Copolypeptide-doped polyaniline nanofibers for electrochemical detection of ultratrace trinitrotoluene
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Polyaniline nanofibers
Trinitrotoluene
Nanostructured polyaniline is the key to greater success of this unique conducting polymer.
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The textile sector is one of the major culprits of water pollution, and demands immediate attention. The coloured textile effluent, loaded with toxic dyes, when mixed with waterbodies, may harm aquatic life, plants, animals, and humans. Although polyaniline in its different forms was utilised for the adsorption of different dyes, the pure nano-fibrous form of polyaniline, i.e., PANI nanofibers, have reportedly not been used for the removal of dyes from wastewater. The present study aimed to employ nano-structured polyaniline, in the form of polyaniline nanofibers (base; PNB—polyaniline nanofiber base) for the elimination of methylene blue (cationic dye; MB) dye from its solution. The polyaniline nanofiber base (PNB) was synthesised by an interfacial polymerisation technique using ammonium persulphate as the oxidant and toluene as the organic solvent, and was characterised by FTIR, SEM, BET, HRTEM and XRD techniques. The HRTEM and SEM results showed that the average size of the synthesised polyaniline nanofiber base (PNB) was about 60 nm. BET revealed the enhanced surface area of polyaniline nanofiber base (PNB), i.e., 48 m2g−1 in comparison to that of conventionally synthesised polyaniline, which is only 14 m2g−1. The electric conductivity of the polyaniline nanofiber base (PNB) was reportedly lesser (2.3 × 10−2 S/cm) than the salt form of the polyaniline, measured by four probe technique. The batch-wise adsorption of MB was conducted onto the polyaniline nanofiber base (PNB), and the influence of the preliminary dye concentration, duration of contact and polyaniline nanofiber base (PNB) dose, etc., were studied. The equilibrium values of these parameters are reported as 6 mg/L, 60 min and 2 g/L, respectively. The results revealed the 91% sorption of dye onto the polyaniline nanofiber base (PNB). The experimental data were best-fitted to Pseudo-second order (R2 = 0.99) and followed Freundlich isotherm model (R2 = 0.97). On desorption, about 86% of the absorbed dye was recovered and the regenerated adsorbent could be used efficiently for three more cycles.
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Abstract Among nano polyaniline materials, polyaniline nanofibers are the most important. The low conductivity and poor processability have become the biggest obstacles to the application of polyaniline as a practical material. The excellent characteristics of new polyaniline nanofiber materials can just overcome the shortcomings of Polyaniline in forming and processing. In this study, a new polyaniline nanofiber was prepared by chemical oxidation, its structure was characterized, the mechanism of improving its conductivity was studied, and its superior electrocatalytic activity was evaluated by Electrochemical performance test. The results show that the diameter of polyaniline nanofibers is 20nm ~ 50nm and the fiber length is 2µm ~ 5µm. The structure is uniform and the conductivity can reach 13.5 S/cm. he electrocatalytic activity of polyaniline nanofibers for oxygen evolution and chlorine evolution was systematically tested. It was found that the electrocatalytic activity of polyaniline nanofibers for oxygen evolution was higher than that of polyaniline nanofibers. The electrocatalytic activity of carbon paper electrode prepared by β-PbO 2 nano powder is superior to that of traditional chlorine evolution anode Ti/RuO 2 .
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The polyaniline nanofibers with different sizes were synthesized by using cyclic voltammetry at different potential scan rates, in the presence of ferrocenesulfonic acid. The potential scan rate controlled the formation and growth of polyaniline nuclei, which plays a key role in controlling nanofiber sizes. The average diameters of nanofibers decreased from about 130 nm to about 80 nm as the potential scan rate increased from 6 to 60 mV s (-1). We first observed an ordered change in the following spectra with the nanofiber sizes of polyaniline. The spectra of the X-ray diffraction indicated that the partially crystalline form existed in the polyaniline nanofibers and that the crystallinity of polyaniline increased with decreasing diameter of polyaniline nanofibers. The ESR spectra revealed the fact that the decrease in the intensity of the ESR signal was accompanied by the increase in the value of the peak-to-peak line width Delta H pp as the diameter of polyaniline nanofibers decreased. The 1H NMR spectra showed that a peak in a triplet caused by the +/- NH free radical was split into two peaks with different intensities and that their relative intensity also changed with the diameter of the polyaniline nanofibers.
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Known for more than 150 years, polyaniline is the oldest and potentially one of the most useful conducting polymers because of its facile synthesis, environmental stability, and simple acid/base doping/dedoping chemistry. Because a nanoform of this polymer could offer new properties or enhanced performance, nanostructured polyaniline has attracted a great deal of interest during the past few years. This Account summarizes our recent research on the syntheses, processing, properties, and applications of polyaniline nanofibers. By monitoring the nucleation behavior of polyaniline, we demonstrate that high-quality nanofibers can be readily produced in bulk quantity using the conventional chemical oxidative polymerization of aniline. The polyaniline nanostructures formed using this simple method have led to a number of exciting discoveries. For example, we can readily prepare aqueous polyaniline colloids by purifying polyaniline nanofibers and controlling the pH. The colloids formed are self-stabilized via electrostatic repulsions without the need for any chemical modification or steric stabilizer, thus providing a simple and environmentally friendly way to process this polymer. An unusual nanoscale photothermal effect called "flash welding", which we discovered with polyaniline nanofibers, has led to the development of new techniques for making asymmetric polymer membranes and patterned nanofiber films and creating polymer-based nanocomposites. We also demonstrate the use of flash-welded polyaniline films for monolithic actuators. Taking advantage of the unique reduction/oxidation chemistry of polyaniline, we can decorate polyaniline nanofibers with metal nanoparticles through in situ reduction of selected metal salts. The resulting polyaniline/metal nanoparticle composites show promise for use in ultrafast nonvolatile memory devices and for chemical catalysis. In addition, the use of polyaniline nanofibers or their composites can significantly enhance the sensitivity, selectivity, and response time of polyaniline-based chemical sensors. By combining straightforward synthesis and composite formation with exceptional solution processability, we have developed a range of new useful functionalities. Further research on nanostructured conjugated polymers holds promise for even more exciting discoveries and intriguing applications.
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The conjugated polymer polyaniline is a promising material for sensors, since its conductivity is highly sensitive to chemical vapors. Nanofibers of polyaniline are found to have superior performance relative to conventional materials due to their much greater exposed surface area. A template-free chemical synthesis is described that produces uniform polyaniline nanofibers with diameters below 100 nm. The interfacial polymerization can be readily scaled to make gram quantities. Resistive-type sensors made from undoped or doped polyaniline nanofibers outperform conventional polyaniline on exposure to acid or base vapors, respectively. The nanofibers show essentially no thickness dependence to their sensitivity.
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The electrical properties of the conducting polymer polyaniline change greatly upon exposure to various chemicals. Specifically, polyaniline undergoes doping and dedoping chemistry with acids and bases that result in conductivity changes of over eight orders of magnitude. This large range in conductivity can be utilized to make polyaniline chemical sensors. Polyaniline nanofibers are chemically synthesized using a simple, template-free method that produces nanofibers with narrow size distributions. They are easily cast on microelectrode arrays and are shown to respond significantly better than conventional films to a number of different gases, such as acids, bases, hydrazine, and organic vapors. This is explained through their high surface area, small diameter, and porous nature of the nanofiber films that appear to allow better diffusion of vapors into the films. Polyaniline nanofibers disperse well in water and, as a result, have been used to make new composite materials with water soluble compounds, such as metal salts. These composite films can then be used to enhance sensing to gases that unmodified polyaniline would otherwise not be able to detect. For example, metal salt/polyaniline nanofiber composite films are used to enhance polyaniline's ability to sense hydrogen sulfide due to a reaction of the metal salt with hydrogen sulfide that releases a strong acid that then dopes the polyaniline, resulting in a significant increase in conductivity. The wide range in gas detection capabilities and the use of composite films makes polyaniline nanofibers versatile chemical sensor materials that have good potential for many chemical detection applications, including homeland security.
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