Effect of the molar concentration of pyrrole monomer on the rate of polymerization, growth and hence the electrochemical behavior of highly pristine PPy flexible electrodes

Selective separation of monovalent anions by PPy/pTS membrane electrodes in redox transistor electrodialysis

Selective separation of nitrate over chloride is crucial for eutrophication mitigation and nitrogen resource recovery but remains a challenge due to their similar ionic radius and the same valence. Herein, a polypyrrole membrane electrode (PME) was fabricated by polymerization of pyrrole (Py) and p-toluenesulfonate (pTS), which was used as a working electrode in redox transistor electrodialysis. The anions in the source solution were first incorporated into the PME at reduction potentials and then released to receiving solution at oxidation potentials. Pulse widths and potentials were optimized to maximize the ion separation performance of PME, resulting in the improvement of NO₃^-/Cl^- separation factor up to 6.93. The ion distributions in various depths of PME indicated that both NO₃^- and Cl^- were incorporated into PME at negative potentials. Then, NO₃^- was preferentially released from PME at positive potentials, but most Cl^- was retained. This was ascribed to the high binding energy between Cl^- and PPy/pTS structure, which was 51.4% higher than that between NO₃^- and PPy/pTS structure. Therefore, the higher transport rate of NO₃^- in comparison with Cl^- was achieved, leading to a high NO₃^- selectivity over Cl^-. This work provides a promising avenue for the selective separation of nitrate over chloride, which may contribute to nitrogen resource recycling and reuse.

CVD Conditions for MWCNTs Production and Their Effects on the Optical and Electrical Properties of PPy/MWCNTs, PANI/MWCNTs Nanocomposites by In Situ Electropolymerization

In this work, the optimal conditions of synthesizing and purifying carbon nanotubes (CNTs) from ferrocene were selected at the first stage, where decomposition time, argon fluxes, precursor amounts, decomposition temperature (at 1023 K and 1123 K), and purification process (HNO₃ + H₂SO₄ or HCl + H₂O₂), were modulated through chemical vapor deposition (CVD) and compared to commercial CNTs. The processing temperature at 1123 K and the treatment with HCl + H₂O₂ were key parameters influencing the purity, crystallinity, stability, and optical/electrical properties of bamboo-like morphology CNTs. Selected multiwalled CNTs (MWCNTs), from 1 to 20 wt%, were electropolymerized through in-situ polarization with conductive polymers (CPs), poly(aniline) (PANI) and poly(pyrrole) (PPy), for obtaining composites. In terms of structural stability and electrical properties, MWCNTs obtained by CVD were found to be better than commercial ones for producing CPs composites. The CNTs addition in both polymeric matrixes was of 6.5 wt%. In both systems, crystallinity degree, related to the alignment of PC chains on MWCNTs surface, was improved. Electrical conductivity, in terms of the carrier density and mobility, was adequately enhanced with CVD CNTs, which were even better than the evaluated commercial CNTs. The findings of this study demonstrate that synergistic effects among the hydrogen bonds, stability, and conductivity are better in PANI/MWCNTs than in PPy/MWCNTs composites, which open a promissory route to prepare materials for different technological applications.