Magnetic Polypyrrole-Gelatin-Barium Ferrite Cryogel as an Adsorbent for Chromium (VI) Removal.

Polypyrrole-gelatin aerogels, containing magnetic barium ferrite (BaFe) particles, (PPy-G-BaFe) were synthesized by oxidative cryopolymerization and used as adsorbents for the removal of Cr(VI) from aqueous media. The removal was performed at pH 4, which was shown to be the optimal value, due to HCrO4- being the dominant species in these conditions and its more favorable adsorption and reduction compared to CrO42-, present at pH > 4. It was found that the presence of magnetic BaFe particles had no effect on the adsorption performance of PPy aerogels in terms of capacity and kinetics, which was attributed to its relatively low content in the composite. After the adsorption, the presence of chromium in the composites was confirmed by EDX and its electrostatic interaction with the adsorbent was pointed at by vibrational spectroscopy, corresponding to the accepted adsorption mechanism. The adsorption kinetics followed the pseudo-second-order model pointing at chemisorption being the rate-limiting step. The adsorption isotherm data was best fitting with the Temkin model. The maximum adsorption capacity, calculated using the Langmuir model, was 255.8 mg g-1 (the maximum experimental value was 161.6 mg g-1). Additionally, the possibility of Cr(VI) adsorption in the presence of Cl-, Br-, NO3- and SO42- as interfering ions was shown.

Highly Electroactive Frozen-State Polymerized Polypyrrole Nanostructures for Flexible Supercapacitors.

The polymerization of pyrrole in the frozen state with the presence of organic dyes (methyl orange (MO) and Acid Blue 25 (AB)) has proven to produce polypyrrole (PPy) nanostructures. Herein, we explore the electrochemical properties of PPy prepared under frozen-state conditions (-24 °C) with and without the presence of organic dyes. The electroactivity of PPy prepared with MO and AB significantly increased in all electrolytic media with a capacitance higher than this of the PPy prepared at room temperature. The highest capacitance (1914 F g-1) was obtained for PPy-MO in 0.2 M HCl solution. The impedance spectra of PPy showed a decrease in charge transfer resistance when the dyes were present. This indicates a conductivity increase of PPy. Improved electrochemical stability was observed for PPy, PPy-MO, and PPy-AB prepared at -24 °C, wherein a steady gain of capacitance was maintained during 5000 potential cycling. In addition, a PPy-based supercapacitor device was fabricated to demonstrate the energy storage characteristics of PPy, where it showed good capacitive behavior and stability. Overall, frozen-state polymerized PPy posed an impressive capacitive performance for flexible supercapacitors.

Tuning of Morphological and Antibacterial Properties of Poly(3,4-ethylenedioxythiophene):Peroxodisulfate by Methyl Violet.

This study demonstrates a one-step synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) in the presence of the methyl violet (MV) dye. The structural properties of PEDOT:peroxodisulfate were studied using Raman and MALDI-TOF spectroscopies. The use of the MV dye in the polymerization process resulted in a change in the typical irregular morphology of PEDOT:peroxodisulfate, leading to the formation of spherical patterns. SEM and TEM analyses revealed that increasing the dye concentration can produce larger spherical aggregates probably due to the hydrophobic and π-π interactions. These larger aggregates hindered the charge transport and reduced the electrical conductivity. Interestingly, at higher dye concentrations (0.05 and 0.075 M), the PEDOT:peroxodisulfate/MV films exhibited significantly improved antibacterial activity against Staphylococcus aureus and Escherichia coli. Furthermore, the PEDOT:peroxodisulfate films with the incorporated MV dye exhibited a well-defined and repeatable redox behavior. The remarkable amalgamation of their optical, electrochemical and antibacterial properties provides the PEDOT:peroxodisulfate/MV materials with an immensely diverse spectrum of applications, including in optical sensors and medical devices.

Polypyrrole Aerogels: Efficient Adsorbents of Cr(VI) Ions from Aqueous Solutions.

Three-dimensional and porous polypyrrole (PPy) aerogels were prepared using a facile two-step procedure in which cryogels were synthesized via the cryopolymerization of pyrrole with iron (III) chloride in the presence of supporting water-soluble polymers (poly(N-vinylpyrrolidone), poly(vinyl alcohol), gelatin, methylcellulose or hydroxypropylcellulose), followed by freeze-drying to obtain aerogels. The choice of supporting polymers was found to affect the morphology, porosity, electrical conductivity, and mechanical properties of PPy aerogels. PPy aerogels were successfully used as adsorbents to remove toxic Cr(VI) ions from aqueous solutions.

Effect of a Zr-Based Metal-Organic Framework Structure on the Properties of Its Composite with Polyaniline.

Composites of polyaniline (PANI) and Zr-based metal-organic frameworks (MOFs), UiO-66 and UiO-66-NH2, were synthesized by the oxidative polymerization of aniline in the presence of MOF templates with the MOF content in the resulting materials (78.2 and 86.7 wt %, respectively) close to the theoretical value (91.5 wt %). Scanning electron microscopy and transmission electron microscopy showed that the morphology of the composites was set by the morphology of the MOFs, whose structure was mostly preserved after the synthesis, based on the X-ray diffraction data. Vibrational and NMR spectroscopies pointed out that MOFs participate in the protonation of PANI and conducting polymer chains were grafted to amino groups of UiO-66-NH2. Unlike PANI-UiO-66, cyclic voltammograms of PANI-UiO-66-NH2 showed a well-resolved redox peak at around ≈0 V, pointing at the pseudocapacitive behavior. The gravimetric capacitance of PANI-UiO-66-NH2, normalized per mass of the active material, was also found to be higher compared to that of pristine PANI (79.8 and 50.5 F g-1, respectively, at 5 mV s-1). The introduction of MOFs into the composites with PANI significantly improved the cycling stability of the materials over 1000 cycles compared to the pristine conducting polymer, with the residual gravimetric capacitance being ≥100 and 77%, respectively. Thus, the electrochemical performance of the prepared PANI-MOF composites makes them attractive materials for application in energy storage.

Polypyrrole-Barium Ferrite Magnetic Cryogels for Water Purification.

Magnetic polypyrrole-gelatin-barium ferrite (PPy-G-BaFe) cryogels/aerogels were synthesized by one-step oxidative cryopolymerization of pyrrole in the presence of various fractions of barium ferrite (BaFe) nanoparticles, dispersed in aqueous gelatin solution. The successful incorporation of BaFe into the composites was confirmed by elemental analysis and scanning electron microscopy paired with an energy-dispersive X-ray detector. The maximum achieved content of BaFe in the resulting material was 3.9 wt%. The aerogels with incorporated BaFe had significantly higher specific surface area and conductivity, reaching 19.3 m2 g-1 and 4 × 10-4 S cm-1, respectively, compared to PPy-G aerogel, prepared in the absence of BaFe (7.3 m2 g-1 and 1 × 10-5 S cm-1). The model adsorption experiment using an anionic dye, Reactive Black 5, showed that magnetic PPy-G-BaFe aerogel, prepared at 10 wt% BaFe fraction, had significantly higher adsorption rate and higher adsorption capacity, compared to PPy-G (dye removal fraction 99.6% and 89.1%, respectively, after 23 h). Therefore, the prepared PPy-G-BaFe aerogels are attractive adsorbents for water purification due to their enhanced adsorption performance and the possibility of facilitated separation from solution by a magnetic field.

Fabrication of polyaniline/poly(vinyl alcohol)/montmorillonite hybrid aerogels toward efficient adsorption of organic dye pollutants.

Fabrication of adsorbents with excellent adsorption capacity, outstanding stability, easy separation ability, excellent recyclability and widely generality for organic dyes removal from wastewater remains challenging. Herein, three-dimensional polyaniline/poly(vinyl alcohol)/montmorillonite (PANI/PVAL/MMT) hybrid aerogels with easy separation performance and highly effective reusable adsorption on both anionic and cationic dyes were fabricated by a simple in-situ polymerization method. As-prepared hybrid aerogels were characterized via infrared and Raman spectra, scanning electron microscopy, energy dispersive spectra mapping, small and wide-angle X-ray scattering, thermogravimetric analysis, mercury intrusion porosimetry and elemental analysis. The results showed that MMT particles were successfully incorporated into aerogel matrix. Well-defined hierarchical structure, where PANI nanofibers are coated on the skeleton wall, can be observed for PANI/PVAL/MMT when the incorporation amount of MMT was around 11.1 wt%. The adsorption performance of as-prepared hybrid aerogels on both anionic and cationic dyes was systemically carried out at different solution pH, adsorbent dosage and initial dye concentration. The data analysis showed that the adsorption process for PVAL/PANI/MMT aerogel for Reactive Black 5, methyl orange and safranin followed Freundlich isotherm and the maximum experimental adsorption capacities were found to be 199, 251 and 57.0 mg g-1 at 25 °C, respectively. Mechanism studies indicated that the electrostatic interaction is the main driving force for the adsorption of dyes. The results demonstrated that the fabricated hybrid aerogel is an efficient adsorbent for the removal of both anionic and cationic organic dyes.

Synthesis and Impedance Spectroscopy of Poly(p-phenylenediamine)/Montmorillonite Composites.

Poly(p-phenylenediamine)/montmorillonite (PPDA/MMT) composites were prepared by the oxidative polymerization of monomers intercalated within the MMT gallery, using ammonium peroxydisulfate as an oxidant. The intercalation process was evidenced by X-ray powder diffraction. The FT-IR and Raman spectroscopies revealed that, depending on the initial ratio between monomers and MMT in the polymerization mixture, the polymer or mainly oligomers are created during polymerization. The DC conductivity of composites was found to be higher than the conductivity of pristine polymer, reaching the highest value of 10-6 S cm-1 for the optimal MMT amount used during polymerization. Impedance spectroscopy was performed over wide frequency and temperature ranges to study the charge transport mechanism. The data analyzed in the framework of conductivity formalism suggest different conduction mechanisms for high and low temperature regions.

Modulation of Differentiation of Embryonic Stem Cells by Polypyrrole: The Impact on Neurogenesis.

The active role of biomaterials in the regeneration of tissues and their ability to modulate the behavior of stem cells in terms of their differentiation is highly advantageous. Here, polypyrrole, as a representantive of electro-conducting materials, is found to modulate the behavior of embryonic stem cells. Concretely, the aqueous extracts of polypyrrole induce neurogenesis within embryonic bodies formed from embryonic stem cells. This finding ledto an effort to determine the physiological cascade which is responsible for this effect. The polypyrrole modulates signaling pathways of Akt and ERK kinase through their phosphorylation. These effects are related to the presence of low-molecular-weight compounds present in aqueous polypyrrole extracts, determined by mass spectroscopy. The results show that consequences related to the modulation of stem cell differentiation must also be taken into account when polypyrrole is considered as a biomaterial.

Frozen-State Polymerization as a Tool in Conductivity Enhancement of Polypyrrole.

Polypyrrole (PPy) is oxidatively polymerized in the frozen state at -24 °C in the presence of various organic dyes as morphology guiding agents in order to form homogeneous 1D PPy nanoforms. The freezing polymerization of pyrrole has a significant influence on the electrical conductivity and thermal stability but negligible influence on the yield compared to widely used room temperature polymerization.

The biocompatibility of polyaniline and polypyrrole 2: Doping with organic phosphonates.

Conducting polymers (CP) can be used as pH- and/or electro-responsive components in various bioapplications, for example, in 4D smart scaffolds. The ability of CP to maintain conductivity under physiological conditions is, therefore, their crucial property. Unfortunately, the conductivity of the CP rapidly decreases in physiological environment, as their conducting salts convert to non-conducting bases. One of the promising solutions how to cope with this shortcoming is the use of alternative "doping" process that is not based on the protonation of CP with acids but on interactions relying in acidic hydrogen bonding. Therefore, the phosphonates (dimethyl phosphonate, diethyl phosphonate, dibutyl phosphonate, or diphenyl phosphonate) were used to re-dope two most common representatives of CP, polyaniline (PANI) and polypyrrole (PPy) bases. As a result, PANI doped with organic phosphonates proved to have significantly better stability of conductivity under different pH. It has also been shown that cytotoxicity of studied materials determined on embryonic stem cells and their embryotoxicity, determined as the impact on cardiomyogenesis and erythropoiesis, depend both on the polymer and phosphonate types used. With the exception of PANI doped with dibutyl phosphonate, all PPy-based phosphonates showed better biocompatibility than the phosphonates based on PANI.

Carbon Materials Derived from Poly(aniline-co-p-phenylenediamine) Cryogels.

Nitrogen-containing carbon derivatives were prepared by the carbonization of poly(aniline-co-p-phenylenediamine) cryogels in inert atmosphere. Lower aniline fraction in the comonomer mixture used for preparation of the cryogels led to the decrease of their thermal stability, a consequent increase of carbonization degree, and less defective structure of carbonized materials. The resulting carbonaceous products had up to 4 orders of magnitude higher specific surface area than their respective cryogel precursors, the highest value 931 m2 g-1 being achieved for carbonized poly(p-phenylenediamine) cryogel. Electrochemical characterization of the carbon derivatives demonstrated that the decrease in aniline concentration during the synthesis of the precursor cryogels led to higher gravimetric capacitance for corresponding carbonized materials. These materials can potentially be used for energy storage applications.

In-Vitro Hemocompatibility of Polyaniline Functionalized by Bioactive Molecules.

Hemocompatibility is an essential prerequisite for the application of materials in the field of biomedicine and biosensing. In addition, mixed ionic and electronic conductivity of conducting polymers is an advantageous property for these applications. Heparin-like materials containing sulfate, sulfamic, and carboxylic groups may have an anticoagulation effect. Therefore, sodium dodecylbenzenesulfonate, 2-aminoethane-1-sulfonic acid and N-(2-acetamido)-2-aminoethanesulfonic acid were used for modification of the representative of conducting polymers, polyaniline, and the resulting products were studied in the context of interactions with human blood. The anticoagulation activity was then correlated to surface energy and conductivity of the materials. Results show that anticoagulation activity is highly affected by the presence of suitable functional groups originating from the used heparin-like substances, and by the properties of polyaniline polymer itself.

Polyaniline colloids stabilized with bioactive polysaccharides: Non-cytotoxic antibacterial materials.

Colloidal polyaniline dispersions stabilized with biocompatible polysaccharides, sodium hyaluronate and chitosan (both with two different molecular weights), were successfully formulated. The colloids were characterized by UV-vis spectra, particle-size distributions and morphology, as well as by their biological properties in terms of cytotoxicity and antibacterial activity. Colloids containing both chitosan and hyaluronate showed only mild cytotoxicities, which were mainly governed by the concentration of conducting polyaniline in the colloid. Antibacterial activity of the samples, however, depended both on the type of polysaccharide and the ratio between the stabilizer and polyaniline mass. The colloid synthetized using 0.2 M aniline hydrochloride, 0.1 M ammonium persulfate, and 1 wt.% sodium hyaluronate of molecular weight of 1.8-2.1 × 106 exhibited the highest antibacterial activity against both gram positive and gram negative bacteria. This formulation, therefore, allowed for the formation of potentially stimuli-responsive antibacterial colloidal particles with low cytotoxicity.

Tailoring of carbonized polypyrrole nanotubes core by different polypyrrole shells for oxygen reduction reaction selectivity modification.

By using methyl orange template, polypyrrole nanotubes were obtained by the oxidative polymerization of pyrrole. The nanotubes were carbonized in inert atmosphere to nitrogen-enriched carbon nanotubes. These were subsequently coated with 20 wt% of polypyrrole prepared in the absence or the presence of anionic dyes (methyl orange or Acid Blue 25). The morphology of all the samples was examined by the electron microscopies, FTIR and Raman spectroscopies. Moreover, X-ray photoelectron spectroscopy and elemental analysis were used to prove the chemical structure and the successful coating process. Electron paramagnetic resonance analysis was used to calculate the spin concentrations. Significant impact of coating method is evidenced with neat polypyrrole coating providing a two-fold capacitance increase compared to uncoated nanotubes, while coating in the presence of Acid Blue 25 decreasing it slightly. With respect to oxygen reduction reaction, coatings irreversibly transformed in the first few cycles in the presence of the products of O2 reduction, presumably hydrogen peroxide, altering the oxygen reduction mechanism. This transformation allows the tailoring of the polymeric shell, over ORR active carbonaceous core, and tuning of the catalyst selectivity and optimization of materials performance for a given application - from alkaline fuel cells to hydrogen peroxide generation.

Exploring the Critical Factors Limiting Polyaniline Biocompatibility.

Today, the application of polyaniline in biomedicine is widely discussed. However, information about impurities released from polyaniline and about the cytotoxicity of its precursors aniline, aniline hydrochloride, and ammonium persulfate are scarce. Therefore, cytotoxicity thresholds for the individual precursors and their combinations were determined (MTT assay) and the type of cell death caused by exposition to the precursors was identified using flow-cytometry. Tests on fibroblasts revealed higher cytotoxicity of ammonium persulfate than aniline hydrochloride. Thanks to the synergic effect, both monomers in combination enhanced their cytotoxicities compared with individual substances. Thereafter, cytotoxicity of polyaniline doped with different acids (sulfuric, nitric, phosphoric, hydrochloric, and methanesulfonic) was determined and correlated with impurities present in respective sample (HPLC). The lowest cytotoxicity showed polyaniline doped with phosphoric acid (followed by sulfuric, methanesulfonic, and nitric acid). Cytotoxicity of polyaniline was mainly attributed to the presence of residual ammonium persulfate and low-molecular-weight polar substances. This is crucial information with respect to the purification of polyaniline and production of its cytocompatible form.

The biocompatibility of polyaniline and polypyrrole: A comparative study of their cytotoxicity, embryotoxicity and impurity profile.

Conducting polymers (CP), namely polyaniline (PANI) and polypyrrole (PPy), are promising materials applicable for the use as biointerfaces as they intrinsically combine electronic and ionic conductivity. Although a number of works have employed PANI or PPy in the preparation of copolymers, composites, and blends with other polymers, there is no systematic study dealing with the comparison of their fundamental biological properties. The present study, therefore, compares the biocompatibility of PANI and PPy in terms of cytotoxicity (using NIH/3T3 fibroblasts and embryonic stem cells) and embryotoxicity (their impact on erythropoiesis and cardiomyogenesis within embryonic bodies). The novelty of the study lies not only in the fact that embryotoxicity is presented for the first time for both studied polymers, but also in the elimination of inter-laboratory variations within the testing, such variation making the comparison of previously published works difficult. The results clearly show that there is a bigger difference between the biocompatibility of the respective polymers in their salt and base forms than between PANI and PPy as such. PANI and PPy can, therefore, be similarly applied in biomedicine when solely their biological properties are considered. Impurity content detected by mass spectroscopy is presented. These results can change the generally accepted opinion of the scientific community on better biocompatibility of PPy in comparison with PANI.

Polyaniline cryogels: Biocompatibility of novel conducting macroporous material.

Polyaniline cryogel is a new unique form of polyaniline combining intrinsic electrical conductivity and the material properties of hydrogels. It is prepared by the polymerization of aniline in frozen poly(vinyl alcohol) solutions. The biocompatibility of macroporous polyaniline cryogel was demonstrated by testing its cytotoxicity on mouse embryonic fibroblasts and via the test of embryotoxicity based on the formation of beating foci within spontaneous differentiating embryonic stem cells. Good biocompatibility was related to low contents of low-molecular-weight impurities in polyaniline cryogel, which was confirmed by liquid chromatography. The adhesion and growth of embryonic stem cells, embryoid bodies, cardiomyocytes, and neural progenitors prove that polyaniline cryogel has the potential to be used as a carrier for cells in tissue engineering or bio-sensing. The surface energy as well as the elasticity and porosity of cryogel mimic tissue properties. Polyaniline cryogel can therefore be applied in bio-sensing or regenerative medicine in general, and mainly in the tissue engineering of electrically excitable tissues.

Cell-compatible conducting polyaniline films prepared in colloidal dispersion mode.

Conducting polyaniline can be prepared and modified using several procedures, all of which can significantly influence its applicability in different fields of biomedicine or biotechnology. The modifications of surface properties are crucial with respect to the possible applications of this polymer in tissue engineering or as biosensors. Innovative technique for preparing polyaniline films via in-situ polymerization in colloidal dispersion mode using four stabilizers (poly-N-vinylpyrrolidone; sodium dodecylsulfate; Tween 20 and Pluronic F108) was developed. The surface energy, conductivity, spectroscopic features, and cell compatibility of thin polyaniline films were determined using contact-angle measurement, the van der Pauw method, Fourier-transform infrared spectroscopy, and assay conducted on mouse fibroblasts, respectively. The stabilizers significantly influenced not only the surface and electrical properties of the films but also their cell compatibility. Sodium dodecylsulfate seems preferentially to combine both the high conductivity and good cell compatibility. Moreover, the films with sodium dodecylsulfate were non-irritant for skin, which was confirmed by their in-vitro exposure to the 3D-reconstructed human tissue model.

Polypyrrole Nanotubes and Their Carbonized Analogs: Synthesis, Characterization, Gas Sensing Properties.

Polypyrrole (PPy) in globular form and as nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in the absence and presence of methyl orange, respectively. They were subsequently converted to nitrogen-containing carbons at 650 °C in an inert atmosphere. The course of carbonization was followed by thermogravimetric analysis and the accompanying changes in molecular structure by Fourier Transform Infrared and Raman spectroscopies. Both the original and carbonized materials have been tested in sensing of polar and non-polar organic vapors. The resistivity of sensing element using globular PPy was too high and only nanotubular PPy could be used. The sensitivity of the PPy nanotubes to ethanol vapors was nearly on the same level as that of their carbonized analogs (i.e., ~18% and 24%, respectively). Surprisingly, there was a high sensitivity of PPy nanotubes to the n-heptane vapors (~110%), while that of their carbonized analog remained at ~20%. The recovery process was significantly faster for carbonized PPy nanotubes (in order of seconds) compared with 10 s of seconds for original nanotubes, respectively, due to higher specific surface area after carbonization.