Showing papers in "Applied Nanoscience in 2013"

Coleus aromaticus leaf extract mediated synthesis of silver nanoparticles and its bactericidal activity

Abstract: The utilization of various plant resources for the biosynthesis of metallic nanoparticles is called green nanotechnology, and it does not utilize any harmful chemical protocols. The present study reports the plant-mediated synthesis of silver nanoparticles using the plant leaf extract of Coleus aromaticus, which acts as a reducing and capping agent. The silver nanoparticles were characterized by ultraviolet visible spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and the size of the silver nanoparticles is 44 nm. The bactericidal activity of the silver nanoparticles was carried out by disc diffusion method that showed high toxicity against Bacillus subtilis and Klebsiella planticola. Biosynthesis of silver nanoparticles by using plant resources is an eco-friendly, reliable process and suitable for large-scale production. Moreover, it is easy to handle and a rapid process when compared to chemical, physical, and microbe-mediated synthesis process.

Facile green synthesis of variable metallic gold nanoparticle using Padina gymnospora , a brown marine macroalga

Abstract: The process of development of reliable and eco-friendly metallic nanoparticles is an important step in the field of nanotechnology. To achieve this, use of natural sources like biological systems becomes essential. In the present work, extracellular biosynthesis of gold nanopar- ticles using Padina gymnospora has been attempted and achieved rapid formation of gold nanoparticles in a short duration. The UV-vis spectrum of the aqueous medium containing gold ion showed peak at 527 nm corresponding to the plasmon absorbance of gold nanoparticles. Scanning electron microscopy showed the formation of well- dispersed gold nanoparticles. FTIR spectra of brown alga confirmed that hydroxyl groups present in the algal poly- saccharides were involved in the gold bioreduction. AFM analysis showed the results of particle sizes (53-67 nm) and average height of the particle roughness (60.0 nm). X-ray diffraction (XRD) spectrum of the gold nanoparticles exhibited Bragg reflections corresponding to gold nano- particles. This environment-friendly method of biological gold nanoparticle synthesis can be applied potentially in various products that directly come in contact with the human body, such as cosmetics, and foods and consumer goods, besides medical applications.

Green synthesis of silver nanoparticles using marine macroalga Chaetomorpha linum

Abstract: The present investigation demonstrates the formation of silver nanoparticles by the reduction of the aqueous silver metal ions during exposure to the seaweed (Chaetomorpha linum) extract. The silver nanoparticles obtained were characterized by UV–visible spectrum, FTIR and scanning electron microscopy. The characteristic absorption peak at 422 nm in UV–vis spectrum confirmed the formation of silver nanoparticles. The colour intensity at 422 nm increased with duration of incubation. The size of nanoparticles synthesized varied from 3 to 44 nm with average of ~30 nm. The FTIR spectrum of C. linum extract showed peaks at 1,020, 1,112, 1,325, 1,512, 1,535, 1,610, 1,725, 1,862, 2,924, 3,330 cm−1. The vibrational bands corresponding to the bonds such as –C=C (ring), –C–O, –C–O–C and C=C (chain) are derived from water-soluble compounds such as amines, peptides, flavonoids and terpenoids present in C. linum extract. Hence, it may be inferred that these biomolecules are responsible for capping and efficient stabilization. Since no synthetic reagents were used in this investigation, it is environmentally safe and have potential for application in biomedicine and agriculture.

Seaweed-mediated biosynthesis of silver nanoparticles using Gracilaria corticata for its antifungal activity against Candida spp.

Abstract: The present study was demonstrated with simple and rapid synthesis of silver (Ag) nanoparticles using marine seaweed, Gracilaria corticata. The visibility of prominent color change at 60 °C within 20 min indicates the formation of Ag nanoparticles. The synthesized Ag nanoparticles were well characterized by UV–vis spectrum, Fourier infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and dynamic light scattering measurements (DLS). Prominent FTIR peaks were obtained corresponding to phenolic compounds, amide I group and aromatic rings which involved in the stabilization of Ag nanoparticles. G. corticata resulted in spherical shaped nanospheres of 18–46 nm as revealed by TEM. The average size distributions of Ag nanoparticles were 51.82 nm and are fairly stable with a zeta potential value of −26.2 mV. The result showed that, biosynthesized Ag nanoparticles from G. corticata have an effective antifungal activity against Candida albicans and C. glabrata.

Synthesis and characterization of whisker-shaped MnO2 nanostructure at room temperature

Abstract: Manganese dioxide nanoparticles have been synthesized, via a facile one-step solution phase approach, by the reduction of potassium permanganate with sodium thiosulphate at room temperature. Upon addition of thiosulphate to the solution of permanganate, a transparent dark-brown color species appeared which was stable for several months. The obtained MnO2 solution was characterized by means of UV–vis spectra, Transmission electron microscopy (TEM), and Fourier transforms infrared spectroscopy. Fourier transforms infrared spectroscopy spectra of pure MnO2 show the occurrence of O–Mn–O vibrational mode at around 600 and 475 cm−1. The chemical composition was obtained by EDX analysis and confirmed the presence of Mn and O in the sample. From the TEM image, the surface morphology of the sample shows uniformly dispersed particles, which are spherical in shape. The selected area electron diffraction patterns revealed that the MnO2 are crystalline in nature.

Structure, optical properties and synthesis of Co-doped ZnO superstructures

Abstract: Co-doped ZnO nanoparticles were synthesized by a simple chemical method at low temperature with Co:Zn atomic ratio from 0 to 7 %. The synthesis process is based on the hydrolysis of zinc acetate dihydrate and cobalt acetate tetrahydrate heated under reflux to 65 °C using methanol as a solvent. X-ray diffraction analysis reveals that the Co-doped ZnO crystallizes in a wurtzite structure with crystal size of 12–5 nm. These nanocrystals self-aggregated themselves in a highly spherical superstructure of broad size distribution. High-resolution transmission electron microscopy image also shows that each sphere is made up of numerous nanocrystals with average interfringe distance of ~0.28 nm. The X-ray diffraction patterns, energy dispersive X-ray, scanning electron microscopy and high-resolution transmission electron microscopy micrographs of doping of Co in ZnO confirmed the formation of spherical superstructure and indicated that the Co2+ is successfully substituted into the ZnO host structure of the Zn2+ site. The optical band gap of ZnO nanoparticles was remarkably from 3.32 to 4.12 eV with increase of Co doping levels from 0 to 7 %. Photoluminescence measurements confirm these results.

Adsorption of methyl green dye onto multi-walled carbon nanotubes decorated with Ni nanoferrite

Abstract: This research was carried out to evaluate the capability of multi-walled carbon nanotubes (CNTs) and NiFe2O4-decorated multi-walled carbon nanotubes (NiFe2O4-CNTs) toward waste water treatment relevant to organic dyes. CNTs were prepared via chemical vapor deposition method. NiFe2O4-CNTs were prepared by in-situ chemical precipitation of metal hydroxides followed by hydrothermal processing. The samples were characterized using XRD and TEM. The adsorption efficiency of CNTs and NiFe2O4-CNTs of methyl green dye at various temperatures was examined. The adsorbed amount increased with the CNTs and NiFe2O4-CNTs dosage. The linear correlation coefficients and standard deviations of Langmuir and Freundlich isotherms were determined. It was found that Langmuir isotherm fitted the experimental results well in both adsorption cases n of methyl green onto CNTs and NiFe2O4-CNTs. Kinetics analyses were conducted using pseudo first-order, second-order and the intraparticle diffusion models. The results showed that the adsorption kinetics was controlled by a pseudo second-order model for adsorption of methyl green onto CNTs and best controlled by pseudo first-order in case of NiFe2O4-CNTs. Changes in the free energy of adsorption (ΔG°), enthalpy (ΔH°), entropy (ΔS°), and the activation energy (Ea) were determined. The ΔH°, ΔG° and Ea values indicated that the adsorption of methyl green onto MWCNTs and NiFe2O4-MWCNTs was physisorption.

A novel biological approach on extracellular synthesis and characterization of semiconductor zinc sulfide nanoparticles

Abstract: The expansion of reliable and eco-friendly process for synthesis of semiconductor nanoparticle is an important step in the emerging field of biomedical nanotechnology. In this communication, the zinc sulfide nanoparticles were biologically synthesized by using Serratia nematodiphila which was isolated from chemical company effluent. The surface plasmon resonance centered at 390 nm on the UV spectrum indicates the presence of zinc sulfide nanoparticles in the reaction mixture (S. nematodiphila and zinc sulfate); EDAX analysis also confirmed the presence of zinc sulfide nanoparticles. Scanning electron microscope image showed that the synthesized zinc sulfide nanoparticles were spherical in nature and nanoparticles of about 80 nm in size were obtained from transmission electron microscope images. The peaks in the XRD spectrum corresponding to (111), (220) and (311) show that the zinc sulfide nanoparticles are crystalline in nature. Fourier transforms infrared spectroscopy shows the functional groups of the nanoparticle in the range of 4,000–400 cm−1. Further, the antibacterial activity of zinc sulfide nanoparticles was examined against Bacillus subtilis and Klebsiella planticola. The maximum zone of inhibition occurred at 200 μl of silver nanoparticles. Due to potent antimicrobial and intrinsic properties of zinc sulfide, it is actively used for biomedical and food packaging applications.

A rapid and versatile method for solvothermal synthesis of Sb2O3 nanocrystals under mild conditions

Abstract: A very simple strategy for preparing Sb2O3 nanostructures under ambient aqueous condition is presented. Sb2O3 nanoparticles with an average size of approximately 44 nm were synthesised using wet chemical method. Senarmontite cubical structure Sb2O3 nanocrystals have been selectively harvested in high yield. The as-obtained nanoproducts were characterized by X-ray powder diffraction, Fourier transform infrared (FTIR), ultraviolet–visible near infrared spectroscopy (UV–Vis-NIR) and scanning electron microscopy (SEM) analyses. The size of the Sb2O3 nanoparticles was found to be in the range 44–385 nm from Debye–Scherrer equation. The X-ray density, surface area and porosity of Sb2O3 nanocrystals were found to be 2.969 g/cm3, 2.0208 × 1014 cm2/g and 1.0185 × 10−3 m, respectively. From the UV–Vis-NIR analysis, the band gap of Sb2O3 nanocrystals was estimated to be 5.6 eV at 220 nm. The various functional groups in the samples were identified using FTIR spectral studies. The SEM images showed a very spiky morphology. Very small spherical-shaped objects were clearly observed within these structures. The extinction coefficient, real and imaginary part of the dielectric constant, electric susceptibility and the refractive index of Sb2O3 nanocrystals were 7.605 × 10−9, 0.2851 × 10−17, 3.747 × 10−8, 0.48322 and 2.4636, respectively.

Wet chemical synthesis and characterization of SnS2 nanoparticles

Abstract: The SnS2 nanoparticles were synthesized at room temperature by simple wet chemical method. Stannic chloride pentahydrate (SnCl4·5H2O) and thioacetamide (C2H5NS) were used as a source of Sn+4 ions and S−2 ions, respectively. The elemental composition of the as-synthesized SnS2 nanoparticles was determined by energy dispersive analysis of X-ray. The structure and lattice parameters were determined by X-ray diffraction. The crystallite size was determined from XRD pattern using Scherrer’s formula and Hall–Williamson plot. The transmission electron microscopy was employed to characterize the nanoparticles. The selected area electron diffraction pattern established the polycrystalline nature of SnS2 nanoparticles. Surface topography of nanoparticles was studied employing scanning electron microscopy (SEM). The bandgap determined from the UV–Vis–NIR spectrum of as-synthesized SnS2 nanoparticles showed blue shift in comparison with the bandgap of bulk SnS2. The photoluminescence spectra at five different excitation wavelengths 250, 300, 350, 400 and 450 nm showed two strong emission peaks at wavelengths 550 and 825 nm. The obtained results are discussed in details.

Synthesis of silver nanoparticles by coastal plant Prosopis chilensis (L.) and their efficacy in controlling vibriosis in shrimp Penaeus monodon

Abstract: The present work investigated the effect of leaf extract from coastal plant Prosopis chilensis on synthesis of silver nanoparticles using AgNO3 as a substrate and to find their antibacterial potential on pathogenic Vibrio species in the shrimp, Penaeus monodon. The leaf extract could be able to produce silver nanoparticles, as evident by gradual change in colour of the reaction mixture consisted of the extract and 1 mM AgNO3 to dark brown. The silver nanoparticles exhibited 2θ values corresponding to the presence of silver nanocrystal, as evident by X-ray diffraction spectrum. The peaks corresponding to flavanones and terpenoids were found to be stabilizing agents of the nanoparticles, as revealed by Fourier transform infrared spectroscopy. The size of silver nanoparticles ranged from 5 to 25 nm with an average of 11.3 ± 2.1 nm and was mostly of spherical in shape, as confirmed by transmission electron microscopy. The silver nanoparticles were found to inhibit Vibrio pathogens viz., Vibrio cholerae, V. harveyi, and V. parahaemolyticus and this antibacterial effect was better than that of leaf extract, as proved by disc diffusion assay. The nanoparticles were then tested in the shrimp Penaeus monodon challenged with the four species of Vibrio pathogens for 30 days. The shrimps fed with silver nanoparticles exhibited higher survival, associated with immunomodulation in terms of higher haemocyte counts, phenoloxidase and antibacterial activities of haemolymph of P. monodon which is on par with that of control. Thus, the present study proved the possibility of using silver nanoparticles produced by coastal Prosopis chilensis as antibacterial agent in controlling vibriosis.

Change in the morphology of ZnO nanoparticles upon changing the reactant concentration

Abstract: ZnO plays an important role in many techno- logical aspects of semiconductors. Because of its interesting properties, it has attracted a great deal of attention for a wide range of applications. In this work, the direct precipitation method was employed for the synthesis of ZnO nanoparticles to study the role of different concentration ratios of reactants on the crystal structure, size, and morphology of the prepared ZnO nanoparticles. The reactant raw materials used in this experiment were zinc acetate dihydrate as a zinc source and NaOH. ZnO nanoparticles were synthesized by calcination of the ZnO precursor precipitates at 250 Cf or 3 h. These calcinated ZnO nanoparticles and their properties were characterized using X-ray diffraction, a scanning electron microscope equipped with an energy dispersive X-ray spectrometer, and transmission electron microscopy. We present the experiment conditions, including result on the different reactant concentration ratios, which affect the control of the size and morphology of the ZnO nanoparticles. The mean size of the ZnO nanoparticles was 18 nm.

Synthesis of ZnO/Al:ZnO nanomaterial: structural and band gap variation in ZnO nanomaterial by Al doping

Abstract: Pure ZnO and Al-doped ZnO nanomaterial have been successfully fabricated using zinc acetate dihydrate in a basic aqueous solution of KOH through solution precipitation method then treated at 600°C in air. The XRD analysis confirms the Wurtzite hexagonal crystal structure of the product with crystallite size in 32–53 nm range. The morphology of the product has been studied under scanning electron microscopy (SEM). The simultaneous differential scanning calorimetry and thermogravimetric analyses were used to investigate thermal decomposition temperature and different phase transitions up to 800°C. The optical properties and variation in band gap of ZnO by Al doping were investigated by ultraviolet–visible spectroscopy.

Enhancement of antidandruff activity of shampoo by biosynthesized silver nanoparticles from Solanum trilobatum plant leaf

Abstract: The present investigation describes simple and effective method for synthesis of silver nanoparticles via green route. Solanum trilobatum Linn extract were prepared by both conventional and homogenization method. We optimized the production of silver nanoparticles under sunlight, microwave and room temperature. The best results were obtained with sunlight irradiation, exhibiting 15–20 nm silver nanoparticles having cubic and hexagonal shape. Biosynthesized nanoparticles were highly toxic to various bacterial strains tested. In this study we report antibacterial activity against various Gram negative (Klebsiella pneumoniae, Vibrio cholerae and Salmonella typhi) and Gram positive (Staphylococcus aureus, Bacillus cereus and Micrococcus luteus) bacterial strains. Screening was also performed for any antifungal properties of the nanoparticles against human pathogenic fungal strains (Candida albicans and Candida parapsilosis). We also demonstrated that these nanoparticles when mixed with shampoo enhance the anti-dandruff effect against dandruff causing fungal pathogens (Pityrosporum ovale and Pityrosporum folliculitis). The present study showed a simple, rapid and economical route to synthesize silver nanoparticles and their applications hence has a great potential in biomedical field.

Electrical and optical studies of pure and Ni-doped CdS quantum dots

Abstract: Quantum dots of CdS and Ni-doped CdS were synthesized through chemical precipitation method using a high-boiling solvent. Nanocrystallinity of the as prepared nanostructure is confirmed using X-ray diffraction (XRD). The mean crystal size obtained by full-width half maxima (FWHM) analysis is 3.33 nm for CdS, 3.37 nm for CdS:Ni (2 mM) and 3.39 nm for CdS:Ni (4 mM). The electrical conductivity data reveal semiconducting behaviour of both pure CdS and Ni-doped CdS nano-crystals. The optical absorption analysis conducted in UV–vis range 200–900 nm reveals the transparency of these nanocrystals in entire visible range but not in ultraviolet range. The results based on optical analysis yield band gap values as 2.65 eV for CdS, 2.59 eV for CdS:Ni (2 mM) and 2.53 eV for CdS:Ni (4 mM) nanoparticles. This implies that pure CdS and Ni doped CdS are blue shifted with respect to the bulk CdS (2.42 eV); however, Nickel doped CdS nanocrystals are red shifted with respect to pure CdS nanocrystals.

Preparation and characterization of Ni–Zn ferrite + polymer nanocomposites using mechanical milling method

Abstract: The insulating properties of Ni–Zn ferrites can be improved by the addition of various types of insulating materials such as polymers, ceramics, etc. In this connection, ferrite–polymer composites have been subjected to extensive research, because they have many applications: electromagnetic interference shielding, rechargeable battery, electrodes and sensors, and microwave absorption. Electrical and magnetic properties of such composites will depend on the size, shape and amount of filler addition. In this paper, we report the preparation and characterization of nanocomposites of Ni–Zn ferrite + paraformaldehyde. These nanocomposites were prepared by using mechanical milling method and characterized by X-ray powder diffraction, scanning electron microscopy (SEM) and Fourier transform infrared spectrometer. The particle size estimated from SEM pictures for composites varies from 36 to 60 nm. Magnetic properties were measured on nanocomposites at room temperature. The complex permittivity and permeability were measured over a wide frequency range from 1 MHz to 1.8 GHz at room temperature. From our studies, it is observed that both the values of permittivity and permeability decrease with an increase in polymer content.

A simple microwave assists aqueous route to synthesis CuS nanoparticles and further aggregation to spherical shape

Abstract: The aggregation of CuS nanoparticles during synthesis by a hassle-free aqueous route under microwave irradiation gave remarkable spherical shape, utilizing Cu(CH3COO)2·H2O as the source of copper and Na2S2O3·5H2O, as sulfur source; these materials were used without assistance of any surfactant or template. An X-ray powder diffraction pattern proved that the product is hexagonal CuS phase. The morphologies of the product were observed by scanning electron microscopy. Thermal behavior, different solid state, and chemical conversion in CuS with respect to temperature were studied by DSC/TGA, which confirmed the thermal oxidation of CuS and its conversion into CuO then to Cu2O.

Influence of particle size of nano zinc oxide on the controlled delivery of Amoxicillin

Abstract: A great effort has been exerted to develop drug carriers aiming at satisfying the requirements, such as safety, greater efficiency, predictable therapeutic response, and prolonged release period. The present study aims at developing the use of zinc oxide nanoparticles as a carrier as a function of particle size for amoxicillin drug delivery system. The amoxicillin-loaded zinc oxide nanoparticles have a good antibacterial activity against infectious Gram-positive and Gram-negative bacteria. Zinc oxide nanoparticles have been prepared by wet chemical precipitation method varying the pH values. Particle size and morphology of the as-prepared ZnO powders are characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscope. Drug loading, in vitro drug release and antibacterial activity have been analyzed. Maximum zone of inhibition is observed for Staphylococcus epidermis. The results show that inhibitory efficacy of drug-loaded ZnO nanoparticles is very much dependent on its chosen concentration, drug loading, and size.

Preparation and characterization of nanostructured nickel oxide thin films by spray pyrolysis

Abstract: Transparent crystalline nanostructured nickel oxide (NiO) thin films were prepared using a simple spray pyrolysis technique from hydrated nickel chloride salt solution (NiCl2� 6H2O) onto glass and silicon (n-type) substrates at different temperatures (280, 320, 360, and 400 C) and with different solution concentrations (0.025, 0.05, 0.075, and 0.1 M). Structural and morphological properties of the grown NiO films were studied using X-ray diffraction (XRD) and atomic force microscope. Optical properties and chemical analysis of the films were char- acterized by UV-visible absorption spectra and Fourier transform infrared spectroscopy, respectively. The XRD result showed that the deposited film has an amorphous structure when deposited at temperature of Ts = 280 C and concentration of 0.025 M. At higher temperatures (Ts = 320, 360, 400 C) and solution concentrations (0.05, 0.075, 0.1 M), the deposited films have cubic polycrystal- line structure formed with preferred orientation along (111) plane. The band gap of NiO film increases from 3.4 to 3.8 eV as the molarity decreased from 0.1 to 0.05 M.

Organic free synthesis of flower-like hierarchical CuO microspheres by reflux condensation approach

Abstract: In the present work, CuO nanostructures with different morphologies were synthesized by a simple one-pot reflux condensation approach using different alkaline precursors. Structural analysis by X-ray diffraction and Fourier transform infrared spectroscopy revealed the formation of single phase CuO with a monoclinic crystal structure. Morphological analysis by scanning electron microscopy showed the formation of spindle-shaped and flower-like CuO architecture when NaOH and NH4OH were used as alkaline precursors, respectively. The flower-like CuO architecture is found to be made up of 2D nanosheets as building blocks, which were self-assembled to form spherical assemblies. Optical analysis by UV–VIS diffused reflectance spectroscopy showed blue-shift in the optical band gap due to quantum confinement effect. Photoluminescence spectra showed both UV and visible emission. The plausible growth mechanism for the formation of different CuO nanostructures was proposed.

Mechanical and thermal studies of unsaturated polyester-toughened epoxy composites filled with amine-functionalized nanosilica

Abstract: The inter-crosslinking networks of unsaturated polyester (UP)-toughened epoxy-nanosilica hybrid nanocomposites have been developed. Epoxy resin was toughened with 5 and 10% (by wt) of unsaturated polyester using benzoyl peroxide as radical initiator and 4,4′-diaminodiphenylmethane (DDM) as a curing agent at appropriate condition, and the resulting product was identified by FT-IR spectra. Unsaturated polyester-toughened epoxy system (10%) was further filled with 1, 3, 5 and 7% (by wt) of amine-functionalized nanosilica particles prepared by sol–gel method. Modified nanosilica-filled hybrid UP–epoxy matrices developed in the form of casting were characterized for their thermal, mechanical properties and water absorption capacity according to ASTM standards. The degree of dispersion of nanosilica in the matrices was investigated by SEM technique. Mechanical testing data indicate that the introduction of UP into epoxy resin has improved the impact strength. Significant improvement in the flexural properties, tensile properties and impact strength were observed in the UP–epoxy blends with increase in the percentage of amine-modified nanosilica particles. The Tg value decreases with UP toughening and increases with concentration of modified nanosilica on the UP–epoxy matrix. The water absorption behavior is found to decrease with UP toughening and concentration of modified nanosilica on the UP–epoxy matrix.

Synthesis and conjugation of ZnO nanoparticles with bovine serum albumin for biological applications

Abstract: Semiconductor nanomaterials tagged with biomarkers may be used for an early fluorescence-based detection of breast cancer. ZnO nanoparticles are water-soluble, non-toxic, photo-chemically stable with highly fluorescence applicability and are regarded for their possible biocompatibility. As a long-term research planning, we are aiming to use QDs conjugated with serum-biomarker for the diagnosis of breast cancer. The present work is a part in the said direction and reports preliminary observations on the synthesis and conjugation of ZnO nanoparticles with a representative protein marker.

An alternative improved method for the homogeneous dispersion of CNTs in Cu matrix for the fabrication of Cu/CNTs composites

Abstract: Copper has a wide range of applications due to its excellent properties (high thermal and electrical conductivity). Carbon nanotubes (CNTs) are widely used as a reinforcing material due to their superior properties. Copper/Carbon nanotube (Cu/CNTs) composites show enhanced mechanical, electrical and thermal properties as compared to pure Cu and Cu composites. Hence, Cu/CNTs composites have tremendous applications. Cu/CNTs are being developed for use as antifungal and antimicrobial agents, which can lead to their further use in biomedical devices and implant materials. The versatility of this material is such that Cu/CNTs are being developed for use in ultra-large scale integrated circuits for use in the latest integrated circuits and semiconductor chips. The composite material is being used as heat sinks for various industries. Cu/CNTs are now also being employed as catalysts for various industrial reactions. Fuel cell electrodes based on Cu/CNTs are being developed to replace expensive Pt/Pd-based electrodes, currently being used. Another application in the energy sector is the use of Cu/CNTs in direct methanol fuel cells and in methanol gas reforming for H2 production. These extensive applications provided motivation for the current work. However, these applications can only be realized if a stable and uniform Cu/CNTs composite powder can be made. The challenges in fabricating Cu/CNTs composites are: (1) homogeneous dispersion of CNTs in Cu matrix, (2) interfacial bonding between CNTs and Cu matrix and (3) retention of structural integrity of CNTs. Powder metallurgy (PM) has been widely used, but dispersion of Cu/CNTs remains an issue. We employed the molecular level mixing method (MLM), coupled with high energy ball milling (BM) to overcome above mentioned issues. To the best of our knowledge, this is a new process for the homogeneous dispersion of CNTs in copper and has been reported for the first time. To produce a homogenous mixture of Cu and CNTs, a combination of MLM and BM was used in the present work. This method involves using a Cu salt/CNTs mixture in desirable weight ratio (CNTs being were taken in a high concentration), followed by chemical reduction in aqueous medium using NABH4 as reducing agent and EDTA as the oxidation control agent. The resultant mixture (Copper/Carbon nanotube) was mixed with pure Cu using BM. The composites were fabricated using PM, in which the composite powders were first cold pressed at 500–550 MPa followed by sintering at 550–900 °C in a vacuum of 10−2 Torr. Characterization was carried out using SEM, XRD and HRTEM, and various mechanical properties were measured using a Universal testing Instron machine.

Influence of Mn substitution on crystal structure and magnetocrystalline anisotropy of nanocrystalline Co1−xMn x Fe2−2xMn2xO4

Abstract: Nanocrystalline Mn substituted cobalt ferrite Co1-xMnxFe2-2xMn2xO4 (x = 0.0-0.4) has been synthe- sized by the standard citrate-gel method. The structural and magnetic characteristics of all samples have been studied using powder X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM) and VSM techniques. Distributions of cations between the two interstitial sites (tetrahedral and octahedral site) have been estimated qualitatively by analyzing the powder X-ray diffraction patterns by employing the Rietveld refinement technique. All samples are found to be mixed spinel with cubic structure (Fd 3 � m space group). The FT-IR study shows the presence of absorption bands in the range of 390- 750 cm -1 , which confirm the spinel structure of the sam- ple. The stoichiometry of Co, Fe, Mn and O ions in the sample has been obtained by using energy-dispersive spectrum with help of an FE-SEM. The magnetizations in saturation have been analyzed by employing the ''law of approach'' technique. The saturation magnetization, coer- civity and magnetocrystalline anisotropy constant depend upon Mn ion concentration and crystallite size.

Structural and optical properties of CdTe/CdSe heterostructure multilayer thin films prepared by physical vapor deposition technique

Abstract: CdTe/CdSe heterostructure multilayer thin films and single layers of CdSe and CdTe thin films were prepared. Sequential thermal evaporation technique is made possible to adjust the layer thickness precisely. XRD studies were used to calculate average size of the crystallites and confirmed the (111) and (100) planes of CdTe and CdSe, respectively. Bulk CdTe has band gap energy of 1.54 eV that can be shifted to larger values by reducing the crystallite size to dimensions smaller than the Bohr radius of the exciton. Experimentally measured energy levels show the spin–orbit split of valance band of CdTe. Crystallite sizes (7–12 nm) were calculated with the predictions of effective mass approximation model (i.e., Brus model) which shows that the diameter of crystallites were much smaller than the Bohr exciton diameter (14 nm) of CdTe. It is found that the emission peaks of the prepared CdTe/CdSe ML samples were shifted from the peaks of CdSe and CdTe single layers toward red region as a characteristic of type II band alignment.

Preparation of nanostructured TiO2 photoelectrode for flexible dye-sensitized solar cell applications

Abstract: Nanocrystalline titanium dioxide (TiO2) thin film was successfully prepared by simple electrodeposition method from alkaline aqueous solution containing potassium titanium oxalate and hydroxylamine. Surface characterization of the electrodeposited films indicates the formation of crystalline TiO2. The dye solar cell constructed from dye-modified electrodeposited TiO2 film achieved an overall light-to-electricity conversion efficiency of 2.1 % under 1 sun illumination, indicating its high potential as a photoelectrode material for the DSCs.

A facile one-pot synthesis of polyaniline/magnetite nanocomposites by micelles-assisted method

Abstract: Magnetic nanocomposites based on polyaniline (PANI) and magnetite nanoparticles (Fe3O4NPs) have been prepared by an in situ self-assembly method in presence of dodecylbenzene sulfonic acid (DBSA) as dopant as well as surfactant. Influence of the aniline to DBSA molar ratio on morphology, magnetic properties, and thermal stability of PANI/Fe3O4NPs composites has been investigated. Spectroscopic results indicated the interaction between PANI nanorods and Fe3O4NPs. Scanning electron microscopy and transmission electron microscopy images indicated that PANI rods were decorated with Fe3O4NPs. Morphologies of nanocomposites were found to be critically dependent on molar ratios of organic acid to monomer. PANI nanorod/Fe3O4NPs composites showed superparamagnetism and higher thermal stability with small mass fraction of Fe3O4NPs.

Polypyrrole–ZnO nanohybrids: effect of CSA doping on structure, morphology and optoelectronic properties

Abstract: Polypyrrole–ZnO (PPy–ZnO) nanohybrid was prepared from PPy and ZnO nanoparticles (NPs). Nanohybrids of PPy–ZnO were doped with camphor sulfonic acid (CSA) with different weight ratios (10–50 %). The CSA-doped nanohybrids obtained were characterized by X-ray diffraction, FTIR, field emission SEM, UV–vis spectroscopy and electrical transport method. Structural investigations using X-ray diffraction shows new peaks appeared at 15.44° and 17.61° in the XRD pattern of CSA-doped PPy–ZnO nanohybrids belong to CSA. The FTIR spectra confirmed the strong interaction between the CSA and PPy–ZnO nanohybrids. The UV–visible spectrums revealed the enhancement of doping level for the 30 % CSA-doped PPy–ZnO nanohybrid film which is assigned to the existence of greater number of charges on the polymer backbone. The room temperature dc electrical conductivity of CSA-doped PPy–ZnO nanohybrids were observed to depend on the CSA doping and the morphology.

Synthesis and characterization of flower-like ZnSe nanostructured thin films by chemical bath deposition (CBD) method

Abstract: Flower-like zinc selenide nanostructured thin films were successfully prepared by a chemical bath deposition method on non-conducting glass substrate in an aqueous alkaline medium using sodium selenosulphate as Se2− ion source. The as-deposited films have been characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), energy-dispersive X-ray analysis (EDX), optical absorption, and photoluminescence spectroscopy (PL). The XRD studies reveal that the as-deposited ZnSe thin film is nanocrystalline with a face-centered cubic phase. SEM image shows the tens to hundreds of petals are self-assembled within a single nanoflower. The direct optical band gap ‘Eg’ for as-deposited flower-like ZnSe thin films is found to be 2.80 eV. Room temperature PL measurement indicates that the as-deposited cubic ZnSe thin films have a near band edge (NBE) emission peaked at around 440 nm (2.81 eV) and broad weak band emission peak from 552 nm (2.24 eV) to 658 nm (1.88 eV). The strong NBE emission from the flower-like ZnSe nanostructured thin films reveals their potential as building for optoelectronic devices.

Absence of free carrier and paramagnetism in cobalt-doped ZnO nanoparticles synthesized at low temperature using citrate sol–gel route

Abstract: Cobalt-doped ZnO nanoparticles have been synthesized using a simple citrate sol–gel auto-combustion method. The XRD confirms nano-single phase and Wurtzite structure. Increased cobalt solubility from 15 to 20 % was observed in ZnO matrix due to low temperature synthesis. Room temperature paramagnetic contribution is observed for all the samples, since cobalt is a neutral dopant and no free carriers are produced. Normally, ferromagnetism is observed in ZnO due to carrier mediated interaction between transition metal ions and free carriers. Hence no ferromagnetism was observed and only paramagnetism was observed due to non-availability of free carriers for long range ferromagnetic interaction in our system. At higher doping, peak broadening of the highly intense XRD peak (101) was observed indicating formation of cobalt cluster (metal–metal) which reduces paramagnetism due to antiferromagnetic interaction and the magnetization value decreases to 0.00456 from 0.0076 emu/g. Absence of photoluminescence peak at 520 nm due to oxygen related defects also supports, the presence of paramagnetism in our samples, since oxygen defects are the another source of ferromagnetism in ZnO. Indirect evidence for the presence of cobalt clustering is also obtained from the photoluminescence studies which lead to concentration quenching of peaks. Photoluminescence studies exhibit NBE peak at 412 nm and defect peaks at 471 and 672 nm. The intensity of red emission peak at 672 nm remains constant whereas the intensity of the peaks at 412 and 471 nm increases and then decreases due to doping induced disorder leading to concentration quenching.