Preparation and characterization of polyacrylamide–silver nanocomposites

Polyacrylamide–silver nanocomposites are successfully prepared by irradiating the aqueous solution of AgNO₃ and acrylamide monomer with ⁶⁰Co γ-ray. The composites are found to contain nanometer silver particles with a narrow size distribution and a homogeneous dispersion. The existing of isopropanol (as a hydroxyl radical scavenger and chain transfer agent) in system affects the properties of both the dispersed phase and matrix of the nanocomposites. The fast-formed polymer chains probably play a key role in preventing the aggregation of silver particles which are reduced later.     

Zeolite-supported silver and silver�Ciron nanoclusters and their activities as photodecomposition catalysts

Catalysts containing nanoclusters of Ag(I) and Fe₂O₃ as dopants with sodalite and Y zeolite supports have been investigated in order to develop a more efficient catalyst for photodecomposition of the pesticide carbaryl and to gain insight about the reaction mechanism. Ag(I)?Csodalite, Ag(I)/Fe₂O₃?Csodalite, Ag(I)?CY zeolite, and Ag(I)/Fe₂O₃?CY zeolite were synthesized by ion-exchange techniques and characterized by powder X-ray diffraction (XRD), solid-state luminescence, UV?Cvisible absorption, and atomic absorption spectroscopy measurements. The luminescence activity of the sodalite-supported and Y zeolite-supported catalysts was significantly different. Catalyst performance studies were conducted using carbaryl as the target compound and specific wavelengths of UV light as photon sources for the experiments. The studies showed that each catalyst??s performance was determined primarily by the specific wavelength of the UV light with which the system was irradiated. The studies also showed that inclusion of Fe₂O₃ as dopant enhanced the reactivity of the catalysts in several instances, with the Ag(I)/Fe₂O₃?Csodalite catalyst and 298 nm irradiation being the most reactive of the systems studied. Additional reactions using each catalyst and 298 nm irradiation, and including either sodium bicarbonate as hydroxyl radical scavenger or D₂O as solvent, showed that hydroxyl radicals were likely intermediates in the catalyzed photodecomposition reaction.     

Temporal stability of standard potentials of silver–silver chloride reference electrodes

The four-year evolution of standard potential of a silver?Csilver chloride reference electrode (denoted further in the text as an Ag/AgCl electrode) is presented together with some suggestions for the improvement of pH primary measurement procedure.     

Review: Multimetallic silver(I)–pyridinyl complexes: coordination of silver(I) and luminescence

This review highlights some structural features and luminescent properties of homo- and hetero-multinuclear silver(I)–pyridinyl complexes. It focuses on the coordination and geometry of the silver(I) ions to the pyridinyl-nitrogen. For this reason, we have considered only pyridinyl-N–Ag(I) complexes whose crystal data are available. In addition, this review does not consider mononuclear silver(I)–pyridinyl complexes as these have been reviewed elsewhere. This is motivated by the fact that multinuclear silver(I)–pyridinyl complexes have been shown to be more stable in solution, possess enhanced properties, and have fascinating structures compared to their mononuclear counterparts. The introduction highlights pyridinyl ligands used in complexation of silver(I) ions. The main body highlights complexation of silver(I) through pyridinyl nitrogen and the interactions found in the multinuclear silver(I)–pyridinyl complexes as well as the coordination number and geometry of silver(I) centers. Though silver(I) has been flaunted to prefer linear twofold coordination geometry, from this review, it is clear that higher coordination numbers in varied geometries are possible. These include distorted trigonal planar, T-shaped, distorted tetrahedral, trigonal bipyramidal, and octahedral geometries. Coordination of silver(I) to pyridinyl ligands and their metalloligands has been observed to impart or enhance luminescent properties in the ensuing complexes.     

Hemoglobin co-immobilized with silver–silver oxide nanoparticles on a bare silver electrode for hydrogen peroxide electroanalysis

Hemoglobin (Hb) and silver–silver oxide (Ag–Ag₂O) nanoparticles were co-immobilized on a bare silver electrode surface by cyclic voltammetry, and were characterized by UV–vis reflection spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. The immobilized Hb was shown to maintain its biological activity well. Direct electron transfer between Hb and the resulting electrode was achieved without the aid of any electron mediator. The reduction currents to hydrogen peroxide (H₂O₂) at co-immobilized electrodes showed a linear relationship with H₂O₂ concentration over a concentration range from 6.0?×?10^?6 to 5.0?×?10^?2 mol L^?1, and a detection limit of 2.0?×?10^?6 mol L^?1 (S/N?=?3).     

Defect of nanocrystalline copper and silver

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Deposition of silver nanoparticles into porous system of sol–gel silica monoliths and properties of silver/porous silica composites

Porous monolithic gels based on silica with pore size from 16 nm to 3–5 μm have been synthesized using sol–gel technology. Parameters of porous structure are determined by the components molar ratio in the reaction mixture. The reduction processes of silver ions by formamide in the synthesized porous gel were studied. It has been shown that at the initial stage of the reaction, silver particles with size up to 10 nm are formed in the absence of any stabilizers. The composites Ag/SiO₂ were synthesized by means of the threefold impregnation of porous monoliths using the solution of silver nitrate in the mixture of methanol and formamide. Their catalytic activity in the CO oxidation was studied. It was discovered that after activation in oxygen and hydrogen the samples display a low temperature activity, which depends on the number of Si–O-nonbridging oxygen groups on the surface of silica porous monoliths.     

Nanosized silver–palm pollen nanocomposite,green synthesis,characterization and antimicrobial activity

Palm pollen (PP) has been widely used in nutrition, pharmaceutical and cosmetic industries. In the present study, we explored the potential of PP in the synthesis of a silver nanoparticle (Ag NP). PP was used as both reducing and stabilizing agent. The Ag/PP nanocomposite was examined by field emission electron microscopy, X-ray diffraction, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet spectroscopy and zeta potential measurement. The biosynthesized NPs showed surface plasmon resonance centered at 425 nm with an average particle size measured to be 23 nm and a zeta potential of ?30.9 mV. Prominent FT-IR signals were obtained and ascribed to phenolic and carbohydrate compounds involved in the formation of the Ag NPs, and proteins which participated in stabilization of the Ag NPs. The biologically synthesized Ag NPs were found to be extremely effective against E. coli (13.8 ± 0.25 mm) with a minimum inhibitory concentration of 20 µg/mL. Thus, such biosynthesized Ag NPs can be used in medicinal applications.     

Silica–silver nanostructured spheres prepared by spray pyrolysis of sol containing silver precursor

Silver–silica nanostructured composites were prepared by spray pyrolysis of aqueous sols of silica nanoparticles containing silver nitrate. The physical and chemical characteristics of the composites prepared at different Ag/Si atomic ratio in the sols and temperatures of pyrolysis were examined by TEM, SEM, XRD, FT-IR and UV-visible spectra. For the low silver ratios up to 0.2, well-dispersed silver particles were produced in the pore of the silica agglomerates with their size and surface plasmon resonance depending on the pore size and silver mobility, in addition to the loading and temperature. The formation of silver silicate and new-phase silica as well as crystallinity of the silver prepared was discussed. There was also explained how the temperature of preparation affected the morphologies of the composites produced with higher Ag/Si ratios greater than 1. Mechanism on the formation of silver–silica composites was proposed for the wide range of the ratios from 0.01 to 3.     

Synthesis and antimicrobial studies of 1-methyl-2-dimethylaminoethyl-substituted benzimidazolium salts and N-heterocyclic carbene–silver complexes

The synthesis and antimicrobial studies of 1-methyl-2-dimethylaminoethyl-substituted carbene precursors and silver complexes are reported. The carbene precursors (1a–d) have been prepared from 1-methyl-2-dimethylaminoethyl-substituted benzimidazole and various alkyl halides. The silver–NHC complexes (2a–d) were synthesized from the benzimidazolium salts and Ag₂O in dichloromethane at room temperature. The new compounds were characterized by ¹H NMR, ¹³C NMR, FT-IR, and elemental analyses. The new carbene precursors and Ag-complexes were tested for their in vitro antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria, as well as for their antifungal activities against Candida albicans and Candida tropicalis.     

Donor–acceptor interactions between resonance-excited silver nanoparticles and halide ions in water solutions

Donor–acceptor interactions between silver nanoparticles (NPs), resonance-excited by optical quanta of light, and halide ions are studied in aqueous solutions. It is shown that deactivation of the plasmon excitation of Ag NP proceeds according to the exchange mechanism of electron transfer. Plasmon excitation quenching constants are determined and a correlation between quenching and the donor properties of halide ions is found. The efficiency of electrostatic interaction between resonantly-excited Ag NPs and halide ions is studied, and their dipole moment is determined.

     

A reversible fluorescent INHIBIT logic gate for determination of silver and iodide based on the use of graphene oxide and a silver–selective probe DNA

We describe a reversible fluorescent DNA–based INHIBIT logic gate for the determination of silver(I) and iodide ions using graphene oxide (GO) as a signal transducer and Ag(I) and iodide as mechanical activators. The basic performance, optimized conditions, sensitivity and selectivity of the logic gate were investigated and revealed that the method is highly sensitive and selective over potentially interfering ions. The limits of detection for Ag(I) and iodide are 10 nM and 50 nM, respectively. This logic gate was successfully applied to the determination of Ag(I) and iodide in (spiked) tap water and river water. It was also used for the determination of iodide in human urine samples with satisfactory results. Compared to other methods, this INHIBIT logic gate is simple in design and has small background interference.

A simple and reversible fluorescent DNA-based INHIBIT logic gate is designed by using graphene oxide as a signal transducer and silver ions and iodide as mechanical activators.

     

Production of chiral matrices with hybrid silver–thiocholesterol nanosystems and study of their properties

A new type of chiral matrix based on silver–thiocholesterol hybrid nanosystems adsorbed on silica gel has been proposed. The molar ratio of stabilized thiocholesterol (L) ligand and silver (Ag) was found to have little effect on the size of the resulting silver nanoparticles (SNPs). The average diameter of SNPs was 2.7 ± 0.4, 2.2 ± 0.4, and 2.1 ± 0.6 nm upon the ratios Ag: L = 1: 5, Ag: L = 1: 2, and Ag: L = 1: 0.5, respectively. The resulting chiral matrices possess enantioselectivity relative to the 1,1’-binaphthyl-2,2’-diamine (BNDA) and trifluoroanthranyl ethanol (TFAE) optical isomers. The TFAE optical isomers were successfully separated using thin layer chromatography (α = 1.56).     

Synthesis,characterization and antibacterial activity of a curcumin–silver(I) complex

The current study reports the synthesis of a curcumin–silver(I) complex and its preliminary tests against four bacterial strains viz. Staphylococcus aureus, Escherichia coli, Bacillus subtilis, and Bacillus cereus using agar well diffusion method. The results were compared with curcumin by testing it in parallel with the sample. Curcumin showed zones of inhibition against all tested strains of bacteria. Among all bacterial strains, S. aureus was the most sensitive to curcumin with zone of inhibition of 12.2 mm. However, the curcumin–Ag(I) complex did not show the expected enhanced activity against all bacteria. This is perhaps due to the replacement of curcumin phenolic protons by silver ions which might have suppressed the antibacterial property of curcumin. The current research findings suggest that while synthesizing curcumin–metal complexes, the phenolic heads may either be left unaltered or need to be replaced by better substituents than hydroxy groups. Based on the current findings, biologically enhanced models have been provided as future recommendations.     

Using a photochemical method and chitosan to prepare surface-enhanced Raman scattering–active silver nanoparticles

In this paper, we report a new strategy for the preparation of surface-enhanced Raman scattering (SERS)-active silver nanoparticles (Ag NPs), using a photochemical method and the presence of chitosan (Ch). First, Ag substrates were subjected to electrochemical oxidation/reduction cycles (ORCs) in deoxygenated aqueous solutions containing 0.1 M HNO₃ and 1 g L⁻¹ Ch (pH 6.9, adjusted by adding 1 M NaOH), resulting in Ag⁺–Ch complexes. These substrates were then irradiated with UV light at various wavelengths to yield the SERS-active Ag NPs. A stronger SERS effect was observed on the SERS-active Ag NPs prepared by using UV irradiation at 310 nm. The pH of the solution and the presence of Ch during the preparation process both affected the resulting SERS activities.     

Synthesis,characterization, luminescent,and catalytic performance of a dinuclear triazenido–silver complex

Our group has developed a series of molecular electrocatalysts for hydrogen generation based on triazenido–metal complexes (such as cobalt, copper, etc.). In this paper, we present the electrocatalytic performance of a new dinuclear silver complex, [Ag₂(L)₂], formed by reaction of the triazenido ligand, 1-[(2-carboxyethyl)benzene]-3-[benzimidazole]triazene (HL) with AgNO₃. The electrocatalytic systems based on this silver complex can afford 91.23 and 473 moles of hydrogen per mole of catalyst per hour (mol H₂/mol catalyst/h) from acetic acid at overpotential (OP) of 991.6 mV and an aqueous buffer at an OP of 837.6 mV, respectively. Electrochemical investigations show both the silver center and the triazenido ligand, HL, play important roles in determining the catalytic activities of the electrocatalytic system. Additionally, the triazenido ligand (HL) can serve as a fluorescent sensor for Ag⁺.     

Thermodynamics of oxygen in dilute liquid silver–tellurium alloys

Abstract  

The activity coefficient of oxygen in liquid Ag and binary Ag–Te dilute alloys were determined between 1,285 and 1,485 K by coulometric titration using the electrochemical cell (Ir, [O] in liquid metal or alloy | yttria stabilized zirconia | air, Pt). The experimental and evaluation procedures described in the literature were adopted. The oxygen activity coefficient was determined in pure liquid silver to be . Next, the oxygen activity coefficient in dilute Ag–(Te)–O alloys for variable X _Te content (from 0.01 to 0.06) was measured. From the obtained results, Wagner’s interaction parameter as a function of temperature was derived in the form . The electrochemical coulometric titration method seems to be very useful to study the thermodynamics of oxygen interaction in liquid silver and its alloys.     

Thiol-functionalized silica–mixed matrix membranes for silver capture from aqueous solutions: Experimental results and modeling

The study deals with an aqueous phase application of mixed matrix membranes (MMMs) for silver ion (Ag⁺) capture. Silica particles were functionalized with 3-mercaptopropyltrimethoxy silane (MPTMS) to introduce free thiol (–SH) groups on the surface. The particles were used as the dispersed phase in the polysulfone or cellulose acetate polymer matrix. The membranes were prepared by the phase inversion method to create more open and interconnected porous structures suitable for liquid phase applications. The effects of the silica properties such as particle size, specific surface area, and porous/nonporous morphology on the silver ion capture capacity were studied. It was demonstrated that the membranes are capable of selectively capturing silver from a solution containing significant concentrations of other metal ions like Ca²⁺. The membranes were studied to quantify the dynamic capacity for silver ion capture and its dependence on residence time through the adjustment of transmembrane pressure. The thiol–Ag⁺ interaction was quantified with quartz crystal microbalance in a continuous flow mode experiment and the observations were compared with the membrane results. One-dimensional unsteady state model with overall volumetric mass transfer coefficient was developed and solved to predict the silver concentration in the liquid phase and the solid silica phase along the membrane thickness at varying time. The breakthrough data predicted using the model is comparable with the experimental observations. The study demonstrates successful application of the functionalized silica–mixed matrix membranes for selective aqueous phase Ag⁺ capture with high capacity at low transmembrane pressures. The technique can be easily extended to other applications by altering the functionalized groups on the silica particles.     

Different coordination modes of the thiosaccharinate anion in dinuclear and one dimensional polymeric silver–azine complexes

The effect of substituted pyridines bases upon the coordination of thiosaccharinate (tsac, C₇H₄NO₂S₂⁻ in ternary silver complexes is analyzed. Four crystalline silver-substituted pyridine complexes with tsac as a coordinating counter anion, [Ag(tsac)(3-methylpyridine)₂]_n, [Ag₂(tsac)₂(4-methylpyridine)]_n, [Ag₂(tsac)₂(quinoline)₂] and [Ag(tsac)(4-methyloxypyridine)]_n were synthesized and characterized by means of spectroscopic (IR and Raman, UV–Vis, and ¹H and ¹³C NMR) and X-ray diffraction techniques. The thiosaccharinate anion showed its versatility coordinating to the metal in each complex by a different way. In the 3-Mepy complex it was coordinated in a μ₂-S mode and in the 4-MeOpy complex it was bound in a μ₃-S form both resulting in polymeric chains. In the 4-Mepy complex the anion was bound in a μ₂-S,N head to head mode and in the quinoline complex in a μ₂-S,N head to tail mode, both showing dinuclear arrangements.