Nano-argent | EPFL Graph Search

vignette|Nanoparticules d'argent, vues au microscope électronique. Le est un nanomatériau à base d'atomes d'argent, produit sous forme de nanoparticules par des nanotechnologies. En solution, il porte le nom d'. En 2008, selon les producteurs, environ /an de nano-argent auraient déjà été produites dans le monde, sous forme d'ions argent, de particules d’argent protéinées (silver proteins) ou de colloïdes utilisés comme biocide. Les nanoparticules les plus vendues et les plus diffusées dans l'environnement en 2004 étaient du nano-argent ou à base de nano-argent (56 % du total de la production), devant le carbone (17 %) et le zinc (7 %). En raison de son échelle nanométrique qui lui confère une énorme surface développée, pouvant s'associer à un grand nombre de ligands, il fait l'objet d'évaluations de son efficacité potentielle comme médicament, de sa toxicité et concernant ses coûts. Le nano-argent a des propriétés très différentes de celles de l'argent massif. C'est un puissant bi

Silver nanoparticle effects on simple stream food webs and ecosystem processes

Carmen Omayra Gil Allué

With the global nanotechnology market growing rapidly, nanomaterials are being increasingly released into aquatic environments, where they can undergo modifications and sedimentation, which will put benthic organisms at risk. Of particular interest is the study of nanomaterial effects on periphyton, a community of auto- and heterotrophic microorganisms embedded in an extracellular polymer matrix that covers submerged surfaces in aquatic ecosystems. Although periphyton assumes important functions in ecosystems, like primary production, little information is available on its sensitivity to nanomaterials and how these might be transferred to higher trophic levels in food webs. In the present thesis, effects of short- and long-term exposures to citrate-coated silver nanoparticles (AgNP, 35 nm) and silver ions (Ag+, dosed as AgNO3) were assessed on periphyton in microcosm studies for periods between 2 hours and 21 days. After exposure, primary production, secondary production, photosynthetic yield, microbial respiration and potential extracellular enzyme activity were measured. Moreover, addition of an aquatic snail, Physa acuta, feeding on periphyton allowed the assessment of effects of AgNP on an aquatic herbivore and trophic transfer efficiency. Contaminated (AgNP and AgNO3) and uncontaminated periphyton was offered to snails in a 5-day experiment to determine silver uptake and the mortality, feeding rate and reproduction of the snails. Our findings show that all endpoints measured in periphyton were affected by both AgNP and AgNO3 during short-term exposure, but AgNO3 was more toxic on a total silver mass basis than AgNP. Concentrations causing a 50% reduction in the different endpoints (EC50) ranged from 17 to 83 µM AgNP and from 2 to 4 µM AgNO3. Exposure of periphyton in the presence of silver ion ligands to complex Ag+ (ca. 1% of total silver in AgNP suspensions) prevented AgNP toxicity to most endpoints, confirming that the observed toxic effects were caused by the bioavailable Ag+. An exception was the extracellular enzyme leucine aminopeptidase, which was directly affected by AgNP. Concentrations of AgNP and AgNO3 that caused low toxicity during short-term exposure also caused effects on periphyton functions upon long-term exposure, with algae and bacteria being differently affected. Periphyton exposed to 10 µM AgNP for 21 days showed a 63% decrease in primary production and a 246% increase in bacterial secondary production per unit of total periphyton biomass. The community composition exposed to AgNP or AgNO3 differed from that of the control and also from each other. Furthermore, AgNP-exposed communities were more tolerant to subsequent AgNP exposure. Trophic transfer of silver from contaminated periphyton to snails occurred efficiently, independently of the silver form. Feeding rate of snails on AgNO3-exposed communities was 50% lower than on controls, and disturbance of digestion was evident upon feeding on both AgNP- and AgNO3-exposed communities. No changes in the mortality or egg production of the snails were observed. However, the hatching success of eggs from snails that fed on contaminated periphyton was reduced by more than 79%, and 28-day old embryos showed malformations. Overall, this study clearly identified damaging effects of AgNP on periphyton, with consequent indirect impacts on a consumer, trophic relationships and stream ecosystem processes.

EPFL2015

Optical Excitation of a Nanoparticle Cu/p-NiO Photocathode Improves Reaction Selectivity for CO2 Reduction in Aqueous Electrolytes

Xueqian Li, Giulia Tagliabue

We report the light-induced modification of catalytic selectivity for photoelectrochemical CO2 reduction in aqueous media using copper (Cu) nanoparticles dispersed onto p-type nickel oxide (p-NiO) photocathodes. Optical excitation of Cu nanoparticles generates hot electrons available for driving CO2 reduction on the Cu surface, while charge separation is accomplished by hot-hole injection from the Cu nanoparticles into the underlying p-NiO support. Photoelectrochemical studies demonstrate that optical excitation of plasmonic Cu/p-NiO photocathodes imparts increased selectivity for CO2 reduction over hydrogen evolution in aqueous electrolytes. Specifically, we observed that plasmon-driven CO2 reduction increased the production of carbon monoxide and formate, while simultaneously reducing the evolution of hydrogen. Our results demonstrate an optical route toward steering the selectivity of artificial photosynthetic systems with plasmon-driven photocathodes for photoelectrochemical CO2 reduction in aqueous media.

2020

Synthesis and Functionalization of Silver Nanoparticles for the Preparation of High Permittivity Nanocomposites

Jose Enrico Quijano Quinsaat

Over the last decade, a growing interest in nanochemistry has emerged due to the interesting features of nanomaterials that vary with size, shape and surface structure. In particular, metal nanoparticles have received much attention due to their properties that enable their use in various scientific disciplines. Although metal nanoparticles exhibit a number of properties that differ from bulk, some properties, such as their infinite permittivity, remain unchanged. As a result, metal nanoparticles have also been used to prepare nanocomposites with polymers in order to provide dielectric materials featuring high permittivities which can be used for applications such as energy storage (capacitors) or as materials for the conversion of electrical energy into mechanical motion (actuators). Despite the large number of publications on the preparation of nanocomposites exhibiting high permittivities which have emerged over the years, there is still room for further improvement in the current materials properties. For instance, dielectric losses are still quite high in some materials, and the use of certain types of filler lead to a large deterioration in the mechanical properties of the nanocomposites, especially with increasing filler content. In addition, a large number of the fillers used for the preparation of the nanocomposites feature poor size and shape control as well as poorly defined surface properties thus adding to the complexity of understanding the resulting material properties. This work tries to address some of the current issues concerning the preparation of dielectric materials. Therefore, silver nanoparticles (AgNPs) were used as filler, while polydimethylsiloxane (PDMS) was employed as the polymeric matrix. The advantages of using AgNPs as filler consist of their relative facile preparation, as well as the possibility of controlling their surface properties due to their resistance towards oxidation and corrosion. The possibility of preparing AgNPs in large amounts with control over the average size of the particles was realized by conducting the polyol synthesis of AgNPs in a Segmented Flow Tubular Reactor (SFTR). A SiO2 layer was grown around the AgNPs to prevent the loss of the insulating nature of the composite due to the formation of conductive pathways, and the thickness dependency of the dielectric properties of the core-shell particles was also investigated in this work. Furthermore, the SiO2 shell also provided the possibility of further surface functionalization, which was conducted in order to compatibilize the core-shell particles with the PDMS matrix. PDMS was chosen as the polymeric matrix due to its good electromechanical properties, which include high elasticity, low viscosity as well as low conductivity and low tangent losses (tan ÎŽ). The resulting nanocomposites featured enhanced permittivities compared to PDMS, while further optimization in the reaction conditions as well as in the processing procedure yielded nanocomposites with high flexibility that can undergo strains as high as 800 % at a silver content of 20 vol%. Other properties such as electric conductivity and the tan ÎŽ were kept low which emphasizes the potential of the nanocomposites to being used as flexible dielectric materials.

EPFL2015

Silver nanoparticle effects on simple stream food webs and ecosystem processes

Carmen Omayra Gil Allué

EPFL2015

Synthesis and Functionalization of Silver Nanoparticles for the Preparation of High Permittivity Nanocomposites

Jose Enrico Quijano Quinsaat

EPFL2015