Argent | EPFL Graph Search

L'argent est l'élément chimique de numéro atomique 47, de symbole Ag. Le corps simple argent est un métal précieux dont le nom désigne aussi en français dans le langage courant les pièces et billets de monnaie, voire par extension une certaine somme « d'argent ». Cependant, les économistes distinguent, à la différence du langage courant, l’argent métal ou réserve métallique de la monnaie comme outil de régulation des échanges économiques. Le faible niveau des réserves de ce métal en fait une matière première minérale critique. Généralités et présentation de l'élément argent Le mot français vient du terme latin argentum, i de même signification. L’origine lointaine du mot, par le grec argyros, viendrait d’un étymon indo-européen commun *arg- signifiant « blanc brillant, laiteux et clair » et serait l’équivalent en sanskrit de ar-jun signifiant également « brillant ». Ce métal précieux, malléable et très ductile, est blanc et brillant, comme le rappelle son nom. Dédié à

Interactions of silver and polystyrene nanoparticles with algae

Xiaomei Li

Nanoparticles have various physicochemical properties attributed by their small dimensions. The global production of nanoparticles lead to a raised concern for their environmental impacts. Algae are of highly ecological importance functioning as primary producers for almost all aquatic life. In the present thesis, interactions of nanoparticles with different fresh water algal strains were examined. First, the toxicity and uptake of citrate-coated silver nanoparticles (AgNP) and AgNO3 were examined in the alga Euglena gracilis, which has no cell wall but a pellicle. Secondly, to examine the role of algal cell wall in determining the particles interactions with algae, four strains were selected, including Euglena gracilis, Haematococcus pluvialis, and Chlamydomonas reinhardtii wild type and a cell wall free mutant. Their interactions with polystyrene nanoparticles (PSNP) of two sizes, 50 nm (PSNP50) and 500 nm (PSNP500), were investigated. Third, interactions of three differently coated AgNP with alkaline phosphatase (AP), an extracellular enzyme used for phosphorus acquisition, were assessed. The selected coatings were citrate (CIT), polyvinylpyrrolidone (PVP) and gelatin (GEL). Exposure to AgNP and AgNO3 for 1-2 hours led to decrease in photosynthetic yield, in a concentration-dependent manner, and changes in cell morphology in E. gracilis. Based on total silver added, AgNP were less toxic than AgNO3. Concentrations causing a 50% reduction in photosynthetic yield were 1.9 µM and 85 for AgNP and AgNO3, respectively. Damaging effects of AgNP were completely prevented by cysteine, suggesting that the toxicity of AgNP was mediated by Ag+ ions. Uptake studies showed that the maximal cell-associated silver was higher in AgNP compared to AgNO3, and the higher silver level was shown to correspond to particles adsorbed to the pellicle. By examining four algal stains, it was found that no strain internalized PSNP, emphasizing the role of algal cell walls as barrier for nanoparticle uptake. Interactions of PSNP with algae were found to be unique for each strain, and depend on particle size. PSNP50 were associated with E. gracilis cells displaying a non-homogenous distribution on pellicle. In H. pluvialis, PSNP50 distributed homogenously around the cells. The wild type and cell wall free mutant of C. reinhardtii cells exposed to PSNP50 were found to clump together packed in the extracellular polymeric substances (EPS). The particles were associated with the EPS. The larger PSNP500 were observed to interact only with the two C. reinhardtii strains. Taken together, these results indicate that the algal cell walls hinder the crossing of nanoparticles. Assessing the sorption of AP to AgNPCIT, AgNPPVP, and AgNPGEL showed that the physiochemical properties of both the particle coatings and the enzyme were determinant for the binding. The enzyme adsorbed to AgNPCIT and AgNPPVP, leading to a 10% and 70% coverage of the particle surface area, respectively. No adsorption was found in the case of AgNPGEL. The three types of AgNP decreased AP activity, however, the inhibitory effects only occurred when the AgNP were added after addition of the substrate to the enzyme, not vice versa. AgNO3 did not affect the AP activity. Thus, the results of this study indicate particle-specific effects due to interactions with the AP-substrate intermediate.

EPFL2015

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

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

The fabrication of defined and high-quality metal nanostructures is an ongoing topic of research. Direct-write deposition of copper nanostructures is of great value for many fields of research and industrial applications. Focused electron beam induced deposition (FEBID) is an additive fabrication technique with extremely high resolution and versatility. Physisorbed, gaseous precursor molecules are locally dissociated by a finely focused electron beam resulting in volatile fragments which desorb and non-volatile fragments forming the deposit. When applying suitable deposition parameters, these deposits can be as small as the beam diameter and have ideally little to no contamination. For electron beam induced metal deposition, metal-organic compounds are chosen as precursors. However, organic ligand material is often co-deposited, which is detrimental to the depositâs properties. This work addresses the study of the perfluorinated copper carboxylate [Cu2(ÎŒ-O2CC2F5)4] (Cu2(pfp)4) and its aminated derivatives Cu2(EtNH2)2(pfp)4 and Cu2(tBuNH2)2(pfp)4 as viable FEBID precursors. 25 at.% of copper was achieved with the amine free compound, and 15 at.% with each of the two aminated complexes. Based on the chemical analysis of the deposits, electron-induced dissociation paths were proposed for the adsorbed species, demonstrating the influence of the ligand chemistry and fragmentation on the deposit composition. In parallel, the perfluorinated silver carboxylate Ag2(pfp)2 was reported and compared directly to its copper equivalent. The silver complex yielded up to 74 at.% metal content and exhibited strong susceptibility to varying electron beam densities throughout the deposit. Cu2(pfp)4 did not manifest the same electron sensitivity. Theoretical models, combining analytical solutions with Monte Carlo simulations of primary and backscattered electrons were successfully fitted to the cross sections of deposits from both carboxylates, determining the growth regimes within a single spot deposit. Additionally, two previously reported Î²-diketonates, Cu(hfac)2 and Cu(tbaoac)2, were directly compared to the other Cu(II) precursors with the aim to determine any dependence of the ligand size, electron density or dwell time on the deposit purity. The investigations concluded that the metal content rather depends on the chemistry of the metal-ligand bond than on the ligand size. This applies to both, the variation of ligands and the variation of the metal center. vii Furthermore, two copper complexes, Cu(hfac)2 and Cu2(pfp)4, were investigated in situ with a dedicated, custom-made setup. The âeQCMâ combines a low energy electron source (10- 100 eV) with a quartz crystal microbalance and serves to study fundamental processes occurring during FEBI deposition. First results yielded the total dissociation cross section for each precursor at varying electron energies. Finally, alternative approaches for the electron induced copper deposition from Cu2(pfp)4 were investigated. A two-step post-purification recipe of as-deposited material was reported to yield pure copper crystals (> 97 at.%). Additionally, direct electron beam lithography in a layer of condensed precursor was explored. This room temperature deposition approach yielded in lower metal contents but could potentially produce high resolution deposition.

EPFL2020

Silver nanoparticle effects on simple stream food webs and ecosystem processes

Carmen Omayra Gil Allué

EPFL2015

Interactions of silver and polystyrene nanoparticles with algae

Xiaomei Li

EPFL2015

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

EPFL2020