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Camenzind A.,Institute of Process Engineering | Caseri W.R.,ETH Zurich | Pratsinis S.E.,Institute of Process Engineering
Nano Today | Year: 2010

Processing of flame-made nanoparticles into polymers is reviewed including surface modification and compounding. Recent advances in combustion and aerosol science enable scalable synthesis of such nanoparticles way beyond today's commercially available nanostructured carbon black and fumed silica. As a result, sophisticated filler nanoparticles with closely controlled size, morphology (aggregates or agglomerates) and composition (segregated or mixed phases or nanothin coatings onto core particles) become available motivating research for their surface functionalization and dispersion. Emphasis is placed on nanocomposite mechanics and optics. Quantitative relations for optimal nanocomposite structure are presented: from the particle-polymer interface to the formation of a percolation network. © 2010 Elsevier Ltd. All rights reserved.

Eggersdorfer M.L.,Institute of Process Engineering | Kadau D.,Institute of Building Materials | Herrmann H.J.,Institute of Building Materials | Pratsinis S.E.,Institute of Process Engineering
Langmuir | Year: 2011

Multiparticle sintering is encountered in almost all high temperature processes for material synthesis (titania, silica, and nickel) and energy generation (e.g., fly ash formation) resulting in aggregates of primary particles (hard-or sinter-bonded agglomerates). This mechanism of particle growth is investigated quantitatively by mass and energy balances during viscous sintering of amorphous aerosol materials (e.g., SiO2 and polymers) that typically have a distribution of sizes and complex morphology. This model is validated at limited cases of sintering between two (equally or unequally sized) particles, and chains of particles. The evolution of morphology, surface area and radii of gyration of multiparticle aggregates are elucidated for various sizes and initial fractal dimension. For each of these structures that had been generated by diffusion limited (DLA), cluster-cluster (DLCA), and ballistic particle-cluster agglomeration (BPCA) the surface area evolution is monitored and found to scale differently than that of the radius of gyration (moment of inertia). Expressions are proposed for the evolution of fractal dimension and the surface area of aggregates undergoing viscous sintering. These expressions are important in design of aerosol processes with population balance equations (PBE) and/or fluid dynamic simulations for material synthesis or minimization and even suppression of particle formation. © 2011 American Chemical Society.

Sotiriou G.A.,Institute of Process Engineering | Sannomiya T.,Biosensors | Teleki A.,Institute of Process Engineering | Krumeich F.,Institute of Process Engineering | And 2 more authors.
Advanced Functional Materials | Year: 2010

The plasmonic properties of noble metals facilitate their use for in vivo bio-applications such as targeted drug delivery and cancer cell therapy. Nanosilver is best suited for such applications as it has the lowest plasmonic losses among all such materials in the UV-visible spectrum. Its toxicity, however, can destroy surrounding healthy tissues and thus, hinders its safe use. Here, that toxicity against a model biological system (Escherichia coli) is "cured" or blocked by coating nanosilver hermetically with a about 2 nm thin SiO 2 layer in one-step by a scalable flame aerosol method followed by swirl injection of a silica precursor vapor (hexamethyldisiloxane) without reducing the plasmonic performance of the enclosed or encapsulated silver nanoparticles (20-40 nm in diameter as determined by X-ray diffraction and microscopy). This creates the opportunity to safely use powerful nanosilver for intracellular bio-applications. The label-free biosensing and surface bio-functionalization of these ready-to-use, non-toxic (benign) Ag nanoparticles is presented by measuring the adsorption of bovine serum albumin (BSA) in a model sensing experiment. Furthermore, the silica coating around nanosilver prevents its agglomeration or flocculation (as determined by thermal annealing, optical absorption spectroscopy and microscopy) and thus, enhances its biosensitivity, including bioimaging as determined by dark field illumination. Nanosilver particles are made by flame aerosol technology and in situ coated by a nanothin silica shell that blocks the toxicity of nanosilver against E. coli bacteria and prevents nanosilver flocculation in aqueous solutions, facilitating its use in bio-imaging and protein biosensing. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sotiriou G.A.,Institute of Process Engineering | Franco D.,Institute of Energy Technology | Poulikakos D.,Institute of Energy Technology | Ferrari A.,Institute of Energy Technology
ACS Nano | Year: 2012

Nanophosphors are light-emitting materials with stable optical properties that represent promising tools for bioimaging. The synthesis of nanophosphors, and thus the control of their surface properties, is, however, challenging. Here, flame aerosol technology is exploited to generate Tbactivated Y 2O 3 nanophosphors (∼25 nm) encapsulated in situ by a nanothin amorphous inert SiO 2 film. The nanocrystalline core exhibits a bright green luminescence following the Tb 3+ ion transitions, while the hermetic SiO 2-coating prevents any unspecific interference with cellular activities. The SiO 2-coated nanophosphors display minimal photobleaching upon imaging and can be easily functionalized through surface absorption of biological molecules. Therefore, they can be used as bionanoprobes for cell detection and for long-term monitoring of cellular activities. As an example, we report on the interaction between epidermal growth factor (EGF)-functionalized nanophosphors and mouse melanoma cells. The cellular uptake of the nanophosphors is visualized with confocal microscopy, and the specific activation of EGF receptors is revealed with biochemical techniques. Altogether, our results establish SiO 2-coated Tb-activated Y 2O 3 nanophosphors as superior imaging tools for biological applications. © 2012 American Chemical Society.

Sotiriou G.A.,Institute of Process Engineering | Schneider M.,Institute of Process Engineering | Pratsinis S.E.,Institute of Process Engineering
Journal of Physical Chemistry C | Year: 2012

Silica-coated and uncoated, Tb-doped (1-5 at % Tb) Y 2O 3 green nanophosphors were made, for the first time, in a single step by flame aerosol technology with controlled crystal phase (cubic and monoclinic) and morphology. The nanophosphors were characterized by X-ray diffraction, N 2 adsorption, high resolution electron microscopy, and photoluminescence spectroscopy. The monoclinic crystal structure of Y 2O 3:Tb 3+ nanophosphors favors the electric dipole 5D 4 → 7F 5 transition driving their green phosphorescence. The phosphorescence of the SiO 2-coated monoclinic Y 2O 3:Tb 3+ nanophosphors is lower than the uncoated ones. Upon annealing these nanophosphors, they were transformed from monoclinic to cubic and their phosphorescence was reduced. This further indicates the superior performance of the monoclinic crystal phase for the electric dipole transitions of Tb 3+ ions. © 2012 American Chemical Society.

Buesser B.,Institute of Process Engineering | Pratsinis S.E.,Institute of Process Engineering
Annual Review of Chemical and Biomolecular Engineering | Year: 2012

Aerosol synthesis of materials is a vibrant field of particle technology and chemical reaction engineering. Examples include the manufacture of carbon blacks, fumed SiO 2, pigmentary TiO 2, ZnO vulcanizing catalysts, filamentary Ni, and optical fibers, materials that impact transportation, construction, pharmaceuticals, energy, and communications. Parallel to this, development of novel, scalable aerosol processes has enabled synthesis of new functional nanomaterials (e.g., catalysts, biomaterials, electroceramics) and devices (e.g., gas sensors). This review provides an access point for engineers to the multiscale design of aerosol reactors for the synthesis of nanomaterials using continuum, mesoscale, molecular dynamics, and quantum mechanics models spanning 10 and 15 orders of magnitude in length and time, respectively. Key design features are the rapid chemistry; the high particle concentrations but low volume fractions; the attainment of a self-preserving particle size distribution by coagulation; the ratio of the characteristic times of coagulation and sintering, which controls the extent of particle aggregation; and the narrowing of the aggregate primary particle size distribution by sintering. Copyright © 2012 by Annual Reviews. All rights reserved.

Tricoli A.,Institute of Process Engineering | Pratsinis S.E.,Institute of Process Engineering
Nature Nanotechnology | Year: 2010

The enhanced performance and reduced scale that nanoparticles can bring to a device are frequently compromised by the poor electrical conductivity of nanoparticle structures or assemblies. Here, we demonstrate a unique nanoscale electrode assembly in which conduction is carried out by one set of nanoparticles, and other device functions by another set. Using a scalable process, nanoparticles with tailored conductivity are stochastically deposited above or below a functional nanoparticle film, and serve as extensions of the bulk electrodes, greatly reducing the total film resistance. We apply this approach to solid-state gas sensors and achieve controlled device resistance with an exceptionally high sensitivity to ethanol of 20 ppb. This approach can be extended to other classes of devices such as actuators, batteries, and fuel and solar cells. © 2010 Macmillan Publishers Limited. All rights reserved.

Strobel R.,Institute of Process Engineering | Pratsinis S.E.,Institute of Process Engineering
Physical Chemistry Chemical Physics | Year: 2011

The effect of solvent composition on particle formation during flame spray pyrolysis of inexpensive metal-nitrates has been investigated for alumina, iron oxide, cobalt oxide, zinc oxide and magnesium oxide. The as-prepared materials were characterized by electron microscopy, nitrogen adsorption, X-ray diffraction (XRD) and disc centrifugation (XDC). The influence of solvent parameters such as boiling point, combustion enthalpy and chemical reactivity on formation of either homogeneous nanoparticles by evaporation/nucleation/ coagulation (gas-to-particle conversion) or large particles through precipitation and conversion within the sprayed droplets (droplet-to-particle conversion) is discussed. For Al2O3, Fe2O 3, Co3O4 and partly also MgO, the presence of a carboxylic acid in the FSP solution resulted in homogeneous nanoparticles. This is attributed to formation of volatile metal carboxylates in solution as evidenced by attenuated total reflectance spectroscopy (ATR). For ZnO and MgO rather homogeneous nanoparticles were formed regardless of solvent composition. For ZnO this is attributed to its relatively low dissociation temperature compared to other oxides. While for MgO this is traced to the high decomposition temperature of Mg(NO3)2 together with Mg(OH)2 ↔ MgO transformations. Cobalt oxide (Co3O4) nanoparticles made by FSP were not aggregated but rather loosely agglomerated as determined by the excellent agreement between XRD- and XDC-derived crystallite and particle sizes, respectively, pointing out the potential of FSP to make non-aggregated particles. © 2011 the Owner Societies.

Righettoni M.,Institute of Process Engineering | Tricoli A.,Institute of Process Engineering | Pratsinis S.E.,Institute of Process Engineering
Analytical Chemistry | Year: 2010

Acetone in the human breath is an important marker for noninvasive diagnosis of diabetes. Here, novel chemo-resistive detectors have been developed that allow rapid measurement of ultralow acetone concentrations (down to 20 ppb) with high signal-to-noise ratio in ideal (dry air) and realistic (up to 90% RH) conditions. The detector films consist of (highly sensitive) pure and Si-doped WO3 nanoparticles (10-13 nm in diameter) made in the gas phase and directly deposited onto interdigitated electrodes. Their sensing properties (selectivity, limit of detection, response, and recovery times) have been investigated as a function of operating temperature (325-500 °C), relative humidity (RH), and interfering analyte (ethanol or water vapor) concentration. It was found that Si-doping increases and stabilizes the acetone-selective e-WO3 phase while increasing its thermal stability and, thus, results in superior sensing performance with an optimum at about 10 mol % Si content. Furthermore, increasing the operation temperature decreased the detector response to water vapor, and above 400 °C, it was (≤0.7) always below the threshold (10.6) for fake diabetes detection in ideal conditions. At this temperature and at 90% RH, healthy humans (≤900 ppb acetone) and diabetes patients (≥1800 ppb) can be clearly distinguished by a remarkable gap (40%) in sensor response. As a result, these solid state detectors may offer a portable and cost-effective alternative to more bulky systems for noninvasive diabetes detection by human breath analysis. © 2010 American Chemical Society.

Rudin T.,Institute of Process Engineering | Pratsinis S.E.,Institute of Process Engineering
Industrial and Engineering Chemistry Research | Year: 2012

Low-cost synthesis of iron phosphate nanostructured particles is attractive for large scale fortification of basic foods (rice, bread, etc.) as well as for Li-battery materials. This is achieved here by flame-assisted and flame spray pyrolysis (FASP and FSP) of inexpensive precursors (iron nitrate, phosphate), solvents (ethanol), and support gases (acetylene and methane). The iron phosphate powders produced here were mostly amorphous and exhibited excellent solubility in dilute acid, an indicator of relative iron bioavailability. The amorphous and crystalline fractions of such powders were determined by X-ray diffraction (XRD) and their cumulative size distribution by X-ray disk centrifuge. Fine and coarse size fractions were obtained also by sedimentation and characterized by microscopy and XRD. The coarse size fraction contained maghemite Fe 2O 3 while the fine was amorphous iron phosphate. Furthermore, the effect of increased production rate (up to 11 g/h) on product morphology and solubility was explored. Using increased methane flow rates through the ignition/pilot flame of the FSP-burner and inexpensive powder precursors resulted in also homogeneous iron phosphate nanoparticles essentially converting the FSP to a FASP process. The powders produced by FSP at increased methane flow had excellent solubility in dilute acid as well. Such use of methane or even natural gas might be economically attractive for large scale flame-synthesis of nanoparticles. © 2012 American Chemical Society.

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