Nicolas Nuns

Toward the understanding of the interfacial dairy fouling deposition and growth mechanisms at a stainless steel surface: a multiscale approach.

The microstructures of two dairy fouling deposits obtained at a stainless steel surface after different processing times in a pilot plate heat exchanger were investigated at different scales. Electron-Probe Micro Analysis, Time-of-Flight Secondary Ion Mass Spectrometry, Atomic Force Microscopy, and X-Ray Photo-electron Spectroscopy techniques were used for this purpose. The two model fouling solutions were made by rehydrating whey protein in water containing calcium or not. Results on samples collected after 2h processing show that the microstructure of the fouling layers is completely different depending on calcium content: the layer is thin, smooth, and homogeneous in absence of calcium and on the contrary very thick and rough in presence of calcium. Analyses on substrates submitted to 1 min fouling reveal that fouling mechanisms are initiated by the deposit of unfolded proteins on the substrate and start immediately till the first seconds of exposure with no lag time. In presence of calcium, amorphous calcium carbonate nuclei are detected in addition to unfolded proteins at the interface, and it is shown that the protein precedes the deposit of calcium on the substrate. Moreover, it is evidenced that amorphous calcium carbonate particles are stabilized by the unfolded protein. They are thus more easily trapped in the steel roughnesses and contribute to accelerate the deposit buildup, offering due to their larger characteristic dimension more roughness and favorable conditions for the subsequent unfolded protein to depose.

Metal-induced malformations in early Palaeozoic plankton are harbingers of mass extinction

Glacial episodes have been linked to Ordovician–Silurian extinction events, but cooling itself may not be solely responsible for these extinctions. Teratological (malformed) assemblages of fossil plankton that correlate precisely with the extinction events can help identify alternate drivers of extinction. Here we show that metal poisoning may have caused these aberrant morphologies during a late Silurian (Pridoli) event. Malformations coincide with a dramatic increase of metals (Fe, Mo, Pb, Mn and As) in the fossils and their host rocks. Metallic toxins are known to cause a teratological response in modern organisms, which is now routinely used as a proxy to assess oceanic metal contamination. Similarly, our study identifies metal-induced teratology as a deep-time, palaeobiological monitor of palaeo-ocean chemistry. The redox-sensitive character of enriched metals supports emerging ‘oceanic anoxic event models. Our data suggest that spreading anoxia and redox cycling of harmful metals was a contributing kill mechanism during these devastating Ordovician–Silurian palaeobiological events.

Nisin adsorption on hydrophilic and hydrophobic surfaces: evidence of its interactions and antibacterial activity

Study of peptides adsorption on surfaces remains a current challenge in literature. A complementary approach, combining X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the antimicrobial peptide nisin adsorption on hydrophilic and hydrophobic surfaces. The native low density polyethylene was used as hydrophobic support and it was grafted with acrylic acid to render it hydrophilic. XPS permitted to confirm nisin adsorption and to determine its amount on the surfaces. ToF‐SIMS permitted to identify the adsorbed bacteriocin type and to observe its distribution and orientation behavior on both types of surfaces. Nisin was more oriented by its hydrophobic side to the hydrophobic substrate and by its hydrophilic side to the outer layers of the adsorbed peptide, in contrast to what was observed on the hydrophilic substrate. A correlation was found between XPS and ToF‐SIMS results, the types of interactions on both surfaces and the observed antibacterial activity. Such interfacial studies are crucial for better understanding the peptides interactions and adsorption on surfaces and must be considered when setting up antimicrobial surfaces. Copyright

Oxygen transport kinetics of the misfit layered oxide Ca3Co4O9+d

The oxygen transport kinetics of the misfit-layered cobaltite, Ca3Co4O9+δ, known for its thermoelectric properties, was investigated by combined application of 18O/16O isotope exchange and electrical conductivity relaxation techniques. Although oxygen diffusion is found to be two orders of magnitude lower than in well-investigated lanthanum nickelates, e.g., La2NiO4+δ, the mixed ionic–electronic conductor Ca3Co4O9+δ is found to exhibit fast surface exchange kinetics (k* = 1.6 × 10−7 cm s−1 at 700 °C to be compared to 1.3 × 10−7 cm s−1 for the nickelate), rendering it a promising electrode for application as an air electrode in solid oxide cells. In parallel, the chemical nature of the outermost surface of Ca3Co4O9+δ was characterized by means of Low Energy Ion Scattering (LEIS) spectroscopy. The absence of cobalt at the samples outermost surface suggests that the Ca2CoO3−δ rock salt layers in the structure may play a key role in the oxygen exchange mechanism.

The deuterium/hydrogen distribution in chondritic organic matter attests to early ionizing irradiation

Primitive carbonaceous chondrites contain a large array of organic compounds dominated by insoluble organic matter (IOM). A striking feature of this IOM is the systematic enrichment in deuterium compared with the solar hydrogen reservoir. This enrichment has been taken as a sign of low-temperature ion-molecule or gas-grain reactions. However, the extent to which Solar System processes, especially ionizing radiation, can affect D/H ratios is largely unknown. Here, we report the effects of electron irradiation on the hydrogen isotopic composition of organic precursors containing different functional groups. From an initial terrestrial composition, overall D-enrichments and differential intramolecular fractionations comparable with those measured in the Orgueil meteorite were induced. Therefore, ionizing radiation can quantitatively explain the deuteration of organics in some carbonaceous chondrites. For these meteorites, the precursors of the IOM may have had the same isotopic composition as the main water reservoirs of the inner Solar System.

Highly active noble metal-free copper-hydroxyapatite catalysts for toluene total oxidation

Hydroxyapatite (Hap) supported Cu materials prepared by the wet impregnation method were designed as noble‐metal‐free catalysts for the total oxidation of toluene. Cu/Hap materials with different Cu loadings (2.5–20u2005wtu2009%) calcined at 400u2009°C were characterized by using inductively coupled plasma optical emission spectroscopy, N2 physisorption, XRD, Raman spectroscopy, IR spectroscopy, X‐ray photoelectron spectroscopy, and time‐of‐flight secondary ion MS. The tenorite CuO phase was detected in all materials, and the libethenite Cu2(PO4)OH phase was observed for the sample with 20u2005wtu2009% Cu. The presence of libethenite was accompanied by the formation of Ca2CO3H+ ions at the Hap surface. Residual NO3− species that interact with Cu and Ca were also found, and their amount increased with the increase of the Cu content in the sample. Interestingly, the specific activity in the total oxidation of toluene increased with the decrease of the Cu content in the catalyst. The rate per mole of Cu was increased by 10 times if the Cu content was decreased by four times. This noticeable result could be related to the presence of acid sites with a moderate strength as well as finely dispersed CuO species on the Hap, which allow the activation of toluene molecules and their oxidation through a redox mechanism. Moreover, Cu2.5u2005wtu2009%/Hap showed a remarkably stable catalytic performance for 45u2005h time‐on‐stream, which evidences that this material has a high potential for applications in the removal of volatile organic compounds.

Extraction of indium-tin oxide from end-of-life LCD panels using ultrasound assisted acid leaching

In this report, indium-tin-oxide (ITO)-layer extraction from end-of-life (EOL) Liquid Crystal Displays (LCDs) was discussed by sulfuric acid leaching with simultaneous application of ultrasonication on the ITO-side of glass/ITO panels, exhibiting various dimensions. Applying this technique presents several advantages compared to the traditional leaching process such as fast and controllable kinetics, high extraction yield of indium and tin, selective recovery of these two metals possible, and the opportunity to recycle the neat glass separately avoiding additional separation processes. ITO-dissolution kinetics from EOL LCD panels were investigated as function of leaching time and acidity of sulfuric acid. At a temperature of 60°C, a nearly quantitative indium yield was obtained using an acid concentration of 18mol/L by simultaneous application of ultrasonication, whereas only 70% were recovered in the absence of ultrasound. Results from ICP-AES agreed well with SEM/BSE observations demonstrating the high efficiency of the ultrasound assisted process since only 3-4min were required to obtain maximum ITO recovery.

Long-term weathering rate of stained-glass windows using H and O isotopes

The understanding of glass alteration is a biogeochemical, industrial, societal (radioactive waste confinement), and cultural heritage issue. Studies have been mainly performed in aqueous conditions. However, glass reactivity under hydraulically unsaturated conditions may be more important than previously recognized. In this context, we evaluate here the role of the alteration layer formed on medieval stained-glass windows on the ongoing alteration in unsaturated conditions. H2O adsorption isotherms were measured to study the relation between the vapor sorption and the relative humidity inside the alteration layer. From it, the average pore radius was calculated, yielding a water vapor diffusion coefficient of 7.8u2009×u200910-7 m²u2009s-1 inside the pore network. Experiments using doped water vapor (D218O) confirm the vapor transport up to the alteration front via fractures and pore network. They also demonstrate that the alteration mainly progresses via an interdiffusion mechanism. The calculated interdiffusion coefficients at 20u2009°C are 3.6u2009×u200910-20u2009m2u2009s-1 at 70% RH and 4.9u2009×u200910-20u2009m2u2009s-1 at 90% RH, which is similar to the values measured on model stained-glass samples altered in short durations (1–4 years). Therefore, this study highlights that, given its morphology, the alteration layer is not protective against vapor transport and interdiffusion.Glass alteration: Understanding unsaturated conditionsIsotopic studies of the glass from stained-glass windows have determined the effects of water vapor on their weathering. Understanding how glasses react to their environment over time is important in contexts such as nuclear-waste storage and artifact conservation. They are known to form an amorphous ‘gel’ layer on their surface and many studies aimed at improving its understanding are carried out in aqueous solution, however, stained-glass windows are exposed to alternating saturated and unsaturated conditions, characterized by liquid water and water vapor respectively. Now a team of scientists based in France, led by Loryelle Sessegolo of the Université Paris-Est Créteil and Université Paris Diderot, have studied how the gel layer present on the stained-glass windows affects its on-going alteration in unsaturated conditions; they find that the layer is not protective against vapor transport or interdiffusion.

A comprehensive protocol for chemical analysis of flame combustion emissions by secondary ion mass spectrometry

RATIONALEnTime-of-flight secondary ion mass spectrometry (TOF-SIMS) is used to provide detailed information on the surface chemical composition of soot. An analytical protocol is proposed and tested on a laboratory flame, and the results are compared with our previous measurements provided by two-step laser mass spectrometry (L2MS).nnnMETHODSnThis work details: (1) the development of a dedicated apparatus to sample combustion products from atmospheric flames and deposit them on substrates suitable for TOF-SIMS analysis; (2) the choice of the deposition substrate and the material of the sampling line, and their effect on the mass spectra; (3) a method to separate the contributions of soot and condensable gas based on impact deposition; and finally (4) post-acquisition data processing.nnnRESULTSnCompounds produced during flame combustion are detected on the surface of different deposition substrates and attributed a molecular formula based on mass defect analysis. Silicon and titanium wafers perform similarly, while the surface roughness of glass microfiber filters results in a reduced mass resolution. The mass spectra obtained from the analysis of different locations of the deposits obtained by impaction show characteristic patterns that are attributed to soot/condensable gas.nnnCONCLUSIONSnA working method for the analysis of soot samples and the extraction of useful data from mass spectra is proposed. This protocol should help to avoid common experimental issues like sample contamination, while optimizing the setup performance by maximizing the achievable mass resolution.