Conducting polymer (CPs), so-called Nobel Prize-winning materials, opened an exciting area of research owing to their substantial electrical conductivity, unique structures, new composite materials, and has wide applications ranging from...

The present work reports the fabrication of polyindole (PIN)/Ni 1– x Zn x Fe 2 O 4 ( x = 0, 0.5, 1) nanocomposites as efficient electromagnetic wave absorbers by a facile in situ emulsion polymerization method for the first time. The samples were characterized through Fourier transform infrared spectroscopy, UV–vis spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, high-resolution transmission electron microscopy, and vibrating sample magnetometry. The resulting polyindole/Ni 1– x Zn x Fe 2 O 4 ( x = 0, 0.5, 1) nanocomposites offer better synergism among the Ni 1– x Zn x Fe 2 O 4 nanoparticles and PIN matrix, which significantly improved impedance matching. The best impedance matching of Ni 1– x Zn x Fe 2 O 4 /polyindole ( x = 0, 0.5, 1) nanocomposites was sought out, and the minimum reflection loss of the composites can reach up to −33 dB. The magnetic behavior, complex permittivity, permeability, and microwave absorption properties of polyindole/Ni 1– x Zn x Fe 2 O 4 ( x = 0, 0.5, 1) nanocomposites have also been studied. The microwave absorbing characteristics of these composites were investigated in the 8–12 GHz range (X band) and explained based on eddy current, natural and exchange resonance, and dielectric relaxation processes. These results provided a new idea to upgrade the performance of conventional microwave-absorbing materials based on polyindole in the future.

A facile two-step strategy has been reported for the preparation of a ternary 3D reduced graphene oxide/Ni0.5Zn0.5Fe2O4/polyindole nanocomposite (GNP) and this composite is applied as an electrode material for supercapacitor applications.

Recently, polyindole (PIN) has quickly started to gain research interest in the field of energy storage applications. Here, we developed a three-dimensional (3D) PIN gel for the first time without using either additives or cross-linkers to explore its efficacy as a supercapacitor. The PIN aerogel obtained by freeze-drying the 3D PIN gel exhibits a larger surface area, enhanced electronic conductivity, and appropriate mechanical properties compared to conventionally synthesized PIN powder. The PIN aerogel is also capable of delivering an improved capacitance of 168 F g–1 at a current density of 0.5 A g–1. Further, we have also demonstrated that PIN can be used as a cross-linking agent in the development of a PIN/graphene hydrogel (PG hydrogel). The PG hydrogel was freeze-dried to obtain PIN/graphene aerogels (PG aerogels). With improved surface areas and 3D porous nanostructures, the PG aerogels demonstrated their potential as high-performance supercapacitor electrodes with a high specific capacitance of ∼399 F g–1 at 0.5 A g–1, better rate capability, and long-term cyclic stability (∼92% capacitance retention after 2000 cycles) in a three-electrode system. Besides, we also report the fabrication of a PG aerogel∥PG aerogel symmetric supercapacitor (SSC) of a two-electrode configuration, which manifests a favorable C sp of 63 F g–1 at 0.5 A g–1 and retains a stability of 99.8% even after 2000 cycles. This SSC device shows a significant energy density of 28.35 Wh kg–1 at a power density of 497.85 W kg–1. The self-aggregation of PIN and the interaction of PIN with graphene was assessed using molecular dynamics (MD) simulations. The MD simulation results were found to be in good agreement with the experimental observations. Overall, our findings evidence that PIN can form 3D architectures in virgin nature and composite with graphene and thus has important implications for future material design of PIN-based electrochemical energy storage devices.

The sensitive monitoring of dopamine levels in the human body is of utmost importance since its abnormal levels can cause a variety of medical and behavioral problems. In this regard, we report the synthesis of nitrogen-doped graphene quantum dots (N-GQDs) from polyindole (PIN) via a facile single-step hydrothermal synthetic strategy that can act as an efficient electrochemical catalyst for the detection of dopamine (DA). The average diameter of N-GQDs was ∼5.2 nm and showed a C/N atomic ratio of ∼2.75%. These N-GQDs exhibit a cyan fluorescence color under irradiation from a 365 nm lamp, while PIN has no characteristic PL. The presence of richly N-doped graphitic lattices in the N-GQDs possibly accounts for the improved catalytic activity of N-GQDs/GCE towards electrocatalytic DA detection. Under optimum conditions, this novel N-GQDs-modified electrode exhibits superior selectivity and sensitivity. Moreover, it could detect as low as 0.15 nM of DA with a linear range of 0.001–1000 µM. In addition, the outstanding sensing attributes of the detector were extended to the real samples as well. Overall, our findings evidence that N-GQDs-based DA electrochemical sensors can be synthesized from PIN precursor and could act as promising EC sensors in medical diagnostic applications.

This review clearly portrays the antimicrobial properties of polyindole based nanocomposites, reported so far for antimicrobial applications and it gives clear insight into the scope and possibilities for further research on the biomedical application of polyindole based nanocomposites.

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