Thermodynamic studies of the surface and transport properties in Ag–In and Ag–Sb liquid alloys

The surface tension, surface concentration, viscosity and mutual diffusion co-efficients of the Ag–In and Ag–Sb liquid alloys have been calculated using energetics and derivables from a statistical mechanical framework which recognises the formation of atom clusters of self associates. Our calculations suggest the existence of some form of local order in the systems. Ag–In showed higher tendencies to heterocoordination in the bulk-manifested higher values of mutual diffusion coefficient throughout the concentration range. The viscosity values of Ag–In and Ag–Sb were calculated using the expression reported by Kucharsky which relates the viscosity of a liquid binary alloy to the activity coefficients of the liquid alloy components that are raised to some power m. This exponent m is a fitted parameter. The calculated viscosity values for Ag–Sb had some reasonable agreement with experiment above 0.5 atomic fraction of Sb, using a fitted parameter value of m = 4.5. The fitted parameter value for the viscosity of Ag–In is expected to be in the range 1.5 ≤ m ≤ 3.5.     

Solid-Phase Surface Adsorption in Ag–Au|F–, H2O and Ag–Au|ClO–4, H2O Systems: Allowing for the Solid-Solution Nonideality

Integral and differential (with respect to the composition) isotherms of changes in the interfacial free energy (_m– ), the charge density q, and the surface composition X _Au of alloys equilibrated with an aqueous surface-inactive electrolyte are obtained in terms of a finite-thickness interfacial layer, with use of concentration dependences of activity coefficients of components of a polycrystalline binary alloy. Using ac measurements of the double-layer parameters, it is stated that the surface-active component in the Ag–Au|F^–, H₂O and Ag–Au|ClO^– ₄, H₂O systems at 298 K is gold. The Ag–Au solid solution shows negative deviations from Raoult's law, except for the compositions X _Au 0.04 and X _Au 0.80, where the solid solution properties approach those of an ideal solution.     

Structural and energetic asymmetry in liquid Ag–Al alloys

The thermodynamic and microscopic structure of Ag–Al liquid alloy at 1273?K has been studied by using regular associated solution model. This model has been utilised to determine the complex concentration in a regular associated solution of Ag and Al. We have then used the complex concentration to calculate the free energy of mixing, enthalpy of mixing, entropy of mixing, activity and concentration fluctuations in long wavelength limit S _CC(0) and the Warren–Cowley short-range parameter α ₁. The analysis suggests that heterocoordination leading to the formation of complex Ag₃Al is likely to exist in the liquid but is of a weakly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Ag-rich region. The alloy behaves like a segregating system in Al-rich region.     

Study on preparation and visible-light activity of Ag–TiO2 supported by artificial zeolite

Research on Chemical Intermediates - The material of Ag–TiO2 supported by artificial zeolite (Ag–TiO2/Z) was synthesized by the sol–gel method. Tetrabutyl titanate was used as the...     

Thermal and Microstructural Analysis of the Y–Ba–Cu–O/Ag Equilibrium Around the Critical Composition YBa2Cu3Ox/Ag 35 mass%

We studied the Y–Ba–Cu–O/Ag equilibrium diagram in oxygen atmosphere around the composition YBa₂Cu₃O_x/Ag35 mass%. We found a high thermal effect: the peritectic decomposition temperature of Y-123 phase is lowered from 1040 to 940°C. We demonstrate here that the nature of the phenomenon is not chemical. We explained it as the result of a mechanical segregation of Y-123 decomposition products from Y-123 phase, performed by silver. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal stability of Ag–Au,Cu–Au,and Ag–Cu bimetallic nanoparticles supported on highly oriented pyrolytic graphite

The formation of Ag–Au, Cu–Au, and Ag–Cu bimetallic particles on the surface of highly oriented pyrolytic graphite was studied by X-ray photoelectron spectroscopy. Samples with the core–shell structure of particles were prepared by sequential thermal vacuum deposition. The thermal stability of the samples was studied over a wide range of temperatures (25-400°C) under ultrahigh-vacuum conditions. The heating of the samples to ~250°C leads to the formation of bimetallic alloy particles with a relatively uniform distribution of metals in the bulk. The thermal stability of the samples with respect to sintering depends on the nature of the supported metals. Thus, the Ag–Au particles exhibited the highest thermal resistance (~350°C) under ultrahigh-vacuum conditions, whereas the Ag–Cu particles agglomerated even at ~250°C.     

Solvothermal preparation,and characterization,of Cu–Ag nanoparticles

Cu–Ag nanoparticles have been successfully synthesized by one-pot solvothermal treatment of a mixture of AgNO₃ and Cu(OAc)₂·H₂O in ethylene glycol solution at 180 °C for 10 h. The samples were characterized by UV–visible absorption, X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). The results showed that Cu–Ag nanoparticles and a small amount of phase-separated Cu–Ag alloy nanoparticles with an average diameter of 100 ± 30 nm were synthesized by the solvothermal treatment procedure. The mechanism of formation is discussed.     

A 3-D inorganic–organic hybrid based on saturated Wells–Dawson polyoxoanion and K+, linked by an Ag–Ag bond

A 3-D complex K₂[Ag₂(biim)₂]₂P₂W₁₈O₆₂ (biim?=?biimidazole) (1) has been hydrothermally synthesized and characterized by IR, thermogravimetric, and single-crystal X-ray diffraction. Single-crystal X-ray structural analysis reveals that 1 exhibits a 1-D wavelike chain constructed from µ₃-bridging oxygen atoms of [P₂W₁₈O₆₂]^6? and [Ag₂(biim)₂]²⁺. The K⁺ link to six oxygen atoms of three P₂W₁₈ clusters and 12 equatorial terminal oxygen atoms of P₂W₁₈ clusters link to six K⁺, resulting in a 3-D framework with a relatively short Ag–Ag bond [2.836?Å]. The electrochemical behavior of 1 modified carbon paste electrode (1-CPE) has been studied. The results indicate that 1-CPE has remarkable stability.     

Global Minimum Search and Bonding Analysis of Tl2Hx and Tl3Hy (x=0–6; y=0–5) Series

A remarkable distinction between boron and carbon hydrides lies in their extremely different bonding patterns and chemical reactivity, resulting in diverse areas of application. Particularly, carbon, characterized by classical two-center – two-electron bonds, gives rise to organic chemistry. In contrast, boron forms numerous exotic and non-intuitive compounds collectively called non-classical structures. It is reasonable to anticipate that other elements of Group 13 exhibit their own unusual bonding patterns; however, our knowledge of the hydride chemistry for other elements in Group 13 is much more limited, especially for the heaviest stable element, thallium. In this work, we performed a conformational analysis of Tl₂H_x and Tl₃H_y (x=0–6, y=0–5) series via Coalescence Kick global minimum search algorithm, DFT, and ab initio quantum chemistry methods; we investigated the bonding pattern using the AdNDP algorithm, thermodynamic stability, and stability toward electron detachment. All found global minimum structures are classified as non-classical structures featuring at least one multi-center bond.     

Isobaric vapor–liquid equilibria for the n-hexane + 2-isopropoxyethanol and n-heptane + 2-isopropoxyethanol systems

Vapor–liquid equilibria (VLE) for the n-hexane + 2-isopropoxyethanol and n-heptane + 2-isopropoxyethanol (at 60, 80, and 100 kPa) systems were measured. Two systems present positive deviations from ideal behavior. And the system n-heptane + 2-isopropoxyethanol shows a minimum boiling azeotrope at all pressures. Experimented data have been correlated with the two term virial equation for vapor-phase fugacity coefficients and the three suffix Margules equation, Wilson, NRTL, and UNIQUAC equations for liquid-phase activity coefficients. Experimental VLE data show excellent agreements with models.     

Measurement and calculation of vapor–liquid equilibria for methanol + glycerol and ethanol + glycerol systems at 493–573 K

The vapor–liquid equilibria for methanol + glycerol and ethanol + glycerol systems were measured by a flow method at 493–573 K. The pressure conditions focused in this work were 3.03–11.02 MPa for methanol + glycerol system and 2.27–8.78 MPa for ethanol + glycerol system. The mole fractions of alcohol in vapor phase are close to unity at the pressures below 7.0 MPa for both systems. The pressures of liquid saturated lines of the liquid phase for methanol + glycerol and ethanol + glycerol systems are higher than that for the mixtures containing alcohol and biodiesel compound, methyl laurate or ethyl laurate.     

Comparative toxicity study of Ag, Au, and Ag–Au bimetallic nanoparticles on Daphnia magna

A comparative assessment of the 48-h acute toxicity of aqueous nanoparticles synthesized using the same methodology, including Au, Ag, and Ag–Au bimetallic nanoparticles, was conducted to determine their ecological effect in freshwater environments through the use of Daphnia magna, using their mortality as a toxicological endpoint. D. magna are one of the standard organisms used for ecotoxicity studies due to their sensitivity to chemical toxicants. Particle suspensions used in toxicity testing were well-characterized through a combination of absorbance measurements, atomic force or electron microscopy, flame atomic absorption spectrometry, and dynamic light scattering to determine composition, aggregation state, and particle size. The toxicity of all nanoparticles tested was found to be dose and composition dependent. The concentration of Au nanoparticles that killed 50% of the test organisms (LC₅₀) ranged from 65–75 mg/L. In addition, three different sized Ag nanoparticles (diameters = 36, 52, and 66 nm) were studied to analyze the toxicological effects of particle size on D. magna; however, it was found that toxicity was not a function of size and ranged from 3–4 μg/L for all three sets of Ag nanoparticles tested. This was possibly due to the large degree of aggregation when these nanoparticles were suspended in standard synthetic freshwater. Moreover, the LC₅₀ values for Ag–Au bimetallic nanoparticles were found to be between that of Ag and Au but much closer to that of Ag. The bimetallic particles containing 80% Ag and 20% Au were found to have a significantly lower toxicity to Daphnia (LC₅₀ of 15 μg/L) compared to Ag nanoparticles, while the toxicity of the nanoparticles containing 20% Ag and 80% Au was greater than expected at 12 μg/L. The comparison results confirm that Ag nanoparticles were much more toxic than Au nanoparticles, and that the introduction of gold into silver nanoparticles may lower their environmental impact by lowering the amount of Ag which is bioavailable.     

A series of Keggin-based AgI-belt/cycle structures constructed from 5-phenyl-1H-tetrazole and its derivative through Ag–N and Ag–C bonds

Three Keggin-based compounds containing Ag^I belts and cycles constructed from 5-phenyl-1H-tetrazole (L¹) and its derivative 5-m-tolyl-1H-tetrazole (L²), [Ag₉L¹₅(PW^VW^VI₁₁O₄₀)]·H₂O (1), [Ag₁₁L¹₆(H₂O)₂(SiMo^VMo^VI₁₁O₄₀)] (2) and [Ag₁₀L²₈(HPMo₁₂O₄₀)]·H₂O (3), have been synthesized under hydrothermal conditions and characterized by IR spectra and single crystal X-ray diffraction. Compound 1 shows a channel-like 3-D metal-organic framework with Keggin anions in channels. Adjacent layers of 2 share the same anions to construct a 3-D framework. Compound 3 has a 2-D metal-organic layer containing Ag^I cycles. Adjacent layers link through sharing Ag–N bonds and a channel-like 3-D framework is formed. Electrochemical and photocatalytic properties of 1–3 have been studied. The experimental results show that 1–3 have excellent catalytic performance for reduction of nitrite and bromate and also have photocatalytic properties for degradation of MB and RhB.     

Synthesis and characterization of Sibunit-supported Pd–Ga,Pd–Zn,and Pd–Ag catalysts for liquid-phase acetylene hydrogenation

Pd/Sibunit and Pd–M/Sibunit (M = Ga, Zn, or Ag) catalysts have been synthesized, and their catalytic properties in liquid-phase acetylene hydrogenation have been investigated. Doping of the palladium catalyst with a metal M leads to the formation of the Pd₂Ga, PdZn, or Pd_0.46Ag_0.54 bimetallic compound. The bimetallic particles are much smaller (1.6–2.0 nm) than the monometallic palladium particles (4.0 nm). Doping with zinc raises the ethylene selectivity by 25% without affecting the activity of the catalyst. Specific features of the effect of each of the dopants on palladium are reported.     

Photocatalytic degradation of acid blue 74 in water using Ag–Ag2O–Zno nanostuctures anchored on graphene oxide

Water pollution due to industrial effluents from industries which utilize dyes in the manufacturing of their products has serious implications on aquatic lives and the general environment. Thus, there is need for the removal of dyes from wastewater before being discharged into the environment. In this study, a nanocomposite consisting of silver, silver oxide (Ag₂O), zinc oxide (ZnO) and graphene oxide (GO) was synthesized, characterized and photocatalytically applied in the degradation (and possibly mineralization) of organic pollutants in water treatment process. The Ag–Ag₂O–ZnO nanostructure was synthesized by a co-precipitation method and calcined at 400 °C. It was functionalized using 3-aminopropyl triethoxysilane and further anchored on carboxylated graphene oxide via the formation of an amide bond to give the Ag–Ag₂O–ZnO/GO nanocomposite. The prepared nanocomposite was characterized by UV–Vis diffuse reflectance spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electronic microscopy (SEM), energy dispersive X-ray spectrometry (EDX), Fourier transformed infrared spectroscopy (FTIR), and Raman spectroscopy. The applicability of Ag–Ag₂O–ZnO/GO nanocomposite as a photocatalyst was investigated in the photocatalytic degradation of acid blue 74 dye under visible light irradiation in synthetic wastewater containing the dye. The results indicated that Ag–Ag₂O–ZnO/GO nanocomposite has a higher photocatalytic activity (90% removal) compared to Ag–Ag₂O–ZnO (85% removal) and ZnO (75% removal) respectively and thus lends itself to application in water treatment, where the removal of organics is very important.     

The Influence of Ag and Ag(In) Alloy on Y–Ba–Cu–O Equilibrium Diagram Around the Y-123 Superconducting Phase

We studied the chemical compatibility of Ag, Ag(In)alloy, Y₂BaCuO₅ (the so-called Y-211 green phase) and YBa₂Cu₃O_7–δ (Y-123) phase in order to check if better grain growth and alignment with minimum contamination were possible during the Y-123melt texturing. We demonstrate that the addition of silver to Y-123 always led to an enhanced texture. The typical microstructure of the composite Y-123 plus Y-211 (that is believed essential for high critical currents in these High Tc superconductors) was not disturbed by addition of silver up to 7.5 wt%, while higher concentrations of metal led to a degradation of the texture. DTA–TG analysis was used to investigate the influence of Ag and Ag(In) alloy on the Y–Ba–Cu–O equilibria around the Y-123 phase. We found a very unexpected thermal behaviour, similar to an eutectic equilibrium, when the silver concentration was increased to35 wt%. We believe that this effect was essentially due to the increasingly higher concentration of silver that could react with the secondary phases present in the melt. This revised version was published online in July 2006 with corrections to the Cover Date.     

Theoretical Study on the Structures and Thermal Properties of Ag–Pt–Ni Trimetallic Clusters

The structures and thermal properties of Ag–Pt–Ni ternary nanoclusters varying with different compositions and sizes are studied by Monte Carlo and molecular dynamics simulations. It can be found that silver atoms tend to occupy the surface and platinum atoms favor the subsurface occupation, whereas the inner is occupied by nickel atoms due to the different surface energies and lattice parameters. In addition, there is a non-monotonous relationship between the melting points and compositions of Ag–Pt–Ni ternary nanoclusters according to molecular dynamics simulations. In addition, a linear decrease in melting point with \(N^{ - 1/3}\) is found for both monometallic and trimetallic clusters. This behavior is consistent with Pawlow’s law.