Persistence of engineered nanoparticles in a municipal solid-waste incineration plant

More than 100 million tonnes of municipal solid waste are incinerated worldwide every year1. However, little is known about the fate of nanomaterials during incineration, even though the presence of engineered nanoparticles in waste is expected to grow2. Here, we show that cerium oxide nanoparticles introduced into a full-scale waste incineration plant bind loosely to solid residues from the combustion process and can be efficiently removed from flue gas using current filter technology. The nanoparticles were introduced either directly onto the waste before incineration or into the gas stream exiting the furnace of an incinerator that processes 200,000 tonnes of waste per year. Nanoparticles that attached to the surface of the solid residues did not become a fixed part of the residues and did not demonstrate any physical or chemical changes. Our observations show that although it is possible to incinerate waste without releasing nanoparticles into the atmosphere, the residues to which they bind eventually end up in landfills or recovered raw materials, confirming that there is a clear environmental need to develop degradable nanoparticles.

High-aspect ratio three-dimensional photoresin-based microstructures doped with luminescent nanocrystals

Jürgen Brugger, Vahid Fakhfouri

Incorporation of nanoparticles into photostructurable polymer materials enables the engineering of novel, highly integrated micro/nanosystems (MEMS/NEMS) with enhanced intrinsic functional properties. For instance, nanoparticles with (semi)conducting, optical or magnetic properties can be incorporated into polymers in order to convey their inherent functionalities to the final material, which can then be exploited for sensor and actuator applications. The current challenge is two-fold: (a) the incorporation of the functional nanoparticles into the polymer matrix and (b) the maintaining of the structurability of photosensitive polymers by UV lithography. In this paper we present a novel approach to further advance this field by combining luminescent nanocrystals (NCs) of cadmium selenide coated by a shell of zinc sulfide (CdSe@ZnS) with epoxy-based photosensitive resins. This class of material is well-known for polymer MEMS applications due to its superb structurability by UV lithography and mechanical properties. Here, colloidal methods have been used to provide luminescent CdSe@ZnS NCs with tunable size, exhibiting size-dependent optoelectronic properties. The presence of an organic ligand shell makes the NCs soluble in organic solvents and thus enables their processing and incorporation into polymers. The luminescent NCs (4.7 nm) were successfully incorporated in the epoxy-based resin by exploiting their solubility in a suitable common solvent. The NC-doped resin has been spin-coated on a silicon wafer, baked, exposed to UV light through a mask and developed. The same processing was applied to un-doped resin used as reference material. The obtained structures were inspected by means of optical, scanning electron, fluorescent and atomic force microscopy, as well as surface profilemetry. The results confirm the overall UV-structuring capability of the modified polymer. The emission properties of the NCs were demonstrated to be retained upon incorporation in the resin and spin coating. The luminescent properties of the NCs were retained after patterning by UV photolithography, although some aggregation of NCs was observed. The presence of organic ligand shell at the colloidal NC surface shows to be relevant for the subsequent processing of the doped photo-resin. The presented route looks promising for the microfabrication of polymer MEMS with inherent functionalities. Further optimization needs to be implemented also in view of a possible extension to incorporation of different types of colloidal NCs.

2006

Luminescent nanocrystal modified photoresin for fabrication of high-aspect ratio three-dimensional microstructures

Jürgen Brugger, Vahid Fakhfouri

The organic polymers incorporating inorganic nanoparticles can result in material possessing with unique size-dependent properties, such as mechanical, optical, electrical, thermal and magnetic, that can be istinctively conveyed into the composite by the suitable nanoparticles. When nano-objects such as luminescent nanocrystals (NCs) particles are embedded into photostructurable polymer materials, they provide a new, highly processable material, which enables the engineering of novel, highly integrated micro/nanosystems (MEMS/NEMS) with enhanced intrinsic functional properties. The current effort aims, on one side, to the incorporation of the functional nanoparticles into the polymer matrix and, on the other side, to preserve the characteristic structurability of photosensitive polymers by UV lithography. In this paper we present a novel composite material obtained from the combination of luminescent nanocrystals (NCs) of cadmium selenide coated by a shell of zinc sulfide (CdSe@ZnS) with epoxy-based photosensitive resins. This class of material is well-known for polymer MEMS applications due to its unique structurability by UV lithography and mechanical properties. Luminescent CdSe@ZnS NCs with tuneable size, exhibiting size-dependent optoelectronic properties have been synthesized by means of colloidal routes methods. The presence of an organic ligand shell makes the NCs soluble in different types of solvents and thus enables their processing and incorporation into polymers. For this purpose a range on different solvents were tested in order to optimize the incorporation of the luminescent NCs (4.7 nm) in the epoxy-based resin. Spectroscopical and microscopical investigation were performed on the prepared composite samples and the effects of the NC concentration, size, surface chemistry and solvent composition were investigated in order to evaluate their role on the spectroscopical and structural behaviour of the nanocomposite properties. The NC-doped resin was then spin-coated on a silicon wafer, baked, exposed to UV light through a mask and developed. The results confirm the overall UV-structuring capability of the modified polymer and the NC emission properties were demonstrated to be retained. Furthermore, the luminescent properties of the NCs were retained after patterning by UV photolithography, although some aggregation of NCs was observed. The presence of organic ligand shell at the colloidal NC surface shows to be relevant for the subsequent processing of the doped photo-resin. The presented route looks promising for the microfabrication of polymer MEMS with inherent functionalities. Further optimization needs to be implemented also in view of a possible extension to incorporation of different types of colloidal NCs.

2006

New Analytical Methods for Size Fractionated, Quantitative, and Element Specific Analysis of Metallic Engineered Nanoparticles in Aerosols and Dispersions

Harald Hagendorfer

The application of engineered nanoparticles (ENP) increased almost exponentially during the last decade. Next to carbon based ENP, metal based ENP are the next most commonly employed. Utilization of such particles for medical applications, remediation of toxic substances, consumer products, new materials, and numerous other fields has been reported already. Despite their extraordinary success and implementation, concerns have been raised about possible negative effects in humans and the environment. Once released, ENP are easily distributed via the atmosphere and the aquatic environment where an exposure to organisms can occur. To understand ENP release, life cycle (fate), and exposure as well as to evaluate their toxicological mechanisms, appropriate, media-specific (aerosols and dispersions) analytical methods are required. First, the development of a new set-up to determine ENP in aerosols is presented. For this purpose online (SMPS) and offline (electrostatic sampling on TEM grids) aerosol particle measurement techniques were combined. The aim was to study the release and fate of metallic ENP from commercial available spray products. Method development and verification was performed employing a well characterized aqueous Ag-NP spray product. The investigations have shown that the method offers the possibility to determine size, and element -specific nanoparticle release. Furthermore information about particle morphology and quantity could be obtained. It was revealed, that the release of nanoparticles strongly depends on the type of spray. Pump sprays did not show to produce airborne ENP in the aerosol, whereas propellant gas sprays released nanoparticles in substantial quantities. The release of nanoparticles was correlated with the droplet size distributions generated from the different spray types. Following method development, the setup was applied to determine ENP release of commercial available sprays, indicated to contain ENP. The obtained data was useful to model the consumer exposure of ENP from such products. Second, a set-up to determine ENP in dispersions was developed. For this purpose an asymmetric flow field flow fractionation (A4F) apparatus was coupled to an UV/Vis, light scattering- and inductively coupled plasma mass spectrometric (ICPMS) detector, simultaneously. In the beginning, method development and systematic investigations of prospects and limitations was performed employing well-characterized Au nanoparticles (Au-NP). The investigation revealed that A4F is a versatile separation technique for metallic ENP. In contrast, size determination with the A4F system, derived from the retention times of nanoparticles in the chromatogram, was erroneous. Unspecific interaction of ENP with the A4F channel membrane led to retention time shifts resulting in biased size information. For this reason, online dynamic light scattering (DLS) was employed and it offered a reliable determination of nanoparticle dimensions. Determination of nanoparticle concentration also proved to be to be problematic. Unspecific loss of nanoparticles in the A4F separation channel led to insufficient recovery prevented direct quantification of nanoparticles. To overcome this problem an alternative method was employed. With ICPMS after ultracentrifugation, quantification of the ionic and particulate -fraction of metallic ENP dispersions was possible. Validation of the set-up was performed with certified Au-NP reference materials obtained from NIST and results showed excellent agreement. Combining both of these new methods provided a comprehensive understanding of the metallic ENP systems. After method development with well defined nanoparticle systems, the set-up was tested for its applicability to "real world" samples. First, the characterization of commercial available, polydisperse, commercial Ag nanoparticle (Ag-NP) products was performed. The new developed set-up allowed obtaining an element specific, mass, and number size distribution. Furthermore, Ag-NP concentrations as well as the toxicological relevant ionic Ag concentration could be determined. Figures of merit compared to transmission electron microscopy (TEM) and batch-DLS results were in good agreement and the new method was advantageous in terms of analysis time and reliability. Furthermore the possibility to characterize SiO2 coated Au nanoparticles (Au@SiO2) was investigated. These particles are employed for Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS). It was shown that in terms of particle size characterization, the method provided excellent data. However, determination of Si concentrations to calculate the shell thickness of such particles was impeded by the poor A4F peak shape as well as the high Si background in ICPMS. In conclusion, both setups show great potential for the characterization of metallic ENP either in aerosols or dispersions, respectively.

EPFL2011

Luminescent nanocrystal modified photoresin for fabrication of high-aspect ratio three-dimensional microstructures

Jürgen Brugger, Vahid Fakhfouri

2006

High-aspect ratio three-dimensional photoresin-based microstructures doped with luminescent nanocrystals

Jürgen Brugger, Vahid Fakhfouri

2006

New Analytical Methods for Size Fractionated, Quantitative, and Element Specific Analysis of Metallic Engineered Nanoparticles in Aerosols and Dispersions

Harald Hagendorfer

EPFL2011