Dielectric studies on the chicken egg membrane deposited with CdS nanoparticles

Results on the studies of dielectric properties of the chicken egg membrane deposited with CdS nanoparticles are presented in this article. The CdS nanoparticles are synthesized in the membrane by the diffusion of the precursor solutions of cadmium acetate and thiourea across the membrane. The AC capacitances of the membrane were measured in the frequency range of 1 kHz–10 MHz. The capacitance of the membrane drops in the entire frequency range of measurement with the deposition of CdS nanoparticles and the extent of the drop being dependent on the reaction parameters. Drop in capacitance is highest for conditions favoring small nanoparticles. The drop in capacitance with the deposition is attributed to the presence of Cd(OH)₂ in the deposits. The volume fraction and capacitance of that component of the deposit responsible for reducing the capacitance of the deposited membrane below that of the undeposited could be estimated by assuming a simple model. X-ray photoelectron spectra (XPS) of the deposited membrane indicate that nanoparticles of CdS are not formed on the surface but formed deep in the pores of the membrane. These particles are found to be cadmium rich, thus supporting the inference that the Cd(OH)₂ is formed along with the CdS nanoparticles.     

The effect of precursor concentration on the size of the CdS nanoparticles synthesized in a chicken egg membrane

Results of the studies on the effect of concentration of the precursors on the size of CdS nanoparticles formed in a chicken egg membrane are presented in this article. CdS is formed by the diffusion of aqueous solutions of cadmium acetate and thiourea across the membrane. The optical absorption spectra of the samples exhibit a blue shift in the absorption edge indicating the formation of CdS particles with the size lying in the nanoscale regime. The band gaps of the samples with small reaction times were higher than that of the bulk value, approaching the bulk band gap value with the increase in reaction time for a fixed concentration. Particle sizes were estimated from the band gap values. At lower concentrations, smaller particles are formed even at large reaction times and offer a better control over the size of the particles. At very low concentrations, it takes some time for the absorption edge to evolve after the membrane is removed from the reaction bath. The particle size saturates at higher reaction time possibly due to an equilibrium being established in the system, resulting in stoppage of the diffusion of the reacting ions. Absorption edge could not be detected even days after the removal of the membrane from the reaction bath at still lower concentrations, despite allowing the reaction to take place for large periods of time.     

Synthesis of borohydride nanoparticles at room temperature by precipitation

Borohydride (LiBH₄, NaBH₄ and KBH₄) nanoparticles were successfully synthesized by a modified ternary anti-precipitation method. A co-solvent was introduced to facilitate the formation of a microemulsion and modify the metastable zone to favour the precipitation of borohydride particles. In this process, the stabilising surfactant's carbon chain length was found to provide an additional mean to further tune particle size due to the resulting steric hindrance. The method reported here finally provides an effective and simple mean to prepare nanosized borohydride particles for hydrogen storage purposes, while minimising the amount of stabilising surfactant that can contaminate the hydrogen release.     

Combustion characteristics of boron nanoparticles

An experimental investigation of the combustion characteristics of boron nanoparticles in the post flame region of a flat flame burner has been conducted. Boron is attractive as a fuel or a fuel supplement in propellants and explosives due to its high heats of combustion on both a gravimetric and volumetric basis. A relatively large database exists for combustion characteristics of large (greater than 1 μm) boron particles, but very little exists for nano-sized boron. Ignition and combustion characteristics have been studied in the post flame region of a fuel lean CH₄/Air/O₂ flame, with burner temperatures ranging from about 1600 K to 1900 K, and oxygen mole fractions ranging between 0.1 and 0.3. As in earlier investigations on boron combustion, a two-stage combustion phenomenon was observed. Ensemble-averaged burning times of boron nanoparticles were obtained, while the ignition time measurements for boron nanoparticles were extended into a lower temperature range previously unavailable in the literature. The measured burning times were between 1.5 ms and 3.0 ms depending on both the temperature and oxygen mole fraction. The ignition times were relatively insensitive to oxygen concentration in the range studied, and were affected only by temperature. The measured ignition times were inversely related to the temperature, ranging from 1.5 ms at 1810 K to 6.0 ms at 1580 K. The burning time results were compared to both diffusion and kinetic limited theories of particle combustion. It was found that the size dependence on particle burning times did not follow either theory.     

Synthesis of magnesium nanoparticles with superior hydrogen storage properties by acetylene plasma metal reaction

In this work, we developed a method to prepare ultrafine Mg nanoparticles around 40 nm by acetylene plasma metal reaction, which is a revised approach for the traditional hydrogen plasma metal reaction. During the preparation, the growth of the Mg nanoparticles was confined by the carbon from the decomposition of acetylene. The size of the Mg particles exhibited a clear decreasing trend with increasing acetylene fraction in the plasma. Due to the short diffusion distance and large specific surface area, the kinetics of hydrogenation and dehydrogenation of the small Mg nanoparticles were improved. From the equilibrium plateau pressures of the absorption and desorption isotherms, the enthalpy and entropy of the reaction were deduced, which were significantly reduced compared to the commercial magnesium.     

Synthesis of supported Pt nanoparticles by sonication for ORR: Effect of the graphene oxide-carbon composite

Pt supported on graphene oxide (GO), reduced graphene oxide (RGO), carbon Vulcan (C) and GO-C composite were prepared by using sonication as a simple synthesis method in the absence of any special capping agent or thermal treatment. X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize the materials synthesized. The electrocatalysts synthesized were evaluated for oxygen reduction reaction (ORR) in acid medium by using cyclic and linear voltammetry tests. The characterization results indicated that the highest dispersion of small Pt particles was observed on the samples supported on GO materials compared to carbon Vulcan due to the oxygen functional surface groups, which promoted a homogeneous distribution of Pt nanoparticles. The electrochemical characterization indicated that Pt/GO-C composite exhibited a 50% more specific and mass activity at 0.85 V for ORR than the conventional Pt/C catalysts, which is associated to Pt-support interaction that modifies the electronic properties of Pt for electrochemical application in fuel cell. GO-C (1:1) can be a promising support for improving the electrochemical activity for ORR.     

Synthesis and characterization of carbon nanotubes decorated with Pt and PtRu nanoparticles and assessment of their electrocatalytic performance

Novel hybrid electrocatalysts were developed based on the attachment of pre-formed capped Pt and PtRu nanoparticles (NPs) on the external surfaces of multi-walled carbon nanotubes (MWCNTs). MWCNTs chemically functionalized by both covalent and non-covalent chemical strategies were tested and evaluated as nanotemplates for the dispersion and stabilization of NPs. The suitable functionalized MWCNTs derivatives were then reacted with pre-formed capped Pt and PtRu NPs yielding the final hybrid materials. The intermediate products as well as the final hybrid materials were characterized in detail with a combination of experimental techniques including Raman spectroscopy, X-ray diffraction, scanning and transmission electron microscopy, while comparative studies regarding their electrocatalytic performance to the oxidation of methanol and ammonia, and to the reduction of hydrogen peroxide were made by performing cyclic voltammetry studies. The results revealed the uniform dispersion of very small NPs along the external surface of functionalized CNTs, while the most suitable electrocatalyst for each particular application is indicated. The chemical strategy followed for the surface functionalization of MWCNTs seems to greatly influence the catalytic activity of the resulting hybrids materials.     

Exciton energies of wurtzite CdS nanoparticles

We have determined exciton energies for wurtzite CdS nanoparticles, both theoretically and experimentally. The empirical pseudopotential method has been used to calculate the bulk band structure. The discretization of reciprocal space was considered to get the energy gap and the corresponding exciton energy as a function of the nanoparticles size. The CdS nanoparticles were prepared by colloidal methods and the exciton energies were determined from optical absorption measurements. A good agreement between the calculated and the experimental exciton energies is obtained when an average over the experimental size distribution of the nanoparticles is included in the calculation.     

One-step synthesis of graphene supported platinum nanoparticles as electrocatalyst for PEM fuel cells

Here in, we describe an ultrafast, single-step microwave irradiation route (MW) to prepare graphene supported Pt nanoparticles, during which the small Pt nanoparticles are distributed uniformly on a reduced graphene oxide surface. This route provides evident advantages namely low cost, easiness, low time consuming and high yield in comparison to actual chemical methods to develop efficient Pt/rGO catalyst with Pt content close to state-of-the-art commercial composition. The structure and composition of prepared samples have been studied by specific techniques, while the electrocatalytic stability has been studied using ex-situ and in-situ measurements. High performance and electrochemically stable catalyst for PEM fuel cells was developed using the sample with highest loading and good dispersion. The fabricated Pt-rGO-based MEA was investigated for durability under fuel starvation in comparison with commercial Pt/C-based MEA. The electrocatalytic activity was investigated and the electrochemical response revealed the higher stability during accelerated degradation test under fuel starvation in comparison with commercial Pt/C. This study promotes the applicability of described preparation method to noble or transition metal nanoparticles embedded on graphene-based materials.     

Influence of the thickness on structural, optical and electrical properties of chemical bath deposited CdS thin films

Cadmium sulfide films of different thicknesses were deposited by chemical bath deposition (CBD) from a bath containing cadmium acetate, ammonium acetate, thiourea, and ammonium hydroxide. The XRD patterns show that the films are of hexagonal phase with preferred (0 0 2) orientation and the grain size increases with the thickness of the film. The band gap of the films was calculated from the transmittance data and it was found that the band gap decreases as the film grows in thickness. The photo-response studies indicate that the film thickness has an influence on the current decay under dark. The observed opto-electronic properties were attributed to the crystallite size and internal microstrain.     

Catalytic activity of platinum-cobalt alloy nanoparticles decorated functionalized multiwalled carbon nanotubes for oxygen reduction reaction in PEMFC

The role of functionalized multiwalled carbon nanotubes (MWNTs) decorated with platinum nanoparticles (Pt/f-MWNTs) and platinum-cobalt alloy nanoparticles (Pt₃Co/f-MWNTs) has been investigated for oxygen reduction reaction (ORR) in a proton exchange membrane fuel cell. The electrocatalysts are synthesized by a conventional sodium borohydride reduction method and modified polyol reduction method. The modified polyol reduction method yields better uniform dispersion, higher loading and optimum particle size of Pt and Pt₃Co alloy nanoparticles over the MWNTs compared to the conventional sodium borohydride reduction method. The electrochemical surface area of the electrocatalysts is calculated using cyclic voltammetry. Pt₃Co/f-MWNTs synthesized via modified polyol reduction method yield the highest performance with a maximum power density of 798 mW cm⁻² at 60 °C without any back pressure. The enhanced catalytic activity of Pt₃Co/f-MWNTs toward ORR is attributed to uniform dispersion and optimum particle size of Pt₃Co alloy nanoparticles over the surface of f-MWNTs.     

Synthesis and characterization of uniform-sized cubic ytterbium scandium co-doped zirconium oxide (1Yb10ScSZ) nanoparticles by using basic amino acid as organic precursor

Cubic ytterbium scandium stabilized zirconium oxide (1Yb10ScSZ) nanoparticles with highly uniform sizes were synthesized using basic amino acid as organic precursor in aqueous medium. The 1Yb10ScSZ materials were prepared by precipitation (P-YbScSZ) and sol–gel (SG-YbScSZ) using l-arginine as the basic amino acid. l-Arginine can form complex gel with metal cation and increase the solution pH. The calcination temperatures were varied from 600 to 700 °C to study the effect of calcination temperature on particle size. The stable cubic phase ensured the high ionic conductivity of the zirconia-based electrolyte material for solid-oxide fuel cells (SOFC). The crystal structures of the nanoparticles obtained from the precipitation and sol–gel methods were cubic, but the nanoparticles obtained from the precipitation method calcined at 600 °C were more uniformly sized. However, the symmetrical cell with SG-YbScSZ powder sintered at 1550 °C/5 h showed a higher ionic conductivity value of 0.012 Ω cm² at 800 °C and a lower activation energy than the cell using the P-YbScSZ powder. This finding demonstrated that the 1Yb10ScSZ electrolyte prepared by the sol–gel method had better properties, higher sinter ability, and ability to obtain sufficient density with better electrical property than that prepared by the precipitation method.     

Mesoporous g-C3N4 decorated by Ni2P nanoparticles and CdS nanorods together for enhancing photocatalytic hydrogen evolution

Ni₂P nanoparticles and CdS nanorods were grew together on a mesoporous g-C₃N₄ through a facile in-situ solvothermal approach. Under visible light (λ > 400 nm), the as-prepared ternary PCN–CdS-5% Ni₂P composite displays a high H₂ evolution rate with 2905.86 μmol g^?1 h^?1, which is about 14, 18 and 279 times that of PCN–CdS, PCN–Ni₂P and PCN, respectively. The enhanced photocatalytic activity is mainly attributed to the improved separation efficiency of the photocarriers by the type II PCN–CdS heterojunction and the effective extraction of photogenerated electrons by Ni₂P. Meanwhile, Ni₂P acts as co-catalyst to provide the photocatalytic active site for hydrogen reduction. In addition, PCN–CdS-5% Ni₂P composite exerts good stability in 12-h cycles.     

Fe2P nanoparticles as highly efficient freestanding co-catalyst for photocatalytic hydrogen evolution

Design of non-noble-metal artificial photosynthesis system that can split water with high apparent quantum yield (AQY) and robust stability remains a fundamental challenge. Here we report that a physical mixture of Fe₂P nanopaticles (NPs) and CdS nanosheets (NSs) can gives AQY of photocatalytic hydrogen production as high as 90% at 420 nm monochromatic light with ethanol as electron donor at strong alkaline conditions. The highest rate for hydrogen production reached about 220 mmol g^?1 h^?1. In this hybrid photocatalyst system, free standing Fe₂P NPs act as efficient and robust noble-metal-free co-catalysts and ultrathin CdS NSs are used as the photosensitizer. PL and TRPL results demonstrate that photoexcited electron can transfer from the conduction band of the excited CdS to Fe₂P, which aided charge separation and enhanced the hydrogen evolution activity. Femtosecond transient absorption result reveals that the time-averaged interfacial electron transfer (ET) rate constant (<k_ET>) from CdS NSs to Fe₂P is about 7.4 × 10⁹ s^?1 under the guarantee of the scavenging of photoexcited hole immediately, which is one order faster than the electron relaxation rate in pure CdS NSs.     

Preparation and electroactivity of polymer-functionalized graphene oxide-supported platinum nanoparticles catalysts

Polymer-functionalized graphene oxide or pristine graphene oxide supported platinum nanoparticles (Pt NPs) was prepared to study the surface modification effects. The catalysts were characterized by transmission electron microscopy, energy dispersive spectrometry, X-ray diffraction and thermogravimetric analysis. The electrochemical activities of Pt NPs were measured by cyclic voltammograms. The poly(diallyldimethylammonium chloride) (PDDA) was used as a modifier agent which formed a functionalized layer on graphene oxide (GO) sheets. As a result, the electrochemical active surface area (ESA) of PDDA functionalized GO supported Pt (Pt/PDDA–graphene) was shown to 66 m²/g that indicated higher hydrogen adsorption amount than 55 m²/g of the pristine Pt/graphene. In addition, an average particle size of Pt/PDDA–graphene NPs was measured to 1.8 nm slightly smaller than 2.0 nm of pristine Pt/graphene NPs.     

Hydrogen-sensitive sensor with stabilized Pd-mixture forming sensing nanoparticles on an interlayer

Pd-based mixtures comprising silicon dioxide (SiO₂) were used as sensing materials in fabrication of GaN-based hydrogen sensors. The mixture as-deposited has a rough surface with many pores. After wet selectively etching to remove SiO₂, the mixture turns into Pd nanoparticles with a size of ∼ 30 nm on an interlayer with oxygen, as indicated by SEM, EDX, and SIMS methods. A careful study of the Pd-mixture on a metal-semiconductor-metal type of hydrogen sensor provides significant information on the roles of oxygen and the interlayer. Experimental results reveal that hydrogen atoms trapped inside the mixture as-deposited cannot contribute to changes in barrier height as an applied voltage is not large enough. Improved sensing properties such as hydrogen dissociation rate, diffusion rate, and storage capability were obtained when Pd nanoparticles were formed by selectively etching the mixture. The situation that hydrogen atoms were blocked and disturbed by oxygen will exist no more. Uniform sensing responses of higher than 10⁵ (defined as (J_H2-J_N2)/J_N2, J_H2 and J_N2 are current densities measured in H₂/N₂ and N₂ ambiences, respectively), voltage shifts of larger than 20 V were obtained at 2.13 ppm H₂/N₂. In addition, hydrogen transport through grain boundaries of Pd nanoparticles is much faster than diffusion through a Pd-mixture layer. A much shorter response time was obtained from the sensors with the Pd-mixture wet etched. Furthermore, stable and reliable sensing characteristics were also expected.     

Synthesis of carbon-coated LiFePO4 nanoparticles with high rate performance in lithium secondary batteries

A novel preparation technique was developed for synthesizing carbon-coated LiFePO₄ nanoparticles through a combination of spray pyrolysis (SP) with wet ball milling (WBM) followed by heat treatment. Using this technique, the preparation of carbon-coated LiFePO₄ nanoparticles was investigated for a wide range of process parameters such as ball-milling time and ball-to-powder ratio. The effect of process parameters on the physical and electrochemical properties of the LiFePO₄/C composite was then discussed through the results of X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), the Brunauer-Emmet-Teller (BET) method and the use of an electrochemical cell of Li|1 M LiClO₄ in EC:DEC = 1:1|LiFePO₄. The carbon-coated LiFePO₄ nanoparticles were prepared at 500 °C by SP and then milled at a rotating speed of 800 rpm, a ball-to-powder ratio of 40/0.5 and a ball-milling time of 3 h in an Ar atmosphere followed by heat treatment at 600 °C for 4 h in a N₂ + 3% H₂ atmosphere. SEM observation revealed that the particle size of LiFePO₄ was significantly affected by the process parameters. Furthermore, TEM observation revealed that the LiFePO₄ nanoparticles with a geometric mean diameter of 146 nm were coated with a thin carbon layer of several nanometers by the present method. Electrochemical measurement demonstrated that cells containing carbon-coated LiFePO₄ nanoparticles could deliver markedly improved battery performance in terms of discharge capacity, cycling stability and rate capability. The cells exhibited first discharge capacities of 165 mAh g⁻¹ at 0.1 C, 130 mAh g⁻¹ at 5 C, 105 mAh g⁻¹ at 20 C and 75 mAh g⁻¹ at 60 C with no capacity fading after 100 cycles.