal impact of metal ions like copper (Cu2+), silver (Ag+), and zinc (Zn2+), also known as the oligodynamic effect has been used for ages to kill or inhibit the growth of microorganisms and to employ long‐term prevention strategies against their biological antagonists. Herein, we report on the synthesis of Cu, Ag, and Zn metal and corresponding oxide nanoparticles immobilized on hollow mesoporous silica capsules (HMSCs) obtained by a hard‐template assisted sol‐gel synthesis followed by reduction of appropriate metal salts in the presence of HMSCs. Compartmentalization of nanosized metal and oxide clusters in Ag@HMSCs, Cu@HMSCs, and ZnO@HMSCs particles prevented their agglomeration and offered high release kinetics of metal ions between 2.0 and 3.7 mM during 24 h, as monitored by UV‐vis analyses. The distribution and morphology of pristine and metal functionalized HMSCs were evaluated by transmission electron microscopy analysis revealing the successful synthesis of Ag, Cu, and ZnO nanoparticles supported on HMSCs. X‐ray photoelectron spectroscopy revealed that mainly Cu(II), Ag(0), and Zn(II) species were present in the modified HMSCs. In addition to the surface attachment of preformed metal (Ag and Cu) and metal oxide (ZnO) cluster, nucleation of metal nanoparticles inside the void of HMSCs provided an internal reservoir which allowed for a time‐dependent release of metal ions through slower dissolution rates leading to a long‐term and sustained bacterial inhibition over several hours. The high antimicrobial efficiency of Ag@HMSCs, Cu@HMSCs, and ZnO@HMSCs particles was investigated toward both Gram‐positive (Bacillus subtilis) and Gram‐negative (Escherichia coli) bacteria by INT assays showing a complete growth inhibition for both bacteria types after 24 h. While Ag@HMSCs and Cu@HMSCs showed a higher susceptibility against Gram‐negative bacteria, ZnO@HMSCs showed a higher susceptibility against Gram‐positive bacteria. This demonstrates the promise of metal‐loaded capsules as antibacterial delivery vehicles with dual‐mode time‐release profiles being potential alternatives for antibiotic drugs.

Molecular modeling of Ag4 cluster formation

Nucleation is the main process which affects on the characteristics of the formed metal nanoparticles. At the same time the mechanism of homogeneous nucleation of metal particles in solutions are still debatable. There are two contrary points of view which briefly may be presented as “Instantaneous” and “Continuous”. Instantaneous nucleation postulated by classical nucleation theory (CNT) means formation of nuclei as a result of supersaturation of solution via set of equilibrium reactions (on the whole nA⇔An) but Continuous nucleation implies step-by-step irreversible addition of monomer to formation of nuclei and/or nanoparticle (A→A2→…→An). Using DFT calculations the thermodynamic parameters of all possible reactions leading to formation of Ag4 cluster which may be considered as intermediate in the nucleation process have been estimated. It was found that formation of Ag4 is thermodynamically possible via both of mechanisms. At the same time it was noted that addition of Ag+ to silver cluster is more preferred than association of uncharged particles. Taking into account the much higher concentration of silver ions compared to silver atoms this fact may indicate on the preference of stepwise mechanism of nucleation of metal nanoparticles in real solutions.

Statistical analysis of homogeneous nucleation of metallic nanoparticles during gas-phase synthesis

In this work, we set out to develop a model of gas-phase nucleation in a mixture of copper and argon atoms, which can be further used for analysing macro-systems. Processes occurring at the atomic level are described using coefficients obtained by statistical analysis of molecular dynamic (MD) data on interactions of metal clusters with metal and argon atoms. The MD simulation results are compared with those obtained using the proposed macroscopic model. It is found that the coefficients obtained by averaging the interaction data suitably represent the integral value of the heat of condensation, although result in the smoothing of the energy distribution functions of the clusters. Analysis of the evolution of the number of clusters has shown that the values of their increase rate were lower than those obtained by MD simulation. The conclusion is made, that in order to improve the precision of the developed gas-phase condensation model, it should be supplemented by cluster coagulation.

Organic Imine Cages: Molecular Marriage and Applications

AbstractImine condensation has been known to chemists for more than a century and is used extensively to synthesize large organic cages of defined shapes and sizes. Surprisingly, in the context of the synthetic methods for organic imine cages (OICs), a self‐sorting/self‐selection (molecular marriage) process has been overlooked over the years. Such processes are omnipresent in nature, from the creation of galaxies to the formation of the smallest building blocks of life (the cell). Such processes have the incredible ability to guide a system toward the formation of a specific product or products out of a collection of equally probable multiple possibilities. This Minireview sheds light on new opportunities in cage design offered by the self‐sorting/self‐selection protocol in OICs. Recent efforts to explore organic cages for various exciting new applications are discussed; for example, for detection of harmful small organic molecules, as templates for nucleation of metal nanoparticles (MNPs), and as proton‐conducting materials.

Organic Imine Cages: Molecular Marriage and Applications.

Imine condensation has been known to chemists for more than a century and is used extensively to synthesize large organic cages of defined shapes and sizes. Surprisingly, in the context of the synthetic methods for organic imine cages (OICs), a self-sorting/self-selection (molecular marriage) process has been overlooked over the years. Such processes are omnipresent in nature, from the creation of galaxies to the formation of the smallest building blocks of life (the cell). Such processes have the incredible ability to guide a system toward the formation of a specific product or products out of a collection of equally probable multiple possibilities. This Minireview sheds light on new opportunities in cage design offered by the self-sorting/self-selection protocol in OICs. Recent efforts to explore organic cages for various exciting new applications are discussed; for example, for detection of harmful small organic molecules, as templates for nucleation of metal nanoparticles (MNPs), and as proton-conducting materials.

Kinetics of Ag300 nanoclusters formation: The catalytically effective nucleus via a steady‐state approach

AbstractThe kinetics of formation of silver nanoparticles consisting of nearly 300 metal atoms is investigated, which were prepared by reduction of silver nitrate with hydrazine in ethylene glycol at 25°C without any stabilizer other than the glycol solvent. The resulting sigmoidal kinetic curves are analyzed by using the 1997 Finke–Watzky two‐step mechanism of slow continuous nucleation with subsequent fast autocatalytic surface growth. The kinetics of homogeneous nucleation of metal nanoparticles was analyzed using the assumption about the stepwise adjunction of precursor and the quasi steady‐state approximation. The equations were proposed to calculate the concentration of the formed metal nanoparticles and their mean size from the experimentally determined values of the Finke–Watzky rate constants. It is shown that a stepwise nucleation process can be described in the terms of the catalytically effective nucleus concept and that the number of atoms in the catalytically effective nucleus can be estimated.

Kinetic Monte Carlo simulation for homogeneous nucleation of metal nanoparticles during vapor phase synthesis

We present a free‐energy driven kinetic Monte Carlo model to simulate homogeneous nucleation of metal nanoparticles (NPs) from vapor phase. The model accounts for monomer‐cluster condensations, cluster–cluster collisions, and cluster evaporations simultaneously. Specifically, we investigate the homogeneous nucleation of Al NPs starting with different initial background temperatures. Our results indicate good agreement with earlier phenomenological studies using the Gibbs# free energy formulation from Classical Nucleation Theory (CNT). Furthermore, nucleation rates for various clusters are calculated through direct cluster observations. The steady‐state nucleation rate estimated using two different approaches namely, the Yasuoka‐Matsumoto (YM) and mean first passage time (MFPT) methods indicate excellent agreement with each other. Finally, our simulation results depict the expected increase in the entropy of mixing as clusters approach the nucleation barrier, followed by its subsequent drastic loss after the critical cluster formation resulting from first‐order phase transitions. © 2017 American Institute of Chemical Engineers AIChE J, 63: 18–28, 2018

Nucleation of Metal Nanoparticles on Amorphous Substrate: Insights into Orientation Preference and Heterogeneous Catalysis

Nucleation of Metal Nanoparticles on Amorphous Substrate: Insights into Orientation Preference and Heterogeneous Catalysis

In situ XAFS Study of Palladium Electrodeposition at the Liquid/Liquid Interface

We report the use of XAFS (X-ray absorption fine structure) as an in situ method to follow the electrochemically driven deposition of palladium nanoparticles at a liquid/liquid interface. A novel glass/plastic hybrid electrochemical cell was used to enable control of the potential applied to the liquid/liquid interface. In situ measurements indicate that the nucleation of metallic nanoparticles can be triggered through chronoamperometry or cyclic voltammetry. In contrast to spontaneous nucleation at the liquid/liquid interface, whereby fluctuations in Pd oxidation state and concentration are observed, under a fixed interfacial potential the growth process occurs at a steady rate leading to a build-up of palladium at the interface. Raman spectroscopy of the deposit suggests that the organic electrolyte binds directly to the surface of the deposited nanoparticles. It was found that the introduction of citric acid results in the formation of spherical nanoparticles at the interface.

Statistical analysis of formation and relaxation of atomic clusters based on data of molecular-dynamic modeling of gas-phase nucleation of metallic nanoparticles

Statistical analysis of the results of molecular-dynamic modeling for nucleation of metal (Cu) vapors in inert gas atmosphere (Ar) is carried out. Features of the initial stage of nucleation are considered for estimation of the probability of the growth of small atomic clusters within a supersaturated nonequilibrium medium and the efficiency of heat removal from them during collisions with inert gas atoms and other metal atoms.

A DFT Study of the Reactivity of Anatase TiO2 and Tetragonal ZrO2 Stepped Surfaces Compared to the Regular (101) Terraces.

It is generally assumed that low-coordinated sites at extended defects of oxide surfaces like steps or edges are more reactive than the regular, fully coordinated sites at the flat terraces. In this work we have considered the properties of stepped surfaces of anatase TiO2 and tetragonal ZrO2 by means of periodic DFT+U calculations. For both oxides, the stability of oxygen vacancies located near the step edges is compared to that of the same defects at the regular terraces. The capability of the steps to induce nucleation of metal nanoparticles on the surface has been evaluated by simulating the adsorption of a single ruthenium adatom. We conclude that, for anatase, step edges have no particular role in favouring the reduction of the oxide by reducing the cost for oxygen abstraction; in the same way, there is no special role of the stepped anatase surface in stabilizing adsorbed Ru atoms. On the contrary, step edges on zirconia display some capability to stabilise oxygen vacancies and ruthenium adatoms.

The formation of silver metal nanoparticles by ion implantation in silicate glasses

It has been shown that glasses containing silver metal nanoparticles are promising photonics materials for the fabrication of all-optical components. The resulting optical properties of the nanocomposite glasses depend on the composition and structure of the glass, as well as on the type of metal ion implanted and the experimental procedures involved. The main aim of this article was to study the influence of the conditions of the ion implantation and the composition of the glass on the formation of metal nanoparticles in such glasses.Four various types of silicate glasses were implanted with Ag+ ions with different energy (330keV, 1.2MeV and 1.7MeV), with the fluence being kept constant (1×1016ionscm−2). The as-implanted samples were annealed at 600°C for 1h. The samples were characterised in terms of: the nucleation of metal nanoparticles (linear optical absorption), the migration of silver through the glass matrix during the implantation and post-implantation annealing (Rutherford backscattering spectroscopy), and the oxidation state of silver (photoluminescence in the visible region).

Manipulating Size and Shape of Silica Nanoparticles with Liquid-Phase Transmission Electron Microscopy

Recently developed liquid-phase transmission electron microscopy (LP-TEM) holds great potential for dynamic imaging of relevant processes taking place in liquids at nanoscale, such as the evolution of nanoparticles during synthesis or structural changes of nanomaterials under working conditions [1]. LPTEM studies performed in the past years mainly focused on the growth of metallic nanoparticles from solutions, and pointed to important effects the electron beam can have on systems under observation [2]. Amongst various electron beam effects observed in LP-TEM, radiolysis of water and aqueous solutions leads to the formation of species such as eaq, H, OH, H2, H2O2, H, OH. These species can locally change the chemistry in the LP-TEM cell, triggering reactions such as reduction of metal ions. In fact, electron beam induced nucleation of metal nanoparticles has been one of the main focuses of the LPTEM studies so far [2].

Light induced nucleation of metallic nanoparticles with frequency controlled shapes

We predict nucleation of pancake shaped metallic nuclei having plasmonic frequencies in resonance with a circularly polarized light. The same field can trigger nucleation of needle shaped metallic particles randomly oriented in the plane of polarization. Because the probabilities of these shapes are frequency dependent, our results pave a way to nucleation of nanoparticles of desired shapes.

Comparative study of metal and non-metal ion implantation in polymers: Optical and electrical properties

The implantation of 1MeV metal (63Cu+, 107Ag+, 197Au+) and non-metal (4He+, 12C+) ions in a polycarbonate (PC) matrix has been studied in order to evaluate the role of ion species in the modification of optical and electrical properties of the polymer. When the ion fluence is above ∼1×1013ionscm−2, the threshold for latent tracks overlapping is overcome and π-bonded carbon clusters grow and aggregate forming a network of conjugated CC bonds. For fluences around 1×1017ionscm−2, the aggregation phenomena induce the formation of amorphous carbon and/or graphite like structures. At the same time, nucleation of metal nanoparticles (NPs) from implanted species can take place when the supersaturation threshold is overcome. The optical absorption of the samples increases in the visible range and the optical band gap redshifts from 3.40eV up to 0.70eV mostly due to the carbonization process and the formation of C0x clusters and cluster aggregates. Specific structures in the extinction spectra are observed when metal ions are selected in contrast to the non-metal ion implanted PC, thus revealing the possible presence of noble metal based NPs interstitial to the C0x cluster network. The corresponding electrical resistance decreases much more when metal ions are implanted with at least a factor of 2 orders of magnitude difference than the non-metal ions based samples. An absolute value of ∼107Ω/sq has been measured for implantation with metals at doses higher than 5×1016ionscm−2, being 1017Ω/sq the corresponding sheet resistance for pristine PC.

Manipulating Local Ligand Environments for the Controlled Nucleation of Metal Nanoparticles and their Assembly into Nanodendrites

Manipulating Local Ligand Environments for the Controlled Nucleation of Metal Nanoparticles and their Assembly into Nanodendrites

Manipulating Local Ligand Environments for the Controlled Nucleation of Metal Nanoparticles and their Assembly into Nanodendrites

Sehen Sie Sternchen oder Punkte? In einem simplen Zweikomponentensystem aus einer Pd-Vorstufe und Oleylamin kann die Geschwindigkeit sowohl der Keimbildung als auch des Wachstums von Nanopartikeln mithilfe der lokalen Ligandenumgebung gesteuert werden, sodass selektiv Pd-Nanodendrite oder monodisperse Pd-Nanopartikel zugänglich sind. Dieser Ansatz verbindet das Design von Nanostrukturen mit grundlegenden Prinzipien der Koordinationschemie. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

New Insights into Selective Heterogeneous Nucleation of Metal Nanoparticles on Oxides by Microwave-Assisted Reduction: Rapid Synthesis of High-Activity Supported Catalysts

Microwave-based methods are widely employed to synthesize metal nanoparticles on various substrates. However, the detailed mechanism of formation of such hybrids has not been addressed. In this paper, we describe the thermodynamic and kinetic aspects of reduction of metal salts by ethylene glycol under microwave heating conditions. On the basis of this analysis, we identify the temperatures above which the reduction of the metal salt is thermodynamically favorable and temperatures above which the rates of homogeneous nucleation of the metal and the heterogeneous nucleation of the metal on supports are favored. We delineate different conditions which favor the heterogeneous nucleation of the metal on the supports over homogeneous nucleation in the solvent medium based on the dielectric loss parameters of the solvent and the support and the metal/solvent and metal/support interfacial energies. Contrary to current understanding, we show that metal particles can be selectively formed on the substrate even under situations where the temperature of the substrate is lower than that of the surrounding medium. The catalytic activity of the Pt/CeO(2) and Pt/TiO(2) hybrids synthesized by this method for H(2) combustion reaction shows that complete conversion is achieved at temperatures as low as 100 °C with Pt-CeO(2) catalyst and at 50 °C with Pt-TiO(2) catalyst. Our method thus opens up possibilities for rational synthesis of high-activity supported catalysts using a fast microwave-based reduction method.