Metal Precursor Concentration Research Articles

Ni and Co doped yolk-shell type Fe2O3 hollow microspheres as anode materials for lithium-ion batteries

Ni and Co doped Fe2O3 hollow microspheres of yolk-shell type were designed and synthesized by using resin (RF-COOH) microspheres as hard template and subsequent calcination. Specific morphologies (walnut-like, jingle-bell-like and ball-like) and compositions of Fe2O3 with different amounts of Ni and Co doping were obtained by tuning metal precursor concentration to optimize their performance in lithium-ion battery application. When Ni and Co doped Fe2O3 hollow microspheres were used as anode materials for lithium-ion batteries, jingle-bell-like and ball-like morphologies showed better electrochemical performance with specific capacities of 415.7 and 414.1 mA h/g, respectively up to 200 cycles due to their stable construction with hollow cavity, porous shell and Ni and Co dopants. However, the specific capacity of Ni and Co doped Fe2O3@TiO2 hollow microspheres increased to 562 mA h/g. This work showed a new avenue for designing and fabricating yolk-shell hollow structures with specific morphologies and compositions in order to optimize their specific capacity for use in lithium-ion batteries.

Controllable synthesis of Co3O4 nanocrystals as efficient catalysts for oxygen reduction reaction

The electrochemical oxygen reduction reaction (ORR) has received great attention due to its importance in fuel cells and metal–air batteries. Here, we present a simple approach to prepare non-noble metal catalyst-Co3O4 nanocrystals (NCs). The particle size and shape were simply controlled by different types and concentrations of metal precursor. Furthermore, different sizes and shapes of Co3O4 NCs are explored as electrocatalysts for ORR, and it has been observed that particles with a similar shape, and smaller particle size led to greater catalytic current densities because of the greater surface area. For particles with a comparable size, the shape or crystalline structure governed the activity of the electrocatalytic reactions. Most importantly, the 9 nm-Co3O4 were demonstrated to act as low-cost catalysts for the ORR with a similar performance to that of Pt catalysts.

Efficient and Environmentally Friendly Microwave-Assisted Synthesis of Catalytically Active Magnetic Metallic Ni Nanoparticles

Pure magnetic metallic nickel was synthesized by a simple and fast microwave-assisted method using a monomode microwave reactor. Nickel chloride was employed as metal precursor, while an environmental-friendly mixture of ethylene glycol and ethanol was simultaneously used as solvent and reducing agent. The parameters combination, for the occurrence of the reaction, of the mixture molar fraction and the metal precursor concentration was developed. The influence of the temperature and the time of the irradiation was investigated. The best performance (71% yield) was achieved at 250°C in 5 minutes of microwave irradiation. The phase and the morphology of the metal were analyzed by X-ray diffraction (XRD), scanning emission microscopy (SEM) and transmission electron microscopy (TEM) while the surface area was determined by nitrogen physisorption. The material exhibited a strong magnetic behavior. The metallic Nickel showed high catalytic activity for the hydrogenolysis of benzyl phenyl ether, a lignin model c...

Facile synthesis of iron-ruthenium bimetallic oxide nanoparticles on carbon nanotube composites by liquid phase plasma method for supercapacitor

Iron-ruthenium bimetallic oxide nanoparticles were precipitated on carbon nanotubes by liquid-phase plasma method. We also evaluated the physicochemical and electrochemical properties of prepared composite for supercapacitor electrode. Polycrystalline about 10 to 25 nm-sized bimetallic nanoparticles were evenly precipitated on the carbon nanotube (CNT) and consisted of Fe3+ and Ru4+. Bimetallic oxide nanoparticles’ composition depended on the ratio of the metal precursor concentration and standard reduction potential. The C-V area and specific capacitance of iron-ruthenium oxide nanoparticle/carbon nanotube (IRCNT) composite electrodes was higher than that of untreated CNT electrode, and increased with increasing ruthenium content. The cycling stability of IRCNT composite electrode was higher than untreated CNT electrode, especially iron element was more stable.

On Metal Segregation of Bimetallic Nanocatalysts Prepared by a One-Pot Method in Microemulsions

A comparative study on different bimetallic nanocatalysts prepared from microemulsions using a one-pot method has been carried out. The analysis of experimental observations, complemented by simulation studies, provides detailed insight into the factors affecting nanoparticle architecture: (1) The metal segregation in a bimetallic nanocatalysts is the result of the combination of three main kinetic parameters: the reduction rate of metal precursors (related to reduction standard potentials), the material intermicellar exchange rate (determined by microemulsion composition), and the metal precursors concentration; (2) A minimum difference between the reduction standard potentials of the two metals of 0.20 V is needed to obtain a core-shell structure. For values ∆ε0 smaller than 0.20 V the obtaining of alloys cannot be avoided, neither by changing the microemulsion nor by increasing metal concentration; (3) As a rule, the higher the film flexibility around the micelles, the higher the degree of mixture in the nanocatalyst; (4) A minimum concentration of metal precursors is required to get a core-shell structure. This minimum concentration depends on the microemulsion flexibility and on the difference in reduction rates.

Comparison of conventional versus microwave heating for polyol synthesis of supported iridium based electrocatalyst for polymer electrolyte membrane water electrolysis

Microwave irradiation heating is a simple and clean technique with many advantages over conventional heating. Microwave irradiation has been used to synthesize numerous organic and inorganic materials; however, it is rarely used to synthesize iridium based electrocatalysts for polymer electrolyte membrane (PEM) water electrolysis. In this work, an electrocatalyst consisting of a complex iridium oxide supported on antimony tin oxide (ATO) was synthesized using a polyol method with two different heating methods: conventional heating and microwave irradiation heating. With microwave heating the primary synthesis step could be completed in 1 min compared to more than 10 h for conventional heating. The morphological and electrochemical properties of the two catalysts were then compared using various characterization techniques. Their BET surface area, particle size/particle size distribution, and elemental compositions were measured using nitrogen physisorption, transmission electron microscopy (TEM), and scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDX). Their electrochemical characteristics were studied using linear sweep and cyclic voltammetry in a three-electrode cell. Additionally, using the microwave irradiation heating method, the effect of various operating parameters such as pH, metal precursor concentration, temperature and the type of polyol on the morphology of the catalyst was studied. The results showed that the catalysts synthesized with both of the heating techniques have comparable physical and electrochemical properties. However, the clusters of iridium species in the conventional heating method were slightly smaller compared to those in the microwave irradiation heating method (2.30 ± 0.04 nm compared to 3.00 ± 0.03 nm).Among the operating parameters tested, the pH of the synthesis solution and the type of polyol were two factors to influence the surface area of the iridium based species the most, each resulted in an increase of approximately 12%.

Methods, Mechanism, and Applications of Photodeposition in Photocatalysis: A Review.

In this review, for a variety of metals and semiconductors, an attempt is made to generalize observations in the literature on the effect of process conditions applied during photodeposition on (i) particle size distributions, (ii) oxidation states of the metals obtained, and (iii) consequences for photocatalytic activities. Process parameters include presence or absence of (organic) sacrificial agents, applied pH, presence or absence of an air/inert atmosphere, metal precursor type and concentration, and temperature. Most intensively reviewed are studies concerning (i) TiO2; (ii) ZnO, focusing on Ag deposition; (iii) WO3, with a strong emphasis on the photodeposition of Pt; and (iv) CdS, again with a focus on deposition of Pt. Furthermore, a detailed overview is given of achievements in structure-directed photodeposition, which could ultimately be employed to obtain highly effective photocatalytic materials. Finally, we provide suggestions for improvements in description of the photodeposition methods applied when included in scientific papers.

Rotating Disk Slurry Au Electrodeposition at Unsupported Carbon Vulcan XC-72 and Ce3+ Impregnation for Ethanol Oxidation in Alkaline Media

A robust electrodeposition method consisting of the rotating disk slurry electrode (RoDSE) technique to obtain Au nanoparticles highly dispersed on a conductive carbonaceous support, i.e., Vulcan XC-72R, for ethanol electrooxidation reaction in alkaline media was developed. Ceria was used as a cocatalyst using a Ce(III)-EDTA impregnation method in order to enhance the catalytic activity and improve the catalyst’s overall stability. The RoDSE method used to obtain highly dispersed Au nanoparticles does not require the use of a reducing agent or stabilizing agent, and the noble-metal loading was controlled by the addition and tuning of the metal precursor concentration. Inductively coupled plasma and thermogravimetric analysis indicated that the Au loading in the catalyst was 9 %. Particle size and characteristic Au fcc crystal facets were determined by X-ray diffraction. The morphology of the catalyst was also investigated using electron microscopy techniques. In addition, X-ray absorption spectroscopy was used to corroborate the presence and identify the oxidation state of Ce in the system and to observe if there are any electronic interactions within the 8 % Au/CeOx/C system. Cyclic voltammetry of electrodeposited 9 % Au/C and Ce-promoted 8 % Au/C showed a higher catalytic current density for ethanol oxidation when compared with commercially available catalysts (20 % Au/C) of a higher precious metal loading. In addition, we report a higher stability toward the ethanol electrooxidation process, which was corroborated by 1 mV/s linear sweep voltammetry and chronoamperometric studies.

Impact of surface modifications on hydrogen uptake by Fe@f-MWCNTs and Cu@f-MWCNTs at non-cryogenic temperatures

A comprehensive study has been conducted to evaluate the hydrogen uptake capacity of carboxylate functionalized multi-walled carbon nanotubes (f-MWCNTs) after strategic incorporation of Fe and Cu nanoparticles on the surface. Metal decorated multi-walled carbon nanotubes (Fe@f-MWCNTs and Cu@f-MWCNTs) were prepared by refluxing various concentrations of metal precursor and f-MWCNTs in different reaction medium such as water, amine and DMF. The prepared materials were characterized by FT-IR, powder XRD, SEM, TEM and BET analyzer. The adsorption isotherms revealed that the hydrogen storage capacity of Fe@f-MWCNTs and Cu@f-MWCNTs was 0.55 and 0.68 wt%, respectively, at 253 K and 70 bar. Similarly, both compounds showed 0.39 and 0.5 wt% adsorption at 298 K and 70 bar, respectively. The uptake of hydrogen by metal decorated multi-walled carbon nanotubes was remarkably enhanced by a factor of 2 and 5 times that of Pristine MWCNT at 253 K and 298 K, respectively.

Nickel Doped WO3 Nanoneedles Deposited by a Single Step AACVD for Gas Sensing Applications

One-step Aerosol Assisted Chemical Vapour Deposition (AACVD) method was used for the first time to grow WO3 nanoneedles (NNs) decorated with NiO metal nanoparticles (NPs) at lower (380°C) deposition temperature. This co-deposition method is demonstrated to be an effective route to incorporate metal NPs into nanostructured materials. A layer of needle-like tungsten oxide film was deposited directly onto transducer alumina substrates from W(CO)6 and Ni(acac)2 precursors. Moreover, the systematic growth study of WO3 NNs + metal NPs allowed the identification of the parameters required for the formation of nanostructured sensing materials having different metal precursor concentration in a range of 2.5 to 15 mg The results show variations in the sensing properties according to the metal precursor concentration. Improved sensing, to some reducing gases, such as EtOH, H2S and NH3 are observed at 200°C with lower doped tungsten oxide films, whereas higher doped tungsten oxide has shown no response.

Development of polyol method for the synthesis of concentrated colloids of PVP-stabilised Ru nanoparticles

In the current work narrowly distributed and stable Ru nanoparticles (NPs) with mean diameters within 1.7 to 2.8 nm interval were prepared by reduction of RuCl3 with ethylene glycol (EG) as a solvent and a reducing agent as well as polyvinylpyrrolidone (PVP) as a stabiliser in the temperature range from 170°C to 198°C. Besides a typical polyol technique, Ru NPs synthesis using microwaves as well as sodium borohydride reduction at room temperature was applied as an effective alternative approach. The effect of heating conditions, Ru/PVP ratio, reducing agent and metal precursor concentrations on the particle size was studied. Microstructure of Ru NPs was characterised by UV Vis, XPS and HRTEM. Higher PVP/Ru ratios and reduction temperature gave slightly smaller nanoparticles with narrower size distributions, while no clear effect was observed when the initial ruthenium concentration was varied.

Directed Self-Assembly of Diblock Copolymer Thin Films on Prepatterned Metal Nanoarrays.

The sequential layer by layer self-assembly of block copolymer (BCP) nanopatterns is an effective approach to construct 3D nanostructures. Here large-scale highly ordered metal nano-arrays prepared from solvent annealed thin films of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer are used to direct the assembly of the same BCP. The influence of initial loading concentration of metal precursor, the type of metal nanoparticle (gold, platinum, and silver), and the nanoparticle-substrate interaction on the directed assembly behavior of the upper BCP layer have been focused. It is found that the upper BCP film can be completely directed by the gold nanoarray with P2VP domain exclusively located between two adjacent gold nanowires or nanodots, which behaves the same way as on the platinum nanoarray. While the silver nanoarray can be destroyed during the upper BCP self-assembly with the silver nanoparticles assembled into the P2VP domain. Based on the discussions of the surface energy of nanoparticles and the interplay between nanoparticle-substrate interaction and nanoparticle-polymer interaction, it is concluded that the effect of immobilization of nanoparticles on the substrate, together with entropy effect to minimize the energetically unfavorable chain stretching contributes to the most effective alignment between each layer.

Synthesis and characterisations of SnO2 nanorods via low temperature hydrothermal method

In the present study, tin oxide (SnO2) nanorods were successfully synthesized through hydrothermal treatment at a relatively low temperature (180 °C) using various concentrations of metal precursor, SnCl4·5H2O (0.04 M–0.16 M) in a mixed solution of ethanol and water before bringing the pH to 13 by adding 6 M NaOH. The effect of concentration on the morphology and structure of SnO2 were comprehensively studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet−visible spectroscopy (UV−vis) and Fourier Transform Infrared (FTIR). It was found that increasing the concentration of tin precursor from 0.04 M to 0.16 M leads to a complete conversion from nanospheres to nanoplates and finally to nanorods. The SEM results confirmed that SnO2 nanorods are obtained for concentrations up to 0.12 M. At synthesis condition of 0.12 M, SnCl4·5H2O and pH 13, single rutile nanorods with preferential growth in the [002] direction were obtained. It was found that the diameter of nanorods formed at 0.12 M is similar to that of nanoplates formed at 0.08 M (20 nm), which suggests that spear-shaped nanorods might have originated from the primary nanoparticles (the particles grown in lower concentration during hydrothermal treatment). Possible reaction mechanisms are proposed to explain the observed morphologies.

Synthesis of Nickel Nanoparticles using Electron Beam Irradiation

A study on the preparation of nickel oxide nanoparticles using electron beam irradiation is described. Nickel nanoparticles were synthesized with nickel chloride hexahydrate as a metal precursor and different sodium hydroxide concentrations using electron beam irradiation. The effects of sodium hydroxide concentration and electron beam absorbed doses were investigated. The samples were synthesized at different sodium hydroxide concentrations and with absorbed doses of 100 to 500 kGy at room temperature. Synthesized nanoparticles were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) and a vibrating sample magnetometer (VSM). The nanoparticle morphologies seemed to be non-spherical and aggregated. The 1:1 molar ratio of nickel chloride hexahydrate and sodium hydroxide showed a higher purity and saturation magnetization value of 13.0 emu/g. The electron beam absorbed dose was increased with increasing nickel nanoparticle nucleation.

Tip-Directed Synthesis of Multimetallic Nanoparticles.

Alloy nanoparticles are important in many fields, including catalysis, plasmonics, and electronics, due to the chemical and physical properties that arise from the interactions between their components. Typically, alloy nanoparticles are made by solution-based synthesis; however, scanning-probe-based methods offer the ability to make and position such structures on surfaces with nanometer-scale resolution. In particular, scanning probe block copolymer lithography (SPBCL), which combines elements of block copolymer lithography with scanning probe techniques, allows one to synthesize nanoparticles with control over particle diameter in the 2-50 nm range. Thus far, single-element structures have been studied in detail, but, in principle, one could make a wide variety of multicomponent systems by controlling the composition of the polymer ink, polymer feature size, and metal precursor concentrations. Indeed, it is possible to use this approach to synthesize alloy nanoparticles comprised of combinations of Au, Ag, Pd, Ni, Co, and Pt. Here, such structures have been made with diameters deliberately tailored in the 10-20 nm range and characterized by STEM and EDS for structural and elemental composition. The catalytic activity of one class of AuPd alloy nanoparticles made via this method was evaluated with respect to the reduction of 4-nitrophenol with NaBH4. In addition to being the first catalytic studies of particles made by SPBCL, these proof-of-concept experiments demonstrate the potential for SPBCL as a new method for studying the fundamental science and potential applications of alloy nanoparticles in areas such as heterogeneous catalysis.

Synthesis, characterization and photocatalytic activity of noble metal-modified TiO2 nanosheets with exposed {0 0 1} facets

Pt, Pd, Ag and Au nanoparticles were photodeposited on the {001} crystal facets of the TiO2 anatase nanosheets. Morphological and surface characterization of the samples as well as photocatalytic activity were studied. The influence of metal precursor concentration used during photodeposition (0.05−0.5%) on size of formed metal nanoparticles together with UV and vis-mediated activity of Pt, Pd, Ag or Au−TiO2 was investigated. Generally, samples obtained by photodeposition of noble metal nanoparticles using their 0.2% precursor solutions revealed highest activity in phenol degradation reaction under visible light (λ>420nm). The photoactivity of the as-prepared samples with respect to the modified metal species was ordered Ag≅Pd>Au>Pt. TEM analysis showed that photodeposited metal nanoparticles appeared only on {001} facets of TiO2. The average degradation rate of phenol in the presence of Pd and Ag−TiO2 was 0.5μmoldm−3min−1 after 60min of irradiation under visible light, and was five times higher than that of pure TiO2 nanosheets.

Electrodeposition and Characterisation of Novel Ni-NbOx Composite Coatings as a Diffusion Barrier for Liquid Solder Interconnects - Part II: Diffusion Barrier Performance

Electronics products are increasingly required to operate at high temperatures in harsh environments, for instance in oil well, geophysical drilling and aerospace applications. Conventional solder interconnects, that have been extensively utilised in consumer electronics, are no longer adequate. This is primarily due to excessive intermetallic compounds (IMCs) that can form and continuously grow during high temperature operation. With the intention of reducing such excessive IMC growth, electrically conducting niobium sub-oxide containing Ni coating has been produced which acts as a barrier layer between the solder and substrate. This then promises the possibility of developing a new solder barrier material with electrical conductivity and chemical resistance as required.The present study considers a novel electrochemical route to produce Ni-NbOx composite coatings of good uniformity, smoothness, compactness and purity. The electrolyte is derived from a Type IV eutectic solvent consisting of NbCl5 and propylene glycol (PG). The addition of a small amount of Ni ions (molar ratio: Ni : Nb=1 : 30) was found to enable the co-deposition of Nb species. The introduction of NaBH4 into the electrolyte has elevated the maximum deposit thickness (above 15 µm), although this led to a reduction in the co-deposited Nb content. The effects of cathodic current density, metal precursor and NaBH4 concentrations on the surface morphology, composition and thickness of the coatings were examined. Scanning transmission electron microscopy (STEM) revealed a nanocrystalline structure resembling that of a simple FCC structure of Ni, with a slightly fluctuating composition across the coating thickness and with Nb uniformly distributed (See Fig. 1). From X-ray photoelectron spectroscopy (XPS), a 0.7 eV shift to lower binding energy for the Nb (V) species signifies the partial chemical reduction of Nb2O5 due to possible Ni-Nb bonding. It is thus proposed that a Ni-NbOx deposit was formed by a two-step mechanism: the simultaneous electrochemical reduction of adherent Ni metal and inadherent niobium oxides on Cu, followed by nickelation of the NbOx. The composite coating’s electrical conductivity, solderability and diffusion barrier characteristics (the latter preventing excessive IMC growth between molten Sn-In solder and Cu substrate) were assessed and showed promising results. From diffusion studies, a Nb-enriched layer was observed at the solder/substrate interface after ageing at 200°C suggesting evident effectiveness of the diffusion barrier characteristics.Figure 1 - STEM cross sectional image a) of a 95Ni-5Nb coating with corresponding Energy-dispersive X-ray spectroscopy (EDX) maps of b) Ni Kα & c) Nb Lα.

Palladium Nanoparticles Stabilized by Glycodendrimers and Their Application in Catalysis

AbstractPalladium nanoparticles stabilized by glycodendrimers (PdDSNs) in water were prepared by coordination of PdII to intradendritic triazole ligands upon reaction of K2PdCl4 with the dendrimer in water followed by aqueous NaBH4 reduction to Pd0. TEM images show that the PdDSNs are small (average diameter: 2.3 nm) and relatively monodisperse owing to a low concentration of metal precursor. The catalytic activity of these PdDSNs was evaluated for the reduction of 4‐nitrophenol (4‐NP) to 4‐aminophenol (4‐AP) by NaBH4 (only 0.2 mol‐% of Pd per mol substrate is used) and for the Miyaura–Suzuki C–C coupling with various substituted aryl bromides (only 0.01 mol‐% of Pd per mol substrate is used). Comparisons of the catalytic activities of these PdDSNs with those of larger PdDSNs (diameter: 14 nm) reveal that smaller NPs catalyze faster 4‐NP reduction than their larger counterparts but lack any notable surface dependency for Suzuki–Miyaura catalysis.

Synthesis and Characterization of the Pd/SiO<sub>2</sub> Nanocomposite by the Sol-Gel Method

The silica supported palladium nano particle were synthesized by using the sol-gel method. The possibility of using palladium (II) nitrate dehydrates as Pd precursor and effect of metal precursor concentration on the final Pd nanoparticle size was investigated. A stable silica sol was prepared via hydrolysis of tetraethyl orthosilicate (TEOS) as a metal alchoxide and condensation reaction.Subsequently, Palladium (II) nitrate dehydrates was added to sol to form the Pd/silica sol. After drying and calcination of the sol, the Pd/SiO2 nanocpmposite has been obtained. Crystallographic information and crystalline size of the synthesized Pd/SiO2 were determined by X-ray diffraction (XRD) method. Morphology of the nanoparticles and hydrogen-bonding interaction between silanol groups and amine ligands were characterized by SEM and Fourier transform infrared (FTIR) spectra, respectively. Finally, the distribution and size of the palladium nanoparticles in the silica was evaluated.

Surface Density Optimization of V-Zr Mixed Oxides Cografted on γ-Al2O3 Using OV(O i Pr)3 and Zr(O n Bu)4 Precursors

Cografted catalysts are synthesized by reacting surface -OH groups of a catalyst support with a solution containing two or more metal precursors. Under these circumstances factors such as temperature, concentration of metal precursors, time of cografting, and variations in metal precursor feeds can affect the surface metal densities. To understand influence of these parameters a compositional range of V-Zr cografted catalysts were synthesized using OV(O i Pr)3 and Zr(O n Bu)4 and studied. These catalysts were then characterized using ICP-OES, XRD, and XPS. XRD revealed that cografting was amorphous and XPS studies indicated that V5+ and Zr4+ were the only species present under ambient conditions.