Bulk Polyaniline Research Articles

Preparation of Anionic Surfactant-Based One-Dimensional Nanostructured Polyaniline Fibers for Hydrogen Storage Applications

Polyaniline fibers were prepared in the presence of anionic surfactant in an ice medium to nucleate in one dimension and were compared to bulk polyaniline prepared at an optimum temperature. Fourier-transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD) were used to investigate the structural analysis of the prepared samples. A conductivity study reveals that polyaniline fibers have high conductivity compared to bulk polyaniline. Hydrogen storage measurements confirm that the polyaniline fibers adsorbed approximately 86% of the total actual capacity of 8-8.5 wt% in less than 9 min, and desorption occurs at a lower temperature, releasing approximately 1.5 wt% of the hydrogen gases when the pressure is reduced further to 1 bar.

Electrical and Structural Characterization of Polyaniline Synthesized in Acid Medium Having Nickel Salts as Impurities

Electrical properties of polyaniline (PANI) synthesized in a solution containing nickel salts are investigated. The structural characterization by scanning electron microscopy shows that PANI yielded in nickel chloride (NiCl2) has thicker structures with high porosity that increases insofar NiCl2 concentration does. The pH variation monitoring due to the nickel salt inclusion in solution shows that mass and thickness are strongly dependent on pH variation. Thermogravimetric investigation reveals that PANI formed in the presence of nickel salts is thermally more stable. This fact is more accentuated in samples produced in nickel nitrate and, also, produces the absorbance peak shift of some functional groups, as well as their intensification, as pointed by the infrared spectroscopy analysis. On the other side, the electrical characterization through the current–potential analysis shows that PANI conductivity is larger in PANI yielded in the presence of sulfates and lower in nitrates, while the impedance electrochemical analysis evidences the formation of a surface passivated PANI region having higher resistance and lower capacitance than PANI in bulk. Concerning the resistance of this region, the difference between surface and bulk PANI is smaller in the sample yielded in NiCl2, but the difference in capacitance is greater.

Two-Dimensional CVD-Graphene/Polyaniline Supercapacitors: Synthesis Strategy and Electrochemical Operation.

Nanocomposites of graphene materials and conducting polymers have been extensively studied as promising materials for electrodes of supercapacitors. Here, we present a graphene/polyaniline heterostructure consisting of a CVD-graphene and polyaniline monolayer and its electrochemical operation in a supercapacitor. The synthesis employs functionalization of graphene by p-phenylene sulfonic groups and oxidative polymerization of anilinium by ammonium persulfate under reaction conditions, providing no bulk polyaniline. Scanning electron microscopy, atomic force microscopy, and Raman spectroscopy showed the selective formation of polyaniline on the graphene. In situ Raman spectroelectrochemistry and cyclic voltammetry (both in a microdroplet setup) confirm the reversibility of polyaniline redox transitions and graphene electrochemical doping. After an increase within the initial 200 cycles due to the formation of benzoquinone-hydroquinone defects in polyaniline, the specific areal capacitance remained for 2400 cycles with ±1% retention at 21.2 μF cm-2, one order of magnitude higher than the capacitance of pristine graphene.

Selective Formation of Polyaniline Confined in the Nanopores of a Metal-Organic Framework for Supercapacitors.

In this study, a strategy that can result in the polyaniline (PANI) solely confined within the nanopores of a metal-organic framework (MOF) without forming obvious bulk PANI between MOF crystals is developed. A water-stable zirconium-based MOF, UiO-66-NH2 , is selected as the MOF material. The polymerization of aniline is initiated in the acidic suspension of UiO-66-NH2 nanocrystals in the presence of excess poly(sodium 4-styrenesulfonate) (PSS). Since the pore size of UiO-66-NH2 is too small to enable the insertion of the bulky PSS, the quick formation of pore-confined solid PANI and the slower formation of well dispersed PANI:PSS occur within the MOF crystals and in the bulk solution, respectively. By taking advantage of the resulting homogeneous PANI:PSS polymer solution, the bulk PANI:PSS can be removed from the PANI/UiO-66-NH2 solid by successive washing the sample with fresh acidic solutions through centrifugation. As this is the first time reporting the PANI solely confined in the pores of a MOF, as a demonstration, the obtained PANI/UiO-66-NH2 composite material is applied as the electrode material for supercapacitors. The PANI/UiO-66-NH2 thin films exhibit a pseudocapacitive electrochemical characteristic, and their resulting electrochemical activity and charge-storage capacities are remarkably higher than those of the bulk PANI thin films.

D.C electrical conductivity of prepared pure and doped polyaniline salt

Pure Polyaniline salt, and protonation PANI by H2SO4 were synthesized by electro-chemical oxidative polymerization of aniline with acidity of H2SO4. The solution was prepared in reaction temperature equal 291 K and the acidity of aqueous solution was 1 molarities. The prepared polyaniline was characterized by FT-IR, the result indicate that the intensity is increase with increasing of applied voltage. The dc conductivity has been measured for bulk polyaniline pure and doped in the form of compressed pellet with evaporated Ohmic Al electrodes in temperature range (303-423) K. The Eav energy of the thermal rate process of the electrical conductivity was determined. The results indicate that the dc conductivity of doped samples are two or three orders of magnitude higher by comparison with the pure sample and found that the increasing in conductivity of prepared samples with applied voltage is systematic.

Preparation and Characterization of WS₂@SiO₂ and WS₂@PANI Core-Shell Nanocomposites.

Two tungsten disulfide (WS2)-based core-shell nanocomposites were fabricated using readily available reagents and simple procedures. The surface was pre-treated with a surfactant couple in a layer-by-layer approach, enabling good dispersion of the WS2 nanostructures in aqueous media and providing a template for the polymerization of a silica (SiO2) shell. After a Stöber-like reaction, a conformal silica coating was achieved. Inspired by the resulting nanocomposite, a second one was prepared by reacting the surfactant-modified WS2 nanostructures with aniline and an oxidizing agent in an aqueous medium. Here too, a conformal coating of polyaniline (PANI) was obtained, giving a WS2@PANI nanocomposite. Both nanocomposites were analyzed by electron microscopy, energy dispersive X-ray spectroscopy (EDS) and FTIR, verifying the core-shell structure and the character of shells. The silica shell was amorphous and mesoporous and the surface area of the composite increases with shell thickness. Polyaniline shells slightly differ in their morphologies dependent on the acid used in the polymerization process and are amorphous like the silica shell. Electron paramagnetic resonance (EPR) spectroscopy of the WS2@PANI nanocomposite showed variation between bulk PANI and the PANI shell. These two nanocomposites have great potential to expand the use of transition metals dichalcogenides (TMDCs) for new applications in different fields.

Tailoring the Diameters of Polyaniline Nanofibers for Sensor Application.

Size control has been successfully achieved in inorganic materials, but it still remains a challenge in organic polymers due to their polydispersity. We here report a facial approach to tailor the diameter of polyaniline (PANI) nanofibers in a range of 200–30 nm via temperature-controlled polymerization from room temperature to −192 °C. It is shown that the formation of PANI nanofibers was directed by the self-assembly of an amphiphilic aniline–glutamic acid complex, which formed micelles with different sizes at various temperatures during polymerization. The size-dependent properties of the resulting PANI nanofibers, such as molecular weights, optical properties, crystallinity, and electron conductivity, have been discussed. Most importantly, we showed a more than 3 magnitude increase in the conductivities of doped PANI nanofibers with a decrease in the diameter from 150 to 30 nm. A homemade sensing device was constructed, and it is shown that PANI nanofibers with smaller diameters exhibit a much faster response than those of larger-sized fibers or bulk PANIs due to their large surface area and high intrinsic conductivities.

Composites of Fe2O3 nanosheets with polyaniline: Preparation, gas sensing properties and sensing mechanism

Fe2O3 nanosheets were in-situ deposited on the interdigitated gold electrodes by hydrothermal treatment of the electrospun nanofibers containing FeCl3 and poly(vinyl butyral). As-prepared electrode was further dip-coated with water-dispersible polyaniline (PANI) to fabricate a resistance gas sensor based on Fe2O3/PANI nanocomposite. The structure and morphology of the nanocomposite were investigated by X-ray diffraction pattern, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. It was found that the nanocomposite sensor exhibited much higher response magnitude towards low concentration of NH3 (0.5–10.7ppm) than the sensors based on either PANI or Fe2O3 at room temperature (∼20°C), indicating an obvious synergetic effect. The nanocomposite sensor was featured with ultra high response magnitude (relative resistance change of ∼3070% towards 10.7ppm of NH3) and excellent selectivity towards NH3. A sensing mechanism has been put forward, which takes into account of the conducting network comprising of bulk PANI and composites of PANI and Fe2O3 nanosheets. It was proposed that the p/n heterojunction established between Fe2O3 nanosheets and PANI coating played a major role in the highly desirable sensing performance of the composite.

Elastomeric Conducting Polyaniline Formed Through Topological Control of Molecular Templates.

A strategy for creating elastomeric conducting polyaniline networks is described. Simultaneous elastomeric mechanical properties (E < 10 MPa) and electronic conductivities (σ > 10 S cm(-1)) are achieved via molecular templating of conjugated polymer networks. Diblock copolymers with star topologies processed into self-assembled elastomeric thin films reduce the percolation threshold of polyaniline synthesized via in situ polymerization. Block copolymer templates with star topologies produce elastomeric conjugated polymer composites with Young's moduli ranging from 4 to 12 MPa, maximum elongations up to 90 ± 10%, and electrical conductivities of 30 ± 10 S cm(-1). Templated polyaniline films exhibit Young's moduli up to 3 orders of magnitude smaller compared to bulk polyaniline films while preserving comparable bulk electronic conductivity. Flexible conducting polymers have prospective applications in devices for energy storage and conversion, consumer electronics, and bioelectronics.

Charge Transport in Polypyrrole Nanotubes.

True metallic conductivity in conjugated polymers has been major challenge for the last few years. Heeger and co-workers have reported metallic conductivity in bulk polyaniline film, but the problem of metallic transport in their nanophase still remains unexplored. In the recent past, our group had observed metallic conductivity in single nanotube by studying I-V characteristics using Atomic Force Microscopy. In the present work, Polypyrrole (PPy) nanotubes with variable wall thickness have been synthesized by chemical route. Electrical measurements--current-voltage characteristics as well as variation of resistance over the temperature range from 12 K to 300 K for these nanotubes with variable wall thickness, have also been carried out. The conductivity varies widely from semiconductor to metallic as the wall thickness decreases. Transmission Electron Microscopic study, further, confirms that very aligned and ordered polymer chains are formed due to directional growth in thin walled polypyrrole nanotubes, results in true metallic conductivity with a positive temperature coefficient of resistance over the whole temperature range. To the best of our knowledge, there is no such systematic study reported so far which embraces variation of charge transport characteristics with varying wall thickness of conjugated polymer nanotubes involving both I-V and R-T measurements supplementing each other, which being the main focus of this communication.

AC electric field for rapid assembly of nanostructured polyaniline onto microsized gap for sensor devices.

Interconnected network of nanostructured polyaniline (PANI) is giving strong potential for enhancing device performances than bulk PANI counterparts. For nanostructured device processing, the main challenge is to get prototypes on large area by requiring precision, low cost and high rate assembly. Among processes meeting these requests, the alternate current electric fields are often used for nanostructure assembling. For the first time, we show the assembly of nanostructured PANI onto large electrode gaps (30-60 μm width) by applying alternate current electric fields, at low frequencies, to PANI particles dispersed in acetonitrile (ACN). An important advantage is the short assembly time, limited to 5-10 s, although electrode gaps are microsized. That encouraging result is due to a combination of forces, such as dielectrophoresis (DEP), induced-charge electrokinetic (ICEK) flow and alternate current electroosmotic (ACEO) flow, which speed up the assembly process when low frequencies and large electrode gaps are used. The main achievement of the present study is the development of ammonia sensors created by direct assembling of nanostructured PANI onto electrodes. Sensors exhibit high sensitivity to low gas concentrations as well as excellent reversibility at room temperature, even after storage in air.

Preparation and Electrochemical Characterization of Mesoporous Polyaniline-Silica Nanocomposites as an Electrode Material for Pseudocapacitors.

Mesoporous polyaniline-silica nanocomposites with a full interpenetrating structure for pseudocapacitors were synthesized via the vapor phase approach. The morphology and structure of the nanocomposites were deeply investigated by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis and nitrogen adsorption-desorption tests. The results present that the mesoporous nanocomposites possess a uniform particle morphology and full interpenetrating structure, leading to a continuous conductive polyaniline network with a large specific surface area. The electrochemical performances of the nanocomposites were tested in a mixed solution of sulfuric acid and potassium iodide. With the merits of a large specific surface area and suitable pore size distribution, the nanocomposite showed a large specific capacitance (1702.68 farad (F)/g) due to its higher utilization of the active material. This amazing value is almost three-times larger than that of bulk polyaniline when the same mass of active material was used.

Abnormally enhanced thermoelectric transport properties of SWNT/PANI hybrid films by the strengthened PANI molecular ordering

Single-walled carbon nanotube (SWNT)/polyaniline (PANI) hybrid films were prepared by casting the suspension containing well-dispersed SWNTs and CSA-doped PANI. The electrical conductivity of the SWNT/PANI film at first increased with the increasing SWNT content and then decreased at high SWNT content, whereas the Seebeck coefficient increased monotonically in the present SWNT content range. Moreover, the electrical conductivity values of the SWNT/PANI composites were much higher than the values calculated based on the series-connected two-component mixture model, whereas the dependence of the Seebeck coefficient on the SWNT content fitted well with the mixture model. Thermal conductivities increased with the SWNT content, but the rate of increase was much lower than the values estimated using the mixture model. The maximum values of electrical conductivity and Seebeck coefficient of hybrid films were up to 769 S cm−1 and 65 μV K−1. Consequently, the maximum thermoelectric power factor and ZT value at room temperature reached 176 μW m−1 K−2 and 0.12, respectively. The optimal TE property of the SWNT/PANI hybrid film was remarkably higher than those of either individual component of the composite, and exhibits the highest values for inorganic–organic composite materials reported so far. XRD and Raman analyses revealed that the PANI molecules in the composite film had a more expanded conformation, and were more orderly arranged compared with both pure PANI bulk and pure PANI film. The abnormally enhanced thermoelectric performance is attributed to the highly ordered PANI interface layer on the SWNT surface, which formed by the synergetic effect of chain expansion by the chemical interactions between PANI and the solvent and chain-ordering due to the π–π conjugation between PANI and CNTs.

Preparation and electrochemical properties of polyaniline nanofibers using ultrasonication

Polyaniline nanofibers have been successfully prepared by applying ultrasonic irradiation during oxidative polymerization of aniline in dilute hydrochloric acid and evaluated for suitability in lithium cells after doping with lithium perchlorate salt. Polyaniline nanofibers are confirmed by Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy, and transmission electron microscopy, and the efficiency of doping is confirmed by DC conductivity measurements at different temperatures. Electrochemical properties of nanofibers are evaluated, of which a remarkable increase in cycle stability is achieved when compared to polyaniline prepared by simple oxidative polymerization of aniline. The cell with nanofibrous polyaniline doped with LiClO4 delivers an initial discharge capacity value of 86mAhg−1 at 1 C-rate which is about 60% of theoretical capacity, and the capacity is slightly lowered during cycle and reaches 50% of theoretical capacity after 40 cycles. The cell delivers a stable and higher discharge capacity even at 2 C-rate compared to that of the cell prepared with bulk polyaniline doped with LiClO4.

Detection of Aniline Oligomers on Polyaniline–Gold Interface using Resonance Raman Scattering

In situ deposited conducting polyaniline films prepared by the oxidation of aniline with ammonium peroxydisulfate in aqueous media of various acidities on gold and silicon supports were characterized by Raman spectroscopy. Enhanced Raman bands were found in the spectra of polyaniline films produced in the solutions of weak acids or in water on gold surface. These bands were weak for the films prepared in solutions of a strong acid on a gold support. The same bands are present in the Raman spectra of the reaction intermediates deposited during aniline oxidation in water or aqueous solutions of weak or strong acids on silicon removed from the reaction mixture at the beginning of the reaction. Such films are formed by aniline oligomers adsorbed on the surface. They were detected on the polyaniline-gold interface using resonance Raman scattering on the final films deposited on gold. The surface resonance Raman spectroscopy of the monolayer of oligomers found in the bulk polyaniline film makes this method advantageous in surface science, with many applications in electrochemistry, catalysis, and biophysical, polymer, or analytical chemistry.

Ammonia Gas Sensing Characteristics of Spin Coated Polyaniline Films

The conductive layer of emeraldine base polyaniline (PANI) thin film coated on silicon has successfully tested for ammonia. The bulk PANI powder was synthesized by oxidative polymerization of aniline using ammonium peroxidisulfate in an acidic medium and dissolved in N-methyl pyrrolidone (NMP) for coating the thin film on Silicon using spin coater. FTIR, UVvisible, and SEM were used to characterize the PANI thin film. The electrical conductivity of the PANI films has been studied by measuring the change in electrical conductivity by Four Probe Set up on exposure to ammonia gas (NH3) at different concentrations from 100 ppm to 500 ppm. margin.

Comparison of Current-Voltage Characteristics of Bulk Polyaniline and Nano Dimensional Polyaniline Particles in Nanoporous Dielectric Matrix of MIL-101

We investigated current-voltage (I-V) characteristics of bulk polyaniline and aniline polymerized inside nanopores of chromium terephthalate dielectric matrix MIL-101. The temperature dependence of electrical conductivity σ (T) of these materials are described by the fluctuation-induced tunneling model (FIT), which means that the main contribution to a net conductivity is caused by contacts between particles of the polyaniline. The comparison of I-V for these two types of materials shown that I-V characteristics of bulk polyaniline are described by the quasi-1D VRH model while for aniline polymerized inside nanopores of chromium terephthalate dielectric matrix MIL-101 by extended FIT model.

Multiresidue determination of pesticides from aquatic media using polyaniline nanowires network as highly efficient sorbent for microextraction in packed syringe

A simple, rapid and sensitive method based on microextraction in packed syringe (MEPS), in combination with gas chromatography–mass spectrometry (GC–MS) was developed. Polyaniline (PANI) nanowires network was synthesized and used as sorbent of MEPS for the multiresidue determination of selected analytes from triazine, organochlrorine and organophosphorous pesticides in aqueous samples. The PANI nanowires network was prepared using soft template technique and its characterization was studied by scanning electron microscopy (SEM). The presence of micelles in this methodology showed to be an important parameter in shaping the growing polymer. Hexadecyltrimethylammonium bromide (HTAB) was used as structure directing agent in PANI preparation procedure and this was led to the formation of nanowires with diameters ranging from 35nm to 45nm. The synthesized PANI nanowires network showed higher extraction capability in comparison with the bulk PANI. Important parameters influencing the extraction and desorption processes including desorption solvent, elution volume, draw–eject cycles of sample, draw–eject mode, pH effect and amount of sorbent were optimized. Limits of detection were in the range of 0.07–0.3ngmL−1 using time scheduled selected ion monitoring (SIM) mode. The linearity of method was in the range from 0.5–200ngmL−1 to 0.2–1000ngmL−1. The method precision (RSD %) with three replicates were in the range of 5.3–18.4% at the concentration level of 5ngmL−1. The developed method was successfully applied to the Zayandeh-rood river water samples and the matrix factor obtained for the spiked real water samples were in the range of 0.79–0.94.

Amplified response and enhanced selectivity of metal-PANI fiber composite based vapor sensors

Nanocomposites of polyaniline (PANI) nanofibers and metal nanoparticles were fabricated using a single-step photo-assisted technique and tested as sensors. Nanofiber composites containing Ag- and Pt-nanoparticles were exposed to toluene and triethylamine and their response was compared to that of bare nanofibers and bulk PANI produced with the same technique. The larger surface areas of the nanofiber-based sensors resulted in shorter response times and in larger changes in conductivity than for bulk PANI sensors for all analytes. Nanofiber sensors with and without Ag or Pt particles had a comparable response when exposed to toluene, an analyte that induces swelling of the composites, but does not alter doping or react strongly with nanoparticles of noble metals. The composites reacted quite differently to triethylamine. The response time of Ag-containing composites was about 3 times faster than that of the nanofibers alone and about 1.5 times faster than that of PANI–Pt nanocomposites. The change in resistivity was about 6 times larger for PANI–Ag nanocomposites and more than 4 times larger than for the PANI–Pt nanocomposites. To better understand the stronger response of PANI–Ag nanocomposites, Raman spectra were taken which indicated that charge was transferred to Ag, and to a lesser extent to Pt, by the nanofibers. That is, Ag acts as a dopant. Exposure to triethylamine reduces the charge transfer and therefore the doping, thereby amplifying the response to the analyte.

Photocatalytic activity of polyaniline-TiO2 nanocomposites

The characteristics of the UV illumination-assisted degradation of Malachite green (MG) on highly active nanostructured-anatase TiO2, bulk Polyaniline (PAni), PAni nanoparticles and PAni-TiO2 nanocomposites have been studied. Dodecylbenzene sulphonic acid doped PAni-TiO2 nanocomposites were synthesized by a water-assisted self-assembly method. Samples were characterized using transmission electron microscopy, X-ray diffraction studies, Fourier Transform Infra red spectroscopy and photoluminescence studies. Photoluminescence intensity of TiO2 nanoparticles was found to decrease with the increase of PAni in the nanocomposite which can be attributed to the reduction of electron-hole pair recombination at the interface of PAni and TiO2 due to electron transfer from TiO2 to PAni. Exposure to UV light brought about the photocatalytic oxidation of MG in contact with bulk PAni, PAni and TiO2 nanoparticles, and PAni-TiO2 nanocomposites. The decrease in absorbance was measured, and its kinetics was analyzed using the Langmuir-Hinshelwood kinetic model. PAni-TiO2 nanocomposites exhibit higher photocatalytic activity than pure TiO2 nanoparticles, bulk PAni and PAni nanoparticles under the same degradation condition for MG. The enhanced photocatalytic activity of nanocomposites is attributed to the electron transfer from TiO2 to PAni resulting in enhancing the oxidative property of the TiO2 nanoparticles.