Citrate Method Research Articles

X-ray diffraction, luminescence, and electron paramagnetic resonance study of LaLuO3:Yb3+ nanopowders

The primary objective of materials science is the study of the properties of the existing materials and the development of new ones. In the present day, the use of solid-state lasers abroad has prompted material scientists globally to develop novel or enhance the properties of the existing active gain media. Materials comprising rare earth elements have historically proven effective in scintillation applications. The synthesis of LaLu1-xYbxO3 monodisperse nanopowders with a particle size of 50–62 nm via the Pechini complexing citrate method has been the subject of investigation using electron paramagnetic resonance (EPR) spectroscopy and photoluminescence (PL) measurements. The EPR data indicate that the Yb³⁺ ions predominantly create a single type of center, whereby the Yb³⁺ ion substitutes for the Lu³⁺ ion. The calculated EPR g-factors are estimated to be g1 = 3.85, g2 = 2.15, g3 = 1.55 and the 171Yb isotope hyperfine interaction constants are A1 = 600 × 10−4 cm−1, A2 = 700 × 10−4 cm−1, A3 ≈ 1800 × 10−4 cm−1. The principal values of the g factors and the hyperfine tensors indicate that the Yb site in LaLu1-xYbxO3 nanopowders exhibits orthorhombic symmetry. The PL measurements in the wavelength range of 350–1800 nm, with excitation provided by either a xenon lamp or a diode laser, indicate the presence of a broad emission band, centered at 404 nm, in addition to the well-known emission spectrum in the IR region (920–1100 nm) arising from Yb3+ ions.

Study of the Kinetics of Nucleation and Growth of Silver Nanoparticles: UV-Visible Spectroscopy vs. Atomic Force Microscopy and Transmission Electron Microscopy

Silver nanoparticles have been the subjects of research interest because of their unique properties and extensive use in modern-day applications. A variety of preparation techniques have been reported for their synthesis but among them mostly recognized is a modified version of the Turkevich citrate method. In this study, we also chose this method of silver nanoparticle synthesis. The synthesized nanoparticles were characterized first, traditionally with UV-Visible spectroscopy and then their sizes and shapes were identified employing Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). From the UV-Vis data were extracted the rate constants for the nucleation ($$k_1$$) and growth ($$k_2$$) of the silver nanoparticles, and then these constants were further used to fit those obtained from AFM and TEM. Using the values of $$k_1$$ and $$k_2$$ independently in the two experimental methods validated and supported the well-acknowledged two-step mechanism of slow nucleation and fast autocatalytic surface growth.

Synthesis and characterisation of high-purity alumina achieved through a dip coating process

ABSTRACT This study focuses on the synthesis of alumina using a modified citrate method. The chelation process involved thermal activation through biphasic drops, employing the hydrated aluminium nitrate precursor and citric acid complex. The thermal behaviour of the resulting gel was investigated using DSC/TGA followed by FTIR, which revealed absorption bands at distinct temperatures leading up to the formation of white crystallised alumina powder at 1000°C. Structural analysis via XRD parameters indicated that the obtained sample is refined in the hexagonal system with the R-3C space group. SEM observations demonstrated morphology akin to an overlapping hive, highlighting significant stoichiometric purity. The semi-colloidal sol was applied in a dip-coating method to reinforce the matrix of a steel substrate, specifically E335. SEM-EDS analyses revealed the adhesion recorded as a brittle intermetallic phase. Additionally, a transformation of 22% haematite to magnetite was observed under the conditions of coating.

One-Pot Synthesis of Pd Nanoparticles Supported on Carbide-Derived Carbon for Oxygen Reduction Reaction.

We explored two methods for synthesizing Pd nanoparticles using three different carbide-derived carbon (CDC) support materials, one of which was nitrogen-doped. These materials were studied for oxygen reduction reaction (ORR) in 0.1 M KOH solution, and the resulting CDC/Pd catalysts were characterized using TEM, XRD, and XPS. The citrate method and the polyol method using polyvinylpyrrolidone (PVP) as a capping agent were employed to elucidate the impact of the support material on the final catalyst. The N-doping of the CDC material resulted in smaller Pd nanoparticles, but only in the case of the citrate method. This suggests that the influence of support is weaker when using the polyol method. The citrate method with CDC1, which is predominantly microporous, led to a higher degree of agglomeration and formation of larger particles in comparison to supports, which possessed a higher degree of mesoporosity. We achieved smaller Pd particle sizes using citrate and NaBH4 compared to the ethylene glycol PVP method. Pd deposited on CDC2 and CDC3 supports showed similar specific activity (SA), suggesting that the N-doping did not significantly influence the ORR process. The highest SA value was observed for CDC1/Pd_Cit, which could be attributed to the formation of larger Pd particles and agglomerates.

Gold Nanoparticles Downregulate IL-6 Expression/Production by Upregulating microRNA-26a-5p and Deactivating the RelA and NF-κBp50 Transcription Pathways in Activated Breast Cancer Cells.

MicroRNAs (miRNAs) are involved in the modulation of pathogenic genes by binding to their mRNA sequences' 3' untranslated regions (3'UTR). Interleukin-6 (IL-6) is known to promote cancer progression and treatment resistance. In this study, we aimed to explore the therapeutic effects of gold nanoparticles (GNP) against IL-6 overexpression and the modulation of miRNA-26a-5p in breast cancer (BC) cells. GNP were synthesized using the trisodium citrate method and characterized through UV-Vis spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). To predict the binding of miR-26a-5p in the IL-6 mRNA's 3'UTR, we utilized bioinformatics algorithms. Luciferase reporter clone assays and anti-miRNA-26a-5p transfection were employed to validate the binding of miR26a-5p in the IL-6 mRNA's 3'UTR. The activity of RelA and NF-κBp50 was assessed and confirmed using Bay 11-7082. The synthesized GNP were spherical with a mean size of 28.3 nm, exhibiting high stability, and were suitable for BC cell treatment. We found that miR-26a-5p directly regulated IL-6 overexpression in MCF-7 cells activated with PMA. Treatment of MCF-7 cells with GNP resulted in the inhibition of IL-6 overexpression and secretion through the increase of miR26a-5p. Furthermore, GNP deactivated NF-κBp65/NF-κBp50 transcription activity. The newly engineered GNP demonstrated safety and showed promise as a therapeutic approach for reducing IL-6 overexpression. The GNP suppressed IL-6 overexpression and secretion by deactivating NF-κBp65/NF-κBp50 transcription activity and upregulating miR-26a-5p expression in activated BC cells. These findings suggest that GNP have potential as a therapeutic intervention for BC by targeting IL-6 expression and associated pathways.

Catalytic Oxidation of CO over LaNi1/3Sb5/3O6 Synthesized by Different Methods

Methods for the synthesis of LaNi1/3Sb5/3O6 with a rosiaite structure have been developed using citrate method and coprecipitation followed by annealing. The influence of synthesis conditions on the morphology of the samples has been demonstrated. A comparative analysis of the catalytic properties of LaNi1/3Sb5/3O6 synthesized by various methods, in the reaction of CO oxidation has been carried out. The catalyst synthesized by the citrate method demonstrated the greatest efficiency and stability (the temperature of 90% CO conversion was T90 = 336°C). The LaNi1/3Sb5/3O6 surface was studied before and after catalysis by in situ diffuse reflectance IR spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed O2 desorption. It has been shown that the catalytic oxidation of CO on the LaNi1/3Sb5/3O6 surface proceeds according to the Mars–van Krevelen mechanism and is accompanied by redox Sb3+ ↔ Sb5+ processes. It has been established that no contamination of the sample surface occurs during the catalysis process.

Removal of Pb(II) ions by cellulose modified-LaFeO3 sorbents from different biomasses

LaFeO3 perovskite is prepared by the cellulose-modified microwave-assisted citrate method using two different biomasses as a cellulose source; rice straw (RS) and banana peel (BP). The prepared samples are assigned as LaFeO3/cellulose-RS and as LaFeO3/cellulose-BP, respectively. Raman Spectra prove the presence of perovskite and cellulose phases, as well as biochar resulted from the thermal treatment of the cellulose. LaFeO3/cellulose-RS has a cauliflower morphology while, two phases are observed for LaFeO3/cellulose-BP, mesoporous cellulose phase and octahedral LaFeO3 nanoparticles as shown by scanning electron microscope (SEM) images. LaFeO3/cellulose-BP has higher porosity and larger BET surface area than LaFeO3/cellulose-RS. Both samples are applied for the removal of Pb(II) ions from aqueous solution by adsorption. The adsorption follows Langmuir isotherm, with maximum adsorption capacities of 524 and 730 mg/g for LaFeO3/cellulose-RS and LaFeO3/cellulose-BP, respectively. Cellulose precursors from different biomasses affect structural and morphological properties of LaFeO3/cellulose samples as well as the sorption performance for Pb(II) ions. BP is more recommended than RS, as a biomass, in the present study.

Magnetic/optical assessments of RFeO3 (R=La, Pr, Nd, and Sm) ceramics: An experimental and theoretical discernment

Experimental and Density Functional Theory (DFT) studies on the structural, magnetic and optical properties of rare-earth orthoferrites RFeO3 (R = La, Pr, Nd, and Sm) were performed. The synthesis was carried out via the Ethylenediaminetetraacetic acid (EDTA)-citrate method. All these perovskites exhibited orthorhombic crystal structures with a space group Pbnm, and their lattice parameters and unit cell volumes decreased as a function of the rare earth ionic radius, as it was expected. The microstructural analysis indicates that all the perovskites share similar textural properties. The magnetic characterization revealed a weak ferromagnetic behavior attributed to the canted antiferromagnetic Fe3+ sublattices, with the dominant magnetic configuration identified as the G-type. Super-exchange interactions between Fe3+-O-Fe3+, R3+-O-Fe3+, and R3+-O-R3+ couplings facilitated a long-range magnetic ordering. The optical characterization indicated d-d electronic transitions, and the perovskites were confirmed as semiconductors with a bandgap of approximately 2.1 eV. The calculation of the transition dipole moment demonstrates two significant aspects: the electronic transition is direct and allowed, and its enhancement is evident in the Sm sample. Overall, this study provides valuable insights into the crystal structure, magnetic properties and optical behavior of RFeO3 perovskites, synthesized via the EDTA-citrate method.

Highly efficient lead removal from water by Nd0.90Ho0.10FeO3 nanoparticles and studying their optical and magnetic properties

Ho-doped NdFeO3 was synthesized using the citrate method. The X-ray diffraction (XRD) illustrated that Nd0.90Ho0.10FeO3 was crystalline at the nanoscale, with a crystallite size of 39.136 nm. The field emission scanning electron microscope (FESEM) illustrated the porous nature of Nd0.90Ho0.10FeO3, which increases the active sites to absorb the heavy metals on the sample surface. Energy-dispersive X-ray (EDX) data assures the prepared sample has the chemical formula Nd0.90Ho0.10FeO3. The magnetic properties of Nd0.90Ho0.10FeO3 were determined using the magnetization hysteresis loop and Faraday’s method. Many magnetic parameters of the sample have been discussed, such as the coercive field, the exchange bias (Hex), and the switching field distribution (SFD). Ho-doped NdFeO3 has an antiferromagnetic (AFM) character with an effective magnetic moment of 3.903 B.M. The UV–visible light absorbance of Nd0.90Ho0.10FeO3 is due to the transfer of electrons from the oxygen 2p state to the iron 3d state. Nd0.90Ho0.10FeO3 nanoparticles have an optical direct transition with an energy gap Eg = 1.106 eV. Ho-doped NdFeO3 can adsorb many heavy metals (Co2+, Ni2+, Pb2+, Cr6+, and Cd2+) from water. The removal efficiency is high for Pb2+ ions, which equals 72.39%. The Langmuir isotherm mode is the best-fit model for adsorbing the Pb2+ ions from water.

In English

Gold nanoparticles (Au NPs) have found a variety of applications in different areas, particularly in biomedical practices. The activity of Au NPs strongly depends on the size and association of particles in colloid, that in turn are greatly affected by experimental parameters of the reaction. The obtaining of Au NPs even via classical procedure of citrate method can be a challenge. In the present work we applied different experimental approaches to affect the process of Au NPs formation in the presence of sodium citrate. Au NPs were obtained using different experimental procedures and varying the ratio of reagents, their concentrations, temperature of reaction, duration of heating, the order of introduction of reagents into the reaction mixture, pH, and so on. Comparative analyses of UV-vis spectra with DLS data by number, volume and intensity basis allowed to trace the changes in Au NPs colloid, find optimal experimental conditions and predict prolonged stability of colloids. Applying size-dependent Hamaker constant to DLVO theory explains experimental results. The formation of Au NPs strongly depends on the ratio of the functional groups of the molecule involved simultaneously in the reduction of metal ions, the binding to the surface of Au NPs and the formation of a charge for stabilization due to electrostatic repulsion. The change in the ratio of components is not enough to get a different size of Au NPs. Big concentration of the reagents mostly affects the aggregation process and colloid aging. Temperature is a critical activation factor, that should be about 100 °C, but prolonged heating causes collision induced aggregation. The initial stage of particles growth (the mechanism) can be affected with the change of pH of the system due to formation of deprotonated carboxyl groups and gold hydroxocomplexes.

Synthesis and Evaluation of Properties of an Additive Based on Bismuth Titanates for Cement Systems.

The development of modern building materials science involves the process of designing innovative materials that exhibit unique characteristics, such as energy efficiency, environmental friendliness, self-healing ability, and photocatalytic properties. This can be achieved by modifying cement with nano- and fine-dispersed additives that can give the material new properties. Such additives include a number of compounds based on the TiO2-Bi2O3 system. These compounds have photocatalytic activity in the near-UV and visible range of the spectrum, which can serve to create photocatalytic concretes. Here, the purpose of this scientific study was to synthesize compounds based on the TiO2-Bi2O3 system using two methods in order to identify the most optimal variant for creating a composite material and determine its properties. Within the framework of this article, two methods of obtaining a photocatalytically active additive based on the TiO2-Bi2O3 system are considered: the solid-state and citrate-based methods. The photocatalytic, mechanical and structural properties of composites containing the synthesized additive are investigated. In this study, it was found that for the creation of photocatalytic concretes, it is advisable to use cement compositions with a bismuth titanate content of 3-10 wt.%. of the cement content, regardless of the method of obtaining the additive. However, the most optimal composition is one containing 5 wt.% of the synthesized additive. It is noted that compositions containing 5% by weight of bismuth titanate demonstrate photocatalytic activity and also show an increase in strength on the first day of hardening by 10% for the solid-state method and 16% for the citrate method.

Detailed investigation on structural, optical, dielectric and magneto-dielectric properties with enhanced magneto-impedance characteristic of NdFeO3 nanoparticles

NdFeO3 (NFO) was synthesized using sol-gel citrate method and subsequent calcination at 1023 K. Utilizing Rietveld refinement analysis of the XRD pattern, it has been verified that NFO exhibits an orthorhombic crystal structure, with space group Pbnm. NFO grains were seen to be strongly agglomerated in a SEM image, despite their irregular shapes. The analysis of optical properties revealed a transmittance range of ∼20%–∼50% and an optical band gap of 2.15 eV for the NFO material. The dielectric properties of NFO were analyzed with respect to their dependence on frequency and temperature, while the ac electrical conductivity was studied in terms of its frequency variation. The dielectric dispersion behavior of NFO is explained by Maxwell Wagner-type polarization. A negative magneto-dielectric (MD) coupling of −19% and −35% was measured for ε and tanδ at 1 kHz for NFO. Magneto-impedance measurements on NFO showed positive magneto-resistance and both positive and negative magneto-capacitance, suggesting that the grain effect had a substantial role in the material's magnetic properties. These results suggest that NFO is an excellent choice for memory-based electronic devices with an appropriate band gap for optoelectronic applications having a large MD effect.

Electrochemical biodetection of glucose using La0.6Sr0.4Co0.8Fe0.2O3 and La1,7Sr0,3CuO4 Nano-Particles modified with black carbon deposited on glassy carbon electrode

Non-enzymatic developed biosensors, especially with noble nanoparticles received tremendous attention in the field of glucose molecule sensing. Herein low-cost, highly sensitive, and more effective nano-sized materials such as La1,7Sr0,3CuO4 and La0.6Sr0.4Co0.8Fe0.2O3 were synthesized by a simple citrate method, and modified with black carbon in purpose to use as electrodes for the simultaneous detection of glucose. The crystallite size, refinement, purity, shape, and morphology of nanomaterials were characterized using X-ray diffraction and Scanning Electron Microscopy techniques. Cyclic voltammetry, Differential Potential Voltammetry, Square Wave Voltammetry, and Electrochemical Impedance Spectroscopy techniques were used as investigative techniques. The modified electrodes showed excellent response and sensitivity for glucose molecule detection compared with previous literature, with a wide linear range from 0.1 M to 0.1 nM for La0.6Sr0.4Co0.8Fe0.2O3 and 0.1 M to 0.001 nM for La1,7Sr0,3CuO4, high sensitivities of 614.7 and 876.3 µA.mM−1.cm−2 and low detection limits of 0.972 nM and 0.0194 nM respectively. The performance of electrodes was checked by using real samples like synthetic urine and human blood. Both of the modified electrodes demonstrated satisfactory and reproducible results in real samples.

Synthesis, characterization, and feasibility investigation of dysprosium-doped samarium iron oxide nano-powder/polydimethylsiloxane (Dy-SmFeO/PDMS) nano-composite for dynamic magneto-mechanical stability

In this study, the synthesis and characterization of a dysprosium-doped samarium iron oxide nano powder/polydimethylsiloxane (Dy-SmFeO/PDMS) nano-composite are described. The sol-gel citrate method was employed for the synthesis, yielding highly polycrystalline nano powders with a polymorphic distribution, as revealed by X-ray diffraction and Rietveld analysis. Raman spectroscopy was utilized to investigate the chemistry of the nano powders. Notably, the readings obtained using a vibrating sample magnetometer highlighted the intriguing ferromagnetic-to-antiferromagnetic coupling behavior of the samples. The field-emission scanning electron microscopy analysis indicated that the orthorhombic crystal surfaces were uniformly encapsulated by PDMS. Furthermore, a dynamic mechanical analysis was conducted under the influence of a magnetic field (1000 mT) revealed the excellent mechanical stability of the composite. This research highlights the potential of the Dy-SmFeO/PDMS composite as a promising magnetic material with desirable properties, opening up possibilities for various applications in fields such as micro-magnetic devices, sensors, spin valves, and actuators.

Magnetic and Terahertz–Infrared Properties of Nanodispersed Hexaferrite SrxBa(1−x)Fe12O19 Solid Solutions

Hexagonal ferrites with the formula SrxBa(1−x)Fe12O19 (x = 0; 0.3; 0.5; 0.7; and 1) were prepared using the citrate method. The main feature of this synthesis is a relatively low calcination temperature of 700 °C. An X-ray diffraction study revealed a single-phase material. According to SEM, the particles were 50−70 nm in diameter. The Curie temperature of the samples that were determined using the DSC method varied in a very narrow range of 455−459 °C. Analysis of the magnetic hysteresis loops obtained at 300 K and 50 K indicated all samples as magnetically hard materials in a single-domain state. The maximal magnetic characteristics encompass strontium hexaferrite. The terahertz spectra of complex dielectric permittivity and the spectra of infrared reflectivity were measured at room temperature in the range of 6–7000 cm−1. The obtained broad-band spectra of the real and imaginary parts of permittivity reveal significant changes associated with structural distortions of the (Sr,Ba)O12 anti-cuboctahedron caused by the substitution of Ba2+ with Sr2+ in the same crystallographic positions.

Ni/Al2O3 supported on cordierite monoliths for methane steam reforming: Influence of catalyst coating methodology

This paper progressed in relation to literature by comparing three methods of Ni/Al2O3 deposition on cordierite monoliths, characterized and evaluated in methane steam reforming. The citrate method presented strong adherence of a uniform catalyst layer but exhibited only 7% of methane conversion at 800 °C and H2O/CH4 = 3. In contrast, Ni/Al2O3 co-precipitated deposition exhibited 99% of methane conversion but the lowest adherence. At least, Al2O3 coating followed by NiO wet impregnation showed strong adherence of the catalyst layer and high activity (98% conversion), attributed to nickel availability on the cordierite surface, proving to be the most efficient and suitable deposition method.

The Effect of Heteroatom-Doped Graphene Supports on the PtNPs Electrocatalytic Activity for ORR

There has been a global shift in energy production emphasizing the reduction of fossil fuels by the augmentation of more renewable energy. Proton-exchange membrane fuel cells (PEMFC) and anion-exchange membrane fuel cells (AEMFC) can mitigate a need for fossil fuels and provide an alternative route of hydrogen-based energy production. Fuel cells utilize a catalyst at both the cathode and anode to increase the overall kinetics of the redox reactions and enhance the cell performance.1 Current fuel cell technology employs a platinum based catalyst due to its efficiency and robust performance in both alkaline and acidic environments.1,2 The drawbacks associated with Pt-based catalysts are centered around its economic viability and its affinity towards surface poisoning.1 A catalyst using platinum nanoparticles (PtNPs) loaded onto a graphene support can address some of the aforementioned drawbacks.1 To maximize the electrocatalytic activity of the PtNPs – all aspects of the PtNPs catalyst must be optimized, which includes the optimization of the support material. The effect that the different commercially available heteroatom-doped graphene had on the activity of the PtNPs was investigated during this study. The PtNPs were synthesized using the citrate method, which produces ≤ 5 nm size particles. Our study confirmed that the choice of doped graphene support has an effect on the overall activity of PtNPs. The results were confirmed via a comparison with PtNPs supported on Vulcan XC-72R carbon. All Pt catalysts supported on the doped graphene showed an improvement in the oxygen reduction reaction (ORR) half-wave potentials (E 1/2) over PtNPs on Vulcan XC-72R carbon (Fig. 1A); with the nitrogen-doped graphene exhibiting the greatest improvements in the half-wave potential with the E 1/2 value of 0.85 V vs. RHE as compared to the 0.77 V of the Pt/C. A comparison of the Tafel slopes (Fig. 1B) confirmed that the transfer of the first electron was the rate-determining step for all of the Pt catalysts supported on doped graphene as all Tafel slopes were around -120 mV per decade. This has been confirmed in literature with Pt on various carbon supports.2 Figure 1. A) Comparison of RDE polarization curves for oxygen reduction on Pt/NGr (pink), Pt/SGr (green) and Pt/N-PGr (blue) with Pt/C (black) at 1900 rpm in a O2-saturated 0.1 M HClO4 solution (v= 10 mV s−1). B) Mass transfer corrected Tafel plots derived from A

Quality indicators of a complex veterinary drug with hepatoprotective effect and their control

Hepatopathy (toxic hepatitis and hepatosis) are widespread among sows kept in industrial complexes. To carry out therapeutic and preventive measures for these diseases, a complex drug with a hepatoprotective effect is in demand. In its industrial production, quality control is necessary with an assessment of the presence and quantity of active components. To control of the quality of the Karnivit drug, organoleptic (appearance and color), chromatographic (high performance liquid chromatography - HPLC) (authenticity and mass concentration of vitamin E and carnitine), qualitative chemical (authenticity of zinc and sodium citrate) were used), titrimetric (mass concentration of zinc), spectrophotometric (mass fraction of sodium citrate) methods. The gravimetric (weight) method was used to assess the moisture content of the preparation. The assessment of the compliance of the obtained values with the regulatory requirements was carried out after the introduction of exactly known amounts of one or another active substance into the preparation (for three series at different shelf life). It was found that the values of quantitative indicators in all cases were within the normative values, qualitative indicators (appearance, color, authenticity) also met the requirements of the norm established by the developer of the drug. These requirements were met by both the calculated average values of the indicators of various series and individual (point) values for each series. Determination of the physicochemical properties of the three series of the drug showed their compliance with the established regulatory requirements at different periods of storage. The developed methods of control are suitable for assessing the compliance of manufactured batches (series) of the drug with the requirements of technical specifications for production.

Oxygen reduction reaction on AgPd nanocatalysts prepared by galvanic exchange

In this work galvanic exchange was employed as bimetallic catalyst preparation method to obtain AgPd nanocatalysts. Ag nanoparticles synthesized by the citrate method and commercial silver nanowires (AgNWs) were used for Pd spontaneous deposition. From transmission electron microscopy images, the particle sizes were determined between 10 and 20 nm and AgPd particles with the Ag/Pd molar ratio of 18:82 obtained using MP-AES were larger compared to those of 89:11 ratio. The galvanic exchange process resulted in porous and half-moon shaped particles. Pd distribution for AgPd/C_1 (18:82) and AgPd/C_2 (56:44) catalysts was rather uniform. Decreasing the amount of Pd salt in the galvanic exchange bath led to only surface decoration of Ag particles as can be seen in the case of AgPd/C_3 (79:21) and AgPd/C_4 (89:11). AgPd120NW and AgPd80NW samples showed the Ag/Pd ratio of 82:18 and 94:6, respectively. The electrocatalysts were studied for oxygen reduction reaction (ORR) in alkaline media using the rotating disk electrode technique. Higher specific activity values for ORR were obtained on larger particles, however galvanic exchange process was not limited to surface layers, thus increasing Pd content resulted in lower mass activities. For all the AgPd catalysts a typical Tafel slope value of ∼−60 mV was observed.

Effects of gold and platinum on the activity of catalysts for the complete oxidation reaction of hydrocarbons and carbon monoxide

This study presents synthesis results of catalysts made of perovskite-like oxide La2-xSrxCuO4 (x=0.0, 0.5, 1.0) using the citrate method and crystallisation at 800°C. The structure of the catalysts was characterised by X-ray diffraction (XRD). The perovskite-like oxide catalyst activity was enhanced with gold (Au) and platinum (Pt). Au was mounted on the perovskite-like oxide catalysts by the sol-gel method. The activity of the perovskite-like oxide La2-xSrxCuO4 (x=0.0, 0.5, 1.0) and the perovskite catalyst LaMnO3/LaCuO3 was evaluated by complete oxidation of volatile hydrocarbons (HCs) in a mixture of toluene and methyl ethyl ketone (MEK) and carbon monoxide (CO) in a microflow analysis system combined with gas chromatography. The results showed that the light-off temperature (the 50% conversion temperature of the catalysts) of the Pt, Au/perovskite catalyst samples decreased significantly. The light-off temperature of the Au/LaSrCuO4 Au nanoparticle catalysts in the complete CO oxidation reaction reached a temperature of 150°C, lower than the Pt/LaSrCuO4 catalyst (170°C), allowing replacement of previous Pt catalysts with Au nanoparticle catalysts. The LaSrCuO4 catalyst had better oxidising activities than the La2CuO4 catalyst, indicating that the addition of strontium (Sr) has increased the catalyst activity, and demonstrates the potential for application in catalytic converters in motorcycles.