Graphene-coated cobalt nanoparticles surface-functionalized with benzylamine groups (CoC-NH(2) nanomagnets) were shown to effectively enrich analytes for surface-assisted laser desorption/ionization mass spectrometry (affinity SALDI-MS) analysis. These CoC-NH(2) nanomagnets are highly suited for use with affinity SALDI-MS because their mean diameter of 30 nm, high specific surface area of 15 m(2) g(-1), and high-strength saturation magnetization of 158 emu g(-1) led to efficient extraction of analytes by magnetic separation, which in turn enabled excellent SALDI-MS performance. Surface modification of CoC nanomagnets with benzylamine groups increased the yield of peptide ions and decreased fragmentation of benzylpyridinium ions, so-called "thermometer ions" formed through soft ionization. The CoC-NH(2) nanomagnets were used to extract perfluorooctanesulfonate from large volumes of aqueous solutions by magnetic separation, which was identified directly by SALDI-MS analysis with high sensitivity even at the sub-part-per-trillion level (∼0.1 ng/L). The applicability of CoC-NH(2) nanomagnets in conjunction with SALDI-MS for the enrichment and detection of pentachlorophenol, bisphenol A, and polyfluorinated compounds (PFCs) with varying chain length, which are environmentally significant compounds, as well as small drugs, was also evaluated.

A systematical examination of the chemical stability of cobalt metal nanomagnets with a graphene-like carbon coating is used to study the otherwise rather elusive formation of nanometer-sized physical defects in few layer graphene as a result of acid treatments. We therefore first exposed the core-shell nanomaterial to well-controlled solutions of altering acidity and temperature. The release of cobalt into these solutions over time offered a simple tool to monitor the progress of particle degradation. The results suggested that the oxidative damage of the graphene-like coatings was the rate-limiting step during particle degradation since only fully intact or entirely emptied carbon shells were found after the experiments. If ionic noble metal species were additionally present in the acidic solutions, the noble metal was found to reduce on the surface of specific, defective particles. The altered electrochemical gradients across the carbon shells were however not found to lead to a faster release of cobalt from the particles. The suggested mechanistic insight was further confirmed by the covalent chemical functionalization of the particle surface with chemically inert aryl species, which leads to an additional thickening of the shells. This leads to reduced cobalt release rates as well as slower noble metal reduction rates depending on the augmentation of the shell thickness.

Concentrating dilute streams is a key operation in numerous industries. The work presented here investigates the use of magnetic nanoparticles as transport reagents to mechanically move specific compounds against concentration gradients. Using a model system (arsenate), a cyclic, two-step process for concentrating solutes can be realized, based on a reversible, pH dependent adsorption equilibrium and two stirred tanks: adsorption of the model ion As(V) from a dilute aqueous stream (large tank) onto chemically functionalized magnetic nanoparticles allows water purification at the mg per liter level. Magnetic separation thereby results in an energy efficient removal of the noxious ion from a large water volume (no pumping, magnetic sedimentation/flocculation) and transfer into a much smaller, separate volume (small tank). Changing the acidity (pH) within the much smaller tank allows desorption of the collected ion As(V) into a small volume and thereby permits efficient enrichment. This process scheme, therefore, splits a highly dilute stream into a purified stream (A) and a concentrate stream (B) by using a true moving bed. Long time recycling of the functional magnetic nanoparticles mainly depends on the efficiency of magnetic filtration, under the conditions of reversible adsorption and by using stable magnetic nanoparticles (carbon-coated metal nanoparticles).

AIMS:Nanomagnets with metal cores have recently been shown to be promising candidates for magnetic drug delivery due to higher magnetic moments compared with commonly used metal oxides. Successful application strongly relies on a safe implementation that goes along with detailed knowledge of interactions and effects that nanomagnets might impart once entering the body.MATERIALS & METHODS:In this work, we put a particular focus on the interactions of ultra-strong metal nanomagnets (≥ three-times higher in magnetization compared with oxide nanoparticles) within the vascular compartment. Individual aspects of possible effects are addressed, including interactions with the coagulation cascade, the complement system, phagocytes and toxic or inflammatory reactions both by blood and endothelial cells in response to nanomagnet exposure.RESULTS:We show that carbon-coated metal nanomagnets are well-tolerated by cells of the vascular compartment and have only minor effects on blood coagulation.CONCLUSION:These findings provide the fundament to initiate successful first in vivo evaluations opening metal nanomagnets with improved magnetic properties to fascinating applications in nanomedicine.

Surface-modified magnetic nanoparticles can be used in extraction processes as they readily disperse in common solvents and combine high saturation magnetization with excellent accessibility. Reversible and recyclable adsorption and desorption through solvent changes and magnetic separation provide technically attractive alternatives to classical solvent extraction. Thin polymer layered carbon-coated cobalt nanoparticles were tagged with β-cyclodextrin. The resulting material reversibly adsorbed organic contaminants in water within minutes. Isolation of the immobilized inclusion complex was easily carried out within seconds by magnetic separation due to the strong magnetization of the nanomagnets (metal core instead of hitherto used iron oxide). The trapped molecules were fully and rapidly recovered by filling the cyclodextrin cavity with a microbiologically well accepted substitute, e.g., benzyl alcohol. Phenolphthalein was used as a model compound for organic contaminants such as polychlorinated dibenzodioxins (PCDDs) or bisphenol A (BPA). Fast regeneration of nanomagnets (compared to similar cyclodextrin-based systems) under mild conditions resulted in 16 repetitive cycles (adsorption/desorption) at full efficiency. The high removal and regeneration efficiency was examined by UV-vis measurements at chemical equilibrium conditions and under rapid cycling (5 min). Experiments at ultralow concentrations (160 ppb) underline the high potential of cyclodextrin modified nanomagnets as a fast, recyclable extraction method for organic contaminants in large water streams or as an enrichment tool for analytics.

Aerosol nanotechnology has rapidly evolved in the past years. This fascinating technology has resulted in the development of functional nanomaterials providing novel solutions in industrial applications. The extensive research on the physical understanding of gas phase processes has strongly contributed to the present industrial use of single and mixed oxides and the design of industrial aerosol reactors. Recent advances have shown that chemical aerosol engineering can be established on the interface between classical aerosol science and chemical engineering. The emerging new methods give access to a much broader class of functional materials including salt and metal nanoparticles. The latter implies that aerosol production units can now be considered as chemical reactors. The incorporation of thermodynamic considerations and chemical kinetics in the modelling of gas phase processes will further boost the development of aerosol engineering and will provide deeper understanding of the fundamentals of particle formation mechanisms. This will ultimately enable access to new multicomponent materials with various structures or morphologies and the development of more sustainable, energy efficient gas phase processes.

Flame spray pyrolysis (FSP) was utilized to fabricate palladium in silica nanocomposites (core-shell structure) in a single step. The nanometer scale transformation of these materials to Pd dispersed on an amorphous silica matrix (oxide-supported noble metal) at elevated temperatures (500-900 degrees C) was investigated using transmission electron microscopy and CO chemisorption. A spatially resolved (1-D) population balance model was utilized to describe the transformation by diffusion and aggregation processes. The model describes the influence of temperature, matrix viscosity, particle sizes, and concentrations and enables a prediction of the morphology (core-shell vs supported) of metal/silica nanocomposites processed at elevated temperatures. The data are discussed in terms of aerosol formation mechanisms (consecutive vs simultaneous coagulation) and compared to literature data on the high-temperature formation of nanocomposites. To illustrate the validity of the physical model and mechanisms, a network modifier (CaO) was added to the glassy matrix of the composite (Pd/CaO/SiO2), decreasing the matrix viscosity and resulting in the predicted morphology.

The present work investigates the potential use of metal-based carbon-coated magnetic nanoparticles for the efficient extraction of gold and platinum at high dilution (milligram to gram per ton ppb to ppm) at a mini-pilot level (0.1 m(3)). Acid-stable nanomagnets were first prepared by reducing flame synthesis and consisted of graphene-like carbon-coated cobalt metal nanoparticles (20-40 nm diameter) with an onion-like core/shell structure. The use of a metal core affords high saturation magnetization, while carbon shells are highly resistant to most chemical conditions. The nanomagnet surface was further coated with a standard noble metal extraction resin-like polymer (thiourea groups on a poly(ethylene imine)). Extraction runs were tested both at laboratory scale (0.1-10 L; Au and Pt removal > 95%; down to the milligram per ton level) and in a tank model (vertical tank section, 4 m height, 0.1 m(3) volume, Pt removal > 80% at 50 mg/ton of acid water). Delivery of freshly dispersed nanomagnet dispersions onto the top layer of the tank model's water zone (top 0.1 m) resulted in agglomeration and subsequent sedimentation through the tank model's water column while simultaneously adsorbing platinum with an efficiency of 90%. At the bottom of the tank model, the nanomagnets could be efficiently collected through sweeping the tank model's bottom surface with an array of permanent magnets. This process circumvents moving a tank's liquid volume (energy costs for pumping) through conventionally used and time-consuming fixed-bed assemblies. In contrast, the presented process only moves a very small mass (<1 mass %) of the noble metal-containing volume and may therefore become an energy-efficient alternative to adsorption onto fixed beds or usually applied chromatography-type processes.

The exposure of cell cultures to aerosols or nanoparticle dispersions offers an experimental access to study particle related toxicology and nanomedicine. The present article discusses the concept of dose for soluble or persistent particles with optional stabilizing shells and/or chemical or catalytic activity. We further investigate the minimal set of experiments and controls required for hands-on experiments feasible in well-equipped standard research laboratories. This article recommends strategies to implement nanotoxicity experiments into laboratory routine and shall assist aerosol scientists to engage into biological/medical questions. The most prominent differences between molecule- and particle-related health effects are additionally discussed as physical (concentration-dependent mobility due to agglomeration) and chemical effects (catalytic/chemically active surfaces, Trojan horse type toxin transport through membranes, long-term risks). In the last part we describe the implementation of these concepts within the Swiss Recommendations for Industrial Use of Nanoparticles as a first attempt to provide a regulatory framework for the risk assessment of nanoproducts.

The combination of immiscible metals has traditionally escaped preparation as such metal's largely different surface energies lead to nonwetting and separation of the two metals during synthesis. The simultaneous preparation of two metals as nanoparticles in a gas phase process can result in the formation of random agglomerates if rapidly cooled. Compaction and subsequent sintering then allows combining otherwise immiscible metals in it bottom-up approach to form metal/metal nanocomposites. In this work, bismuth and cobalt were chosen as model materials which cannot be alloyed by traditional metallurgy due to their large difference in physical properties such as hardness and melting point. Combining bismuth with cobalt (continuous phase) at the nanometer scale resulted in a metal/metal nanocomposite. This class of materials is formally an extension of the current oxide/metal nanocomposites which we conceptually demonstrated through the combination of two distinctly different properties of the composite's base metals: The bismuth/cobalt nanocomposite displayed a low friction Value of around 0.2 (a property or soft bismuth) while maintaining a high hardness (a property of nanocrystalline cobalt). These previously difficult to access properties are attractive For the development of lead-free bearings in energy efficient engines.

In order to investigate the sintering evolution of core/shell metal/glass nanoparticles, two model compounds were synthesized and their structural evolution was investigated. Silica glass coated Ag nanoparticles were synthesized by flame spray pyrolysis, pressed into bulk pills and subsequently sintered at different temperatures finally resulting in composites with a highly conductive percolated silver network embedded in a ceramic matrix. By synthesizing two glass silver nanocomposites differing in their glass composition and corresponding glass transition temperature, the direct influence of the glass matrix on the percolation network formation and the conductive properties could be investigated. The analysis of the two systems by X-ray diffraction, scanning and transmission electron microscopy and by energy-dispersive X-ray detection clearly showed that the formation of the percolated network is initiated at the glass transition temperature of the matrix.

Metal nanoparticles have distinctly different chemical and physical properties than currently investigated oxides. Since pure metallic nanoparticles are igniting at air, carbon stabilized copper nanoparticles were used as representative material for this class. Using copper as a representative example, we compare the cytotoxicity of copper metal nanoparticles stabilized by a carbon layer to copper oxide nanoparticles using two different cell lines. Keeping the copper exposure dose constant, the two forms of copper showed a distinctly different response. Whilst copper oxide had already been reported to be highly cytotoxic, carbon-coated copper nanoparticles were much less cytotoxic and more tolerated. Measuring the two material's intra- and extracellular solubility in model buffers explained this difference on the basis of altered copper release when supplying copper metal or the corresponding oxide particles to the cells. Control experiments using pure carbon nanoparticles were used to exclude significant surface effects. Reference experiments with ionic copper solutions confirmed a similar response of cultures if exposed to copper oxide nanoparticles or ionic copper. These observations are in line with a Trojan horse-type mechanism and illustrate the dominating influence of physico-chemical parameters on the cytotoxicity of a given metal.

Attachment of EDTA-like chelators to carbon coated metal nanomagnets results in a magnetic reagent for the rapid removal of heavy metals from solutions or contaminated water by three orders of magnitude to concentrations as low as microg L(-1).

The industrial application of paints today involves the handling of millions Of tons of pigment dispersions. Shear and mechanical stress during pumping, storage, or processing significantly affect color and shelf life. Currently, mainly empirical test series and pilot-scale process models are used to assess the stability Of Such dispersions and provide marginal guidance when developing or testing large-scale paint applications. Scaling the stability against shear stress is particularly important for water-based metal pigment dispersions where damage to the pigment flakes causes their deterioration. The present work investigates the scaling of shear stress from the production line (> 1000 tons/yr) to laboratory scale (100-g scale). We analytically show why the integrated shear stress on a specific dispersion can be deconvoluted into a series of individual shear stress contributions. These individual contributions can be accurately reproduced in the laboratory using a Couette-type shearing setup similar to a classical rheometer. As a representative example, a stable and a shear-sensitive paint from an automotive production line was sampled over 4 months of production. The evolving deterioration, color changes, and dispersion instability could be accurately reproduced using the scaling method outlined here.

The elusive chemistry of gold has made refining from ores a difficult task and often involves handling of large volumes of water at low pH values with associated high environmental burden. As a result, the broader use of gold in environmental catalysis, organic synthesis and in electronics is still limited in spite of its most attractive chemistry. Present gold extraction suffers from metal loss in the form of gold adsorbed on active carbon particles that are washed out of the extraction process. Here, we investigate the use of magnetic carbon in the form of carbon-coated metal nanomagnets for ionic gold recovery. In contrast to acid-labile iron oxide nanoparticles, the carbon/cobalt nanomagnets resisted dissolution in acidic refining/recycling waters. Repetitive extraction runs demonstrated the possibility to recycle the magnetic reagent. A series of dilution studies showed a high affinity of the ionic gold to the carbon surfaces of the nanomagnets which enabled gold extraction down to the part per billion level (microgram per litre). Detailed investigations on the morphology of the Au-loaded nanomagnets after use suggest a mechanism based on the selective reduction of ionic gold on the C/Co surface and transfer of cobalt through the carbon shell. The resulting irreversible deposition of metallic gold correlated with the release of oxidized (ionic) cobalt into the aqueous phase.

The exceptional electronic and optical properties of graphene have caught the attention of physicists and materials scientists since the first effective preparation of this two-dimensional form of carbon by Novoselov et al. in 2004. Much effort is currently being invested in the large-scale production of graphene surfaces 3] and in the investigation of its peculiar quantum effects. Graphene is viewed as a potential alternative to silicon as a material for the construction of nanoscale electronic circuits. The use of graphene in this way would require control of its electronic band structure and the withdrawal or injection of electron density to adjust or tilt the Fermi level in a graphene sheet. Such pattern-resolved control of the energy level is the two-dimensional equivalent of n or p doping in classical semiconductors. In contrast to silicon, graphene has a continuous band structure with zero band gap. Thus, single adsorbed molecules modify the band structure and affect the electronic properties of graphene significantly, 10] which makes graphene difficult to handle. Device fabrication requires reliable and permanent control over the different electronic states and the Fermi energy of an air-stable material. The adsorption of organic molecules can result in p-type doping through a sandwichlike p-stacking arrangement on graphene. The injection of electrons is possible through n-type doping with potassium; however, such materials are highly sensitive to air and water. In the search for a robust and highly precise doping method, we investigated well-established protocols from organic radical chemistry to attach an air-stable dopant covalently and thus permanently alter the electronic structure of graphene sheets. The relative surface charge levels were measured by Kelvin force microscopy (KFM). The application of the linear free-enthalpy relationship for substituted aromatic compounds enabled the direct prediction of the charge-withdrawing or charge-injecting effect of graphene modification. We therefore concluded that this approach should enable direct control of the surface potential, Y, of modified graphene. Furthermore, the Hammett concept enabled a precise correlation between the observed change in the surface potential, DY, and the structure of the covalently bonded reagents. This concept was confirmed experimentally by using strongly electron withdrawing (p-nitrophenyl, s = 0.78) and electron donating substituents (p-methoxyphenyl, s = 0.23). For our experiments, we used the top graphene layer of highly ordered pyrolytic graphite (HOPG) as a model material. From a physical point of view, this model is not representative for detailed investigations on band structure or electronic effects. However, from a chemical point of view, the reactivity of the graphene stacks of HOPG is comparable to that of single-walled carbon nanotubes, which can be considered as rolls of graphene. For additional experimental validation, we also carried out the graphene modifications described herein on carbon-coated nanoparticles (two or three layers of graphene on copper). Detailed structural evidence was then provided by diffuse reflectance FTIR to characterize the products and confirm the direct covalent attachment of the modifying groups to the top graphene layer. This functionalization approach extends p and n doping based on adsorbed molecules or ions to make it a systematic and robust method with which molecular electronics elements can be attached perpendicular to the graphene plane in a third dimension. The experimental approach to covalent graphene modification is shown in Figure 1. The model material (top layer of a monocrystalline graphene stack) was first patterned by lithography, so that a plain (unfunctionalized) graphene surface would be preserved below the photoresist. The unmasked areas were functionalized by exposure to highly diluted diazonium reagents (see the Supporting Information). After removal of the photoresist, the graphene surface was investigated by scanning electron microscopy (SEM) and Kelvin force microscopy (KFM) in tapping mode to image the relative surface-potential levels of modified and native areas of the graphene surface. The chemical derivatization depends [*] MSc Chem. Eng. F. M. Koehler, MSc Mat. Sci. N. A. Luechinger, Dipl.-Chem.-Ing. E. K. Athanassiou, Dr. R. N. Grass, Prof. Dr. W. J. Stark Institute for Chemical and Bioengineering Department of Chemistry and Applied Biosciences, ETH Zurich Wolfgang-Pauli-Strasse 10, 8093 Zurich (Switzerland) Fax: (+ 41)44-633-1083 E-mail: wendelin.stark@chem.ethz.ch Homepage: http://www.fml.ethz.ch

Nach der Ära des Siliciums: Die Verbindung zwischen Radikalchemie unter Standardbedingungen und Reinraumlithographie kann die elektronische Struktur von Graphenlagen durch kovalente chemische Funktionalisierung permanent verändern. Die Potentialveränderung folgt der Hammett-Beziehung. Diese einfache Methode ist ein vielversprechender Ansatz für die graphenbasierte Elektronik. 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.

Metallic copper nanoparticles were synthesized by a bottom-up approach, and in situ coated with protective shells of graphene in order to get a metal nanopowder of high air stability and chemical inertness. Using an amphiphilic surfactant, a water-based copper nanocolloid could be prepared and successfully printed onto a polymer substrate by conventional ink-jet printing using household printers. The dried printed patterns exhibited strong metallic gloss and an electrical conductivity of > 1 S cm(-1) without the need for a sintering or densification step. This conductivity currently limits use in electronics to low current application or shielding and decorative effects. The high stability of graphene-coated copper nanoparticles makes them economically a most attractive alternative to silver or gold nanocolloids, and will strongly facilitate the industrial use of metal nanocolloids in consumer goods.

Eine Synthese – ein Tag! Kohlenstoffbeschichtete Metallnanopartikel können mit Diazoniumverbindungen kovalent funktionalisiert werden. Diese kolloidalen Reagentien ermöglichen die magnetische Funktionalisierung von Ausgangsstoffen oder Zwischenstufen, sodass die gewünschten Produkte innerhalb von Sekunden abgetrennt werden können.

The preparation of carbon-coated copper nanoparticles with different carbon layers resulted in materials with a highly sensitive pressure and temperature dependent conductivity. The core/shell geometry of these carbon/metal composites afforded two distinctly different electrical behaviors depending on the carbon layer properties. Graphene layers with a predominant sp2 character showed an ill-defined bandgap structure as evidenced by UV–vis diffuse reflectance spectroscopy. The resulting composites were weak conductors with low sensitivity. Use of predominately insulating carbon layers with a well-defined bandgap of above 1.9eV resulted in composites with a material constant β of over 4700K which is comparable to currently used commercial spinels. A theoretical analysis and detailed material characterization by Raman spectroscopy, X-ray diffraction, 13C NMR spectroscopy and thermoanalysis suggested a tunneling based conduction mechanism in these core/shell materials. This interpretation was supported by a good correlation between experimental data and the estimated effects arising from the theoretical analysis of the tunneling effects.