Formation Of Metal Particles Research Articles

Producing carbon nanotubes from thermochemical conversion of waste plastics using Ni/ceramic based catalyst

As the amount of waste plastic increases, thermo-chemical conversion of plastics provides an economic flexible and environmental friendly method to manage recycled plastics, and generate valuable materials, such as carbon nanotubes (CNTs). The choice of catalysts and reaction parameters are critical to improving the quantity and quality of CNTs production. In this study, a ceramic membrane catalyst (Ni/Al2O3) was studied to control the CNTs growth, with reaction parameters, including catalytic temperature and Ni content investigated. A fixed two-stage reactor was used for thermal pyrolysis of plastic waste, with the resulting CNTs characterized by various techniques including scanning electronic microscopy (SEM), transmitted electronic microscopy (TEM), temperature programmed oxidation (TPO), and X-ray diffraction (XRD). It is observed that different loadings of Ni resulted in the formation of metal particles with various sizes, which in turn governs CNTs production with varying degrees of quantity and quality, with an optimal catalytic temperature at 700 °C.

Deactivation of a Single-Site Gold-on-Carbon Acetylene Hydrochlorination Catalyst: An X-ray Absorption and Inelastic Neutron Scattering Study

Single-site Au species supported on carbon have been shown to be the active sites for acetylene hydrochlorination. The evolution of these single-site species has been monitored by Au L3 X-ray Absorption Spectroscopy (XAS). Alternating between a standard reaction mixture of HCl/C2H2 and the single reactants, has provided insights into the reaction mechanism and catalyst deactivation processes. We demonstrate that oxidative addition of HCl across an Au(I) chloride species requires concerted addition with C2H2, in accordance with both the XAS measurements of Au oxidation state and the reaction kinetics being 1st order with respect to each reactant. The addition of excess C2H2 changes the Au speciation and results in the formation of oligomeric acetylene species which were detected by inelastic neutron scattering. Catalyst deactivation at extended reaction times can be correlated with the formation of metallic Au particles. The presence of this Au(0) species generated during the sequential gas experiments or after prolonged reaction times, results in the analysis of the normalised near edge white line intensity of the Au L3 X-ray absorption spectrum alone becoming an unsuitable guide for identifying the active Au species, affecting the strong correlation between normalized white line height and VCM productivity usually observed in the active catalyst. Thus, a combination of scanning transmission electron microscopy and detailed modelling of whole XAS spectrum was required to distinguish active Au(I) and Au(III) species from the spectator Au(0) component.

Effect of the Polymer Molecular Weight on the Catalytic Properties of Polyacrylonitrile-Based Cobalt Composites in the Carbon Monoxide Hydrogenation Reaction

The effect of the polymer molecular weight on the catalytic properties of cobalt composites based on polyacrylonitrile (PAN) in the carbon monoxide hydrogenation reaction has been studied. It has been found that the CO conversion tends to 100% in the presence of any of the systems. It has been revealed that for the system based on PAN with a higher molecular weight, a quantitative CO conversion is observed at a lower temperature. It has been assumed that during the synthesis of the composite materials, the active phases undergo encapsulation differently. X-ray diffraction (XRD) analysis has revealed that the formation of metallic cobalt particles occurs regardless of molecular weight.

Forming a Highly Active, Homogeneously Alloyed AuPt Co-catalyst Decoration on TiO2 Nanotubes Directly During Anodic Growth.

Au and Pt do not form homogeneous bulk alloys as they are thermodynamically not miscible. However, we show that anodic TiO2 nanotubes (NTs) can in situ be uniformly decorated with homogeneous AuPt alloy nanoparticles (NPs) during their anodic growth. For this, a metallic Ti substrate containing low amounts of dissolved Au (0.1 atom %) and Pt (0.1 atom %) is used for anodizing. The matrix metal (Ti) is converted to oxide, whereas at the oxide/metal interface direct noble metal particle formation and alloying of Au and Pt takes place; continuously these particles are then picked up by the growing nanotube wall. In our experiments, the AuPt alloy NPs have an average size of 4.2 nm, and at the end of the anodic process, these are regularly dispersed over the TiO2 nanotubes. These alloyed AuPt particles act as excellent co-catalyst in photocatalytic H2 generation, with a H2 production rate of 12.04 μL h-1 under solar light. This represents a strongly enhanced activity as compared to TiO2 NTs decorated with monometallic particles of Au (7 μL h-1) or Pt (9.96 μL h-1).

Formation of metal (nano-)particles in drying latex films by means of a reducing plasma: a route to auto-stratification

Subjecting drying latex films, the water phase of which contains metal ions, to a reducing, low-temperature atmospheric pressure plasma results in the formation of metal (nano-)particles or a metal film. The process is demonstrated with gold and silver. A continuous metal layer forms on top of the film, when the salt concentration is high enough. At lower concentrations, particles are created inside the film. In the case of gold these are mostly nanoparticles, which are enriched at the top. The reduction drives an auto-stratification process.

Formation of metallic silver and copper in non-aqueous media by ultrasonic radiation

Concentrated suspensions of silver and copper salts in silicone oil were heated to 200 °C and irradiated with ultrasonic energy for different time durations. Characterization of the products was done using X-ray powder diffraction. In most cases, metallic Ag or Cu were obtained, together with their oxide forms Ag2O and Cu2O. The salts, used as precursors, do not dissolve in silicone oil but rather form a heterogeneous system, and we assume that local heating, caused by the acoustic cavitation, enhanced their thermal decomposition and the formation of metallic particles. It was found that the presence of silver particles enhances the formation of metallic copper. This phenomenon was observed in the experiment with the acetate salts mixture.

Development of the electrochemical synthesis method of ultrafine cobalt powder for a superalloy production

The electrochemical synthesis method for the preparation of ultrafine cobalt powder from the sulfate-ammonium electrolyte for the preparation of superalloys , has been developed. It was proposed to introduce ammonia to the electrolyte until рН=11. The electrolyte composition and the mechanism behind electrochemical processes during cobalt powder synthesis have been studied. The formation of the Co 2+ ammine complex has been observed. The precipitate dissolved in the mother liquor during a week, with the formation of a purple-red solution. By recording cathodic and cyclic cathodic-anodic curves, it was discovered that the solution with dissolved precipitate contained Со 3+ . It was revealed that the synthesis process occurs in two stages «Со 3+ –Со 2+ –Со 0 », which results in the increased polarization and formation of ultrafine cobalt powder. The influence of electrolyte temperature on electrolysis and powder characteristics has been studied. It was revealed that higher temperatures lead to larger particle size and formation of compact metal particles. It has been determined that the maximum electrolyte temperature should not exceed 30 °С. It is shown that under these conditions, the Co powder is composed of spherical particles that form coral-like aggregates with the size of 35–150 µm, which can be easily ground. The cobalt powder forms with the cathodic current yield of 39 % and specific power consumption of 48 kW·h/kg, which indicates a high effectiveness of the developed method.

Definition of synthesis parameters of ultrafine nickel powder by direct electrolysis for application in superalloy production

The optimization of the synthesis method of ultrafine nickel powder for the production of superalloys, by means of direct electrolysis of the nickel ammine complex, has been conducted. The influence of electrolyte temperature and ammonia concentration on the electrolysis process and powder characteristics has been studied. It has been revealed that an increase in electrolyte temperature leads to a larger particle size of the powder and formation of compact metal particles. It has been determined that the maximum electrolyte temperature must not exceed 50 °С. By recording the polarization curves, it was established that an increase in ammonia concentration leads to increased polarization of nickel formation and formation of finer powder. Lowering of ammonia concentration leads to contamination of the powder with barely soluble hydroxyl compounds of nickel. Analysis of the anodic curves has revealed that the nickel anode is partly soluble. It has been discovered that the addition of Trilon B to the electrolyte has a positive effect on powder characteristics. The powder formed under optimal conditions was composed of coral-like particles with the size of 40–70 µm, which could be easily ground to their spherical components if no compact metal particles were present. High purity of the powder was confirmed by the EDX. The cathodic and anodic current yields were determined to be: 35–41 % and 5–8 % respectively.

Synthesis and Application of Cerium-Incorporated SBA-16 Supported Ni-Based Oxygen Carrier in Cyclic Chemical Looping Steam Methane Reforming

Hydrogen, as a clean energy carrier, could be produced aided by cyclic oxidation-reduction of oxygen carriers (OCs) in contact with carbonaceous fuel in chemical looping steam methane reforming (CL-SMR) process. In this study, the cerium was incorporated into the SBA-16 support structure to synthesize the Ni/Ce-SBA-16 OC. The supports were synthesized using hydrothermal method followed by impregnation of Ni and characterized via low and wide angle X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), coupled with energy dispersive X-ray (EDX) spectroscopy, and transmission electron micrograph (TEM) techniques. In addition, the effect of various Si/Ce molar ratios (20–60) in the support structure, Ni loading (10–30 wt %), reaction temperature (500–750 °C), and life time of optimal oxygen carrier over 16 cycles were investigated. The results of wide angle XRD and SEM revealed that the incorporation of CeO2 in the channels of SBA-16 caused the formation of nickel metallic particles with smaller size and prevents the coke formation. The results showed that OC with 15 wt % Ni and Si/Ce molar ratio of 40 (15Ni/Ce-SBA-16(40)) has the best performance when compared with other OCs in terms of catalytic activity and structural properties. The methane conversion of about 99.7% was achieved at 700 °C using 15Ni/Ce-SBA-16(40) OC. We anticipate that the strategy can be extended to investigate a variety of novel modified mesoporous silica as the supporting material for the Ni based OCs.

Hydrogenation of Nitro and Unsaturated Organic Compounds over Catalysts Containing Nanosized Palladium Particles

The activity of palladium catalysts prepared on the basis of ZnO modified with polyethylene glycol (1 wt % Pd–PEG/ZnO) with molecular weights of 4000 and 6000 in the hydrogenation reaction of a series of nitro and unsaturated organic compounds has been studied. The catalysts are characterized by the formation of small metal particles with a size from 3 to 8 nm which uniformly coat the support surface. The results obtained have been compared to the catalytic properties of palladium-containing nanodiamonds and activated carbon under similar conditions.

Green synthesis of stabilized spherical shaped gold nanoparticles using novel aqueous Elaeis guineensis (oil palm) leaves extract

In the last decade, development of bioinspired protocols to synthesize gold nanoparticles (AuNPs) using plants and their extracts have been dealt by researchers due to their low cost, renewability and non-toxic features. A simple, cheap and ecofriendly method is reported to synthesize stabilized AuNPs of size 35–75 nm at room temperature using aqueous Elaeis guineensis (oil palm) leaves extract without addition of any external agent. Oil palm leaves mediated AuNPs were characterized using FTIR, UV–vis spectrophotometer, EDAX, XPS, FESEM, TEM, DLS and TGA. FTIR spectra results revealed contribution of phenolic, carboxylic, amines and amides in reduction of trivalent gold ions and stabilization of formed gold atoms. Reaction solution color change and UV–vis spectra confirmed reduction of gold ions to generate gold atoms. Reaction mechanism explained the role of phenolic compounds in reduction reaction using FTIR and UV–vis spectra results. EDAX and XPS results further validated the formation of metallic gold particles through bioreduction of gold ions. Crystal structure of metallic gold particles was confirmed through XRD peaks indexing to (111), (200), (220) and (311) planes. TEM and FESEM particles size measurements exhibited the formation of nanostructured AuNPs. Synthesis of well scattered and spherical shaped AuNPs was revealed through FESEM and TEM images. The excellent stability of AuNPs was shown through high negative zeta potential value (−14.7 ± 4.68 mV) and uniform dispersion in aqueous media. Our results disclosed the excellent potential of Elaeis guineensis (oil palm) leaves as reducing and stabilizing agents in green synthesis of well scattered spherical shaped AuNPs, which can be employed as strong candidates in medical drug delivery and industrial applications.

Metal transformation as a strategy for bacterial detoxification of heavy metals.

Microorganisms can modify the chemical and physical characters of metals leading to an alteration in their speciation, mobility, and toxicity. Aqueous heavy metals solutions (Hg, Cd, Pb, Ag, Cu, and Zn) were treated with the volatile metabolic products (VMPs) of Escherichia coli Z3 for 24 h using aerobic bioreactor. The effect of the metals treated with VMPs in comparison to the untreated metals on the growth of E. coli S1 and Staphylococcus aureus S2 (local isolates) was examined. Moreover, the toxic properties of the treated and untreated metals were monitored using minimum inhibitory concentration assay. A marked reduction of the treated metals toxicity was recorded in comparison to the untreated metals. Scanning electron microscopy and energy dispersive X-ray analysis revealed the formation of metal particles in the treated metal solutions. In addition to heavy metals at variable ratios, these particles consisted of carbon, oxygen, sulfur, nitrogen elements. The inhibition of metal toxicity was attributed to the existence of ammonia, hydrogen sulfide, and carbon dioxide in the VMPs of E. coli Z3 culture that might responsible for the transformation of soluble metal ions into metal complexes. This study clarified the capability of E. coli Z3 for indirect detoxification of heavy metals via the immobilization of metal ions into biologically unavailable species.

A Gallium-Based Magnetocaloric Liquid Metal Ferrofluid.

We demonstrate a magnetocaloric ferrofluid based on a gadolinium saturated liquid metal matrix, using a gallium-based liquid metal alloy as the solvent and suspension medium. The material is liquid at room temperature, while exhibiting spontaneous magnetization and a large magnetocaloric effect. The magnetic properties were attributed to the formation of gadolinium nanoparticles suspended within the liquid gallium alloy, which acts as a reaction solvent during the nanoparticle synthesis. High nanoparticle weight fractions exceeding 2% could be suspended within the liquid metal matrix. The liquid metal ferrofluid shows promise for magnetocaloric cooling due to its high thermal conductivity and its liquid nature. Magnetic and thermoanalytic characterizations reveal that the developed material remains liquid within the temperature window required for domestic refrigeration purposes, which enables future fluidic magnetocaloric devices. Additionally, the observed formation of nanometer-sized metallic particles within the supersaturated liquid metal solution has general implications for chemical synthesis and provides a new synthetic pathway toward metallic nanoparticles based on highly reactive rare earth metals.

G-C3N4 Hydrogen-Bonding Viologen for Significantly Enhanced Visible-Light Photocatalytic H2 Evolution

Graphitic carbon nitride (g-C3N4) has recently emerged as a promising metal-free photocatalytic material for the conversion of solar energy into chemical energy under visible-light irradiation. Unfortunately, the photocatalytic activity of g-C3N4 is still unsatisfactory due to the serious recombination of photogenerated electron–hole pairs. Here, we develop a strategy to construct a type of g-C3N4-based composite photocatalyst (C3N4/CBV2+), a g-C3N4 surface coupled with a viologen redox mediator (1,1′-bis(4-carboxylatobenzyl)-4,4′-bipyridinium dichloride, denoted as CBV2+) through hydrogen bonds, for enhanced H2 production from water under visible-light irradiation. The CBV2+ molecules not only provide sites for metal particle formation but also act as an efficient electron transfer mediator to transfer the photoinduced electrons from g-C3N4 to platinum nanoparticles (Pt NPs). The vectorial charge transfer results in an efficient spatial separation of electrons and holes in the C3N4/CBV2+ composite photoc...

Two-step photochemical inorganic approach to the synthesis of Ag-CeO2 nanoheterostructures and their photocatalytic activity on tributyltin degradation

Abstract Herein, we report a simple, sustainable and low-cost approach to design Ag-CeO 2 nanoheterostructures in pure aqueous and ethanol containing aqueous solutions via photochemical UV-light driven process with no capping agents nor stabilizers required. To this end, photochemically synthesized CeO 2 nanoparticles were applied as photoactive compounds in order to generate formation of metallic silver nanoparticles. Irradiation of deaerated CeO 2 suspensions in the presence of Ag + resulted in the rise of a strong surface plasmon resonance band with a maximum at 393–422 nm in the absorption spectra of the solutions, indicating formation of small metallic silver particles. Faster formation of Ag nanoparticles with the lower amount of silver precursor being required was observed when ethanol was introduced to the reaction solution before the irradiation. This implies that oxidative reactions can be strongly suppressed in deaerated ethanol containing solutions with respect to the pure aqueous media. Not only was the overall efficiency of the process remarkably increased by the use of alcohol, but also smaller and more uniform silver nanoparticles with a size comparable to that of ceria nanoparticles (around 15 nm) were formed when compared to those synthesized without radical scavengers as revealed by TEM analysis. The proposed photochemical approach enables the production of silver-semiconductor system without employing organic stabilizers, thus resulting in formation of nanoparticles with “clean”, highly reactive metal surface. The as-synthesized silver-ceria nanoheterostructures demonstrated enhanced visible light driven photocatalytic activity on tributyltin (TBT) degradation if compared to pure ceria nanoparticles.

Low-Pressure Hydrogenation of CO2 to CH3OH Using Ni-In-Al/SiO2 Catalyst Synthesized via a Phyllosilicate Precursor

The overall objective of this research is to convert the increasingly concerning CO2 and renewable H2 to highly demanded methanol (CH3OH), which creates a win–win scenario for simultaneous climate change prevention and sustainable economic development. The key to the success of this targeted CO2 utilization technology is the development of low-pressure methanol synthesis catalysts (NiaInbAl/SiO2; a = 0–8.3, b = 0–9.1) by means of a phyllosilicate precursor, allowing for formation of well-dispersed metallic particles with an average diameter of 2.5–3.5 nm. The catalysts were characterized with various methods including ICP-OES, N2 physisorption, XRD, SEM, TEM, TGA, H2 TPR, DRIFTS, and XPS. The performances of the NiaInbAl/SiO2 catalysts and conventional catalyst were compared under various evaluation temperatures at ambient pressure. It was found that catalysts with Ni/In ratios of 0.4–0.7 showed the highest activity. Ni3.5In5.3Al/SiO2 (NIA-0.7) with 15% metal loading was the best among the tested NiaInbAl...

Formation of Pd-group VIII bimetallic nanoparticles by the “water-in-oil” microemulsion method

Pd-based bimetallic catalysts PdM-0.1/C where M=Au, Pt, Ru, Ir with total metal loading of 2wt % and a Pd: M molar ratio of 10: 1 were synthesized by the “water-in-oil” microemulsion method. Metal particles are prepared by directly adding the reducing agent (NaBH4) as a powder to the metal salts − containing microemulsion (water/Triton X-114/cyclohexane). The monometallic Pd/C, Pt/C, Au/C, Ru/C and Ir/C catalysts were prepared with the same procedure. Physicochemical (XRD, XPS, SEM, HRTEM, EDS) and electrochemical (cyclic voltammetry) methods were applied to characterize the structure, morphology and surface properties of the synthesized catalysts. The microscopic results show that the mono- and bimetallic particles are monodisperse and well distributed on the carbon support. It is suggested that nucleation processes are mainly responsible for the metal particle formation if one uses the single-microemulsion procedure. The average size of the monometallic particles increased from Ir to Au. The size of all bimetallic PdM particles is smaller than that of Pd and they differ in the extent of surface segregation. The segregation is most pronounced in the PdAu and PdPt systems, resulting in a surface enrichment with Pd and Pt, respectively, whereas the PdRu and PdIr systems, in contrast, exhibit practically homogeneous alloy microstructure. It has been shown that these microstucture-induced surface effects are related to the catalytic properties of the PdM-0.1/C samples in the cinnamaldehyde hydrogenation reaction.

Multifunctional ferrimagnetic glass–ceramic for the treatment of bone tumor and associated complications

Silver-containing ferrimagnetic glass–ceramic (Ag-SC45) was synthesized by means of melt and quenching technique. Samples were subjected to morphological, compositional, structural analyses, ability to generate heat, magnetic measurements at high and low magnetic field and antibacterial test using S. aureus strain. The influence of silver introduction and the effect of annealing process were investigated. Morphological, compositional and structural analyses evidenced the formation of metallic silver particles embedded in the glass–ceramic. The hysteresis cycles showed slight differences in the hysteresis cycle area ratio and coercive field values as a function of the annealing treatment and of silver presence, while no difference was evidenced in the specific power loss. All samples demonstrated the ability to produce heat when exposed to an alternating magnetic field. Finally, preliminary antibacterial test showed that Ag-SC45 samples not subjected to annealing possessed an antibacterial effect.

Tuned interactions of silver nanoparticles with ZSM-5 zeolite by adhesion-promoting poly(acrylic acid) deposited by electrospray ionization (ESI)

The electrospray ionization (ESI) method was used for deposition of thin films of poly(acrylic acid) (PAA) on Cu/ZSM-5 (5 wt.% Cu) and Ag–Cu/ZSM-5 (1 wt.% Ag and 4 wt.% Cu) composites. For comparative purposes, the ZSM-5 zeolite was synthesized under hydrothermal conditions and loaded with PAA under the same treating conditions as the composites. This method allowed the formation of uniform polymer films of controlled thickness on conductive substrates. The structural characteristics were characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, atomic force microscopy and X-ray diffraction (XRD). The deposited PAA layer over ZSM-5 acts as a common dispersing and stabilizing agent through coordination-driven guest-templated polymer via interaction of Ag+ and Cu2+ with carboxylic acid groups, thus increasing and controlling the adhesion and the release of metallic species. A short exposure to light and temperature has reduced the metal ions to Cu0 and Ag0 metallic nanoparticles. The results of XRD analysis let suggest that the interaction of Cu and Ag with carboxylic groups of PAA inhibits the formation of large metallic silver particles. These samples were being studied for their potential as antibacterial agents toward the bacterial strains such as Staphylococcus pneumonia, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa as Gram positive and Gram negative bacteria, respectively. Aspergillus fumigatus and Candida albicans as Fungi were also evaluated. The Cu/ZSM-5 and Ag–Cu/ZSM-5 nanocomposites coated with a 10 nm thick PAA layer exhibit significant antibacterial activity.

Биметаллические Pd-Cu-композиты полианилина в электрокаталитическом гидрировании фенилацетилена

Bimetallic Pd-Cu-composites of polyaniline prepared by introducing metals (II) chlorides in the process of oxida-tive polymerization of aniline with and without chemical reduction by sodium borohydride are applied to copper cath-ode activation in electrohydrogenation of phenylacetylene in basic aqueous ethanolic solutions of catholyte. Electro-catalytic activity of composites that they exhibited in the process is due to formation of metal particles (and their al-loys) by electrochemical reduction of metal cations in the polymer matrix. The main hydrogenation products are ethyl benzene and 1,4-diphenylbutane, the yields of which influence metal content in the studied composites.