Silver Precipitation Research Articles

Facile Synthesis and Characterization of Silver Nanoparticle/Bis(<I>o</I>-phenolpropyl)Silicone Composites Using a Gold Catalyst

The generation of silver nanoparticle/bis(o-phenolpropyl)silicone composites have been facilitated by the addition of sodium tetrachloroaurate or gold(Ill) chloride (< 1 wt% of NaAuCl4 or AuCl3) to the reaction of silver nitrate (AgNO3) with bis(o-phenolpropyl)silicone [BPPS, (o-phenolpropyl)2(SiMe2O)n, n = 2,3,8,236]. TEM and FE-SEM data showed that the silver nanoparticles having the size of < 20 nm are well dispersed throughout the BPPS silicone matrix in the composites. XRD patterns are consistent with those for polycrystalline silver. The size of silver nanoparticles augmented with increasing the relative molar concentration of AgNO3 added with respect to BPPS. The addition of gold complexes (1-3 wt%) did not affect the size distribution of silver nanoparticles appreciably. In the absence of BPPS, the macroscopic precipitation of silver by agglomeration, indicating that BPPS is necessary to stabilize the silver nanoparticles surrounded by coordination.

A novel approach to fingerprint visualization on paper using nanotechnology: reversing the appearance by tailoring the gold nanoparticles' capping ligands

Gold nanoparticles, AuNPs, capped with mercaptocarboxylic acids followed by silver precipitation develop latent fingermarks on paper as high quality "negative" impressions. This effect stems from hydrogen bonding between the carboxylic group and the paper cellulose and may improve the yield of latent fingermarks since the results are less dependent on sweat composition.

Visualization of Latent Fingermarks by Nanotechnology: Reversed Development on Paper—A Remedy to the Variation in Sweat Composition

Don′t sweat it: “Negative” fingermarks are developed on paper by the application of gold nanoparticles (gold circles) that are capped by a bifunctional ligand, and then silver precipitation. In this process, paper is the substrate and the fingermarks serve as a mask. This approach may contribute to the successful recovery of latent fingermarks by law enforcement agencies.

A second generation universal microarray for subtyping influenza a virus

The microchip for influenza A subtyping was developed, functioning on a principle "one spot--one subtype". Each spot contains the set of oligonucleotide probes, specific for a particular subtype of hemagglutinin, neuraminidase or matrix gene. Reliability of the proposed chip version is the same as for earlier created in our group full-size microchip for separate hemagglutinin and neuraminidase subtyping. To visualize the image, analyzed DNA can be labeled by either fluorescent dye or biotin with the further fixation in system streptavidin-gold nanoparticles and image development by silver precipitation. In the second case common version of scanner can be used for the image analysis, that essentially simplifies procedure of influenza A subtyping.

Ultrastructural and Spectrophotometric Study on the Effects of Putative Triggers on Aortic Valve Interstitial Cells in In Vitro Models Simulating Metastatic Calcification

Metastatic calcification of cardiac valves is a common complication in patients affected by chronic renal failure. In this study, primary bovine aortic valve interstitial cells (AVICs) were subjected to pro-calcific treatments consisting in cell stimulation with (i) elevated inorganic phosphate (Pi = 3 mM), to simulate hyperphosphatemic conditions; (ii) bacterial endotoxin lipopolysaccharide (LPS), simulating direct effects by microbial agents; and (iii) conditioned media (CM) derived from cultures of either LPS-stimulated heterogenic macrophages (commercial murine RAW264.7 cells) or LPS-stimulated fresh allogenic monocytes/macrophages (bCM), simulating consequent inflammatory responses, alone or combined. Compared to control cultures, spectrophotometric assays revealed shared treatment-dependent higher values of both calcium amounts and alkaline phosphatase activity for cultures involving the presence of elevated Pi. Ultrastructurally, shared peculiar pro-calcific degeneration patterns were exhibited by AVICs from these latter cultures irrespectively of the additional treatments. Disappearance of all cytomembranes and concurrent formation of material showing positivity to Cuprolinic Blue and co-localizing with silver precipitation were followed by the outcropping of such a material, which transformed in layers outlining the dead cells. Subsequent budding of these layers resulted in the formation of bubbling bodies and concentrically laminated calcospherulae mirroring those in actual soft tissue calcification. In conclusion, the in vitro models employed appear to be reliable tools for simulating metastatic calcification and indicate that hyperphosphatemic-like conditions could trigger valve calcification per se, with LPS and allogenic macrophage-derived secretory products acting as possible calcific enhancers via inflammatory responses.

Recovery of silver from X-ray film processing effluents by hydrogen peroxide treatment

In this study, recovery of silver from X-ray film processing effluents by precipitation was studied. Hydrogen peroxide was used as the precipitating agent. A full factorial design (42) approach was adopted for the study. The results have shown that precipitation process is highly exothermic in nature with the evolution of copious amount of heat apparently owing to the concomitant oxidation of thiosulphate. The precipitation of silver by hydrogen peroxide is a fast reaction, which is almost complete within minutes. It is also an acid consuming reaction with the tendency of pH to increase towards neutral/alkaline conditions. The concentration of hydrogen peroxide was proved to be statistically the most significant factor affecting the precipitation process. High silver recoveries (≥95%) from the waste solution (1.1g/L Ag, 113g/L S2O32−) were obtained only at high levels of H2O2 (≥37.6g/L). Over the reaction period, a substantial increase in the concentration of sulphate was noted indicating the consumption of H2O2 mainly by the oxidation of thiosulphate. Increasing pH was found to have a beneficial effect on the recovery of silver noticeably at low H2O2 concentrations. The addition of ethylene glycol (0.5–10mL) enhanced the recovery of Ag (by 1.3–18.7%) presumably due to its stabilising effect on H2O2. SEM–EDS and XRD analyses of the precipitates have revealed that silver is present mainly as fine silver sulphide. These findings demonstrate that the waste photoprocessing solutions can be suitably treated by hydrogen peroxide to recover silver and remove thiosulphate.

Sintering and Contact Formation of Glass Containing Silver Pastes

The silver paste composition for the front side has a strong influence on the firing behaviour, contact formation and resulting efficiency of the solar cell. It is state of the art that the paste glass is needed for etching the ARC silicon nitride during firing and also plays a major role for the transport of silver to the silicon surface. However, the kinetics of the silver transport is still under discussion. A main challenge to understand the underlying mechanisms is the analysis of the microstructure evolution of the paste during firing in the high speed PV firing cycle. In this work PV high speed firing conditions were simulated by usage of a simple laboratory furnace. The microstructural evolution of a model paste was observed and correlated to obtained contact resistances. Moreover, systematic variations of the paste glass were investigated. The overall contact formation kinetics can be divided into two independent but strongly interacting single kinetic phenomena: (i) the reaction kinetics at the wafer surface and (ii) the phase transport kinetics of the silver paste. The reaction kinetic at the wafer surface is composed by three important single reactions: silver solution and precipitation in the amorphous interface layer, interface layer growth, and silicon etching. The phase transport kinetics of the metallization paste determines the quantity of glass that is mixed with the etching products in the interface layer and is dominated by the densification rate of the silver powder and the viscous flow of the paste glass. The paste glass has crucial influence for both kinetics (i) and (ii). In this study the paste glass chemistry has a dominating impact compared to the glass rheology. By an appropriate choice of the raw materials regarding the sinter behaviour and targeted selection of the powder properties substantial control over the paste contacting performance is possible.

Corrosion protection of metal surfaces by atmospheric pressure plasma jet treatment

In this paper the corrosion protection of silicon-organic coatings applied by an atmospheric pressure plasma jet system was studied on copper (Cu) and aluminium (Al). The influence of a plasma pre-treatment on the defect density and the adhesion of the subsequently deposited plasmapolymer coating are presented. The quality of the coating was studied via visualization of defects by means of silver precipitation. Use of a reductive gas mixture for the plasma pre-treatment led to a significant reduction of the defect density. Additionally, the implementation of chromate-free corrosion inhibitors in the plasmapolymer layer enables an active corrosion protection of Al surfaces.

Cluster size polymorphism of active human ribosomal genes and simulation of the conditions of its stability through generations

Based on selective silver nitrate staining of active ribosomal gene (AcRG) clusters in nucleolus organizer regions (NORs) of human metaphase chromosomes, a technique was developed earlier to estimate the AcRG dosage in individual genomes as a sum of arbitrary units (0-3) ascribed to the silver precipitate (AgNOR) on ten NORs. The AcRG dosage was considered to be an additive quantitative trait determined by five polymorphic autosomal loci (with for allelic forms for each locus). A database was created to contain the data on AcRG cluster variants for more than 1000 individual human genomes. In this study, the population frequencies of AcRG cluster variants were determined. The results agreed with the hypothesis that stabilizing selection acts at the zygotic and/or early embryogenetic stage to restrain the AcRG genomic dosage (copy number) within a range from 14.9 to 23.7 arbitrary units (the cell is unviable when the trait is beyond this range). The average zygotic losses due to selection were estimated at 9.1-9.9% for a real population. A computer model where the AcRG dosage of a progeny results from a random combination of the AgNORs of the five acrocentric chromosome pairs of the parents was developed and used to simulate the formation of a certain AcRG genomic dosage through generations in a human panmictic population with nonoverlapping generations. A combination of stabilizing selection by total AcRG copy number and a certain spontaneous mutation rate (the probability of changes in the cluster size of a NOR as a result of unequal crossingover in meiotic prophase) was shown to be a sufficient condition for the restrain of equilibrium population frequencies of AgNOR size variants in a human panmictic population. Using the model, the most probable spontaneous mutation frequency was predicted to be (2.1-2.3) x 10(-2) per NOR per generation for human AgNORs. The predicted frequency was within the 95% confidence interval of the experimental rate, which was determined by studying the inheritance of AgNOR variants in real families.

Differential Effect of Common Ligands and Molecular Oxygen on Antimicrobial Activity of Silver Nanoparticles versus Silver Ions

The antibacterial activity of silver nanoparticles (AgNPs) is partially due to the release of Ag(+), although discerning the contribution of AgNPs vs Ag(+) is challenging due to their common co-occurrence. We discerned the toxicity of Ag(+) versus a commercially available AgNP (35.4 ± 5.1 nm, coated with amorphous carbon) by conducting antibacterial assays under anaerobic conditions that preclude Ag₀ oxidation, which is a prerequisite for Ag(+) release. These AgNPs were 20× less toxic to E. coli than Ag(+) (EC₅₀: 2.04 ± 0.07 vs 0.10 ± 0.01 mg/L), and their toxicity increased 2.3-fold after exposure to air for 0.5 h (EC₅₀: 0.87 ± 0.03 mg/L) which promoted Ag(+) release. No significant difference in Ag(+) toxicity was observed between anaerobic and aerobic conditions, which rules out oxidative stress by ROS as an important antibacterial mechanism for Ag(+). The toxicity of Ag(+) (2.94 μmol/L) was eliminated by equivalent cysteine or sulfide; the latter exceeded the solubility product equilibrium constant (K(sp)), which is conducive to silver precipitation. Equivalent chloride and phosphate concentrations also reduced Ag(+) toxicity without exceeding K(sp). Thus, some common ligands can hinder the bioavailability and mitigate the toxicity of Ag(+) at relatively low concentrations that do not induce silver precipitation. Furthermore, low concentrations of chloride (0.1 mg/L) mitigated the toxicity of Ag(+) but not that of AgNPs, suggesting that previous reports of higher AgNPs toxicity than their equivalent Ag(+) concentration might be due to the presence of common ligands that preferentially decrease the bioavailability and toxicity of Ag(+). Overall, these results show that the presence of O₂ or common ligands can differentially affect the toxicity of AgNPs vs Ag(+), and underscore the importance of water chemistry in the mode of action of AgNPs.

Recovery of Silver from X-Ray Film Processing Effluents Using Trimercapto-s-triazine (TMT)

In this study, the recovery of silver from waste X-ray photographic solutions by precipitation using trimercapto-s-triazine (TMT) was studied. Taguchi L25 (53) orthogonal design was adopted for the study. The effects of concentration of thiosulphate (5.2–200 g/L), TMT (Ag:TMT = 6.6–2.2), temperature (20–60°C) and pH (4.37–8.00) on the extent of the precipitation of silver were investigated. The findings have shown that the concentration of TMT and pH are the most significant factors affecting the recovery of silver while the effect of temperature (20–60°C) is insignificant under the conditions tested. The increase in the concentration of TMT and pH was found to improve the extent of precipitation of silver. TMT was also found to be an effective agent to reduce silver concentrations below the regulatory limit value of 5 ppm. Characterization of the precipitates was performed to identify silver-TMT compounds formed.

Effect of Chlorhexidine Pretreatment on Bond Strength Durability of Caries–affected Dentin Over 2-Year Aging in Artificial Saliva and Under Simulated Intrapulpal Pressure

To evaluate the influence of 2% and 5% chlorhexidine (CHX) pretreatment on bond durability of a self-etching adhesive to normal (ND) and caries-affected (AD) dentin after 2-years of aging in artificial saliva and under simulated intrapulpal pressure (IPP). One hundred twenty freshly extracted carious teeth were ground to expose ND and AD. Specimens were distributed into three equal groups (n=40) according to whether the dentin substrates were pretreated with 2% or 5% CHX or with water (control). Clearfil SE Bond (Kuraray) was applied to both substrates and composite cylinders (0.9 mm diameter and 0.7 mm height) were formed. Pretreatment and bonding were done while the specimens were subjected to 15 mm Hg IPP. After curing, specimens were aged in artificial saliva at 37°C and under IPP at 20 mm Hg until being tested after 24 hours or 2 years (n=20/group). Microshear bond strength was evaluated. Failure modes were determined using a scanning electron microscope (SEM) at 400× magnification. Data were statistically analyzed using three-way analysis of variance (ANOVA); one-way ANOVA tests, and t-test (p<0.05). Additional specimens (n=5/group) were prepared to evaluate interfacial silver precipitation. For the 24-hour groups, there were no significant differences among the ND groups and AD groups. For ND aged specimens, the 5% CHX group had the highest value followed by the 2% CHX and control groups, although the difference was statistically insignificant. For AD aged specimens, the 5% CHX group revealed statistically higher bond values compared to the 2% CHX and control groups. Fracture modes were predominately adhesive and mixed. Different interfacial silver depositions were recorded. Two percent or 5% CHX pretreatment has no adverse effect on the 24-hour bonding to ND and AD. Five percent CHX was able to diminish the loss in bonding to AD after 2years of aging in artificial saliva and under simulated IPP.

Silver Precipitation in Energy-Scavenging Aluminum Nitride Resonators

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Thiosulfate stimulates growth and alleviates silver and copper toxicity in tomato root cultures

The influence of supplemented thiosulfate (S2O3 2−) as well as a complex of either Ag+ or Cu2+ with S2O3 2− in the culture medium on proliferating root cultures of tomato (Solanum lycopersicum) was investigated. The presence of 10–300 μM sodium thiosulfate (Na2S2O3) in half-strength Murashige and Skoog (MS) basal salt medium promoted root elongation and proliferation of lateral roots. Growth was enhanced by 1–2 μM AgNO3, but was completely arrested at 5 μM AgNO3; moreover, growth inhibition was elicited by dissolved silver (Ag+) and by silver in silver precipitate particles. Root elongation was also inhibited by 50 μM CuSO4 supplemented to the basal medium. Roots subjected to either AgNO3 or CuSO4 growth inhibiting treatments were unable to recover following transfer to medium lacking either Ag+ or Cu2+. When the basal medium was supplemented with either silver or copper in the form of silver thiosulfate complex or copper thiosulfate complex, root cultures continued to elongate and proliferate, thus either completely alleviating or diminishing the inhibitory effects of Ag+ and Cu2+, respectively. It was concluded that tomato roots sensed and responded to S2O3 2−, hence root proliferation could be promoted by adding Na2S2O3 to the medium. Moreover, a complex of Ag+ with S2O3 2− detoxified dissolved Ag+ and prevented the generation of toxic silver particle precipitates. Consequently, silver thiosulfate was superior to AgNO3 in enhancing root culture. Finally, a complex of Cu2+ with S2O3 2− ligand reduced toxicity of Cu2+ to root cultures of tomato.

Influence of carbon dioxide on the impregnation of the nervous tissue by silver

It has been shown that 4% carbon dioxide (CO2) in the air above reaction mixture inhibits the initiation of the formation of silver nanoparticles from complexes with biogenic amines (noradrenaline and serotonin). At the same concentration of CO2 in the air above solution of AgNO3, which is used for staining nerve tissues by the method of Golgi, neurons are preferentially stained, whereas at a concentration of 0.06%, vessels and poor neurons are stained. It is suggested that the entry of free silver ions to neurons is due to the inhibition of sites of initiation of silver nanoparticles in vessels at high CO2 concentrations, while the lack of inhibition leads to silver precipitation in vessels at low CO2 concentrations. It can be assumed that, for stable silver impregnation, the concentration of CO2 must be controlled.

Thermal precipitation of silver nanoparticles and thermoluminescence in tellurite glasses

Silver metal and/or oxide precipitation of nanoparticles in thermally treated Ag-doped tellurite glasses was studied by optical absorption (OA) and transmission electron microscopy (TEM). The Lorentzian adjusted silver nanoparticles plasma resonance OA band was compared to the Drude model approach. The silver nanoparticles size distribution on the surface rather than in the bulk was determined by TEM. A model for the metallic silver precipitation is proposed. The characterization of the formation of silver nanoparticles was carried out with differential thermal analysis (DTA) to determine the glass transition temperature (Tg) and of crystallization (Tc). Previously γ-irradiated samples exhibited thermoluminescence (TL) peaks and the defect centers TeOHC, NBOHC and TeEC were identified by electron paramagnetic resonance (EPR), but no Ag 0 signal was detected. The silver nanoparticles are known to introduce desired third-order optical nonlinearities in the composites, at wavelengths close to the characteristic surface-plasmon resonance of the metal precipitates. An increase of the glass density and refractive index with increasing AgNO 3 content was observed.

Development and evaluation of a new detection tool—visual DNA microarray for simultaneous and specific detection of human immunodeficiency virus type-1 and hepatitis C virus

Human immunodeficiency virus type-1 (HIV-1) and hepatitis C virus (HCV) are transfusion-transmitted human pathogens that have a major impact on blood safety and public health. Based on multiplex asymmetrical PCR and coupled with gold labelled silver stain (GLSS), we developed the visual DNA microarray for sensitive and specific detection of these two viruses. Capturing probes of 5'-end-amino-modified oligonucleotides were immobilized on glass surface to bind the complement biotinylated target DNA. The Au-streptavidin probe was introduced to the microarray for specific binding to biotin. Black images of microarray spots which result from the precipitation of silver onto Au-streptavidin probes, were visualized by naked eyes. In order to improve the efficiency of microarray hybridization, triplex asymmetrical PCR of HIV-1, HCV and Human enterovirus 71 (EV-71, used as positive control) were performed to prepare abundant biotinylated single-stranded target DNA. The sensitivity of visual DNA microarray (10(3) copies/ml) was higher than conventional PCR (10(4) copies/ml) and was identical to FQ-PCR (10(3) copies/ml). Total 152 blood samples containing the two viruses were tested using the DNA microarray and fluorescence quantitative real-time PCR (FQ-PCR). The results were identical (P > 0.05). So this system has high sensitivity and may have potential in clinical applications.

A Stable Ag/Ceramic-Membrane/Ag2O Electroosmotic Pump Built with a Mesoporous Phosphosilicate-on-Silica Frit Membrane

Low-voltage non-gassing electro-osmotic pumps were built of phosphorylated silica frit membranes, formed meso-porous silica particles of 0.7-1.0 μm diameter, sandwiched between porous, consumable, Nafion-coated Ag/Ag2O electrodes. The flow rates of pumps with membranes formed of the meso-porous silica particles were stable, remaining constant within ±12% until ≥80% of the 2.6 coulomb capacity of the Ag or Ag2O electrodes, sufficient for pumping about 5 mL water, was exhausted. The cause of the decay of the flow in these pumps is Ag+-accumulation at the non-mesoporous membrane surface, observed by metallic silver precipitation caused blackening of the light-exposed non-mesoporous membranes. When the membranes were made with the mesoporous particles, there was no silver precipitate on the membrane; instead, all of the silver was electrodeposited at the cathode. The stability of the flow of pumps made with meso-porous silica membranes is thus attributed to the rapid transport of Ag+-transport to the cathode.

Copper and Cyanide Recovery in Cyanidation Effluents

Cyanidation is the main process for gold and silver recovery from its ores. In this study, a process is proposed to recover copper and cyanide from barren solutions from the Merrill-Crowe cementation process with zinc dust. This technology is based on inducing nucleated precipitation of copper and silver in a serpentine reactor, using sodium sulfide as the precipitator, and sulfuric acid for pH control. Results show that pH value has a significant effect on copper cyanide removal efficiency, and it was determined the optimal pH range to be 2.5 - 3. At this pH value, the copper cyanide removal efficiency achieved was up to 97 and 99%, when copper concentration in the influent was 636 and 900 ppm. respectively. In this process (sulphidization-acidification-thickening-HCN recycling), the cyanide associated with copper cyanide complexes, is released as HCN gas under weakly acidic conditions, allowing it to be recycled back to the cyanidation process as free cyanide. Cyanide recovery was 90%. Finally, this procedure was successfully run at Minera William in México.

Nature of the silver precipitation obtained by cementation from thiosulphate solutions

Abstract The morphology and composition of the deposits formed on the surface of magnesium disk during cementation from thiosulphate solutions (0.0025–0.1M) [Ag(S2O3)2]3− + 0.5M S2O3 2− have been studied. A porous deposit with low adhesion is formed on the surface of the magnesium metal substrate. Within a wide range of [Ag(S2O3)2]3− ion concentrations, sulfur as well as silver are constituents of the deposit at the initial stages of cementation and at the end of the reaction. This is attributed to the electrochemical behaviour of magnesium in thiosulphate solutions resulting in the exceeding of current limit on cathode for pure silver reduction. Hence, parallel electrochemical reactions take place that are very close in their values to the standard redox potentials of reduction of [Ag(S2O3)2]3− ions to Ag0 and S2O32− ions to S2−. Sulfur content in the cement deposits increases with the decrease in [Ag(S2O3)2]3− ion concentration and increase in cementation time. This tendency is also observed with the decreasing solution temperature.