Vishal Udmale - Academia.edu (original) (raw)

Papers by Vishal Udmale

Oriental journal of chemistry, 2013

Our paper reviews the use of conductive polymer composite materials in various applications for s... more Our paper reviews the use of conductive polymer composite materials in various applications for semi conductive, static-dissipative, anti-corrosive, electromagnetic interference (EMI) shielding and stealth composite coatings. The composite consists of conductive fillers and the insulating polymer network. The composite becomes electrically conductive as the filler content exceeds a certain critical value, generally called as Percolation Threshold Value (PTV). The PTV for a particular polymer composite can be drastically reduced by using nano-sized conductive fillers. The higher the aspect ratio (length:width) of the nano-fillers, the lower is the concentration for achieving the PTV. Traditionally the metals, carbon-black particles and alloys have been used as electrically conductive fillers; however, very high level of these fillers can be detrimental for the process ability, surface quality of the material, density, the cost and mechanical properties of the composite. By the use of...

The photocatalytic degradation processes are gaining importance in the area of wastewater treatme... more The photocatalytic degradation processes are gaining importance in the area of wastewater treatment, not only in academics also in industries, since these processes result in complete mineralization with operation at mild conditions of temperature & pressure. In this new era of nanotechnology Carbon based TiO2 composites have attracted much attention and become a very active field of research due to their unique properties & promising applications for the big problem of pollution. Our work deals with the comparison between photo-catalytic degradation of some textile Acid dyes using nano sized TiO2 & MWCNT-TiO2 thin films coated on various substrates. The synergistic effect has observed for nanocomposites of MWCNT/TiO2 on the photocatalytic degradation of acid-azo dyes. The higher photo-catalytic activity of the MWCNT-TiO2 composites might be attributed to the homogenous distribution of MWCNT-TiO2 complexes and play important role as an energy sensitizer for improving the quantum eff...

This work is devoted to synthesize different semiconductor nanoparticles and their metal-hybrid n... more This work is devoted to synthesize different semiconductor nanoparticles and their metal-hybrid nanocomposites such as TiO 2 , Au/TiO 2 , ZnO, and Au/ZnO. The morphology and crystal structure of the prepared nanomaterials are characterized by the TEM and XRD, respectively. These materials are used as catalysts for the photodegradation of Malathion which is one of the most commonly used pesticides in the developing countries. The degradation of 10 ppm Malathion under ultraviolet (UV) and visible light in the presence of the different synthesized nanocomposites was analyzed with high-performance liquid chromatography (HPLC) and UV-Visible Spectra. A comprehensive study is carried out for the catalytic efficiency of the prepared nanoparticles. Different factors influencing the catalytic photodegradation are investigated, as different light source, surface coverage, and nature of the organic contaminants. The results indicate that hybrid nanocomposite of the semiconductor-metal hybrid serves as a better catalytic system compared with semiconductor nanoparticles themselves.

Abstract: Our paper reviews the use of conductive polymer composite materials in various applicat... more Abstract: Our paper reviews the use of conductive polymer composite materials in various applications for static-dissipative, semi conductive, electromagnetic interference (EMI) shielding, anticorrosive and stealth composites. A composite consisting of conductive fillers and an insulating polymer becomes electrically conductive as the filler content exceeds a certain critical value, generally termed as Percolation Threshold Value (PTV). The PTV for a particular polymer composite can be drastically reduced by using nano-sized conductive fillers. The higher the aspect ratio (length-to-width ratio) of the filler particles, the lower is the concentration for achieving the PTV. Traditionally, metals, alloys and carbon-black particles have been used as electrically conductive filler materials, however, too high a level of these fillers can be detrimental for the process ability, density, surface quality of the material, the cost and mechanical properties of the composite. By using nano co...

Journal of crystal …, 2000

ABSTRACT

Journal of Applied …, 2008

We show an efficient way to investigate the magnetic behavior of nanotube stubs based on the embe... more We show an efficient way to investigate the magnetic behavior of nanotube stubs based on the embedding of aligned iron-filled carbon nanotubes in silicon oxide using thermal chemical vapor deposition and gradual mechanical polishing afterwards. On the one hand, during the covering process the saturation magnetization moment rises due to the transformation of Fe3C into body-centered-cubic-Fe and graphite. On the other hand, the coercivity drops, mainly induced by changes in the shape of the nanowires. Further magnetization measurements of the embedded sample point to most of the ferromagnetic nanowires being located near the surface of the substrate. The coercivity increases when reducing the thickness of the nanotube array. The anomalous high coercivity of the Fe nanowires encapsulated by non magnetic carbon nanotubes make them suitable for high density data storage applications.

Carbon, 2004

A facile method is proposed to use LaNi 2 hydrogen storage alloy as a catalyst precursor to produ... more A facile method is proposed to use LaNi 2 hydrogen storage alloy as a catalyst precursor to produce metallic nickel filled carbon nanotubes. Multi-walled carbon nanotubes filled with long continuous nickel nanowire with several microns in length are synthesized through chemical vapor deposition at low temperature (550°C). It is more efficient to fill Ni nanowires into nanotubes after the oxidation treatment of LaNi 2 alloy at low temperatures, while the oxidation treatment at high temperature results in the forming of herringbone carbon nanofibers with tips of Ni nanoparticles. The metallic Ni nanowires inside the cores of carbon nanotubes could not be eliminated during the purification process in concentrated hydrochloric acid. The analysis of transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray diffraction (XRD) reveals that the metallic nickel nanowires filled inside carbon nanotubes exist as a single crystalline with fcc structure.

Various applications of carbon nanotubes require their chemical modification in order to tune/con... more Various applications of carbon nanotubes require their chemical modification in order to tune/control their physicochemical properties. One way for achieving this control is by carrying out doping processes through which atoms and molecules interact (covalently or noncovalently) with the nanotube surfaces. The aim of this chapter is to emphasize the importance of different types of doping in carbon nanotubes (single-, double- and multiwall). There are three main categories of doping: exohedral, endohedral and inplane doping. We will review the most efficient ways to dope carbon nanotubes and discuss the effects on the electronic, vibrational, chemical, magnetic and mechanical properties. In addition, we will discuss the different ways of characterizing these doped nanotubes using spectroscopic techniques, such as resonant Raman, X-ray photoelectron, electron energy loss spectroscopy and others. It will be demonstrated that doped carbon nanotubes could be used in the fabrication of nanodevices (e.g., sensors, protein immobilizers, field emission sources, efficient composite fillers, etc.). We will also present results related to the importance of inplane-doped nanotubes for attaching various metal clusters and polymers covalently using wet chemical routes.

Carbon, 2006

The thermal decomposition of ferrocene combined with a catalyst-assisted structuring of a Si-subs... more The thermal decomposition of ferrocene combined with a catalyst-assisted structuring of a Si-substrate surface is a favourable way to produce Fe-filled carbon nanotubes in good quality and in high yields. In this work we have studied the growth of such aligned filled nanotubes on iron and cobalt pre-coated Si-substrates and their dependence on the deposition time. The nanotube diameter depends on the used catalyst metal on the substrate surface. Magnetization measurements were carried out perpendicular (along tube axis) and parallel to the substrate and show excellent coercivities, a strong uniaxial anisotropy (ratios of H c,per /H c,par up to 6) and high saturation magnetization moments per substrate square. The magnetic behavior has been also interpreted as a function of deposition time and of the catalyst metal on the substrate. These investigations were complemented by X-ray diffraction, which revealed a majority fraction of a-Fe and a small amount of Fe 3 C.

Journal of Physics: …, 2007

ABSTRACT Multifunctional nanocontainers can be produced based on partially filled Fe-multi walled... more ABSTRACT Multifunctional nanocontainers can be produced based on partially filled Fe-multi walled carbon nanotubes (MWCNTs). Using thermal decomposition ferrocene filled nanotubes can be grown aligned on substrates. The encapsulated metal nanowires have diameters of 5-30 nm and a length up to few microns. They consist of single-crystalline of α and γ-Fe- phases. Using heat treatment, it is possible to transform γ-Fe into α-Fe. With the aid of wet chemical methods the nanotubes can be opened and additionally filled with an agent, e.g., therapeutic agents (carboplatin) or other metals (copper). Initial studies do not show a high toxicity over a period of 440 days. These materials can be used for drug delivery and hyperthermia. The specific absorption rate (SAR) is greater than 100W/(g-α-Fe) in a magnetic field of 18kA/m (f = 250kHz).

Carbon, 2005

A straightforward, one-step method for the preparation of novel carbon nanotube/iron nanoparticle... more A straightforward, one-step method for the preparation of novel carbon nanotube/iron nanoparticle hybrids with some degree of shape control is reported herein. These carbon nanostructures differ from those reported previously: the nanoparticles were not attached to or coated onto the surface of carbon nanotubes but embedded inside the carbon wall. They were synthesized in good yield by thermolysis of ferrocene

Journal of applied …, 2005

ABSTRACT By optimization of the synthesis of ferromagnetic-filled carbon nanotube ensembles on Si... more ABSTRACT By optimization of the synthesis of ferromagnetic-filled carbon nanotube ensembles on Si substrates (catalytic decomposition of ferrocene) and following annealing at 645 ° C , marked hysteresis loops can be measured by the alternating-gradient method. Unusually high coercivities and strong anisotropies with an easy magnetic axis parallel to the alignment of the nanotubes are observed from the as-grown samples, whereas an enhanced magnetic saturation moment (up to a factor of 2) and a decreased anisotropy are realized after annealing at 645 ° C . The increase of the magnetic saturation moment of the Fe-filled carbon nanotube ensembles is caused by the entire transformation within the tubes of the γ- Fe and Fe 3 C phases to ferromagnetic α- Fe and graphite. X-ray diffraction with different glancing incidence shows that the γ- Fe is predominantly at the tips of the nanotubes, while the iron carbide resides closer to the substrate. However, after the annealing process only α- Fe is found. At an annealing temperature of 675 ° C the nanotube structures are destroyed and the magnetic characteristics are dramatically altered (viz., the disappearance of anisotropy and reduction in coercivity).

Journal of Crystal Growth, 2009

This investigation deals with the effect of growth temperature on the growth behavior of Fe fille... more This investigation deals with the effect of growth temperature on the growth behavior of Fe filled multi-walled carbon nanotubes (MWCNTs). Carbon nanotube (CNT) synthesis was carried out in a thermal chemical vapor deposition (CVD) reactor in the temperature range 650–950 °C using propane as the carbon source, Fe as the catalyst material, and Si as the catalyst support. Atomic force microscopy (AFM) analysis of the catalyst exhibits that at elevated temperature clusters of catalyst coalesce and form macroscopic islands. Field emission scanning electron microscopy (FESEM) results show that with increased growth temperature the average diameter of the nanotubes increases but their density decreases. High-resolution transmission electron microscopy (HRTEM) studies suggest that the nanotubes have multi-walled structure with partial Fe filling for all growth temperatures. The X-ray diffraction (XRD) pattern of the grown materials indicates that they are graphitic in nature. The characterization of nanotubes by Raman spectroscopy reveals that the optimized growth temperature for Fe filled CNTs is 850 °C, in terms of quality. A simple model for the growth of Fe filled carbon nanotubes is proposed.

Chemical vapor …, 2006

Ferromagnetic-filled carbon nanotubes are new nanostructured materials with many possible applica... more Ferromagnetic-filled carbon nanotubes are new nanostructured materials with many possible applications. They can be synthesized using the thermal decomposition of metallocenes of the iron triad. Two different methods (solid and liquid source CVD) are suitable for producing, at very high filling rates, filled nanotubes on precoated Si substrates. The diameters of deposited filled nanotubes are particularly dependent on the size of catalyst particles on the substrate, while the lengths depend more on the sublimation and decomposition rate of metallocene. The growth mechanism of filled carbon nanotubes is based on the root growth mode. Multiwalled carbon nanotubes, filled with body-centered cubic Fe, show unusual magnetic properties. Aligned-growth nanotube ensembles can reach coercivities up to 130 mT (bulk iron 0.09 mT). Ferromagnetic-filled carbon nanotubes can be successfully used both as cantilever tips in magnetic force microscopy and as a nanocontainer for new therapies in medicine.

IEEE Transactions on Magnetics, 2009

We synthesize ferromagnetic Co nanowire, and Co/Pd multisegment nanowires encapsulated inside mul... more We synthesize ferromagnetic Co nanowire, and Co/Pd multisegment nanowires encapsulated inside multi-walled carbon nanotubes CNTs (MWCNTs) by plasma-enhanced chemical vapor deposition (PECVD). High-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) patterns and energy dispersive X-ray spectroscopy (EDS) were used to characterize the microstructures and elemental analyses of the nanowires. Quantitative magnetization measurements of Co nanowires encapsulated inside MWCNTs were experimentally established by TEM off-axis electron holography at room temperature. The MWCNTs grew up to 100-110 nm in diameter and 1.5-1.7 m in length. The typical bright-field TEM images revealed both Co nanowire and Co/Pd multisegment nanowires encapsulated inside vertically aligned MWCNTs on the same substrate. The composition of metal encapsulated inside MWCNTs were characterized by EDS. Experimental results revealed that the Co nanowire encapsulated inside MWCNT was always presented as the face-centered-cubic (fcc) Co structure. The component of magnetic induction was then measured to be 1.2 0.1 T based on TEM off-axis electron holography results, which is lower than the expected saturation magnetization of fcc Co bulk of 1.7 T. The partial oxidation of the ferromagnetic metal during the process and the magnetization direction may play an important role in the determination of the quality of the remanent states. The ferromagnetic metal nanowires encapsulated inside CNTs demonstrate very high potential in providing the required magnetic properties, low dimensionality, and small volume for future nanoscale devices.