Daniel Lemordant

Removal of hexavalent chromium by nanofiltration

Abstract Removal of chromate CrO42− from water was investigated using nanofiltration as a possible alternative to the conventional methods of CrVI removal from aqueous solution. Retention measurements with single reference salt revealed that Donnan exclusion plays an important role. The phenomenological parameters σ and P were calculated using the Spiegler-Kedem equation. The rejection rate depends on the ionic strength and pH. The increasing of ionic strength decreases the retention. The effect of pH was clarified by using a stable diagram of the CrVIH2O system. Better retention was obtained at basic pH.

The streaming potential method for the characterization of ultrafiltration organic membranes and the control of cleaning treatments

Abstract Streaming potential measurement of ultrafiltration (UF) membranes have been realised a new design. This new design is more convenient to determine the streaming potential on a function of the pressure for all kinds of modules (planar, hollow fiber.h.). The effects of pH, ionic strength and size of pores have been studied. Isoelectric points of different materials (polyethersulfone, celloulse acetate, cellulose triacetate and polysulfone membranes) have been experimentally determined from ν variations with pH at a given ionic are, respectively, 3.1, 4.2, 3.4 and 0.5. The study of the charge organic membranes studied has been shown that adsorbing ions are those of water itself. Then the surface charge of the membrane is a dependent on the pH and at the isoelectric point, the charge density and the streaming potential vanished. The polyethersulfone membrane surface has been modified with TX100 adsorption and the modification observed with our design compared to contact angle and permeabilities measurements. The orientation angle of the surfactant at the membrane surface is obtained: θ=5°, and shows that a flat adsorption occurs. The impact of membranes cleaning procedures have been studied in term of permeability completed by streaming potential measurements. It appeared clearly that streaming potential is a useful tool for the control of cleaning procedures.

Aggregation behavior in water of new imidazolium and pyrrolidinium alkycarboxylates protic ionic liquids.

A novel class of anionic surfactants was prepared through the neutralization of pyrrolidine or imidazole by alkylcarboxylic acids. The compounds, namely the pyrrolidinium alkylcarboxylates ([Pyrr][C(n)H(2n+1)COO]) and imidazolium alkylcarboxylates ([Im][C(n)H(2n+1)COO]), were obtained as ionic liquids at room temperature. Their aggregation behavior has been examined as a function of the alkyl chain length (from n=5 to 8) by surface tensiometry and conductivity. Decreases in the critical micelle concentration (cmc) were obtained, for both studied PIL families, when increasing the anionic alkyl chain length (n). Surprisingly, a large effect of the alkyl chain length was observed on the minimum surface area per surfactant molecule (A(min)) and, hence the maximum surface excess concentration (Gamma(max)) when the counterion was the pyrrolidinium cation. This unusual comportment has been interpreted in term of a balance between van der Waals and coulombic interactions. Conductimetric measurements permit determination of the degree of ionization of the micelle (a) and the molar conductivity (Lambda(M)) of these surfactants as a function of n. The molar conductivities at infinite dilution in water (Lambda(infinity)) of the [Pyrr]+ and [Im]+ cations have been then determined by using the classical Kohlraush equation. Observed change in the physicochemical, surface, and micellar properties of these new protonic ionic liquid surfactants can be linked to the nature of the cation. By comparison with classical anionic surfactants having inorganic counterions, pyrrolidinium alkylcarboxylates and imidazolium alkylcarboxylates exhibit a higher ability to aggregate in aqueous solution, demonstrating their potential applicability as surfactant.

Wide band electrochromic displays based on thin conducting polymer films

Abstract New, wide band, flexible electrochromic displays have been realized with microporous membranes metallized with gold that acts both as an electrode and a reflecting layer. A control of the relative contribution of specular and diffuse reflectance to the optical response of displays can be achieved by varying the size of pores in the membrane. The active layer is a thin conducting polymer layer electrochemically deposited on the metallized membrane. Polydiphenylamine and poly(3,4-ethylenedioxythiophene), which show good electrochemical and optical properties, were used as active layers. These devices exhibit great contrast in the visible/near infrared (IR) spectral region with high reflectance in their reflecting state. IR reflectance measurements showed that swelling can induce reversible wide band contrast in mid-IR and far-IR. These results were correlated to morphological changes induced by ions movements in the polymer films by using EQCM measurements with fast simultaneous acquisition of frequency and impedance.

Ion transport theory of nonaqueous electrolytes. LiClO4 in γ-butyrolactone: the quasi lattice approach

As a part of a study on the optimisation of the electrolyte for high-density energy lithium batteries, transport properties of concentrated LiClO4 solutions in γ-butyrolactone (BL) have been investigated. The effect of the salt concentration (C) on the viscosity (η) of BL solutions has been discussed in term of the Jones–Dole equation. At concentrations higher than 0.2 M, the molar conductivity (Λ) of LiClO4 solutions follow a C1/3 cube root law which is predicted by the quasi lattice model first introduced by Gosh. In this model, the ions of the strong binary electrolyte are distributed in a lattice-like arrangement (fcc). The experimental value found for the slope of Λ vs. C1/3 relation is in fair agreement with the calculated one. The effect of the temperature on the viscosity and the conductivity of electrolyte solutions have been examined. These two transport processes are well described by Arrhenius type laws from which the activation energies for the viscosity Eaη and conductivity EaΛ are deduced. The variations of Eaη and EaΛ with salt concentration are respectively dependent on C and C4/3 as predicted by the quasi lattice model.

Membrane characterization using microscopic image analysis

Abstract Five organic ultrafiltration membranes, made of different materials (PES, PVDF and PAN), have been visualized by a field emission scanning electron microscope (FESEM). Obtained images have been treated by the processing and analysis program NIH image and parameters such as, porosity ( A k ), pore density ( N ), mean pore radius ( r p ) and pore size distribution have been quantified for each membrane. The mean pore size obtained from image analysis agrees well with rejection data of fluorescein isothiocyanate dextrans, using the Ferry’s law approximation. The membrane thickness Δ x has been also measured on images. Results allowed the comparison between the A k /Δ x values obtained from image analysis and the A k /Δ x values obtained by diffusion experiments. Results, combined with porosity and water permeability values, gave information on the material hydrophilicity.

Alkylammonium-Based Protic Ionic Liquids Part I: Preparation and Physicochemical Characterization

Novel alkylammonium-cation-based protic acid ionic liquids (PILs) were prepared through a simple and atom-economic neutralization reaction between an amine, such as diisopropylmethylamine, and diisopropylethylamine, and a Brønsted acid, HX, where X is HCOO-, CH 3COO-, or HF2-. The density, viscosity, acidic scale, electrochemical window, temperature dependency of ionic conductivity, and thermal properties of these PILs were measured and investigated in detail. Results show that protonated alkylammonium such as N-ethyldiisopropyl formate and N-methyldiisopropyl formate are liquid at room temperature and possess very low viscosities, that is, 18 and 24 cP, respectively, at 25 degrees C. An investigation of their thermal properties shows that they present a wide liquid range up to -100 degrees C and a heat thermal stability up to 350 degrees C. Alkylammonium-based PILs have a relatively low cost and low toxicity and show a high ionic conductivity (up a 8 mS cm(-1)) at room temperature. They have wide applicable perspectives for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media and catalysts as replacements of conventional inorganic acids.

Absorption ability and kinetics of a liquid electrolyte in PVDF–HFP copolymer containing or not SiO2

Abstract Gel polymer electrolytes have been prepared from PVDF–HFP copolymer with various silica contents incorporating Gamma valerolactone (VL) or VL/EC (80/20 in mole) (EC: ethylene carbonate) solutions of lithium bis(trifluoromethane sulfone) imide (LiTFSI). The influence of temperature, salt content and silica addition on the kinetics of absorption and wettability of the copolymer has been investigated. An empirical model, taking into account gel swelling during the absorption allows us to relate, at constant temperature, the wetting time and the volumetric fraction of trapped electrolyte, which is a critical factor for ionic conductivity of the gel. Increasing the silica content in the dry copolymer increases the porosity and consequently the rate of absorption and thus the amount of incorporated liquid phase at saturation. To a lower extent, an increase in the temperature of absorption has the same effects. The prepared gels have good mechanicals properties and conductivities. As an example, a gel of composition: PVDF – HFP / SiO 2 / VL / EC / LiTFSI of molar percentages 36/6.7/42/10.5/4.8 exhibits a conductivity of 2.9 mS cm − 1 at 293 K.

Cycling Ability of γ-Butyrolactone-Ethylene Carbonate Based Electrolytes

The cycling ability of a carbon electrode in γ-butyrolactone (BL)-ethylene carbonate (EC) based mixtures has been investigated in the presence of lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ). lithium bis(trifluoromethylsulfone)imide (LiTFSI), and lithium tetrafluoroborate (LiBF 4 ). LiBF 4 is the only salt, which permits full charge-discharge cycles in BL-EC mixtures. The passivation film formed at the carbon electrode has been studied by microscopy and X-ray photoelectron spectroscopy. The cycling ability of the carbon and Li x CoO 2 electrodes has been evaluated in two BL-EC mixtures (9:1 and 1:1) using LiBF 4 (1 M) as an added salt. The wettability of the Celgard separator used in the full-cell configuration has been enhanced by the addition of a surfactant: tetraethylammonium perfluorooctanesulfonate (TEAFOS). This additive does not perturb the quality of the passivative film and increases the wettability by lowering the surface tension of the electrolyte. The electrolyte BL-EC (9:1) + LiBF 4 (I M) has been selected for full-cell cycling experiments at different temperatures (-15 to 25°C) in the presence of TEAFOS (0.014 M).

Electrolytic characteristics of ethylene carbonate–diglyme-based electrolytes for lithium batteries

Dependencies of viscosity (η) and conductivity (κ) on temperature and solvent composition are examined for solutions of LiPF6 and of LiClO4 in ethylene carbonate (EC):diglyme (DG) binary mixtures to identify organic electrolyte systems with the highest conductivity as possible at room temperature. The energies of activation for viscous flow and for conductivity, determined as functions of the composition of the mixed solvent, show these two transport processes to be strongly related. Conductivities of electrolyte solutions prepared with LiPF6 and LiClO4 are comparable, but lower activation energy is required for LiClO4. A flat maximum of conductivity at about 50% (v/v) in EC is observed when the composition of the mixed solvent is varied. A high value, independent of the considered temperature, has been found for the product κ η, meaning that free ions are the predominant ionic species in these media. As a consequence, the macroscopic viscosity of electrolytes under study mainly governs their conductivity. Cyclic voltammetry, performed on negative (LixC) and positive (LixNiO2) intercalation electrodes in the optimized electrolyte (LiClO4 or LiPF6 (1 M)-50:50 EC:DG), gives evidence for the formation of passive layers during the first cycle and reversible electrochemical intercalation during the following cycles. DSC results show that this electrolyte system is a potential candidate for Li secondary batteries or electrochromic devices working at ambient or higher temperatures as it is safe and stable at least to 200°C.