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Journal of Nanoparticle Research, 8 (1), ISSN:1388-0764, ISSN:1572-896X

Quantitative studies on the uptake of nanoparticles into biological systems should consider simultaneous agglomeration, sedimentation, and diffusion at physiologically relevant concentrations to assess the corresponding risks of nanomaterials to human health. In this paper, the transport and uptake of industrially important cerium oxide nanoparticles, into human lung fibroblasts is measured in vitro after exposing thoroughly characterized particle suspensions to a fibroblast cell culture for particles of four separate size fractions and concentrations ranging from 100 ng g(-1) to 100 microg g(-1) of fluid (100 ppb to 100 ppm). The unexpected findings at such low but physiologically relevant concentrations reveal a strong dependence of the amount of incorporated ceria on particle size, while nanoparticle number density or total particle surface area are of minor importance. These findings can be explained on the basis of a purely physical model. The rapid formation of agglomerates in the liquid is strongly favored for small particles due to a high number density while larger ones stay mainly unagglomerated. Diffusion (size fraction 25-50 nm) or sedimentation (size fraction 250-500 nm) limits the transport of nanoparticles to the fibroblast cells. The biological uptake processes on the surface of the cell are faster than the physical transport to the cell at such low concentrations. Comparison of the colloid stability of a series of oxide nanoparticles reveals that untreated oxide suspensions rapidly agglomerate in biological fluids and allows the conclusion thatthe presented transport and uptake kinetics at low concentrations may be extended to other industrially relevant materials.

Journal of Materials Research, 18 (1), ISSN:0884-2914, ISSN:2044-5326

International Journal of Materials Research, 17 (6), ISSN:1862-5282, ISSN:2195-8556

Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.

Removal of volatile organic compounds (VOC) and indoor air quality regulation through adsorbers required exchange or maintenance of active materials. In this work, we combine well known VOC adsorbers with oxidation catalysts as intimate particulate mixtures. We demonstrate how typical VOC can subsequently adsorb on such mixed material fixed beds (usually days to weeks; the common state of the system, adsorption phase) using small organic compounds (diethyl ether, triethylamine), monoterpenes such as linalool and limonene, and hexanoic acid. Occasional regeneration runs through heat up of the fixed bed results in simultaneous desorption and oxidation of the accumulated VOC, thus regenerating full adsorption capacity for a next adsorption phase. We investigated both small pore zeolites (H-ZSM-5) and larger pore zeolites (13X) and found a distinct interplay between the pore size and the type of VOC. Thermogravimetry coupled with mass spectroscopy was used to quantitatively study the effects of mixing composition and temperature on adsorber performance and regeneration. The here investigated bi-functional systems combine very low maintenance costs and materials requirement with low air flow and exchange costs, thus suggesting mixed (two-functional) bed adsorbers with catalytic function as sustainable alternatives to currently used single use systems based on granulated zeolites or activated carbon. In this work we show the ability of zeolite/cerium oxide physical mixtures to adsorb and capture different classes of VOC at room temperature and release them for oxidation at higher temperatures in a regenerative and sustainable process.

Magnetic hybrid materials have been synthesized as recyclable catalysts for alkene hydrogenation. The materials consist of magnetic nanobeads functionalized with imidazolium-based ionic liquids and optional polymer shells. Palladium nanoparticles (NPs) were synthesized on the surface of these supports by two different methods and evaluated as catalysts for alkene hydrogenation. Deposition of palladium(0) onto the magnetic nanobeads by microwave decomposition of Pd2(dba)3·CHCl3 leads to more efficient catalysts than the reduction of a Pd(II) precursor. Reactivity, recycling ability and ease of separation of the catalysts are compared. A hybrid material without polymer shells and a quite flexible ionic liquid was identified as the most promising for stabilizing Pd NPs resulting in a catalyst that shows high activity (TOF up to 330 h−1), good recycling ability, and minor metal leaching into the product. Notably, the activity of this catalyst increases with an enhanced Pd loading, contrasting related systems for which a decrease of activity is observed due to agglomeration. Therefore, this recyclable, high-capacity system is especially attractive for large-scale applications, requiring just a minimal amount of supporting material for the recycling of expensive Pd that is readily achieved by magnetic decantation.

Spraying cerium and zirconium precursors dissolved in carboxylic acids into a methane-oxygen flame resulted in well-structured nanocrystals of ceria-zirconia mixed oxides with high temperature stability and surface area.

Magnetic nanoparticle dispersions are traditionally made from superparamagnetic materials since the absence of magnetic particle–particle attraction under normal conditions (no external field) easily allows preparation of stable dispersions. For inductive heating in medicinal chemistry or material science, however, the much higher magnetization of ferromagnetic metals over the currently used oxides is attractive. Traditional attempts to prepare stable dispersions of ferromagnetic particles, however, failed since the strong magnetic particle–particle attraction usually overcomes repulsive effects from surfactants or steric stabilizers (typically polymers). In the present work, we demonstrate how the direct, covalent attachment of highly charged polymers can circumvent stabilizer detachment and loss, and permits preparation of stable dispersions of ferromagnetic particles. More specifically, carbon-coated metal nanoparticles were covalently functionalized with positively charged polymer brushes via surface initiated atom transfer radical polymerization (SI-ATRP). Particle size distributions with an average diameter of 24 nm provided a ferromagnetic liquid with unprecedented stability in water over several months. The stability was discussed by comparison of the potentials of non-functionalized and modified nanomagnets within a modified Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Measurements for inductive heating at different frequencies and various field strengths showed an average specific absorption rate of 360 W g−1. Altogether, this suggests that efficiently stabilized dispersions of ferromagnetic nanoparticles could be an alternative to superparamagnetic iron oxide particles in a number of applications.

A mussel-inspired synthetic adhesive based on dopamine containing methacrylate copolymers was developed to bond polymers to metal surfaces at an adhesion strength of up to 20 MPa for bulk samples.

Lanthanum oxide nanoparticles were utilized to scavenge phosphate from microbial growth media for the use of targeted nutrient starvation as an antimicrobial strategy. Only in phosphate poor environments a toxic effect was observed. The effect was shown on Escherichia coli, Staphylococcus carnosus, Penicillium roqueforti, and Chlorella vulgaris.

This work aims at the investigation and optimization of a hybrid start-up process for a self-sustained reactor for n-butane to syngas conversion in intermediate temperature, micro-solid oxide fuel cell (micro-SOFC) power plants. The catalytic reaction is carried out in the presence of Rh-doped Ce0.5Zr0.5O2nanoparticles in a disk-shaped reactor. For the start-up, a resistance heater is embedded inside the catalytic bed and is activated until the exothermic oxidative reaction is initiated. The self-sustained temperature and reforming performance are demonstrated to be highly dependent on the fuel to oxygen (C/O) ratio and the catalytic activity at different space times. It is shown that a C/O ratio of 0.8 is a very good choice in terms of achieved steady-state temperature, syngas selectivity and start-up time. At a reactor inlet temperature of 809 °C for a C/O ratio of 0.8 and a space time as low as 8 ms, a syngas selectivity of 69.6% and a temperature of 529 °C at the simulated micro-SOFC membrane are demonstrated. After only 15 s from ignition, a temperature of 600 °C at the reactor inlet is reached. The hybrid start-up process is optimized with respect to a specific setup as an example, but is of general nature and utility to similar systems.

We synthesized highly ferromagnetic, thermoresponsive nanomagnets with a graphene coated cobalt metal core to which amphiphilic N-isopropylacrylamide polymer branches were covalently attached. This novel hybrid material could be further end-group modified with a Pd–phosphine complex to catalyze Suzuki–Miyaura cross-coupling reactions. The heterogenized metal-complex could act as a ‘self-separating’ catalyst. Thermally triggered switching of poly-NIPAM coated C/Co-nanoparticles in typical biphasic water/toluene reaction systems allowed controlled shift from the organic to water phase and back. This enabled catalysis in the organic layer (reaction temperature) and return into the aqueous layer once the reaction mixture was cooled (ambient temperature; magnetic removal and reuse of the catalyst). Thus, the product phase was isolated via simple extraction/decantation. Moreover, the supported catalyst was recycled from the aqueous phase by taking advantage of the magnetic cores and reused over ten times.

Silica nanowire arrays were grown directly onto plain glass substrates by scalable flame spray pyrolysis of organometallic solutions (hexamethyldisiloxane or tetraethyl orthosilicate). The silicon dioxide films consisted of a network of interwoven nanowires from a few to several hundred nanometres long (depending on the process conditions) and about 20 nm in diameter, as determined by scanning electron microscopy. These films were formed rapidly (within 10-20 s) at high growth rates (ca 11-30 nm s(-1)) by chemical vapour deposition (surface growth) at ambient conditions on the glass substrate as determined by thermophoretic sampling of the flame aerosol and microscopy. In contrast, on high purity quartz nearly no nanowires were grown while on steel substrates porous SiO(2) films were formed. Functionalization with perfluorooctyl triethoxysilane converted the nanowire surface from super-hydrophilic to hydrophobic. Additionally, their hermetic coating by thin carbon layers was demonstrated also revealing their potential as substrates for synthesis of other functional 1D composite structures. This approach is a significant step towards large scale synthesis of SiO(2) nanowires facilitating their utilization in several applications.

Metal sulfide nanoparticles have attracted considerable interest because of their unique semiconducting and electronic properties. In order to prepare these fascinating materials at an industrial scale, however, solvent-free, dry processes would be most advantageous. In the present work, we demonstrate how traditional oxide nanoparticle synthesis in flames can be extended to sulfides if we apply a careful control on flame gas composition and sulfur content. The ultra-fast (1 ms) gas phase kinetics at elevated temperatures allow direct sulfidization of metals in flames ([Formula: see text]). As a representative example, we prepared air-stable Mn(2 + ) doped zinc sulfide nanoparticles. Post-sintering of the initially polycrystalline nanopowder resulted in a material of high crystallinity and improved photoluminescence. An analysis of the thermodynamics, gas composition, and kinetics in these reducing flames indicates that the here-presented extension of flame synthesis provides access to a broad range of metal sulfide nanoparticles and offers an alternative to non-oxide phosphor preparation.

Direct and rapid removal of pathogens or noxious metabolites from a patient is the most straightforward cure imaginable. Dialysis and plasma filtration/exchange are the current broadly applicable methods to perform a direct removal of disease-causing factors from a patient. We describe the use of stable nanomagnets to rapidly and selectively remove heavy metal ions, overdosed steroid drugs and proteins from human blood. This nanomagnet-based purification method avoids fouling of filter membranes and benefits from a high external surface area, and a correspondingly fast diffusion.

A new family of elastomeric nanocomposites has been developed from a soft elastomer poly(glycerol sebacate, PGS) and nanoparticles of Bioglass®. The new nanocomposites have been characterised in terms of materials science and evaluated for their potential clinical applications as cell delivery vehicles and cardiac support devices in the heart patch strategy. The addition of alkaline Bioglass® effectively counteracts the acidity caused by the degradation of PGS without severely compromising the compliance of PGS. As a result, the newly developed PGS–nanoBioglass (

The rapidly growing applications of nanotechnology require a detailed understanding of benefits and risks, particularly in toxicology. The present study reviews the physical and chemical differences between particles and molecules when interacting with living organisms. In contrast to classical chemicals, the mobility of nanoparticles is governed by agglomeration, a clustering process that changes the characteristic size of the nanomaterials during exposure, toxicity tests or in the environment. The current status of nanotoxicology highlights non-classical toxic interactions through catalytic processes inside living cells and the enhanced heavy metal transport into the cytosol through the 'Trojan horse mechanism'. The safety of nanoparticles in consumer goods is proposed to be rendered inherently safer by substituting the currently used persistent oxides through biodegradable materials.

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.

This study had two aims: (i) to determine the effects of calcination temperature on the hydraulic reactivity of three nanosized X-ray amorphous tricalcium phosphate (ATCP) powders, and (ii) to try to bring a better understanding of the poor reactivity of α-tricalcium phosphate (α-TCP) nanoparticles obtained by calcining ATCP powders. For those purposes, five calcination temperatures were selected in the range of 500 to 800 °C. Calcination led to the formation of powders consisting of ATCP (500 °C), α-TCP (600, 650 and 700 °C) and β-tricalcium phosphate (β-TCP; 700 and 800 °C). The powder reactivity was assessed by mixing 0.2 g of powder and 1 mL Na2HPO4 0.2 M solution in an isothermal calorimeter. The total reaction time was a function of the calcination temperature: from a few minutes for ATCP powders and ATCP powder calcined at 500 °C, it increased to several hours for ATCP powder calcined at 600, 650 and 700 °C. Interestingly, this change of reaction time was mostly due to an increase of the so-called induction time, i.e. time to start the reaction. It increased from a few seconds to a few hours. Strikingly, the induction time and the total reaction time were reduced by an increase of the calcination temperature from 650 to 700 °C. The results were attributed to the formation of a defect-free surface upon calcination and the concomitant difficulty in creating surface defects to allow dissolution and hence reaction.

Bone regeneration in infected tissue or areas with high bacteria concentrations such as the oral cavity requires combining disinfection with biomaterial properties. Classical antibiotics typically provide excellent short term protection against re-infection of a defect but are typically washed out of an operation site within days. The present work investigates the use of silver on amorphous tricalcium phosphate (TCP) nanoparticles for electrospun, highly porous poly(lactide-co-glyclolide) (PLGA) fibrous composites. In vitro bioactivity tests of the wool-like composite PLGA/Ag-TCP (80 : 20) containing 0.5 wt% silver showed rapid hydroxyapatite deposition on the nanocomposite within 2 days. Antibacterial tests using E. coli demonstrated a strongly prolonged antibacterial effect of the scaffolds containing finely dispersed silver on TCP if compared to current clinically used methods based on soaking the scaffolds with a tetracycline solution prior to implantation.

Building construction takes time, in part because the binding process of cement is based on the slow re-crystallization and precipitation of calcium silicate species. Since the material's reactivity is surface area limited, a reduction in particle size of Portland cements has been used to prepare faster binding formulations. The present work investigates a new and direct, one-step preparation of calcium silicate-based nanoparticles of a typical Portland cement composition by flame spray synthesis. Isothermal calorimetry revealed that the hardening of this new nano-cement corroborated a more than tenfold increase of initial reactivity with different reaction kinetics if compared to conventionally prepared cements. At present, the unfavourably high porosity of nano-cements, however, underlines the need for additional improvements of chemical composition and formulation to make these highly reactive materials applicable to modern construction work, where load-bearing strength is of importance.

The application of an external magnetic field on a metallic cobalt nanoparticle loaded exhaust gas stream produced by reducing flame synthesis resulted in the formation of self-aligned metallic cobalt nanowires of 20?50?nm diameter. This template free, continuous and rapid production method afforded nanowires with an aspect ratio of over 1000 (length/diameter) at a production rate of over 30?g?h?1. At high magnetic fields the nanowires formed bundles with distinctive parallel orientation. In the absence of a directing magnetic field, thermophoresis promoted an irregular growth and resulted in highly branched and porous nanomeshes on cooled, stainless steel collectors. The high production rates of this template free preparation method suggest application of the process for large scale manufacturing of magnetic nanomeshes for filtration or nanowires for magnetic storage and anisotropic functional materials.

Bulk nanocrystalline cobalt was prepared from reducing flame-spray-derived cobalt nanopowders exclusively in the face-centred cubic (fcc) modification. Compacts of approximately 60% density were obtained from uniaxial compression at room temperature and showed a strong resistance towards grain growth upon subsequent sintering to 90% relative density. The nanocrystalline structure remained stable well above 1000 degrees C and resulted in a pore-rich metal with about 10(15) nanovoids cm(-3). These sintered compacts displayed an up to three times higher bulk hardness if compared to conventional cobalt and local ductility as evidenced from scanning electron microscopy and nanoindentation. The strong grain-growth resistance and consequent increase in material hardness are discussed in respect of the presence of nanovoids, twin boundaries and material contamination.

Metal based composites account for a large part of technically used alloys. Their favorable thermal and mechanical properties have been repeatedly suggested to strongly profit from the possible application of nanosized metals and ceramics as starting materials. The present work therefore explores the simultaneous production of both constituents by controlling the gas composition and reduction potential in an oxygen deficient flame spray process and choosing appropriate metal/ceramic compounds. More specifically, metallic bismuth and ceria (CeO2) nanoparticles were prepared in a single process step at a production rate of >30 g h−1 and resulted in a highly homogeneous mixture of oxide and metal particles. After characterization by X-ray diffraction, electron microscopy and energy dispersive X-ray spectroscopy, the powder was compacted at room temperature to rods of 1.2 cm diameter. These bulk samples with ceramic loadings as high as 35 vol% combined metallic (high gloss, electrical conductivity of above 100 S m−1) and ceramic properties such as a Vickers hardness comparable to steel (>100 HV), while pure bismuth can be indented with a finger nail. Thermodynamic calculations illustrate how the presented reducing flame spray based process can simultaneously manufacture the metal and ceramic phase of these nano-composites. This direct route to metal/oxide nano-composites avoids the currently unsolved problem of homogeneously mixing non-wetting nano-sized ceramic and metal constituents.

The development of injectable bone cements requires a detailed understanding of the reactivity of tricalcium phosphate (TCP)-based cements. The present study systematically investigates a broad set of materials with varying particle size, crystal phase and degree of crystallinity prepared by solid state reaction or flame spray synthesis and sintering. Amorphous TCP nanoparticles of 13, 19 and 40 nm particle diameter were highly reactive and set to calcium deficient hydroxyapatite (CDHA) within minutes. A pronounced increase in reactivity was observed for smaller nanoparticles while the total energy release during setting was constant. The use of α- or β-TCP as starting material confirmed the importance of phase composition in determining cement reactivity. These crystalline phases were much less reactive or even inactive and showed a pronounced influence of the preparation method. The experimentally measured kinetics was used to formulate a physical model of the cement setting reaction based on the shrinking core model. This detailed theoretical understanding of the cement setting processes can now assist the development of injectable cements for minimally invasive orthopedic surgery.

Ce 0.9 Gd 0.1 O 1.95 (CGO10) and in situ cobalt oxide-doped CGO10 were prepared by pilot-scale flame spray synthesis, yielding powders with an average particle size of 40 nm. Cobalt oxide was shown to be a very effective sintering aid for CGO10 and lowered the maximum sintering temperature from 1450° to about 1200°C. Sintering studies revealed that in situ cobalt oxide-doped CGO10 exhibited a temperature of maximum shrinkage rate of 880°C for a dopant concentration of 1 mol% CoO 1-x , whereas for conventionally cobalt oxide-doped CGO10, this temperature was 914°C. This decrease is believed to be a result of a more homogeneous dopant distribution of the in situ cobalt oxide-doped CGO nanopowders as compared with the powders in which the doping was introduced as nitrates.

The preparation of amorphous nanopowders by flame synthesis opens access to common soda-lime, metal-doped glasses or bioglasses in the range of 20-80 nm and offers an alternative to conventional wet-phase preparation, solid state reactions or melting.

Calcium carbonate nanoparticles of 20-50 nm size were obtained from a flame spray process where combustion of specific calcium-containing precursors results in amorphous or crystalline calcium carbonate particles depending on the spray flow conditions.

Non-oxidic salts such as NaCl, CaF2, SrF2 and BaF2 were synthesised using a flame spray method; optional doping of such fluorides with rare earth elements suggests possible applications in optics.

Silica- and alumina-doped nanocrystalline ceria/zirconia (Ce0.5Zr0.5O2) were prepared in one step by flame-spray pyrolysis. Structural and textural properties were characterized using high-resolution electron microscopy, nitrogen adsorption and X-ray diffraction. Oxygen exchange capacity was studied by pulse thermal analysis using H2 as reducing agent. Adding silica (up to 20 wt%) or alumina (up to 16 wt%) altered the particle morphology from polyhedral to spherical particles. In doped ceria/zirconia, the oxygen exchange capacity (OEC) was affected by the silica content but very little by the alumina content. The highest OEC (450 mmol O2 kg−1) was measured for ceria/zirconia doped with 3 wt% silica, whereas for flame-made ceria/zirconia (360 mmol O2 kg−1) and corresponding precipitated silica- or alumina-doped materials the OEC was considerably lower. For high dopant contents (20 wt% silica) an amorphous layer was formed on top of a crystalline core. This layer acted as a diffusion barrier, so that the OEC dropped to about 76 mmol O2 kg−1.

In search of highly active nanoparticles for catalytic applications, flame aerosol technology turns out to be a promising method for its capacity to consistently produce highly pure nanoparticles. Starting with the production of simple oxides such as silica and titania in the forties, flame aerosol technology now facilitates production of nanoparticles in megaton quantities. Fundamental research on particle formation in the gas phase and the influence of process parameters and reactor design on final product properties have advanced the field to a stage where multicomponent materials can be produced. Flame production of vanadia/titania catalysts for NOx removal from exhaust gases by selective reduction by ammonia affords enhanced activity at low temperature when compared to corresponding materials prepared by wet-chemical methods. Furthermore, flame synthesis of titania/silica yields catalysts for the epoxidation of olefins with high accessibility of the active titanium sites and improved selectivity. Spectroscopic studies revealed that the same active sites as in the wet-phase derived catalysts are produced by flame synthesis but at a higher content. The high temperature during the preparation favors the formation of well-defined species on a hydrophobic surface. The flame synthesis of heterogeneous catalysts is brought from laboratory scale to pilot scale production at up to 500 g/h to make the novel materials suitable for industrial performance tests.

A process for close control of primary particle size, morphology and crystallinity of flame-made nanoparticles is presented. According to this, freshly made titania aerosol nanoparticles are rapidly quenched in a critical flow nozzle, essentially freezing particle growth at desired levels. The nanoparticles are produced in a methane/oxygen diffusion flame reactor by oxidation of titanium-tetra-isopropoxide (TTIP). Precise control of the average primary particle size, reduced agglomeration and phase composition is achieved by positioning of the quenching nozzle above the burner and controlling gas and precursor flow rates.