AgBr Research Articles

Measurement of Crystallite Size of Method and Evaluation of Crystal Defects

The size of crystallites in mono-dispersed cubic silver bromide grains was measured by applying a powder X-ray diffraction method and Scherrer's equation to grains that were suspended in swollen gelatin layers. In order to evaluate the existence of defects, the measured crystallite size was compared to those measured by using a scanning electron microscope. In the case of the grains prepared by the controlled double jet method, the size of crystallites was equal to the edge length of the grains that had edge lengths smaller than 400 nm. This result proved the usefulness of the above-stated method for measuring the size of crystallites and also evaluating the presence of any crystal defect in each grain. In the case of the grains, which were precipitated in the presence of a sensitizing dye and potassium iodide, the size of crystallites was smaller than the edge's length, indicating the discontinuities in the grains introduced during the precipitation process.

Synthesis of silver halide nanocomposites templated by amphiphilic graft copolymer and their use as olefin carrier for facilitated transport membranes

A novel amphiphilic comb-like copolymer consisting of poly(vinyl chloride) (PVC) main chains and poly(4-vinyl pyridine) (P4VP) side chains, i.e. PVC- g-P4VP with 65:35 wt% is synthesized via atom transfer radical polymerization (ATRP). This self-assembled copolymer is used to template the growth of silver bromide (AgBr) nanoparticles with diameters of 10–50 nm, as characterized by UV–vis spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Upon introduction of ionic liquid, i.e. 1-methyl-3-octylimidazolium nitrate (MOIM +NO 3 −), the surface of AgBr nanoparticles is more partially positively charged due to the interactions between NO 3 − ions and the surfaces of nanoparticles, as revealed by FT-Raman and X-ray photon spectroscopy (XPS). We also demonstrate the ability of AgBr as a new type of olefin carrier by tuning the interactions of positively charged AgBr with the C C bond of olefin molecules. As a result, the membranes containing AgBr nanocomposites exhibit highly stable separation performances for propylene/propane mixture, i.e. a mixed gas selectivity of 6 and a permeance of 5.7 GPU.

Synthesis of Copper(I) Complexes of N‐Heterocyclic Carbene–Phenoxyimine/amine Ligands: Structures of Mononuclear Copper(II), Mixed‐Valence Copper(I)/(II), and Copper(II) Cluster Complexes

AbstractCopper(I) bromide complexes (2a and 2b) of NHC–phenolimine ligand precursors {3‐[(1R,2R)‐2‐{[1‐(3,5‐di‐tert‐butyl‐2‐hydroxyphenyl)meth‐(E)‐ylidene]amino}cyclohexyl]‐1‐isopropyl‐4‐phenyl‐3H‐imidazol‐1‐ium bromide (1a) and 3‐[(1R,2R)‐2‐{[1‐(2‐hydroxyphenyl)meth‐(E)‐ylidene]amino}cyclohexyl]‐1‐isopropyl‐4‐phenyl‐3H‐imidazol‐1‐ium bromide (1b), respectively} have been prepared. Complexes 2a and 2b exhibit copper coordination only through the carbene carbon atom (C) and do not spontaneously eliminate HBr to give additional phenoxyimine (NO) bonds, which is attributed to intramolecular hydrogen bonding. Crystallisation of 2a and 2b gives 2a′ and 2b′, respectively, that contain (C) copper(I) bromide and (NO)2 copper(II) coordination. Complex 2b′ also exhibits intermolecular CuIBr interactions giving a Cu2Br2 bridge that links two molecules of 2b′ resulting in an ellipse motif. Reduction of the ligand precursor imine group of 1a allows synthesis of silver(I) and copper(I) NHC–phenolamine complexes 6 and 7, respectively, that also retain the phenol hydrogen atom. Attempts to selectively prepare 2a′ gave a copper(II) complex 9 that exhibits an (NO)2CuII structure with pendant imidazolium salt groups. Reaction between the silver(I) bromide derivative of 1a and CuCl2·2H2O gives a complex derived from a Cu6(O)(OH)4Cl3 core and two (NO) and one (CNO) ligands, respectively. The use of 2a and 7 as precatalysts for 1,4‐conjugate addition to enones and aziridination of alkenes was studied, showing that, whilst both catalysts are active, enantioselectivities are low, which is attributed to the lack of Cu‐(NO) coordination. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

EPR and optical spectra of Ni2+-VAg in silver chloride and silver bromide

The optical absorption and EPR spectra of Ni2+-VAg centres in the AgCl:Ni2+ and AgBr:Ni2+ systems have been investigated theoretically on the basis of the complete energy matrices including the electron–electron repulsion interaction, the ligand field interaction, the spin–orbit coupling interaction, and Zeeman interaction. Because the charge compensation forms a silver ion vacancy (VAg) which makes the attractive force acted on the each ligand ion different, it was determined that the Ni–X (X = Cl, Br) distance next to VAg is shorter than others for both AgCl:Ni2+ and AgBr:Ni2+ systems in the tetragonal symmetry. Besides, it was found that the local lattice structure of (NiX6)4− clusters in AgCl and AgBr crystals exhibit a compression distortion. This compression distortion may be ascribed to the fact that the Ni2+ ion has a smaller ionic radius and more effective charge than the Ag+ ion.

Silver-catalyzed cross-coupling reactions of alkyl bromides with alkyl or aryl Grignard reagents

Treatment of secondary or tertiary alkyl bromides with alkyl Grignard reagents in the presence of catalytic amounts of silver bromide and potassium fluoride in CH 2Cl 2 afforded the corresponding cross-coupling products in reasonable yields. Moreover, silver showed catalytic activity for the cross-coupling reactions of alkyl bromides with aryl Grignard reagents.

Azimuthal structures of produced particles in heavy-ion interactions

The angular structures of particles produced in 208Pb at 158 A GeV/c and 197Au at 11.6 A GeV/c induced interactions with Ag(Br) nuclei in emulsion detector have been investigated. Nonstatistical well-ordered ring-like structures of produced particles in azimuthal plane of a collision have been found, and their parameters have been determined.

The physicochemical properties of the low-temperature ionic liquid silver bromide-1-butyl-3-methylimidazolium bromide

The physicochemical properties of the low-temperature ionic liquid based on 1-butyl-3-methylimidazolium bromide (BMImBr) and silver bromide were studied. Differential scanning calorimetry, Fourier transform IR spectroscopy, densimetry, viscometry, and conductometry measurements were performed to determine the dependences of the parameters under study on the concentration of AgBr. It was shown that the temperature and concentration behavior of the physicochemical properties of BMImBr-AgBr melts characterized the interaction between the system components with the formation of complex particles.

Application of the comet assay in erythrocytes of Oreochromis niloticus (Pisces): a methodological comparison

The present study applied the comet assay to erythrocytes of Oreochromis niloticus with the aim of improving protocols to detect DNA damage in these cells, by using two distinct pHs (pH = 12.1 and pH > 13) and evaluating whether there is a correspondence between silver and ethidium bromide staining. Comets were visually examined and, the frequency of cells with and without damage was obtained, as well as the distribution of classes and scores. By using the Kruskal-Wallis test, our results revealed that pH 12.1 is more effective, although both pHs can be used. Our findings also suggest that silver staining can substitute ethidium bromide, an expensive and highly toxic stain that requires specific equipment for examination.

Partial structures in molten AgBr

The structure of molten AgBr has been studied by means of neutron and X-ray diffractions with the aid of structural modeling. It is confirmed that the Ag–Ag correlation has a small but well-defined first peak in the partial pair distribution function whose tail penetrates into the Ag–Br nearest neighbor distribution. This feature on the Ag–Ag correlation is intermediate between that of molten AgCl (non-superionic melt) and that of molten AgI (superionic melt). The analysis of Br–Ag–Br bond angle reveals that molten AgBr preserves a rocksalt type local ordering in the solid phase, suggesting that molten AgBr is clarified as non-superionic melt like molten AgCl.

Self-assembly in tetrameric 1:1 silver(I) halide:tri- p-tolylphosphine complexes: An in-depth structural investigation

The reaction of silver(I) bromide with tri( p-tolyl)phosphine in MeCN solution in 1:1 molar ratios resulted in a complexes of the formula [AgBr{P(4-MeC 6H 4) 3}] 4. This compound has a tetrameric structure with a concave coordination polyhedron, in between a cube and a stella quadrangula. Weak silver–silver interactions were observed. The current compound is compared to the Cl and I analogs using distance–distance plots. The silver–silver interactions seem to dominate the geometry of these tetrameric type of complexes.

Long-wavelength limit of the static structure factors for mixtures of two simple molten salts with a common ion and generalized Bhatia–Thornton formalism: Molecular dynamics study of molten mixture Ag(Br0.7I0.3)

Abstract The relation between thermodynamic properties and the long-wavelength limit of the structure factors for mixtures of two simple molten salts with a common ion is derived. While the long-wavelength limit of the partial structure factors for binary ionic systems is directly related to the isothermal compressibility, for ternary ionic systems it is shown that it is also related to the mean square thermal fluctuation in the relative concentration of the non-common ions. This result leads to a generalization of the Bhatia–Thornton formalism. From the local fluctuations in the total number-density, charge-density, and relative concentration, six static structure factors, and the corresponding spatial correlation functions, are defined. By introducing three complementary structure factors, it is possible to describe either these mixtures as a system of cations and anions irrespective of the species of the non-common ions, or solely the binary subsystem of the non-common ions. The generalized structure factors and their long-wavelength limits are illustrated by molecular dynamics simulation results of the molten mixture Ag(Br 0.7 I 0.3 ). The mixture retains the charge order characteristic of pure molten monovalent salts and the topological order observed in monovalent ionic melts in which the cations are smaller than the anions, while the main trends of the anionic chemical order are those of simple binary alloys. The long-wavelength fluctuations in the local relative concentration are found to be very sensitive to the choice of the short-range interactions between the non-common ions.

Cetyltrimethylammonium Bromide Silver Bromide Complex as the Capping Agent of Gold Nanorods

A complex between cetyltrimethylammonium bromide (CTAB) surfactant and silver bromide (CTASB) is recognized by NMR and X-ray photoelectron spectroscopy (XPS) to be the entity at the surface of gold nanorods, resulting from an in situ formation in the classical scheme of synthesis. It can thus be introduced directly along with the initial reactants in place of silver(I) salt to produce a new effective synthesis of these objects. Complementary XPS and quartz crystal microbalance (QCM) measurements on macroscopic gold surfaces confirm a strong adsorption of CTASB that is higher than that of CTAB and any other CTAX surfactants. The role of CTASB as a rod inducing agent by surface complexation is stressed.

Effect of Size on Electron Transfer to Silver Clusters

The electronic properties of silver clusters containing up to eight atoms and adsorbed to a positive kink on the (001) surface of silver bromide in contact with aqueous solution are calculated. The necessary reorganization energies and standard free energies of reaction are computed so that the activation energy for transferring an electron from a reducing molecule in solution to silver clusters could be determined with diabatic Marcus electron transfer theory for different cluster sizes. The activation energy oscillates between odd- and even-sized neutral clusters and decreases with increasing size. In the presence of aqueous silver ions, a minimum cluster size of four atoms can be deduced for electron transfer from several reducing agents. These calculated results are discussed in relation to many experimental results. The calculations involve a self-consistent density functional method used to obtain solid state properties of the adsorbed silver clusters and a continuum solvation model (IEF-PCM) used t...

Pecularities in produced-particle emission in 208Pb+ Ag(Br) interactions at 158 A GeV/c

The angular structures of particles produced in 208Pb-induced collisions with Ag(Br) nuclei in an emulsion detector at 158 A GeV/c have been investigated. Nonstatistical ringlike substructures in the azimuthal plane of the collision have been found and their parameters have been determined. An indication of the formation of ringlike substructures from two symmetrical emission cones, one in the forward and the other in the backward direction in the center-of-mass system, has been obtained. The ringlike substructures’ parameters have been determined. The experimental results are in an agreement with I.M. Dremin’s idea that the mechanism of the ringlike substructures’ formation in nuclear collisions is similar to that of Cherenkov electromagnetic radiation.

Development of a holographic sensor for the detection of calcium dipicolinate—A sensitive biomarker for bacterial spores

An enzyme-linked holographic sensor for the detection of spore-specific calcium dipicolinate (Ca-DPA) is described. Small, acid-soluble spore proteins (SASPs) extracted from dormant spores are exploited as holographic matrices. Reflection holograms are incorporated into SASP films using a diffusion method for the distribution of ultra-fine silver bromide grains into pre-formed polymers, followed by holographic recording using a frequency doubled Nd:YAG (532 nm) laser. Changes in holographic diffraction intensity are used to characterise the structural integrity of SASP-based matrices in response to proteolytic attack by recombinant germination protease (GPRS), following activation with Ca-DPA; the holographic response manifests as an irreversible reduction in diffraction intensity due to progressive fringe removal caused by SASP degradation. This work demonstrates proof-of principle of a Ca-DPA-activated enzyme-linked holographic sensor, highlighting the potential of a system whereby Ca-DPA released from germinating spores may activate GPR in the vicinity of an SASP-based holographic matrix; such a sensor system presents a novel platform for the selective detection of bacterial spores with intrinsic signal amplification.

Multifunctional Silane Polymers for Persistent Surface Derivatization and Their Antimicrobial Properties

We demonstrate a versatile methodology combining both covalent surface anchoring and polymer cross-linking that is capable of forming long-lasting coatings on reactive and nonreactive surfaces. Polymers containing reactive methoxysilane groups form strong Si-O-Si links to oxide surfaces, thereby anchoring the polymer chains at multiple points. The interchain cross-linking of the methoxysilane groups provides additional durability to the coating and makes the coatings highly resistant to solvents. By tailoring the chemical structure of the polymer, we were able to control the surface energy (wetting) of a variety of surfaces over a wide range of water contact angles of 30-140 degrees . In addition, we synthesized covalently linked layer-by-layer polymeric assemblies from these novel methoxysilane polymers. Finally, antibacterial agents, such as silver bromide nanoparticles and triiodide ions, were introduced into these functional polymers to generate long-lasting and renewable antiseptic coatings on glass, metals, and textiles.

Novel Expanded Ring N-Heterocyclic Carbenes: Free Carbenes, Silver Complexes, And Structures

The addition of aromatic formamidines to dihaloalkanes proceeds in air under mildly basic conditions and in polar solvents to afford the corresponding amidinium salts in high yields. To demonstrate the wide scope of this methodology, several five-, six-, and seven-membered saturated N-heterocyclic amidinium salts have been prepared. The free carbenes 7-Mes, 7-Xyl, 7-Pri, 6-Mes, and 6-Xyl have also been isolated as stable white solids, and for the first time the solid state structures of free seven-membered N-heterocyclic carbenes have been determined (7-Mes and 7-Xyl). The syntheses and characterization of their Ag(I) halide complexes are also described and the X-ray structures for Ag(6-Pri)Br, Ag(7-Mes)Br, Ag(7-Xyl)I, and Ag(Xyl7-Mes)Br determined. On the basis of NMR data the silver halide species form either neutral, Ag(NHC)X, or ionic, [Ag(NHC)2][AgX2] complexes in solution. A feature of the expanded ring carbenes is the extremely large NCN angle (≥120°) and the consequential steric impact of the N-substituents on the metal center. For the free seven-membered ring carbenes the 13C NMR shifts are 258−260 ppm, well down field from those observed for the six- and five-membered ring carbenes.

Thermodynamic Properties of AgCl and AgBr

Temperatures and enthalpies of fusion as well as the heat capacity of silver chloride and silver bromide were measured by differential scanning calorimetry. A polynomial heat capacity dependence on temperature was used to fit the experimental data. The thermodynamic functions of AgCl and AgBr were calculated by combining these heat capacity results with the entropy at 298.15 K, temperatures, and enthalpies of fusion.

Evolution of Absorption Spectra in the Process of Nucleation in Photo-Thermo-Refractive Glass

Photo-thermo-refractive (PTR) glass belongs to a class of photosensitive multicomponent silicate glasses which demonstrate photo-thermo-induced precipitation of a crystalline phase. Photo-induced crystallization of sodium fluoride results in refractive index variations in exposed areas of PTR glass which was successfully applied for phase hologram recording. However, even if this glass is widely used for advanced optical applications such as the stabilization of laser diodes or spectral beam combining, the detailed mechanism of its photosensitivity is not well known. We present in this paper an analysis of the evolution of the absorption spectra of UVexposed PTR glass at the early stages of the thermal treatment (nucleation). Absorption spectra were measured on samples nucleated at constant temperature for different periods. Analysis of the structure of these spectra shows that the optimum of the nucleation process is associated with the appearance of a new absorption band in visible range that disappears when the crystal growth process starts. Analogous study was performed during the nucleation process. High temperature spectroscopic measurements were performed during the thermal treatment. It was found that absorption spectra evolve with a change of temperature, i.e. the band structure of these spectra is different whether or not the temperature is decreased below a temperature of ~400°C. We associate this process with the change of phase of the silver bromide nuclei (liquid/solid) that appears during the cooling or heating processes.

Size Confinement Effects on Electronic and Optical Properties of Silver Halide Nanocrystals as Probed by Cryo-EFTEM and EELS

Cryo-energy-filtering transmission electron microscopy and electron energy-loss spectroscopy have been applied to study size confinement effects on electronic, dielectric, and optical properties of Ag(Br, I) nanocrystals. The dielectric permittivity, optical joint density of states, refractive index, extinction, and absorption for nanocrystals derived via Kramers–Kronig relations have been compared with experimental data for Ag(Br, I) tabular microcystals and ab initio linear muffin-tin orbital method in its atomic spheres approximation calculations for AgBr. Contrast tuning with the selected energy window between 0 and 100 eV enabled visualizing valence electron excitations in silver halides because of plasmons superimposed with interband transitions and Mott–Wannier excitons. The nonuniform contrast of nanocrystals revealed by cryo-energy-filtering transmission electron microscopy was referred to a size-confined coupling of surface and volume losses that could lead to oscillations of the image intensity with the nanocrystal size. A size-dependent enhancement of interband transitions \(\Gamma _8^ - ,\Gamma _6^ - \to \Gamma _6^ + \) at 4 eV correlated with the enhancement of exciton luminescence from nanocrystals because of contributions to the energy-level structure from carrier confinement and surface states.