Kinetics and thermodynamic studies of Methyl Orange removal by polyvinylidene fluoride-PEDOT mats.

We report the preparation of poly(3,4-ethylene dioxythiophene) (PEDOT)-modified polyvinylidene fluoride electrospun fibers and their use as a novel adsorbent material for the removal of the anionic dye Methyl Orange (MO) from aqueous media. This novel adsorbent material can be used to selectively remove MO on a wide pH range (3.0-10.0), with a maximum capacity of 143.8 mg/g at pH 3.0. When used in a recirculating filtration system, the maximum absorption capacity was reached in a shorter time (20 min) than that observed for batch mode experiments (360 min). Based on the analyses of the kinetics and adsorption isotherm data, one can conclude that the predominant mechanism of interaction between the membrane and the dissolved dye molecules is electrostatic. Besides, considering the estimated values for the Gibbs energy, and entropy and enthalpy changes, it was established that the adsorption process is spontaneous and occurs in an endothermic manner. The good mechanical and environmental stability of these membranes allowed their use in at least 20 consecutive adsorption/desorption cycles, without significant loss of their characteristics. We suggest that the physical-chemical characteristics of PEDOT make these hybrid mats a promising adsorbent material for use in water remediation protocols and effluent treatment systems.

Improvement of Baker's yeast-based fuel cell power output by electrodes and proton exchange membrane modification.

The production of more efficient yeast-based fuel cells (YFCs) depends on a combination of effective proton exchange membranes, electron mediators and current collectors. The adhesion of organisms on electrode surface plays a key role in the electron transfer process optimizing the generated power density. In this work, it is reported the preparation of a new YFC prototype using membranes of polyvinyl alcohol/ phosphoric acid and anodes of carbon nanotubes/polyurethane. The high surface area for yeast adhesion and the strong interaction established between cells/carbon nanotubes favor the energy generation in fuel cell. To evaluate the influence of external mediators and the consumption of feed solution (glucose) on performance of YFC, the kinetics of current generation of resulting fuel cells was analyzed. Results reveal that increases in the impedance of electrodes on generated power can be minimized by periodical infusion of feed fuel, preserving 70% of maximum power, representing an important condition for prolonged activity of fuel cell.

A novel nucleic acid fluorescent sensing platform based on nanostructured films of intrinsically conducting polymers.

When fluorophores attach to nanostructured films of intrinsically conducting polymers (ICPs), a quenching of their fluorescence may occur. We have exploited these characteristics for the development of polymeric films that can be used in a simple and efficient molecular diagnosis protocol based on the selective detection of nucleic acids. Our procedure rests on the fact that the fluorescence of 6-carboxyfluorescein-labeled single-stranded DNA (FAM-ssDNA) probes is quenched upon their immobilization on nanostructured ICP - polypyrrole (PPY) and polyaniline (PANI) - films deposited on polyethylene terephthalate (PET) substrates. Hybridization occurs whenever a sample with the complementary sequence is brought in contact with the immobilized probe, with the newly formed ds-DNA chains detaching from the flexible polymeric film and causing the restoration of the fluorescence. This sensing system exhibits a low background signal that depends on both the thickness and hydrophobicity of the films. As a model system, we used a FAM-ssDNA probe specific for the Leishmania infantum parasite. The results confirm this procedure as a simple, fast and highly sensitive scheme for the recognition of the target DNA, with a detection limit of the 1.1 nM and 1.3 nM for the PPY/PET and PANI/PET films, respectively. In addition, this biosensor has excellent stability and exhibits a good and reproducible performance even when used for the direct detection of ssDNA in relatively complex biological samples.

Usnic acid-loaded polyaniline/polyurethane foam wound dressing: preparation and bactericidal activity.

The improved bactericidal activity of new composites for wound dressing prototypes represents an important strategy for development of more efficient devices that make use of synergistic interaction between components. The doping level of polyaniline represents a critical parameter for its corresponding biologic activity. In this work, it is explored the doping effect of usnic acid on undoped polyaniline, that introduces important advantages namely, improved bactericidal activity of polyaniline and the anti-biofilm properties of lichen derivative. The deposition of the resulting material on polyurethane foam potentializes its applicability as wound dressing, characterizing a new platform for application against Escherichia coli and Staphylococcus aureus.

Hierarchical composite polyaniline-(electrospun polystyrene) fibers applied to heavy metal remediation.

We describe the in situ preparation of a multipurpose hierarchical polyaniline-polystyrene (PANI-PS) composite based in the chemical polymerization of PANI on nonwoven (NW) electrospun PS mats. We performed a detailed study of the properties of these materials to select the best strategies to incorporate PANI chains into pristine NW PS mats without compromising the original porosity and mechanical flexibility of the matrices. The resulting composites presented nanostructured PANI chains highly dispersed in the interior of the NW PS mat and showed good electrical properties and surface-wetting characteristics that could be easily controlled. In particular, we show that these NW PANI-PS mats exhibit interesting properties in their interaction with heavy metal ions. For instance, their high adsorption capacities toward dispersed Hg(II), Cd(II), Pb(II), Cr(VI), and Cu(II) ions make them promising materials for water remediation, by providing a simple manner of collecting and removing these metals from aqueous systems. In fact, the NW electrospun mats here presented do not suffer from the usual limitations found in materials commonly employed as adsorbents, such as a tendency to agglomerate or accumulate in the environment because of difficulties of properly recovering them after use. To better understand the nature of each pairwise metal-PANI interaction, we performed a thorough investigation of the optical and electrical changes induced by the metal adsorption in the NW PANI-PS mats. As a consequence of their interaction with the metal ions, the visual aspect of the mats change, a fact more evident in the case of Cr(VI) removal, when the matrices vary their color from green to purple. These changes are related to the variation of the oxidation state of the PANI chains: as the ion metals are progressively adsorbed into the mat, they promote the conversion in varying degrees of the PANI chains from salt emeraldine to the pernigraniline form, and the mats become more resistive. We implemented an electrical impedance investigation of the charge transport characteristics of NW PANI-PS mat, and the results indicate that they are sensitive to the type of metal ion adsorbed and that the amount of ions adsorbed in each case is mostly related to the standard electrode potential of the metal considered.