Synthesis and magnetic properties of size-controlled FeNi alloy nanoparticles attached on multiwalled carbon nanotubes

FeNi alloy nanoparticles with controllable sizes were attached on the multiwalled carbon nanotubes by adjusting the atomic ratio of metal to carbon in the mixed solution of nitrate with Fe:Ni=1:1 (atomic ratio) via wet chemistry. Transmission electron microscopy (TEM) and high-resolution TEM indicated that quasi-spherical FeNi alloy nanoparticles with sizes in the range 12-25 nm are obtained. FeNi alloy composed of major face center cubic (fcc) and minor body center cubic (bcc) structures, which is proved by the X-ray powder diffraction (XRD). Magnetization measured by vibrating sample magnetometer demonstrated that both the coercive force and saturation magnetizations decrease as the size of the FeNi alloy nanoparticles decreased. The chemical method is promising for fabricating FeNi alloy nanoparticles attached on carbon nanotubes for magnetic storage and ultra high-density magnetic recording applications.     

2D siloxene supported NiO/Co3O4 electrocatalyst for the stable and efficient hydrogen evolution reaction

The activity of NiO/Co₃O₄ for the hydrogen evolution reaction (HER) during water splitting was increased by depositing these metal oxides on siloxene multi-sheets. The improvement in active sites due to siloxene was used to increase the catalytic activity. The hierarchical structure of the composite with the synergistic effect of metal oxides helped enhance the catalytic activity to show a low overpotential of 110 mV at 10 mA/cm² in 1 M KOH and stability at 10 mA/cm² over 20 h without an obvious change in voltage. The as-prepared catalyst can be a promising electrocatalyst for the HER owing to the low cost of transition metal oxides, the abundance of silicon on Earth, and the simplicity of the synthesis process.     

Synthesis and microwave absorbing properties of FeNi alloy incorporated ordered mesoporous carbon–silica nanocomposite

Ordered mesoporous carbon–silica/FeNi nanocomposite were prepared by a sol–gel method and following sintering process. The electromagnetic parameters were measured in the 0.5–18 GHz range. Compared with ordered mesoporous carbon–silica composite, the permittivity of ordered mesoporous carbon–silica/FeNi nanocomposite decreases, while the permeability almost remains unchanged. The optimal reflection loss of ordered mesoporous carbon–silica/FeNi nanocomposite can reach ?45.6 dB at 11.1 GHz for a layer thickness of 3.0 mm. The enhanced microwave absorption of the mesoporous carbon–silica/FeNi nanocomposite is due to better balance between the complex permittivity and permeability, geometrical effect, as well as multiple reflections by the ordered mesoporous structure.     

NiWO3 Nanoparticles Grown on Graphitic Carbon Nitride (g‐C3N4) Supported Toray Carbon as an Efficient Bifunctional Electrocatalyst for Oxygen and Hydrogen Evolution Reactions

Catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are at the heart of water oxidation reactions. Despite continuous efforts, the development of OER/HER electrocatalysts with high activity at low cost remains a big challenge. Herein, a composite material consisting of TC@WO₃@g‐C₃N₄@Ni‐NiO complex matrix as a bifunctional electrocatalyst for the OER and HER is described. Though the catalyst has modest activity for HER, it exhibits high OER activity thereby making it a better nonprecious electrocatalyst for both OER and HER and is further improved by g‐C₃N₄. The catalytic activity arises from the synergetic effects between WO₃, Ni‐NiO, and g‐C₃N₄. A Ni‐NiO alloy and WO₃ nanoparticles decorated on the g‐C₃N₄ surface supported toray carbon (TC) matrix (TC@WO₃@g‐C₃N₄@Ni‐NiO) by a facile route that show an excellent and durable bifunctional catalytic activity for OER and HER in the alkaline medium are developed. This carbon nitride with binary metal/metal‐oxide matrix supported with TC exhibit an overpotential of 0.385 and 0.535 V versus RHE at a current density of 10 mA cm^?2 (Tafel slopes of 0.057 and 0.246 V dec^?1 for OER and HER, respectively), in 0.1 m NaOH . The catalyst is tested in water electrolysis for 17 h.     

A Facile Strategy to Synthesize Cobalt‐Based Self‐Supported Material for Electrocatalytic Water Splitting

Designing and developing active, robust, and noble‐metal‐free catalysts with superior stability for electrocatalytic water splitting is of critical importance but remains a grand challenge. Here, a facile strategy is provided to synthesize a series of Co‐based self‐supported electrode materials by combining electrospinning and chemical vapor deposition (CVD) technologies. The Co, Co₃O₄, Co₉S₈ nanoparticles (NPs) are formed in situ simultaneously with the formation of carbon nanofibers (CNFs) during the CVD process, respectively. The Co‐based NPs are uniformly distributed through the CNFs and they can be directly used as the electrode materials for hydrogen evolution reaction (HER) in acid and oxygen evolution reaction (OER) in alkaline. The Co₉S₈/CNFs membrane exhibits the best HER activity with overpotential of 165 mV at j = 10 mA cm^?2 and Tafel slope of 83 mV dec^?1 and OER activity with overpotential of 230 mV at j = 10 mA cm^?2 and Tafel slope of 72 mV dec^?1. The onion‐like graphitic layers formed around the NPs not only improve the electrical conductivity of the electrode but also prevent the separation of the NPs from the carbon matrix as well as the aggregation.     

The effect of vacuum annealing on the remediation abilities of iron and iron−nickel nanoparticles

Zero-valent iron nanoparticles are effective remediators of uranium from solution. It is postulated that the improved core crystallinity and the migration of impurity phases to the nanoparticle surfaces induced by annealing may improve their corrosion resistance and reactive lifespan. The ability of annealed and non-annealed Fe and FeNi nanoparticles to remediate a U-contaminated effluent from AWE, Aldermaston was investigated. Nanoparticles (of diameter typically between 0 and 100 nm) were introduced to the effluent and allowed to react for 7 days during which the liquid and nanoparticulate solids were periodically sampled. In all the systems, the maximum U-uptake occurred within 1 h of introduction, with variable efficiency. The Fe nanoparticles removed 98% of the total U from solution, resulting in a final U-concentration of <4 μg/L. A rapid release of Fe into solution was recorded early in the reaction period: attributed to limited partial dissolution of the nanoparticles. Annealing the Fe nanoparticles did not affect their efficiency but the dissolution of Fe was significantly reduced and X-ray Photoelectron Spectroscopy indicated slower progressive oxidation. The performance of the FeNi nanoparticles was significantly improved by annealing, with U-uptake increasing from 50 to 94%. Although the dissolution of Ni was completely inhibited by annealing, the Fe dissolution increased compared to that observed for the non-annealed FeNi nanoparticles, in contrast to behaviour exhibited by Fe-annealed nanoparticles. In all the systems, U was reduced to U(IV) and retained on the surfaces of the nanoparticulate solids for up to 48 h; the U-stability was not affected by annealing the Fe or the FeNi nanoparticles before use.     

Three-dimensional flower-like NiS2/MoS2 assembly of randomly oriented nanoplate for enhanced hydrogen evolution reaction

The continually worsening energy crisis has stimulated research into energy conversion technology to produce pure hydrogen, H₂. Transition metal-based compounds have attracted great attention as electrocatalysts for hydrogen evolution reaction (HER) as alternatives to commercial, high-cost, and scarce noble metal-based catalysts. In this work, a 3D flower-like NiS₂/MoS₂ is synthesized with the advantages of a three-dimensional (3D) morphology and the compositing of different metal compounds, thus leading to enhanced electrocatalytic performance. The structure of 3D flower-like NiS₂/MoS₂ augments the specific surface areas resulting from nanoplate assemblies as well as the heterointerface ascribed to two different phases of NiS₂ and MoS₂. These characteristics are confirmed by electrocatalytic measurements of the lower overpotential of 165 mV at 10 mA/cm² with high charge transfer ability, thus demonstrating the structure's potential for advanced electrocatalysts for the HER.     

Mass and charge transport in hierarchically organized storage materials. Example: Porous active materials with nanocoated walls of pores

To enhance the kinetics of poorly conducting cathode materials for Li batteries, the authors have proposed a number of strategies based on crushing the active material into nanopowder and embedding the powder into a carbon-based web or coating. Using the well-elaborated example of LiFePO4, we demonstrate that the same goal can be achieved with a different approach where the active material remains in a form of large (1–20 μm) single crystals. Instead of crushing the material, we make it porous—with average pore size around 50 nm and pore surface area of 25 m²/g. The walls of the pores (but also the outer surfaces of crystals) are covered with ca. 1-nm-thick carbon film. Most surprisingly, such a unique nanoarchitecture can be prepared using a simple sol–gel based procedure including a single heat treatment. The crucial part is the selection of appropriate carbon precursor. For example, citric acid decomposes quite vigorously into gases and solid carbon at temperatures up to ca. 450 °C. This range matches exactly the first solidification of LiFePO₄. Thus, the evolving gases can create an interconnected web of pores while the solid parts (carbon) are deposited simultaneously on the walls of pores. We further show that a carbon content of less than 3% is already sufficient for surpassing the percolation threshold with respect to surface conductivity of carbon. Using more carbon can decrease the rate performance so a fine balance is required in this respect. Most importantly, carbonization at a temperature of slightly less than 700 °C is sufficient to achieve a composite conductivity of the order of 10^− 2 S cm^− 2—more than sufficient for good cathode kinetics. In the end, we show new evidence that the phase that is responsible for high conductivity of LiFePO₄–C composites is indeed the carbon phase.     

Sonochemical approach for synthesis of zinc oxide-poly methyl methacrylate hybrid nanoparticles and its application in corrosion inhibition

Hybrid nanoparticles (HNPs) with zinc oxide and polymethyl metha acrylate (inorganic/ polymer) were synthesized through the exploitation of ultrasound approach. The synthesized HNPs were further characterized employing transmission electron microscopy and x-ray diffraction. ZnO-PMMA based HNPs exhibit excellent protection properties to mild steel from corrosion when gets exposed to acidic condition. Electrochemical impendence spectroscopy (EIS) analysis was accomplished to evaluate the corrosion inhibition performance of MS panel coated with 2 wt% or 4 wt% of HNPs and its comparison with bare panel and that of loaded with only standard epoxy coating., Tafel plot and Nyquist plot analysis depicted that the corrosion current density (I_corr) decreases from 16.7 A/m² for bare material to 0.103 A/m² for 4% coating of HNPs. Applied potential (E_corr) values shifted from negative to positive side. These results were further supported by qualitative analysis. The images taken over a period of time indicated the increase in lifetime of MS panel from 2 to 3 days for bare panel to 10 days for HNPs coated panel, showing that ZnO-PMMA HNPs have potential application in metal protection from corrosion by forming a passive layer.     

Magnetic and electromagnetic absorption properties of FeNi alloy nanoparticles supported by reduced graphene oxide

FeNi alloy nanoparticles (NPs) supported by reduced graphene oxide (RGO) (FeNi/RGO nanocomposites) were successfully synthesized through in‐situ reduction. Large amounts of sphere‐like FeNi NPs are uniformly deposited on the RGO nanosheets. The magnetic hysteresis measurement reveals the ferromagnetic behavior of the nanocomposites at room temperature. According to the electromagnetic (EM) characteristics, the FeNi/RGO nanocomposites show outstanding EM absorption properties in the 2–18 GHz range, as evidenced by the wide effective absorption bandwidth (up to 3.3 GHz, with reflection loss R_L < –10 dB) and a minimal R_L (–32 dB) at 12.4 GHz with a thickness of 1.5 mm. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Genesis of supported carbon-coated Co nanoparticles with controlled magnetic properties,prepared by decomposition of chelate complexes

Following procedures formerly developed for the preparation of supported heterogeneous catalysts, carbon-coated cobalt nanoparticles dispersed on porous alumina have been prepared by impregnation of γ-Al₂O₃ with (NH₄)₂[Co(EDTA)] and thermal decomposition in inert atmosphere. Below 350 °C, Co(II) ions are complexed in a hexa-coordinated way by the EDTA ligand. The thermal treatment at 400–900 °C leads to the EDTA ligand decomposition and recovering of the support porosity, initially clogged by the impregnated salt. According to X-ray absorption spectroscopy, and due to in situ redox reactions between the organic ligand and Co(II), both oxidic and metallic cobalt phases are formed. Characterisation by transmission electron microscopy, X-ray diffraction and magnetic measurements reveals that an increase in the treatment temperature leads to an increase of the degree of cobalt reduction as well as to a growth of the cobalt metal particles. As a consequence, the samples prepared at 400–700 °C exhibit superparamagnetism and a saturation magnetisation of 1.7–6.5 emu g⁻¹ at room temperature, whilst the sample prepared at 900 °C has a weak coercivity (0.1 kOe) and a saturation magnetisation of 12 emu g⁻¹. Metal particles are homogeneously dispersed on the support and appear to be protected by carbon; its elimination by a heating in H₂ at 400 °C is demonstrated to cause sintering of the metal particles. The route investigated here can be of interest for obtaining porous magnetic adsorbents or carriers with high magnetic moments and low coercivities, in which the magnetic nanoparticles are protected from chemical aggression and sintering by their coating.     

Mid-infrared laser absorption spectrometers based upon all-diode laser difference frequency generation and a room temperature quantum cascade laser for the detection of CO, N2O and NO

We describe the performance of two mid-infrared laser spectrometers for carbon monoxide, nitrous oxide and nitric oxide detection. The first spectrometer for CO and N₂O detection around 2203 cm^-1 is based upon all-diode laser difference frequency generation (DFG) in a quasi-phase matched periodically-poled lithium niobate (PPLN) crystal using two continuous-wave room-temperature distributed feedback diode lasers at 859 and 1059 nm. We also report on the performance of a mid-infrared spectrometer for NO detection at ∼ 1900 cm^-1 based upon a thermoelectrically-cooled continuous-wave distributed feedback quantum cascade laser (QCL). Both spectrometers had a single-pass optical cell and a thermoelectrically cooled HgCdZnTe photovoltaic detector. Typical minimum detection limits of 2.8 ppmv for CO, 0.6 ppmv for N₂O and 2.7 ppmv for NO have been demonstrated for a 100 averaged spectra acquired within 1.25 s and a cell base length of 21 cm at ∼ 100 Torr. Noise-equivalent absorptions of 10^-5 and 10^-4 Hz^-1/2 are typically demonstrated for the QCL and the DFG based spectrometers, respectively. PACS  42.55.Px; 42.62.Fi; 42.65.-k; 42.72.Ai; 42.68.Ca     

Electrochemical synthesis of flake-like Fe/MWCNTs nanocomposite for hydrogen evolution reaction: Effect of the CNTs on dendrite growth of iron and its electrocatalytic activity

Fe/multi-walled carbon nanotubes (Fe/MWCNTs) nanocomposite was produced using electrochemical techniques onto platinum substrate. Linear sweep voltammetry (LSV) analysis revealed that deposition rate of the nanocomposite is higher than of the pure Fe deposition. X-ray diffraction (XRD) was used to confirm nanocomposite formation. Scanning electron microscopy (SEM) images showed dendrite growth of the pure Fe onto a flake-like (thickness of about 90 nm) structure with a filamentous carbon network. The morphology of the nanocomposite consisted of only uniform nanoflakes with thickness of about 50 nm. Adsorption of the MWCNTs on the flakes led to decrease the nucleation energy and avoided formation of the prisms that are essential for dendrite growth. The nanocomposite showed superior catalytic activities for hydrogen evolution reaction (HER), twice of the pure Fe when the overpotential of −1.3 V was applied. The overpotential–time results indicated that HER activity of thin films decreased during the long-term working. But, nanocomposite was more stable than the pure Fe.     

Performance assessment of Cu2SnS3 (CTS) based thin film solar cells by AMPS-1D

A relative performance assessment of copper tin sulfide (CTS) thin film solar cells with different phases such as, cubic, tetragonal, and orthorhombic as an absorber layer has been carried out by AMPS-1D simulation software. Based on the proposed device architecture, the effects of thickness and carrier concentration for the absorber layer as well as the back metal contact with various work function are studied in order to improve the performance of CTS solar cell. It is found that 10¹⁸ cm⁻³ and 2500–3000 nm are optimum values for carrier concentration and thickness for all the investigated CTS absorber layer phases, respectively. On the other hand, back contact metal work function of 5.28 eV, 5.67 eV and 5.71 eV are identified to be the optimal values for cubic, tetragonal, and orthorhombic phases, respectively. We have analyzed in detail the output performance of CTS thin film solar cell with respect to its fabrication, which can serve a constructive research pathway for the thin film photovoltaic industry.     

Utilization of surface plasmon resonance of Au/Pt nanoparticles for highly photosensitive ZnO nanorods network based plasmon field effect transistor

Hydrothermally processed highly photosensitive ZnO nanorods based plasmon field effect transistors (PFETs) have been demonstrated utilizing the surface plasmon resonance coupling of Au and Pt nanoparticles at Au/Pt and ZnO interface. A significantly enhanced photocurrent was observed due to the plasmonic effect of the metal nanoparticles (NPs). The Pt coated PFETs showed I_on/I_off ratio more than 3 × 10⁴ under the dark condition, with field-effect mobility of 26 cm² V⁻¹ s⁻¹ and threshold voltage of −2.7 V. Moreover, under the illumination of UV light (λ = 350 nm) the PFET revealed photocurrent gain of 10⁵ under off-state (−5 V) of operation. Additionally, the electrical performance of PFETs was investigated in detail on the basis of charge transfer at metal/ZnO interface. The ZnO nanorods growth temperature was preserved at 110 °C which allowed a low temperature, economical and simple method to develop highly photosensitive ZnO nanorods network based PFETs for large scale production.     

Performances of different metals in optical fibre-based surface plasmon resonance sensor

The capability of various metals used in optical fibre-based surface plasmon resonance (SPR) sensing is studied theoretically. Four metals, gold (Au), silver (Ag), copper (Cu) and aluminium (Al) are considered for the present study. The performance of the optical fibre-based SPR sensor with four different metals is obtained numerically and compared in detail. The performance of optical fibre-based SPR sensor has been analysed in terms of sensitivity, signal-to-noise (SNR) ratio and quality parameter. It is found that the performance of optical fibre-based SPR sensor with Au metal is better than that of the other three metals. The sensitivity of the optical fibre-based SPR sensor with 50 nm thick and 10 mm long Au metal film of exposed sensing region is 2.373 μm/RIU with good linearity, SNR is 0.724 and quality parameter is 48.281 RIU^− 1. The thickness of the metal film and the length of the exposed sensing region of the optical fibre-based SPR sensor for each metal are also optimized.     

FeNi Layered Double‐Hydroxide Nanosheets on a 3D Carbon Network as an Efficient Electrocatalyst for the Oxygen Evolution Reaction

An efficient electrocatalyst for oxygen evolution has been prepared via the deposition of iron–nickel layered double‐hydroxide (FeNi‐LDH) nanosheets on 3D carbon network as the building scaffold in a one‐step hydrothermal process. It is found that upon the assembling of FeNi‐LDH nanosheets with graphene into the 3D cross‐linked hybrid, the FeNi‐LDH/graphene hybrid features a well‐improved catalytic activity towards the oxygen evolution reaction (OER) with a good stability during the long‐term cycling experiment. Moreover, the hybrid catalyst is also active in the oxygen reduction reaction (ORR), qualifying it as a new type of bifunctional catalyst that can work in metal–air batteries.     

Growth of multiwalled carbon nanotubes from acetylene over in situ formed Co nanoparticles on MgO support

The performance of Co catalysts supported on MgO at different Co loading (10%-75%) for the formation of carbon nanotubes through acetylene decomposition at 600 ^°C with H₂/C₂H₂ mixture for 1 h is investigated. The yield of MWNTs increases with an increase in Co loading (up to 50%). Starting from 1 g of catalyst precursor, about 8 g of MWNTs was obtained. The XRD patterns of catalyst precursor indicate the presence of cobalt in oxidic phase that eventually transformed into the catalytically active Co nanoparticles (12-18 nm) under the influence of acetylene and was responsible for the growth of coiled-like multi-walled CNTs as revealed by SEM and HRTEM images. It is suggested that bending in coil shaped MWNTs has the potential for functionalization for its biomedical applications.     

Ultrahigh Electron Emissive Carbon Nanotubes with Nano-sized RuO2 Particles Deposition

Multi-wall carbon nanotubes (MWNTs) have a great commercial potential as electron field emitters, but suffer from fundamental problems such as stability and brightness. By depositing the MWNTs with nano-sized ruthenium dioxide (RuO₂) particles, a new high performance emitter has been developed. When compared to MWNTs, the MWNTs impregnated with 1–2 nm sized RuO₂ have superior and more efficient electrical characteristics. MWNTs supported by a silicon substrate showed a reduction in the onset voltage from 5.4 to 4 V/μm after RuO₂ impregnation. The long-term stability of the impregnated MWNTs is also demonstrated with only a 20% increase in applied voltage required after 700 h operation at 40 mA/cm².     

Supercapacitive electrochemical performance of graphene-containing carbon aerogel prepared using polyethyleneimine-modified graphene oxide

Graphene-containing carbon aerogel was prepared by a sol–gel polymerization of resorcinol-formaldehyde (RF) method using polyethyleneimine (PEI)-modified chemically exfoliated grapheme oxide, and its electrochemical performance as an electrode for supercapacitor was examined. The effect of PEI in the preparation of RFGO (resorcinol-formaldehyde and graphene oxide) solution on the physicochemical and electrochemical properties of graphene-containing carbon aerogel (CAPG) was investigated. For comparison, graphene-containing carbon aerogel was prepared using PEI-free graphene oxide (CAG). Graphene-free carbon aerogel (CA) was also prepared. CAPG showed the highest BET surface area (792 m²/g) and the largest pore volume (1.64 cm³/g) with well-developed porous structure. Various electrochemical measurements revealed that CAPG showed high specific capacitance (205 F/g), low equivalent series resistance (0.55 Ω), and superior capacitive behavior. The PEI-modified graphene oxide played an important role in enhancing physicochemical properties and supercapacitive electrochemical performance of CAPG.