Prashant S. Alegaonkar

Graphene nanoribbon–PVA composite as EMI shielding material in the X band

A very thin graphene nanoribbon/polyvinyl alcohol (GNR/PVA) composite film has been developed which is light weight and requires a very low concentration of filler to achieve electromagnetic interference (EMI) shielding as high as 60 dB in the X band. Atomic force microscope studies show very well conjugated filler concentration in the PVA matrix for varying concentrations of GNR supported by Raman spectroscopy data. The films show 14 orders of increase in conductivity with a GNR concentration of 0.75% [corrected] in PVA. This is possible because of the interconnected GNR network providing a very low percolation threshold as observed from the electrical measurements. Local density of states study of GNR using scanning tunnelling spectroscopy shows the presence of localized states near the Fermi energy. There are multiple advantages of GNR as an EMI shielding material in a polymer matrix. It has good dispersion in water, the conductive network in the composite shows very high electrical conductivity for a very low concentration of GNR and the presence of localized density of states near Fermi energy provides the spin states required for the absorbance of radiation energy in the X band.

Nano-carbon: preparation, assessment, and applications for NH3 gas sensor and electromagnetic interference shielding

We report on the preparation and characterization of nano-carbon for applications in NH3 sensing and electromagnetic interference shielding (EMI, X-band, 8–12 GHz). Nano-carbon was synthesized by combustion of 1,7,7-trimethyl-bi-cycloheptan (camphor, C10H16O) deposited at 77 K. Morphological analysis showed nano-carbon was spherically concentric shells (40–50 nm); interconnected spatially. In Raman, vibration modes observed at 1390 (D) and 1580 (G) cm−1, indicated presence of sp3 within sp2 shells. UV-visible and photoluminescence spectroscopic analysis revealed that, band gap of nano-carbon was 4.5 eV with midgap of 2.7 eV and two flouro-excited states; making it useful for Fabry–Perot interferometer optical fibre gas sensor. Details of sensor system, its mechanism and transfer function analysis is presented. The system sensitivity was 3 ppm with response and recovery time, respectively, 5 and 8 s. The molecular imprint of NH3 on nano-carbon (1–5 ppb C-loss/10 cycles; 2 : 1, sp3 : sp2 rupture) was obtained that set life time of sensor probe. In EMI, % reflection of nano-carbon was comparable with copper. The losses due to hopping and migration current were large in nano-carbon and attributed to in-plane σ-bond and tetrahedral sites in nano-carbon that interacted with radiation at higher skin depth, around four times more than that of copper. Details of EMI shielding mechanism is presented.

Microwave absorption properties of reduced graphene oxide strontium hexaferrite/poly(methyl methacrylate) composites

The key factors to consider when designing microwave absorber materials for eradication of electromagnetic (EM) pollution are absorption of incident EM waves and good impedance matching. By keeping these things in mind, flexible microwave absorber composite films can be fabricated by simple gel casting techniques using reduced graphene oxide (RGO) and strontium ferrite (SF) in a poly(methyl methacrylate) (PMMA) matrix. SF nanoparticles are synthesized by the well known sol-gel method. Subsequently, reduced graphene oxide (RGO) and SF nanocomposite (RGOSF) are prepared through a chemical reduction method using hydrazine. The structure, morphology, chemical composition, thermal stability and magnetic properties of the nanocomposite are characterized in detail by various techniques. The SF particles are found to be nearly 500 nm and decorated on RGO sheets as revealed by field emission scanning electron microscopy and transmission electron microscopy analysis. Fourier transform infrared and and Raman spectroscopy clearly show the presence of SF in the graphene sheet by the lower peak positions. Finally, ternary polymer composites of RGO/SF/PMMA are prepared by an in situ polymerization method. Magnetic and dielectric studies of the composite reveal that the presence of RGO/SF/PMMA lead to polarization effects contributing to dielectric loss. Also, RGO surrounding SF provides a conductive network in the polymer matrix which is in turn responsible for the magnetic loss in the composite. Thus, the permittivity as well as the permeability of the composite can be controlled by an appropriate combination of RGO and SF in PMMA. More than 99% absorption efficiency is achieved by a suitable combination of magneto-dielectric coupling in the X-band frequency range by incorporating 9 wt% of RGO and 1 wt% of SF in the polymer matrix.

Corrigendum: Graphene nanoribbon–PVA composite as EMI shielding material in the X band (2013 Nanotechnology 24 455705)

There was an error in calculating the weight percentage of the graphene nanoribbon (GNR) in PVA. There were three films made with different concentrations of GNR. The correct weight percentage of GNR in PVA in three films should be 0.75%, 1.5% and 2.5% instead of 0.0075 wt%, 0.015 wt%, and 0.025 wt% respectively. Reference to the weight percentage has been made in the abstract, line 5; page 3, paragraph 5, second line; page 4, paragraph 1; page 6, paragraph 2, line 6; figure caption 4; figure caption 10 and figures 9 and 10, the corrected versions of which are shown below.

Electroless nickel coated nano-clay for electrolytic removal of Hg(II) ions

The footprint existence and accumulation of cataclysmic Hg(II) ions in aqueous media poses a severe threat to biological ecosystems and necessitates immediate measures for its regulation. In this context, we have elucidated an electrolytic removal of Hg(II) ions from a prepared solution, which is akin to an effluent system, utilizing novel electroless nickel coated nanoclay electrodes. The dependence of adsorption efficiency on several parameters, including the initial pH (pH = 3 to 8), initial metal ion concentration (25–100 mg L−1), amount of nickel coated on nanoclay, has been studied. The optimized removal percentage of 70% was recorded at pH 6, when distance between the electrodes was 4 cm and a current density ranging from 2–2.5 A dm−2 was passed for duration of 60 minutes. No considerable differences in removal efficiency were registered with varying initial metal ion concentration (25–100 mg L−1). Moreover, the removal efficiency was observed to be high at slightly acidic pH (pH = 6), however, in a highly acidic solution (pH = 3–4), low adsorption efficiency was recorded due to electrostatic repulsion caused by H+ ions. Nickel coating over the nanoclay of 15% (v/v) or greater was found to exhibit an optimised conductivity. SEM and FESEM analysis affirmed the uniform deposition of nickel over the nanoclay. The uptake of Hg(II) ions predominantly followed pseudo second-order kinetics, which was validated by the high values of regression coefficient at all concentrations, and Freundlich equilibrium isotherm model was observed to be better for predicting equilibrium adsorption based on linearized correlation coefficient (R2 = 0.99).

Enhanced response and improved selectivity for toxic gases with functionalized CNT thin film resistors

ABSTRACT High surface area of CNTs makes them an extremely sensitive detection element for a wide variety of analytes present in minute quantities of ppb and ppm levels. CNTs does not inherit selectivity for a particular gas/analyte, it can be introduced in CNT based gas sensor by means of functionalization, along with improvement in gas sensors response. Effects of Carboxylated group and gold nano-particles were studied on the response of CNT sensors towards toxic gases such as NO2 and NH3. Gold nanoparticles have found to enhance the response for NO2 and NH3, while oxygenated functional have brought selectivity towards NH3.

Decoration of gold nanoparticles on thin multiwall carbon nanotubes and their use as a glucose sensor

Thin multiwall carbon nanotubes (MWCNTs) have been decorated with gold nanoparticles (Au NPs) with polyaniline (PANI) as an inter-linker by a simple wet chemical method. The synthesized AuNPs:MWCNT:PANI composite was studied with UV–vis, FTIR, Raman spectroscopy, x-ray diffractometer, transmission electron microscopy (TEM) and atomic force microscopy (AFM). Conducting AFM (C-AFM) images of the composite reveal the role played by the two components in electrochemical reactions. The size of the Au NPs was found to be 13 ± 2 nm in the composite as observed from TEM. The synthesized AuNPs:MWCNT:PANI composite was further drop casted onto a glassy carbon electrode (GCE) for electrocatalytic study. The resulting composite exhibits good electrocatalytic activity towards reduction of H2O2 and O2. A glucose biosensor was developed by immobilizing glucose oxidase into AuNPs:MWCNT:PANI composite film on GCE. The fabricated sensor demonstrates good linear response to glucose (i.e. R = 0.9975) in the range of 2 to 12 mM.

Exchange Interaction of Itinerant Electron Donors of Tetrakis (Dimethylamino) Ethylene with Localized Electrons in Graphene

We report on indirect exchange interaction between itinerant and localized electron in tetrakis(dimethylamino) ethylene (TDAE)–treated graphene. TDAE, after getting attached to the graphene, forms fragments such as, tetrakisdimethylamino–1,2–dioxetane, tetramethylurea, tetramethyloxamide, tetramethylhydrazine, bis(dimethylamino)methane, and dimethylamine. These fragments, carrying itinerant electrons on charge–transfer generates spin ordering in localized electrons at host carbon network. The nature of interaction between itinerant and localized electrons is short range, repulsive, and indirect exchange. The strength of interaction depends upon the ratio of coulombic repulsive energy to hopping energy. Possible mechanism of magnetization in TDAE-treated graphene is discussed.

Gold-graphene nanocomposite based ultrasensitive electrochemical glucose sensor

Gold-graphene (Au-G) nanocomposite has been synthesized by wet chemical method. Synthesized Au-G nanocomposite was examined under the UV-vis spectroscopy and transmission electron microscopy (TEM). Further Au-G nanocomposite was drop casted onto the glassy carbon electrode (GCE) by immobilizing glucose oxidase (GOx) into it for the electrochemical detection of glucose. Fabricated sensor demonstrates good linear response to glucose in the range 3 to 18 mM with linearity coefficient 0.964.

Assessment of ecologically prepared carbon-nano-spheres for fabrication of flexible and durable supercell devices

We report the production parameters of single-stage, ecologically fabricated, flexible Carbon-Nano-Spheres (CNS) supercells. These supercells can deliver a total energy, ED, of 100.0 W h kg−1 and power density, PD, of 50.0 W kg−1@38.4 V and 20 mA for a payload of 15 g (5.0 × 2.5 cm2). According to the material analysis, CNS consists of a spherically (40.0 to 50.0 nm) coagulated, interconnected, 3D network of hetero-structured sp2/sp3 carbon with a low crystalline length, La, of ∼3.0 nm and containing a native O-moiety (12.0 at%). They have an appreciably high specific surface area, SA, of ∼790.0 m2 g−1 and an average pore size of ∼3.42 nm combined with multi-channel pore size distribution. Upon integration in electrodes, CNS provided excellent electrochemical performance without any material modification. CNS showed a nearly rectangular cyclic voltammetry (CV) response in 1 M HCl for both two- and three-electrode systems, yielding superior specific capacitances, CSP, of ∼1080.0 and 570.0 F g−1, respectively (@10 mV s−1). They maintained a high cyclic stability of ∼86.0% (@20 000 cycles), with no material degradation according to post-investigations at a molecular level. The electrode showed hybrid battery/electric double layer capacitor (EDLC) behavior, as revealed by Ragone studies. In Nyquist studies, a shift in the Knee frequency with cycling indicated mitigation of the charge transfer process. In Bode studies, the ionic phase shift decreased insignificantly from ∼80 ° to ∼77 ° after 1000 cycles. The performance characteristics of CNS from laboratory scale measurements to supercell-level device development are discussed.