Aircraft and MiniCAST soot at the nanoscale

International audienc

Surface-Enhanced Nitrate Photolysis on Ice

Heterogeneous nitrates photolysis is the trigger for many chemical processes occurring in the polar boundary layer and is widely believed to occur in a quasi-liquid layer (QLL) at the surface of ice. The dipole forbidden character of the electronic transition relevant to boundary layer atmospheric chemistry and the small photolysis/photoproducts quantum yields in ice (and in water) may confer a significant enhancement and interfacial specificity to this important photochemical reaction at the surface of ice. Using amorphous solid water films at cryogenic temperatures as models for the disordered interstitial air/ice interface within the snowpack suppresses the diffusive uptake kinetics thereby prolonging the residence time of nitrate anions at the surface of ice. This approach allows their slow heterogeneous photolysis kinetics to be studied providing the first direct evidence that nitrates adsorbed onto the first molecular layer at the surface of ice are photolyzed more effectively than those dissolved within the bulk. Vibrational spectroscopy allows the ~3-fold enhancement in photolysis rates to be correlated with the nitrates’ distorted intramolecular geometry thereby hinting at the role played by the greater chemical heterogeneity in their solvation environment at the surface of ice than in the bulk. A simple 1D kinetic model suggests 1-that a 3(6)-fold enhancement in photolysis rate for nitrates adsorbed onto the ice surface could increase the photochemical NO[subscript 2] emissions from a 5(8) nm thick photochemically active interfacial layer by 30%(60)%, and 2-that 25%(40%) of the NO[subscript 2] photochemical emissions to the snowpack interstitial air are released from the top-most molecularly thin surface layer on ice. These findings may provide a new paradigm for heterogeneous (photo)chemistry at temperatures below those required for a QLL to form at the ice surface

Etude par absorption X de materiaux ceramiques obtenus par pyrolyse de precurseurs organosilicies

SIGLEINIST T 71463 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Caractérisation de la réaction de formation d'eau sur des nanoparticules et des nano-îlots de palladium supportés sur le graphite et l'oxyde de cérium par la fonction de travail

International audienceThe water forming reaction (WFR) between oxygen and hydrogen on metal surfaces is an important reaction in heterogeneous catalysis. Related research mostly focused on crystalline metal surfaces and thick films, however, supported nanoparticles (NP) have been rarely considered as well as a possible influence of the support on the NP catalytic activity. Here, we report on the WFR on graphite supported palladium NPs and nanoislands (NI), which are characterized at room temperature and under ultrahigh vacuum conditions (UHV) by scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), Kelvin probe force microscopy (KPFM) and X-ray photoemission spectroscopy (XPS). We show that during the first cycles of sequential O 2 and H 2 pulses, atomic H reacts off preadsorbed atomic O, which can be followed by KPFM via monitoring the change of work function (WF) at the NPs and NIs. However, after a few WFR cycles, the WF changes get smaller and the mean WF of the Pd increases due to an irreversible deactivation of the catalyst: a filament structure is formed on the facets by O and C, which the latter gets probably released from the graphite during the WFR. In strong contrast to the Pd/graphite catalyst, the WFR can be followed without any changes during an unlimited amount of cycles on a carbon-free Pd/cerium oxide/Cu(111) catalyst, which clearly shows that the support plays a role in the WFR on nanometer sized Pd catalysts

Quantification and prediction of water uptake by soot deposited on ventilation filters during fire events

International audienceSoot samples from different fuels were produced in small and pilot combustion test benches at various O2 concentrations, and were then characterized in terms of primary particle diameter, specific surface area and oxygen content/speciation. Water sorption measurements were then carried out for soot compacted into pellet form and in powder form, using both a gravimetric microbalance and a manometric analyser. Water adsorption isotherms are all found to be Type V, and reveal the central role of the specific surface area and the oxygen content of soot. A single parametrization of the second Dubinin-Serpinsky model gives a proper fit for all isotherms. To the best of our knowledge, this is the first study to provide physico-chemical parameters and water sorption results for fire soot. This enables a better description of the soot cake formed on filters during a fire, in particular in industrial confined facilities as simulated in this study. Humidity can be then explicitly considered in the same way as other parameters influencing the aeraulic resistance of soot cakes. These results can be used to improve predictions of the consequences of fires on the containment of toxic materials within industrial facilities

Caractérisation physico-chimique des aérosols dans la zone côtière : preuve de la persistance de la suie de carbone dans la couche limite atmosphérique marine de fond (MABL)

International audienceAerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component issued from natural and/or anthropogenic sources. The aim of this paper is to study how the aerosols mix in the coastal marine atmosphere to evaluate the impact of the background pollution on the atmospheric aerosols. To this end, we have carried out a qualitative analysis of particulate matter sampled at two French coastal areas using a non-destructive methodology combining scanning electron microscopy (SEM)/X-ray fluorescence, transmission electron microscopy (TEM), X-ray diffraction, and Raman spectroscopy. Our analysis shows a dominant contribution of anthropogenic aerosols through strong levels of submicronic carbon soot and sulfate particles, even observed when the aerosol is sampled during pure maritime-air mass episodes. Our results also evidence the non-mixing between sea-spray, mainly composed of coarse aerosol particles, and this anthropogenic particulate matter of smaller sizes.Les particules d'aérosols dans les zones côtières résultent d'un mélange complexe entre les aérosols d'embruns générés localement à la surface de la mer par le déferlement des vagues et une composante continentale issue de sources naturelles et/ou anthropiques. L'objectif de cet article est d'étudier comment les aérosols se mélangent dans l'atmosphère marine côtière pour évaluer l'impact de la pollution de fond sur les aérosols atmosphériques. Pour cela, nous avons réalisé une analyse qualitative des particules prélevées sur deux zones côtières françaises en utilisant une méthodologie non-destructive combinant la microscopie électronique à balayage (MEB)/fluorescence X, la microscopie électronique à transmission (MET), la diffraction des rayons X et la spectroscopie Raman. Notre analyse montre une contribution dominante des aérosols anthropiques à travers de forts niveaux de particules submicroniques de suie de carbone et de sulfate, même observés lorsque l'aérosol est échantillonné lors d'épisodes de masse d'air maritime pure. Nos résultats mettent également en évidence la non-mixité entre les embruns marins, principalement composés de grosses particules d'aérosols, et cette matière particulaire anthropique de plus petite taille

Caractérisation physico-chimique des aérosols dans la zone côtière : preuve de la persistance de la suie de carbone dans la couche limite atmosphérique marine de fond (MABL)

International audienceAerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component issued from natural and/or anthropogenic sources. The aim of this paper is to study how the aerosols mix in the coastal marine atmosphere to evaluate the impact of the background pollution on the atmospheric aerosols. To this end, we have carried out a qualitative analysis of particulate matter sampled at two French coastal areas using a non-destructive methodology combining scanning electron microscopy (SEM)/X-ray fluorescence, transmission electron microscopy (TEM), X-ray diffraction, and Raman spectroscopy. Our analysis shows a dominant contribution of anthropogenic aerosols through strong levels of submicronic carbon soot and sulfate particles, even observed when the aerosol is sampled during pure maritime-air mass episodes. Our results also evidence the non-mixing between sea-spray, mainly composed of coarse aerosol particles, and this anthropogenic particulate matter of smaller sizes.Les particules d'aérosols dans les zones côtières résultent d'un mélange complexe entre les aérosols d'embruns générés localement à la surface de la mer par le déferlement des vagues et une composante continentale issue de sources naturelles et/ou anthropiques. L'objectif de cet article est d'étudier comment les aérosols se mélangent dans l'atmosphère marine côtière pour évaluer l'impact de la pollution de fond sur les aérosols atmosphériques. Pour cela, nous avons réalisé une analyse qualitative des particules prélevées sur deux zones côtières françaises en utilisant une méthodologie non-destructive combinant la microscopie électronique à balayage (MEB)/fluorescence X, la microscopie électronique à transmission (MET), la diffraction des rayons X et la spectroscopie Raman. Notre analyse montre une contribution dominante des aérosols anthropiques à travers de forts niveaux de particules submicroniques de suie de carbone et de sulfate, même observés lorsque l'aérosol est échantillonné lors d'épisodes de masse d'air maritime pure. Nos résultats mettent également en évidence la non-mixité entre les embruns marins, principalement composés de grosses particules d'aérosols, et cette matière particulaire anthropique de plus petite taille

Yellowing of laser-cleaned artworks: Formation of residual hydrocarbon compounds after Nd:YAG laser cleaning of gypsum plates covered by lamp black

International audienc

Quantifying the Extent of Ligand Incorporation and the Effect on Properties of TiO2 Thin Films Grown by Atomic Layer Deposition Using an Alkoxide or an Alkylamide

International audienceAtomic layer deposition (ALD) of TiO2 thin films on a Si substrate has been investigated using titanium isopropoxide (TTIP) and tetrakis(dimethylamino)titanium (TDMAT) in combination with water. The deposition rate and the chemical stability of the films are significantly different depending on the Ti precursor and process temperature (TALD). When the films are annealed a significant thickness shrinkage is reported for the first time on TiO2. A comprehensive analysis of the films with X-ray photoelectron spectroscopy, Fourier transform infrared, ellipsometry, and porosimetry demonstrates that some precursor ligands are incorporated (most likely as isopropanol) when ALD is performed at low temperature (i.e., TALD < 200 °C) using TTIP. The trapped ligand molecules can be removed by annealing but make the film porous and thus have a detrimental effect on the dielectric properties. Higher-quality nonporous films are grown by using TTIP at TALD ≥ 200 °C or by using TDMAT. It is shown that measuring the refractive index is a simple, nondestructive, and reliable way to determine film quality. Numerical simulations of ligand coverage show that the measured growth rates are consistent with a self-limiting ALD mechanism albeit with partial incorporation of ligands from TTIP at low temperature (TALD < 200 °C), which renders part of the surface inactive toward growth. Aside from this, the higher growth rate of TDMAT is due to more desorption of ligands during the Ti precursor pulse. The overall decrease in the growth rate with temperature is related quantitatively to decreasing coverage of hydroxyl groups on TiO2. Comparing the TTIP and TDMAT processes in this way reveals new aspects of the gas-surface chemistry during self-limiting ALD and how this affects film morphology and electrical properties