Nanjundan Ashok Kumar

Polyaniline Grafted Reduced Graphene Oxide for Efficient Electrochemical Supercapacitors

An alternative and effective route to prepare conducting polyaniline-grafted reduced graphene oxide (PANi-g-rGO) composite with highly enhanced properties is reported. In order to prepare PANi-g-rGO, amine-protected 4-aminophenol was initially grafted to graphite oxide (GO) via acyl chemistry where a concomitant partial reduction of GO occurred due to the refluxing and exposure of GO to thionyl chloride vapors and heating. Following the deprotection of amine groups, an in situ chemical oxidative grafting of aniline in the presence of an oxidizing agent was carried out to yield highly conducting PANi-g-rGO. Electron microscopic studies demonstrated that the resultant composite has fibrillar morphology with a room-temperature electrical conductivity as high as 8.66 S/cm and capacitance of 250 F/g with good cycling stability.

Electrochemical supercapacitors from conducting polyaniline–graphene platforms

Energy storage devices such as electrochemical supercapacitors, with high power and energy densities are required to address the colossal energy requirements against the backdrop of global warming and the looming energy crisis. Nanocarbon, particularly two-dimensional graphene and graphene-based conducting polymer composites are promising electrode materials for such energy storage devices. Owing to their environmental stability, the low cost of polymers with high electroactivity and pseudocapacitance, such composite hybrids are expected to have wide implications in next generation clean and efficient energy systems. In this feature article, an overview of current research and important advances over the past four years on the development of conducting polyaniline (PANI)-graphene based composite electrodes for electrochemical supercapacitors are highlighted. Particular emphasis is made on the design, fabrication and assembly of nanostructured electrode architectures comprising PANI and graphene along with metal oxides/hydroxides and carbon nanotubes. Comments on the challenges and perspectives towards rational design and synthesis of graphene-based conducting polymer composites for energy storage are discussed.

Plasma-Assisted Simultaneous Reduction and Nitrogen Doping of Graphene Oxide Nanosheets

An environmentally benign and scalable route for the production of gram scale quantities of nitrogen-doped graphene using a downstream microwave plasma source is reported. Simultaneous reduction and doping of graphene oxide is achieved and the process negates the need for high temperatures and toxic solvents associated with existing methods. This gas-phase low temperature process is completely dry and, thus, minimises re-aggregation of graphene flakes which is typically associated with liquid phase reduction methods. The resulting material has many potential uses, particularly in electrochemical energy.

Functionalization of chemically derived graphene for improving its electrocapacitive energy storage properties

Chemically derived graphene holds great promise as an electrode material for electrochemical energy storage owing to its unique physical and chemical properties. Recent years have witnessed tremendous research breakthroughs in the field of graphene-based materials for electrochemical capacitors. This article presents a review of the latest developments in the functionalization of chemically derived graphene for improving its electrocapacitive properties. Beginning with a brief description of supercapacitors, graphene, and chemically derived graphene, we discuss the preparation, electrocapacitive properties, and drawbacks of chemically derived graphene and its derivatives, followed by a discussion on how to functionalize chemically derived graphene for improving its double-layer capacitance and pseudocapacitance. Emphasis is made on comparing and highlighting demonstrated approaches to functionalizing chemically derived graphene. Future research towards developing advanced electrochemical capacitors, perspectives and challenges are outlined.

A facile synthesis, antibacterial, and antitubercular studies of some piperidin-4-one and tetrahydropyridine derivatives.

The raise in clinical significance of multidrug-resistant bacterial pathogens has directed us to synthesize 2,6-diarylpiperidin-4-one and Delta(3)-tetrahydropyridin-4-ol based benzimidazole and O-arylsulfonyl derivatives. X-ray crystal structure of tetrahydropyridinol (23) confirmed a change in conformation and orientation of substituents upon amide formation. Antibacterial activities evaluated against a wide number of bacterial pathogens (both sensitive and multidrug-resistant) revealed that 19, 27 against Staphylococcus aureus, 27 against Enterococcus faecalis, and 19, 21, 23, and 27 against Enterococcus faecium are significantly good at lowest MIC(90) (16 microg/mL). Inhibitory power noticed by 23 against Vancomycin-Linezolid-resistant E. faecalis and 27 against Vancomycin-resistant E. faecium are onefold better than the standard Linezolid and Trovafloxacin drugs, respectively. Moreover, antitubercular activity for the selected compounds against Mycobacterium tuberculosis H37Rv revealed that compounds 23, 24, and 27 expressed onefold improved potency compared to the standard Rifampicin drug.

Highly Conducting and Flexible Few-Walled Carbon Nanotube Thin Film

We report an effective route to prepare highly conducting and flexible few-walled carbon nanotube (FWNT) thin films. The free-standing thin films were fabricated by functionalizing FWNTs with 4-ethoxybenzoic acid (EBA) via a direct Friedel-Crafts acylation reaction in a nondestructive polyphosphoric acid/phosphorus pentoxide medium. The resulting ethoxybenzoyl-functionalized FWNT (EBA-f-FWNT) was readily dispersible in water. EBA-f-FWNT thin films were formed by a simple suction filtration of the dispersed solution. Electron microscopic studies were employed to characterize the morphologies of the resulting thin films. The obtained results indicate that the structure of FWNTs was not perturbed by the incorporation of EBA moieties, which were uniformly grafted onto FWNTs forming the FWNT networks. Room temperature electrical conductivity of the thin films was obtained using standard four-probe measurements, which revealed a value as high as 29 400 S m(-1), while the tensile strength and modulus of the film were found to be about 80 MPa and 15 GPa, respectively. Cyclic voltammograms revealed a rectangular shape, with superior capacitive behaviors nearing 133 F/g for the thin films, which is very attractive for capacitor applications.

Electrochemical supercapacitors based on a novel graphene/conjugated polymer composite system

An efficient method for the preparation of a highly conducting hybrid material from graphene oxide nanosheets (GNS) and a novel conjugated polymer, poly(3,4-propylenedioxythiophene), is demonstrated. A functionalized monomer based on 3,4-propylenedioxythiophene, namely ProDOT–OH, was covalently functionalized with GNS, followed by oxidative polymerization to prepare GNS-f-PProDOT composites. The covalent functionalization process of GNS with the monomer ProDOT–OH was activated through the simple esterification reaction between the acyl chloride derivative on the nanosheets and the pendant hydroxyl group present in the monomer. Furthermore, the monomer functionalized GNS were co-polymerized with thiophene resulting in hybrid graphene nanostructures coated with highly conducting co-polymers with a room temperature electrical conductivity as high as 22.5 S cm−1. The resulting hybrid materials were characterized using a range of analytical techniques. The specific capacitance value of the composite and the co-polymer hybrids at a scan rate of 10 mV s−1 has been determined to be 158 and 201 F g−1 respectively and hence particularly promising for supercapacitors.

Nitrogen-doped reduced graphene oxide electrodes for electrochemical supercapacitors

Herein we use Nitrogen-doped reduced Graphene Oxide (N-rGO) as the active material in supercapacitor electrodes. Building on a previous work detailing the synthesis of this material, electrodes were fabricated via spray-deposition of aqueous dispersions and the electrochemical charge storage mechanism was investigated. Results indicate that the functionalised graphene displays improved performance compared to non-functionalised graphene. The simplicity of fabrication suggests ease of up-scaling of such electrodes for commercial applications.

Synthesis of high quality reduced graphene oxide nanosheets free of paramagnetic metallic impurities

A facile and cost-effective method to prepare paramagnetic-metal free graphene nanosheets based on stannous chloride reduction of graphene oxide (GO) in a strongly acidic medium is reported. Simultaneous exfoliation and reduction is achieved in this room temperature process. Compared to the chemical reduction of GO using hydrazine or iron, the present method showed that Sn–rGO is several orders of magnitude less magnetic and hence does not contain any paramagnetic metallic impurities. With high reduction degree, this simple method shows promising application in energy and magnetic related studies.

Novel amino-acid-based polymer/multi-walled carbon nanotube bio-nanocomposites: highly water dispersible carbon nanotubes decorated with gold nanoparticles

A well-reproducible and completely green route towards highly water dispersible multi-walled carbon nanotubes (MWNT) is achieved by a non-invasive, polymer wrapping technique, where the polymer is adsorbed on the MWNTs surface. Simply mixing an amino-acid-based polymer derivative, namely poly methacryloyl beta-alanine (PMBA) with purified MWNTs in distilled water resulted in the formation of PMBA-MWNT nanocomposite hybrids. Gold nanoparticles (AuNPs) were further anchored on the polymer-wrapped MWNTs, which were previously sonicated in distilled water, via the hydrogen bonding interaction between the carboxylic acid functional groups present in the polymer-modified MWNTs and the citrate-capped AuNPs. The surface morphologies and chemistries of the hybrids decorated with nanoparticles were characterized by transmission electron microscopy (TEM) and UV-visible absorption spectroscopy. Additionally, the composites were also prepared by the in situ free radical polymerization of the monomer, methacryloyl beta-alanine (MBA), with MWNTs. Thus functionalized MWNTs were studied by thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM) and TEM. Both methods were effective in the nanotube functionalization and ensured good dispersion and high stability in water over three months. Due to the presence of the high densities of carboxylic acid functionalities on the surface of CNTs, various colloidal nanocrystals can be attached to MWNTs.