[Show abstract][Hide abstract] ABSTRACT: Heterometal clusters containing Ru and Au, Co and/or Pt are anchored onto carbon nanotubes and nanofibers functionalized with chelating phosphine groups. The cluster anchoring yield is related to the amount of phosphine groups available on the nanocarbon surface. The ligands of the anchored molecular species are then removed by gentle thermal treatment in order to form nanoparticles. In the case of Au-containing clusters, removal of gold atoms from the clusters and agglomeration leads to a bimodal distribution of nanoparticles at the nanocarbon surface. In the case of Ru-Pt species, anchoring occurs without reorganization through a ligand exchange mechanism. After thermal treatment, ultrasmall (1-3 nm) bimetal Ru-Pt nanoparticles are formed on the surface of the nanocarbons. Characterization by high resolution transmission electron microscopy (HRTEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) confirms their bimetal nature on the nanoscale. The obtained bimetal nanoparticles supported on nanocarbon were tested as catalysts in ammonia synthesis and are shown to be active at low temperature and atmospheric pressure with very low Ru loading.
[Show abstract][Hide abstract] ABSTRACT: In an original approach to trace water reactivity upon surface treatment by ambient “open air” plasma, the H–D exchange processes induced in polyethylene by an Ar-D2O post-discharge are investigated using time-of-flight secondary ion mass spectrometry, both at the surface and along the sample depth. The surface characterization points out the strong influence of the sample-torch distance. The most important chemical modifications, excluding polymer overheating, occur at 5 mm of distance, with 25% of deuterated monomer units at the surface. For the first time, ultra-shallow molecular depth-profiling by Ar noble gas clusters shows the detailed variation of the deuteration of the polymer repeat unit in the topmost surface layer. Our results indicate that the fraction of deuterated monomer units is reduced by a factor >2 over a depth of ∼3 nm.
Plasma Processes and Polymers 05/2015; DOI:10.1002/ppap.201400248 · 2.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An ordered mesoporous carbon (OMC) was functionalized with ammonium or chelating phosphine ligands. In both cases, the functionalization procedure started by oxidation by nitric acid treatment, followed by activation of surface carboxylic acid groups with thionyl chloride, then formation of amide bonds with diamines. The pendant amine groups were then either quaternized or further reacted with phosphine. The introduced functions were used as anchors for molecular mixed-metal clusters. These organometallic grafted species could then be thermally transformed into hetero-metallic nanoparticles (NP) embedded within the mesoporous framework. The NP/OMC nanocomposites could find application in hydrogenation heterogeneous catalysis or as electrodes in fuel cells.
[Show abstract][Hide abstract] ABSTRACT: The functionalization of poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) polyelectrolyte multilayers by silanes reacted from the gas phase, is studied depending on reaction time and temperature, pH of multilayer assembly, and nature of the reacting silane group. Whereas monochlorosilanes only diffuse in the multilayer and graft in limited amount, trichloro- and triethoxy-silanes form rapidly a continuous gel layer on the surface of the multilayer, with a thickness of ca. 10-20 nm. The reactivity is lower in the strongly-paired regime of the multilayers (neutral assembly conditions), but otherwise not affected by the pH of multilayer assembly. Silanization considerably broadens the range of possible functionalities for (PAH/PAA) multilayers: hydrophobicity, surface-initiated polymerization, and grafting of fluorescent probes by the formation of disulfide bridges are demonstrated. Conversely, our results also broaden the range of substrates that can be functionalized by silanes, using (PAH/PAA) multilayers as ubiquitous anchoring layers.
[Show abstract][Hide abstract] ABSTRACT: Despite their wide use in the oil refining process, little is known about the distribution of aluminium and silicon atoms in amorphous aluminosilicates (ASAs). In this paper, we report the synthesis of both Al/SiO2 and Si/Al2O3 ASAs by grafting aluminium and silicon alkoxides on silica respectively alumina under various conditions. For both supports, we evidence the central roles of the precursor molecule size and reactivity in the grafting yield and the deposit structure. Unless hydrolysis of the alkoxy groups by water and/or thermal decomposition occurs, deposition is saturated at a monolayer of precursor molecules on the support oxide surface. Additional species can be deposited by repeating the grafting process provided that hydroxyl groups of the top layer are recovered after calcination. 27Al NMR indicates the presence of five-coordinated aluminium species on Al/SiO2 materials prepared by two successive grafting steps. Transmission electron microscopy (TEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirm the controlled deposition of species by selecting the appropriate synthesis conditions. Homogeneous and regular deposition is favoured in anhydrous condition and at low temperature, while water addition during synthesis leads to inhomogeneous deposits. In case of Al/SiO2 grafting in aqueous conditions, alumina nanoparticles form. The accurate knowledge of the surface structure of these ASAs opens the way to a better understanding of the origin of their Brönsted acidity.
[Show abstract][Hide abstract] ABSTRACT: The adsorption of an antiglutamate dehydrogenase (Anti-GDH) antibody on different surfaces was studied to probe its orientation and bioactivity. Three different situations were investigated: physisorption on a −COOH-terminated thiols self-assembled monolayer (SAM) on gold, covalent grafting on the same SAM using NHS-EDC activation, and physisorption on a −CH3 SAM. The orientation of the antibody was investigated combining time-of-flight secondary ion mass spectrometry and principal component analysis. Several orientations are proposed for each case and compared to the results of biorecognition measurements with the antigen (GDH). At each step, protein layers were characterized ex-situ with polarization-modulated infrared reflection absorption spectroscopy and in situ (i.e., in the liquid phase) with quartz crystal microbalance with dissipation monitoring. Biorecognition measurements showed interesting correlations with proposed protein orientations. The role of hydrophobic and/or electrostatic interactions and that of covalent bonding are discussed to underline the influence of the orientation on the bioactivity of adsorbed Anti-GDH.
The Journal of Physical Chemistry C 01/2014; 118(4):2085–2092. DOI:10.1021/jp410845g · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: With the recent developments in secondary ion mass spectrometry (SIMS), it is now possible to obtain molecular depth profiles and 3D molecular images of organic thin films, i.e. SIMS depth profiles where the molecular information of the mass spectrum is retained through the sputtering of the sample. Several approaches have been proposed for "damageless" profiling, including the sputtering with SF5(+) and C60(+) clusters, low energy Cs(+) ions and, more recently, large noble gas clusters (Ar500-5000(+)). In this article, we evaluate the merits of these different approaches for the in depth analysis of organic photovoltaic heterojunctions involving poly(3-hexylthiophene) (P3HT) as the electron donor and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as the acceptor. It is demonstrated that the use of 30 keV C60(3+) and 500 eV Cs(+) (500 eV per atom) leads to strong artifacts for layers in which the fullerene derivative PCBM is involved, related to crosslinking and topography development. In comparison, the profiles obtained using 10 keV Ar1700(+) (∼6 eV per atom) do not indicate any sign of artifacts and reveal fine compositional details in the blends. However, increasing the energy of the Ar cluster beam beyond that value leads to irreversible damage and failure of the molecular depth profiling. The profile qualities, apparent interface widths and sputtering yields are analyzed in detail. On the grounds of these experiments and recent molecular dynamics simulations, the discussion addresses the issues of damage and crater formation induced by the sputtering and the analysis ions in such radiation-sensitive materials, and their effects on the profile quality and the depth resolution. Solutions are proposed to optimize the depth resolution using either large Ar clusters or low energy cesium projectiles for sputtering and/or analysis.
The Analyst 09/2013; 138(22). DOI:10.1039/c3an01035j · 4.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract Biomolecule adsorption is the first stage of biofouling. The aim of this work was to reduce the adsorption of proteins on stainless steel (SS) and titanium surfaces by modifying them with a poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO triblock copolymer. Anchoring of the central PPO block of the copolymer is known to be favoured by hydrophobic interaction with the substratum. Therefore, the surfaces of metal oxides were first modified by self-assembly of octadecylphosphonic acid. PEO-PPO-PEO preadsorbed on the hydrophobized surfaces of titanium or SS was shown to prevent the adsorption of bovine serum albumin (BSA), fibrinogen and cytochrome C, as monitored by quartz crystal microbalance (QCM). Moreover, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry were used to characterize the surfaces of the SS and titanium after competitive adsorption of PEO-PPO-PEO and BSA. The results show that the adsorption of BSA is well prevented on hydrophobized surfaces, in contrast to the surfaces of native metal oxides.
[Show abstract][Hide abstract] ABSTRACT: In the present study, the feasibility of synthesizing chlorinated films by a dielectric barrier discharge at atmospheric pressure is assessed. Two different liquid monomers (hexachlorobuta-1,3-diene C4Cl6 and 1,1,1,2-tetrachloroethane C2H2Cl4) are tested and results show that organic coatings rich in chlorine can be deposited. The correlation and complementarity of water contact angle, X-ray photoelectron spectroscopy, secondary ion mass spectrometry and ellipsometry techniques have provided information to compare the properties of the perchlorinated layers built up from monomers with different Cl/C ratios and hydrogen concentrations. The bond dissociation energies of C–Cl2, C–Cl and C–C/Cdouble bond; length as m-dashC/C–H are used to provide an explanation for the differences in films structure recorded by X-ray photoelectron spectroscopy and secondary ion mass spectrometry. Finally, dynamic-secondary ion mass spectrometry complemented by ellipsometry is used to calculate a deposition rate ranging from 40 to 70 nm/min depending on the plasma conditions. These measurements also show a good homogeneity of the film throughout its thickness.
[Show abstract][Hide abstract] ABSTRACT: The adsorption of a globular protein on chemically well controlled surfaces was investigated in order to correlate its orientation to the surface properties. To this end, three different alkyl thiols, differing by their end group (−COOH, −CH3, and −NH2), were used to build up self-assembled monolayers (SAMs) on gold substrates. β-Lactoglobulin (βLG) was then adsorbed on these SAMs by immersion in a phosphate buffer solution. The surface modification with alkyl thiols and the subsequent adsorption of proteins were characterized ex situ by polarization modulated infrared reflection–absorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). The adsorption behavior of proteins was also monitored in situ using quartz crystal microbalance with dissipation measurements (QCM-D). Direct evidence regarding the protein orientation in the adsorbed state was obtained by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). Principal component analysis (PCA), performed on the ToF-SIMS results, enables to separate the samples and shows that the proteins display different distributions of amino acids at the surface depending on the conditioning thiol layer. Our results revealed that the adsorption mode of the protein is influenced by the thiol end groups, and specific orientations of the protein on the surface are proposed for the different substrates.
The Journal of Physical Chemistry C 05/2013; 117(22):11569–11577. DOI:10.1021/jp311964g · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mesoporous Re–Si–Al, Re–Al, and Re–Si mixed oxides were obtained via a one-step non-hydrolytic sol–gel route followed by calcination. The texture and surface properties of the resulting catalysts were characterized by a combination of EDX, XRD, N2-physisorption, XPS, ToF-SIMS, and NH3-TPD. The loss of rhenium during calcination, the texture and the acidity of the catalysts depended on their composition. Migration of rhenium toward the surface occurred during the calcination treatment, as evidenced by XPS and ToF-SIMS. After calcination, ToF-SIMS showed the presence of well-dispersed ReOx surface species. The influence of the composition of Re–Si–Al catalysts on their performances in the cross-metathesis of ethene and butene to propene was investigated. The specific activity of the Re–Si–Al catalysts was much higher than that of Re–Al catalysts, whereas the Re–Si sample was not active. The best Re–Si–Al catalysts displayed excellent specific activities (up to 45 mmol g−1 h−1) and apparent TOF values (98 × 10−3 s−1).
Journal of Catalysis 05/2013; 301:233-241. DOI:10.1016/j.jcat.2013.02.016 · 6.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study focuses on the microscopic modeling of 0–25 keV Bi1–3–5 and C60 cluster impacts on three different targets (Au crystal, adsorbed Au nanoparticle, and organic solid), using molecular dynamics simulations, and on the comparison of the calculated quantities with recent experimental results, reported in the literature or obtained in our laboratory. The sputtering statistics are reported, showing nonlinearity of the sputtering yields with the number of cluster atoms at the same incident velocity for Bi1–5 bombardment. They are compared to experiments (especially for the organic target), and the microscopic explanation of the observations is analyzed. The results show that the respective behaviors and performances of the different projectiles are strongly dependent on the target, with clusters of heavy Bi atoms being more efficient at sputtering gold and, conversely, fullerene clusters inducing the largest sputtering yields of the organic material (mass matching). For organic targets, some important and novel conclusions of this work are the following: (i) The increase of the sputtering yield when going from Bi atoms to Bi clusters is insufficient to explain the much larger increase of characteristic ion yields, suggesting a projectile-dependent ionization probability. (ii) The extent of molecular fragmentation follows the order of Bi > Bi3 > Bi5 > C60, that is, softer emission with larger clusters. (iii) Even 5–10 keV Bi atoms create collective molecular motions and craters in the polymeric solid, though the collision cascades are rather dilute. Finally, a second series of simulations performed at low energies predict that 0.1–1 keV Bin clusters should not provide better results for sputtering and depth profiling than isoenergetic single atoms.
The Journal of Physical Chemistry C 02/2013; 117(6):2740–2752. DOI:10.1021/jp308411r · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Multi-walled carbon nanotubes (MWCNT) and nanofibers (CNF) have been functionalized at their surfaces with chelating phosphine (PPh2) and ammonium (NMe3+) groups, as anchoring sites for metal complexes. The surface functionalization has been monitored by XPS, elemental analyses, N2 physisorption and/or SEM surface morphology analysis at each step. Bimetallic Fe–Co nanoparticles from two different starting cluster complexes, [HFeCo3(CO)12] (1) and (NEt4)[FeCo3(CO)12] (2), have been deposited onto the surfaces of the functionalized MWCNT and CNF as well as their pristine forms for comparison. The samples have been fully characterized before and after thermal treatment. The obtained nanoparticles were shown by TEM to be better dispersed and of smaller size on functionalized than on pristine supports. Magnetic characterization revealed blocked superparamagnetic Fe–Co nanoparticles together with paramagnetic ions on CNF as well as MWCNT.
[Show abstract][Hide abstract] ABSTRACT: A growing number of nano-objects such as nanotubes, capsules or beads are being developed for various biological and medical applications. In particular, the use of polymer templates for the synthesis of nanomaterials, using layer-by-layer assembly, has become a method of choice due to its simplicity and versatility in shapes and dimensions. However, chemical characterisation of these nano-objects still remains challenging. Here, we report the use of ToF-SIMS, especially in the imaging mode, for the characterisation of collagen-based nano- and microtubes deposited on surfaces, with a view to applications in biomaterials science.
The classical univariate or multivariate Principal Component Analysis (PCA) spectral data treatments do not display any significant differences between the nanotubes with different layer sequences (protein-polymer or polymer-protein). However, the layer sequences are clearly differentiated by the ToF-SIMS images acquired at high lateral resolution (0.3 µm), combined with high mass resolution (m/Δm > 5000 @ 29 m/z), because of the complexity of the protein spectral pattern. These results highlight the importance of imaging for chemical analysis of nanoparticles-coated samples. This study has particular relevance for nanoscale imaging of biointerfaces. Copyright