Showing papers in "Advanced Materials Letters in 2014"

Synthesis of air stable copper nanoparticles and their use in catalysis

Abstract: The undertaken study describes synthesis of air resistant copper nanoparticles (Cu NPs) in an aqueous phase using sodium borohydride as a reducing agent via chemical reduction method. The hydrosol has resistant to oxidation by atmospheric oxygen for several days. The air stability was induced by capping Cu NPs with anionic surfactant “sodium dodecyl sulfate (SDS)”. Ascorbic acid was used as an antioxidant. These Cu NPs were characterized by ultraviolet-visible (UV-VIS) spectroscopy, which contributed towards the understanding of surface plasmon resonance (SPR) generation and optical behavior of Cu NPs. It was used as an optical tracer for size control and confirmation of Cu NPs and was found to be affected by various parameters like reaction time, pH, concentration of copper sulfate and the surfactant SDS. SPR peaks were found to shift from 597 to 569 nm, while apparent color changes from yellow to brick red. Further characterization studies were carried out by using fourier transform infrared (FT-IR) spectroscopy to investigate the co-ordination between Cu NPs and SDS. X-ray diffraction (XRD) was used for phase purity of Cu NPs. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used the size and morphological characterization. The average size of the Cu NPs was found to be 15 nm in diameter with an average height of 14 nm. The Cu NPs showed excellent catalytic activity in the reductive degradation of Eosin B (EB) dye in just 16 sec of reaction time and maintained their catalytic activity when reused multiple times. The degradation rate was found to follow first order reaction kinetics with the EB degradation. The Cu NPs enhanced the rate of EB degradation 30 times more than the control test. Copper was found an attractive catalyst in the nanosize regimes. The Cu NPs are more economical as compared to noble metals. The Cu NPs are expected to be suitable alternative and play an imperative role in the fields of catalysis and environmental remediation. Copyright © 2014 VBRI press.

Green Synthesis, Characterization And Optical Properties Of Zinc Oxide Nanosheets Using Olea Europea Leaf Extract

Abstract: In this paper, a green method is reported for synthesis and characterization of zinc oxide nanosheets using Olea europea leaf extract. ZnO nanosheets were characterized by UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FT- IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The UV-vis absorption spectrum shows an absorption band at 374 nm due to ZnO nanosheets. XRD characterize the final product as highly crystalline ZnO with sizes in the range 18- 30 nm. The SEM results reveal a presence of network of randomly oriented ZnO nanosheets or nanoplatelets with an average size of 500 nm and thicknesses of about 20 nm. This facile and green approach may provide a useful tool to large scale synthesis other nanoparticles that have potential biotechnology. Copyright © 2014 VBRI press

Dielectric And Impedance Spectroscopic Studies Of Multiferroic BiFe1-xNixO3

Abstract: Multiferroic bismuth ferrites (BFO) and Ni substituted bismuth ferrites (BFNO) were synthesized by standard solid state reaction route. The structural and microstructural studies were carried out. The effect of Ni substitution on dielectric constant and dielectric loss of the samples was studied in a wide range of frequency (100 Hz- 1 MHz) and temperature (27 o C – 420 o C). It has been observed that the dielectric constant increases with increase in Ni doping concentration and attained a maximum value for BFNO(x = 0.075) sample while the dielectric loss has been found to decrease with the doping concentration. This implies a reduction in the conductivity and hence improved the dielectric properties of Ni doped BFO. The anomalous peaks in temperature dependent dielectric studies indicate the increase in antiferromagnetic ordering temperature and possible existence of spin glass states upon Ni substitution in place of Fe. The complex impedance spectroscopic analysis suggests purely the intrinsic nature of the dielectric anomalies. Temperature dependent non-Debye type of dielectric relaxation has also been observed. The Nyquist plots show the negative temperature coefficient of resistance behavior of these compounds. Further it would be interesting to study their magnetic and magnetoelectric properties with the aim of identifying new multifunctional device applications. Copyright © 2014 VBRI press.

Chemical Vapour Sensing Properties Of Electrospun Nanofibers Of Polyaniline/ ZnO Nanocomposites

Abstract: Zinc oxide (ZnO) nanoparticles were synthesized by simple route of sol-gel method and nanofibers of polyaniline (PANI) and PANI/ZnO nanocomposites prepared using the electrospinning technique. Electrospun nanofibers of PANI and PANI/ZnO nanocomposites were collected on aluminum substrate for characterization and on Cu-interdigited electrodes to prepare chemiresistor sensor. Electrospun nanofibers of PANI and PANI/ZnO nanocomposites have been characterized by UV-Visible (UV-Vis), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). UV-Visible spectra of nanofibers of PANI/ZnO nanocomposites show hypsochromic shift as that of PANI and some interaction due to ZnO in PANI matrix. The observed changes in the FTIR spectra of the fibers of PANI/ZnO nanocomposites are assosciated with the formation of H-bonding between ZnO and the N-H group present in the PANI chains. X-ray diffraction patterns exhibits hexagonal wurtzite structure of ZnO and broad amorphous peaks of PANI. Heterogeneous structures with fibrous characteristics of diameter less than 300nm of PANI/ZnO nanocomposites are identified in the SEM images. The electrical properties were characterized by I-V characteristic measurements. The changes in resistance of the chemiresistor sensor were utilized for detection of HCl and NH3 chemical vapour at room temperature. The resistance of the sensors was found to be decreased when they were exposed to HCl vapours whereas the resistance of the sensors was found to be increased when they were exposed to NH3 vapours. It was observed that PANI/ZnO nanocomposite sensor shows a high response and sensitivity with good repeatability as compared to that of pure PANI. Sensitivity result shows that PANI/ZnO nanocomposite is highly sensitive to chemical vapours even at room temperature and at very low concentration. Copyright © 2014 VBRI press.

Investigations Of Impedance And Electric Modulus Properties Of Pb1-xSmx(Zr0.45 Ti0.55)1-x/4O3 Ceramics

Abstract: Pb1-xSmx(Zr0.45Ti0.55)1-x/4O3 (PSZT; x = 0.00, 0.03 and 0.06) ceramic samples were prepared by high temperature mixed oxide method. Using complex impedance spectroscopy (CIS) technique, the complex impedance (Z*) and modulus (M*) properties of the materials were analyzed within a wide range of temperature and frequency. Impedance analysis indicates the presence of mostly bulk resistive (grain) contributions which is found to decrease with the increase in temperature. It suggests about the negative temperature coefficient of resistance (NTCR) type behaviour of the materials. Complex modulus plots exhibit the presence of grain (bulk) as well as grain boundary contributions in the materials and also support their NTCR type behaviour. Both the complex impedance and complex modulus plots confirm the presence of non-Debye type of relaxation in the materials. At higher temperatures, bulk resistance is found to increase with the increase in Sm 3+ concentration in PSZT along with the increase in relaxation phenomenon. Copyright © 2014 VBRI press.

Effect Of UV Rays On Degradation And Stability Of High Performance Polymer Membranes

Abstract: Acid doped polybenzimidazole membranes have emerged as an efficient electrolyte for high temperature polymer electrolyte membrane fuel cells (HTPEMFCs). The long term stability of polybenzimidazole membranes has been recognized as an important issue for commercial applications. Here, we report the oxidative degradation of polybenzimidazole membranes. The photoirradiation of poly(2,2'-ethylene-5,5'-bibenzimidazole) (PBIE) under accelerated photodegradation conditions was carried out by ultraviolet (UV) rays (λ > 300 nm) and characterized by Fourier transform infra red (FT-IR) spectroscopy, scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD) and contact angle measurements (CAM). The thermal properties of PBIE membranes were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) which revealed a lowering in thermal stability after photodegradation. FT-IR spectra revealed high absorbance in the carbonyl region in photoirradiated membranes whereas SEM showed nano structures / defects on the polymer film surface. CAM results showed enhancement in hydrophilic behavior and WAXD revealed increase in amorphous nature upon irradiation. Copyright © 2014 VBRI press.

Oxides for spintronics: A review of engineered materials for spin injection

Abstract: An experimental study consisting 70 tests have been conducted to study the influence of addition of reinforcing fibers on concrete specimens. The experimental program included concrete specimens that were tested with modified Arcan test machine with different notch lengths. The reinforcing effect of highly dispersed multi-walled carbon nanotubes (MWCNTs) in concrete has been investigated. The results revealed that inclusion of CNTs in the design mix improve both the tensile fracture characteristics and compressive strength when not mixed with a surfactant compound. The improvement in the mechanical properties specimens with the addition of CNTs are observed more clearly with increasing curing age. The mixing process to achieve uniformly dispersed and properly mixed mortar however requires specialized equipment, such as ultrasonic mixers. The results also indicated some dependency on the size of the specimens, which is a well known phenomenon that is observed for brittle heterogenous materials such as concrete. Copyright © 2014 VBRI press.

Electrical and microstructural properties of (Cu, Al, In)-doped SnO 2 films deposited by spray pyrolysis

Abstract: The effect of Cu, Al and In doping on the microstructural and the electrical properties of the SnO2 films were studied. The undoped, Cu, Al and In (2 at. %) doped SnO2 films were deposited on the glass substrate by spray pyrolysis from 0.8 M SnCl2– ethanol solution at substrate temperature 400 °C. The microstructural properties of films were investigated by X-ray diffraction (XRD) method. It was determined that the films formed at polycrystalline structure in tetragonal phase and structure was not changed by dopant species. The lattice parameters (a), (c) and crystallite size (D) were determined and obtained in the range of 4.90-4.92 A, 3.26-3.31 A and 34-167 A, respectively. The optical transmittance of thin films was measured and the optical band gap Eg values of the films were obtained in the range of 3.96-4.00 eV, using the Tauc relation. The electrical transport properties of undoped, Cu, Al and In-doped SnO2 films were investigated by means of conductivity measurements in a temperature range of 120-400 K. The electrical transport mechanism of the undoped, Cu, Al and In-doped SnO2 films was determined by means of the tunneling model through the back-to-back Schottky barrier and the thermionic field emission model in the temperature range of 120-300 K and 300-400 K, respectively. Copyright © 2014 VBRI press.

Structural, Dielectric And Magnetic Properties Of Nanocrystalline BaFe12O19 Hexaferrite Processed Via Sol-gel Technique

Abstract: In the present work BaFe12O19 nano-hexaferrite had been synthesized by sol-gel method and then characterized for its structural, electric, dielectric and magnetic properties. X-ray diffraction studies confirmed the hexagonal structure of the prepared nanohexaferrite with no secondary phase and the particle size was found to be of the order of 49 nm. Further, the morphology of the sample has been studied by using transmission electron microscopy (TEM). A high value of the DC resistivity (5.5 × 10 6 Ω cm), has been obtained at room temperature. The dielectric properties such as dielectric constant (e'), dielectric loss tangent (tan δ) and ac electrical conductivity (σac) are investigated as a function of frequency. The dielectric constant and loss tangent are found to be decreasing with the increase in frequency while ac electrical conductivity is observed to be increasing with the increase in frequency. The dielectric properties have been explained on the basis of Maxwell-Wagner's two-layer model and hopping of the charge. The magnetic properties such as initial permeability (µi) and relative loss factor (RLF) have been investigated as a function of frequency in the range 75 kHz to 30 MHz .Fairly constant value of initial permeability and low values of RLF of the order of 10 -4 over a wide frequency range are the cardinal achievements of the present work. The room temperature M-H study shows that present nanohexaferrite has high value of coercivity (2151.3 Oe) and high saturation magnetization (32.5 emu/gm), which make present nanohexaferrite very suitable for magnetic applications. The M-T study shows that prepared nano-hexaferrite has high Tc (746 K). Copyright © 2014 VBRI press.

Effective Antimicrobial Filter From Electrospun Polyacrylonitrile-silver Composite Nanofibers Membrane For Conductive Environments

Abstract: Electrospun nanofibers based antimicrobial filter were examined for their capability to build conductive environment. An antimicrobial agent, silver nitrate (AgNO3), was added to the nanofibers membrane for its ability to prevent growth of microorganisms over the filter media. In this direction in the present investigation the different fractions of silver nanoparticles were in-situ synthesized in PAN solution and then polyacrylonitrile (PAN)-silver composite nanofibers membrane filter was prepared by electrospinning technique. The resultant solution and PAN-silver composite nanofibers was characterized by UV- visible spectroscopy, scanning electron microscope, atomic force microscope and X-ray diffraction. Antibacterial property of PAN silver composite nanofibers were investigated against gram positive Staphylococcus aureus and gram negative Escherichia coli microorganisms. The formation of clear zone suggests that composite nanofibers containing silver nanoparticles show strong antibacterial activity and it increases with increasing silver content in the composite nanofibers. The PAN-silver composite nanofibers sheet was also examined for filtration of microorganisms and dust particles. It was observed that PAN-silver composite nanofibers filter proven to be an excellent filter for creating microorganism and dust free hygienic environment. Thus electrospun PAN nanofibers filters containing an antibacterial agent can be a promising solution for effective microorganism filtration from indoor air in hospitals or other places which are more prone to bacterial infections. Copyright © 2014 VBRI press.

Conductive polymer composites and coated metals as alternative bipolar plate materials for all-vanadium redox-flow batteries

Abstract: In this study polypropylene (PP) based conductive composites and metal doped diamond like carbon (DLC) coated metallic substrates are studied as alternative bipolar materials for all-vanadium redox flow battery (VRFB). Graphite and carbon nanotube (CNT) filled PP based bipolar plates were produced via twin-screw co-rotating extruder and injection molding. Addition of 3 wt. % CNTs into highly filled graphite-PP matrix increased in-plane and through-plane electrical conductivities from 10 S/cm to 50 S/cm and from 2 S/cm to 10 S/cm respectively. PP composites with 78 wt. % graphite and 2 wt. % CNT filling ratio showed flexural strength value of 48,01 MPa. Produced bipolar plates were examined with galvanostatic charge- discharge test in a single-cell VRFB. Energy efficiency of 85,43 % at 25 mA/cm2 and discharge power density of 78,48 mW/cm2 at 75 mA/cm2 were achieved and those values were found to be comparable with commercial bipolar plates. Titanium, vanadium, chromoium and tungsten doped diamond-like coating (DLC) films were coated on metallic substrates (e.g. stainless steel 1.4301 and titanium alloy 3.7165) by a physical vapor deposition. The metallic dopant is necessary to achieve high conductivities in the order of ~100 S/cm. The values range from 0.5 to 35 S/cm for in-plane and from 10 to 110 S/cm for through-plane. The hydrogen evolution reaction (HER) and the anodic corrosions stability in 2 molar sulfuric acid constituted the main focus area for our investigations on metallic bipolar plates. An interesting material for coated metallic bipolar plate is the 10 µm Ti-DLC on 1.4301 which exhibits the highest hydrogen evolution overpotential of all investigated materials (710 mV µA/cm²). It also showed improved corrosion stability for anodic potentials. Copyright © 2014 VBRI press.

Development of nanocomposites based on polypyrrole and carbon nanotubes for supercapacitors

Abstract: Supercapacitors are recognized as one of the most promising energy storage devices for a wide range of civilian and military applications in electric vehicles, uninterruptible power supplies. Conducting polymer nanocomposites are new functional materials suitable for supercapacitors due to synergistic effect of individual components. In present work, polypyrrole/CNT nanocomposites have been prepared by an in-situ chemical polymerization method and studied for supercapacitor. CNTs were well functionalized using 3:1 ratio of H2SO4 and HNO3 before polymerizing the pyrrole. Analytical techniques such as SEM, UV-VIS and FTIR were used to characterize the synthesized materials. The SEM images reveal that the materials have rough and granular morphology. The composites showed good interaction based on the shift to longer wavelengths in the electronic transition, indicating the interaction between PPy and functionalized CNTs as observed in their UV-VIS and FTIR spectra. The electrochemical performance was evaluated by using cyclic voltammetry (CV) in 1M Na2SO4 electrolyte and specific capacitance was obtained at 0.5 V/s for pure polypyrrole and PPy/CNT nanocomposites. Nanocomposite showed the enhanced electrochemical performance as compared to that of pure polypyrrole. The specific capacitance obtained at the scan rate 0.5V/s was found to be 0.825 F/cm -2 for pure polypyrrole and 1.0619 F/cm -2 for PPy/CNT nanocomposite material respectively, indicates that PPy/CNT nanocomposite is suitable

High Rate Capability Of Coconut Kernel Derived Carbon As An Anode Material For Lithium-ion Batteries

Abstract: Carbon has been prepared by pyrolysis of grated, milk-extracted coconut kernel at 600 o C under nitrogen atmosphere. The disordered carbon has sheet like morphology. The carbon exhibits a high reversible Li + intercalation capacity in a non-aqueous electrolyte. The initial charge and discharge capacities are 990 and 400 mAh g -1 , thus resulting in an irreversible capacity loss of 590 mAh g -1 . Nevertheless, subsequent discharge capacity is stable over a large number of charge-discharge cycles. The electrodes withstand charge-discharge currents as high as 1257 mA g -1 and they deliver discharge capacity of 80 mAh g -1 . Diffusion coefficient of Li + obtained from galvanostatic intermittent titration is 6.7 x 10 -12 cm 2 s -1 . Thus the coconut kernel derived carbon is a suitable anode material for Li-ion batteries. Copyright © 2014 VBRI press.

Thermodynamics And Electrochemical Characterization Of Core-shell Type Gold-coated Superparamagnetic Iron Oxide Nanoparticles

Abstract: In continuation to our previous work, the superparamagnetic Fe3O4@Au core-shell type nanoparticles (NPs) were further characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), electrical conductivity, impedance and cyclic voltammetry measurements. From the analysis of DSC and TGA results with our Fe3O4@Au NPs of about 6.25 ± 0.6 nm size, we observed a clear endothermic peak at 310°C due to the decomposition of the oleic acid/oleylamine surface ligands and the particles found to contain more than 80% of the metallic content from the mixed compositions of gold and iron oxide. Because of the conduction through the Fe3O4@Au grain, the impedance profile of the pellet exhibited a well- resolved semi-circle and an inclined spike in a far low-frequency region. The electrical conductivity of the Fe3O4@Au material found to be increased with an increase of temperature. The standard Gibbs free energy (ΔG) of the reaction provided a criterion for spontaneous changes in the equilibrium of the material. From the analysis of the results of Δ G, it appears that at 25°C temperature, ΔS found to be negative. The calculated enthalpy, Δ H = -0.635 kJ/mol, at the corresponding entropy of Δ S = - 0.132 kJ/mol. Finally, the activation energy in temperature range of 25-200°C for the Fe3O4@Au core-shell material was calculated using Line fitting and the surface characterization by using cyclic voltammetry. The electrochemical redox property of the Fe3O4@Au quasi-reversible wave corresponding to Au 3+ /Au 2+ . In addition, the electrochemical parameters for

Novel biodegradable polymeric flocculants based on cationic polysaccharides

Abstract: Novel flocculants for wastewater and industrial effluents treatment have been developed in authors’ laboratory based on modified polysaccharides. These flocculants have unique characteristics i.e. they are efficient with low dose usage like synthetic flocculants (e.g. polyacrylamide) and controlled biodegradable, shear resistant and inexpensive like polysaccharides. As contaminants have varying ionocity, various kinds of nonionic, anionic and cationic flocculants have been developed in authors’ laboratory. The recent approaches on the removal of toxic materials, removal of colour and reduction of total pollutant content from various wastewaters using modified polysaccharides is becoming more important in the present frontier research, because of their worst impact towards environment as well as human health. The present article deals with the recent developments which took place in authors’ laboratory on the synthesis of novel cationic flocculants based on modified polysaccharides derived from starch, amylose, amylopectin, chitosan, guar gum, glycogen, and tamarind kernel. The applications of these modified polysaccharides as flocculants for the treatment of various wastewaters including municipal sewage wastewater and as adsorbent for removal of reactive black dye from its aqueous solution have been discussed. The main objective of this article is to provide recent information about the most important features of these polymeric materials developed in authors’ laboratory and to show the advantages gained from the use of flocculants based on cationic polysaccharides in wastewater treatment. Copyright © 2014 VBRI press.

Synthesis And Photoluminescence Property Of RE3+ Activated Na2CaP2O7 Phosphor

Abstract: As host materials, phosphate compounds offer great potential for lanthanides to display luminescence characteristics. In this work luminescence behaviour of Na2CaP2O7:RE 3+ are presented for the first time. Na2CaP2O7 novel phosphors activated with the trivalent rare earth ions ((RE = Ce, Eu, Tb, Sm) were synthesized by solid state diffusion method. Phosphors were characterized for phase purity and luminescent properties. The emission and excitation spectra were followed to explore the luminescence attributes. The as prepared powders of Ce 3+ , Eu 3+ ,Tb 3+ and Sm 3+ doped Na2CaP2O7 emit near-uv, red, green and orange reddish light as result of f-d and f-f transitions respectively. The study is novel as no such luminescence data are available for this compound. The results are promising in view of the requirement for pc-white LEDs for solid state lighting applications. Copyright © 2014 VBRI press.

Structural And Magnetic Properties Of Undoped And Mn Doped CdS Nanoparticles Prepared By Chemical Co-precipitation Method

Abstract: Undoped and Mn doped CdS nanoparticles with varying Mn concentration of 10,15 and 20 mol % have been prepared by chemical co-precipitation method with polyvinylpyrrolidone (PVP) as capping agent at room temperature. EDAX has shown that no foreign impurities are present in the synthesized nanoparticles and X-ray diffraction (XRD) revealed that undoped and Mn doped CdS nanoparticles possess cubic phase with crystallite size ranging from 4-6 nm. Transmission electron microscopy (TEM) images indicated that nanoparticle sizes are between 2-6 nm and exhibits polycrystalline nature as seen from selected area electron diffraction (SAED) pattern. Raman spectra of undoped and Mn-doped CdS nanoparticles have shown 1LO and 2LO phonon modes and their intensity ratio decreases as Mn concentration increases. Magnetic susceptibility clearly pointed out that undoped CdS behaves as diamagnetic whereas Mn doped CdS as paramagnetic and varies nonlinearly with Mn concentration in CdS. Rapid increase in magnetization below 50 K temperature is observed in M-T curves which can be assigned to Mn ions isolated in CdS crystal field or extrinsic defects. The M-H curve at 5 K and 300 K for 20% Mn doped CdS nanoparticles at different magnetic fields showed no hystersis. In near future Mn doped CdS nanoparticles can be used for application in dilute magnetic semiconductor and fabrication of solar cells. The result and discussion drawn from this work are elaborated in detail in the paper. Copyright © 2014 VBRI press.

Structural, optical and magnetic properties of (Fe, Ag) co-doped ZnO nanostructures

Abstract: The (Fe, Ag) co-doped ZnO nanostructures are developed through chemical precipitation method at various percentages of Fe. The X-ray diffraction studies suggest that all the as-synthesized (Fe, Ag) doped ZnO nanopowders have single phase wurtzite structure with no secondary phases. However, the positions of diffracted peaks slightly shifted towards lower (2θ) angles. Photoluminescence studies reveal that 1 mol% of Fe doped ZnO sample has the best ultra violet (UV) emission properties than the other samples. On the other hand, 5 mol% of Fe doped ZnO nanopowders consists of strong green emission band, which belongs to oxygen interstitial defect states. Magnetization analysis shows that 5 mol% of Fe doped ZnO nanopowders have highest room temperature ferromagnetism (RTFM) than the RTFM of other samples. The observed RTFM in co-doped ZnO nanopowders is discussed with the help of structural and emission studies. The results strongly suggest the future development of efficient luminescence and magnetic materials at normal laboratory temperatures with (Fe, Ag) co-doped ZnO nanostructures. Copyright © 2014 VBRI press.

Preparation of ZnS-graphene nanocomposite and its photocatalytic behavior for dye degradation

Abstract: In the present work, ZnS-Gaphene (ZnS-GNS) composite was prepared by microwave irradiation method. The prepared samples were characterized by X-ray diffraction (XRD), to confirm the formation of GNS by reducing Graphite as well as ZnSGNS nanocomposite. Raman spectroscopy identified D and G photon vibration mode of GNS in the ZnS-GNS composite. Xray photoelectrons spectra are also detected presence of graphene in ZnS. UV/VIS Spectra are studied for evaluation of photocatalytic activity. The composite is explored as photocatalysts to study dye degradation using methylene blue dye in aqueous slurry under irradiation of 663 nm wavelength. Under the same conditions the photocatalytic activity of the pure ZnS is also examined. The ZnS-GNS composite is found in enhancing the rate of photodegradation of toxic dyes as compared to pure ZnS. This Graphene based metal sulphide/oxide semiconductor nanocomposites are high potential material for Photodegradation of toxic dyes, and act as good photocatalyst. Copyright © 2014 VBRI press.

Investigation On Magnetic Behaviour Of BiFeO3: SPIN Glass View Point

Abstract: Field cooled (FC) and zero field cooled (ZFC) magnetization measurements of Bismuth Ferrite (BiFeO3) multiferroic obtained by microwave-assisted gel combustion method are reported. The structural investigation of sythesized and calcined sample is done by XRD and the obtained data is well fitted with Rietveld refinement using full-pro software suite. M-H hysterisis shows that BFO nanoparticles exhibit ferromagnetic properties at room temperature, which is unusally observed in BFO. The M-T plot at H = 1 and 2 kOe shows that the FC and ZFC magnetization curve start to differ at below 331K and 236 K respectively with sharp cusp around 124 K revealing spin glass behaviour of BiFeO3. Both ferromagnetic properties and spin-glass-like behavior are observed in BFO nanoparticles. Ferromagnetic behavior is attributed to a partial destruction in nanoparticles of the long-wavelength cycloid spin structure expected in bulk BFO. Spin-glass-like behavior is assigned to diffusion of domain walls, with possible contributions from pinning of the cycloid spin structure at the nanoparticle surface. Copyright © 2014 VBRI press.

Magnetic, Magnetocapacitance And Dielectric Properties Of BiFeO3 Nanoceramics

Abstract: Single phase Bismuth ferrite (BiFeO3, BFO) nanoparticles (particle size ~ 50-100 nm) were synthesized by a novel chemical sol-gel technique. The detailed microstructural analysis has been performed through HRXRD, HRTEM and FESEM techniques. The nanoparticles are found to crystallize with distorted rhombohedral structure having R3c space group. The dielectric constant and tan δ loss are found to vary monotonically with temperature measured at different frequency ranging from 1 kHz to 1 MHz. The M (H) hysteresis behavior at 5 K reveals weak ferromagnetic nature of the BiFeO3 nanoparticles having coercivity (Hc) ~ 720 Oe and magnetization (Ms) ~ 1 emu/g at 5 T from SQUID measurements. The multiferroic character of BFO nanoparticles is confirmed through magnetoelectric response. The typical value of magnetodielectric response is observed to be 0.4% at 4300 Oe at room temperature at a frequency of 1 kHz. All the results suggest that the BFO nanoparticles are technologically very promising as far as magnetoelectric properties are concerned. Copyright © 2014 VBRI press.

Green syntheis of silver nanoparticles and its activity on SiHa cervical cancer cell line

Abstract: Biosynthesis and characterizations of nanoparticles has become an important branch of nanotechnology nowadays. In this paper, green synthesis of silver nanoparticles (AgNPs) using the alcoholic extract of Argemone mexicana Linn. as a reducing and stabilizing agent, has been discussed. This biosynthetic method is simple, cost-effective and reproducible. Formation of AgNPs was established by X-ray diffraction, transmission electron microscopy and UV-Visible spectroscopic techniques. Nanoparticles almost spherical in shape having a size of 2-6 nm are found. UV-visible study revealed the surface plasmon resonance at 414 nm. A possible involved mechanism for the biosynthesis of silver nanoparticles has also been proposed. Further, it was found that AgNPs sol when applied to the SiHa cancer cell line was found to inhibit the growth by 70-80%. It is cumulative effect of the unutilized plant extract and nanosilver. The work signifies the importance of medicinal plants in synthesis of nanomaterials as it bestows double benefit in terms of drug delivery as well as safety. It may open a fresh avenue in future cancer therapeutics. Copyright © 2014 VBRI press.

Synthesis and evaluation of swelling characteristics of fullerene (C 60 ) containing cross-linked poly(2-hydroxyethyl methacrylate) hydrogels

Abstract: Fullerene (C60) containing cross-linked poly (2-hydroxyethyl methacrylate) polymers (CFPH) with varying C60 content were synthesized by free radical polymerization. The fullerene content in the cross-linked polymers was determined by TGA analysis. The swelling properties of these fullerene containing hydrogels (CFPH) were studied in distilled water (pH=7.2) at room temperature (25 o C) and compared to the corresponding hydrogel without fullerene (CPHEMA). The equilibrium swelling ratio is lower for the fullerene containing hydrogels (54.68% and 40.0% for hydrogels having 6.0 wt% and 18.0 wt% fullerene respectively) due to the presence of hydrophobic fullerene moieties inside the hydrogels than that of the hydrogel (68.75%) without fullerene. The hydrophobic fullerene nanomaterials acting as inherent nanofillers obstruct the path of water permeation inside the polymers thereby taking more time to achieve equilibrium swelling for fullerene containing hydrogels than that of the hydrogel without fullerene. The kinetics of swelling behavior of such fullerene containing cross-linked hydrogels (CFPH) was observed to follow Fickian behavior. Increase of temperature and ionic strength of the medium decrease the water uptake capacity of the fullerene containing cross-linked hydrogels. Fullerene containing hydrogels may be useful in drug delivery system and other biomedical applications. Copyright © 2014 VBRI press.

Fabrication and characterization of efficient hybrid photocatalysts based on titania and graphene for acid orange seven dye degradation under UV irradiation

Abstract: Simple and proficient methodology has been proposed for the preparation of hybrid photocatalyst based on titanium dioxide (TiO2)-graphene (GR) nanocomposite for acid orange 7 (AO7) dye degradation under UV irradiation. High Resolution Transmission Electron Microscopy (HRTEM) and Scanning Electron Microscopy (SEM) studies revealed that TiO2 nanoparticles were uniformly dispersed on GR surface. TiO2-GR hybrid nanocomposite has also been characterized by Ultraviolet Diffusive Reflectance Spectroscopy (UV-DRS), Raman spectroscopy and X-ray diffraction (XRD) studies. Electrochemical Impedance spectroscopy (EIS) measurement revealed that the incorporation of GR with TiO2 nanoparticles significantly enhanced the electrical conductivity.The peak intensity of PL spectra of GR containing catalysts are lower than that of pristine TiO2, indicating that the electron–hole recombination rate of self-trapped excitations in TiO2 is reduced by the

Formation of TiO2 thin films by a modified sol-gel route and characterization of structural, optical and electrochromic properties

Abstract: Through a modified sol gel route with titanium isopropoxide (TIP) and acetic acid, titanium dioxide (TiO2) thin films were deposited by dip coating. Employing acetic acid as modifier and without inclusion of water in hydrolysis leaded to control the degree of condensation-oligorimerization of the precursor and formation of anatase phase only upon annealing. Direct allowed energy band gap 3.87 eV verified the anatase phase of the film. Impact of temperature on structural properties was deduced by FTIR and UV-Visible spectroscopies. Due to the reduction in band gap with increase in annealing temperature, injected Li + charge amount dropped in anatase compared to the amorphous (unannealed) films. Copyright © 2014 VBRI press.

Nanocrystalline nickel ferrite reinforced conducting polyaniline nanocomposites

Abstract: Nanocrystalline nickel ferrite (NiFe2O4) powder of crystallite size 20 nm was synthesized by refluxing method. Electrically conductive polyaniline-nickel ferrite (PANI/NiFe2O4) nanocomposites have been synthesized by an in-situ polymerization of aniline monomer in the presence of as-prepared NiFe2O4 in different weight percentage (5%, 10%, and 15%). These nanocomposites were subsequently characterized for morphological, crystalline, structural, electrical and magnetic properties by Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Four Probe Resistivity (FPR) and Vibrating Sample Magnetometer (VSM). Existence of NiFe2O4 in the nanocomposites was confirmed by XRD, FTIR and TEM analysis. The change in morphology with crystallite size  50 nm was observed for the nanocomposites clearly indicate the coating of PANI on NiFe2O4. Nanocomposites showed increase in saturation magnetization as compared to that of PANI and increase in electrical conductivity as compared to that of NiFe2O4 indicating the synergistic effect of individual components. The saturation magnetization drastically increased as nickel ferrite content changed from 5 to 15% in nanocomposites. The conductivity of nanocomposites increased with temperature, exhibiting typical semiconductor behavior. The nanocomposites show semiconducting and ferromagnetic behavior. The electrical conductivity of nanocomposites decreased from 1.089 to 0.268 S/cm, but saturation magnetization increased from 0.97 to 2.803 emu/g, when ferrite content changed from 5 to 15 wt%, indicates such nanocomposites are good for electromagnetic devices. Copyright © 2014 VBRI press.

Improving the mechanical and thermal properties of semi-coke based carbon/copper composites reinforced using carbon nanotubes

Abstract: Multiwalled carbon nanotubes (MWCNT)- reinforced carbon/copper (C/Cu) composites were developed by powder metallurgy technique and mixed powders of C and Cu were consolidated into plates without using any extra binder followed by sintering at 1000 o C in inert atmosphere. Samples were characterized for structural, mechanical, electrical and thermal properties w.r.t. different mass fraction of MWCNT in C-Cu matrix. In comparison to C/Cu composite, addition of minute amount (0.25 wt%) of CNT in C-Cu substantially improved the mechanical, electrical and thermal properties of composites. These composites were mechanically stable and strong and exhibited high bending strength of 162 MPa, indicating a homogeneous dispersion of MWCNTs in the C-Cu matrix. Maximum thermal conductivity of 37.60 W/mK perpendicular to the pressing direction was obtained for 0.50 wt% CNT reinforced C-Cu composite exhibiting an improvement of 45% over pure C-Cu composite processed under identical conditions. High thermal conducting and mechanically strong composites can be used as heat sink for long time. Copyright © 2014 VBRI press.

Electrical properties of Ir/n-InGaN/Ti/Al Schottky barrier diode in a wide temperature range

Abstract: The temperature dependent current-voltage (I-V) and capacitance-voltage (C-V) characteristics of Ir/n-InGaN Schottky contacts have been investigated and analysed in the temperature range of 100-400 K. The estimated barrier heights and ideality factor of Ir/n-InGaN Schottky diode are 0.30 eV (I-V), 1.15 eV (C-V) and 3.05 at 100 K, and 0.94 eV (I-V), 0.97 eV (C-V) and 1.20 at 400 K respectively. The barrier height (Φ b ), ideality factor (n) and series resistance (R S ) of Ir/n-InGaN Schottky diode are also evaluated using Cheung's and Norde methods. Results show that the barrier heights (I-V) increase while ideality factor and series resistance decease with increasing temperature. Further, the discrepancy between Schottky barrier heights estimated from I-V and C-V measurements is also explained. It is observed that the interface state density N ss decreases with an increasing temperature. Experimental results showed that the conduction current is dominated by Poole-Frenkel emission in the temperature range from 100 K to 340 K and by Schottky emission above 340 K. The dominate conduction mechanism changed from Poole-Frenkel to Schottky emission in the temperature range from 340 K to 370 K. Finally, it is concluded that the temperature-dependent I-V characteristics of the Ir/n-InGaN Schottky diode can be successfully explained on the basis of thermionic emission (TE) mechanism. Copyright © 2014 VBRI press.

Magnetic, Electronic Structure And Interface Study Of Fe/MgO/Fe Multilayer

Abstract: MgO based magnetic tunnel junctions (MTJs) exhibit high tunneling magnetoresistance (TMR) and have potential applications in magnetic random access memories. This study addresses the role of interface in the Fe/MgO/Fe based MTJs. For present investigation, Fe/MgO/Fe multilayer stack on Si substrates is grown by electron beam evaporation method and has been investigated for structural, magnetic and electronic properties. All the layers in the stack were of polycrystalline in nature as evidenced from X-ray diffraction studies, and the magnetic measurements show the attributes perpendicular magnetic anisotropy. Results from near edge X-ray absorption spectra at Fe L-edges measured by total electron yield mode and X-ray reflectometry indicate the formation of FeOx at the Fe/MgO interface. These are associated with hybridization of Fe (3d)-O(2p) levels at Fe/MgO interface in the stack and thickness of layers in the stacks. Absence of magnetic de-coupling between top and bottom ferromagnetic layers has been attributed to interface roughness and oxidation at Fe/MgO interface. This study highlights the role of interface and oxidation that need to be considered for improving the TMR for devices.