Polyaniline is an organic semiconductor. It is prepared by the oxidative chemical or electrochemical oxidations of aniline in acidic aqueous media. The course of the oxidation can be followed by monitoring changes in temperature or pH. Depending on acidity conditions, polyaniline has globular, nanofibrilar, or nanotubular morphology. Polyaniline may also be obtained as thin films, coatings, or as colloidal dispersions. The conducting polyaniline salt convers to nonconducting polyaniline base under alkaline conditions. Its reprotonation by various acids offers a route for preparation of polyanilines with various properties. These processes are reflected in UV–vis, FTIR, and Raman spectra. The mechanism of conduction is based on the presence of delocalized polarons and protons. Polyaniline exhibits both the electronic and ionic conductivity. The stability of polyaniline at elevated temperature and in aggressive media is good. Polyaniline is converted to nitrogen‐containing carbon in inert atmosphere at 600°C. Biological properties and antimicrobial activity of polyaniline are outlined. The applications of polyaniline in batteries, corrosion protection, fuel cells, sensors, and supercapacitors are briefly reviewed.
The paper is focused on oxidative polymerization of aniline proceeding in an acid medium with a strong oxidant; formation of polyaniline (PANI) granular structures in different steps of the synthesis was studied. The relationship between the processes of self-organization of the growing polymer into supramolecular structures and the steps of molecular synthesis has been revealed. It was shown that during the induction period (the initial synthesis step), insoluble non-conducting products are formed. They are characterized by the absorption band at 430 nm corresponding to the wavelength of the phenazinium cation radical peak. In the second step, the polymer chain growth, conducting PANI granules with the diameter of 50 nm were obtained. These granules consist of spherical particles with the diameter as small as several nanometers. Then, the granule dimensions increased to 200 nm due to the growth of the spheres; the sphere diameter reached 20 nm. The number of spheres in a granule remained constant. Both precipitate and PANI film consist of common structural elements, polymer spheres, organized into granules and larger structures. Suppression of the polymer chain growth leads to the formation of non-conducting aniline oligomers which are self-organized into large particles with fractal structure. To describe the self-organization processes of a growing polymer chain, the diffusion-limited aggregation mechanism was used.
The sorption properties of polymers with a polyconjugated chain structure (polyaniline and polypyrrole) are considered. The molecular mechanism of sorption by these polymers of various compounds such as heavy metal ions, toxic organic compounds and micropathogens, which are the most hazardous and stubborn contaminants in water, is discussed. The use of such sorbents to purify water from micropathogens, including bacteria and viruses, is addressed for the first time. The adsorption capacity of polyconjugated polymers for these types of contaminants, the efficiency of water treatment by these sorbents and characteristics of the currently used sorbents are analyzed. The applicability of polyaniline and polypyrrole and composites based on them as high-performance versatile sorbents for water treatment is discussed, taking into account the sorbent properties such as high stability, lack of solubility, lack of toxicity and ability to be regenerated and reused. The bibliography includes 194 references.
The present feature article offers a concise overview of recent research progress of the authors working in the design of macroporous conducting materials represented by polypyrrole-coated melamine sponges. The article highlights innovative results from the authors and suggests a perspective for future directions in the field of macroporous conducting polymer composites. The article also overviews this particular subject area and defines key challenges for this emerging field. The feasibility of diverse applications of polypyrrole/melamine sponges is demonstrated and includes deformation-sensitive materials, electromagnetic radiation shielding and electrically heated insulation materials. Cytotoxicity is addressed with respect to applications in biomedicine, and the adsorption of an organic dye serves as an example of the uses in environmental water-pollution treatment. A single-step deposition of polypyrrole during the oxidative polymerization of pyrrole provides the uniform coating of the sponge with an organic conducting phase. The conductivity of sponges was of the order of 10 -3 S cm -1 , increased with polypyrrole loading, and also by two orders of magnitude after the compression. Derived materials have also been prepared and tested. They are represented by polypyrrole-coated sponge converted by pyrolysis to a macroporous nitrogencontaining carbon, magnetic ferrosponge obtained by incorporation of magnetite, or the conventional globular polypyrrole coating replaced with polypyrrole nanotubes. Polypyrrole can also be simply decorated with silver nanoparticles. The macroporous conducting polypyrrole/melamine sponges and derived materials are considered to be of future scientific interest with broad application potential.
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