Au-doped Samples Research Articles

Study on Method of Doping Au Nanoparticles on ZnO Stratified Microstructure to Enhance Photocatalytic Ability and Antibacterial Activity

In this study, stratified microstructure gold/zinc oxide (Au/ZnO) composites were successfully prepared by the method of dispersing Au nanoparticles (Au NPs) on the surface of the hierarchical flower ZnO via HAuCl4 reduction in the presence of different reducing agents such as sodium citrate (SC), sodium borohydride (SB), sodium hydroxide and ethanol (SE), and Hg lamp 250W. Au-doped samples were named Au/ZnO-SC, Au/ZnO-SB, Au/ZnO-SE, and Au/ZnO-Hg lamp, respectively. Au/ZnO-SC and Au/ZnO-SB revealed the uniform distribution of Au nanoparticles on the ZnO substrate, meanwhile, Au nanoparticles were very densely distributed in Au/ZnO-SE and Au/ZnO-Hg lamp samples. The pure ZnO only showed an absorption peak in the ultraviolet (UV) region, Au/ZnO samples indicated additional absorption peaks in the visible light region (500-600 nm), which were characteristic of the surface plasmon resonance (SPR) effect of Au NPs in composites. Therefore, their bandgap energy was reduced compared to ZnO (3.202 eV), leading to increased photocatalytic efficiency under visible light irradiation. Among the doped samples, Au/ZnO-SC (with Au content as 5 wt%) had the largest surface area (26.23 m2/g) and the highest pore volume (0.263 cm3/g) and average pore width (33.2 nm). As a result, it showed the highest catalytic efficiency through complete degradation of tartrazine (TA) within 30 min with a reaction rate of 0.124 min−1 under Hg lamp 250 irradiation. In addition, both pure ZnO and Au/ZnO nanocomposites exhibited high antimicrobial activity in killing Escherichia coli (E. coli), and their enhancing effect of them was reliant on the weight ratio of Au on ZnO and the concentration of tested samples. These results indicated that Au/ZnO material has prominent potential for applications in water environment treatment. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Evaluation of magnetotransport properties of Au added YBCO ceramics: combination of experimental and advanced theoretical approaches

The purpose of this work is to investigate the change of flux pinning ability, superconducting and physical properties of gold particle addition in the YBa2Cu3O7-x (YBCO) superconducting matrix using temperature dependent resistivity measurements under different applied magnetic fields; namely 0.0, 0.3, 1.0, 2.0, 5.0 and 7.0 T. The room temperature resistivity, transition temperature (Tc), transition width (∆Tc) and mobile hole carrier concentration values for each sample have separately been determined. In addition, we estimated the field-dependent activation energy (U0), irreversibility field (µ0Hirr), upper critical field (µ0Hc2), penetration depth (λ) and coherence length (ξ) with the quantum mechanical approaches related to the fluxoid mechanism for all the samples prepared. It was found that the flux pinning energy values evaluated by Thermally Activated Flux Creep (TAFC) model were determined to be about 11,455 K, 13,413 K, 10,350 K and 9320 K for the undoped, 1 wt%, 5 wt% and 20 wt% Au doped samples, respectively. Moreover, the results obtained showed that the critical temperature, activation energy, irreversibility and upper critical field values were found to depend strongly on the gold content and applied magnetic field strength. The values of µ0Hirr, µ0Hc2, λ and ξ (∆Tc) initially exhibited a slight increment (decrement) followed by a decrease (increase) for the samples with the higher gold-doping concentrations. The possible reasons regarding the observed changes in flux pinning and fundamental superconducting properties due to gold-doping in YBCO superconductors were discussed in detail. We indicated that a certain amount of gold doping has an effective role to form the nucleation centers that serve as the active flux pinning regions in the YBCO system so that the quality of interaction between the superconducting grains and inter-granular coupling strength in the adjacent multilayers can increase remarkably.

Highly sensitive isoprene gas sensor using Au-loaded pyramid-shaped ZnO particles

Highly sensitive sensors to detect small amounts of gases are expected to be used for monitoring air quality and analyzing breath for medical diagnosis. We report a highly sensitive isoprene gas sensor using Au-loaded pyramid-shaped ZnO particles. The pyramid-shaped ZnO particles with (0001) base and {10 1¯1¯} six side surfaces were synthesized solvothermally. Loading of 0.5 % Au nanoparticles successfully increased the sensor response. The response value (the resistivity ratio in air and isoprene gas) to 50 ppb isoprene gas was 42 at 350 °C in dry air, which is remarkably higher than that of previously reported sensors of metal-oxide semiconductors. Under 80 % relative humidity, the response value to 50 ppb was 4.8. The isoprene concentration dependence of the sensor response implied that 10 ppb can be detected with a response value of 1.4 and that diagnosis of liver diseases and sleep state is possible. Enhanced selectivity compared to acetone, ethanol and hydrogen was confirmed in Au-doped samples.

Modeling of Micro-Hardness in the Au-Doped YBCO Bulk Superconductors

In this study, in order to investigate the effect of Au doping on mechanical properties of YBCO, Au-doped (from x = 1 wt% to x = 20 wt%) and pure YBa2Cu3O7-x samples were prepared by standard solid-state reaction method. The indentation load versus diagonal length of the samples under various indentation loads in the range of 0.245–2.940 N is measured. The micro-indentation measurements showed that the load-dependent micro-hardness value for Au-doped samples is lower in comparison with that of the pure sample. The values of the hardness are found to be load and Au content-dependent. For each sample, the reverse indentation size effect (RISE) is observed in which micro-hardness value increased with increasing the load. In addition, we extract the load-independent (true) micro-hardness using Meyer’s law, Kick’s law, proportional specimen resistance, modified proportional specimen resistance, the Hays-Kendall, and the indentation-induced cracking (IIC) models and compare the true hardness with the apparent hardness. Among the investigated models, IIC model is determined to be the most successful one describing the mechanical properties of our samples.

Optical excitation of electron glasses

Electron-glasses can be readily driven far from equilibrium by a variety of means. Several mechanisms to excite the system and their relative merits are reviewed. In this study we focus on the process of exciting electron-glasses by interaction with near infrared radiation. The efficiency of this protocol varies considerably among different electron-glasses, but it only weakly depends on their resistance at liquid helium temperatures. A dramatic enhancement of the excitation efficiency is observed upon doping crystalline indium-oxide with Au. Some enhancement is observed also in samples doped with Pb but this enhancement fades away with time unlike the situation in the Au-doped samples. Several structural and analytical tools are used to characterize the changes in the materials that may be responsible for these effects. Possible routes by which high-frequency electromagnetic fields take the system far from equilibrium are discussed.

The mechanism of surface doping in vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride: The role of Au promoter

This paper studies the role of Au as a promoter for vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride. Samples were prepared with a stoichiometric P/V ratio (P/V = 1.0), and then doped with increasing amounts of Au. It was found that the addition of the Au promoter had a profound influence on its catalytic behaviour, as samples containing the greater amount of Au (3 wt%) showed a behaviour that was similar to that of optimal catalysts which were prepared with a slight excess of P. In fact, the presence of Au allowed all the phenomena that typically lead to the worst catalytic behaviour of stoichiometric vanadyl pyrophosphate to be minimised, i.e. both the over-oxidation of vanadium and the development of the very active but poorly selective α I-VOPO 4. This was attributed to the enhanced reducibility of V 5+ that was observed in Au-doped samples, as compared to the undoped ones.

In situ growth approach for preparation of Au nanoparticle-doped silica aerogel

Gold (Au) nanoparticle-doped silica aerogels were prepared via the in situ growth approach. The Au ions were reduced to Au nanoparticles by hydroxylamine during the prehydrolysis oligomer process. Then, the samples were followed through with continuous supercritical extraction with CO 2. Ultraviolet–visible (UV–Vis) spectrophotometry was employed following the reduction of Au ions and the growth of Au nanoparticles. The size of the Au particles at the inner surface of the silica aerogel was within the 5–7 nm range. The morphology and microstructure characteristics of both silica aerogel and Au-doped samples were obtained through SEM, HRTEM, BET, and BJH. The total pore volume of obtained aerogel ranged within 2.9–3.45 cm −3/g, and the mean pore diameter was about 15 nm.

Non-Linear Optical Effects in Au Nanoparticle-Deposited ZnO Nanocrystalline Films

Applying a bicolor coherent treatment of a Nd-YAG laser with wavelength 1.32 μm and its second harmonic generation, we have investigated photoinduced SHG in Au nanoparticledeposited ZnO nanocrystallinne (NC) films. We have established that coexistence of the such crystallites gives substantially better results compared to the pure ZnO NC deposited onto the glass substrate. It was shown that the value of the second order susceptibility obtained for the large incident angles of the fundamental and writing beams is equal to about 23 pm/V. The better results are obtained during the phototreatment at temperatures near the 60 oC for the Au doped samples and is almost non-sensitive to temperature for the pure samples. The further increase of the temperature leads to decay of the optical second harmonic generation

Calculation of the diffusion coefficient of Au in Bi-2223 superconductors

Undoped Bi-2223 samples were prepared using a conventional solid-state reactionmethod. Doping of Au in Bi-2223 was carried out by means of diffusion from anevaporated Au film on pellets. We have investigated the effect of Au diffusion anddiffusion-annealing duration on the microstructure and superconducting properties ofAu-doped samples by performing x-ray diffraction (XRD), scanning electron microscopy(SEM), dc resistivity and critical current density measurements. Gold diffusion inBi1.8Pb0.35Sr1.9Ca2.1Cu3Oy has been studied over the temperature range500–800 °C using the technique of successive removal of thin layers and the measurementsof lattice parameters from XRD patterns at room temperature. The diffusiondoping of Bi-2223 by Au causes a significant increase of the lattice parameterc by about 0.19%. This observation is used for calculation of the Au diffusion coefficient inBi-2223. The Au diffusion coefficient decreases as the diffusion-annealing temperaturedecreases. The temperature dependence of the Au diffusion coefficient in the range500–800 °C is describedby the relation D = 4.4 × 10−4exp(−1.08 eV/kBT). Au doping of the sample increased the critical transition temperature and the critical current densityfrom 100 ± 0.2 to 104 ± 0.2 K andfrom 40 to 125 A cm−2, in comparison with those of undoped samples. The critical transition temperature and criticalcurrent density of Au-doped samples increased with increasing diffusion-annealing time from10 to 50 h. Au doping of the sample also improved the surface morphology and increased thehigh-Tc phase ratio. The possible reasons for the observed improvement in superconductingproperties of the samples due to Au diffusion are discussed.

Role of diffusion-annealing time on the mechanical properties of bulk Bi-2223superconductors diffusion-doped with Au

In order to investigate the role of Au doping and diffusion-annealingduration on the mechanical properties of Bi–Pb–Sr–Ca–Cu–O,Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors were prepared by standard solid-state reaction methods. Doping ofBi-2223 was carried out by means of gold diffusion during sintering from an evaporatedgold film on pellets. The effect of the diffusion-annealing duration on the mechanical andsuperconducting properties of these compounds was investigated using scanning electronmicroscopy, dc resistivity and hardness measurements. These measurements indicated thatthe Au doping and diffusion-annealing time increased the superconducting transitiontemperature, Vickers hardness, Young’s modulus, yield strength, fracture toughness valuesand improved the grain connectivity. The mechanical properties of the samples werefound to be load dependent. In addition, we calculated the load independenthardness, Young’s modulus, yield strength and fracture toughness of the samples.These mechanical properties of the Au-doped samples were dependent on thediffusion-annealing time. Possible reasons for the observed improvements in thesuperconducting and mechanical properties due to Au diffusion are discussed.

Photoluminescent and electronic properties of nanocrystalline silicon doped with gold

Doping nanocrystalline silicon (nc-Si) films grown by laser ablation with gold leads to a considerable suppression of the nonradiative recombination of the charge carriers and excitons, an increase in the intensity and stability of the visible photoluminescence, and enhancement of the low-energy (1.5–1.6 eV) photoluminescence band. In Au-doped samples, the magnitude of the photovoltage and the rate of electron capture by traps in the film are reduced, and the density of boundary electron states and the concentration of deep electron traps at the single-crystal silicon (c-Si) substrate are decreased as well. The observed effect of doping on the photoluminescent and electronic properties of nc-Si films and nc-Si/c-Si structures is caused by the passivation of dangling Si bonds with Au and by the further oxidation of silicon at the surface of nanocrystals, which results in the formation of high-barrier SiO2 layers.

Using magnetoresistance to investigate magnetic interface anisotropy

The ability to grow high quality thin metallic layers has brought about the discovery of the giant magnetoresistance (GMR) in multilayers and equally the perpendicular anisotropy exhibited by certain ferromagnetic thin films such as Co. In this article, we will describe magnetoresistance and magneto-optical Kerr effect (MOKE) measurements of molecular beam epitaxy-grown multilayers of Co/Cu(111). It is demonstrated that by controlled doping of the interface between the Co and Cu with submonolayer amounts of Au we are able to increase the magnitude of the GMR. Analysis of MOKE data shows that there is an increase in the perpendicular anisotropy of the Au-doped samples compared to those without Au which can account for the increase in the GMR.