Catalytic Metal Nanoparticles Research Articles

A step towards controlled-diameter single walled carbon nanotubes

This research treats a particularly challenging undertaking in carbon nanoscience: controlling the diameter distribution of single walled carbon nanotubes (SWCNTs) grown using CVD. To do so requires the fabrication of well-separated and monodispersed catalytic metal nanoparticles which can be uniformly distributed on a substrate. We propose a new strategy involving the preparation of a monolayer of chemisorbed nickel acetylacetonate which is shown by infrared spectroscopy and coupled thermogravimetric–mass spectrometry analyses to be anchored to the surface silanol groups of the substrate. After decomposition of this precursor, the nickel remains bonded with these surface silanol groups which upon further heating results in good dispersion of the nanoparticles over the silica surface. Using this catalyst, SWCNTs with a very discrete chiral preference and a narrow diameter distribution were synthesized at moderate temperature. This work thus opens new perspectives for the fabrication of uniform-diameter carbon nanotubes.

Environmentally-Benign Electrochemical Method for Formation of Catalytic Metal Nanoparticles in a Chitosan Matrix On a Stainless Steel Electrode

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Effect of the Carrier Gas Flow Rate on the Microstructure Evolution and the Generation of the Charged Nanoparticles During Silicon Chemical Vapor Deposition

The generation of charged nanoparticles in the gas phase has been continually reported in many chemical vapor deposition processes. Charged silicon nanoparticles in the gas phase were measured using a differential mobility analyzer connected to an atmospheric-pressure chemical vapor deposition reactor at various nitrogen carrier gas flow rates (300-1000 standard cubic centimeter per minute) under typical conditions for silicon deposition at the reactor temperature of 900 degrees C. The carrier gas flow rate affected not only the growth behavior of nanostructures but also the number concentration and size distribution of both negatively and positively charged nanoparticles. As the carrier gas flow rate decreased, the growth behavior changed from films to nanowires, which grew without catalytic metal nanoparticles on a quartz substrate.

Highly uniform platinum nanoparticles supported on graphite nanoplatelets as a catalyst for proton exchange membrane fuel cells

Graphite nanoplatelets (GNPs), which consist of layers of graphene, are an ideal electrocatalyst support due to their high electrical and thermal conductivity, excellent chemical stability, and easy availability. However, GNPs are somewhat chemically inert, which makes the even deposition of catalytic metal nanoparticles on their surface difficult. In this paper, we present a facile method to prepare highly uniform Pt nanoparticles on GNPs, which are decorated with 1-pyrenecarboxylic acid (PCA). When the hydrophobic pyrene group of the PCA is adsorbed on the surface of GNPs via π–π interaction, its carboxylic group can serve as an anchor for the Pt deposition. This decoration facilitates a narrow size profile, which is centered at approximately 2–3 nm, and an even spatial distribution on the GNPs surface for the Pt nanoparticles. The resultant Pt/GNPs catalyst exhibits a noticeably higher durability and electrochemical activity than the commonly used Pt/C catalyst and is therefore a promising cathodic catalyst for proton exchange membrane fuel cells.

Perovskite chromates cathode with resolved and anchored nickel nano-particles for direct high-temperature steam electrolysis

Doped lanthanum chromates are now commonly used to prepare composite cathodes for direct steam electrolysis. However, the limitation of electrochemical performances and cell current efficiency by insufficient electro-catalytic activity is a major challenge. This paper reports the use of reversibly exsolved catalytic metallic Ni nano-particles on A-site deficient and B-site excess perovskite (La0.75Sr0.25)0.95(Cr0.8Ni0.2)0.95Ni0.05O3−δ (LSCNNi), in order to achieve an activity-enhanced composite cathode via high-temperature reduction under reducing atmospheres. The electrical properties of the ceramic are investigated methodically and correlated with the performances of the composite electrodes in symmetric and electrolysis cells. XRD, SEM, EDS and XPS results, confirm that the exsolution or dissolution of nano metallic catalyst is reversible in redox treatment cycles. The Faradic efficiency reaches approximately 80% for the LSCNNi cathode with the flow of 5%H2/Ar. Ultimately, the unified effect of metallic catalyst and redox-stable ceramic produce striking redox stability as well as electrochemical performances of the titled composite cathode. The results signify that the composite cathode with exsolved nickel nano-particles, is a good potential fuel electrode for direct steam electrolysis in an oxygen-ion conducting solid oxide electrolyzer.

Graphene nano-cutting using biologically derived metal nanoparticles

We have developed a novel technique to cut graphene films using catalytic metal nanoparticles derived from ferritin, which is one of the proteins that contain a constant amount of Fe oxide in its inner core. For site-selective adsorption of ferritin molecules to sapphire surfaces that are partially covered with graphene films, two methods, dipping and spin-coating, were used. Graphene films were etched by the Fe-catalytic reaction with hydrogen gas at elevated temperatures. It was found that ferritin adsorption sites are controlled by graphene film edges, atomic steps of the sapphire substrate, and solution condition such as molecular concentration and ionic strength. We demonstrate that high density nanoribbons can be fabricated by using the uniformly-sized catalyst nanoparticles derived from ferritin and the aligned etching technique guided by the atomic structures of the substrate surface.

A self-heated silicon nanowire array: selective surface modification with catalytic nanoparticles by nanoscale Joule heating and its gas sensing applications

We demonstrated novel methods for selective surface modification of silicon nanowire (SiNW) devices with catalytic metal nanoparticles by nanoscale Joule heating and local chemical reaction. The Joule heating of a SiNW generated a localized heat along the SiNW and produced endothermic reactions such as hydrothermal synthesis of nanoparticles or thermal decomposition of polymer thin films. In the first method, palladium (Pd) nanoparticles could be selectively synthesized and directly coated on a SiNW by the reduction of the Pd precursor via Joule heating of the SiNW. In the second method, a sequential process composed of thermal decomposition of a polymer, evaporation of a Pd thin film, and a lift-off process was utilized. The selective decoration of Pd nanoparticles on SiNW was successfully accomplished by using both methods. Finally, we demonstrated the applications of SiNWs decorated with Pd nanoparticles as hydrogen detectors. We also investigated the effect of self-heating of the SiNW sensor on its sensing performance.

High-performance fuel electrodes based on NbTi0.5M0.5O4 (M = Ni, Cu) with reversible exsolution of the nano-catalyst for steam electrolysis

This paper investigates potential fuel electrode materials NbTi0.5M0.5O4 (M = Ni, Cu) for solid oxide steam electrolysers. Efficient catalytic metallic Ni and Cu nanoparticles are exsolved and anchor onto the surface of the highly electronically conducting material Nb1.33Ti0.67O4, forming an enhanced composite fuel electrode in the in situ reduction. The XRD, SEM, EDS and XPS results together confirm that the exsolution or dissolution of the nanometallic catalyst is completely reversible in the redox cycles. The electrical properties of the reduced NbTi0.5M0.5O4 ceramic fuel electrode is systematically investigated and correlated to the electrochemical performance of the composite fuel electrodes in symmetric cells or electrolysis cells. The synergetic effect of the metallic catalyst and ceramic fuel electrode leads to the excellent stability as well as the superior performance of the direct steam electrolysis without a flow of reducing gas over the composite fuel electrodes. The Faradic efficiencies of the steam electrolysis reach 95% and 97% for the Ni- and Cu-enhanced fuel electrodes on flowing reducing gas over the fuel electrodes, respectively, however, comparable performance is achieved for the direct steam electrolysis with Ni- and Cu-enhanced fuel electrodes without flowing reducing gas over the composite fuel electrodes.

Needles and Haystacks: Influence of Catalytic Metal Nanoparticles on Structural and Vibrational Properties and Morphology of Silicon Nanowires Synthesized by Metal-Assisted Chemical Etching

ABSTRACTMetal-assisted chemical etching (MACE) of silicon (Si) is a simple and low-cost process to fabricate Si nanostructures with varying aspect ratio and properties. In this work, we report on the structural and vibrational properties of Si nanostructures synthesized with varying metal catalyst. The morphology of the synthesized nanowires was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical and vibrational properties of the Si nanostructures were studied by photoluminescence and Raman spectroscopy using three different excitation sources (UV, visible and near-infrared) and are correlated to their microstructures. We propose that the excessive injection of holes into Si at the metal-Si interface and its diffusion to the nanowire surfaces facilitate the etching of Si on these surfaces, leading to a mesoporous network of Si nanocrystallites. When etched with catalytic Au nanoparticles, “hay-stacked” mesoporous Si nanowires were obtained. The straighter nanowires etched with Ag nanoparticles, consisted of a single crystalline core with a thin porous layer that decreased in thickness towards the base of the nanowire. This difference is due to the higher catalytic activity of Au compared to Ag for H2O2 decomposition. The SERRS observed during UV and visible Raman with Ag-etched Si nanowires and near-infrared Raman with Au-etched Si nanowires is due to the presence of the sunken metal nanoparticles. In addition, we explored the influence of varying H2O2 and HF concentration as well as the influence of increased etching temperature on the resultant nanostructured Si morphology. Such Si nanostructures may be useful for a wide range of applications such as photovoltaic and biological and chemical sensing.

Haloaurate and halopalladate imidazolium salts: structures, properties, and use as precursors for catalytic metal nanoparticles

The synthesis and characterisation of a series of new gold- and palladium-containing symmetrical imidazolium salts are described which display significant cation-dependent effects determined by the structure of the alkyl chains of the imidazolium motifs. Whereas direct reduction of the Pd salts can produce stable nanoparticles (NPs) coated by imidazolium salts, the addition of strong base to the Pd or Au salts before reduction gives stable NPs, potentially pacified by N-heterocyclic carbene units. The possibility of NP surface protection by metal-carbon bonds in these systems is investigated by spectroscopic, synthetic, and catalytic investigations, providing support for the hypothesis. Significantly, the catalytic activity of the NPs is not inhibited by the continued presence of the ligands.

Electro-colorimetric hydrogen gas sensor based on Pt-functionalized In2O3 nanopushpins and InGaN/GaN multiple quantum wells

A novel electro-colorimetric gas sensing technique based on the catalytic metal nanoparticles decorated metal oxide nanostructures integrated with multiple quantum wells (MQWs) has been proposed. The working principle has been demonstrated by the sensing device derived from the composite consisting of In0.15Ga0.85N/GaN MQWs and Pt-functionalized In2O3 nanopushpins for the detection of hydrogen gas. The pronounced changes in emission as well as Raman scattering spectra of InGaN/GaN MQWs under different target gas concentrations clearly illustrate the feasibility of our newly designed composites for the derivative of contact-free, simple and highly sensitive gas sensors with optical detection

Effects of Catalytic Site Position on the Performance and Lifetime of Carbon Nanotubes Supported Cobalt Fischer-Tropsch Synthesis Nano Catalyst

The effects of confinement in carbon nanotubes on the performance and lifetime of carbon nanotubes (CNT) supported cobalt Fischer–Tropsch (FT) catalysts are reported. A method was developed to control the position of the catalytic sites on either inner or outer surface of carbon nanotubes. TEM analyses revealed that about 80-85% of cobalt oxide particles can be controlled to be positioned at inner or outer surface of the nanotubes. Deposition of cobalt oxide inside the nanotube pores decreased the average size of the cobalt oxide particles from 16.6 to 7.2 nm and shifted the reduction peak temperature of cobalt oxide species to lower temperatures (from 330 to 318oC, and 446 to 428oC) and improved the reducibility of the catalyst by 7%. The catalysts were assessed in terms of their activity, selectivity and lifetime in a fixed-bed micro reactor. The catalyst with catalytic sites inside the pores showed 30.5% higher initial activity than the catalyst with catalytic sites outside the pores. Also, the catalyst with cobalt particles inside the pores exhibited higher selectivity to heavier hydrocarbons (79.5% vs. 76.2% C5 + selectivity). Deposition of cobalt particles on interior surface of the nanotubes resulted in a more stable catalyst, while its counterpart experienced 50.4% deactivation within a period of 20 days due to catalytic sites sintering. It is concluded that encapsulation of the catalytic metal nanoparticles inside the nanotubes prevents the catalytic site agglomeration. Keywords: Fischer-Tropsch, cobalt nano particles, Carbon nanotubes, Confinement, Activity, Selectivity, Deactivation

ChemInform Abstract: Synthesis of Supported Catalysts by Atomic Layer Deposition

AbstractReview: 36 refs.

Catalytic membranes with palladium nanoparticles: From tailored polymer to catalytic applications

A new polymer–metal nanocomposite containing catalytic metal nanoparticles and useful for the preparation of catalytic membranes was developed. Pd0 nanoparticles were grown by intermatrix synthesis methodology on polymeric membranes made of either sulfonated and non sulfonated polyethersulphone with Cardo group or Nafion. The synthesized polymer, the developed membranes and the corresponding nanocomposites were characterized by chemical and microscopic techniques and their catalytic efficiency was tested following a model reaction: the reduction of p-nitrophenol to p-aminophenol.

ChemInform Abstract: Reactions in “Sacrificial” Solvents

AbstractReview: 233 refs.

Synthesis of Supported Catalysts by Atomic Layer Deposition

A promising new method of catalyst synthesis is atomic layer deposition (ALD). ALD is a variation on chemical vapor deposition wherein metals, oxides and other materials are deposited on surfaces via a sequence (usually binary) of self-limiting reactions. The self-limiting character of the reactions makes it possible to achieve uniform deposits on high-surface-area porous solids and, hence, produce practical catalytic materials. The ability to deposit uniform layers in a sequence makes it possible to fabricate the support and then construct the catalytic metal and/or metal oxide species and add modifier layers in any desired order. This article will provide a short introduction to the technique of ALD and its application to the synthesis of supported catalytic metal nanoparticles and oxide monolayers.

Thermal stability of multilayer graphene films synthesized by chemical vapor deposition and stained by metallic impurities

Thermal stability is an important property of graphene that requires thorough investigation. This study reports the thermal stability of graphene films synthesized by chemical vapor deposition (CVD) on catalytic nickel substrates in a reducing atmosphere. Electron microscopies, atomic force microscopy, and Raman spectroscopy, as well as electronic measurements, were used to determine that CVD-grown graphene films are stable up to 700 °C. At 800 °C, however, graphene films were etched by catalytic metal nanoparticles, and at 1000 °C many tortuous tubular structures were formed in the film and carbon nanotubes were formed at the film edges and at catalytic metal-contaminated sites. Furthermore, we applied our pristine and thermally treated graphene films as active channels in field-effect transistors and characterized their electrical properties. Our research shows that remnant catalytic metal impurities play a critical role in damaging graphene films at high temperatures in a reducing atmosphere: this damage should be considered in the quality control of large-area graphene films for high temperature applications.

Porous Alumina Template based Versatile and Controllable Direct Synthesis of Silicon nanowires

ABSTRACTHighly densely packed, self-organized silicon nanowires with very narrow diameter distribution were synthesized within porous anodic alumina templates with electrodeposited catalytic metal nanoparticles. For successful catalytic metal nanoparticle deposition, electrochemical-, and chemical barrier layer thinning process was investigated following anodization process. Controlled pulsed electrodeposition process was carried out for a volume calibration of desired catalytic metal nanoparticle deposition inside nanopore arrays using different metal-ion containing electrolyte. Not only single metal nanoparticles, but also multi metal nanoparticles layers were filled inside PAA to enhance metal filling aspect, and to control the volume of nanoparticles more precisely. Using multilayered metal nanoparticles resulted on different SiNW’s growth behavior depending on the types of underlying metal nanoparticles.SiNWs were successfully synthesized using hot-filament assisted chemical vapor deposition system. Although silicon precursor gas can generally be dissociated at relatively low temperatures, the use of a hot filament activation help decreasing process temperature, and also, highly activated atomic hydrogen generation via the tungsten hot filament placed at gas inlet helps preventing parasitic amorphous silicon deposition on either the alumina membrane surface or the pore wall which hinders appropriate growth of SiNWs in PAA by nanopores clogging. Such densely packed, self-organized SiNWs are of high interest in many application fields like nanoelectronics, optoelectronics, and energy storage/conversion devices etc.

Macromol. Rapid Commun. 22/2011

Front Cover: The facile one-pot synthesis of functional metal nanoparticle-polymer hybrids using a simple photo-chemical method is reported. The hierarchically arranged ionic domains provide well-defined nanoreactors for the synthesis of catalytic metal nanoparticles. Further details can be found in the article by H. Ahn and M. J. Park* on page 1790.

Catalytic formation of carbon phases in metal modified, porous polymer derived SiCN ceramics

A novel method for the simultaneous formation of catalytic active metal nanoparticles, multiwall carbon nanotubes (MWCNTs) and/or turbostratic carbon and porous M@SiCN (M = Fe, Co, Pt, Cu, Ag, Au) ceramics during pyrolysis of metal modified polysilazanes and polyethylene (PE) particles as sacrificial filler is described. The thermal decomposition of the polyethylene leads not only to the generation of the porosity but also to an in situ reduction of the metal compounds to the metal nanoparticles, due to the reductive atmosphere. Depending on the metal, carbon nanotubes as well as turbostratic carbon were formed in different amounts, due to the chemical vapor deposition (CVD) like conditions. The resulting carbon phases, ceramics and metal nanoparticles were investigated using the combination of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) measurements, giving evidence for the presence of the carbon phases and the metal particles.