Tània Gumí

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 activated composite membranes by solute transport, contact angle measurement, AFM and ESR

Abstract In this article, various characterization techniques are used to determine the structural membrane properties of various activated composite membranes (ACMs), which have been developed in the last years in our laboratories of the Universitat Autonoma de Barcelona (UAB) . The mentioned ACMs were developed in an attempt to enhance the stability and lifetime of the well-known selective liquid membranes, for their application on selective transport of heavy metals and organic species, such as chiral compounds. Four different characterization techniques have been investigated with the aim to reach an actual microscopic information of the ACMs, and in that way, ascertain their future applications, by modifying their preparation methodology when needed. The characterization techniques here employed are: solute transport, contact angle measurement, atomic force microscopy (AFM) and electron spin resonance (ESR). The simultaneous employment of these techniques provide evidence of the presence, dimension and distribution of pores in membrane surface, as well as useful information about its hydrophilic properties, and confirmation of the immobilization of selective carriers into the membrane. Actual values of pores size and distribution on the membrane surfaces were reached by comparison of the different techniques, and the presence of the selective transport agents checked was detected.

Characterization of polysulfone and polysulfone/vanillin microcapsules by 1H NMR spectroscopy, solid-state 13C CP/MAS-NMR spectroscopy, and N2 adsorption-desorption analyses.

Textile detergent and softener industries have incorporated perfume microencapsulation technology to improve their products. Perfume encapsulation allows perfume protection until use and provides a long-lasting fragrance release. But, certain industrial microcapsules show low encapsulation capacity and low material stability. Polysulfone capsules have been already proposed to solve these drawbacks. Among them, PSf/Vanillin capsules were considered as a desirable system. They present both good material stability and high encapsulation capacity. However, several factors such as the final location of the perfume in the polymeric matrix, the aggregation state that it has in the capsule and its interaction with the capsule components have not been studied yet. These factors can provide vast information about the capsule performance and its improvement. With the aim to characterize these parameters, the physical and chemical properties of PSf/Vanillin capsules have been investigated by nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and N(2) adsorption-desorption measurements. AFM micrograph and N(2) isotherms confirm that the presence of vanillin modify the physical structure of PSf/Vanillin microcapsules as it is trapped in the capsule porosity. NMR results show that vanillin is present in solid state in PSf/Vanillin microcapsules.

Characterization of a Supported Liquid Membrane Based System for the Enantioseparation of SR‐Propranolol by N‐Hexadecyl‐L‐hydroxyproline

Abstract A supported liquid membrane (SLM) containing the chiral selector N‐hexadecyl‐L‐hydroxyproline (HHP) was characterized for the enantioseparation of a β‐blocking drug. SR‐propranolol was the target racemic mixture to be resolved by the membrane separation system. The different affinity shown by the selected carrier, HHP, for the two propranolol enantiomers produced a discrimination of their transport through this SLM. We investigated the influence of various chemical parameters involved in that system, such as the acidity of feed and receiving phases, as well as the carrier concentration in the membrane. Valuable knowledge on the transport mechanisms within this system was thus attained.

Enantioselective Separation of Propranolol by Chiral Activated Membranes

Abstract In this work, chiral activated membranes have been tested for the enantioseparation of the racemic drug propranolol. Polysulfone (PS)‐based membranes have been prepared for this purpose, using N‐hexadecyl‐L‐hydroxyproline (HHP) and L‐di‐n‐dodecyltartrate (L‐DDT) as chiral carriers, respectively. Kinetic experiments have been carried out using a membrane module with two rectangular channels separated by the membrane, which allows for a well‐defined hydrodynamics of the feed and stripping phases. Propranolol transport across the membrane depends on its diffusion rate from the bulk solution to the membrane surface and also on the relative amount of carrier present in the membrane. Therefore, the influence of both the solute/carrier ratio and the flow rates of the feed and stripping phases on the rate of extraction and on the selectivity of the process was evaluated for both chemical systems. Modeling of kinetic experiments has been performed, and mass transfer coefficients obtained for both systems were compared. This work has been supported by M. C. Y. T. (Project ref: PPQ2002‐04267‐C03‐01 and PPQ2002‐04201‐C02‐01) and “Fundação para a Ciência e Tecnologia” (project POCTI/FCB/43942/2001). The support by the CRUP (Portugal) and the DGICT (Spain) through the programmes “Acções Integradas Luso‐Espanholas” and “Acciones Integradas entre Espana y Portugal,” for exchange of researchers are also acknowledged. T. Gumí acknowledges the Ministerio de Educación, Cultura y Deporte for the predoctoral fellowship. Rui M.C. Viegas acknowledges the financial suport of Fundação para a Ciência e Tecnologia through the research grant PRAXIS XXI/BD/9034/96.

Plasmonic-polymer hybrid hollow microbeads for surface-enhanced Raman scattering (SERS) ultradetection.

Hybrid composites are known to add functionality to plasmonic nanomaterials. Although these substrates can be produced by common synthetic methods, the percentage of metal loaded into the functional material is usually small. Herein, we exploit a phase inversion precipitation method to incorporate large amounts of silver nanoparticles inside the polymeric matrix of polysulfone microbeads. The composite material combines the high SERS activity resulting from the plasmonic coupling of highly interacting nanoparticles and the ability to accumulate analytes of the polysulfone porous support. This allows for the quantitative SERS detection down to the nanomolar level, with a liner response that extends over an impressive concentration range of five orders of magnitude.

Concentration and Fractionation of Polyphenols by Membrane Operations

BACKGROUND This review aims to present the relevant background information and current research status in concentration of polyphenols using membrane technologies. The potential implementation of membrane separation to bioactive compounds like soluble phenolics from aqueous and organic solvent solutions is gaining increasing interest in the recent years. This review does not pretend to cover the abundant published literature on the subject, but to be representative for the observed tendencies in membrane processes applications for concentration of polyphenols derived from natural products. The first part of the article includes general information regarding the polyphenols and the traditional methods for their separation (such as: thin layer chromatography; paper chromatography; gas chromatography; high performance liquid chromatography; capillary electrophoresis), while the second part presents a review of different membrane processes applied for concentration of polyphenols. Three main sources for such implementations are discussed: (1) aqueous or organic solvent extracts from plant material, (2) fruits, and (3) recovery of polyphenols from industrial waste liquids. A diversity of membrane processes are considered in a large scope of implementations ranging from lab-scale studies to pilot and semiindustrial scale operations. CONCLUSION Membrane technology is an excellent candidate to make a paradigm shift in biological active compounds fractionation/separation processes. Presented results clearly demonstrate that membrane processes are of great advantages over traditionally used methods; however, characterization of separated polyphenols has to be improved. Most of citied authors concentrated their investigation only on the total amount of polyphenols determination. Exhaustive studies including: antioxidant activities, retention index, total soluble solids, or volume reduction factor, have been only carried out by a few authors.

PVDF Membrane Morphology - Influence of Polymer Molecular Weight and Preparation Temperature

In this study, we successfully prepared nine non-woven, supported polyvinylidene fluoride (PVDF) membranes, using a phase inversion precipitation method, starting from a 15 wt % PVDF solution in N-methyl-2-pyrrolidone. Various membrane morphologies were obtained by using (1) PVDF polymers, with diverse molecular weights ranging from 300 to 700 kDa, and (2) different temperature coagulation baths (20, 40, and 60 ± 2 °C) used for the film precipitation. An environmental scanning electron microscope (ESEM) was used for surface and cross-section morphology characterization. An atomic force microscope (AFM) was employed to investigate surface roughness, while a contact angle (CA) instrument was used for membrane hydrophobicity studies. Fourier transform infrared spectroscopy (FTIR) results show that the fabricated membranes are formed by a mixture of TGTG’ chains, in α phase crystalline domains, and all-TTTT trans planar zigzag chains characteristic to β phase. Moreover, generated results indicate that the phases’ content and membrane morphologies depend on the polymer molecular weight and conditions used for the membranes’ preparation. The diversity of fabricated membranes could be applied by the End User Industries for different applications.

Emerging application of vanillin microcapsules

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is one of the most important aromatic aldehydes and also one of the most-used flavoring agents worldwide. Its functional groups include aldehyde, hydroxyl, and ether. It is the primary component of the extract of the vanilla bean. However, synthetic vanillin is now used more often than natural vanilla extract. Figure 1 shows the chemical structure of vanillin [1] and Table 1 summarizes its main physicochemical properties [2].

Characterization of Metal-Doped Methylated Microporous Silica for Molecular Separations

Novel silica xerogels are prepared and developed by sol-gel method in the present study. The preparation involves cobalt-doping within the organic templated silica matrices, where methyltriethoxysilane (MTES), which contains methyl groups as a covalently bonded organic template is used. The synthesis and surface properties of cobalt-doped methylated microporous silica xerogels with different MTES and cobalt content are revealed by surface and microstructural techniques, such as TGA, FTIR, X-ray and N2 adsorption measurements. The doping process enhances the thermal stability of the silica xerogels up to ~ 560 °C in oxidizing atmosphere. Besides, this process has no significant effect on the incorporation of the organic template within the silica matrix. As result of the promoted densification of the xerogels either by increasing MTES content and heat treatment, there is structural change of the silica xerogels such as decreasing the micropore volume and broadening of the pore size distribution. Heat treatment and increasing the cobalt oxide content from 5 to 10% weight ratio resulted in samples with approximately the same structural parameters. This suggests that the cobalt particles are homogeneously dispersed in the silica matrix. The novel silica xerogels exhibit trend toward micropores formation suggesting that these doped silica xerogels can be precursor materials for molecular sieve silica membranes applications. Two silica membranes, hydrophobic and cobalt-doped hydrophobic, are prepared and their performance is examined by the study of transport of He, H2 and N2. Preliminary results show that the microporous structure obtained in the unsupported cobalt-doped hydrophobic material are preserved after coating inside the tubular support.