Hyderabad, India
Hyderabad, India

Time filter

Source Type

Milanese C.,University of Pavia | Girella A.,University of Pavia | Garroni S.,University of Sassari | Bruni G.,University of Pavia | And 5 more authors.
Nanoscience and Nanotechnology Letters | Year: 2012

Mg-Ni-C-TiO 2 mixtures with fixed Mg: Ni: C ratio (80.75 wt%: 14.25 wt%: 5 wt%) and TiO 2 content increasing from 0.5 wt% to 2.0 wt% were prepared by high energy ball milling (BM) under Ar for 2 different times (45 min and 90 min) and characterized with respect to their kinetic and thermodynamic hydrogen sorption properties. The aim of the work was to study the influence of the TiO 2 presence on the activation behavior and the sorption properties of the Mg: Ni: C ternary system, studied in detail in a previous paper. When TiO 2 is added to the mixtures, the hydrogen active phases remain "free Mg" and Mg 2Ni, that fully hydrogenate during the charging runs, with formation of β-MgH 2 and Mg 2NiH 4, but the number of charging/discharging cycles needed for the sorption activation (performed at 623 K and 35 bar/0.9 bar hydrogen pressure) is reduced from 10 to 7. Moreover, the addition of TiO 2: (a) does not lead to a decrease in the gravimetric capacity with respect to the ternary system (6.4 wt% H 2), suggesting that the oxide increases the sorption efficiency of the active phases; (b) does not affect the equilibrium pressures of the Mg/MgH 2 and Mg 2Ni/Mg 2NiH 4 systems; (c) leads to a small decrease in the hydrides starting dehydrogenation temperatures (5 K and 4 K respectively at H 2 pressure = 0.9 bar) and to a very small increase (1 kJ/mol H 2) in the desorption enthalpy; (d) is responsible of an appreciable increase in the sorption rates (up to 10 times for absorption and to 2.7 times for desorption). Copyright © 2012 American Scientific Publishers All rights reserved.

Rao S.V.,University of Hyderabad | Prasad A.K.,Cochin University of Science and Technology | Giribabu L.,Nanomaterials Laboratory | Tewari S.P.,University of Hyderabad
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Herein we present our results from the picosecond and nanosecond nonlinear optical studies of two novel phthalocyanines {[(SO3Na) 4CuPc] and [(SO3Na)4NiPc]} using the Z-scan technique. Open aperture Z-scan data revealed that the picosecond nonlinear absorption was dominated by three-photon absorption while in the nanosecond domain reverse saturable absorption prevailed. Closed aperture data with nanosecond pulses indicated strong thermal, negative nonlinearity while picosecond excitation demonstrated positive nonlinearity. The nonlinearity in CuPc was higher than in NiPc in both the time domains. The nonlinear coefficients extracted from the fits to experimental data were large compared to some of the recently reported works on similar molecules. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Joshi S.,RMIT University | Joshi S.,Nanomaterials Laboratory | Satyanarayana L.,Nanomaterials Laboratory | Manjula P.,Nanomaterials Laboratory | And 2 more authors.
ISPTS 2015 - 2nd International Symposium on Physics and Technology of Sensors: Dive Deep Into Sensors, Proceedings | Year: 2015

Heterojunction nanocomposites were realized between p-Type CuO and n-Type SnO2 by simple hydrothermal route, further incorporation with 0.5wt.% silver showed an efficient sensor response of 72.02% towards carbon dioxide at a comparably low operating temperature of 300°C. The synthesized samples were characterized extensively by XRD and UV-DRS. Morphological evaluations carried out using transmission electron microscope not only provided information on the size and shape of the materials but also revealed that the hierarchical assembly remained intact for CuO-SnO2 nanocomposite. Furthermore, carbon dioxide gas sensing properties (sensitivity, sensor response, and recovery time) of the as-synthesized nanocomposites were investigated to demonstrate the ability of p-n heterojunction. Owing to the porous structure and large surface area, the nanocomposite exhibited superior sensitivity with short response/recovery times at concentrations of 10,000 ppm of CO2 gas balanced in air. Finally, it was concluded that embellishing 0.5wt.% silver on the surface activated these nanocomposites. This surface activation reduced the operating temperature and also promoted excellent sensitivity, selectivity, recovery time towards carbon dioxide. A detailed insight into sensing mechanism based on UV-DRS spectroscopy studies was presented. © 2015 IEEE.

Manna J.,Nanomaterials Laboratory | Begum G.,Nanomaterials Laboratory | Kumar K.P.,Indian Institute of Chemical Technology | Misra S.,Indian Institute of Chemical Technology | Rana R.K.,Nanomaterials Laboratory
ACS Applied Materials and Interfaces | Year: 2013

Herein, we present an environmentally benign method capable of mineralization and deposition of nanomaterials to introduce antibacterial functionalities into cotton fabrics under mild conditions. Similar to the way in which many naturally occurring biominerals evolve around the living organism under ambient conditions, this technique enables flexible substrates like the cotton fabric to be coated with inorganic-based functional materials. Specifically, our strategy involves the use of long-chain polyamines known to be responsible in certain biomineralization processes, to nucleate, organize, and deposit nanostructured ZnO on cotton bandage in an aqueous solution under mild conditions of room temperature and neutral pH. The ZnO-coated cotton bandages as characterized by SEM, confocal micro-Raman spectroscopy, XRD, UV-DRS, and fluorescence microscopy demonstrate the importance of polyamine in generating a stable and uniform coating of spindle-shaped ZnO particles on individual threads of the fabric. As the coating process requires only mild conditions, it avoids any adverse effect on the thermal and mechanical properties of the substrate. Furthermore, the ZnO particles on cotton fabric show efficient antibacterial activity against both gram-positive and gram-negetive bacteria. Therefore, the developed polyamine mediated bioinspired coating method provides not only a facile and "green" synthesis for coating on flexible substrate but also the fabrication of antibacterial enabled materials for healthcare applications. © 2013 American Chemical Society.

Reddy T.N.,Nanomaterials Laboratory | Reddy T.N.,Indian Institute of Chemical Technology | Manna J.,Nanomaterials Laboratory | Rana R.K.,Nanomaterials Laboratory | Rana R.K.,Indian Institute of Chemical Technology
ACS Applied Materials and Interfaces | Year: 2015

A bio-inspired approach for the fabrication of reduced graphene oxide (rGO) embedded ZnO nanostructure has been attempted to address issues pertaining to charge recombination and photocorrosion in ZnO for application as an effective photocatalyst. Herein we demonstrate the synthesis of rGO-ZnO nanostructures in a single step using polyamines, which simultaneously aid in the mineralization of ZnO nanostructures from zinc nitrate, reduction of graphene oxide (GO), and finally their assembly to form rGO-ZnO composite structures under environmentally benign conditions. The interspersed nanocomponents in the assembled heterostructures result in enhanced photocatalytic activity under UV light, indicating an effective charge separation of the excited electrons. Furthermore, the composite structure provides stability against photocorrosion for efficient recyclability of the catalyst. © 2015 American Chemical Society.

Bala Murali Krishna M.,University of Hyderabad | Giribabu L.,Nanomaterials Laboratory | Narayana Rao D.,University of Hyderabad
Journal of Porphyrins and Phthalocyanines | Year: 2012

Synthesis and measurements of third order nonlinear optical (NLO) coefficients of water soluble zinc octacarboxy phthalocyanine (ZnOCPc) are reported here using different laser pulse durations. Nonlinear absorption and refraction behaviour in the nanosecond (ns), picosecond (ps) and femtosecond (fs) time domains were studied in detail. Three-photon absorption was the prevalent mechanism with femtosecond laser excitation whereas strong reverse saturable absorption due to dominant two-photon absorption (TPA) was observed with picosecond and nanosecond excitations. We have evaluated the sign and magnitude of the third order nonlinearity in fs, ps, and ns regimes. We observed large off-resonant second order hyperpolarizability (γ) with ultrafast nonlinear optical response in the femtosecond domain using degenerate four wave mixing (DFWM) technique. We also report the optical limiting characteristics and figure of merit (FOM) of ZnOCPc for optical switching. © 2012 World Scientific Publishing Company.

Hamad S.,University of Hyderabad | Podagatlapalli G.K.,University of Hyderabad | Giribabu L.,Nanomaterials Laboratory | Tewari S.P.,University of Hyderabad | Rao S.V.,University of Hyderabad
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

We present our results of nonlinear optical properties of Tritolyl Corrole (TTC) and Triphenyl Corrole (TPC) studied in the form of solution using Z-scan technique with 660 nm, ∼2 picosecond (ps) pulses and 800 nm, ∼40 femtosecond (fs) pulses excitation. Picosecond open-aperture Z-scan data revealed these molecules exhibited strong saturable absorption. These molecules possessed negative nonlinear refractive index (n2). The estimated value of n2 was 6×10 -15 cm 2/W and 8×10 -15 cm 2/W for TPC and TTC, respectively. We have recently reported NLO properties of Corroles with 800 nm excitation where they exhibited strong two-photon absorption (2PA) at higher intensities and effective two-photon absorption at lower intensities in the ps regime. Femtosecond open aperture Z-scan studies indicated the presence of strong saturable absorption with effective nonlinear absorption coefficients (β) of ∼0.8×10 -13 cm/W and ∼2.7×10 -13 cm/W for TPC and TTC, respectively. We have also estimated the sign and magnitude of real part of third order nonlinearity through the closed aperture scans. We discuss the nonlinear optical performance of these organic molecules. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

El-Sheshtawy H.S.,South Valley University | Abd El Sadek M.S.,Nanomaterials Laboratory | Yahia I.S.,Nano Science Laboratory | Yahia I.S.,King Khalid University
Nanoscience and Nanotechnology Letters | Year: 2014

The highly fluorescent thiol capped CdTe nanocrystals were synthesized by the aqueous synthesis route. In this method we used sodium tellurite (Na 2TeO3) as the Te source in contrast to the previous reported methods, which used NaHTe and H2Te that need a pretreatment for the unstable precursor. The structure of CdTe nanocrystals was investigated by means of X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), UV-visible, Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The results showed the crystallinity of the CdTe nanocrystals and the average size of CdTe QDs was 3.2 nm. An aqueous solution of CdTe capped with mercaptopropionic acid (MPA) shows a characteristic fluorescent peak at 590 nm, which decrease under the influence of both the pH and temperature. The labeling affinity of the water-soluble MPA- CdTe and some selected antibiotics such as Ceftazidime and Rifampicin were investigated in 50 mM sodium acetate buffer pH 7.4. Both antibiotics show the ability to interact with QDs nanocrystal that probed by fluorescence spectroscopy. The interaction between MPA-CdTe and Rifampicin shows a dynamic quenching process while the reaction between QDs and Ceftazidime was initiated by ground-state complex formation (static quenching) .© 2014 American Scientific Publishers All rights reserved .

Hamad S.,University of Hyderabad | Podagatlapalli G.K.,University of Hyderabad | Giribabu L.,Nanomaterials Laboratory | Tewari S.P.,University of Hyderabad | Rao S.V.,University of Hyderabad
AIP Conference Proceedings | Year: 2011

We report our results on femtosecond (fs) and picosecond (ps) nonlinearities in two novel Corroles (a) Tritolyl Corrole (TTC) (b) Triphenyl Corrole (TPC) studied using the Z-scan technique. Both open and closure aperture Z-scan curves were recorded with ∼40 fs and open Z-scan curves were recorded with ∼2 ps laser pulses at same wavelength of 800 nm and nonlinear coefficients were extracted for both studies. Picosecond open aperture data clearly suggested the presence of three photon absorption (3PA) for both the molecules. One of the molecule, TPC, possessed positive refractive index with a value 2×10-17cm2/W and TTC possessed negative refractive index with a value of 3×10-18cm2/W in the fs domain. Solvent contribution to the nonlinearity was also identified. We discuss the nonlinear optical performance of these organic molecules. © 2011 American Institute of Physics.

Canjeevaram Balasubramanyam R.K.,Joint Research Center | Canjeevaram Balasubramanyam R.K.,RMIT University | Kumar R.,Joint Research Center | Kumar R.,Indian Institute of Chemical Technology | And 7 more authors.
Journal of Physical Chemistry C | Year: 2016

A series of quadrupolar (A-π-D-π-A) tetra-aryl 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) derivatives synthesized are showcased as potential organic resistive memory (ORM) devices for the first time. The experimental observations coupled with density functional theory (DFT) calculations probe in detail the role of terminal substituent groups (p-NH2, p-Cl, p-CN, p-NO2, m-NO2) on the optical and electrical properties. Electrochemical studies reveal that the 3- and 4-dinitro derivatives form an unusual class of tetra-aryl DHPPs that exhibit intrinsic amphoteric redox behavior contrary to the literature reports. The bipolar nature within a single molecule was harnessed to design operational ORMs. Interestingly, the memory devices fabricated using the structural isomers exhibited dissimilar memory characteristics. While the p-NO2 derivative displays permanent Write Once Read Many times (WORM) memory, its meta-counterpart represents a behavior akin to rewriteable flash memory. The noticeably higher ON/OFF ratio (∼104) for the p-NO2 derivatives could be ascribed to their matched redox energy levels with the work function of active electrodes favoring better charge injection. Rational interpretation of these findings strongly suggests that the choice and strategic positioning of terminal substituents can significantly alter the nature of "charge traps" affecting the device outcome. These encouraging findings open up a relatively less chartered territory of air stable fused pyrrole systems that holds great promise for realizing next generation organic memory devices. © 2016 American Chemical Society.

Loading Nanomaterials Laboratory collaborators
Loading Nanomaterials Laboratory collaborators