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.     

Synthesis and stability studies of thiophenol capped CdS nanoparticles

The results of the studies on the preparation and stability of thiophenol-capped CdS nanoparticles prepared by a non-aqueous chemical method are reported. Solutions of cadmium acetate and sodium sulphide were taken as the precursors and thiophenol was used as a capping agent to control the growth and also to prevent flocculation of the synthesized particles. The synthesized CdS nanoparticles were characterized by the optical absorption and X-ray diffraction (XRD) studies. The blue shift of the optical absorption edge indicated the formation of particles in the nanometer size regime. The particle sizes were estimated from the band gap values obtained from the optical absorption spectra using effective mass approximation (EMA). The CdS powder sample was used for the X-ray Diffraction studies. Broadening of the diffraction peaks with an increase in the stabilizer concentration also suggests the decrease in particle size with increase in the stabilizer concentration. Particle sizes calculated from the X-ray diffraction studies agree fairly well with those estimated from the optical absorption studies. The particle size could be conveniently controlled by adjusting the concentration of the stabilizer. X–ray diffraction studies were also carried out at higher temperatures. Particle size did not change with temperature as indicated by XRD. Stability of the synthesized nanoparticles was studied by recording the optical absorption spectra for 45 days. A change in particle size was observed at lower stabilizer concentrations for the first few days. But at higher stabilizer concentrations there was no change in particle size with time.     

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.     

A novel pathway toward efficient improvement of the photocatalytic activity and stability of CdS-based photocatalyst for light driven H2 evolution: The synergistic effect between CdS and SrWO4

It has been a research hot spot how to efficiently heighten the photocatalytic activity and stability of CdS-based photocatalysts for H₂ evolution. Here, SrWO₄/CdS nanoparticles which contained CdS/SrWO₄ heterojunctions were prepared. Meanwhile, their photocatalytic performance and stability were investigated in detail for H₂ evolution. At last, the photocatalytic mechanism of the SrWO₄/CdS nanoparticles was discussed roughly. The results show that the photocatalytic performance of CdS can be heightened significantly due to introduction of SrWO₄. The fastest evolution rate of H₂ over the SrWO₄/CdS nanoparticles is 392.5 μmol g⁻¹ h⁻¹, which is 5.8 times as high as that over the pure CdS nanomaterial. More interestingly, the SrWO₄/CdS nanoparticles possess excellent stability. The evolution rate of H₂ over the photocatalyst used 10 times can be up to 473 μmol g⁻¹ h⁻¹, which is the same as that over the once used sample, even is 37% higher than that over of the fresh one. In contrast, after used five times, the photocatalytic activity of the pure CdS nanomaterial is only 57% of that of the fresh sample. This study will supply a new idea for the design and development of highly stable and efficient CdS-based photocatalysts for H₂ evolution in the future.     

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.     

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.     

Synthesis of gaseous hydrogen and nanoparticles of silicon and silicon oxide by pyrolysis of tetraethoxysilane in an electric discharge under the action of ultrasound

In this work, we studied the process of synthesis of gaseous hydrogen, as well as silicon and silica nanoparticles under the action of intensive ultrasonic cavitation in a plasma discharge in a tetraethoxysilane medium.It is shown that a new form of plasma discharge arising in a liquid in an intensive ultrasonic field above the cavitation threshold, characterized by a volumetric glow in the entire space between the electrodes and falling volt-ampere characteristics, can be effectively used to initiate various physical and chemical processes. It was shown that ultrasonic action in combination with an electric discharge is capable to decompose tetraethoxysilane molecules with the formation of hydrogen, carbon oxides, and also solid-phase products - silicon and silica nanoparticles.Experiments on the production of hydrogen and nanoparticles were carried out on a special experimental setup for the implementation of a plasma discharge in liquid-phase media. The setup consists of an ultrasonic generator, a piezoceramic transducer, a discharge power source, a reaction chamber, and discharge electrodes.The results of the analysis of gaseous reaction products by gas chromatography show that during the pyrolysis of liquid tetraethoxysilane, hydrogen with a content of about 90% and carbon oxides are formed. The synthesized silicon and silica nanoparticles were isolated and studied using the methods of physicochemical analysis - infrared spectroscopy, X-ray phase analysis and transmission electron microscopy to determine the composition, shape and size of nanoparticles.The study of nanoparticles by electron microscopy showed that particles of a corner shape are obtained during the synthesis. The size of the synthesized nanoparticles is 50–100 nm. It was also shown by electron microscopy that, upon aggregation, the particles do not become larger in size, but form composite associates. It is also important to note that the advantage of this method for the synthesis of nanoparticles is their activated surface, which has a high reactivity as a result of exposure to intense ultrasound.The resulting nanoparticles and their agglomerates can also be used as functional materials, fillers, and components of composite materials.     

Deposition of CdS and Au nanoparticles on TiO2(B) spheres towards superior photocatalytic performance

TiO₂(B)/CdS/Au and TiO₂(B)/Au/CdS heterostructures were synthesized to investigate the effect of the selected deposition of CdS and Au nanoparticles (NPs) on H₂ generation. TiO₂(B) spheres (phase B) consisted of nanosheets were synthesized via a hydrothermal reaction. The deposition of CdS and Au NPs were carried out using wet-chemical method and a reduction reaction, respectively. The size and amount of Au and CdS NPs were adjusted to optimize the resulting properties and discuss the change of band gap. Two kinds of heterogeneous revealed different photocatalytic hydrogen generation which indicated the position of Au NPs affect the transfer of photogenerated carriers. The hydrogen production rate of TiO₂(B)/CdS/Au heterostructures reached up to 12100 μmol g⁻¹ h⁻¹, which is about 3.8 times of that of pure TiO₂(B) spheres. This is ascribed to the structure of heterostructures. CdS NPs increase the separation of photogenerated electrons and Au NPs accelerated the transfer of the electrons. The result provided a utilizable strategy for efficient photocatalysis H₂ generation.     

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.     

Revisiting the materials and mechanism of metal oxynitrides for photocatalysis

Photocatalysis has been recognized to be a promising process for the energy and environmental applications. Eventually, photocatalytic materials are largely modified in their physical and chemical structures. The former involves the size and shape dependent properties, while the latter involves the process of doping, composites, co-catalyst loading, etc. The doping process conventionally includes the cationic substitution, where it largely modifies the conduction band of the photocatalyst, not the valence band. However, the modification of VB is also required for the fine tuning of band edge potentials of the photocatalyst towards developing them for their versatile photocatalytic applications. In this direction, oxynitrides-based semiconductors demonstrate the possibilities of simultaneous tuning of the potential energy of VB and CB to construct the photocatalytic materials for the favorable and sustainable photocatalytic process. Accordingly, this review has been constructed to provide insights into the materials and mechanism of metal oxynitrides for their various photocatalytic applications.     

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.     

Thermal synthesis of Pt nanoparticles on carbon paper supports

A thermal method of synthesis and fixation of Pt nanoparticles (Pt NPs) on carbon paper is proposed in this paper. Carbon paper was coated with H₂PtCl₆ by simple immersion in an ethanol solution containing the Pt precursor. Thereafter, H₂PtCl₆ was decomposed in inert atmosphere into Pt NPs by applying a temperature of 600 °C. Formed Pt NPs were able to oxidize the surrounding carbon fiber surface. This local thermal oxidation of carbon promoted the generation of nano-roughness and Pt NPs were embedded in the carbon fiber, thus favoring their fixation on carbon paper. Pt load can be easily controlled by the number of coating processes applied. The proposed method combines the advantage of achieving small size nanoparticles (5–10 nm) with enhanced fixation of Pt NPs when compared with electrochemical synthesis. The optimal number of coatings applied was three, which produced a complete coverage of carbon paper surface (with a Pt load of 0.18 mg cm^?2).     

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.     

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.