Showing papers in "Applied Nanoscience in 2012"

Biosynthesis of silver nanoparticles using lemon leaves extract and its application for antimicrobial finish on fabric

Abstract: Preparation of silver nanoparticles have been carried out using aqueous extract of lemon leaves (Citrus limon) which acts as reducing agent and encapsulating cage for the silver nanoparticles. These silver nanoparticles have been used for durable textile finish on cotton and silk fabrics. Remarkable antifungal activity has been observed in the treated fabrics. The antimicrobial activity of silver nanoparticles derived from lemon leaves showed enhancement in activity due to synergistic effect of silver and essential oil components of lemon leaves. The present investigation shows the extracellular synthesis of highly stable silver nanoparticles by biotransformation using the extract of lemon leaves by controlled reduction of the Ag+ ion to Ag0. Further the silver nanoparticles were used for antifungal treatment of fabrics which was tested by antifungal activity assessment of textile material by Agar diffusion method against Fusarium oxysporum and Alternaria brassicicola. Formation of the metallic nanoparticles was established by FT–IR, UV–Visible spectroscopy, transmission electron microscopy, scanning electron microscopy, atomic force microscopy.

Synthesis and characterization of chitosan-silver nanocomposite

Abstract: Chitosan–silver (CS–Ag) nanocomposite materials were synthesized by a simple chemical method. The synthesized CS–Ag nanocomposite contains 20 wt% silver. Silver nanoparticles were synthesized by chemical reduction method as well. The CS–Ag nanocomposite was characterized using Field emission scanning electronic microscope (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The XRD pattern indicated the presence of both silver and chitosan in the nanocomposite. It is observed from the XRD pattern of silver that it is of cubic structure. The spherical morphology of silver nanoparticles was confirmed from the FESEM image. FTIR spectroscopy was used for the structural elucidation. CS–Ag nanocomposite exhibits good antimicrobial and antitumor properties.

Antimicrobial chitosan–PVA hydrogel as a nanoreactor and immobilizing matrix for silver nanoparticles

Abstract: Hydrogels are water-insoluble crosslinked hydrophilic networks capable of retaining a large amount of water. The present work aimed to develop a novel chitosan–PVA-based hydrogel which could behave both as a nanoreactor and an immobilizing matrix for silver nanoparticles (AgNPs) with promising antibacterial applications. The hydrogel containing AgNPs were prepared by repeated freeze–thaw treatment using varying amounts of the crosslinker, followed by in situ reduction with sodium borohydride as a reducing agent. Characterization studies established that the hydrogel provides a controlled and uniform distribution of nanoparticles within the polymeric network without addition of any further stabilizer. The average particle size was found to be 13 nm with size distribution from 8 to 21 nm as per HR-TEM studies. Swelling studies confirmed that higher amount of crosslinker and silver incorporation inside the gel matrices significantly enhanced the porosity and chain entanglement of the polymeric species of the hydrogel, respectively. The AgNP-hydrogel exhibited good antibacterial activity and was found to cause significant reduction in microbial growth (Escherichia coli) in 12 h while such activity was not observed for the hydrogel without AgNPs.

Antibacterial potential of biosynthesised silver nanoparticles using Avicennia marina mangrove plant

Abstract: The present study was aimed to identify the antibacterial potential of biosynthesised silver nanoparticles using different plant parts (leaves, bark and root) of Avicenna marina mangrove plant. Of the selected three different parts, the leaf extract showed the maximum synthesis of silver nanoparticles. The in vitro antibacterial assay (100 μg disk−1 concentration) showed the results of maximum zone of inhibition with the E. coli (18.40 ± 0.97 mm), and minimum (10.87 ± 1.33 mm) zone of inhibition with S. aureus but the concentrations of MIC and MBC values ranged between 6.25 and 50.0 μg ml−1 between the selected bacterial strains. The FTIR results of most potent leaf extract-synthesized silver nanoparticles showed the prominent peaks (620.967; 1,061.02; 1,116.58; 1,187.94; 1,280.50; 1,353.79; 1,384.64; 1,598.50; 1,629.56; 2,854.14 and 2,927.42) in different ranges. Further, the results of XRD analysis showed the 2θ intense values (38.11 and 70.57) within the ranges of Bragg’s reflection. In addition, the AFM analysis showed the results of particle sizes (71–110 nm), particle roughness (11.8 nm), maximum height of the particle roughness (111.8 nm), and average maximum height of the particle roughness (57.5 nm). It can be concluded from the present findings that, the biosynthesis of silver nanoparticles from the leaf extract of A. marina can be used as potential antibacterial agents.

Effect of Y-doping on optical properties of multiferroics BiFeO3 nanoparticles

Abstract: We have synthesized yttrium-doped bismuth ferrite nanoparticles through a modified Pechini technique. X-ray diffractometer, transmission electron microscope (TEM) and ultraviolet-visible spectrophotometer (UV- Vis) probes have been utilized to characterize the nano- particles. Average particle size estimated from TEM found to be 29 nm for Bi0.99Y0.01FeO3 samples. The band gap of the prepared BFO and BYFO nanoparticles varies from 1.97 to 2.29 eV, that is, within the visible range of the sunlight. This property of these nanoparticles can be uti- lized in photo catalytic decomposition of organic contam- inants, such as Rhodamine-B (RhB) under visible light irradiation. We have explored and observed that RhB degrade up to 8 % while mixed with Bi0.90Y0.1FeO3 for 1 h under 40 W lamp due to photo catalysis together with sensitization.

Electrolytes for high-energy lithium batteries

Abstract: From aqueous liquid electrolytes for lithium–air cells to ionic liquid electrolytes that permit continuous, high-rate cycling of secondary batteries comprising metallic lithium anodes, we show that many of the key impediments to progress in developing next-generation batteries with high specific energies can be overcome with cleaver designs of the electrolyte. When these designs are coupled with as cleverly engineered electrode configurations that control chemical interactions between the electrolyte and electrode or by simple additives-based schemes for manipulating physical contact between the electrolyte and electrode, we further show that rechargeable battery configurations can be facilely designed to achieve desirable safety, energy density and cycling performance.

Graphene oxide nanostructures modified multifunctional cotton fabrics

Abstract: Surface modification of cotton fabrics using graphene oxide (GO) nanostructures was reported. Scanning electron microscopic (SEM) investigations revealed that the GO nanostructure was coated onto the cotton fabric. The molecular level interaction between the graphene oxide and the cotton fabric is studied in detail using the Fourier transform infra-red (FTIR) spectra. Thermogravimetric analysis (TGA) showed that GO loaded cotton fabrics have enhanced thermal stability compared to the bare cotton fabrics. The photocatalytic activity of the GO-coated cotton fabrics was investigated by measuring the photoreduction of resazurin (RZ) into resorufin (RF) under UV light irradiation. The antibacterial activity was evaluated against both Gram-negative and Gram-positive bacteria and the results indicated that the GO-coated cotton fabrics are more toxic towards the Gram-positive ones. Our results provide a way to develop graphene oxide-based devices for the biomedical applications for improving health care.

Synthesis and characterization of TiO 2 /SiO 2 nano composites for solar cell applications

Abstract: The use of titania–silica in photocatalytic process has been proposed as an alternative to the conventional TiO2 catalysts. Mesoporous materials have been of great interest as catalysts because of their unique textural and structural properties. Mesoporous TiO2, SiO2 nanoparticles and TiO2/SiO2 nanocomposites were successfully synthesized by sol–gel method using titanium (IV) isopropoxide, tetra-ethylorthosilicate as starting materials. The synthesized samples are characterized by X-ray diffraction, UV–Vis spectroscopy, Fourier transform infrared spectroscopy, Brunauett–Emmett–Teller and field-dependent photoconductivity. The UV–Vis spectrum of as-synthesized samples shows similar absorption in the visible range. The crystallite size of the as-synthesized samples was calculated by Scherrer’s formula. The BET surface area for TiO2/SiO2 nanocomposite is found to be 303 m2/g and pore size distribution has average pore diameter about 10 nm. It also confirms the absence of macropores and the presence of micro and mesopores. The field-dependent photoconductivity of TiO2/SiO2 nanocomposite shows nearly 300 folds more than that of TiO2 nanoparticle for a field of 800 V/cm.

Magnetoelectric properties of PbZr 0.53 Ti 0.47 O 3 –Ni 0.65 Zn 0.35 Fe 2 O 4 multiferroic nanocomposites

Abstract: A different kind of multiferroics with ferroelectric–ferrimagnetic (FE–FM) composites: (1 − x) PbZr0.53Ti0.47O3–x Ni0.65Zn0.35Fe2O4 with x = 0.10, 0.20 and 0.30, were synthesized by a powder-in-sol precursor hybrid processing route. Structural analysis with X-ray diffraction (XRD) data revealed the presence of both PbZr0.53Ti0.47O3 (PZT) and Ni0.65Zn0.35Fe2O4 (NZFO) pure phases in the PZT–NZFO composites. Scanning electron micrographs (SEM) clearly disclose distribution of both PZT and NZFO phases throughout the sample. Dielectric and electrical properties of the system have been investigated in a wide range of frequency at different temperatures. Dielectric constant (er) as a function of temperature reveals the paraelectric–FE transition temperature at ~408 °C having maximum value of er at the peak [e r max = 1,200] with another low temperature anomaly at ~297 °C, very close to the magnetic Curie temperature of the NZFO ferrite (Tc = 300 °C) for the x = 0.1 FE–FM composite. The impedance spectroscopy data of these composites show clearly, contribution of both grain and grain boundary effect in the electrical properties of the composites. Negative temperature coefficient of resistance (NTCR) behavior of the materials indicates their semi-conducting nature. The ac conductivity spectrum is found to obey Johnscher’s power law very well. The temperature-dependent magnetization hysteresis (M–H) loops of the PZT/NZFO composite show excellent non-saturating ferrimagnetic behavior with increase in both coercive field (Hc) and remanent magnetization (Mr) when the NZFO content in the composite is increased. Polarization (P) versus electric field (E) studies at 300 K give conclusive evidence of the presence of spontaneous polarization in all the three composites (x = 0.1, 0.2 and 0.3). However, area of P–E loop, coercive field (Ec) and remanent polarization (Pr) are found to decrease noticeably with the increase of the NZFO content (x) in these composites.

Chemical growth of hexagonal zinc oxide nanorods and their optical properties

Abstract: A simple wet chemical method has been successfully deployed to fabricate hexagonal zinc oxide nanorods. The structural characteristics were investigated through X-ray diffraction. The crystal unit cell of the nanorods was found to be hexagonal. The morphology of the nanostructures was studied using field emission scanning electron microscopy and transmission electron microscopy. The nanorods are hexagonal in shape. The Zn–O bond formation was confirmed through Fourier transformed infrared spectroscopic analysis. Raman shift measurements revealed various vibrational modes present in the ZnO crystal. The photoluminescence spectrum shows shallow deep level visible emission due to various defect states. Thus, our investigation will be very helpful in the development of ZnO based light emitting/optoelectronic device applications.

Effect of aggregation on thermal conductivity and viscosity of nanofluids

Abstract: Nanofluids have drawn large attention because they exhibit anomalous behaviour in their thermo physical properties. There has been an enormous innovation in heat transfer applications of these fluids especially to industrial sectors including transportation, power generation, cooling, thermal therapy for cancer treatment, etc. In the present work, we have studied the anomalous increase in the thermal conductivity and viscosity of nanofluids by taking clustering as one of the causes. It is assumed that the nanoparticles may aggregate on dispersion. Few of these nanoparticles may just touch each other, whereas others may do so along with interfacial layer developed around them (analogous to porous media). The variation in thermal conductivity has been studied with particle concentration, concentration of aggregates and thickness of interfacial layer. The concept of aggregation and equivalent volume fraction has also been used in Kreiger and Dougherty (K-D) model to study the viscosity of nanofluids. The obtained results for thermal conductivity agree well with the available experimental results when the effect of different types of clusters is taken into account. Viscosity increases with the increase in particle aggregate (ra) and is found to match well for ra = 3r at low concentration.

First principles calculation on the structure and electronic properties of BNNTs functionalized with isoniazid drug molecule

Abstract: One-dimensional nanostructures such as nanowires and nanotubes are stimulating tremendous research interest due to their structural, electronic and magnetic properties. We perform first principles calculation using density functional theory on the structural, and electronics properties of BNNTs adsorbed with isoniazid (INH) drug via noncovalent functionalization using the GGA/PBE functional and DZP basis set implemented in SIESTA program. The band structure, density of states and projected density of states (PDOS) plots suggest that isoniazid prefers to get adsorbed at the hollow site in case of (5,5) BNNT, whereas in (10,0) BNNT it favours the bridge site. The adsorption energy of INH onto (5,5) BNNT is smaller than in (10,0) BNNT which proposes that (10,0) BNNT with a larger radius compared to (5,5) BNNT is more favourable for INH adsorption as the corresponding distortion energy will also be quite lower. Functionalization of (5,5) and (10,0) BNNTs with isoniazid displays the presence of new impurity states (dispersionless bands) within the HOMO–LUMO energy gap of pristine BNNT leading to an increase in reactivity of the INH/BNNT system and lowering of the energy gap of the BNNTs. The PDOS plots show the major contribution towards the dispersionless impurity states is from INH molecule itself rather than from BNNT near the Fermi energy region. To summarize, noncovalent functionalization of BNNTs with isoniazid drug modulates the electronic properties of the pristine BNNT by lowering its energy gap with respect to the Fermi level, as well as demonstrating the preferential site selectivity for adsorption of isoniazid onto the nanotube sidewalls of varying chirality.

Effect of manganese doping on the photoluminescence characteristics of chemically synthesized zinc sulfide nanoparticles

Abstract: The studies on luminescent II-VI semiconducting nanomaterials have attracted widespread attention recently, due to their potential applications in optoelectronic and biophotonic devices. Amongst other II-VI semiconductor nanoparticles (NPs), Mn2+-doped ZnS NPs having large exciton binding energy and wide direct band gap at room temperature have drawn considerable attention for exploring its interesting optical properties. However, in this report, water-soluble Mn2+-doped ZnS (ZnS:Mn) NPs with Mn2+ concentration varying between 1.5 and 5% (wt%) have been synthesized by chemical co-precipitation method at room temperature. X-ray diffraction (XRD) studies and the analysis of the selected area electron diffraction (SAED) pattern, obtained from transmission electron microscopy (TEM), confirmed the formation of zinc blende structure in all the synthesized samples. The particle sizes of the samples, as obtained from the optical absorption studies, varies between 2.2 and 2.7 nm with the increase of Mn2+ concentration between 1.5 and 5%. The room temperature photoluminescence (PL) emission measurements revealed the presence of yellow-orange emission band in all the Mn2+-doped samples which is attributed to Mn incorporation in ZnS. The Gaussian fittings of the measured PL spectra of all the samples show the presence of four PL peaks. Amongst the four PL peaks three peaks appeared at 445, 476, and 520 nm in all the samples but the fourth yellow-orange emission peak suffered a red shift from 593 to 600 nm with increasing Mn2+ concentration from 1.5 to 5%. In this report no quenching of yellow-orange emission peak is observed up to 5% Mn2+ doping concentration in ZnS. The synthesized water-soluble ZnS:Mn NPs can be further functionalized for using them as biolabels.

Effect of ablation time and laser fluence on the optical properties of copper nano colloids prepared by laser ablation technique

Abstract: Copper (Cu) nanoparticles of average sizes (radius in nm) varying between 1.7 and 6 nm have been prepared by 1,064 nm Nd:YAG laser ablation of solid copper target in water medium. The nanostructures of the samples have been characterized using high-resolution transmission electron microscopes (HRTEM). The UV–visible absorption spectra obtained with a UV–visible spectrophotometer show sharp absorptions in the ultraviolet region and visible region due to the interband transition and surface plasmon resonance (SPR) oscillations in Cu nanoparticles, respectively. The increase in the linewidth of the SPR absorption peaks with the reduction in particle sizes are observed due to the intrinsic size effects. The behaviour of the UV–visible spectra associated with the Cu nanoparticles is studied as a function of laser fluence and laser ablation time.

The novel and economical way to synthesize CuS nanomaterial of different morphologies by aqueous medium employing microwaves irradiation

Abstract: CuS nano/submicro materials with different morphologies were synthesized with spherical, tubular, leaf-like and strip type structures in a simple aqueous system under microwave irradiation and sunlight and employing Cu (CH3COO)2, CuSO4·5H2O, CuCl2, and as copper source and H2NCSNH2, Na2S2O3·5H2O and CH3CSNH2 as sulfur sources. The starting materials were used without assistance of any surfactant or template. An X-ray powder diffraction pattern confirms that the product was CuS with hexagonal phase. Scanning electron microscopy was used to observe the morphologies of the product. Different Phase transitions in CuS with respect to temperature are studied by DSC/TGA. The dependence of morphologies of product on different experimental conditions was also discussed.

Synthesis and characterization of nanocomposites based on polyaniline-gold/graphene nanosheets

Abstract: Polymer nanocomposites (NSPANI/AuNP/GR) based on nanostructured polyaniline, gold nanoparticles (AuNP) and graphene nanosheets (GR) have been synthesized using in situ polymerization. A series of nanocomposites have been synthesized by varying the concentration of GR and chloroauric acid to optimize the formulation with respect to the electrochemical activities. Out of these series of NSPANI/AuNP/GR nanocomposites, it has been found that only one particular nanocomposite has the best electrochemical properties, as analyzed by cyclic voltammetry (CV) and differential pulse voltammetry and conductivity. The best nanocomposite has been characterized by Fourier transform infrared Raman spectroscopy, UV–vis spectroscopy, X-ray diffraction studies, transmission electron microscopy, scanning electron microscopy and atomic force microscopy. The CV of the best nanocomposites show the well-defined reversible redox peaks characteristic of polyaniline, confirming that the polymer maintains its electro activity in the nanocomposites. Another nanocomposite has been prepared with identical composition (as found with the best nanocomposite) by mixing of pre-synthesized nanostructured polyaniline with chloroauric acid and graphene dispersion in order to predict the mechanism of in situ polymerization. It is inferred that the nanocomposite prepared by blending technique loses its property within 48 h indicating phase separation whereas the nanocomposite prepared by in situ technique is highly stable.

Examining microstructural composition of hardened cement paste cured under high temperature and pressure using nanoindentation and 29 Si MAS NMR

Abstract: Microstructural composition of the hardened cement pastes are analyzed using nanoindentation and 29Si MAS NMR after curing time periods of 7 and 28 days. Two curing conditions, room condition (20°C with 0.1 MPa pressure) and an elevated condition (80°C with 10 MPa pressure) are prepared to hydrate cement pastes [water to cement (w/c) ratio of 0.45]. The degree of hydration of the cement paste quantified using nanoindentation was compared with that from 29Si MAS NMR. From nanoindentation of the hardened cement pastes, microstructural hydration products are characterized with respect to the corresponding modulus of elasticity. A hydration product, which has a relatively high modulus of elasticity over other known hydration products, was found in the hardened cement paste cured in elevated temperature and pressure. The effect of high pressure on the composition of the hydration product is discussed and it is hypothesized that the packing density of calcium-silicate-hydrate (C-S-H) might increase when a cement paste is hydrated under high temperature and pressure.

Magnetic and structural characterization of transition metal co-doped CdS nanoparticles

Abstract: We report the structural and magnetic properties of the CdS nanoparticles co-doped with Ni and Cu; 3% Ni, Cu co-doped CdS nanoparticles were synthesized by using wet chemical synthesis process. From high-resolution transmission electron microscopy (HR-TEM), it is found that the average diameter of the Ni, Cu co-doped CdS nanoparticles is about 5 nm. X-ray diffraction (XRD) studies show the zinc blende (cubic) structure of Ni, Cu co-doped CdS nanoparticles. Energy dispersive spectroscopy (EDS) confirms the elemental composition of the doped sample. Room temperature magnetic studies are made by the analysis of M-H curves, obtained using superconducting quantum interference device (SQUID). The magnetic behavior has been shown by CdS nanoparticles doped with 3% nickel as well as CdS nanoparticles co-doped with 3% Ni and Cu.

Structural and magnetic properties of nanocrystalline BaFe12O19 synthesized by microwave-hydrothermal method

Abstract: Nanocrystalline BaFe12O19 powders were prepared by microwave-hydrothermal method at 200 °C/45 min. The as-synthesized powders were characterized by using X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA). The present powders were densified at different temperatures, i.e., 750, 850, 900 and 950 °C for 1 h using microwave sintering method. The phase formation and morphology studies were carried out using XRD and field emission scanning electron microscopy (FE-SEM). The average grain sizes of the sintered samples were found to be in the range of 185–490 nm. The magnetic properties such as saturation magnetization and coercive field of sintered samples were calculated based on magnetization curves. A possible relation between the magnetic hysteresis curves and the microstructure of the sintered samples was investigated.

Impact of CuO nanoleaves on MWCNTs/GCE nanocomposite film modified electrode for the electrochemical oxidation of folic acid

Abstract: The salient features of the present work focus on the synthesis of CuO nanoleaves by alcoholic reduction of Cu(II) chloride in the presence of poly(diallyldimethylammonium chloride) (PDDA) for the application of folic acid oxidation in simulated body fluid environment. PDDA-assisted polyol process allows a conventional impregnation method for the formation of CuO with well-defined leaf-like structure. The structure and morphology of the CuO nanoleaves were characterized by Fourier-transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) analysis. Field emission scanning electron microscope (FESEM) image confirms the formations of CuO with leaf-like morphology and branched side edges. The average size of the resultant CuO nanoleaves was calculated to be 400 nm in length and 150 nm in width. The electrochemical performance of the CuONs/MWCNTs/GCE nanocomposite modified electrode was characterized by cyclic voltammetric (CV) studies. The CuONs/MWCNTs/GCE nanocomposite modified electrode shows good electrochemical activity and it was also found that it possessed prominent electrocatalytic activity toward the oxidation of folic acid with as high a sensitivity as 3.35 μA/μM and a low detection limit (3σ) of 15.2 nM (S/N = 3). Besides, the CuO nanocomposite modified electrode lowers the over potential of folic acid oxidation than the unmodified electrodes.

Efficacy of highly water-dispersed fabricated nano ZnO against clinically isolated bacterial strains

Abstract: Versatile use of zinc oxide nanoparticles (ZNPs) in semiconductors, optical device and solar cells has already been established. Herein we describe synthesis of surface-functionalized ZNP to highly water dispersible constituent and its antibacterial efficiency against clinically isolated bacterial system. ZNP was synthesized by single-step microwave-assisted route using an aqueous buffer solution. Surface of ZNP was functionalized by grafting of phosphonoacetic acid as the coupling agent. Transmission electron microscopy image suggested that functionalized ZNP was smaller in size in comparison with unfunctionalized one. Antibacterial activity against clinically isolated bacterial strains of Escherichia coli, Staphylococcus aureus and Klebseilla sp. was detected with dose dependency. Functionalized ZNP claimed hexagonal crystal structure and exhibited higher dispersibility in aqueous solution which resulted in the production of greater reactive oxygen species and hence destruction of cell membrane leading to its biocidal efficacy. It is worth mentioning that functionalized dispersed fabricated ZNP would be used as potent biocides in medical as well as agricultural sector.

Investigations on nanocrystalline BST-LSMO magnetodielectric composites

Abstract: The paper reports the synthesis of Ba1−xSrxTiO3 (BST) for x = 0.20, 0.25, and 0.30 via hydroxide co-precipitation route to result into the BST nanoparticles of size nearly 50 nm. The La0.67Sr0.33MnO3 (LSMO) is also synthesized using co-precipitation route to achieve nanocrystaline particles. Further, the magnetodielectric (MD) composites of BST0.20, BST0.25, and BST0.30 are formed by addition of the LSMO at y = 0.1 and 0.2. The parent BST compositions are analysed for its dielectric properties. The composite LSMO-BST (LBST) is investigated for the variation of dielectric constant and impedance spectra as a function of applied magnetic field for the frequency between 500 Hz to 1 MHz. The observations on MD effect show that the dielectric constant possesses contributions due to magnetic field dependant interfacial polarization and variations due to the induced stress.

Gold on oxide-doped alumina supports as catalysts for CO oxidation

Abstract: The effect of doping a commercial alumina support with metal oxides of Ce, Co, Cu, Fe, La, Mg, Mn, Ni and Zn was investigated. Doped δ-Al2O3 samples were obtained by simple physical mixture (PM) of the alumina with the desired commercial oxide and by traditional impregnation of alumina with precursor salts of the same metals followed by calcination (IC). The metal load (7% wt.) was the same in both cases. Gold (1% wt.) was loaded using a liquid phase reductive deposition method. The obtained materials were characterized by adsorption of N2 at −196°C, temperature programmed reduction, X-ray diffraction, energy-dispersive X-ray spectrometry and transmission electron microscopy. Both samples prepared by PM and IC showed a mixture of the δ-alumina phase with the respective metal oxide, but the BET surface areas of the IC samples were, in general, higher than those of the PM materials. The particle size of the oxide phases were larger for the PM samples than for the IC materials. Nevertheless, catalytic experiments for CO oxidation showed that PM samples were much more active than IC. That could be explained by the size of gold nanoparticles, well known to be related with catalytic activity, that was lower in samples prepared by PM (7–16 nm) than by IC (11–17 nm). Gold was found to be in the metallic state. The most active samples were aluminas containing Zn and Fe prepared by PM that had the smallest gold nanoparticles sizes (7–13 and 8–12 nm, respectively) and had room temperature activities for CO conversion of 0.62 and 1.34 mol CO h−1 g Au −1 , respectively, which are larger than those found in the literature for doped γ-alumina samples.

Wet-electrospun CuNP/carbon nanofibril composites: potential application for micro surface-mounted components

Abstract: Wet electrospinning of polyacrylonitrile (PAN) and dimethylformamide (DMF) with copper nanoparticles (CuNP) at different concentrations from 0.2 to 1 wt% have been studied under certain spinning conditions. A specific coagulating water bath has been used to collect different fibroses and fibril diameters, the effect of spinning height on the produced nanofiber and CuNP/PAN nanofibril composites have been studied from 1 to 7 cm heights. A minimum average diameter of 64 nm has been reported at 7-cm spinning height. Two heat treatment steps have been used to enhance the electrical properties of CuNP/PAN nanofibril composites. SEM has been used to study the morphological characteristics of the electrospun nanofibroses membranes. Preliminary electrical measurements using 4-point probing system showed a noticeable improvement in the electrical conductivity of the produced nanofibril composite membranes. Also, electrical property of a single CuNP/carbon nanofibril composite has been theoretically calculated based on Lichtenecker formula. The produced membranes have been used to build a micro surface-mounted components (MSMC) such as Micro Field Effect Transistor (MFET). A high transconductance has been reported for such a device which will open the door for many promising applications especially in Electronics and Biomedicine.

Carbon nanotubes and polyaniline supported Pt nanoparticles for methanol oxidation towards DMFC applications

Abstract: A microwave reduction route was employed for the synthesis of Pt nanoparticles supported on multi-walled carbon nanotubes (MWCNT). The as-prepared Pt-MWCNT electrocatalysts were characterized by FT-IR, XRD and TEM analysis. Further, the as-prepared catalysts were probed for its electrocatalytic activity towards methanol oxidation by cyclic voltammetry (CV) in 0.5 M CH3OH + 0.5 M H2SO4 solution. Two kinds of electrocatalysts viz. Pt-MWCNT and Pt-MWCNT/PANI were probed to study the effect of both carbon nanotubes and polyaniline (PANI) towards methanol oxidation. The effect of scan rate, concentration and long-term cycle stability analysis has been investigated in detail. Results show that the presence of MWCNT and PANI improves the electrocatalytic efficiency towards methanol oxidation. Pt-MWCNT/PANI shows high peak current density towards methanol oxidation and good long-term stability even after 600 cycles indicating that the catalyst could be used for practical applications.

Effect of PVD process parameters on the quality and reliability of thin (10–30 nm) Al2O3 dielectrics

Abstract: Over the last decade, dielectric scaling in non-volatile memories (NVM) and CMOS logic applications has reached a point where better innovations will be required to meet the reliability and performance requirements of future products. For both these applications, high k materials are being explored as possible candidates to replace the traditional SiO2 and oxide/nitride/oxide-based films used today. While there are several attractive candidates to replace these materials, HfO2 and Al2O3 are considered as the most promising ones. Although there has been a lot of work on CVD-based Al2O3, there has not been much reported for PVD-based Al2O3 for NVM applications, especially in the thickness regime of 10–30 nm. This paper discusses the effects of process parameters such a plasma power and annealing conditions on the quality of Al2O3 dielectrics. It was observed that a post deposition anneal in O2 ambient at 700°C for 15 s is essential to obtain a fully oxidized film with high density. While higher power (1,500 W) results in thicker films with better k values, they also lead to more substrate damage and poorer reliability. Annealing done at temperatures greater than 700°C for 60 s or more results in failure of the film possibly due to diffusion of silicon into Al2O3 and its subsequent reaction.

Hydrothermal synthesis method of nickel phosphide nanoparticles

Abstract: Nanometer nickel phosphide compounds (Ni2P and Ni12P5) were synthesized via a mild hydrothermal method with red phosphor and nickel chloride as raw materials. XRD, EDS, TEM and SEM analysis were employed to characterize the obtained products. The results showed that the as-prepared products were well crystallized and particle sizes ranged from 10 to 40 nm. Effects of raw material ratios and initial pH of reaction system on the final products were investigated. The result showed that increased P/Ni ratio benefited the formation of Ni2P but went against obtaining Ni12P5 and nanoparticles were obtained only in alkaline environment.

Fabrication and electrical characterization of highly ordered copper nanowires

Abstract: The template-assisted electrodeposition technique has been employed to synthesize highly ordered: uniformly dense, well-aligned, parallel and homogeneous copper nanowires. Their morphological studies have been carried out using the scanning electron microscopy and transmission electron microscopy. The X-ray diffraction study exhibits cubic structure of the nanowires and their preferred orientation along the direction [111]. Their elemental composition has been done by energy dispersive X-ray analysis. The photoluminiscence spectra of copper nanowires show two excitation peaks at 209 and 268 nm; both these absorption pathways yield fluorescence at 296 nm. Their UV–Vis absorption spectra have been found to give a prominent peak at 570 nm. The current–voltage characteristics of the nanowires reveal their non-linear behavior. The impedance spectroscopy has also been carried out and it shows an increase in their impedance at higher frequencies.

Self-organized growth of bamboo-like carbon nanotube arrays for field emission properties

Abstract: Well-aligned nitrogen-doped carbon nanotube (N-CNTs) film was fabricated on silicon substrate by thermal chemical vapor deposition process with varying the growth temperature. The effect of growth temperature on morphology, microstructure and crystallinity for the growth of N-CNTs was studied. At all growth temperatures, the bamboo-like morphology of graphene layers with compartments in CNTs were observed in transmission electron microscope micrographs. The doping level and the type of nitrogen-related moieties were determined by X-ray photoelectron spectroscopy analysis. The compartment distance decreases with increase in nitrogen doping level in hexagonal graphite network. The increase in nitrogen doping level in N-CNTs will lead to decrease in crystallinity and in-plane crystallite size. Field emission study of nitrogen-doped carbon nanotubes grown at optimum parameters showed that they are good emitters with a turn-on and threshold field of 0.3 and 1.6 V/μm, respectively. The maximum current density was observed to be 18.8 mA/cm2 at the electric field of 2.1 V/μm. It is considered that the enhanced field emission performance of doped nanotube is due to the presence of lone pairs of electrons on nitrogen atom that supplies more electrons to the conduction band.

Studies on the de/re-hydrogenation characteristics of nanocrystalline MgH2 admixed with carbon nanofibres

Abstract: In the present investigation, we have synthesized different morphologies of carbon nanofibres (CNFs) to investigate their catalytic effect on the hydrogenation characteristics of 25 h ball-milled MgH2 (nano MgH2). The TEM analysis reveals that 25 h of ball-milling leads to the formation of nanocrystalline particles with size ranging between 10 and 20 nm. Different morphologies of CNFs were synthesized by catalytic thermal decomposition of acetylene (C2H2) gas over LaNi5 alloy. Helical carbon nanofibers (HCNFs) were formed at a temperature 650 °C. By increasing the synthesis temperature to 750 °C, planar carbon nanofibres were formed. In order to explore the effectiveness of CNFs towards lowering the decomposition temperature, TPD experiments (at heating rate 5 °C/min) were performed for nano MgH2 with and without CNFs. It was found that the decomposition temperature is reduced to ~334 and ~300 °C from 367 °C for the PCNF and HCNF catalysed nano MgH2. It is also found that HCNF admixed nano MgH2 absorbs ~5.25 wt% within 10 min as compared with pristine nano MgH2, which absorbs only ~4.2 % within the same time and same condition of temperature and pressure. Thus the HCNF possesses better catalytic activity than PCNF. These different levels of improvement in hydrogenation properties of HCNF catalysed nano MgH2 is attributed to the morphology of the CNFs.