Ni Nanomaterials Research Articles

Thermal Conductivity Enhancing Mechanisms of Nickel-Water Nanofluids

Nowadays, nanofluids proved as a capable choice to the traditional heat transfer agents. In this study, Nickel (Ni)-distilled water (DW) nanofluids consisting sodium dodecyl benzene sulfonate (SDBS) dispersant at 0.1 vol.% and 0.3 vol.% are coined by two-step technique. The Ni nanomaterials are characterized by energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR). The temperature and nanomaterial volume fraction dependent thermal conductivity is accurately estimated through 3ω technique within the range of the temperature of 30°C-60°C. The experimental results show that the thermal conductivity improves with increasing Ni concentration and temperature. Further, this study discusses the factors affecting the thermal conductivity of Ni nanomaterial dispersed DW and possible thermal conductivity enhancing mechanisms of different volume fractions of Ni-DW nanofluids.

Simple fabrication of Ni nanodots decorated Ni/Ketjen black composite for sulfur host in lithium‐sulfur battery

Ni nanomaterials exhibit excellent adsorption and catalytic ability in the redox reaction of Li-S batteries. Hence, Ni nanodots are embedded in the micropores and mesopores of commercial Ketjen black (KB) to obtain Ni/KB composite nanomaterials by an in situ preparation method with low cost and high yield. The prepared Ni nanodots with 5 to 30 nm diameter act as the active sites in KB matrix and enhance the intrinsic activity; they can not only adsorb lithium polysulfides (LiPSs) by the Ni-S bond but also promote the conversion rate of LiPSs. Consequently, with 3.1 mg cm−2 S loading on positive electrode, the initial discharge capacity of Ni/KB/S electrode at 0.05 C reaches 1253 mAh g−1 and the initial discharge capacity at 0.5 C reaches 818.4 mAh g−1, with the stable cycle exceeding over 500 cycles.

Nickel Based Electrospun Materials with Tuned Morphology and Composition.

Nickel is set to play a crucial role to substitute the less-abundant platinum in clean electrochemical energy conversion and storage devices and catalysis. The controlled design of Ni nanomaterials is essential to fine-tune their properties to match these applications. A systematic study of electrospinning and thermal post-treatment parameters has been performed to synthesize Ni materials and tune their morphology (fibers, ribbons, and sponge-like structures) and composition (metallic Ni, NiO, Ni/C, Ni3N and their combinations). The obtained Ni-based spun materials have been characterized by scanning and transmission electron microscopy, X-ray diffraction and thermogravimetric analysis. The possibility of upscaling and the versatility of electrospinning open the way to large-scale production of Ni nanostructures, as well as bi- and multi-metal systems for widened applications.

Controlled growth of Cu–Ni nanowires and nanospheres for enhanced microwave absorption properties

Copper is a good dielectric loss material but has low stability, whereas nickel is a good magnetic loss material and is corrosion resistant but with low conductivity, therefore Cu–Ni hybrid nanostructures have synergistic advantages as microwave absorption (MA) materials. Different Cu/Ni molar ratios of bimetallic nanowires (Cu13@Ni7, Cu5@Ni5 and Cu7@Ni13) and nanospheres (Cu13@Ni7, Cu5@Ni5 and Cu1@Ni3) have been successfully synthesized via facile reduction of hydrazine under similar reaction conditions, and the morphology can be easily tuned by varying the feed ratio or the complexing agent. Apart from the concentrations of Cu2+ and Ni2+, the reduction parameters are similar for all samples to confirm the effects of the Cu/Ni molar ratio and morphology on MA properties. Ni is incorporated into the Cu–Ni nanomaterials as a shell over the Cu core at low temperature, as proved by XRD, SEM, TEM and XPS. Through the complex relative permittivity and permeability, reflection loss was evaluated, which revealed that the MA capacity greatly depended on the Cu/Ni molar ratio and morphology. For Cu@Ni nanowires, as the molar ratio of Ni shell increased the MA properties decreased accordingly. However, for Cu@Ni nanospheres, the opposite trend was found, that is, as the molar ratio of the Ni shell increased the MA properties increased.

Effect of Ni morphology on removal of pentachlorophenol with Fe/Ni nanomaterials

Chlorinated phenols are a kind of environmental priority pollutant that attract much attention. Nanosized Fe and Fe/Ni materials are considered as promising options for chlorinated phenol removal. The effect of Ni morphology on the removal of pentachlorophenol (PCP) with Fe/Ni nanomaterials was investigated in this study. Iron nanoparticles and nickel nanomaterials with different shapes were synthesized using a chemical reduction method and wet chemical techniques, respectively. The concentrations of PCP and chloride in solutions were measured with and without Ni present. The intermediates of PCP were also analyzed. The results showed that the dechlorination of PCP was promoted by Ni nanomaterials, among which the tubular porous Ni nanomaterials expressed the most promotion, then those with net shape and nanochains. However, the tubular porous Ni nanomaterials inhibited the removal of PCP, and the other two expressed a certain promotion. In the Fe/Ni system, Fe nanoparticles transformed into magnetite (Fe3O4) and/or maghemite (Fe2O3), and Ni nanomaterials were still pure Ni after reaction. The introduction of Ni nanomaterials would improve dechlorination of PCP, but the removal of PCP might be inhibited or improved as the morphology of Ni changed.

Magnetic Properties of Nanostructured Co and Ni Synthesized by Modified NaBH4 Reduction Route

Nanomaterials based on Co and Ni are technologically important because of their potential technological applications in recording media, catalysis, drug delivery systems, and so on. Recent research interests lie on the synthesis of Co and Ni nanomaterials by chemical synthesis, characterizations and studying for their interesting magnetic properties. In this investigation, we have focused on the synthesis of cobalt and nickel nanoparticles (NPs) in aqueous medium at ambient conditions by sodium borohydride reduction route. We have successfully stabilized the nanospheres comprising of Co and Ni by using polyethylene glycol (PEG) as capping agent. The Co and Ni nanomaterials were exhaustively characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and magnetic measurements. The phase purity and crystallite sizes were ascertained by using powder XRD method. Co and Ni NPs crystallize in face centered cubic (fcc) structure with lattice parameters (a) equal to 3.54 Å and 3.52 Å, respectively. The XRD lines were broad and indicate the fine particle nature of the materials. The estimated crystallite sizes were found to be 42 and 29 nm for Co and Ni, respectively. SEM micrograph studies show the particle sizes to be 80 and 70 nm, whereas TEM studies confirm the sizes to be 47 and 65 nm for Co and Ni, respectively. The electron micrograph studies indicate the appearance of agglomerates of the nanoparticles consisting of several crystallites. The specific magnetization versus field characteristics of Co and Ni nanoparticles shows the signature of the size and surface effects. The values of saturation magnetizations are found to be 122 and 47 emu/g, whereas the coercivity values are 111 Oe and 84 Oe for Co and Ni, respectively. In summary, we have synthesized high moment Co and Ni nanostructured materials with reduced coercivities, which may be useful for soft magnetic applications.

In Situ Observation of Cu–Ni Alloy Nanoparticle Formation by X‐Ray Diffraction, X‐Ray Absorption Spectroscopy, and Transmission Electron Microscopy: Influence of Cu/Ni Ratio

AbstractSilica‐supported, bimetallic Cu–Ni nanomaterials were prepared with different ratios of Cu to Ni by incipient wetness impregnation without a specific calcination step before reduction. Different in situ characterization techniques, in particular transmission electron microscopy (TEM), X‐ray diffraction (XRD), and X‐ray absorption spectroscopy (XAS), were applied to follow the reduction and alloying process of Cu–Ni nanoparticles on silica. In situ reduction of Cu–Ni samples with structural characterization by combined synchrotron XRD and XAS reveals a strong interaction between Cu and Ni species, which results in improved reducibility of the Ni species compared with monometallic Ni. At high Ni concentrations silica‐supported Cu–Ni alloys form a homogeneous solid solution of Cu and Ni, whereas at lower Ni contents Cu and Ni are partly segregated and form metallic Cu and Cu–Ni alloy phases. Under the same reduction conditions, the particle sizes of reduced Cu–Ni alloys decrease with increasing Ni content. Estimates of the metal surface area from sulfur chemisorption and from the XRD particle size generally agree well on the trend across the composition range, but show some disparity in terms of the absolute magnitude of the metal area. This work provides practical synthesis guidelines towards preparation of Cu–Ni alloy nanomaterials with different Cu/Ni ratios, and insight into the application of different in situ techniques for characterization of the alloy formation.

TiO2/Ni nanocomposites: Biocompatible and recyclable magnetic photocatalysts

An effective, recyclable, and biocompatible photocatalyst, TiO 2 /Ni composite, has been successfully synthesized by coating TiO 2 films onto one-dimensional (1D) Ni nanostructures. The used 1D Ni nanomaterials have urchin-like structures, which makes them easily be coated by TiO 2 nanocrystals. The TiO 2 /Ni nanocomposites have the functions of both TiO 2 and Ni. The photocatalytic and biocompatibility studies show that the composite has outstanding photocatalytic activities for the decomposition of organic pollutants and great biocompatibility. The existence of magnetic Ni nanostructure makes the composite also has good magnetic properties, which enable the photocatalysts to be easily separated and recycle-used. ► TiO 2 /Ni composite was easily synthesized using urchin-like Ni structures as template. ► TiO 2 /Ni composite has the functions of both TiO 2 and Ni. ►The composite remains great photocatalytic activity and biocompatibility of TiO 2 . ►The photocatalysts can be easily separated and recycle-used.

Synthesis of α-Ni(OH)2 with hydrotalcite-like structure: Precursor for the formation of NiO and Ni nanomaterials with fibrous shapes

α-Ni(OH)2 with hydrotalcite-like structure was prepared by precipitation of nickel acetate and sodium carbonate aqueous solution with the mediation of ethylene glycol at 393 K. Thermal calcination of this nickel hydroxide precursor at 573–1073 K resulted in the formation of fibrous nickel oxides with diameter of 4–8 nm and length of several hundreds of nanometers. Further reduction of these NiO samples with hydrogen at 773 K led to the formation of metallic Ni with fibrous-like morphology. Most promisingly, these novel nanostructured Ni materials showed much higher catalytic activities not only for the decomposition of methane to hydrogen and carbon nanofibers, but also for the hydrogenation reactions of unsaturated organic compounds.