Maria Muñoz

Facilitated transport of lead(II) and cadmium(II) through novel activated composite membranes containing di-(2-ethyl-hexyl)phosphoric acid as carrier

Abstract This paper describes an approach to the chemical characterisation of the facilitated transport of lead(II) and cadmium(II) by an activated composite membrane (ACM) containing immobilised di-(2-ethyl-hexyl)phosphoric acid (DEHPA). Such membranes were prepared, by interfacial polymerisation and characterised physically and chemically. The ACMs were used to experimentally determine their transport behaviour for Pb(II) and Cd(II). So, the influence of some chemical parameters (i.e. DEHPA concentration on the ACM, the feed solution composition, the concentration of nitric acid in the stripping solution, and the ionic strength of the feed and stripping aqueous solutions) was assayed for each metal ion. A correlation of the chemical behaviour of those ACM systems with the physical characterisation of those membranes, prior to and after their use, is reported. The optimum chemical conditions for Pb(II) and Cd(II) transport enhance the lifetime of the ACMs, giving higher DEHPA immobilisation on the polymeric phase of the composite membrane.

Characterization of novel activated composite membranes by impedance spectroscopy

The paper reports the results obtained on the physicochemical characterization of activated composite membranes (ACM). Membrane samples containing different concentrations of di-2-ethyl-hexylphosphoric acid (DEHPA) as a carrier were prepared and in situ characterized by impedance spectroscopy (IS). The results obtained by this technique, based on the linear correlation between the electrical resistance of the membrane and the carrier content allows not only for an in situ characterization of the working membrane but also for a novel analytical method to direct determination of actual carrier content in the membrane. These results also correlate with those obtained by the application of other spectroscopic techniques to ACM samples. Thus, a linear correlation between the carrier content in the membrane and that in the casting solution was obtained from the results of the membrane analysis by using the inductively coupled plasma (ICP) technique. The carrier distribution in the membrane was evaluated by X-ray microanalysis (EDS), which allowed us to determine that DEHPA is trapped in the polymeric phase of the composite membrane. The results obtained by the indicated techniques correlate with good agreement and allow characterization of the membrane performance under different working conditions.

Extraction of palladium with tri-isobutylphosphine sulphide (cyanex 471) in toluene from chloride solutions containing thiocyanate

The extraction of PD(II) by tri-isobutylphosphine sulphide, TIBPS (Cyanex 47 1x), in toluene from aqueous chloride solutions (containing small amounts of thiocyanate) has been investigated. The extraction is enhanced by the presence of thiocyanate, owing to formation of mixed-ligand Pd(II)-Cl(-)-SCN(-)-TIBPS complexes. Analysis of the metal distribution suggests the formation of PdCl(SCN).TIBPS, PdCl(SCN).2TIBPS, Pd(SCN)(2).TIBPS and Pd(SCN)(2).2TIBPS in the organic phase. The equilibrium constants are logK(111) =9.56, logK(112) =12.70, logK(121) =14.73 and logK(122) =17.17, respectively. The ultraviolet absorption spectra of the organic phase support the hypothesis of formation of mixed-ligand complexes.

Polymer-stabilized palladium nanoparticles for catalytic membranes: ad hoc polymer fabrication

Metal nanoparticles are known as highly effective catalysts although their immobilization on solid supports is frequently required to prevent aggregation and to facilitate the catalyst application, recovery, and reuse. This paper reports the intermatrix synthesis of Pd0 nanoparticles in sulfonated polyethersulfone with Cardo group membranes and their use as nanocomposite catalytic membrane reactors. The synthesized polymer and the corresponding nanocomposite were characterized by spectroscopic and microscopic techniques. The catalytic efficiency of catalytic membranes was evaluated by following the reduction of p-nitrophenol in the presence of NaBH4.

Selective transport of zinc through activated composite membranes containing di(2-ethylhexyl)dithiophosphoric acid as a carrier

Abstract The transport phenomena of transition metal cations through supported activated composite membrane (ACM) containing di-(2-ethylhexyl)dithiophosphoric acid (DTPA) as a carrier have been studied. The polyamide top layer of the ACM immobilizes DTPA by trapping it in the polymer net during the interfacial polymerization process. The comparison of ACM with the corresponding supported liquid membrane (SLM) shows far higher stability of the former. Thus, the results of a comparative study of SLM and ACM under identical conditions show that no metal ions transport through SLM is observed after 1 day working experiment, while ACM demonstrate sufficiently stable transport properties within several weeks of their use. A membrane-based process for zinc recovery from hydrometallurgical effluents has been developed. Zinc selectively diffuses from the feed solution through the ACM into the receiver solution containing 2.2 M hydrochloric acid, due to the facilitated transport with DTPA acting as carrier in the membrane. The selectivity of DTPA based ACM towards different metal ions is presented and discussed. At pH 2 in the feed phase, the membrane provides a selective transport of zinc ionic species to the stripping compartment of the membrane cell, while other metal ions (Al, Ca, Mg, Mn and Ni) with sufficiently high stability of the DTPA-complexes remain in the feed compartment. Such a selectivity is based on the differences of the dynamic behaviour of the metal ions transport.

Evaluation of different mediator-modified screen-printed electrodes used in a flow system as amperometric sensors for NADH

This work presents a comparative study between two different methods for the preparation of mediator-modified screen-printed electrodes, to be used as detectors in a reliable flow injection system for the determination of the nicotinamide adenine dinucleotide (NADH) coenzyme. The best strategy was selected for the final development of compact biosensors based on dehydrogenase enzymes. For the first immobilisation strategy, different redox mediators were electropolymerised onto the SPE surface. The second immobilisation strategy was carried out using polysulfone-graphite composites, which were deposited by screen-printing technology onto the screen-printed electrode (SPE) surface. Both methods achieved an effective and reliable incorporation of redox mediators to the SPE configuration. Finally, a flow system for ammonium determination was developed using a glutamate dehydrogenase (GlDH)-Meldolas Blue (MB)-polysulfone-composite film-based biosensor. The stability of the redox mediators inside the composite films as well as the negligible fouling effect observed on the electrode surface improve the repeatability and reproducibility of the sensors, important features for continuous analysis in flow systems. Furthermore, the optimised bio/sensors, incorporated in a flow injection system, showed good sensitivities and short response times. Such a good analytical performance together with the simple and fast sensor construction are interesting characteristics to consider the polysulfone-composite films as attractive electrochemical transducer materials for the development of new dehydrogenase-based SPEs.

Novel potentiometric sensors based on polysulfone immobilized metallothioneins as metal-ionophores.

We show here the use of immobilized metal-binding biomolecules for metal analysis by using novel potentiometric sensors. To this end and as a model, Ag(+)-ISEs were developed using polysulfone matrix embedding metallothioneins as ionophores (mouse MT1 (P1) or sea urchin SpMTA (P2)). Polysulfone, a porous polymer that was not used until the present in potentiometric biosensors, has the advantage of being compatible with biological materials. Also, the phase inversion procedure allows protein incorporation into the membrane with minima alterations, since it always remains in the aqueous phase. Construction of these biosensors required small amounts of protein; they can be dry-stored and have long lifetimes. They exhibited linear responses with slopes of ca. 61mV per decade within the 10(-5) to 10(-2)M Ag(+) concentration range, detection limits of about 10(-5)M, and worked in the 2-to-8 pH range. Except for Hg(2+), the Pb(2+), Zn(2+), Cd(2+), Cu(2+) cations do not interfere with Ag(+) determination. Significantly, different affinities of Pb(2+) and Zn(2+) towards P1- and P2-ISE were found, in good correlation with the higher affinity of these cations towards SpMTA than to MT1. Consequently, the distinct metal-binding features of each MT are conserved and determine the differential properties of their biosensors. These results open a broad range of possibilities for the use of proteins as ionophores in what could be considered a new type of potentiometric biosensor if their response mechanism is taken into account.

Novel strategies for preparation and characterization of functional polymer-metal nanocomposites for electrochemical applications*

Stabilization of metal nanoparticles (MNPs) in polymeric matrices of different types has proven to be one of the most promising strategies to prevent their aggregation and to retain their properties. Polymer-stabilized MNPs (PSMNPs) and those based on polymer-metal nanocomposite materials are starting to find wide application in various fields of science and technology. In this paper, we demonstrate that metal-polymer nanocomposite membranes (MPNCMs) containing MNPs can easily be prepared in an ion-exchange such as, for example, sulfonated polyetherether ketone (SPEEK) matrix by using the polymeric membranes as nanoreactors for synthesis and to characterize the composition and structure of the formed MNPs. Metal ions (or metal ion complexes) are first incorporated into the polymeric matrix where they undergo reduction, leading to formation of corresponding MPNCMs. Since this technique allows successive metal loading-reduction cycles to be carried out, it enables synthesis of both monometallic and bimetallic (e.g., core-shell) MNPs. The proposed approach is illustrated by synthesis and characterization of MPNCMs containing both monometallic and bimetallic core-shell MNPs, formed by combinations of Pd, Pt, Co, Ni, and Cu, along with their application in electrochemical sensor and biosensor constructions.

Intermatrix synthesis: easy technique permitting preparation of polymer-stabilized nanoparticles with desired composition and structure

The synthesis of polymer-stabilized nanoparticles (PSNPs) can be successfully carried out using intermatrix synthesis (IMS) technique, which consists in sequential loading of the functional groups of a polymer with the desired metal ions followed by nanoparticles (NPs) formation stage. After each metal-loading-NPs-formation cycle, the functional groups of the polymer appear to be regenerated. This allows for repeating the cycles to increase the NPs content or to obtain NPs with different structures and compositions (e.g. core-shell or core-sandwich). This article reports the results on the further development of the IMS technique. The formation of NPs has been shown to proceed by not only the metal reduction reaction (e.g. Cu0-NPs) but also by the precipitation reaction resulting in the IMS of PSNPs of metal salts (e.g. CuS-NPs).

Transport of vanadium(V) through a tricaprylylmethylammonium solid supported liquid membrane from aqueous acetic acid/acetate solutions

Abstract A liquid membrane system for vanadium transport has been designed by using tricaprylylmethylammonium chloride (Aliquat 336®) dissolved in isopropylbenzene (cumene) or dodecane as carrier. The work has been undertaken by first determining the liquid-liquid distribution of vanadium(V) between aqueous solutions of different acidity and an organic solution containing the carrier. Optimum conditions for both extraction (4 Transport experiments were carried out at low vanadium(V) concentration (ppm level). The study of the liquid membrane included the influence of hydrodynamic and chemical conditions, i.e., stirring speed, organic solvent, carrier concentration, ionic strength and pH of the aqueous phases. Dodecane membranes provided higher transport of vanadium(V) than cumene membranes. Dodecanol, ranging from 0 to 10% (v/v), was added to the dodecane solution of Aliquat 336® to enhance its solubility. The effect of acidity of the feed solution on vanadium transport showed a similar behaviour to that obtained for the liquid-liquid distribution studies. On the contrary, selectivity properties of the liquid membrane showed clear differences with the corresponding data of solvent extraction, i.e., molybdate extracted by Aliquat 336® was not transported through the liquid membrane. The results obtained in both batch distribution experiments and dynamic membrane transport indicated that vanadium(V) was extracted by means of metavanadate chemical species.