Metal Precursor Concentration Research Articles

Studies on Surface Plasmon Resonance of Murdannia loriformis Silver Nanoparticles

In this work, surface plasmon resonance (SPR) was investigated over the effect of concentration of metal precursor, concentration of reducing agent, reaction time and pH on formation of silver nanoparticles (AgNPs) using biological method. In this method, Murdannia loriformis extract (MLE) was used as reducing agent and silver nitrate as metal precursor. SPR of Murdania loriformis silver nanoparticles (MLE-AgNPs) was measured through UV-vis spectrophotometer over a range of 380 – 800 nm wavelength. It was found that, as the concentration of MLE, pH and reaction time increases, the SPR peak of MLE-AgNPs at 430 - 490 nm also increases. However, for effect of concentration of metal precursor, the result showed that SPR peak of MLE-AgNPs increases when 1 to 5 mM of silver nitrate was used but decreases for 10 and 15 mM. Significant of this study is to identify the optimum conditions for synthesis of MLE-AgNPs.

Noble metal aerogels rapidly synthesized by ultrasound for electrocatalytic reaction

Noble metal aerogels (NMAs), belonging to the porous material, have exhibited excellent catalytic performance. Although the synthesis method continues to improve, it still exists some problems which hindered the experimental process, such as high concentration of noble metal precursors, long synthesis cycle, expensive production cost, and uncontrollable ligament length. In this work, ultrasonic wave and reducing agent NaBH4 were simultaneously applied to gelation process. With the cavitation of ultrasound, it can generate huge energy with heating and stirring, thus gelation reaction proceeded quickly, and even completed the process in only a few seconds, that is much faster than the recorded. A wide concentration range was successfully expanded from 0.02 mmol/L to 62.5 mmol/L. Further, we extended this method to a variety of noble metal elements (Au, Ru, Rh, Ag, Pt, Pd), and this method is adaptive for the synthesis of single metal aerogels (Au, Ag, Ru, Rh, Pd), bimetal and trimetal aerogels (Au-Ag, Au-Rh, Au-Ru, Au-Pt, Au-Pd, Au-Pt-Pd). In addition, the ligament size of alloy aerogels are 10 nm or less. Moreover, their brilliant properties were demonstrated in hydrogen evolution reaction (HER) and ethanol oxidation reaction (EOR).

Determination of the yield, mass and structure of silver patches on colloidal silica using multiwavelength analytical ultracentrifugation

Anisotropic nanoparticles offer considerable promise for applications but also present significant challenges in terms of their characterization. Recent developments in the electroless deposition of silver patches directly onto colloidal silica particles have opened up a simple and scalable synthesis method for patchy particles with tunable optical properties. Due to the reliance on patch nucleation and growth, however, the resulting coatings are distributed in coverage and thickness and some core particles remain uncoated. To support process optimization, new methods are required to rapidly determine patch yield, thickness and coverage. Here we present a novel approach based on multiwavelength analytical ultracentrifugation (MWL-AUC) which permits simultaneous hydrodynamic and spectroscopic characterization. The patchy particle colloids are produced in a continuous flow mixing process that makes use of a KM-type micromixer. By varying the process flow rate or metal precursor concentration we show how the silver to silica mass ratio distribution derived from the AUC-measured sedimentation coefficient distribution can be influenced. Moreover, through reasoned assumptions we arrive at an estimation of the patch yield that is close to that determined by arduous analysis of scanning electron microscopy (SEM) images. Finally, combining MWL-AUC, electrodynamic simulations and SEM image analysis we establish a procedure to estimate the patch thickness and coverage.

Biofabrication and characterization of cyanobacteria derived ZnO NPs for their bioactivity comparison with commercial chemically synthesized nanoparticles

Due to unique properties of the nanoparticles (NPs) with biocompatibility, their application as drug in drug delievery and diagnostics, the recent scientific branch nanotechnology has emerged as hope in modern medicine. Zinc oxide nanoparticles (ZnO NPs) have gained tremendous interest due to their potential use as chemotherapeutic and antimicrobial agents. They are included in the category of “generally recognized as safe (GRAS) metal oxide”. There is an urgent need for developing additional sources of ZnO NPs. Therefore, in the present study 30 cyanobacterial extracts were screened for ZnO NPs synthesis.. The color change of the reaction mixture from blue to pale white indicated the synthesis of ZnO NPs. It was further confirmed by UV–Visible spectroscopy that showed the absorption peak at 372 nm. The SEM analysis during screening revealed that Oscillatoria sp. synthesized smallest ZnO NPs (~40 nm) that were further optimized for their higher yield by altering reaction conditions (pH, temperature, reaction time, concentration of extract and metal precursor). Best conditions for ZnO NPs synthesis are (0.02 M zinc nitrate, 10 ml of extract volume, pH 8, at 80 °C for 3 h). The NPs were purified through calcination at 350°C and characterized by UV–Vis, FTIR, XRD, SEM-EDAX, TEM, Zeta potential and DLS analysis. The comparative analysis of purified biogenic ZnO NPs with commercial chemically synthesized ZnO NPs (CS), exhibited their superior nature as antioxidant and anti-bacterial agent against both gram-positive and gram-negative bacteria. Synergistic effects of biogenic ZnO NPs and streptomycin additionally favored for their future use as a potential biomedical agent.

Interplaying Role of Particle Size and Polymer Layer Thickness on the Large Tunable Optical Response of Polymer-coated Silver Nanostructures

The interplaying role of particle size and polymer layer thickness on the tunable optical response of polymer-coated Ag nanoparticles (NPs) has been studied experimentally and theoretically. A large redshift ( $$\sim$$ 38 nm) of surface plasmon resonance (SPR) peak position has been observed experimentally for Ag NPs of sizes in the range of 8−18 nm synthesized by polyol process with the varying concentration of metal precursor (AgNO $$_{3}$$ ) and using a surfactant (PVP) as a stabilizer. The observed large redshift of the SPR peak position of Ag NPs coated with PVP has been argued due to mainly change of NP size as well as change of local dielectric environment in the vicinity of the Ag NPs. The experimentally observed SPR peak shift has been explained by considering the system as a metal-core polymer-shell nanostructure. The change of local dielectric environment of the surrounding of the NPs is due to the change in the PVP layer on the NPs. Such observation has been confirmed through the theoretical studies considering the changes of NP size as well as the effective thickness of the PVP layers on the NPs. The SPR peak of the system with core-shell nanostructure has been found to vary linearly with the increase in radius of core and thickness of shell together. However, it changes exponentially with particle size alone. It has been found from a detailed study that the change in the ratio of radius of core and thickness of the shell is responsible for the observed redshift. Thus, the redshift of SPR peak position of Ag NPs cannot be justified by only considering the increase in particle size. Rather shell thickness has been found to play a prominent role in the SPR peak shift. This study can be used to understand the optical response of noble metal NPs coated with organic polymers.

Facile fabrication of malonic acid capped silver nanoparticles and their antibacterial activity

The successful management of infections caused by human pathogenic bacteria is becoming a challenge for clinicians. Therefore, new strategies to circumvent the growth of pathogens need to be developed. The current study was therefore aimed to synthesize silver nanoparticles (AgNPs) through chemical reduction process of silver nitrate by tri sodium citrate or sodium borohydride and evaluated their antibacterial activity. During the synthesis process, AgNPs were capped by malonic acid (a dicarboxylic acid). We have exploited two approaches of cold (reduction by NaBH4) and hot (reduction by trisodium citrate) process for the synthesis of AgNPs which revealed maximum absorbance of AgNPs at 412 nm and 397 nm respectively. The malonic acid (MA) functionalized AgNPs (AgNPs/MA) were systematically characterized for their size, surface changes and morphology. These colloidal AgNPs were stable and polydisperse in nature with an average diameter of 20 nm. The zeta potential (ZP) analysis showed stable AgNPs. The AgNPs synthesis was optimized in a set of different reactions where concentration of metal precursor, concentration of capping agent, temperature, time of stirring and duration of reaction were variable. The AgNPs/MA were found poly-dispersed in nature with predominantly spherical shape. The antibacterial potential of AgNPs was then assessed against both Gram positive (Staphylococcus aureus) and Gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, and Klebsiella pneumoniae) by antimicrobial disc susceptibility assay with three replicates per treatment which showed promising antibacterial activity of AgNPs. The AgNPs/MA possessing remarkably smaller size exhibited encouraging antibacterial activity against human bacterial pathogens suggesting their potential application in controlling bacterial infections in clinical settings and can be utilized in further biomedical applications.

Nano‐spaced Gold on Glassy Carbon Substrate for Controlling Cell Behavior

AbstractThis approach involves the synthesis of gold nanoparticles (GNPs) within the carbonizing photoresist (SU8) to achieve GNPs trapped glassy carbon (GNPs‐GC) substrates. Surface size distribution and interparticle separation of GNPs is primarily controlled by changing the metal precursor concentration. Chemical stability and fabrication control are achieved by selecting sodium tetrachloroaurate (NaAuCl4) over a more conventional aurochloric acid (HAuCl4) as the gold precursor. Seeding of gold nuclei in a photocrosslinking polymer is a classical representation of simultaneous homogeneous and heterogeneous nucleation. GNPs growth during the carbonization process is tracked and explained using pertinent mechanisms. With the nanoparticle spacing ranging from 260 to 50 nm, GNPs‐GC thin films are employed as interfaces for fibroblast cell adhesion. GNPs act as potential anchor points for cell adhesion and their nanoscale arrangement regulates the structural behavior of the cells. GNPs' density‐dependent fibronectin physisorption significantly improves cell adhesion and proliferation. Intraparticle spacing around 160 nm offers ideal biointerface for fibroblast attachment and spreading. Fabrication of 3D GNPs composite carbon microelectromechanical systems is achieved as a demonstration of the studied GNPs‐GC synthesis mechanism. Sub‐micron patterning of GNPs‐GC combined with its biofunctional nature presents vast opportunities in the field of bioelectronics, biophotonics, and lab/organ‐on‐a‐chip technology.

The gas-phase formation of tin dioxide nanoparticles in single droplet combustion and flame spray pyrolysis

Tin dioxide (SnO2) nanoparticles synthesized via flame spray pyrolysis (FSP) have promising applications for gas sensors. The formation of SnO2 nanoparticles in the gas-phase has been investigated using single droplet combustion and FSP. Precursor solutions of Tin (II) 2-ethylhexanoate dissolved in Xylene with varying Sn concentrations were selected as the precursor-solvent system. The selected precursor-solvent system has its stability and ability to synthesize homogeneous nanoparticles, compared to metal nitrate based precursor solutions. The precursor-solvent system was studied using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and thermogravimetric analysis (TGA). The SnO2 nanoparticles were characterized using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and transmission electron microscopy (TEM). Droplet surface micro-explosions were observed during the single droplet combustion of the precursor solutions. It is because of the heterogeneous vapor-phase nucleation, which is beneath the liquid droplet surface and caused by precursor thermal decomposition. The results show that the size of nanoparticles obtained both from FSP and single droplet combustion increases with increasing metal-precursor concentration. The TEM images of the particles from such droplet combustion reveal two types of nanoparticles with different sizes and morphologies. The current work provides fundamental understanding of precursor decomposition and particle formation during single droplet combustion, which help in-depth understanding of the flame spray pyrolysis.

Biogenic synthesis of AuPd nanocluster as a peroxidase mimic and its application for colorimetric assay of acid phosphatase

Based on the oxidation-redox mechanism of naturally occurring NADH along with its metal coordination properties, biogenic AuPd nanoclusters are directly synthesized with low concentration of metal precursors, showing outstanding peroxidase mimicking activities. Ultrasmall bimetallic nanozymes can rapidly form under the reduction and the stabilization of NADH, and their physicochemical properties are closely associated to the molar ratio of [Na2PdCl4]/[HAuCl4]. Synergistic effects between Au and Pd play a particular role in both growth kinetics and catalytic performance of AuPd nanoclusters. The strong Au-Pd interactions remarkably adjust the electronic properties of both Au and Pd species in bimetallic NCs, thereby contributing to their superior enzymatic activities over two monometallic counterparts. Based on the peroxidase-like activity of AuPd nanoclusters at acidic pH, a colorimetric test is developed for monitoring acid phosphatase quantitatively, giving the limit of detection of 0.53 U/L. The linear response lies in the concentration range of 1–14 U/L. This method is also suitable for estimating ACP activity in biological fluid.

Synthesis of Boron Nitride Nanotubes Incorporated with Pd and Pt Nanoparticles for Catalytic Oxidation of Carbon Monoxide

Facile synthesis of Pd and Pt nanoparticles supported on the boron nitride nanotubes (Pd-BNNT and Pt-BNNT, respectively) for CO oxidation was explored. The reduction agent and stabilizer-free synthesis solely relies on the ultrasound treatment of the aqueous Pd2+ and Pt4+ precursors under the presence of BNNT. Reduction of Pd and Pt nanoparticles on the surface of BNNT was observed by means of the transmission electron microscopy and X-ray diffraction patterns. Quantitative analysis of Pd and Pt attached on the BNNT surface was also carried out using inductively coupled plasma atomic emission spectroscopy, showing that the concentration of metal nanoparticles on BNNT could be controlled by varying the initial concentration of metal precursors and the ultrasound treatment time. The morphological evolution of the nanoparticles on the surface of BNNT was observed by raising the temperature up to 800 °C in an air and up to 900 °C in vacuum. It was found that the nanoparticles were thermally stable up to 600 °...

Response surface methodology and reaction optimization to product zero-valent iron nanoparticles for organic pollutant remediation

Abstract Zero-valent metals such as Al0, Zn0, Ti0, and Fe0 with well explored catalytic activity have gained wide spread applications in the remediation proposes. Due to extremely high surface to volume ratio, nanoscale zero-valent metals showed increased catalytic potential and introduced as promising catalysts. Among zero-valent metal nanoparticles, zero-valent iron nanoparticles (ZVINPs) are one of the most employed nanostructures in remediation studies. These particles are effective Fenton-like catalysts and employed to remove organic contaminations. Recent studies indicated that plant mediated synthesized ZVINPs are more efficient in this regard than chemically synthesized nanoparticles. The extract of green tea is extensively used for green synthesis of various metallic nanoparticles and iron based nanoparticles. In the present work, design of experiments (DoE) and response surface methodology (RSM) was applied to find out effective reaction parameters and optimal reaction condition for maximum production of ZVINPs by using green tea extract. For this purpose, at first, a fractional factorial design was used to screen the reaction parameters (reaction time, temperature, amount of leaf extract, and metal precursor concentration) in the synthesis process. Subsequently, the central composite face (CCF) design was utilized for reaction optimization. Amount of green tea extract and iron precursor concentration were found to be the most effective parameters. In a regular 10 mL reaction, maximum productivity was achieved by employing 9 mL tea extract and 25 mM (final concentration) ferric chloride. The prepared nanoparticles were identified to be amorphous ZVINPs with a low magnetization value of 80 memu/g. The particles diameter was measured to be 5–20 nm with 11.2 nm mean size. The particles pose effective catalytic activity for organic contaminants removal. Methyl orange was tested as a common model compound and particles were capable to eliminate more than 50% of the initial dye in just 2 h.

Integration of Sequential Reactions in a Continuous Flow Droplet Reactor: A Route to Architecturally Defined Bimetallic Nanostructures

AbstractMicroreactors for nanoparticle (NP) synthesis offer advantages over batch reactions in terms of scale‐up and integration with online analyses. Herein, two microreactors (i.e., a duo‐microreactor) are integrated to achieve sequential reactions for the synthesis of bimetallic NPs with architectural control. The generality of the duo‐microreactor is shown with the synthesis of branched Pd‐Pt NPs and core@shell Pd@Au NPs, both achieved by synthesizing Pd nanocubes in the first part of the duo‐microreactor and then using those nanocubes downstream as seeds for Pt or Au deposition. Control of the dimensions of these NPs is further demonstrated and achieved by tailoring metal precursor concentrations inline. This microreactor methodology is anticipated to be applicable to other bimetallic NP systems.

Palladium nanostructures with well-controlled morphologies obtained by one-pot and one-step polyol method

The physical and chemical properties of metal nanomaterials are closely tied to their size and shape. A well-controlled synthesis protocol is needed to control over particle morphologies. Although the shape and size of metal nanostructures have been controlled by various pathways, such as soft templates and seed-mediated protocol method, most of the methods are involved with complicated multi-step synthesis. In this work, the morphology of palladium nanostructures, including nanorods, nanoparticles, and nanocubes, were well controlled by a simple one-step/one-pot polyol method in the presence of poly(vinylpyrrolidone) and KBr. A detailed study of the relationship between the morphology and controlling factors, such as reaction temperature, the concentration of metal precursor, PVP, reducing agent, and potassium bromide is presented. Well-controlled morphologies of Pd nanorods, nanospheres, and nanocubes are obtained via tuning these reaction parameters. The results from this work provide a basis for optimizing palladium nanocrystals growth through the simple one-pot/one-step polyol method.

Plant Arabinogalactan Gum Synthesized Palladium Nanoparticles: Characterization and Properties

An ecofriendly and facile autoclaving method was devised for palladium nanoparticle synthesis utilizing biocompatible, biodegradable, nontoxic, renewable plant arabinogalactan gum, tragacanth. The formed nanoparticles were characterized with UV–Visible spectroscopy (UV–Vis), zeta sizer, X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The formation of dark brown colour and wide continuous spectra in UV–Vis confirmed the formation of palladium nanoparticles (Pd NP). Also, various reaction conditions such as concentrations of reductant, metal precursor and reaction time were optimized to obtain stable Pd NP preparation. Based on UV–Vis and zeta sizer data, the optimized preparation was at 0.5% gum, 0.5 mM palladium chloride and 30 min of autoclaving. The Pd NP were predominantly polydisperse, anisotropic including triangles, tetragons, pentagons and hexagons. The particle size ranged from 5 to 31.2 nm and the mean particle size was about 14.3 ± 7.2 nm. The NP exhibited face centered cubic (fcc) crystal structure and FTIR confirms the role of sugars and proteins in reduction and stabilization. Further, the characterized NP were explored for their antibacterial, antifungal, antioxidant, catalytic and peroxidase mimicking properties. The biogenic Pd NP were non antimicrobial and exhibited significant antioxidant and dye decolourizing catalytic activities. The current investigation can be exploited for environmental remediation of toxic dyes and pigments. In addition, the peroxidase mimicking activity of Pd NP was optimized with respect to pH, temperature and concentrations of substrates. Especially, the superior peroxidase activity of the NP can have vast utilization in colorimetric detection of hydrogen peroxide in various matrices such as water, milk, honey and other food products.

Transition metal – Graphene oxide nanohybrid materials as counter electrodes for high efficiency quantum dot solar cells

Abstract We report the synthesis of new nanocomposite hybrids, based on graphene oxide (GO) incorporating Cu and Co transition metals. GO was produced through graphite oxidation using powerful oxidizing reagents and consecutively was functionalized with the use of CTAB and PSS surfactants. The resulting materials were further decorated with Cu and/or Co using an electrostatic self-assembly process through solvothermal treatment with the corresponding metal chlorides in an autoclave. The influence of metal precursor concentration in the final material characteristics was examined, using mass ratios of 1/4.5 and 1/9 for GO/Cu and GO/Co, and 1/4.5, 1/9 and 1/18 for the bimetallic GO/(Cu-Co) nanohybrid materials, respectively. The produced nanohybrid materials (GO/Cu, GO/Co and GO/(Cu-Co)) were characterized morphologically, structurally and electrochemically and consequently, they were incorporated in quantum dot sensitized solar cells (QDSCs). The novel hybrid materials work effectively as counter electrodes (CE) in CdS-ZnS/CdSe-based QDSCs presenting high photocurrent density (Jsc) and open-circuit voltage (Voc) values leading to enhanced photovoltaic performance. Optimization of the electrocatalytic activity as a function of the GO/(Cu-Co) mass ratio results in cells with a power conversion efficiency (PCE) of 8.73%.

Design and scale-up of a Cr-free Fe-Al-Cu catalyst for hydrogen production from waste-derived synthesis gas

Herein, we have prepared a series of Cr-free Fe-Al-Cu catalysts by the homogeneous one-step co-precipitation method and examined their ability to promote the water gas shift (WGS) reaction and thus facilitate the production of hydrogen from waste-derived synthesis gas. The prepared catalysts are confirmed to possess γ-Fe2O3, which can be more easily transformed into Fe3O4 than α-Fe2O3. The surface area, Fe3O4 crystallite size, reducibility, and Cu dispersion of these catalysts significantly depend on the concentrations of metal precursor. The catalysts effectively promote the WGS reaction without facilitating undesirable side reactions, achieving efficient hydrogen production and high CO conversion. The characteristics of the best-performing sample are preserved when the production is scaled up by a factor of 40 and thus obtained large-scale Fe-Al-Cu catalyst exhibits excellent reducibility and high CO conversion. Both commercial Fe-Cr and large-scale Fe-Al-Cu catalysts achieve close-to-equilibrium CO conversions at a gas hourly space velocity (GHSV) of 3000 mL g−1 h−1, but the latter showed a higher conversion than the former at a GHSV of 40,057 mL g−1 h−1 owing to the promotional effect of Cu on the easier reducibility of Fe species and the formation of additional Cu active sites. Thus, we demonstrate the possibility of finding Cr-free alternatives and show that the reducibility, Fe3O4 crystallite size, and Cu dispersion of the best-performing catalyst could be maintained upon upscaling, which made this catalyst well suited for converting waste-derived synthesis gas into H2.

High performance of AuPt deposited on Ni nanoparticles in ethylene glycol oxidation

The electrochemical deposition of small amounts of Au and Pt on the surface of Ni nanoparticles supported on reduced graphene oxide and the electrooxidation of ethylene glycol on the AuPt-decorated Ni/reduced graphene oxide catalysts in alkaline solution are investigated. By selecting a short deposition time, a low concentration of metal precursors, and a positive applied potential, AuPt loadings of less than 1.0 μg cm−2 are obtained. Physical and electrochemical characterizations of AuPt/Ni/reduced graphene oxide reveal a much lower content of Pt relative to Au. However, AuPt/Ni/reduced graphene oxide behaves similar to monometallic Pt/reduced graphene oxide rather than to Au/reduced graphene oxide in ethylene glycol oxidation, while Ni/reduced graphene oxide and Pt-decorated Ni/reduced graphene oxide show no activity. Compared to Pt/reduced graphene oxide or Au/reduced graphene oxide, the peak intensities of AuPt/Ni/reduced graphene oxide are somewhat higher in terms of the glassy carbon substrate, but are significantly higher in terms of the AuPt mass loading. Another attractive feature of AuPt/Ni/reduced graphene oxide is low cost resulted from the low AuPt loading. The result of this study indicates that decorating the surface of non-noble metal with a small amount of two noble metals is an efficient method to fabricate highly active catalysts.

Systematic Shape Evolution of Gold Nanocrystals Achieved through Adjustment in the Amount of HAuCl4 Solution Used

Past work on the synthesis of gold nanocrystals has revealed that changing the reaction cell potential enables particle shape evolution. Although various parameters in the Nernst equation has been used to achieve this, adjusting the metal precursor concentration has not been demonstrated before. Using the reported synthetic conditions with cetyltrimethylammonium chloride (CTAC) surfactants to grow gold nanocubes, rhombic dodecahedra, and octahedra as the starting points, fixing the ascorbic acid volume, and tuning the volume of HAuCl4 solution introduced allow the formation of the same series of crystal shape evolution from rhombic dodecahedral to trisoctahedral and cubic structures in the presence of a tiny amount of NaBr. In another series, by gradually increasing the HAuCl4 solution volume but fixing potassium iodide and ascorbic acid volumes, gold nanocrystals with tunable morphologies from octahedra to corner-truncated octahedra, edge- and corner-truncated octahedra, and rhombic dodecahedra can be sy...

Vulcan Xc-72R Supported Silver-Based Bimetallic Nanoparticles As Novel Electrocatalytic Platforms for Improve Performance in Oxygen Reduction Reactions

The Oxygen Reduction Reaction (ORR) is an essential process for energy transformation required by technological devices such as batteries and fuel cells.1,2 This reaction is responsible for controlling the activity and the activity of such devices suffers from a slow kinetic drawback at the cathode which hinders its overall performance.3 Thus, to accelerate ORR kinetics in a fuel cell, an active catalyst is required with qualities such as low cost and high catalytic stability.3 Platinum has proven to be the optimal catalyst for ORR but, due to its high cost and low abundance, adequate efforts have been made to be able to replace it.4 As of now, researchers have focused on silver metal because it is inexpensive and has proven to be a good catalyst for ORR in alkaline media.5 Hence, to improve the ORR in a fuel cell, we are depositing silver nanoparticles (NPs) onto electrochemically reduced vulcan XC-72R to achieve greater conductivity and surface area to the nanocomposite. Silver bimetallics have proven to be five times better in performance than pure silver in alkaline media. Thus, we will compare our Ag/GOx NPs with bimetallic NPs (Ag/Au) and (Ag/ Pd) at a 4:1 ratio to examine the catalytic activity for ORR. These nanocatalysts will be obtained directly using a robust electrodeposition method consisting of the rotating disk slurry electrode (RoDSE) technique in powder form, to obtain Ag nanoparticles highly dispersed on Vulcan XC-72R for ORR in alkaline media minimizing the time spent in catalyst preparation(fig 1). Afterwards, the sample’s electrochemical activity will be assessed for the ORR using both: cyclic voltammetry and spectroscopic analysis. The RoDSE method used to obtain highly dispersed Ag 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. This technique consists of dissolving a salt of the precursor metal in a carbon support to form the slurry solution in which a constant reducing potential is applied at a constant speed to achieve the electrodeposition of metal in the carbon support instead of the electrode.Particle size and characteristic of the bimetallic fcc crystal facets were determined by X-ray diffraction with an approximate size of 21.6, 18.8 and 19.8 nm for Ag, Ag/Au and Ag/Pd respectively. Cyclic voltammetry of electrodeposited 12 % Ag/Pd/Vulcan XC-72R showed a higher catalytic current density for oxygen reduction reaction when compared with the others bimetallic under study.

Facile one‐step high‐temperature spray pyrolysis route toward metal carbide nanopowders

AbstractFine ultrahigh‐temperature ceramic (UHTC) powders have found very important applications in many fields. In this work, a facile high‐temperature spray pyrolysis (HTSP) approach is implemented for the synthesis of HfC and TaC UHTC nanopowders starting from organic solvent (e.g., ethanol or 1‐pentanol) solutions of metal precursors (HfCl4 or TaCl5). It is proposed that, during HTSP, the precursor solution droplets would continuously undergo rapid drying, thermolysis (i.e., removal of low molecular weight species such as H2, H2O, and CO), and finally in situ carbothermal reduction (CTR) process to give rise to metal carbide nanopowders. The as‐obtained materials are shown by SEM as uniform and separated nanoparticles (~90 nm), whereas TEM reveals the carbide (e.g., HfC) nanoparticles are actually even smaller (~10‐20 nm) and embedded in amorphous carbon from excess solvent decomposition. It is found that among different processing parameters, the organic solvent used and the metal precursor concentration could largely influence the formation of metal carbide. In addition, lower HTSP temperatures (≤~1500°C for HfC) only lead to oxide‐carbon mixtures while higher temperatures (≥~1650°C) promote carbide formation. The HTSP method developed in this work is simple, low‐cost and efficient, and could potentially be optimized further for future large‐scale manufacturing of ultrafine UHTC nanopowders.