Narrow Results

We report on the effects of using various doping 3d, 4d and 5d transition metal elements on the stability of the supersaturated FCC Ag–Cu solid solution prepared by mechanical alloying. We find that the addition of W does not have any influence on the stability of the Ag–Cu solid solution. Moderate effects are observed for Ru, Fe and Co, while the addition of Ni partially destabilizes the Ag–Cu solid solution. The results are discussed in the framework of kinetic and thermodynamic processes.

Spark plasma sintering (SPS) is employed to fabricate self-lubricating Al₂O₃-SrSO₄ nanocomposites incorporated with and without Ag addition. The friction and wear properties have been evaluated using a high temperature friction and wear tester from room temperature to 600°C in dry sliding against alumina ball. X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analyzer were used to investigate microstructure and self-lubrication mechanisms of nanocomposites after wear tests at different temperatures. Al₂O₃-SrSO₄ nanocomposites with optimum compositional combinations exhibit low and stable friction coefficients of 0.22 and wear rates in the order of 10^-5 mm³/Nm at high temperatures. At low temperature, the Ag additives in the composite form a discontinuous lubricating film to effectively reduce friction and wear. With increasing test temperature, plastic deformation of SrSO₄ during sliding plays an important role in formation of lubricating films on worn surfaces to reduce the friction and wear.

The superconductors Bi₂Sr₂CaCu₂O_x (Bi2212 ) and Ag/Bi2212 composites samples were prepared by the powder metallurgy method. The frictional behaviors of Bi2212 pins in contact with stainless steel plate were examined from -196 to 20°C on friction and wear tester. When the temperature was lower than the superconducting transition temperature, the friction coefficient of Bi2212 dropped sharply, and it kept 0.11 with increase of the test time. The microstructure and morphology of Ag/Bi2212 composites were investigated by means of X-ray diffraction (XRD), transmission electronic microscope (TEM) and high resolution transmission electronic microscope (HRTEM). The elemental compositions of the worn surfaces of Ag/Bi2212 composites were determined by using energy dispersive X-ray analysis (EDXA). The results showed that the superconducting structure of Bi2212 was not changed and Ag was distributed in the Bi2212 matrix. Ag doping improved the toughness of oxide ceramics Bi2212. The friction test results of Ag/Bi2212 composites showed the tribological properties were improved at room temperature. The friction coefficient of 10%Ag/Bi2212 against stainless steel showed a lower value (0.2) and the wear rate of 15%Ag/Bi2212 was minimum (9.5×10^-5 mm³·(N·m)^-1 ). The lubrication of soft metallic film and load of hard matrix were the mechanism of decreased friction and anti-wear of Ag/Bi2212 composites.

The viscosity of the eight binary systems (Cu–X ($\mathrm{\text{X}}=\mathrm{\text{Ag}}$, Al, Sn, Mg) system and Ag–X ($\mathrm{\text{X}}=\mathrm{\text{Sn}}$, Sb, In, Au)) was re-assessed, employing a new CALPHAD-type equation model proposed in our previous work. The calculated viscosities of the binary alloys were compared with the experimental data. It was found that this CALPHAD-type equation is very effective in fitting with the experimental data. Therefore, this work proves the validity of our new CALPHAD-type equation model for accurate viscosity predictions in alloys with varying component compositions.

The growth mode of Ag atoms on the W(110) plane has been studied using LEED and Low Energy Ion Scattering Spectroscopy (ISS). We find that Ag atoms grow in SK mode after annealing at 700°C for the coverage ~ 3.0 ML. The grown three-dimensional Ag islands have the (111) plane surface. The direction of the Ag islands is rotated 4.4° from (001) direction of the W(110) surface. Using the ISS technique the surface structure of the two-dimensional Ag islands is investigated. The Ag adsorption height measured from the first layer of the W(110) surface is found to be 2.79 Å.

The segregation energy of diluted species in a matrix can be calculated by first principles. These calculations are generally very computational demanding. The existing empirical models which use the difference in surface tensions to predict the segregation energy are limited, because they do not take the surface orientation of the matrix into account. In this investigation a model was developed which can estimate the segregation energies of segregating species in a binary system. The model makes use of the sublimation energies and takes the orientation of the surface into account. The model shows that the driving force for segregation is not the difference in surface tensions (between the surface tension of the pure element and the surface tension of the element in the alloy) but the difference in surface energies. The results of the calculations were used to simulate the Ag and Sb segregation to the (111) surface of copper.

Bamboo charcoal (BC) accompanied silver (Ag) nanocomposite is synthesized through sol–gel method. The produced BC/Ag nanocomposite was surface modified by air and oxygen plasma treatments. Silver ions (Ag${}^{+}$) will serve to improve the antibacterial activity as well as the surface area of BC. Plasma treatment has improved the surface functional groups, crystalline intensity and antibacterial activity of the prepared nanocomposite. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies show that Ag nanoparticles have good agreement with BC and the particle size has a mean diameter of 20–40nm. We observe the carboxyl functional groups in Fourier transform infrared spectroscopy (FTIR) after the oxygen plasma treatment. Moreover surface area and adsorption were analyzed by using the Brunauer, Emmett and Teller (BET) surface area ($S_{\mathrm{\text{BET}}}$) and UV–Vis spectroscopy.

Recently, silver as an electrochemical deposit on copper substrate has been attracting much attention in the microelectronics field. To deposit nano-scale silver particles on copper, immersion plating using cyanide-based baths is commonly used. In this study, non-toxic ethanol was used as the plating solution. Sputtered copper samples were immersed in an ethanol-based solution containing 0.2 g·L^-1 silver for silver deposition. The silver deposits were characterized by a field emission scanning electron microscope (FE-SEM), an energy dispersive X-ray spectroscope (EDS), and an atomic force microscope (AFM). It was found that the deposited particles are metallic silver. After 3 s immersion, fine particles whose diameters were around 6 nm had covered about 40% of the surface of the copper substrate. After 10 s immersion, the copper surface was completely covered by silver particles, the diameters of which have increased to about 10–15 nm. After the whole surface was covered, a dense and smooth silver coating was obtained.

Ag/Bi₄Ti₃O₁₂ heterostructure with high photocatalytic activity was synthesized via a simple and practical hydrothermal method by using Bi₄Ti₃O₁₂ nanobelts as substrate materials. The as-prepared Ag/Bi₄Ti₃O₁₂ heterostructure included Ag quantum dots assembling uniformly on the surface of Bi₄Ti₃O₁₂ nanobelts. Comparing with pure Bi₄Ti₃O₁₂ nanobelts, the composite photocatalyst exhibited enhanced photocatalytic activity under visible light irradiation in the decomposition of rhodamine B aqueous solution. The enhancement performance is believed to be induced by the intimate contact interface, where silver quantum dots serve as good electron acceptor for facilitating quick photoexcited electron transfer and thus decreasing electron-hole recombination. It was also found that the photodegradation of rhodamine B molecules is mainly attributed to the oxidation action of the generated radicals.

A novel nanomaterial composed of copper and carbon nanofibers (CuCNFs) decorated with Ag-doped TiO₂ (Ag–TiO${}_2)$ nanoparticles was prepared through electrospinning, carbonization and solvothermal treatment. The composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS). The obtained composites were mixed with laccase and Nafion to construct novel hydroquinone biosensor. The electrochemical behavior of the novel biosensor was studied using cyclic voltammetry (CV) and chronoamperometry. The results demonstrated that the biosensor possessed a wide detection linear range (1.20–176.50$\mu$M), a good selectivity, repeatability, reproducibility and storage stability. This work provides a new material to design more efficient laccase (Lac) based biosensor for hydroquinone detection.

A series of hamburger-like Ag@ZnO/C core–shell plasmonic photocatalysts have been synthesized via a simple solvothermal method for degradation of tetracycline (TC) under visible light irradiation, possessing high photocatalytic activity and good stability. The presence of localized surface plasmon resonance (LSPR) in the Ag core has increased the photocatalytic activity over an extended wavelength range. The plasmon-induced resonant energy transfer (PIRET) and direct electron transfer (DET) have facilitated the excitation and separation of photogenerated $e^{-}/h^{+}$ pairs, which has been further confirmed by electrochemical investigations. The presences of hydroxyl radicals ($\cdot \mathrm{\text{OH}}$), superoxide radicals ($\cdot {\mathrm{\text{O}}}_2^{-})$ and singlet oxygen (¹O${}_2)$ in the photocatalytic reaction system of Ag@ZnO/C photocatalyst have been demonstrated by electron spin resonance (ESR) measurements. All of the experiment results indicate that the ternary structure of Ag@ZnO/C can effectively enhance the photocatalytic activity. Furthermore, the effects of introduced Ag contents and carbon source dosage were researched by comparative photocatalytic experiments, and the potential structures of photodegradation products were studied by HPLC-MS.

Silver-coated Ti₂Nb${}_{10}$O${}_{29}$ composite microspheres were successfully prepared by a solvothermal method with a subsequent post-annealing treatment. Effect of the coating Ag nanoparticles on the electrochemical properties was extensively studied. The XRD pattern shows that high purity Ti₂Nb${}_{10}$O${}_{29}$ was formed and no impurity phases are observed. Moreover, SEM, XPS and EDX clearly revealed that Ag nanoparticles were combined on the surface area of formed Ti₂Nb${}_{10}$O${}_{29}$ microspheres. The electrochemical performance of the Ag/Ti₂Nb${}_{10}$O${}_{29}$ composite microspheres was characterized via cyclic voltammograms (CV) measurements. The CV curves indicate that the coating Ag nanoparticles minimize the polarization of pristine Ti₂Nb${}_{10}$O${}_{29}$. The EIS indicates that the excellent rate capability of Ag/Ti₂Nb${}_{10}$O${}_{29}$ composite microspheres can be ascribed to the improved electronic conductivity due to the incorporation of Ag nanoparticles.

Nanomaterials are promising alternatives to antibiotics with the potential to handle the menace of emerging multidrug resistance in pathogenic microbes. We report a simple biosynthetic approach to prepare Ag nanoparticles (NPs) with strong antibacterial and antifungal actions by using Piper nigrum fruit extract as a bioreducing agent. The biosynthesized material was characterized by SEM, AFM, TEM, HRTEM, XRD and UV–Visible absorption spectroscopy. SEM, AFM and TEM analyses provided evidence that the average diameter of the Ag NPs was 18nm, while XRD and HRTEM confirmed the FCC structure of Ag NPs. The biosynthesized Ag NPs demonstrated extremely strong antibacterial activity against Bacillus oceanisediminis and Escherichia coli, and showed extremely strong antifungal action against Schizosaccharomyces pombe, inhibiting their growth at very low concentrations of 3$\mu$g/mL, 4$\mu$g/mL and 3$\mu$g/mL, respectively. The molecular origin of their antibacterial and antifungal activity was studied using various molecular and biochemical assays. The results of these assays revealed a major role for reactive oxygen species (ROS) in the antifungal and antibacterial actions of the biosynthesized Ag NPs. Furthermore, morphological changes in cells and cell wall damage upon Ag NP treatment were observed by scanning electron microscopy. In addition, significant enhancement in protein leakage and fragmentation of DNA was also observed upon treatment of S. pombe, B. oceanisediminis and E. coli with Ag NPs. In conclusion, the observed extremely strong antibacterial and antifungal activities of biosynthesized Ag NPs are due to the oxidative stress triggered by ROS, causing cell wall damage and subsequent protein leakage and DNA fragmentation.