Boosting Gas-Phase TiO2 Photocatalysis with Weak Electric Field Strengths of Volt/Centimeter.

Among semiconductor nanomaterials, titanium dioxide is at the forefront of heterogeneous photocatalysis, but its catalytic activity greatly suffers from the loss of photoexcited charge carriers through deleterious recombination processes. Here, we investigate the impact of an external electric field (EEF) applied to conventional P25 TiO2 nanopowder with or without Au nanoparticles (NPs) to circumvent this issue. The study of two redox reactions in the gas phase, water splitting and toluene degradation, reveals an enhancement of the photocatalytic activity with rather modest electric fields of a few volt/centimeters only. Such an improvement arises from the electric-field-induced quenching of the green emission in anatase, allowing the photoexcited charge carriers to be transferred to the adsorbed reactants instead of pointless radiative recombinations. Applying an EEF across a trap-rich metal oxide material, such as TiO2, which, when impregnated with Au NPs, leads, respectively, to 12- and 6-fold enhancements in the production of hydrogen and the oxidation of toluene for an electric field of 8 V/cm, without any electrolysis, is a simple and elegant strategy to meet higher photocatalytic efficiencies.

Direct photodegradation of internally mixed sodium chloride and malonic acid single aerosols: Impact of the photoproducts on the hygroscopic properties of the particles.

Sea-salt aerosols (SSA) are one of the key natural aerosols in our atmosphere, consisting predominantly of sodium chloride (NaCl). Throughout their atmospheric transport, these aerosols undergo complex internal mixing, giving rise to a rich variety of inorganic and organic species, including dicarboxylic acids. This study investigates firstly the composition and deliquescence properties of coarse particles containing pure malonic acid (MA2, CH2(COOH)2) and internally mixed NaCl and MA2, by means of an acoustic levitation system coupled with a Raman microspectrometer. Secondly, we report here the first experimental observation and characterization of the products arising from photochemical reactions under UV-Visible irradiation (338 ≤ λ ≤ 414 nm) in the absence of an oxidant under acoustic levitation conditions in MA2 and NaCl/MA2 aerosols. Furthermore, the impact of photodegradation on the hygroscopic properties of these particles is examined. We confirmed the irreversible formation of monosodium malonate (NaMA, HOOCCH2COONa), which coexists with NaCl or MA2 on non-irradiated particles. We also demonstrated the formation of oxalic acid (OA2, HOOC-COOH) within irradiated MA2 droplets and the appearance of glyoxylic acid (GlyA, HCOCOOH) in NaCl containing droplets. The photolysis process exerts a marked effect on the hygroscopic properties of the particles, resulting in a shift in deliquescence transitions toward higher relative humidity (RH) values. This study contributes to the understanding of the intricate physicochemical processes involved in SSA during their atmospheric transport. Likewise, this work sheds light on the impacts of these types of aerosols on cloud formation and climate change.

Assessment of Essential Information in the Fourier Domain to Accelerate Raman Hyperspectral Microimaging.

In the context of multivariate curve resolution (MCR) and spectral unmixing, essential information (EI) corresponds to the most linearly dissimilar rows and/or columns of a two-way data matrix. In recent works, the assessment of EI has been revealed to be a very useful practical tool to select the most relevant spectral information before MCR analysis, key features being speed and compression ability. However, the canonical approach relies on the principal component analysis to evaluate the convex hull that encapsulates the data structure in the normalized score space. This implies that the evaluation of the essentiality of each spectrum can only be achieved after all the spectra have been acquired by the instrument. This paper proposes a new approach to extract EI in the Fourier domain (EIFD). Spectral information is transformed into Fourier coefficients, and EI is assessed from a convex hull analysis of the data point cloud in the 2D phasor plots of a few selected harmonics. Because the coordinate system of a phasor plot does not depend on the data themselves, the evaluation of the essentiality of the information carried by each spectrum can be achieved individually and independently from the others. As a result, time-consuming operations like Raman spectral imaging can be significantly accelerated exploiting a chemometric-driven (i.e., based on the EI content of a spectral pixel) procedure for data acquisition and targeted sampling. The usefulness of EIFD is shown by analyzing Raman hyperspectral microimaging data, demonstrating a potential 50-fold acceleration of Raman acquisition.

Comparative Analysis of G-Layers in Bast Fiber and Xylem Cell Walls in Flax Using Raman Spectroscopy.

In a response to gravitropic stress, G-layers (gelatinous layers) were deposited in xylem cell walls of tilted flax plants. G-layers were produced in both tension wood (upper side) as expected but were also observed in opposite wood (lower side). Raman spectral profiles were acquired for xylem G-layers from the tension and opposite side as well as from the G-layer of bast fibers grown under non-tilted conditions. Statistical analysis by principal component analysis (PCA) and partial least square-discriminant analysis (PLS-DA) clearly distinguished bast fiber G-layers from xylem G-layers. Discriminating bands were observed for cellulose (380-1150-1376 cm-1), hemicelluloses (517-1094-1126-1452 cm-1) and aromatics (1270-1599-1658 cm-1). PCA did not allow separation of G-layers from tension/opposite-wood sides. In contrast, the two types of xylem G-layers could be incompletely discriminated through PLS-DA. Overall, the results suggested that while the architecture (polymer spatial distribution) of bast fibers G-layers and xylem G-layers are similar, they should be considered as belonging to a different cell wall layer category based upon ontogenetical and chemical composition parameters.

Raman spectroscopy mapping of changes in the organization and relative quantities of cell wall polymers in bast fiber cell walls of flax plants exposed to gravitropic stress.

Flax is an important fiber crop that is subject to lodging. In order to gain more information about the potential role of the bast fiber cell wall in the return to the vertical position, 6-week-old flax plants were subjected to a long-term (6 week) gravitropic stress by stem tilting in an experimental set-up that excluded autotropism. Stress induced significant morphometric changes (lumen surface, lumen diameter, and cell wall thickness and lumen surface/total fiber surface ratio) in pulling- and opposite-side fibers compared to control fibers. Changes in the relative amounts and spatial distribution of cell wall polymers in flax bast fibers were determined by Raman vibrational spectroscopy. Following spectra acquisition, datasets (control, pulling- and opposite sides) were analyzed by principal component analysis, PC score imaging, and Raman chemical cartography of significant chemical bonds. Our results show that gravitropic stress induces discrete but significant changes in the composition and/or spatial organization of cellulose, hemicelluloses and lignin within the cell walls of both pulling side and opposite side fibers.

First historical cements in France from Boulogne sur Mer: Investigations on 19th century's manufactured cement-based monuments.

The Boulogne-Sur-Mer area in the North of France is one of the cradles of the French cement industry (the other main one is Grenoble region due to Joseph Vicat's first cement works). From fast setting (Roman) to Portland, those cements were famous in France and have been used throughout the entire country. The main objective of this study is to give a preliminary insight of the type of binders used since there is currently few and scattered data on those specific structures and to assess the efficiency of traditional analytical techniques [X-ray diffraction (XRD), optical (OM) and scanning electron microscopy (SEM) observations, coupled with EDS analysis] used to differentiate natural and artificial cements.

Impact of the particle mixing state on the hygroscopicity of internally mixed sodium chloride-ammonium sulfate single droplets: a theoretical and experimental study.

Sodium chloride (NaCl) is the main constituent of sea-salt aerosols. During atmospheric transport, sea-salt aerosols can interact with gases and other particles including secondary aerosols containing ammonium sulfate ((NH4)2SO4). This paper reports on the deliquescence relative humidity (DRH) of internally mixed sodium chloride-ammonium sulfate (NaCl/(NH4)2SO4) coarse particles by means of an acoustic levitation system fitted with a confocal Raman microscope (CRM). The chemical composition and physical state of individual levitated particles of different initial NaCl mole fractions were monitored during the deliquescence cycle by CRM. Experimental results were compared to the data predicted by the thermodynamic model E-AIM (Extended-Aerosol Inorganics Model). We demonstrated that NH4Cl, Na2SO4 and NH4NaSO4·2H2O are formed in recrystallized particles and coexist with NaCl and (NH4)2SO4. All these products are randomly distributed within the particles. Deliquescence curves described two or three-stage phase transitions depending on the initial composition of the droplet. Significant discrepancies between the model and the laboratory experiments were observed for NaCl mole fractions varying between 0.40 and 0.77 due to a divergence between the predicted and the truly present products in the particles' solid fraction during the humidification cycle.

Enhancing Double-Beam Laser Tweezers Raman Spectroscopy (LTRS) for the Photochemical Study of Individual Airborne Microdroplets.

A new device and methodology for vertically coupling confocal Raman microscopy with optical tweezers for the in situ physico- and photochemical studies of individual microdroplets (Ø ≤ 10 µm) levitated in air is presented. The coupling expands the spectrum of studies performed with individual particles using laser tweezers Raman spectroscopy (LTRS) to photochemical processes and spatially resolved Raman microspectroscopy on airborne aerosols. This is the first study to demonstrate photochemical studies and Raman mapping on optically levitated droplets. By using this configuration, photochemical reactions in aerosols of atmospheric interest can be studied on a laboratory scale under realistic conditions of gas-phase composition and relative humidity. Likewise, the distribution of photoproducts within the drop can also be observed with this setup. The applicability of the coupling system was tested by studying the photochemical behavior of microdroplets (5 µm < Ø < 8 µm) containing an aqueous solution of sodium nitrate levitated in air and exposed to narrowed UV radiation (254 ± 25 nm). Photolysis of the levitated NaNO3 microdroplets presented photochemical kinetic differences in comparison with larger NaNO3 droplets (40 µm < Ø < 80 µm), previously photolyzed using acoustic traps, and heterogeneity in the distribution of the photoproducts within the drop.

Photodegradation of methyl thioglycolate particles as a proxy for organosulphur containing droplets.

Understanding the formation and transformation of sulphur-rich particles is of prime importance since they contribute to the global atmospheric sulphur budget. In this work, we performed a series of experiments on a photoactive organosulphur compound namely, methyl thioglycolate, as a model of an organosulphur species of marine origin. By investigating the photoproducts within levitated droplets, we showed that elemental sulphur (α-S8) and sulphate (SO42-) can be photochemically generated at the gas-liquid interface by heterogeneous interaction with gaseous O2 and H2O. These results demonstrate that the surface of levitated droplets facilitate the oxidation of methyl thioglycolate in the dark, while illumination is necessary to produce the oxidation in bulk experiments.

Hydrothermal synthesis of ZTO/graphene nanocomposite with excellent photocatalytic activity under visible light irradiation.

A facile and efficient one-step hydrothermal approach for the synthesis of Zn2SnO4 nanoparticles/reduced graphene oxide (ZTO/rGO) nanocomposites using zinc acetate, tin chloride and graphene oxide (GO) as precursors, and sodium hydroxide as reducing agent has been developed. This approach allows simultaneous reduction of GO and growth of spinel ZTO nanoparticles (NPs) on the rGO sheets. The morphology and microstructure characterizations of ZTO/rGO nanocomposites revealed that this method leads to close interfacial contact of ZTO NPs and rGO and efficient dispersion of ZTO NPs on the surface of rGO sheets. The photocatalytic activity of the ZTO/rGO nanocomposite was investigated for the reduction of rhodamine B under visible light irradiation. Compared to pure ZTO NPs, ZTO/rGO nanocomposite exhibited superior photocatalytic activity with a full degradation of rhodamine B within 15min. The enhanced photocatalytic performance of ZTO/rGO was mainly attributed to excellent electron trapping and effective adsorption properties of rGO.

Pushing back the limits of Raman imaging by coupling super-resolution and chemometrics for aerosols characterization.

The increasing interest in nanoscience in many research fields like physics, chemistry, and biology, including the environmental fate of the produced nano-objects, requires instrumental improvements to address the sub-micrometric analysis challenges. The originality of our approach is to use both the super-resolution concept and multivariate curve resolution (MCR-ALS) algorithm in confocal Raman imaging to surmount its instrumental limits and to characterize chemical components of atmospheric aerosols at the level of the individual particles. We demonstrate the possibility to go beyond the diffraction limit with this algorithmic approach. Indeed, the spatial resolution is improved by 65% to achieve 200 nm for the considered far-field spectrophotometer. A multivariate curve resolution method is then coupled with super-resolution in order to explore the heterogeneous structure of submicron particles for describing physical and chemical processes that may occur in the atmosphere. The proposed methodology provides new tools for sub-micron characterization of heterogeneous samples using far-field (i.e. conventional) Raman imaging spectrometer.

The interplay between the paracetamol polymorphism and its molecular structures dissolved in supercritical CO2 in contact with the solid phase: In situ vibration spectroscopy and molecular dynamics simulation analysis.

The aim of this paper is to characterize the distribution of paracetamol conformers which are dissolved in a supercritical CO2 phase being in equilibrium with their corresponding crystalline form. The quantum calculations and molecular dynamics simulations were used in order to characterize the structure and analyze the vibration spectra of the paracetamol conformers in vacuum and in a mixture with CO2 at various thermodynamic state parameters (p,T). The metadynamics approach was applied to efficiently sample the various conformers of paracetamol. Furthermore, using in situ IR spectroscopy, the conformers that are dissolved in supercritical CO2 were identified and the evolution of the probability of their presence as a functions of thermodynamic condition was quantified while the change in the crystalline form of paracetamol have been monitored by DSC, micro IR and Raman techniques. The DSC analysis as well as micro IR and Raman spectroscopic studies of the crystalline paracetamol show that the subsequent heating up above the melting temperature of the polymorph I of paracetamol and the cooling down to room temperature in the presence of supercritical CO2 induces the formation of polymorph II. The in situ IR investigation shows that two conformers (Conf. 1 and Conf. 2) are present in the phase of CO2 while conformer 3 (Conf. 3) has a high probability to be present after re-crystallization.

Microscopic interactions of the imidazolium-based ionic liquid with molecular liquids depending on their electron-donicity.

Microscopic interactions of an imidazolium-based ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C2mimTFSI), with dimethyl sulfoxide (DMSO), methanol (MeOH), and acetonitrile (AN) have been analyzed by means of Raman, attenuated total reflectance infrared (ATR-IR), (1)H and (13)C NMR spectroscopy techniques. The magnitude of the red-shift of the C(2)-H vibration mode of the imidazolium ring and the deshielding of the C(2)-H hydrogen and carbon atoms, compared with that of the other atoms of the ring or the anion, indicated a strong interaction between the C(2)-H hydrogen atom and the molecular liquids in the following order; DMSO ≫ MeOH > AN. This correlates with the order of the electron donicities of these molecular liquids which allows us to suggest a hydrogen bonding character of these interactions. The behavior of S= O vibration of DMSO as a function of the DMSO molar fraction xDMSO also suggested that DMSO molecules are stoichiometrically hydrogen-bonded with the three hydrogen atoms, C(2,4,5)-H, of the ring. In contrast, the hydrogen bonding between MeOH and the C(4,5)-H atoms is much weaker than that in DMSO. AN hardly forms hydrogen bonds with the C(4,5)-H atoms. Instead, AN molecules may interact with the imidazolium ring through the π-π interaction. The interactions between the imidazolium ring and the molecular liquids lead to the loosening of the TFSI anion from the cation; this correlates with both the blue-shift of the S=O stretching vibration of TFSI and the deshielding of the trifluoromethyl carbon atoms with an increase in the molar fraction of the molecular liquid xML. The latter is weak in the MeOH solutions, and may be explained by the possible hydrogen bonding of the MeOH hydroxyl group as an electron-acceptor with the TFSI anion. Furthermore, the organization of MeOH molecules around the ethyl and methyl groups of the cation is discussed in terms of the chemical shift of the hydrogen and carbon atoms in these groups as a function of xML.

Combined use of quantitative ED-EPMA, Raman microspectrometry, and ATR-FTIR imaging techniques for the analysis of individual particles.

In this work, quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA) (called low-Z particle EPMA), Raman microspectrometry (RMS), and attenuated total reflectance Fourier transform infrared spectroscopic (ATR-FTIR) imaging were applied in combination for the analysis of the same individual airborne particles for the first time. After examining individual particles of micrometer size by low-Z particle EPMA, consecutive examinations by RMS and ATR-FTIR imaging of the same individual particles were then performed. The relocation of the same particles on Al or Ag foils was successfully carried out among the three standalone instruments for several standard samples and an indoor airborne particle sample, resulting in the successful acquisition of quality spectral data from the three single-particle analytical techniques. The combined application of the three techniques to several different standard particles confirmed that those techniques provided consistent and complementary chemical composition information on the same individual particles. Further, it was clearly demonstrated that the three different types of spectral and imaging data from the same individual particles in an indoor aerosol sample provided richer information on physicochemical characteristics of the particle ensemble than that obtainable by the combined use of two single-particle analytical techniques.

The organization pattern of root border-like cells of Arabidopsis is dependent on cell wall homogalacturonan.

Border-like cells are released by Arabidopsis (Arabidopsis thaliana) root tips as organized layers of several cells that remain attached to each other rather than completely detached from each other, as is usually observed in border cells of many species. Unlike border cells, cell attachment between border-like cells is maintained after their release into the external environment. To investigate the role of cell wall polysaccharides in the attachment and organization of border-like cells, we have examined their release in several well-characterized mutants defective in the biosynthesis of xyloglucan, cellulose, or pectin. Our data show that among all mutants examined, only quasimodo mutants (qua1-1 and qua2-1), which have been characterized as producing less homogalacturonan, had an altered border-like cell phenotype as compared with the wild type. Border-like cells in both lines were released as isolated cells separated from each other, with the phenotype being much more pronounced in qua1-1 than in qua2-1. Further analysis of border-like cells in the qua1-1 mutant using immunocytochemistry and a set of anti-cell wall polysaccharide antibodies showed that the loss of the wild-type phenotype was accompanied by (1) a reduction in homogalacturonan-JIM5 epitope in the cell wall of border-like cells, confirmed by Fourier transform infrared microspectrometry, and (2) the secretion of an abundant mucilage that is enriched in xylogalacturonan and arabinogalactan-protein epitopes, in which the cells are trapped in the vicinity of the root tip.

Effect of stabilized iodized oil emulsion on experimentally induced hepatocellular carcinoma in rats.

PURPOSE: Previous studies have shown that the use of Lipiodol UltraFluid (LUF) emulsified with water leads to an increase in the tumoral uptake of iodine I 131-labeled LUF and reduced pulmonary uptake. Although emulsions containing LUF are currently used for chemoembolization of hepatocellular carcinomas (HCCs), this approach is impossible with intraarterial radiation therapy (RT) because of the problems of radiation protection linked to instability of the emulsions. The aims of this study were to develop stabilized emulsions of radiolabeled LUF of different particle sizes and viscosities and to study its biodistribution in rats with HCC. MATERIALS AND METHODS: An emulsifier made of polyethylene glycol and hydrogenated castor oil was used to stabilize emulsions containing water and technetium Tc 99m-labeled Super Six Sulfur LUF. The various emulsions were injected in the hepatic arteries of rats with HCC. Twenty-four hours after injection, the rats were killed and the liver, tumor, and lungs were removed to perform ex-vivo gamma-counting to quantify tumoral, hepatic, and pulmonary uptake. RESULTS: Emulsions of oil in water and water in oil of different viscosities (0.68-1.06 Pa.S) and particle size distributions (21-45 mum) were prepared and kept stable for more than 24 hours. Whatever the type of emulsion, the observed effect on tumoral uptake was the opposite of that expected. Indeed, a decrease in tumoral activity was observed (P < .05 in three of five cases) and a tendency toward increased pulmonary activity was observed (P < .05 in two of five cases) rather than any significant decrease. CONCLUSIONS: This study made it possible to develop emulsions of radiolabeled iodized oil that remain stable for more than 24 hours. However, studies of biodistribution in rats with HCC failed to demonstrate any improvement in tumoral targeting, but rather showed a decrease in tumoral uptake that renders this approach impractical for intraarterial radiolabeled iodized oil RT as well as for intraarterial iodized oil chemoembolization. These results may possibly be explained by the use of an emulsifier containing lipophilic and hydrophilic components that modify the properties of LUF.

188Re-SSS lipiodol: radiolabelling and biodistribution following injection into the hepatic artery of rats bearing hepatoma.

BACKGROUND: Although intra-arterial radiation therapy with 131I-lipiodol is a useful therapeutic approach to the treatment of hepatocellular carcinoma, various disadvantages limit its use. AIM: To describe the development of a method for the labelling of lipiodol with 188Re-SSS (188Re (S2CPh)(S3CPh)2 complex) and to investigate its biodistribution after injection into the hepatic artery of rats with hepatoma. METHODS: 188Re-SSS lipiodol was obtained after dissolving a chelating agent, previously labelled with 188Re, in cold lipiodol. The radiochemical purity (RCP) of labelling was checked immediately. The 188Re-SSS lipiodol was injected into the hepatic artery of nine rats with a Novikoff hepatoma. They were sacrificed 1, 24 and 48 h after injection, and used for ex vivo counting. RESULTS: Labelling of 188Re-SSS lipiodol was achieved with a yield of 97.3+/-2.1%. The immediate RCP was 94.1+/-1.7%. Ex vivo counting confirmed a predominantly hepatic uptake, with a good tumoral retention of 188Re-SSS lipiodol, a weak pulmonary uptake and a very faint digestive uptake. The 'tumour/non-tumoral liver' ratio was high at 1, 24 and 48 h after injection (2.9+/-1.5, 4.1+/-/4.1 and 4.1+/-0.7, respectively). CONCLUSIONS: Using the method described here, 188Re-SSS lipiodol can be obtained with a very high yield and a satisfactory RCP. The biodistribution in rats with hepatoma indicates a good tumoral retention of 188Re-SSS lipiodol associated with a predominant hepatic uptake, a weak pulmonary uptake and a very faint digestive uptake. This product should be considered for intra-arterial radiation therapy in human hepatoma.

On the characterization of disordered and heterogeneous carbonaceous materials by Raman spectroscopy.

The applicability of Raman spectroscopy to characterize disordered and heterogeneous carbonaceous materials (CM) is discussed, by considering both natural and synthetic CM. First, different analytical mismatches during the measurement are discussed and technical indications are provided in order to eliminate them. Second, the accuracy and relevance of the different parameters obtained by the decomposition of spectra by conventional fitting procedure, is reviewed. Lastly, a new Raman technique (Raman area mode microspectroscopy) giving an homogeneous repartition of power within a large laser beam is presented, this technique being powerful to study strongly heterogeneous CM and/or photosensitive samples.