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Sivakumar N.,University of Madras | Sivakumar N.,Amrita Center for Nanosciences
Materials Chemistry and Physics | Year: 2013

In the present study, nanostructured manganese zinc ferrite of 11 nm grain size was synthesized by co-precipitation technique and subsequently suitably heat treated to obtain higher grain sizes. The plot of temperature dependence of dc conductivity shows the semiconducting nature of samples. The observed changes in the electrical conductivity have been attributed with the influence of structural ordering upon annealing. The observed decrease in conductivity when the grain size is increased from 11 to 69 nm upon annealing is clearly due to the structural ordering which is evident from FESEM. © 2012 Elsevier B.V. All rights reserved.


Ranjusha R.,Amrita Center for Nanosciences | Lekha P.,Amrita Center for Nanosciences | Subramanian K.R.V.,Amrita Center for Nanosciences | Shantikumar V.N.,Amrita Center for Nanosciences | Balakrishnan A.,Amrita Center for Nanosciences
Journal of Materials Science and Technology | Year: 2011

Vertical ZnO nanotube (ZNT) arrays were synthesized onto an indium doped tin oxide (ITO) glass substrate by a simple electrochemical deposition technique followed by a selective etching process. Scanning electron microscopy (SEM) showed formation of well-faceted hexagonal ZNT arrays spreading uniformly over a large area. X-ray diffraction (XRD) of ZNT layer showed substantially higher intensity for the (0002) diffraction peak, indicating that the ZnO crystallites were well aligned with their c-axis. Profilometer measurements of the ZNT layer showed an average thickness of ~7 μm. Diameter size distribution (DSD) analysis showed that ZNTs exhibited a narrow diameter size distribution in the range of 65-120 nm and centered at ~75 nm. The photoluminescence (PL) spectrum measurement showed violet and blue luminescence peaks that were centered at 410 and 480 nm, respectively, indicating the presence of internal defects. Ultra-violet (UV) spectroscopy showed major absorbance peak at ~348 nm, exhibiting an increase in energy gap value of 3.4 eV. By employing the formed ZNTs as the photo-anode for a dye-sensitized solar cell (DSSC), a full-sun conversion efficiency of 1.01% was achieved with a fill factor of 54%. Quantum efficiency studies showed the maximum of incident photon-to-electron conversion efficiency in a visible region located at 520-550 nm range. © 2011 The Chinese Society for Metals.


Lakshmi V.,Amrita Center for Nanosciences | Ranjusha R.,Amrita Center for Nanosciences | Vineeth S.,Amrita Center for Nanosciences | Nair S.V.,Amrita Center for Nanosciences | Balakrishnan A.,Amrita Center for Nanosciences
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2014

A peculiar architecture of a novel class one dimensional β-Ni(OH)2 nanorods synthesized by an optimized surfactant-free aqueous precipitation route has been lucratively exploited to fabricate highly efficient microporous electrodes for supercapacitors. These fabricated electrodes comprised of a highly porous overlay of interconnected nanoscale units with rod-shaped profile which terminates into jagged-like morphology. The surface area of these nanorods was found to be ~91m2g-1. This architecture transcribes into a superior cycling performance (capacitance of 1150Fg-1 was achieved) with more than 99% of the initial capacitance being retained after 5000 charging/discharging cycles. Their outstanding intercalation/de-intercalation prerogatives have also been exploited to fabricate supercapacitor coin cells which reveal a significant power density of 52kWkg-1 and energy density of 4Whkg-1 with extremely fast response time of 1.2ms. © 2014 Elsevier B.V.


Prasanth R.,Pondicherry University | Gopinath D.,Amrita Center for Nanosciences
Applied Physics Letters | Year: 2013

Development of a therapeutic drugs based on nanoparticles requires a better understanding of the mechanism of selective cyto-toxic effects of nanopaticles over cancer cells. Scanning electrochemical microscopy provides opportunity to measure the real time chemical process at cell proximity in the presence of nanoparticle. Herein, the respiration process in nasopharyngeal cancer cells is investigated with the help of scanning electrochemical microscopy. The cell viability has been tested with MTT assay. The results show that ZnO nanoparticles have time and dose dependent effect in nasopharyngeal cancer cells and the cell respiration rate decreases with time. © 2013 American Institute of Physics.


Joseph J.,Amrita Center for Nanosciences | Rajagopalan R.,Amrita Center for Nanosciences | Anoop S.S.,Amrita Center for Nanosciences | Amruthalakshmi V.,Amrita Center for Nanosciences | And 3 more authors.
RSC Advances | Year: 2014

The present study demonstrates a novel, low temperature synthetic approach by which 3-D bouquets of nickel hydroxide nitrate were processed into high surface area electrodes for supercapacitor applications. The synthesized micro-bouquets comprised randomly arrayed microporous nanoflakes (pore size: 2-6 nm) and exhibited a surface area of 150 m2 g-1. Morphological evolution studies were performed to elucidate how surface morphology of these electrode materials affect redox reactions and their ultimate performance as a supercapacitor. The electrodes were tested in three different electrolytes, namely lithium hydroxide, potassium hydroxide and sodium hydroxide. From the detailed electrochemical analysis, an intrinsic correlation between the capacitance, internal resistance and the surface morphology was deduced and explained on the basis of relative contributions from the faradaic properties in different electrolytes. Depending on the surface morphology and electrolyte incorporated, these nano/micro-hybrid electrodes exhibited specific mass capacitance value of as high as 1380 ± 38 F g-1. Inductively coupled plasma-atomic emission spectroscopy was used to determine the electrode dissolution in the given electrolyte and the findings were co-related with the cycling stability. By employing this low cost electrode design, high stability (>5000 cycles with no fading) was achieved in lithium hydroxide electrolyte. Furthermore, a working model supercapacitor in a coin cell form is also shown to exhibit peak power and energy density of 3 kW kg -1 and 800 mW h kg-1, respectively. © 2014 the Partner Organisations.


Anjali P.,Amrita Center for Nanosciences | Sonia T.S.,Amrita Center for Nanosciences | Shakir I.,King Saud University | Nair S.V.,Amrita Center for Nanosciences | Balakrishnan A.,Amrita Center for Nanosciences
Journal of Alloys and Compounds | Year: 2014

The present study demonstrates a novel approach by which 'bulk nanostructured' NiO micro bouquets can be processed into a high surface area electrode for supercapacitor applications. A detailed study has been performed to elucidate the impact of porosity and redox reactions on the electrochemical behavior. The spheres were synthesized using a soft template technique. An intrinsic correlation between the surface area, capacitance and the internal resistance has been deduced and explained on the basis of relative contributions from the faradic properties of NiO. These NiO spheres exhibited specific mass capacitance values as high as 1950 F g-1. Further, coin cells employing these rechargeable electrodes were also demonstrated which exhibits energy and power densities of 17 W h kg-1and 24 kW kg-1. It has been shown that these electrodes based on such bulk nanostructures can allow significant room for high performance supercapacitor devices. © 2014 Elsevier B.V. All rights reserved.


Ranjusha R.,Amrita Center for Nanosciences | Sreeja R.,Amrita Center for Nanosciences | Mini P.A.,Amrita Center for Nanosciences | Subramanian K.R.V.,Amrita Center for Nanosciences | And 2 more authors.
Materials Research Bulletin | Year: 2012

Vertical ZnO nanotubes were electrochemically deposited onto an indium doped tin oxide glass substrate. These nanotubes were surface treated with zinc acetate and annealed at 450°C, resulting in a nanotubes/nanoparticles composite layer. Scanning electron microscopy of the surface treated samples showed nanoparticles been dispersed uniformly along the ZnO tubular matrix, which was confirmed by X-ray diffractrometry. Photoluminescence and fluorescence microscopy showed untreated ZnO nanotubes exhibiting blue emission, while the treated samples exhibited green emissions. Ultra-violet spectroscopy of treated samples revealed lower band gap values compare to their untreated counterparts. Lifetime measurements showed higher excitonic lifetimes in treated samples. Conductance studies using atomic force microscopy showed significant improvement in the conductance values for the treated samples. A significant increase in photocurrent was observed in treated samples when used as photo-anodes in dye sensitized solar cells. © 2012 Elsevier Ltd. All rights reserved.


Sujith K.,Amrita Center for Nanosciences | Asha A.M.,Amrita Center for Nanosciences | Anjali P.,Amrita Center for Nanosciences | Sivakumar N.,Amrita Center for Nanosciences | And 3 more authors.
Materials Letters | Year: 2012

Highly porous (∼ 70%) polyaniline-carbon black composite nanofiber mats with good conductivity were fabricated via electrospinning. The fiber mat was electrospun using polyvinyl alcohol as carrier solution which was later decomposed at ∼ 230 °C to get a complete conducting nanofiber network. This heat treatment reduced the fiber diameter from ∼ 250 nm to ∼ 170 nm and the porosity of the fiber mat increased from ∼ 41% to 70%. The removal of the carrier phase was confirmed by Fourier transform infrared spectroscopy and did not result into any structural collapse. The localized conductance measurements using scanning electro-chemical microscopy showed that the removal of insulating carrier solution substantially reduced the percolation threshold and increased the fiber-mat conductance. © 2011 Elsevier B.V. All rights reserved.


Nair S.V.,Amrita Center for Nanosciences | Balakrishnan A.,Amrita Center for Nanosciences | Subramanian K.R.V.,Amrita Center for Nanosciences | Manu A.,Amrita Center for Nanosciences | And 2 more authors.
Bulletin of Materials Science | Year: 2012

The main objective of this study is to show the effect of TiO 2 nanotube length, diameter and intertubular lateral spacings on the performance of back illuminated dye sensitized solar cells (DSSCs). The present study shows that processing short TiO 2 nanotubes with good lateral spacings could significantly improve the performance of back illuminated DSSCs. Vertically aligned, uniform sized diameter TiO 2 nanotube arrays of different tube lengths have been fabricated on Ti plates by a controlled anodization technique at different times of 24, 36, 48 and 72 h using ethylene glycol and ammonium fluoride as an electrolyte medium. Scanning electron microscopy (SEM) showed formation of nanotube arrays spread uniformly over a large area. X-ray diffraction (XRD) of TiO 2 nanotube layer revealed the presence of crystalline anatase phases. By employing the TiO 2 nanotube array anodized at 24 h showing a diameter ̃80 nm and length ̃1·5 μm as the photo-anode for back illuminated DSSCs, a full-sun conversion efficiency (η) of 3·5%was achieved, the highest value reported for this length of nanotubes. © Indian Academy of Sciences.


Paravannoor A.,Amrita Center for Nanosciences | Ranjusha R.,Amrita Center for Nanosciences | Asha A.M.,Amrita Center for Nanosciences | Vani R.,Amrita Center for Nanosciences | And 6 more authors.
Chemical Engineering Journal | Year: 2013

Nanowires of NiO were successfully synthesized using a simple hydrothermal route. The nanowires were characterized for phase composition and morphology by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques, respectively. XRD analysis showed that the powders produced were of high purity cubic NiO phase. Selected area electron diffraction (SAED) analysis during TEM showed the growth direction of NiO nanowires in (100), while exhibiting an average diameter of ∼ 65nm. BET analysis showed these nanowires exhibiting a surface area of 153.2m2/g. These nanowires were electrophoretically deposited on titanium foils as thin layer (∼5μm thickness) and were studied for their capacitive behavior as electrodes for supercapacitor applications. Image analysis and atomic force microscopy (AFM) studies revealed the thin film coating to be highly porous (>50%). Cyclic voltammetry (CV) studies on these electrodes exhibited a specific mass capacitance of 750F/g with 12% capacitance fade at the end of 1000 cycles. The present study elucidates how NiO surface morphology and OH- adsorption/desorption behaviors underlying these electrodes impact the chemical and structural stability performance. © 2013 Elsevier B.V.

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