Composite sulfonated cation-exchange membranes modified with polyaniline and applied to salt solution concentration by electrodialysis

A method is developed for obtaining anisotropic composites based on the sulfonated cation-exchange MF-4SK and MK-40 membranes and the electroactive polymer polyaniline (PANI). The kinetics of aniline polymerization by successive diffusion in these membranes is investigated, and differences in the transport characteristics of the resulting MF-4SK/PANI and MK-40/PANI composites are identified. It is established from results of electroosmotic and diffusion experiments that the composite MF-4SK/PANI-1 membrane (after 1 h of aniline polymerization) suppresses electrolyte and water flow the most. Diffusion permeability drops by an order of magnitude, and water transport numbers are reduced by 50–70%. In the process of sodium chloride concentration by electrodialysis, the salt content of the concentrate increases by 50–70% with the composite MF-4SK/PANI-1 membrane compared to the base MF-4SK membrane and by 15–20% compared to the electrodialysis MK-40 membrane. Transport characteristics of the membrane pairs under investigation are calculated from the model of limiting concentration by electrodialysis: current efficiency, water transport numbers, osmotic and diffusion permeability. The dominant influence of the electroosmotic mechanism of water transport on the effect of salt solution concentration is established.     

Electrochemical synthesis of a novel sulfonated polyaniline and its electrochemical properties

A novel N-substituted aniline, N-(4-sulfonicbutyryl)aniline was synthesized and subsequently to be electropolymerized to yield a new conductive polymer, poly(N-(4-sulfonicbutyryl)aniline). X-ray photoelectron spectrum (XPS) of the polymer film was examined to propose the polymer molecular structure. The sulfonated polyaniline was also characterized by ¹H NMR, TGA, DTA, FTIR, and UV–vis spectra. The sulfonated polyaniline showed high conductivity in neutral aqueous solutions, which is two orders of magnitude higher than that of poly(N-acetylaniline) (PNAANI).     

Molecular properties of sulfonated polyaniline

The molecular characteristics of internally doped sulfonated polyaniline with a sulfonation degree of ∼1 are studied by the methods of viscometry and dynamic light scattering. In diluted aqueous-saline solutions, the molecules of sulfonated polyaniline are individual entities; they do not form intermolecular associates and do not dissociate into separate components. An increase in the concentration of NaCl in solution from 0 to 1 mol/l brings about a sharp gain in the intrinsic viscosity of the polymer and in the hydrodynamic radius of molecules. This effect results from the decomposition of zwitterion pairs responsible for the compact conformation of polymer molecules in water. The equilibrium rigidity of sulfonated polyaniline molecules is calculated from the hydrodynamic characteristics determined in a 1 M NaCl solution, where the electrostatic interaction may be considered to be suppressed. A length of the Kuhn segment of 1.46 nm is higher by a factor of 1.5 than the corresponding length for the initial polyaniline.     

Ohmic contacts between sulfonated polyaniline and metals

We have compared the resistivity, ρ, of sulfonated polyaniline (SPAN) prepared via three different synthetic routes: electrochemical synthesis with a supporting electrolyte (camphorsulfonic acid), ρ =340 Ω·m; electrochemical synthesis without a supporting electrolyte, ρ =530 Ω·m, and; chemical synthesis, ρ =166 Ω·m. Independent of the metal contact (Al, Au, Cu), SPAN forms ohmic contacts with the metal and the contact resistance r _c ~5 Ω does not correlate with the metal's work function. Electronic Publication     

Protonation of polyaniline with lightly sulfonated polystyrene

Protonation of polyaniline base with lightly sulfonated polystyrene in polar solvents such as dimethyl sulfoxide and N-methyl-2-pyrrolidone was investigated by UV-Vis absorption spectra. As the molar ratio of sulfonated polystyrene/polyaniline increases, the conversion from polyaniline base form to salt form is observed owing to increased protonation. The isosbestic point clearly shows that quinoid unit and semiquinoid unit are in equilibrium. They are functions of the sulfonic acid concentration and solvent media.     

Raman spectroelectrochemical study of polyaniline and sulfonated polyaniline in solutions of different pH

Raman spectroelectrochemical study has been done with electrochemically prepared films of polyaniline and a copolymer of polyaniline and metanilic acid using a green laser excitation (532 nm). The experimental variables included solutions of different pH between 0.5 and 9.0, and varying electrode potential between 0.0 and 0.8 V versus Ag/AgCl. Raman bands within the wavenumber limits of 500–1700 cm⁻¹ have been analysed, and their changes, proceeding with varying of electrode potential and solution pH, have been interpreted. It has been stressed that the spectral changes of polymer films proceed continuously rather than stepwise by changing the electrode potential. Considering leucoemeraldine and pernigraniline forms of polyaniline as fully reduced and oxidised structures, respectively, it could be concluded that many different redox forms can exist between these two limiting forms, rather than the only possible emeraldine form.     

Synthesis and characterization of single‐wall‐carbon‐nanotube‐doped emeraldine salt and base polyaniline nanocomposites

Nanocomposites of polyaniline (PANI) and single‐wall carbon nanotubes (SWNTs) were prepared and characterized via resonance Raman and electronic absorption spectroscopy (ultraviolet–visible/near‐infrared). The chemical synthesis of PANI was performed in the presence of SWNTs in concentrations ranging from 10 to 50 wt % (SWNT/PANI). The obtained materials were hydrophilic, homogeneous composite compounds. The chemical interaction between PANI (in the conducting emeraldine salt form and in the insulating emeraldine base form) and metallic and semiconducting nanotubes was investigated. The emeraldine salt form of the polymer was significantly stabilized in the composite in comparison with plain PANI. A selective electronic interaction process between PANI and metallic SWNTs was found. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 815–822, 2005     

Partially sulfonated polyaniline: conductivity and spectroscopic study

Polyaniline and set of copolymers of aniline with orthanilic acid (OA) were prepared by oxidation of monomers with ammonium peroxydisulfate. Amount of OA in mixture of comonomers was varied from 0 to 10%. The higher amount of OA resulted in decrease of conductivity and increased steepness of temperature dependence of conductivity. The X-ray photoelectron spectroscopy showed content of self-doping groups in surface layer slightly higher than expected from the feed ratio of comonomers. Shifts of positions of bands of ring stretching vibrations towards their position in polyaniline base and shift of the band of protonated units Q=NH⁺–B or B–NH^+?–B in the FTIR spectra observed with increasing amount of OA have shown increase of electron localization in copolymers. Finally, Raman spectroscopy proved that sulfonic groups act as structural defects in polymer’s geometry. Polarons are expected to be localized on short isolated segments between the structural defects.     

Adsorption kinetics and thermodynamics of acid dyes on a carboxymethylated chitosan-conjugated magnetic nano-adsorbent

The monodisperse chitosan-conjugated Fe(3)O(4) nanoparticles with a mean diameter of 13.5 nm were fabricated by the carboxymethylation of chitosan and its covalent binding onto Fe(3)O(4) nanoparticles via carbodiimide activation. The carboxymethylated chitosan (CMCH)-conjugated Fe(3)O(4) nanoparticles with about 4.92 wt.-% of CMCH had an isoelectric point of 5.95 and were shown to be quite efficient as anionic magnetic nano-adsorbent for the removal of acid dyes. Both the adsorption capacities of crocein orange G (AO12) and acid green 25 (AG25), as the model compounds, decreased with increasing pH, and the decreasing effect was more significant for AO12. On the contrary, the increase in the ionic strength decreased the adsorption capacity of AG25 but did not affect, obviously, the adsorption capacity of AO12. By the addition of NaCl and NaOH, both AO12 and AG25 could desorb and their different desorption behavior could be attributed to the combined effect of pH and ionic strength. From the adsorption kinetics and thermodynamics studies, it was found that both the adsorption processes of AO12 and AG25 obeyed the pseudo-second-order kinetic model, Langmuir isotherm, and might be surface reaction-controlled. Furthermore, the time required to reach the equilibrium for each one was significantly shorter than those using the micro-sized adsorbents due to the large available surface area. Also, based on the weight of chitosan, the maximum adsorption capacities were 1 883 and 1 471 mg x g(-1) for AO12 and AG25, respectively, much higher than the reported data. Thus, the anionic magnetic nano-adsorbent could not only be magnetically manipulated but also possessed the advantages of fast adsorption rate and high adsorption capacity. This could be useful in the fields of separation and magnetic carriers. [formula in text].     

Adsorption of xanthene dyes by lysozyme crystals

Adsorption characteristics of cross-linked lysozyme crystals of different morphologies (tetragonal, orthorhombic, triclinic and monoclinic) were examined using four anionic dyes (fluorescein, eosin, erythrosin, and rose bengal), one zwitterionic dye (rhodamine B), and one cationic dye (rhodamine 6G). The adsorption isotherms were of the Langmuir type for all examined systems with the exception of rhodamine B adsorption by monoclinic crystals. The weakest adsorption was observed for the cationic dye, rhodamine B, whereas dianionic dyes, eosin, rose bengal, and erythrosin were strongly adsorbed on the protein surface. The adsorption capacities of the crystals for the dyes were found to depend on both charge and hydrophobicity of the dye, reflecting the heterogeneous character of the lysozyme pore surface. The adsorption affinity of the crystals for the dyes was a function of the dyes' hydrophobicity. Furthermore, the crystal morphology was identified as an additional factor determining capacity and affinity for dye adsorption. Differences between crystals prepared in the presence of the same precipitant were lower than between morphologies prepared with different precipitants.     

One-step preparation of sulfonated carbon and subsequent preparation of hybrid material with polyaniline salt: a promising supercapacitor electrode material

The present trend to increase the energy density of electrochemical supercapacitor is to hybrid the electrochemical double layer capacitance electrode materials of carbon with loading or encapsulation of transition metal oxide or conductive polymeric pseudocapacitor materials as the binary or ternary hybrid electrochemical active materials. In this work, we selected polyaniline salt-sulfonated carbon hybrid (PANI-SA?C _SA ) as a cheaper electrode material for supercapacitor electrode. Sulfonated carbon (C _SA ) was prepared from hydrothermal carbonization of furaldehyde and p-toluenesulfonic acid. Polyaniline-sulfate salt containing sulfonated carbon was prepared by chemical oxidative polymerization of aniline using ammonium persulfate in presence of sulfuric acid and sulfonated carbon via aqueous, emulsion and interfacial polymerization pathways. Formation of hybrid material was confirmed from scanning electron microscopy. Among the hybrid prepared with three different polymerization pathways, hybrid prepared by aqueous polymerization pathway showed better electrochemical performance. The specific capacitance of the hybrid prepared via aqueous polymerization was 600 F g^?1, which is higher than that of the pristine PANI-SA (350 F g^?1) and C _SA (30 F g^?1). Hybrid material was subjected for 8000 charge-discharge cycles and at 8000 cycles; it showed 88% retention of its original specific capacitance value of 485 F g^?1 with coulombic efficiency (97–100%). These results showed that C _SA micro spheres prevent the degradation of PANI-SA chains during charge/discharge cycles. Specific capacitance, cycle life, low solution resistance, low charge transfer resistance and high phase angle value of PANI-SA?C _SA supercapacitor cell indicates a higher performance supercapacitor system.

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Graphical abstract Synthesis of hybrid of sulfonated carbon with polyaniline sulfate salt and its supercapacitor performance Ravi Bolagam, Palaniappan Srinivasan,^* Rajender Boddula

     

Adsorption of direct dyes from aqueous solutions by carbon nanotubes: determination of equilibrium, kinetics and thermodynamics parameters

This study examined the feasibility of removing direct dyes C.I. Direct Yellow 86 (DY86) and C.I. Direct Red 224 (DR224) from aqueous solutions using carbon nanotubes (CNTs). The effects of dye concentration, CNT dosage, ionic strength and temperature on adsorption of direct dyes by CNTs were also evaluated. Pseudo second-order, intraparticle diffusion and Bangham models were adopted to evaluate experimental data and thereby elucidate the kinetic adsorption process. Additionally, this study used the Langmuir, Freundlich, Dubinin and Radushkevich (D-R) and Temkin isotherms to describe equilibrium adsorption. The adsorption percentage of direct dyes increased as CNTs dosage, NaCl addition and temperature increased. Conversely, the adsorption percentage of direct dyes decreased as dye concentration increased. The pseudo second-order model best represented adsorption kinetics. Based on the regressions of intraparticle diffusion and Bangham models, experimental data suggest that the adsorption of direct dyes onto CNTs involved intraparticle diffusion, but that was not the only rate-controlling step. The equilibrium adsorption of DR86 is best fitted in the Freundlich isotherm and that of DR224 was best fitted in the D-R isotherm. The capacity of CNTs to adsorb DY86 and DR224 was 56.2 and 61.3 mg/g, respectively. For DY86, enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were 13.69 kJ/mol and 139.51 J/mol K, respectively, and those for DR224 were 24.29 kJ/mol and 172.06 J/mol K, respectively. The values of DeltaH(0), DeltaG(0) and E all indicate that the adsorption of direct dyes onto CNTs was a physisorption process.     

Extraction-chromatographic determination of sulfonated azo dyes in aqueous solutions

The extraction of sulfonated azo dyes E102, E110, E122, E124, and E129 from aqueous solutions using hydrophilic solvents and their mixtures in the presence of a salting-out agent (ammonium sulphate) has been studied. Some regularities of extraction have been revealed. The composition of the mobile phase has been optimized and a procedure has been proposed for the identification and determination of the dyes in aqueous solutions by thin-layer chromatography in concentrations of 0.1–0.01 μg/L. An office scanner and a personal computer have been used to process the results of the separate determination of the dyes.     

Adsorption of bile acid by chitosan-orotic acid salt and its application as an oral preparation

The orotic acid (OT) salt of chitosan (CS), CS-OT, and that of a CS derivative, CP, were prepared, and the adsorption of primary or secondary bile acid was investigated. Calcium-induced alginate gel beads (Alg-Ca) containing CS-OT were also prepared and autoclaved, and the possibility of these beads to act as a vehicle for oral administration to prevent hyperlipidemia was investigated. When taurocholate (TCA) and glycocholate (GCA) were present together in the medium, CS-OT adsorbed identical amounts of both bile acids. This trend was seen in all CPs, although the capacity to adsorb bile acid was affected by the number and/or structure of the amino groups in the CP. On the other hand, taurodeoxycholate, a secondary bile acid was preferentially adsorbed over TCA and GCA. Alg-Ca containing CS-OT took up bile acids in a similar manner as CS-OT irrespective of the water content of the gel matrix. As all elements can be taken as a food, Alg-Ca containing CS-OT could serve as a useful dietary agent for the prevention of hyperlipidemia, which is a lifestyle-related disease.     

Determination of sulfonated azo dyes in river water samples by capillary zone electrophoresis

A method based on capillary zone electrophoresis coupled with photodiode-array detection has been developed to determine several sulfonated dyes, including a sulfonated dye (acid yellow 1), and the sulfonated azo dyes acid orange 7, acid orange 12, acid orange 52, acid red 26, acid red 27 and acid red 88. A CElect-FS75 CE column is used. The electrophoresis buffer contains a 1:5 dilution of 10 mM phosphoric acid and tetrabutylammonium hydroxide buffer (pH 11.5), and 25 mM of triethylamine, the final pH being 11.55. The detection limits for the seven dyes ranged from 0.1 to 4.53 microg/ml. Spiked river water samples (100 ml), containing different concentration levels (0.025-0.150 microg/ml) of the dyes were analyzed after acidification (pH 3) and pre-concentration in disposable SPE Oasis HLB, 1 ml cartridges.     

Characterization of sulfonated azo dyes and aromatic amines by pyrolysis gas chromatography/mass spectrometry

Sixteen sulfonated and unsulfonated azo dyes as well as eleven sulfonated and unsulfonated aromatic amines were analyzed and qualitatively characterized by means of pyrolysis gas chromatography/mass spectrometry at different temperatures. Aniline and aminonaphthalene were found to be the dominant pyrolysis products of sulfonated aromatic amines and dyes. Azo dye and dye class specific key compounds such as benzidine, vinyl-p-base and 4-aminoazobenzene could be identified by pyrolysis gas chromatography/mass spectrometry of commercial acid, cationic, direct, reactive and solvent dyes. 500 degrees C was the optimal pyrolysis temperature for most of the pyrolyzed compounds. The method was applied to a dried sample of a textile wastewater concentrate from a dyeing process. Reactive azo dyes of the group of Remazol dyes and anthraquinone dyes could be identified as the major compounds of the sample. The finding of caprolactam (a printing additive) suggests that the wastewater contained effluent from a process of heat-activated printing with reactive dyes. p-Chloraniline, a banned aromatic amine, was identified. Chemical reduction of the wastewater sample prior to pyrolysis resulted in the release of volatile aromatic amines and aided the classification of several products of pyrolysis.     

Adsorption of anionic dyes on chitosan beads. 1. The influence of the chemical structures of dyes and temperature on the adsorption kinetics

In this work, chitosan beads were synthesized in acidic medium and cross-linked in 1% glutaraldehyde solution. The characterization of the materials using TG/DTG, XRD, and BET surface areas showed that the beads did not modify their characteristics after the cross-linking reaction. The cross-linked beads were utilized as adsorbents for the removal of the yellow-, blue-, and red-anionic reactive dyes from aqueous solutions at pH 2.0. Adsorption of the yellow-dye increased from 25 to 50 degrees C. However, adsorption of the blue-dye decreased from 25 to 50 degrees C. Interestingly, the adsorption of the red-dye decreased from 25 to 35 degrees C and increased from 45 to 50 degrees C. The kinetic data were evaluated using an Avrami kinetic model, where the parameter n was related to the determination of changes in the adsorption mechanisms. Adsorption data of the dyes in relation to the contact time, the chemical structures of the dyes, and temperature were presented and were discussed.     

Influence of different copper(II) salts on the oxidation and doping reactions of emeraldine base polyaniline

A spectroscopic investigation of the products formed in the reaction of emeraldine base (EB-PANI) with copper(II) ions in dimethylacetamide (DMA) is presented. It is well known that metal cations can dope emeraldine base polyaniline (EB-PANI) through a pseudo-protonation reaction. Resonance Raman, UV–vis-NIR, and EPR data, obtained for Cu²⁺/EB-PANI solutions prepared using CuCl₂·2 H₂O, Cu(NO₃)₂· 3 H₂O or Cu(CH₃COO)₂·H₂O as Cu²⁺ sources, showed that the species formed in reactions of EB-PANI and Cu²⁺ ions are dependent on the anions of the copper salt employed. EPR spectra pointed out that the environments of Cu²⁺ ions with acetate, chloride or nitrate as anions in DMA solution are distinct. Resonance Raman and UV–vis-NIR data demonstrated that the main reactions are the oxidation of EB-PANI to pernigraniline base (PB-PANI) and doping of EB-PANI to ES-PANI (emeraldine salt) when a direct coordination of Cu²⁺ ions to PANI exists. With nitrate as very weak coordinating anion, ES-PANI is formed preferentially. When copper chloride is used, both oxidation and doping of EB-PANI are verified. Conversely with acetate, the dimeric cage structure of this copper salt is preserved in solution, and oxidation of EB-PANI to PB-PANI is the only observed reaction. These results demonstrate the possibility of modulating the products of reaction between Cu²⁺ ions and EB-PANI in DMA solution by changing the counter ion of the Cu²⁺ source.     

Adsorption of carbon disulfide on activated carbon modified by Cu and cobalt sulfonated phthalocyanine

A series of adsorbents were studied for removal efficiency of carbon disulfide (CS₂) under micro-oxygen conditions. It was found that activated carbon modified by Cu and cobalt sulfonated phthalocyanine (CoSPc) denoted as ACCu–CoSPc showed significantly enhanced adsorption ability. Reaction temperature was found to be a key factor for adsorption, and 20 °C seems to be optimal for CS₂ removal. Samples were analyzed by N₂-BET, XRD, XPS, SEM–EDS and CO₂-TPD. The characterization results demonstrated that large quantities of SO₄ ^2? anions were formed and adsorbed in the reaction process. SO₂, CS₂ and COS were detected in the effluent gas generated from the temperature programmed desorption of ACCu–CoSPc–CS₂. Therefore, it can be concluded that ACCu–CoSPc most likely acted as a catalyst in the adsorption/oxidation process on the surface of the impregnated sample. The generated sulfide and sulfur oxide can cover the active sites of adsorbents, resulting in pronounced reduction of adsorbent activity. Finally, the exhausted ACCu–CoSPc can be regenerated by thermal desorption.