[Show abstract][Hide abstract] ABSTRACT: We describe an infrared multispectral imaging spectrometer capable of monitoring up to 76,800 spectra in less than 3 min. In this article, measurements collected using this set-up are presented and discussed, emphasizing the resolution (spatial and temporal), accuracy and capabilities of the instrument. Finally, some applications of multispectral imaging are presented.
[Show abstract][Hide abstract] ABSTRACT: New 2-6 wt% RuO2/ZnO heterojunction nanocatalysts were synthesized by a straightforward two-step procedure. They were composed of a porous network of aggregated 25-nm wurtzite ZnO nanocrystallites modified with RuO2 and showed enhanced light absorption in the visible region due to surface plasmon resonance. In order to investigate the energetic structure of the photocatalyst XPS core line and valence band spectra of in-situ in UHV prepared heterointerfaces were compared to results obtained from the particles. The shift of Zn 2p3/2 and O 1s core level spectra were determined to be at least 0.80 ± 0.05 eV for the in situ prepared heterojunction whereas it was found to be 0.40 ± 0.05 and 0.45 ± 0.05 eV, respectively in the photocatalysts. The different values were ascribed to the reduced size of the particles and the different measurability of band bending at the interface of the heterojunction RuO2/ZnO compared to the nanoparticles. The RuO2/ZnO photocatalysts showed higher photocatalytic activity and recyclability than pure ZnO for the degradation of various dyes under UV light irradiation due to vectorial charge separation of photogenerated electrons and holes resulting from internal electric field, the ruthenium oxide acting as a quasi-metallic contact.
Full-text · Article · Jan 2015 · Physical Chemistry Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: Background
Illuminated manuscripts are complex multi-layer and multi-material objects. To this difficulty, from the analytical point of view, is added the impossibility of removing samples from these paintings for the study of their materials and techniques. There are relatively few analytical methods that satisfy these constraints as the availability of non-invasive techniques adapted to painted manuscripts is limited and mainly focused on the characterization of inorganic compounds. In the context of a research project on the analytical study of the forty miniatures in the Marcadé collection (Treasury of the Saint-André Cathedral of Bordeaux, XIII to XVI century), the potential of two non-invasive methods, hyperspectral imaging (HSI) and spectrofluorimetry is explored.
The methodological development of these techniques as well as preliminary tests on miniatures recreated according to medieval recipes and materials, allowed the validation of the analytical parameters and the creation of a database of reference spectra (parchments, pigments, binders). Hyperspectral imaging associates reflectance spectra with each pixel of the image and treats the signal received in various wavelengths. The characteristics of the spectral signal in VIS range or NIR are used to get an identification and a localization of the components. It allows the study of the entire image and offers lots of ways to work: comparison of spectra, mapping, principal component analyses and false color images. Spectrofluorimetry is a sensitive method which gives information on fluorescent organic compounds under UV or visible light. Emission and excitation spectra of five red pigments in binding media have been collected. These methods were compared with X-ray fluorescence spectrometry for the qualitative analysis and mapping of the inorganic elements in a facsimile which had been purposely reproduced by an illumination painter who worked with original medieval recipes for the sake of developing the present study.
The combination of all these techniques allows good identification of all the materials used on an illuminated manuscript. The pertinent selection of the wavelengths used with the HSI system and a preliminary database and study of materials under UV and white light is described in this paper
[Show abstract][Hide abstract] ABSTRACT: Probing specific RNA sequences is an issue of major significance for which fluorescence dominates most of the investigation strategies and relies heavily on the use of specific labels. In this paper, we report the detection by SERS (surface-enhanced Raman scattering) of unlabeled model purified oligonucleotides RNA polyadenosine (5′-AAAAAAAAAA-3′) and polycytosine (5′-CCCCCCCCCC-3′) combining silver nanoparticles as enhancing surfaces with microfluidic platforms to control species movement and the aggregation state of the nanoparticles, which is critical for the sensitivity. Two types of microfluidic platforms have been evaluated and compared: one based on laminar streams and the other involving flowing droplets acting as chemical reactors. Both platforms provide homogeneous and controlled mixing conditions of nanoparticles with oligonucleotides: laminar streams induce mixing driven by diffusion, whereas droplets permit fast and efficient mixing through internal fluid recirculation and prevent channel clogging by nanoparticles. We demonstrate that in both cases, the bases can be detected selectively. In the droplet microfluidic system, the Raman maximum enhancement is localized in the center of the droplet and observed after a certain period of mixing time that appears specific for each base, after droplet formation. It appears to be a highly promising approach for probing unlabeled nucleotides using SERS.
Full-text · Article · Jun 2014 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: Polymeric bulk heterojunction (BHJ) organic solar cells represent one of the most promising technologies for renewable energy with a low fabrication cost. Control over BHJ morphology is one of the key factors in obtaining high-efficiency devices. This review focuses on formulation strategies for optimizing the BHJ morphology. We address how solvent choice and the introduction of processing additives affect the morphology. We also review a number of recent studies concerning prediction methods that utilize the Hansen solubility parameters to develop efficient solvent systems. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.
No preview · Article · Jun 2014 · Journal of Photonics for Energy
[Show abstract][Hide abstract] ABSTRACT: The effects of various fluoride fluxes on the crystallization of blue phosphor BaMgAl10O17:Eu2+ were characterized using a wide panel of experimental methods. LiF appeared as the most efficient, with a significant increase of the photoluminescence yield under excitation at 280 nm. Besides, the recrystallization resulted in a redistribution of the dopant among the three crystallographic sites, leading to a strong increase of the excitation in the near-UV domain. This allowed the emission to increase by 40 % under a 400 nm irradiation, typically of interest for possible LED-blue phosphor systems. At last, the shaping into hexagonal single crystals allowed both a reduction of the thermal degradation under air, and the discovery of a novel regeneration process at moderate temperature.
No preview · Article · Jun 2014 · Key Engineering Materials
[Show abstract][Hide abstract] ABSTRACT: In bulk heterojunction (BHJ) polymeric organic solar cells (OSCs), the use of processing additives in the material formulation has emerged as a promising, cost-effective, and widely applicable method for optimizing the phase separation between the donor (D) and acceptor (A) materials, thus increasing their efficiency. So far, however, there has been no systematic approach for identifying suitable processing additives for a given D:A system. A method based on the Hansen solubility parameters (HSPs) is proposed for guiding the selection of processing additives for a given D:A combination. The method is applied to the archetypical poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) system. The HSPs of these materials are determined and used to define a set of numerical criteria that need to be satisfied by a processing additive in order for it to be effective in realizing a higher efficiency OSC. Applying the selection criteria results in the identification of three novel processing additives. OSCs made of these formulations demonstrate an increase in their short-circuit current density (JSC) and power conversion efficiency (PCE). These results demonstrate the efficiency of these novel processing additives and show that the HSPs represent a useful tool to determine and explore new types of processing additives for BHJ-OSCs.
[Show abstract][Hide abstract] ABSTRACT: Double-stranded (ds) DNA of a λ-phage virus are combed on octadecyltrichlorosilane (OTS)-modified borosilicate glass substrates and investigated by means of tip-enhanced Raman spectroscopy (TERS) using tips coated with an Ag/Au bilayer. Owing to an enhancement factor higher than 6 ×102 and a lateral spatial resolution better than 9 nm (which is below the size of the tip apex radius), cross-sections of nanowire-shaped thin DNA bundles can be spatially resolved. TER spectra reveal vibrational modes typical of DNA nucleobases and backbone, as confirmed by confocal Raman measurements carried out on dense stacks of DNA strands. While the TER signature of nucleobases is congruent with observations in single-stranded (ss) DNA,
additional modes tied to the DNA backbone can be discerned in ds DNA. TERS enables ss and ds DNA samples to be distinguished from each other and hence can be exploited for the detection of DNA hybridization. Moreover, no TER contribution of the OTS layer appears, suggesting that functionalized DNA strands could be studied without spectral perturbation from the substrate. This work paves the way toward the nanoscale spectral study of organized DNA-based nanostructures.
Full-text · Article · Jan 2014 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: Processing additives are widely used to increase the efficiency of solution processed organic solar cells. We use the Hansen solubility parameters (HSPs) to investigate novel processing additives. The HSPs predict pyrrolidinone derivatives to be efficient processing additives for OSC systems based on poly(3-hexylthiophene)/[6,6]-phenyl-C61- butyric acid methyl ester (P3HT/PCBM). Two pyrrolidinone derivatives are identified: 1-methyl-2-pyrrolidinone and 1- benzyl-2-pyrrolidinone. The processing additives are introduced with various concentrations in the formulation of P3HT and PCBM solution. The electrical characterizations show that the two processing additives significantly increase the short circuit current and thus the power conversion efficiency of the OSCs. The results thus highlight HSPs as an effective and relatively straightforward tool that can be employed to optimize OSC morphology from a theoretical standpoint. Such a tool will be invaluable for identifying additives for novel high efficiency polymer species as they are synthesized, and thus to streamline the device fabrication and device optimization process.
No preview · Article · Jan 2014 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Thanks to infrared thermography, we have studied the mechanisms of CO 2 capture by solid adsorbents (CO2 capture via gas adsorption on various types of porous substrates) to better understand the physico-chemical mechanisms that control CO2-surface interactions. In order to develop in the future an efficient process for post-combustion CO 2 capture, it is necessary to quantify the energy of adsorption of the gas on the adsorbent (exothermic process). The released heat (heat of adsorption) is a key parameter for the choice of materials and for the design of capture processes. Infrared thermography is used, at first approach, to detect the temperature fields on a thin-layer of adsorbent during CO2 adsorption. An analytical heat transfer model was developed to evaluate the adsorption heat flux and to estimate, via an inverse technique, the heat of adsorption. The main originality of our method is to estimate heat losses directly from the heat generated during the adsorption process. Then, the estimated heat loss is taken for an a posteriori calculation of the adsorption heat flux. Finally, the heat of adsorption may be estimated. The interest in using infrared thermography is also its ability to quickly change the experimental setup, for example, to switch from the adsorbent thin-layer to the adsorbent bed configuration. We present the first results tempting to link the thin-layer data to the propagation speed of the thermal front in a millifluidics adsorption bed, also observed by IR thermography.
Full-text · Article · Jan 2014 · Mechanics and Industry
[Show abstract][Hide abstract] ABSTRACT: Thermal degradation of blue phosphor BAM:Eu2 + under air is investigated using XPS, XRD, EPR and photoluminescence (PL) in order to analyze the loss of intensity in terms of modifications of the dopant distribution in the crystal cell and between crystal bulk and surface. This study reveals the key role played by oxidation-driven 2D diffusion of europium and barium, that results in important concentration gradients and makes degradation strongly dependent on both microstructure and cooling speed. Also based upon cation mobility, a possible regeneration effect is evidenced at moderate temperature. Flux treatments, known to increase the intensity of photoluminescence, also appear to reduce thermal degradation by lowering specific surface; they also enhance the regeneration process by forming extended single-crystal domains conducive to cation diffusion.
No preview · Article · Dec 2013 · Solid State Ionics
[Show abstract][Hide abstract] ABSTRACT: In the aim of understanding the relations between the spectroscopic properties of blue phosphor BaMgAl10O17:Eu2+ and its crystal structure, microstructure and chemical composition, three fluoride fluxes (LiF, MgF2 and NH4F) have been added before final thermal treatment and their effect analyzed. LiF changes the polycrystalline and spherical grains into hexagonal platelets without significant cations exchange and improves the luminescence. NH4F and MgF2 only have a limited effect, the former because of its low point of decomposition, the latter because of the formation of spurious MgAl2O4 that reduces the luminescence. In a general way, re-crystallization results in variations of the dopant distribution between the three host sites of the structure. Chromaticity is only faintly affected, but important variations of the absorption and excitation spectra are observed, allowing a strong increase of photoluminescence intensity under near-UV excitation.
No preview · Article · Aug 2013 · Materials Research Bulletin
[Show abstract][Hide abstract] ABSTRACT: The role of carbon dioxide on the climate change and the depletion of fossil resources prompt to develop new and original approaches to limit CO2 emissions through its capture or its utilization. The simplest idea, before any recycling of CO2, consists in fixing it in a reversible way at the surface of solid materials.
This paper describes the research made by a consortium of four laboratories in order to characterize the parameters of CO2 adsorption on various samples (rare earth oxides, carbon materials, grafted silica) and guide the search for new performing materials. Samples are tested via in situ and coupled experiments (thermometry, infrared spectroscopy), mimicking the capture of CO2 by an adsorption column. The access to a temperature field by infrared thermometry will allow the total analysis of industrial process mock-up.
Full-text · Article · Jan 2013 · L'Actualité chimique
[Show abstract][Hide abstract] ABSTRACT: Nanoporous SnO2-ZnO heterojunction nanocatalyst was prepared by a straightforward two-step procedure involving, first, the synthesis of nanosized SnO2 particles by homogeneous precipitation combined with a hydrothermal treatment and, second, the reaction of the as-prepared SnO2 particles with zinc acetate followed by calcination at 500 degrees C. The resulting nanocatalysts were characterized by X-ray diffraction (XRD), FTIR, Raman, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption desorption analyses, transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectroscopy. The SnO2-ZnO photocatalyst was made of a mesoporous network of aggregated wurtzite ZnO and cassiterite SnO2 nanocrystallites, the size of which was estimated to be 27 and 4.5 nm, respectively, after calcination. According to UV visible diffuse reflectance spectroscopy, the evident energy band gap value of the SnO2 ZnO photocatalyst was estimated to be 3.23 eV to be compared with those of pure SnO2, that is, 3.7 eV, and ZnO, that is, 3.2 eV, analogues. The energy band diagram of the SnO2 ZnO heterostructure was directly determined by combining XPS and the energy band gap values. The valence band and conduction band offsets were calculated to be 0.70 0.05 eV and 0.20+/-0.05 eV, respectively, which revealed a type-II band alignment. Moreover, the heterostructure SnO2 ZnO photocatalyst showed much higher photocatalytic activities for the degradation of methylene blue than those of individual SnO2 and ZnO nanomaterials. This behavior was rationalized in terms of better charge separation and the suppression of charge recombination in the SnO2 ZnO photocatalyst because of the energy difference between the conduction band edges of SnO2 and ZnO as evidenced by the band alignment determination. Finally, this mesoporous SnO2-ZnO heterojunction nanocatalyst was stable and could be easily recycled several times opening new avenues for potential industrial applications.
No preview · Article · Jun 2012 · Inorganic Chemistry
[Show abstract][Hide abstract] ABSTRACT: Ionic liquids based on three‐membered ring aziridinium cations have been synthesized for the first time using a straightforward synthetic route. N‐butyl‐N‐methylaziridinium bis(trifluoromethanesulfonyl)imide, N‐propyl‐N‐ethylaziridinium bis(trifluoromethanesulfonyl)imide, N‐butyl‐N‐[2‐(2‐methoxyethoxy)ethyl]aziridinium bis(trifluoromethanesulfonyl)imide, N‐butyl‐N‐methylaziridinium dicyanamide, and N‐butyl‐N‐ethylaziridinium dicyanamide were thus obtained in good yields and satisfactory purity and fully characterized.
No preview · Article · May 2012 · Journal of Heterocyclic Chemistry
[Show abstract][Hide abstract] ABSTRACT: Surface-enhanced Raman scattering (SERS)-based microfluidic platforms are investigated to optimize the detection of biomolecules using silver nanoparticles. The method is established using pefloxacin (an antibacterial agent) as a probe. We first monitor the continuous SERS signal of a 10–5 M pefloxacin solution diffusing continuously into a silver nanoparticle stream across the shared interface separating the two-phase, segmented microfluidic laminar flow system. Diffusion of the pefloxacin adsorbate begins immediately after the two streams merge, generating silver aggregates and producing a huge enhancement of the Raman bands of pefloxacin. We show that the evolution of the SERS signal presents a diffusion-like behavior, whose dynamics can be easily monitored as the signal measured in the flow-wise direction is proportional to the reaction time. Finally, we demonstrate that it is possible to optimize SERS intensity spectra by adding a controlled amounts of chloride ions through a side channel to control silver particles aggregation and further enhance Raman scattering.
No preview · Article · Feb 2012 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: Accurate chemical and structural characterization of free-standing zinc oxide (ZnO) and hematite (α-Fe2O3) nanorods has been carried out using an AFM/Raman correlative technique under polarized light. ZnO nanorods are found to be wurtzite-type single crystalline objects homogeneous in composition and grown along their principal axis of symmetry. Hematite specimens are rhombohedral corundum-type single crystals grown along a direction orthogonal to their principal axis of symmetry and exhibiting structural disorder. Certain hematite nanorods turn out to be very sensitive to laser heating. These studies reveal the high potential of the coupled AFM/Raman technique to examine the properties of these promising nanomaterials.
Full-text · Article · Sep 2011 · Chemical Physics Letters
[Show abstract][Hide abstract] ABSTRACT: Surface-Enhanced Raman Spectroscopy (SERS) was performed to detect label-free RNA. We defined conditions which make it possible to probe the four bases of RNA, in single strands of polyadenosine (pA), polyuridine (pU), polycytosine (pC) and polyguanosine (pG). We therefore present below a quantitative analysis of mixtures of non-hybridized single strands, based on the deconvolution of the SERS mixture spectrum into the relative contributions of the SERS spectra of each constituent.
Full-text · Article · Jul 2011 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: Unprecedented stable hybrid materials with cyclopentadienyl-titanium bonds have been obtained from the hydrolysis of suitable precursors. Their inorganic network is not fully condensed and they show variable short-range self-organizations, the type of which depends on the shape of the ligands.
No preview · Article · Mar 2011 · Chemical Communications