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

Aerogels of Polypyrrole/Tannic Acid with Nanofibrillated Cellulose for the Removal of Hexavalent Chromium Ions

The preparation of conducting polymer aerogels is an effective strategy to produce innovative materials with enhanced physicochemical properties. Herein, polypyrrole (PPy) aerogels were oxidatively prepared in the presence of tannic acid (TA) with different concentrations (2.5, 5, and 10% mole ratio to pyrrole monomer) under freezing conditions. Nanofibrillated cellulose (NFC) was added during the PPy/TA synthesis to enhance mechanical stability. The effect of TA concentration on the aerogels' morphology, conductivity, thermal stability, and adsorption capacity was investigated. The conductivity of 9.6 ± 1.7 S cm-1 was achieved for PPy/TA prepared with 2.5% TA, which decreased to 0.07 ± 0.01 S cm-1 when 10% TA was used. PPy/TA aerogels have shown high efficacy in removing Cr(VI) ions from aqueous solutions. Adsorption experiments revealed that all the aerogels follow pseudo-second-order kinetics. PPy/TA prepared with NFC has a maximum adsorption capacity of 549.5 mg g-1.

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.

Ten-Minute Synthesis of Highly Conductive Polymer Nanosheets on Ice Surfaces: Role of Ice Crystallinity

Conducting polymers have been studied widely over the past decades for use as organic electrode materials owing to their high electrical conductivity and low-cost synthesis. Among the various synthesis methods reported, the recently established ice-assisted approach for developing conducting polymer nanosheets is regarded as an advanced technology that allows for easy fabrication in an eco-friendly manner. However, the role of the crystallinity of the underlying ice surface in determining the physicochemical properties of the conducting polymers remains unclear. Here, the electronic properties and packing structures of polyaniline (PANI) nanosheets formed on ice surfaces are studied by controlling the ice crystallinity. Intriguingly, the crystallinity of the PANI nanosheets resembles that of the ice surfaces, in that the anisotropic growth of the PANI crystals with a face-on orientation occurs preferentially on high-crystalline ice surfaces. In addition, it is found that the development of highly crystalline PANI nanosheets results in efficient charge transport, owing to polaron delocalization in PANI with extended chain conformations and the improvement in the degree of backbone ordering because of the preorganized aniline moieties on the ice surface.