Brominated carbon black: An EDXD study

An energy dispersive X-Ray study of pure and brominated carbon black was carried out. The analysis of the diffraction patterns reveals that the low bromine load (ca.1% mol) is trapped into the structure, without significantly modifying it. This allows the application of the difference methods, widely tested for electrolyte solutions, inorganic matrices containing metals and isomorphic substitutions

Higher fullerenes: Compositional analysis by EDXD and molecular dynamics

A carbon soot of higher fullerenes was studied by Energy Dispersive X-ray Diffraction (EDXD) aiming at defining the overall structure as accurately as possible to define the overall structure, without lengthy separation and purification procedures. EDXD pattern was compared with model curves obtained for single homogeneous fullerenes already crystallized and for the hypothesized C180. All fullerenes contribute to the overall experimental curve to different extents, with C96 giving the best agreement. The presence of even higher fullerenes is very likely, since the hypothesized C180 gives a very good match as well

Detection of heavy metals in water using graphene oxide quantum dots: an experimental and theoretical study

In this work, we investigate by ab initio calculations and optical experiments the sensitivity of graphene quantum dots in their use as devices to measure the presence, and concentration, of heavy metals in water. We demonstrate that the quenching or enhancement in the optical response (absorption, emission) depends on the metallic ion considered. In particular, two cases of opposite behaviour are considered in detail: Cd2+, where we observe an increase in the emission optical response for increasing concentration, and Pb2+ whose emission spectra, vice versa, are quenched along the concentration rise. The experimental trends reported comply nicely with the different hydration patterns suggested by the models that are also capable of reproducing the minor quenching/ enhancing effects observed in other ions. We envisage that quantum dots of graphene may be routinely used as cheap detectors to measure the degree of poisoning ions in water

Mesoscopic structural organization in fluorinated pyrrolidinium based room temperature ionic liquids

In this contribution the microscopic and mesoscopic structural organization in a series of fluorinated room temperature ionic liquids, based on N-methyl-N-alkylpyrrolidinium cations and on bis(perfluoroalkylsulfonyl)imide anions, is investigated, using a synergy of experimental (X-ray and neutron scattering) and computational (Molecular Dynamics) techniques. The proposed ionic liquids are of high interest as electrolyte media for lithium battery applications. Together with information on their good ion transport properties in conjunction with low viscosity, we also describe the existence of nm-scale spatial organization induced by the segregation of fluorous moieties into domains. This study shows the strong complementarity between X-ray/neutron scattering in detecting the complex segregated morphology in these systems at mesoscopic spatial scales and MD simulations in successfully delivering a robust description of the segregated morphology at atomistic level

Self-Association of Organic Solutes in Solution: A NEXAFS Study of Aqueous Imidazole

N K-edge near-edge X-ray absorption fine-structure (NEXAFS) spectra of imidazole in concentrated aqueous solutions have been acquired. The NEXAFS spectra of the solution species differ significantly from those of imidazole monomers in the gas phase and in the solid state of imidazole, demonstrating the strong sensitivity of NEXAFS to the local chemical and structural environment. In a concentration range from 0.5 to 8.2 mol L−1 the NEXAFS spectrum of aqueous imidazole does not change strongly, confirming previous suggestions that imidazole self-associates are already present at concentrations more dilute than the range investigated here. We show that various types of electronic structure calculations (Gaussian, StoBe, CASTEP) provide a consistent and complete interpretation of all features in the gas phase and solid state spectra based on ground state electronic structure. This suggests that such computational modelling of experimental NEXAFS will permit an incisive analysis of the molecular interactions of organic solutes in solutions. It is confirmed that microhydrated clusters with a single imidazole molecule are poor models of imidazole in aqueous solution. Our analysis indicates that models including both a hydrogen-bonded network of hydrate molecules, and imidazole–imidazole interactions, are necessary to explain the electronic structure evident in the NEXAFS spectra

Water and hexane in an ionic liquid: Computational evidence of association under high pressure

High pressures may strongly affect the mesoscopic structure of some ionic liquids. In particular, the so called sponge-like structure is gradually destroyed when an increasing pressure is applied. Here we show how a polar solute, an apolar solute or a mixture thereof behave in the ionic liquid trihexyl, tetradecylphosphonium bis (trifluoromethyl-sulfonyl) imide when the pressure is raised up to 10 kbar. Our calculations clearly show an association between molecules that would not interact in ordinary conditions

A COMBINED MOLECULAR DYNAMICS AND X-RAY DIFFRACTION STUDY OF PROTIC IONIC LIQUID/WATER MIXTURES.

Ionic Liquids (ILs) have received considerable attention in recent years due to their potential as an environmentally friendly alternative to traditional organic solvents and due to a number of unique physicochemical properties that make them appropriate candidates for several scientific and technological applications, such as in catalysis and organic/inorganic synthesis. A subset of ILs are protic ionic liquids (PILs) which result from the proton transfer reaction between a Bronsted acid and a Bronsted base. The key properties that distinguish PILs from other ILs is the proton transfer from the acid to the base, leading to the presence of proton-donor and -acceptor sites, which can be used in PILs to build up a hydrogen-bonded network. The significance of the interaction between water and ILs has been well-recognized, given the fact that the ILs are hygroscopic and can absorb a significant amount of water from the atmosphere. Nevertheless, to date, our knowledge of the interaction between water and ILs remains somewhat empirical. In this respect, Molecular Dynamics (MD) simulations are a powerful tool for characterizing, at an atomistic level, the structural and dynamic properties of IL/water mixtures. However, in the case of disordered systems, such as ILs, the combination of theoretical and experimental techniques is essential to obtain reliable information. Among other approaches, the combined use of simulation methods and X-ray diffraction techniques has been shown to be particularly well-suited to provide a reliable description of liquid systems. In this poster we present our results of a combined Molecular Dynamics and X-ray diffraction investigation of mixtures of water with two PILs, namely Ethylammonium nitrate and n-Propyl ammonium nitrate. The focus will be on the changes of the structural properties of these PILs caused by the addition of water

Nanoscale Density Fluctuations in Ionic Liquid Binary Mixtures with Nonamphiphilic Compounds: First Experimental Evidence

A complex mesoscopic organization is observed in systems containing ethylammonium nitrate (EAN) and two nonamphiphilic compounds, using wide and small angle X-ray scattering and molecular dynamics simulations. The macroscopically homogeneous mixtures exhibit a separation where an ionic liquid-rich region is percolating a molecular liquid-rich one, but no unmixing is observed. This effect was already reported in EAN-alcohol mixtures, but the models proposed so far cannot explain this behavior for a nonamphiphilic compound

Dimerisation of urea in water solution: a quantum mechanical investigation

The effect of water solvation on the structure and stability of cyclic dimers of urea has been investigated with the aid of density functional theory at the B3LYP/ 6-311 + + G** level. Several hydration models have been discussed. Specific solvent effects have been simulated through single and multiple water - urea interactions involving all the hydration sites of urea. The bulk solvent effects have been estimated through polarised continuum models. Under all the hydration patterns cyclic dimers continue to be stable structures although the solvent weakens the urea - urea interaction. Single and multiple specific urea - water interactions are competitive with urea dimerisation. The anticooperative nature of the two intermolecular interactions is largely due to the changes on sigma- and pi- electron density of urea caused by hydrogen bonding with water. The stability of the dimer is however, lost within a few ps when the hydrated dimer is described by a quantum mechanical molecular dynamics approach (ADMP). The cyclic dimer evolves towards structures where urea molecules are linked not more directly but through water molecules which have a bridge function