V. Sai Muthukumar

Microwave-assisted solid-state grafting of multi-walled carbon nanotubes on polyurethane for the synthesis of a composite with optical limiting properties

Microwave-assisted, solid-state grafting of multiwalled carbon nanotubes is presented for the synthesis of a thermal polyurethane composite. This one-step method reduced the reaction time to the order of minutes and allowed the polyurethane to be directly attached to the nanotubes, thus forming a highly solvent-dispersible composite. The composite showed excellent optical limiting characteristics at 532 as well as 1064 nm, with a threshold of 0.10 J cm−2 at 532 nm, and a higher value (1.0 J cm−2) at the latter wavelength.

Synthesis and characterization of gold graphene composite with dyes as model substrates for decolorization: a surfactant free laser ablation approach.

A facile surfactant free laser ablation mediated synthesis (LAMS) of gold-graphene composite is reported here. The material was characterized using transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, powdered X-ray diffraction, Raman spectroscopy, Zeta potential measurements and UV-Visible spectroscopic techniques. The as-synthesized gold-graphene composite was effectively utilized as catalyst for decolorization of 4 important textile and laser dyes. The integration of gold nanoparticles (AuNPs) with high surface area graphene has enhanced the catalytic activity of AuNPs. This enhanced activity is attributed to the synergistic interplay of pristine golds electronic relay and π-π stacking of graphene with the dyes. This is evident when the Rhodamine B (RB) reduction rate of the composite is nearly twice faster than that of commercial citrate capped AuNPs of similar size. In case of Methylene blue (MB) the rate of reduction is 17,000 times faster than uncatalyzed reaction. This synthetic method opens door to laser ablation based fabrication of metal catalysts on graphene for improved performance without the aid of linkers and surfactants.

Enhanced dielectric properties and energy storage density of interface controlled ferroelectric BCZT-epoxy nanocomposites

Abstract Polymer nanocomposites with ferroelectric fillers are promising materials for modern power electronics that include energy storage devices. Ferroelectric filler, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) nanopowder, was synthesized by sol-gel method. X-ray diffraction (XRD) studies confirmed the phase purity and the particle size distribution was determined by transmission electron microscopy (TEM). Extended aromatic ligand in the form of naphthyl phosphate (NPh) was chosen for surface passivation of BCZT nanoparticles. Surface functionalization was validated by thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy using slurry technique. The dielectric constant of surface-passivated BCZT nanopowder was ~155, whereas pristine BCZT nanopowder dielectric constant could not be assessed due to high innate surface conductivity. Furthermore, BCZT–epoxy nanocomposite films were prepared and analyzed by differential scanning calorimetry (DSC), dielectric spectroscopy, dielectric breakdown strength (DBS), and scanning electron microscopy (SEM). Owning to stronger polymer–particle interface, dielectric measurements of 5 vol.% NPh surface functionalized BCZT–epoxy nanocomposites indicated improved DBS and glass transition temperature (Tg), reduced dielectric loss, and enhanced energy storage density compared to untreated BCZT–epoxy composites and pure epoxy. The energy storage density of 30 vol.% NPh surface functionalized BCZT–epoxy nanocomposite of 20 μm film thickness was almost three times that of pure epoxy polymer of identical film thickness.

Enhanced optical limiting of solubilized carbon nanotubesdecorated with Pt/Pd nanoparticles

We report here the nonlinear optical response of Solubilized Multiwalled Carbon Nanotubes (MWNTs) and these decorated with Platinum and Palladium Nanoparticles. Pristine MWNTs were functionalized with COOH group through microwave assisted synthesis route which rendered them soluble in water and other solvents too. Metal salts of Platinum and Palladium were further reduced to metal nanoparticles in presence of MWNT-COOH under microwave irradiation. These hybrid metal decorated carbon nanostructures were morphologically and functionally well characterized using SEM, EDAX, FTIR, UV-Visible etc., Using Z-scan technique, we carried out nonlinear optical studies on aqueous dispersions (stable) of these metal decorated (Pt/Pd-MWNT-COOH) using a high power Nd:YAG Laser with 532 nm excitation with 10 nanosecond pulse width. These samples exhibited significant nonlinear absorption and scattering. The metal decorated MWNT-COOH (Pt-MWNT-COOH:2 Jcm-2; Pd-MWNT-COOH: 1.7Jcm-2) exhibited enhanced optical limiting which is more than plain MWNT-COOH samples and similar Metal-Graphene hybrid dispersions reported earlier in literature. These could be ideally suited for optical power limiting applications.

Vanadium pentoxide nanoparticles based saturable absorbers

Vanadium pentoxide (V2O5) nanoparticles were synthesized by solution combustion method. The particle size reduction of the as-synthesized sample was achieved through ball milling. The as-synthesized and the ball milled samples were further characterized using XRD, TEM, EDX, UV-Visible and FTIR spectroscopy. Open-aperture z-scan technique was employed to study the nonlinear optical behavior of the synthesized samples and the commercially available V2O5 (bulk) using a second harmonic (532 nm) of Nd: YAG laser with 15 ns pulse width. We observed that the nonlinear absorption process was dependent on particle size as the synthesized and ball milled nanoparticles exhibited saturable absorption behavior while bulk V2O5 exhibited a transition to reverse saturable absorption behavior at the same incident laser intensity.

Low-Cost Plasmonic Carbon Spacer for Surface Plasmon-Coupled Emission Enhancements and Ethanol Detection: a Smartphone Approach

Surface plasmon-coupled emission (SPCE) has led to significant advancements in analytical techniques on account of its unique characteristics that include highly polarized photon-sorting ability. In this study, we report the use of a low-cost activated carbon as a plasmonic spacer in the SPCE substrate for achieving 30-fold enhancement in fluorescence emission. We extend the use of this spacer in the presence of Rhodamine B Base, a lactone dye as the sensing material for smartphone-based ethanol detection on the SPCE platform. Ethanol detection from 1 to 6% concentration highlights the potential use of this technique in monitoring fermentation processes.