Ferromagnetism in nanoscale BiFeO3

A remarkably high saturation magnetization of ~0.4mu_B/Fe along with room temperature ferromagnetic hysteresis loop has been observed in nanoscale (4-40 nm) multiferroic BiFeO_3 which in bulk form exhibits weak magnetization (~0.02mu_B/Fe) and an antiferromagnetic order. The magnetic hysteresis loops, however, exhibit exchange bias as well as vertical asymmetry which could be because of spin pinning at the boundaries between ferromagnetic and antiferromagnetic domains. Interestingly, like in bulk BiFeO_3, both the calorimetric and dielectric permittivity data in nanoscale BiFeO_3 exhibit characteristic features at the magnetic transition point. These features establish formation of a true ferromagnetic-ferroelectric system with a coupling between the respective order parameters in nanoscale BiFeO_3.Comment: 13 pages including 4 figures; pdf only; submitted to Appl. Phys. Let

A nonenzymatic reduced graphene oxide-based nanosensor for parathion

Organophosphate-based pesticides (e.g., parathion (PT)) have toxic effects on human health through their residues. Therefore, cost-effective and rapid detection strategies need to be developed to ensure the consuming food is free of any organophosphate-residue. This work proposed the fabrication of a robust, nonenzymatic electrochemical-sensing electrode modified with electrochemically reduced graphene oxide (ERGO) to detect PT residues in environmental samples (e.g., soil, water) as well as in vegetables and cereals. The ERGO sensor shows a significantly affected electrocatalytic reduction peak at -0.58 V (vs Ag/AgCl) for rapid quantifi-cation of PT due to the amplified electroactive surface area of the modified electrode. At optimized experimental conditions, square-wave voltammetric analysis exhibits higher sensitivity (50.5 mu A center dot mu M-1 center dot cm(-2)), excellent selectivity, excellent stability (approximate to 180 days), good reproducibility, and repeatability for interference-free detection of PT residues in actual samples. This electro-chemical nanosensor is suitable for point-of-care detection of PT in a wide dynamic range of 3 x 10(-11)-11 x 10(-6) M with a lower detection limit of 10.9 pM. The performance of the nanosensor was validated by adding PT to natural samples and comparing the data via absorption spectroscopy. PT detection results encourage the design of easy-to-use nanosensor-based analytical tools for rapidly monitoring other environmental samples

Water soluble blue-emitting AuAg alloy nanoparticles and fluorescent solid platforms for removal of dyes from water

Chicken egg shell membrane, a naturally abundant protein membrane, was used to synthesize gold (Au), silver (Ag) and their bimetallic (AuAg) alloy nanoclusters at room temperature without the use of any reducing agent or catalyst. The as-formed gold and alloy clusters were highly fluorescent and exhibited intense blue emission around 435 +/- 5 and 440 +/- 5 nm, respectively. This is the first report confirming the formation of fluorescent alloy clusters exhibiting nanosecond lifetimes by a biomembrane-induced reduction process. We have also explored the capability of these metal cluster immobilized inexpensive ESMs in removing organic dyes from water. The results confirmed that it is the strong adsorption of the dye molecules in the presence of the metal particles that has helped to convert ESM into an effective platform for water purification. This process has the dual advantages of utilizing an inexpensive, abundant and eco-friendly food waste (egg shell membrane) for in situ reduction and formation of metal nanoparticles and the utilization of the same as an effective platform for the removal of anionic dyes from waste water. An Au-immobilized ESM showed a better efficiency in dye molecules removal than those of the Ag-ESM and AuAg-ESM membranes

Correlation between extrinsic electroresistance and magnetoresistance in fine-grained La0.7Ca0.3MnO3

We report our observation of a correlation between the extrinsic electroresistance (EER) and magnetoresistance (EMR) via grain size in fine-grained La0.7Ca0.3MnO3. The nature of dependence of EER and EMR on grain size (~0.2-1.0 micron) indicates that for finer grains with low-resistive boundaries both of them follow similar trend whereas they differ for coarser grains with high-resistive boundaries. This could be due to a crossover in the mechanism of charge transport across the grain boundaries - from spin-depedent scattering process to spin-polarized tunneling one - as a function of grain size.Comment: 19 pages including 4 figures; pdf onl

Orbital order-disorder transition in La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) and La(1-x-y)Nd(yx)Sr(y)MnO(3) (x = 0.1; y = 0.05,0.1)

The nature of orbital order-disorder transition has been studied in the La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) series which covers the entire range between two end points - LaMnO(3) and NdMnO(3) - as well as in La(0.85)Nd(0.1)Sr(0.05)MnO(3) and La(0.8)Nd(0.1)Sr(0.1)MnO(3). It has been observed that the first-order nature of the transition gives way to higher order with the increase in "x" in the case of pure manganites. The latent heat (L) associated with the transition, first, drops with a steeper slope within x = 0.0-0.3 and, then, gradually over a range 0.3<x<0.9. This drop could, possibly, be due to evolution of finer orbital domain structure with "x". In the case of Sr-doped samples, the transition appears to be of higher-order nature even for a doping level 5 at%. In both cases, of course, the transition temperature T(JT) rises systematically with the drop in average A-site radius or rise in average Mn-O-Mn bond bending angle while no apparent correlation could be observed with doping induced disorder sigma^2. The cooperative nature of the orbital order, therefore, appears to be robust.Comment: 15 pages including 4 figures; pdf onl

High-Pressure Phase Transitions of Morphologically Distinct Zn2SnO4 Nanostructures

Many aspects of nanostructured materials at high pressures are still unexplored. We present here, high-pressure structural behavior of two Zn2SnO4 nanomaterials with inverse spinet type, one a particle with size of similar to 7 nm zero dimensional (0-D)] and the other with a chain-like one dimensional (1-D)] morphology. We performed in situ micro-Raman and synchrotron X-ray diffraction measurements and observed that the cation disordering of the O-D nanoparticle is preserved up to similar to 40 GPa, suppressing the reported martensitic phase transformation. On the other hand, an irreversible phase transition is observed from the 1-D nanomaterial into a new and dense high-pressure orthorhombic CaFe2O4-type structure at similar to 40 GPa. The pressure-treated 0-D and 1-D nanomaterials have distinct diffuse reflectance and emission properties. In particular, a heterojunction between the inverse spinet and quenchable orthorhombic phases allows the use of 1-D Zn2SnO4 nanomaterials as efficient photocatalysts as shown by the degradation of the textile pollutant methylene blue

Effect of metal ion concentration on synthesis and properties of La0.84Sr0.16MnO3 cathode material

A reactive powder of La0.84Sr0.16MnO3 is synthesized as a cathode material for solid oxide fuel cells by a citrate–nitrate auto-ignition process and characterized by thermal analysis, X-ray diffraction and electrical conductivity measurements. The effect of starting metal ion concentration in the precursor solution on the properties of the final oxide is studied and correlated through particle size analyses, sintering studies and microstructural examination. Sintered La0.84Sr0.16MnO3 ceramics of relative density around 93% can be fabricated by preferably keeping the metal ion concentration in the precursor to less than 0.8 M, whereas to make porous ceramics (relative densities of 75–80%) a higher metal ion concentration is preferred. At 1000 °C, the 93% dense ceramics exhibit electrical conductivities of around 168–169 S cm−1 and the porous ceramics of around 136–146 S cm−1

Fluorescent carbon nanoparticles from Citrus sinensis as efficient sorbents for pollutant dyes

Here, we report a simple, green and economic process for the synthesis of highly fluorescent carbon nanoparticles (CPs) through low-temperature carbonization of a fruit waste, Citrus sinensis peel. This approach allows the large-scale production of aqueous CPs dispersions without any additives and post-treatment processes. The as-prepared CPs were of small particle size, exhibited bright blue fluorescence under UV irradiation ((max)=365nm) with excellent colloidal stability in water. The chemical composition, structure and morphology of the as-prepared CPs were analyzed using various spectroscopic techniques such as X-ray diffraction, transmission electron microscopy and raman spectroscopy. The formed CPs were turbostratic in nature, with a large number of functional groups on the surface. We explored the adsorption characteristics of the formed CPs for wastewater treatment. Because of the negative surface of the CPs, as evident from the zeta value, it is possible to use them for selective adsorption of the cationic dye methylene blue from a mixture of dyes. The equilibrium adsorption isotherm revealed that the Langmuir model better describes the adsorption process than the Freundlich model. As-prepared CPs rapidly adsorbed similar to 84% of the methylene blue within 1min and can be regenerated and used repeatedly. Copyright (c) 2016 John Wiley & Sons, Ltd

Antiviral activity of ethanolic extract of Nilavembu Kudineer against dengue and chikungunya virus through in vitro evaluation

Abstract Background Currently, no vaccines or modern drugs are available for dengue and chikungunya and only symptomatic relief is provided to the patients. Siddha medicine, a traditional form of indigenous medical system uses specific polyherbal formulations for the treatment of such infections with considerable success. One such polyherbal formulation for the treatment of chikungunya and dengue is Nilavembu kudineer (NVK). The mechanistic details of this drug as an antiviral for chikungunya virus (CHIKV) and dengue virus (DENV) is poorly understood. Objectives The current study was undertaken to study the efficacy of NVK as an antiviral formulation against CHIKV and DENV. Materials and methods Cytotoxicity assays (MTT) were performed to determine the role of NVK as an antiviral during chikungunya and dengue infections in the following conditions-i). post infection, ii). during active infections and iii) protective, not allowing virus infection. Results It was observed that NVK provides protection against CHIKV and DENV-2 during active infection as well can help to prevent virus infection in the cells and it mainly depends on the cellular availability of drugs for maximum protection against both the infections. Conclusion Our study establishes that extraction protocols are important to ensure maximum efficacy of NVK along with the time of addition of the drug during CHIKV and DENV infections in the cells. This study provides insights to the possible mode of action of NVK in in vitro condition during CHIKV and DENV infection

Performance of colloidal CdS sensitized solar cells with ZnO nanorods/nanoparticles

As an alternative photosensitizer in dye-sensitized solar cells, bovine serum albumin (BSA) (a nonhazardous protein) was used in the synthesis of colloidal CdS nanoparticles (NPs). This system has been employed to replace the commonly used N719 dye molecule. Various nanostructured forms of ZnO, namely, nanorod and nanoparticle-based photoanodes, have been sensitized with colloidal CdS NPs to evaluate their effective performance towards quantum dot sensitized solar cells (QDSSCs). A polysulphide (S-x(2-))-based electrolyte and CuxS counter electrode were used for cell fabrication and testing. An interesting improvement in the performance of the device by imposing nanorods as a scattering layer on a particle layer has been observed. As a consequence, a maximum conversion efficiency of 1.06% with an open-circuit voltage (V-OC) of 0.67 V was achieved for the ZnO nanorod/nanoparticle assembled structure. The introduction of ZnO nanorods over the nanoparticle led to a significant enhancement of the overall efficiency compared to the corresponding bare nanoparticles