Utpal Rana

Graphene oxide/polyaniline nanostructures: transformation of 2D sheet to 1D nanotube and in situ reduction

The formation of unique polyaniline nanotubes has been reported in presence of graphene oxide (GO) which plays crucial dual role as dopant and soft template, simultaneously. GO in nanotubes is in situ reduced to reduced GO with restoration of electrical conductivities and enhanced thermal stabilities.

Facile Decoration of Polyaniline Fiber with Ag Nanoparticles for Recyclable SERS Substrate

Facile synthesis of polyaniline@Ag composite has been successfully demonstrated by a simple solution-dipping method using high-aspect-ratio benzene tetracarboxylic acid-doped polyaniline (BDP) fiber as a nontoxic reducing agent as well as template cum stabilizer. In BDP@Ag composite, BDP fibers are decorated with spherical Ag nanoparticles (Ag NPs), and the population of Ag NPs on BDP fibers is controlled by changing the molar concentration of AgNO3. Importantly, Ag-NP-decorated BDP fibers (BDP@Ag composites) have been evolved as a sensitive materials for the detection of trace amounts of 4-mercaptobenzoic acid and rhodamine 6G as an analyte of surface-enhanced Raman scattering (SERS), and the detection limit is down to nanomolar concentrations with excellent recyclability. Furthermore, synthesized BDP@Ag composites are applied simultaneously as an active SERS substrate and a superior catalyst for reduction of 4-nitrothiophenol.

Azo Anion Radical Complex of Rhodium as a Molecular Memory Switching Device: Isolation, Characterization, and Evaluation of Current–Voltage Characteristics

Two rare examples of azo anion diradical complexes of Rh(III) are reported. These complexes showed excellent memory switching properties with a large ON/OFF ratio and are suitable for RAM/ROM applications. Their electronic structures have been elucidated using a host of physical methods, including X-ray crystallography, variable-temperature magnetic susceptibility measurement, cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory. The results indicate a predominant triplet state description of the systems with two ferromagnetically coupled radicals.

In situ preparation of fluorescent polyaniline nanotubes doped with perylene tetracarboxylic acids

Herein, we report an easy preparation of polyaniline (PANI) nanotubes in the presence of perylene tetracarboxylic acid acting as a dopant. These tubes are crystalline and fluorescent in nature as a result of controlled confinement of dopant molecules in the tubes.

Benzene tetracarboxylic acid doped polyaniline nanostructures: morphological, spectroscopic and electrical characterization

The in situ preparation of polyaniline nanotubes via assembly of an aromatic dopant acid is a challenging task at present in polymer chemistry. Here, we report the formation of PANI nanostructures doped with benzene 1,2,4,5-tetracarboxylic acid (BTCA), which simultaneously acts as a dopant acid as well as a structure-directing agent to produce high aspect ratio nanotubes having more or less uniform diameter. The diameter of the fibers is intricately tuned by changing the ratio of BTCA to aniline. The effect of dopant concentration in the polymer composites has been investigated with the help of 1H-NMR, UV-Vis and IR studies. It has also been demonstrated that the dopant acid plays an important role in the fiber formation, particularly in the nanotube formation. A comparative investigation with other tetracarboxylic acids has been made in the light of the variation of diameter. The outer diameter (OD) of PANI nanotubes depends on the size of the dopant tetracarboxylic acid under identical reaction conditions and it follows the order ODPTCA > ODNTCA > ODBTCA. Furthermore, it has been found that the conductivities of the BTCA–PANI nanotubes depend on the BTCA to aniline molar ratios, and the low temperature charge transports in these composites predominantly follow the three dimensional variable range hopping mechanism.

One pot green synthesis of polyaniline coated gold nanorods and its applications

Morphology controlled high aspect ratio worm-like polyaniline (PANI) layer coated Au-nanostructures (Au/PANI) have been successively synthesized by in situ polymerisation techniques using aniline as a monomer with HAuCl4 as an oxidising agent in the absence and presence of citric acid (CA). Synthesized composites were characterized by HRTEM, FESEM, XRD, XPS, UV-vis and FTIR study. Spherical morphologies are seen in the absence of CA and Au nanoparticles are coated by a PANI thin layer with ∼30 nm thickness. In the presence of CA, as well as depending upon the CA to aniline molar ratio, morphology varies from irregular assembly to regular fiber to spherical-like nanostructures. The nanostructures show fibrous morphology with an average diameter of ∼100 nm and lengths of more than 5 μm when CA to aniline molar ratios are 1.0 and 0.2. When the ratios are 2.0 and 0.1, the nanostructure represents the granular-like morphology. Nanofiber formation takes place by the assembly of the CA capped tiny Au-nanorods in the presence of aniline during the polymerisation, and all Au-nanorods are finely coated by a PANI thin layer of ∼5 nm thickness. Importantly, fibrous Au/PANI nanostructures show superior catalytic activity compared to spherical/irregular Au/PANI nanostructures towards the reduction of toxic aromatic nitro compounds like 4-nitrophenol (4-NP), 4-nitroaniline (4-NA), 2,4-dinitrophenol (2,4-DNP) and 2,4,6-trinitrophenol (2,4,6-TNP). This is because of the coating thickness of PANI over Au-nanoparticles in fibrous Au/PANI nanostructures as well as enhanced surface area.

Aromatic bi-, tri- and tetracarboxylic acid doped polyaniline nanotubes: effect on morphologies and electrical transport properties

Polyaniline nanotubes have been prepared in a facile manner via the chemical polymerization of aniline in an aqueous medium using ammonium persulphate (APS) and ten different dopant acids. The formation of PANI in the composite was confirmed using 1H-NMR, UV-Vis and FTIR spectroscopic studies. An intensive FESEM investigation indicated that the dopant acid plays an important role in the formation of the PANI nanotubes. In particular, the symmetrical positioning of –COOH groups in the aromatic dopant acid is key for forming PANI nanotubes. Symmetrical BTA-1 produces PANI nanotubes, whereas BTA-2 and BTA-3 only generate granular aggregates of PANI. The diameter of the observed nanotubes varies with the molar ratio of BTA-1 to aniline and the diameter of the nanotubes increases with the increasing number of –COOH groups in dopant acids that have the same central core. A comparative study with other tricarboxylic acids shows that the outer diameter (OD) of the PANI nanotubes depends on the size of the dopant under identical reaction conditions and follows the order: ODTPCA > ODBPCA > ODBTA-1. Low temperature charge transport in these composites mainly follows a three dimensional variable range hopping mechanism.

Effect of a three-dimensional hyperbranched structure on the ionic conduction of metallo-supramolecular polymers

Fe(II)-, Co(II)- and Ni(II)-based metallo-supramolecular polymers with three-dimensional (3D) hyperbranched structures (3D-polyFe, 3D-polyCo and 3D-polyNi) showed highly humidity-responsive ionic conductivity. The 3D polymers exhibited 10–100 times higher ionic conductivity than their 1D linear equivalents due to the improved ion conduction pathway in the amorphous 3D structure.

One-Dimensional Anhydrous Proton Conducting Channel Formation at High Temperature in a Pt(II)-Based Metallo-Supramolecular Polymer and Imidazole System

One dimensional (1D) Pt(II)-based metallo-supramolecular polymer with carboxylic acids (polyPtC) was synthesized using a new asymmetrical ditopic ligand with a pyridine moiety bearing two carboxylic acids. The carboxylic acids in the polymer successfully served as apohosts for imidazole loaded in the polymer interlayer scaffold to generate highly ordered 1D imidazole channels through the metallo-supramolecular polymer chains. The 1D structure of imidazole loaded polymer (polyPtC-Im) was analyzed in detail by thermogravimetric analysis, powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and ultraviolet-visible and photoluminescence spectroscopic measurements. PolyPtC-Im exhibited proton conductivity of 1.5 × 10-5 S cm-1 at 120 °C under completely anhydrous conditions, which is 6 orders of magnitude higher than that of the pristine metallo-supramolecular polymer.

Geometrically isomeric Pt( ii )/Fe( ii )-based heterometallo-supramolecular polymers with organometallic ligands for electrochromism and the electrochemical switching of Raman scattering

Heterometallo-supramolecular polymers with Pt(II) and Fe(II) ions introduced alternately (cis-polyPtFe and trans-polyPtFe) in a precise way were prepared successfully by the 1:1 complexation of Fe(II) ions with cis- or trans-conformational organo-Pt(II) ligands. The conformational difference between cis- and trans-greatly changed the morphology, crystallinity, ionic conductivity, electrochromic properties, and redox-triggered fluorescence of the polymers. The cis-polyPtFe exhibited better crystallinity and low ionic conductivity, whereas trans-polyPtFe showed an amorphous nature with high ionic conductivity. Both the polymers exhibited reversible electrochromism between purple and yellow colors due to the redox of Fe(II)/(III) upon applying a potential of 0 V or +3 V. The trans-polyPtFe showed better electrochromic stability and response times compared to cis-polyPtFe. In addition, the trans-polyPtFe also showed an improved response in redox-triggered Raman scattering switching compared to cis-polyPtFe over a long time range.