Effect of dissolved salt on the anomalies of water at negative pressure

Adding salt to water at ambient pressure affects its thermodynamic properties. At low salt concentration, anomalies such as the density maximum are shifted to lower temperature, while at large enough salt concentration they cannot be observed any more. Here we investigate the effect of salt on an anomaly recently observed in pure water at negative pressure: the existence of a sound velocity minimum along isochores. We compare experiments and simulations for an aqueous solution of sodium chloride with molality around $1.2\,\mathrm{mol\,kg^{-1}}$, reaching pressures beyond $-100\,\mathrm{MPa}$. We also discuss the origin of the minima in the sound velocity and emphasize the importance of the relative position of the temperatures of sound velocity and density anomalies.Comment: 10 pages, 13 figures, 1 appendix. Added minor simulation detail

Photoluminescent Copper Nanoclusters in “Turn-Off/Turn-On” Sensing of Picric Acid/Hydrogen Peroxide

In this paper, we illustrate the synthesis, characterization, and application of a Bovine Serum Albumin-stabilized copper nanocluster (BSA@CuNCs)-based photoluminescence (PL) bifunctional sensor for the selective and rapid sensing of picric acid (PA) and hydrogen peroxide (H2O2). Blue-emitting copper nanoclusters were synthesized using one-pot synthesis at room temperature. The PL intensity of BSA@CuNCs was shown to be quenched (“Turn-off”) with an increase in the concentration of PA and intensified (“Turn-on”) with the addition of H2O2. The quenching of PL intensity of BSA@CuNCs was shown to be extremely selective and rapid towards PA. A linear decrease in the PL emission intensity of BSA@CuNCs was observed with a PA concentration in the range of 0–15 μM. An extremely low detection limit of 60 nM (3σ/k) was calculated. The as-prepared BSA@CuNCs also exhibited superior selectivity for PA detection in aqueous medium. The developed sensor was also utilized for the sensing of PA in natural water samples. The probe was found to be extremely sensitive towards the detection of H2O2. An increase in the PL intensity of BSA@CuNCs was seen with the addition of H2O2, with a detection limit of 0.11 μM

Brillouin spectroscopy of fluid inclusions proposed as a paleothermometer for subsurface rocks

International audienceAs widespread, continuous instrumental Earth surface air temperature records are available only for the last hundred fifty years, indirect reconstructions of past temperatures are obtained by analyzing "proxies". Fluid inclusions (FIs) present in virtually all rock minerals including exogenous rocks are routinely used to constrain formation temperature of crystals. The method relies on the presence of a vapour bubble in the FI. However, measurements are sometimes biased by surface tension effects. They are even impossible when the bubble is absent (monophasic FI) for kinetic or thermodynamic reasons. These limitations are common for surface or subsurface rocks. Here we use FIs in hydrothermal or geodic quartz crystals to demonstrate the potential of Brillouin spectroscopy in determining the formation temperature of monophasic FIs without the need for a bubble. Hence, this novel method offers a promising way to overcome the above limitations

Preparation of Functionalized Superparamagnetic Fe3O4@Dopamine@Metal Ions (Cu+,Ru2+) Nanocomposites and its Catalytic Applications

In this work, we present a simple method for the synthesis of metal ions stabilized on dopamine modified iron oxide nanoparticles (Fe3O4@DA@Mx+) and their catalytic applications in important organic transformation reactions. Two different metal ions (Cu+1 and Ru2+) are studied in this work. It is observed that both synthesized Fe3O4@DA@Cu+ and Fe3O4@DA@Ru2+ can effortlessly be separated from the reaction medium by positioning an external magnetic field. Dopamine, which is used as an anchor between Fe3O4 and metal ions, increases the solubility of catalyst in reaction medium and prevents leaching of metal ions from the catalyst surface. Here Fe3O4@DA@Cu+ is used in the synthesis of 1,2,3-triazole derivatives via azide-alkyne cycloaddition reactions and Fe3O4@DA@Ru2+ is used for transfer hydrogenation reaction of various aryl ketones. The Fe3O4@DA@Mx+ nanocomposite is characterized via powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), atomic absorption spectroscopy (AAS), thermogravimetric analysis (TGA) and vibrating-sample magnetometer (VSM). The Fe3O4@DA@Mx+ catalytic systems can be reused in the reaction mixture up to five times without significant loss in their catalytic activity.</p

Water-Soluble Photoluminescence <i>On–Off–On</i> Probe for Speedy and Selective Detection of Fluoride Ions

A CdTe QDs based new type of water-soluble switch <i>on–off–on</i> photoluminescence (PL) probe has been developed for specific detection of fluoride ions (F^–). Europium ions (Eu³⁺) stabilized by the carboxylic groups of 3-mercaptopropanoic acid (MPA) capped CdTe QDs result in quenching of PL (switch <i>off</i>) of QDs. PL is regained (switch <i>on</i>) with the addition of F^– due to the formation of EuF₃ as Eu³⁺ has higher bonding affinity with F^– compared to carboxylic acid groups. The quenching of the PL property of CdTe-MPA QDs toward Eu³⁺ and its regeneration in the presence of F^– is highly selective, sensitive (detection limit 5 ppm to 75 ppm), and prompt (less than 10 s). The technique has been successfully applied for the detection of HF vapors, which is actually an important issue from the industrial perspective. To the best of our knowledge, this is the first report of the use of one step synthesized water-soluble 3-MPA capped CdTe QDs, as a rapid, efficient, and most importantly selective photoluminescence <i>on–off–on</i> probe for fluoride ion detection

Blue phase III widening in CE6-dispersed surface-functionalised CdSe nanopa

The phase transition behaviour of the chiral CE6 liquid crystal with spherical surface-functionalised nanoparticles has been examined by means of high-resolution adiabatic scanning calorimetry and polarising microscopy. The addition of nanoparticles results in an essentially stabilised blue phase III. The phase diagram is displayed upon heating and cooling and the enthalpy changes involved in the conversion between the blue phases are determined. This method is prominent for the stabilisation of blue phase III, potentially useful for applications, especially if applied on liquid crystals that exhibit a blue phase III close to the ambient temperature.status: publishe

Different modulated structures of topological defects stabilized by adaptive targeting nanoparticles

It is demonstrated that interactions between nanoparticles and topological defects induce a twist-grain boundary phase in a chiral liquid crystal. The occurrence of this phase, the analogue of the Shubnikov phase in type-II superconductors, is driven by direct interactions between surface-functionalized CdSe quantum dots and screw dislocations. It is shown that, within an adaptive-defect-core-targeting mechanism, nanoparticles of appropriate size and functionalization adapt to qualitatively different cores of topological defects such as disclination lines and screw dislocations. This mechanism enables the effective reduction of the energetically costly, singular defect core volume, while the surrounding phase ordering remains relatively weakly affected. The findings suggest new pathways towards the controlled assembly of superstructures in diverse, symmetry-broken, condensed-matter systems, ranging from nanoparticle-decorated liquid crystals to superconductors.status: publishe

Electrical conductivity and glass formation in nitrile-functionalized pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids: chain length and odd–even effects of the alkyl spacer between the pyrrolidinium ring and the nitrile group

The electrical conductivity of a series of pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids, functionalized with a nitrile (cyano) group at the end of an alkyl chain attached to the cation, was studied in the temperature range between 173 K and 393 K. The glass formation of the ionic liquids is influenced by the length of the alkyl spacer separating the nitrile function from the pyrrolidinium ring. The electrical conductivity and the viscosity do not show a monotonic dependence on the alkyl spacer length, but rather an odd-even effect. An explanation for this behavior is given, including the potential energy landscape picture for the glass transition