Jean-François Verchère’s research while affiliated with French National Centre for Scientific Research and other places

Novel chelating membranes for heavy metal ions were prepared by the semi-interpenetrated polymer networks technique. The matrix is a crosslinked network of poly(vinyl alcohol) (PVA) that immobilises a commercial or synthetic chelating polymer (CP). The membranes were characterised for the effectiveness of the crosslinking by measurement of swelling ratio and infra-red spectrometry, thermal stability, exchange and sorption capacities. In this paper, the removal of Hg(II), Pb(II), Cd(II) and Cu(II) ions by the most versatile membrane, the PVA/poly(ethyleneimine) (PEI) membrane was studied. The effects of parameters such as temperature, water hardness, the presence of complexing chloride anions and of other metal cations were investigated. The dissolution of the PVA/PEI membrane in water was slow and limited to 5% after two months, showing the efficiency of the crosslinking process. The sorption isotherms obey the Langmuir model and show high retention capacities for Pb(II), Cd(II) and Cu(II) ions. The sorption capacity was greater for metal ions that hydrolyse easily. The maximum sorption capacities of the membrane were 0.729 mmol g−1 for Pb(II), 0.692 mmol g−1 for Cu(II) and 0.525 mmol g−1 for Cd(II), whereas the theoretical and experimental exchange capacities were 9.30 mmol g−1 and 2.78 mmol g−1, showing that most internal complexing sites of the membrane were not accessible for sorption of ions. Sorption experiments using mixtures of 2, 3 or 4 metal ions showed the selectivity order: Hg(II) > Cu(II) > Pb(II) > Cd(II). The thermodynamical sorption parameters showed a large entropic effect. The retention ratios were remarkably insensitive to the presence of calcium or chloride ions, which suggest possible use for the purification of real wastewaters by filtration.

A poly(vinyl alcohol)/poly(4-vinylpyridine) (PVA/P4VP) filtration membrane was modified by two techniques for increasing its porosity, resulting in improved permeate flows. In the impregnation technique, silica particles were added, then removed by dissolution in alkaline medium. The second technique was a phases inversion in acetone that formed an asymmetric membrane. The creation of pores within both membranes was verified by SEM imaging and measurements of water flows. The water flows were 0.5, 18 and 11cm3h−1 for the unmodified, silica modified and phases-inversion membrane, respectively. The elimination ratios of Hg(II) ions in frontal filtration (E=98–100%), show that all membranes had a high efficiency for Hg(II) retention. The sorption capacities were: PVA/P4VP (silica): 656mgg−1>PVA/P4VP (unmodified): 460mgg−1>PVA/P4VP (phases inversion): 251mgg−1. By comparison with the theoretical value, 764mgg−1, the porosity increase due to silica impregnation revealed enhanced accessibility to most of the complexing sites within the membrane. The sorption isotherms followed the Langmuir formalism, indicating that mercury was sorbed by a complexation mechanism. The increase of the filtration flows offers a real possibility of using these membranes for low pressure filtration of polluted water.

Removal of Hg(II) ions from aqueous solutions by a novel complexing membrane was investigated by performing sorption and filtration experiments. The membrane, prepared by the technique of semi-interpenetrated polymer networks, consists in a matrix of poly(vinylalcohol), crosslinked by gaseous dibromoethane, that immobilizes chains of poly(vinylimidazole), a complexing polymer synthesised for this purpose. The morphology of the membrane was observed by scanning electron microscopy, showing an homogeneous structure, but surface unevenness. The dissolution of the membrane in water was slow and limited to 8% in 2 months, showing the efficiency of the crosslinking process. Efficient retention of Hg(II) was observed at pH 2.5. The kinetics of sorption were studied. The sorption equilibrium was satisfactorily represented by the Langmuir model. Isotherms performed at different temperatures allowed the calculation of the thermodynamical parameters. The sorption of mercury was endothermic, with a large positive entropy change that was ascribed to proton release. The effects of parameters such as water hardness, and the presence of complexing chloride anions were investigated, showing little influence on the retention ratio. Fast and efficient regeneration of the membrane was performed with a 0.5 M HNO3 solution. The maximum capacity of the membrane was 120 mg Hg g−1, whereas the theoretical exchange capacity was 853 mg Hg g−1, showing that most internal complexing sites of the membrane were not accessible to mercury ions in sorption experiments. When used in the filtration mode, the elimination ratio of Hg(II) was ≥99.4% for solutions containing 91.6 or 17.5 mg Hg L−1.

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A supported liquid membrane (SLM) containing a resorcinarene carrier, previously used for the transport of aldoses and alditols, has been used for the selective transport of methyl-α-d-glucopyranoside, methyl-β-d-glucopyranoside, methyl-β-d-galactopyranoside, methyl-α-d-mannopyranoside, and methyl-β-d-xylopyranoside from concentrated (0.20–0.025M) aqueous solutions. The membrane is made of a microporous polytetrafluoroethylene film (PTFE), impregnated with a 0.01M solution of the carrier in CCl4. The permeabilities of the SLM for all studied methyl aldopyranosides were calculated. On the basis of the flux dependence on the initial concentrations of carrier and methyl aldopyranoside, the rate-determining step in the transport mechanism is shown to be the migration of the (1/1) carrier–carbohydrate complex in the immobilized organic phase. The flux of sugar is related to the initial concentration of methyl aldopyranoside in the feed phase by a saturation law, which allowed the determination of the apparent diffusion coefficients and the stability constants of the resorcinarene complexes of methyl aldopyranosides formed in the liquid membrane. The stability constants of the complexes fall into two classes: aldopyranosides with trans HO groups form complexes of low stabilities (K≈0.36±0.01) whereas aldopyranosides with cis HO groups form complexes of high stabilities (K≈0.84±0.01).

A novel poly(vinyl alcohol)/poly(4-vinylpyridine) (PVA/P(4)VP) complexing membrane for removal of Hg(II) ions from aqueous solutions represents a significant improvement over a previously reported PVA/poly(ethylenimine) (PEI) membrane. This membrane was prepared by the semi-interpenetrating polymer network technique, and its cross-linking by three different agents was studied. The best results were obtained with gaseous 1,2-dibromoethane at 140 degrees C for 1 h that gave a membrane with a swelling ratio of 0.66. The sorption reaction of Hg(II) followed a first-order rate law, and the rate-limiting step was shown to be the association of Hg(II) ions with the complexing sites of P(4)VP. Sorption experiments at pH 2.5 showed that the retention ratio could reach 100% under optimized conditions for the initial concentration of Hg(II) and mass of membrane, c(0) = 100 mg L(-1) and m(D) = 100 mg, respectively. The retention ratio was remarkably insensitive to water hardness or the presence of NaCl, suggesting possible use for the purification of real wastewaters. The retention capacity of the membrane was 450 mg g(-1) compared to 311 mg g(-1) reported for the PVA/PEI membrane. Sorption isotherms were determined at various temperatures, according to the Langmuir model, for the determination of the thermodynamical parameters. When T increased, mercury uptake at equilibrium did not change, whereas the sorption coefficient b decreased and the change in free energy DeltaG degrees decreased. This result is probably due to a large favorable entropic effect, ascribed to the displacement of protons from the protonated sites of P(4)VP while they bind with Hg(II) ions. The membrane could be regenerated by 0.5 M nitric acid with less than 3% loss of efficiency. The membrane was used for filtration experiments. The elimination ratio was 99.9% or more for filtration of Hg(II) solutions in the c(0) = 16.6-89.1 mg L(-1) range.

A supported liquid membrane was prepared by impregnation of commercial microporous polymer film with methyl cholate in cyclohexane and was used to study transport of various sugars. The stability constant and apparent diffusion coefficient of carrier-sugar complex were determined. The absence of a percolation threshold excludes a fixed-site jumping mechanism and supports a solution–diffusion mechanism of carrier–sugar complex in the membrane. However, the existence of a relation of inverse proportionality between the stability constant and the apparent diffusion coefficient suggests a mobile-site jumping mechanism where the sugar is relayed along a sequence of mobile carriers. The notable difference between the values of the stability constant of the various sugars studied confirms their molecular recognition by the methyl cholate. The HOCH2 group is necessary for stable carrier–sugar complexes, this can be explained by the long distance between O-3 and O-12 of methyl cholate.

The separation of aqueous mixtures of monosaccharides has been carried out with a supported liquid membrane (SLM) containing methyl cholate as carrier in cyclohexane. Special attention has been paid to optimizing conditions for effective separation, while retaining large permeabilities. The SLM selectivity slightly increased with increasing substitution of the solvent and decreasing pore size, but at the cost of unacceptable decrease of permeability. The selectivity of the SLM was determined from separation experiments of binary mixtures. The permeabilities are smaller in the mixtures than for the individual components, due to competition between the two monosaccharides of the mixture to form a complex with the limited amount of carrier. This competition depends on the difference of the stability constants between the two carrier-sugar complexes (CS). The SLM allowed some interesting separations (α > 1.25). The separation of the monosaccharides depends on three parameters: functional groups, chain length and configuration.

Colourless tungstate complexes of the sugar acids, l-manonnic, d-glucaric and galactaric acids have been studied in aqueous solutions. Multinuclear 13C and 183W NMR have been used to identify the structures of the complexes and the sites of chelation of each ligand. Indirect photometry has been used to determine the stoichiometry and the stability constants of the complexes.For mannonic acid, two complexes of the lactic type with a mono-nuclear and a di-nuclear tungsten core have been identified at acidic pH. In these complexes, a (OH) group at the carbon atom in α position is necessary to the formation of the complex and only the hydroxyl groups (OH) of the carboxyl function and of the carbon atom in α position belongs to the site of chelation. Upon increasing the pH, the lactic complexes disappear: first the mono-nuclear, then also the di-nuclear lactic complexes, however a new complex of mixed (lactic+erythro) type with a (5, 2) composition has been observed. Upon increasing the pH a single erythro complex appears and at pH 10 a small amount of threo (tetradentate) type complex has been observed.For glucaric and galactaric acids , a new tri-nuclear complex (3, 3, 6) is formed in acid medium, this complex is composed of three mono-nuclear bidentate sites of chelation related one to the other. Upon increasing the pH, these new tri-nuclear complexes disappear and only for the W-galactarate system there is formation of a di-nuclear tetradentate complex of type erythro analogous to the complex of the mannonic acid.