Excess Of Silver Ions Research Articles

P-type Sn0.98Ag0.02Se with low thermal conductivity synthesized by hydrothermal method

Tin selenide exhibits outstanding thermoelectric properties. Among its various forms, multicrystalline SnSe stands out as a more practical choice compared to single-crystal SnSe, owing to its straightforward chemical synthesis process, enhanced processability, and scalability. Herein, we synthesized p-type polycrystalline Sn1−xAgXSe bulk materials (x = 0, 0.01, 0.015, 0.02, 0.025, 0.03) using a simple hydrothermal and hot pressing method. Characterization methods such as XRD, Raman and XPS were used to demonstrate the successful doping of Ag+ into the SnSe matrix. When the doping concentration reached Sn0.98Ag0.02Se (x = 0.02), Ag+ reached the optimal concentration in the SnSe matrix, causing significant lattice distortion which increased phonon scattering and lowered the thermal conductivity, resulting in Sn0.98Ag0.02Se achieving ZTmax= 1.14. However, when the doping concentration exceeded Sn0.98Ag0.02Se (x > 0.02), excess silver ions precipitated, partially acting as charge carriers, leading to a significant increase in electrical conductivity, resulting in Sn0.97Ag0.03Se having an electrical conductivity of 6860 s/m at 773 K. Compared to the pure phase, the electrical conductivity of Sn0.97Ag0.03Se increased by 259 %, and the ZT value of Sn0.98Ag0.02Se increased by 178%. This work demonstrates that Ag+ is an effective p-type dopant in the SnSe system and indicates that high ZT values in SnSe can be achieved through a simple, low-cost, and environmentally friendly method.

Study of Photo-transformation of Ag Nanoparticles under Green LEDs Light Source and their Changes Induced by Z-scan Technique

Background: The study of metallic nanoparticles is important since they present nonlinear optical properties crucial for modern photonic science and technology. Moreover, their mechanical, chemical, and optical properties are different from those presented with respect to volumetric material. Said properties can be adjusted by controlling the size and shape of the studied nanoparticles, and various methodologies have been developed to obtain nanoparticles by chemical and physical means. Methods: Spherical nanoparticles were synthesized by chemically reducing silver nitrate, sodium borohydride, and sodium citrate precursors. Different amounts of silver nitrate were added to the original spherical nanoparticles and then exposed to a green LED light source to convert the spherical nanoparticles to triangular prisms. The changes in the samples were monitored using absorption spectra obtained with a UV-Vis spectrophotometer. The nonlinear refractive index was determined with Z-scan measurements, and a scanning electron microscope was used to observe the silver nanoparticles before and after laser irradiation. Results: The absorption spectra show a band of around 418 nm for the original spherical nanoparticles, which shifted to blue after the irradiation with green LED light. Furthermore, a new band was obtained, centered around 565 nm, which indicates the presence of triangular prisms. From SEM images, it was confirmed that the spherical nanoparticles were transformed into triangular nanoprisms. The non-linear (negative) refractive index depends on the shape and number of nanoparticles; however, using the Z-scan technique caused photo-melting and photofragmentation of the triangular prisms, which was corroborated by SEM images. Conclusion: These results suggest that the shape and amount of AgNPs can be controlled with excess silver ions and irradiation time. In addition, the Z-scan technique causes photo-melting and photo-fragmentation of AgNPs, and their nonlinear refraction index is negative due to thermal origin.

Mechanism underlying visible-light photocatalytic activity of Ag/AgBr: Experimental and theoretical approaches

Silver/silver halides (Ag/AgX) are potential visible-light (VL) photocatalysts due to synergistic effects of surface plasmon resonance (SPR) and semiconductor photocatalysis. However, many contradictory opinions are found in published literature about the mechanism underlying photocatalytic oxidation (PCO) by Ag/AgX. In this study, Ag/AgBr particles were prepared by a simple one-pot synthesis method and used for degradation of Reactive Black 5 (RB5) as a model pollutant aiming to understand the effect of concentration of excess silver ions on SPR phenomenon, and to employ experimental and theoretical approaches to pinpoint the reactive oxidative species (ROS) responsible for RB5 degradation. 16.2% of initial 50 mg/L RB5 was degraded using 0.5 g/L AgBr (Ag+:AgBr = 0, i.e. no excess Ag+) under 60 min VL irradiation. Under identical experimental conditions, RB5 degradation increased to 86.5% using Ag/AgBr synthesized as Ag+:AgBr = 0.4, due to improved SPR effect. Experimental evidence supported by theoretical calculations revealed that superoxide radicals (•O2) played a prime role in PCO followed by photo-generated holes, whereas the contribution of •OH was negligible. The presence of Ag0 on AgBr greatly influenced band energies and regulated the formation of ROS. With an increase in ratio Ag+:AgBr, the conductance and valence bands increasingly became more electro-negative and electro-positive, respectively, as compared to that at Ag+:AgBr = 0. The presence of Cl ̅ and SO42− ions adversely affected RB5 degradation, whereas CO32− did not cause any adverse impact. Ag/AgBr could be successfully immobilized over bacterial cellulose which, under identical conditions, provided 79.1% RB5 degradation in 60 min. The Ag/AgBr-BC could be reused five times.

Cell viability and bacterial reduction activity of Ag-modified bentonite

Abstract The interest on the potential biomedical applications of clay materials are recently growing. Among the clay minerals, it was found that the smectite group clays are the most suitable for adsorption processes. This group includes bentonite in which the structure is composed of octahedral and tetrahedral layers of silica. In this study, bentonite clays from SAILE Industries, Inc. in Mangatarem, Pangasinan, Philippines were characterized and fabricated as Ag-bentonite composites to determine the potential of the mineral for biomedical applications. Bentonite clay powder was mixed with silver nitrate solution via ion-exchange process. The synthesized powders were filtered using centrifugation and washed with deionized water to remove any excess silver ions. Drying followed at 60°C and stored in a dark container prior to characterization. XRD and XRF was used to evaluate the phase composition and chemical analysis of the Ag-bentonite composite, respectively. The biological tests were also done to investigate the antibacterial and cell viability of the sample.XRD result showed that the sample is composed of the montmorrilonite, hectorite and mordenite phases. Chemical analysis revealed the presence of Ag in the bentonite structure with a content of about 14.24±0.13%. Antibacterial activity of the sample was evaluated using plate reduction method where about 99% reduction of S. Aureus was observed after 24 h. Moreover, approximately 89±4.37% live cells was detected after the 24-h incubation of the sample using lymphocyte culture. With these results, the synthesized AgB samples may find suitable future biomedical use due to its stable structure, antibacterial and biocompatibility properties

Zeta Potential and Hydrodynamic Radii of Silver Sulfide Nanoparticles in a Colloidal Solution with Mercaptopropylsilane

The dependence of the zeta potential and hydrodynamic radii of silver sulfide nanoparticles (Ag2S) in an aqueous colloidal solution on the concentration of stabilizer 3-mercaptopropyltrimethoxysilane (MPS) is determined. A model for the structure of a surface layer of Ag2S nanoparticles coated with MPS is proposed that explains the observed dependence and the extrema on it. It is found that the values of the zeta potential and the hydrodynamic radii of the Ag2S nanoparticles depend substantially on the means of creating an excess of silver ions in the solution. This dependence is explained by the dynamics of the formation of a stabilizer layer on the surface of nanoparticles.

(Ag,Cu)(In,Ga)Se2 thin films fabricated on flexible substrates via non-vacuum process

(Ag,Cu)(In,Ga)Se2 thin films with various contents of silver ions were successfully fabricated on the stainless steel substrates using the non-vacuum spin-coating process. The solar cells with the stainless steel/Mo/ACIGS/CdS/i-ZnO/ITO structure were prepared. After selenization at 550 °C for 30 min, the monophasic chalcopyrite-structured (Ag,Cu)(In,Ga)Se2 thin films were formed. The conversion efficiency of (Ag,Cu)(In,Ga)Se2 solar cells was significantly increased from 4.34 to 6.29% when the molar ratio of Ag ions to total (Ag + Cu) ions was increased from 0 to 0.2. The increase in conversion efficiency was attributed to the liquid phase that was formed from (Ag,Cu)2In intermediate compound. The formed liquid phase facilitated the grain growth and promoted the densification of thin films. The densified thin films of (Ag,Cu)(In,Ga)Se2 suppressed the additional shunt path and decreased the value of shunt conductance (G) to 12.57 mS/cm2. In addition, the values of ideal factor (A), saturated current density (J0), and series resistance (Rs) were respectively decreased to 2.96, 0.08 mA/cm2, and 0.23 Ωcm2 due to suppressing the additional shunt path. When an excess of silver ions were doped into the CIGS thin films, the microstructures of the prepared thin films became porous, and the conversion efficiency of the solar cells was reduced. This research reveals that adding an appropriate amount of silver ions effectively improved the performance of (Ag,Cu)(In,Ga)Se2 solar cells.

Influence of Ultra-Violet Radiation on Sublimation Energy of Silver Chloride (AgCl)

Influence of silver chloride synthesis conditions on its heat of sublimation after ultra-violet irradiation was explored. It was determined that silver chloride synthesized in excess of silver ions after irradiation was characterized by heat of sublimation about 6813 J/g, which meant that the original value increased in ~ 1.8 times. At the same time silver chloride synthesized in excess of chloride ions was characterized by decrease in value of heat of sublimation by ~ 2 times. Growth of heat of sublimation of silver chloride with excess of silver ions is connected with energy expenditure on sublimation due to decrease in proportion of surface which is not covered with silver. Reduction of heat of sublimation of silver chloride with excess of chloride ions is explained by absence of silver solid surface film and catalytic effect of silver klasters formed during the process of irradiation.

Development and validation of HTS assay for screening the calcium-activated chloride channel modulators in TMEM16A stably expressed CHO cells

Calcium-activated chloride channels (CaCCs), for example TMEM16A, are widely expressed in a variety of tissues and are involved in many important physiological functions. We developed and validated an atomic absorption spectroscopy (AAS)-based detection system for high-throughput screening (HTS) of CaCC modulators. With this assay, Cl(-) flux from CHO cells stably transfected with TMEM16A is assayed indirectly, by measuring excess silver ions (Ag(+)) in the supernatant of AgCl precipitates. The screening process involved four steps: (1) TMEM16A CHO cells were incubated in high-K(+) and high-Cl(-) buffer with test compounds, and with ionomycin as Ca(2+) ionophore, for 12min; (2) cells were washed with a low-K(+), Cl(-)-free and Ca(2+)-free buffer; (3) CaCC/TMEM16A were activated in high-K(+), Cl(-)-free buffer with ionomycin (10μmolL(-1)) for 12min; and (4) excess Ag(+) concentration was measured using an ion channel reader (ICR, an AAS system). The assay can be used to screen CaCC activators and inhibitors at the same time. With this assay, positive control drugs, including NPPB, CaCCinh-A01, flufenamic acid (Flu) and Eact, all had good concentration-dependent effects on CaCC/TMEM16A. NPPB and CaCCinh-A01 inhibited the CaCC/TMEM16A currents completely at 300μmolL(-1), with IC50 values of 39.35 ± 4.72μmolL(-1) and 6.35 ± 0.27μmolL(-1), respectively; and Eact, activated CaCC/TMEM16A, with an EC50 value of 3.92 ± 0.87μmolL(-1).

In-situ prepared polyaniline–silver composites: Single- and two-step strategies

Conducting polymer–metal composites, such as polyaniline–silver, can efficiently be prepared by two ways: (1) by the oxidation of aniline with silver ions or (2) by the reduction of silver ions with polyaniline. Both approaches yield the composites with limited conductivity. In order to increase the content of silver, and thus increase the conductivity, two strategies are proposed: (1) an increase of oxidant-to-aniline mole ratio in the oxidation of aniline with silver nitrate above stoichiometric value in a single step, and thus reduce excess silver ions to silver metal with produced polyaniline, or (2) in two steps, by preparing polyaniline–silver composite at first and then using polyaniline for the reduction of silver ions. The second approach yields the composites of higher conductivity of the order 100Scm−1. The role of aniline oligomers and interfacial barriers is discussed on the basis of UV–vis and FTIR spectra, and on morphology assessment. The changes in conductivity of composites after deprotonation and reprotonation of polyaniline part are also reported. Surprisingly, the conversion of conducting polyaniline salt to a non-conducting polyaniline base may be associated with an increase of composite conductivity.

Mononuclear and Polynuclear Chain Complexes of a Series of Multinucleating N/S Donor Ligands

AbstractWe have prepared a series of five ligands with potentially N,S‐bidentate chelating arms derived from 3‐[2‐(methylsulfanyl)phenyl]pyrazole linked to central aromatic spacers by methylene units. Complexes with a variety of architectures have been obtained, including simple mononuclear complexes and polynuclear chain complexes. The p‐xylyl‐spaced ligand L1 forms one‐dimensional helical coordination polymers with copper(I) and silver(I) ions. These polymers display interligand aromatic stacking interactions within each helical chain. The m‐xylyl‐spaced ligand L2 forms a coordination polymer with copper(I) but a mononuclear complex with the larger silver(I) ion in which the central phenyl ring is involved in an η1 π‐type Ag···C interaction with the AgI. The 3,3′‐biphenyl‐spaced ligand L3 also forms one‐dimensional polymers with silver(I) and copper(I) ions, but in this case the sequence of bridging ligands between one metal centre and the next follows a zig‐zag path rather than being helical. The 1,8‐naphthyl‐spaced ligand L4 only forms mononuclear complexes with copper(I) and silver(I) ions showing that this spacer is not large enough to enforce a bridging coordination mode. The three‐armed ligand L5, prepared from 2,4,6‐tris(bromomethyl)mesitylene, also forms a mononuclear complex with silver(I) ions, where one of the three arms is pendant. However, when excess silver(I) ions are present two of these mononuclear complexes can be assembled into the trinuclear complex [Ag3(L5)2](ClO4)3. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Silver absorption and antibacterial efficacy of silver dressings

To evaluate the patterns of silver release from selected sustained silver-release dressings and the protective role of proteins in wound exudate and wound scale. The bactericidal action of silver in chronic wound therapy is also examined. Sequential microbiological examination of wound swabs from seven patients with chronic wounds and sampling of wound exudate and wound scale. Silver content was measured using atomic absorption spectrometry. The ability of Contreet Foam to absorb exudate and release silver was studied in punch biopsy wounds in a rodent model. Silver accumulation in wound exudate correlated well with its viscosity and protein content. Silver bound to wound scale and debris was approximately proportional to the silver ion release from dressings. Bacterial burden was controlled, but not eliminated, following chronic silver therapy. Silver dressings (Acticoat-7, Actisorb Silver, Contreet Foam, Aquacel Ag and Flamazine) were found to be safe for use in chronic wound therapy. Excess silver ion is bound by wound exudate and wound scale as a protective mechanism. Silver-release dressings are not likely to result in germ-free wounds. Further studies are needed to examine potential silver resistance.

Ab initio simulations on AgCl(1 1 1) surface and AgCl(1 1 1)/α-Al 2O 3(0 0 0 1) interface

The defect chemistry and ionic transport properties of the AgCl(1 1 1)/α-Al 2O 3(0 0 0 1) interface were considered by using ab initio slab calculations. These calculations were performed in the framework of plane-wave basis set combined with the density functional theory (DFT), as implemented into the VASP computer code, and Gaussian basis set combined with the Hartree–Fock method (CRYSTAL-98 code). We analyze the electron density distribution on the interface and the electrostatic potential distribution near the AgCl surface. The size of the silver ion is too great to enter the corundum surface layer and to create excess silver ions in this way. This is in agreement with the experiments on heterogeneous doping of AgCl revealing α-alumina to be inactive compared with γ-alumina. The energy to thermally create a vacancy in the first layer at the expense of an interstitial ion is large compared with the bulk Frenkel energy. Despite the calculated low activation energy for vacancy transport in the first layer ( Δ H s # = 0.23 eV), the vacancy concentration will be too small to generate perceptible surface conductivity. The striking similarity of Δ H s # with the bulk value is due to the quite symmetrical arrangement of the considered interface.

Indirect potentiometric titration of sulphamethoxazole in the presence of trimethoprim in co-trimazole tablets using copper based mercury film electrode.

A simple and rapid indirect potentiometric titration of sulphamethoxazole in the presence of trimethoprim contained in co-trimazole tablets is described. The method is based on the formation of a complex of sulphamethoxazole with a known excess of silver ions and the titration of unreacted silver ion potentiometrically using an inexpensive lab-made copper based mercury film electrode (CBMFE). The titration conditions have been optimized for the determination of 1.0-10.0 mg of sulphamethoxazole in pure and dosage forms. The precision and accuracy of the method have been assessed by the application of lack of fit test and other statistical methods. Overall mean recovery and relative standard deviations obtained were 99.88% and 1.32% (n=7) respectively. No interference was caused by other excipients present in pharmaceutical dosage forms. The application of this method for sulphamethoxazole assay in the presence of trimethoprim in tablets was validated by the comparison of results obtained by the proposed method with that of the British Pharmacopoeia (BP) method using F- and t-statistical tests of significance.

Effect of Ligands on the Redox Reactions of Silver Metal Clusters

The reduction of silver ions and their subsequent agglomeration was studied in aqueous solutions in the presence of N-(hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), iminodiacetic acid, 5-aminotetrazole, benzotriazole, and 2-mercaptobenzimidazole as ligands. The presence of ligands in the solution affects the early processes via the complexation of Ag+ ions with the carboxyl and amino moieties of the ligands. Also, it reduces somewhat the rate of reduction by hydrated electrons. The transient absorption spectra of Ag0, Ag2+ and Ag20 and their successive rate constants have been determined. The red shift in the band of silver atoms was found to be more pronounced when the ligand interaction is stronger. This was correlated with the ligand-induced redox properties of the silver couple. These effects are also more pronounced in the presence of excess silver ions in the solution. It was observed that silver N-(hydroxyethyl)ethylenediaminetriacetic acid and silver nitrilotriacetic acid are not directly reduced by (CH3)2CO•-. This confirms that the redox potential of the silver couple is lowered in the presence of HEDTA and NTA. In addition, HEDTA stabilizes silver metal particles against corrosion due to the shift in the redox potential. Silver particles prepared by γ irradiation and combined with hydrothermal treatment were characterized using transmission electron microscopy and showed particle sizes of 10−20 nm.

Indirect spectrophotometric determination of thiamine in pharmaceutical preparations.

An indirect, sensitive spectrophotometric method for the assay of thiamine is described. The procedure is based on the formation of a mercaptide by thiamine, with a known excess of silver ions in a buffered medium of pH 9.0 +/- 0.1. The unreacted silver ions are determined by the formation of an ion-pair complex with 1,10-phenanthroline and 2,4,5,7-tetrabromofluorescein, which shows an absorption maximum at 550 nm. The absorbance is found to decrease linearly with increasing concentrations of thiamine, which is corroborated by the calculated correlation coefficient value of -0.998. The system obeys Beer's law for 0-25 micrograms of thiamine in an overall aqueous volume of 10 ml. The molar absorptivity and relative standard deviation (RSD) were calculated to be 7.8 x 10(4) l mol-1 cm-1 and 2.5% (n = 10), respectively. The proposed method was applied successfully to the determination of thiamine in pharmaceutical preparations. The reliability of the assay was established by parallel determination by the standard thiochrome method and recovery studies.

Reduction and aggregation of silver ions and mixed aggregates in aqueous solutions of carboxymethyl cellulose

Radiolytic reduction of silver ions and its aggregates were studied in aqueous carboxy methyl cellulose (CMC) solutions. The early processes of silver gets affected in the presence of CMC via complexation. The ratio of silver ions to CMC chains decreases or accelerates the processes that involve silver ions. Presence of excess silver ions enhances the stability of small clusters in the presence of CMC. Mixed aggregates of thallium/silver and cadmium/silver get stabilised in the presence of CMC. It is concluded that Co + do not transfer electron to Pb 2+ and Tl +. Also, no electron transfer reaction was observed between either Tl 2 + and Co 2+ or Pb 0 and Cd 2+. However, Zn + transfers electron to Pb 2+ and Tl 2 + transfers electron to Cu 2+ with a rate of 4.2×10 7 M −1s −1 and 3.5×10 9 M −1s −1, respectively. The reactions are discussed in terms of the electrochemical potential of the metal ions (or metals) involved.

Early stages of metal clusters in aqueous solution: Reaction of Zn + and Cd + with Ag +

Zn + and Cd + are pulse radiolytically generated in solutions which also contain low concentrations of silver ions. Both of these monovalent ions react rapidly with the silver ion yielding a free silver atom (Ag 0) through electron transfer, or a mixed metal cluster [(CdAg) 2+], respectively. The free silver atom and the cluster subsequently react with excess silver ions producing dimer (Ag 2 +) and trimer (Ag 3 2+) silver ions, which are also observed in a solution containing only silver ions.

Application of computers for optimisation of end-point determination in catalytic titrimetry

The problem of establishing an optimum procedure for the determination of the end-point of catalytic titrations was studied using computer facilities. All procedures were tested using simulated titration curves recorded in either the integral or the derivative mode. The effects of a number of factors that influence the accuracy of determination are discussed. The results were compared with those obtained by experiments in which milligram amounts of bromide and iodide were determined using a new indicator reaction, persulphate-sulphanilic acid-2,2′-bipyridine, catalysed by a small excess of silver ion. In this instance, the method of graphical extrapolation of straight portions of the integral catalytic titration curve before and after the equivalence point appeared to be the best procedure for the end-point determination.

Growth mechanisms of silver halide clusters from the molecule to the colloidal particle

Studies of growing silver halide clusters, from the molecular level to colloidal-size particles, have been undertaken and correlations between particle size and physical properties have been investigated. The production of halide ions by dissociative electron attachment following pulse radiolysis of methylene halide solutions was utilized to instantaneously produce homogeneous, supersaturated solutions of halide and silver ions. The growth of silver halide particles in these solutions has been examined by conductance, absorption spectroscopy, and light scattering measurements. Conductivity measurements show that the initial reaction between the ions occurs at a diffusion-controlled rate and allow determination of the stability constants of molecular silver halide species. In solutions containing excess silver ions, particle growth of silver iodide and silver bromide occurs via a diffusion-controlled aggregation mechanism during the first seconds. The growth rate is reduced significantly, due to electrostatic repulsion between particles, when the concentration of halide ions is almost equal to or greater than the stoichiometric concentration of silver ions. The absorbance of silver iodide suspensions produced in this manner has also been measured. The initial absorbance, due to AgI molecules, occurs at wavelengths of 280 nm and below. The lowest energy exciton band appears {approximately} 50 {mu}s after initiation of themore » reaction. This band initially peaks at around 320 nm and shifts toward 425 nm (the wavelength of exciton absorption in bulk silver iodide). The surface potential at the interface evolves at about the same rate as the bulk properties of the material. For the mostly dissociated AgCl molecules growth by addition of ions to a small number of particles of critical size was observed.« less

Silver bromate precipitation in bromate oscillators treated with excess silver ion. A comment

Silver bromate precipitation in bromate oscillators treated with excess silver ion. A comment