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[Display omitted] • Cu/ZSM-5 core enveloped by S-1 shell with confined Ag0 nanoparticles. • Core-shell architecture fosters the generation of abundant active Ag0 nanoparticles. • Silicalite-1 shell hinders Ag0 migration and preserves active Cu2+ sites. • Discretely distributed Cu2+ and Ag0 centers underpin a catalytically robust system. • Cu/ZSM-5@Ag/S-1 exhibits superior hydrothermal stability and NH 3 -SCO activity. A judiciously devised core–shell NH 3 -SCO catalyst featuring a Cu/ZSM-5 core enveloped by an Ag/silicalite-1 shell (Cu/ZSM-5@Ag/S-1) was rationally constructed. Integrating the silicalite-1 shell effectively suppresses the migration of Ag into Cu/ZSM-5 core, conserving the active Cu2+ sites for the catalytical conversion of byproducts NO x. Concurrently, the shell averts the formation of positively charged Ag species, facilitating the generation of abundant Ag0 nanoparticles encapsulated in the S-1 shell. Comprehensive characterizations reveal abundant Ag0 species within the core–shell Cu/ZSM-5@Ag/S-1 catalyst, boosting O 2 activation and NH 3 dehydrogenation and thereby contributing to superior low-temperature activity in NH 3 -SCO reactions. Furthermore, the hydrophobic S-1 shell effectively reinforces the hydrothermal stability of the core–shell Cu/ZSM-5@Ag/S-1. DRIFTS coupled with DFT studies elucidate that the core–shell sample follows the imide mechanism, while the shell-free sample adheres to the hydrazine mechanism. This work advances our understanding of catalyst design and presents a promising solution with practical implications for ammonia oxidation processes. [ABSTRACT FROM AUTHOR]

The physical and chemical properties of materials are greatly influenced by the state of their surface layers. In turn, the characteristics of the surface depend, for example, on the processes of absorption from a gas medium. In this study, by in situ measurements, the surface layers of polycrystalline silver exposed to external activated oxygen from different sources are investigated. For sources of activated oxygen, water vapor at a temperature of 1073 K and an ion source that makes it possible to obtain an oxygen ion beam with the energy 100–300 eV (5 μA/cm2) are used. It is established that, after treatment, the composition of AgO and Ag2O in the surface layers of silver includes, apart from atomic oxygen, molecular oxygen and silver in the zero-valence state. From estimates of the ratio between the intensities of spectroscopy peaks related to silver and oxygen components, it can be concluded that there exist associative forms of oxygen in the surface layers of silver. An increase in Ag 3d5/2–Ag 3d3/2 spin–orbit splitting is detected, which suggests that there are oxidized silver nanoparticles on the surface. [ABSTRACT FROM AUTHOR]

A facile and green approach has been developed to synthesize silver nanoparticle (Ag-NPs). This was carried out by a biosynthetic route using Justicia Adhatoda root extract as reducing and stabilizing agent. The structure, composition, average particle size (~25 nm) and surface morphology of Ag-NPs were characterized by the X-ray diffraction, transmission electron microscope and atomic force microscope analyses. The possible functional groups in the plant extracts were identified by FT-IR analysis. Electrochemical property of the Ag- NPs was analysed by cyclic voltammetry that displayed an oxidation peak potential at Epa = 0.438 V. Mechanism of the formation of Ag-NPs was proposed which showed that the phenolic compounds of the root extract respond for the reduction of silver ions to silver nanoparticles. Ag-NPs exhibit good antioxidant and antibacterial activities. This biosynthetic approach could open a path for environmentally friendly, simple, cost effective, alternate for conventional synthesis. This prevented hazardous chemicals and was useful for applications in medicine and large scale production of metallic nanoparticles. [ABSTRACT FROM AUTHOR]

Background: Knowledge about silver nanoparticles in soils is limited even if soils are a critical pathway for their environmental fate. In this paper, speciation results have been acquired using a silver ion selective electrode in three different soils. Results: Soil organic matter and pH were the most important soil properties controlling the occurrence of silver ions in soils. In acidic soils, more free silver ions are available while in the presence of organic matter, ions were tightly bound in complexes. The evolution of the chemical speciation of the silver nanoparticles in soils was followed over six months. Conclusion: During the first few hours, there appeared to be a strong sorption of the silver with soil ligands, whereas over time, silver ions were released, the final concentration being approximately 10 times higher than at the beginning. Ag release was associated with either the oxidation of the nanoparticles or a dissociation of adsorbed silver from the soil surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Polymer–silver nanocomposites modified cotton fabrics were prepared by in situ chemical oxidative polymerization using pyrrole and silver nitrate. In a redox reaction between pyrrole and silver nitrate, silver ions oxidize the pyrrole monomer and get reduced. This reduced silver as nanoparticles deposited on/into the polypyrrole/cotton matrix layer and the interaction between silver and polypyrrole was by adsorption or electrostatic interaction. The structure and composite formation on cotton fiber was investigated using SEM, FT-IR, XPS and XRD. The results showed that a strong interaction existing between silver nanoparticles with polypyrrole/cotton matrix. FT-IR studies clearly indicated that the interaction between polypyrrole (h name="sbnd" />H) and cellulose (>Cy hydrogen bonding. It is observed that the conductivity of the composite coated fabrics has been increased by the incorporation of silver nanoparticles. In the synthesized composites, silver content plays an important role in the conductivity and antimicrobial activity rate of the fabrics against gram positive Staphylococcus aureus and gram negative Escherichia coli bacteria. [Copyright &y& Elsevier]

For nearly a decade, researchers have debated the mechanismsbywhich AgNPs exert toxicity to bacteria and other organisms. The mostelusive question has been whether the AgNPs exert direct “particle-specific”effects beyond the known antimicrobial activity of released silverions (Ag+). Here, we infer that Ag+is the definitivemolecular toxicant. We rule out direct particle-specific biologicaleffects by showing the lack of toxicity of AgNPs when synthesizedand tested under strictly anaerobic conditions that preclude Ag(0)oxidation and Ag+release. Furthermore, we demonstratethat the toxicity of various AgNPs (PEG- or PVP- coated, of threedifferent sizes each) accurately follows the dose–responsepattern of E. coliexposed to Ag+(addedas AgNO3). Surprisingly, E. colisurvivalwas stimulated by relatively low (sublethal) concentration of alltested AgNPs and AgNO3(at 3–8 μg/L Ag+, or 12–31% of the minimum lethal concentration (MLC)),suggesting a hormetic response that would be counterproductive toantimicrobial applications. Overall, this work suggests that AgNPmorphological properties known to affect antimicrobial activity areindirect effectors that primarily influence Ag+release.Accordingly, antibacterial activity could be controlled (and environmentalimpacts could be mitigated) by modulating Ag+release,possibly through manipulation of oxygen availability, particle size,shape, and/or type of coating. [ABSTRACT FROM AUTHOR]

Nitrification inhibition by silver nanoparticles (nanosilver) was evaluated by extant respirometry using enriched nitrifying bacteria isolated from wastewater treatment plants. Silver nanoparticles were more toxic than silver ions or silver chloride colloids, all of which did not disrupt cell membrane integrity at 1 mg/L Ag. The toxicity of silver nanoparticles was reduced in the presence of various anions, especially sulfide. The results suggest that silver nanoparticles have the same behaviour of surface complexation as silver ions, and inhibition by nanosilver in wastewater treatment may be removed by reaction of silver nanoparticles with soluble sulfide species. [ABSTRACT FROM AUTHOR]

The physical and chemical properties of silver nanoparticles that are responsible for their antimicrobial activities have been studied with spherical silver nanoparticles (average diameter approximately 9 nm) synthesized by the borohydride reduction of Ag+ ions, in relation to their sensitivity to oxidation, activities towards silver-resistant bacteria, size-dependent activities, and dispersal in electrolytic solutions. Partially (surface) oxidized silver nanoparticles have antibacterial activities, but zero-valent nanoparticles do not. The levels of chemisorbed Ag+ that form on the particle’s surface, as revealed by changes in the surface plasmon resonance absorption during oxidation and reduction, correlate well with the observed antibacterial activities. Silver nanoparticles, like Ag+ in the form of AgNO3 solution, are tolerated by the bacteria strains resistant to Ag+. The antibacterial activities of silver nanoparticles are related to their size, with the smaller particles having higher activities on the basis of equivalent silver mass content. The silver nanoparticles aggregate in media with a high electrolyte content, resulting in a loss of antibacterial activities. However, complexation with albumin can stabilize the silver nanoparticles against aggregation, leading to a retention of the antibacterial activities. Taken together, the results show that the antibacterial activities of silver nanoparticles are dependent on chemisorbed Ag+, which is readily formed owing to extreme sensitivity to oxygen. The antibacterial activities of silver nanoparticles are dependent on optimally displayed oxidized surfaces, which are present in well-dispersed suspensions. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) have shown to be toxic to freshwater cyanobacterial species, and sodium hypochlorite (NaOCl) is a common oxidant for the treatment of cyanobacterial cells. AgNPs have a high possibility of co-existing with the cyanobacterial cells in the aqueous environments leading to its exposure to NaOCl during water treatment; however, their combined effects on the cyanobacterial cells are largely undocumented. This work compares the individual and combined effect of AgNP and NaOCl on the integrity and toxin (microcystins) release of Microcystis aeruginosa at varying levels. The results show that the AgNP (0.2–0.6 mg/L) alone has negligible effects on the cell lysis, while NaOCl alone shows concentration-dependent (0.2 < 0.4 < 0.6 mg/L) rupturing of cells. In contrast, the AgNP + NaOCl (0.2–0.6 mg/L) samples show increasing loss in cell integrity at higher AgNP (0.4 and 0.6 mg/L) levels than the NaOCl only samples. NaOCl exposure results in increasing dissolution of AgNPs with time, releasing silver ions (Ag+), affecting its size and morphology. The cell-associated total Ag declines over time with an increase in NaOCl levels, maybe due to increasing cell-lysis or NaOCl induced oxidative dissolution of AgNPs. The cell-associated total Ag and released Ag+ possibly weaken the cellular membrane, thus assisting NaOCl in faster cell-lysis. The combined exposure of AgNP and NaOCl also results in a higher release of toxin from the cells. This work collectively reveals that the AgNPs combined with NaOCl can enhance the cell lysis and release of toxins. [Display omitted] • The combined effect of AgNPs and NaOCl on Microcystis aeruginosa is studied. • Joint exposure of AgNPs and NaOCl enhances the cell-lysis. • The enhanced cell rupture is AgNP concentration-dependent. • The joint exposure could increase the release of intracellular microcystins. [ABSTRACT FROM AUTHOR]

The correlation between the chemical nature of capping agents used to prepare colloidal silver dispersions and kinetic characteristics of the process of oxidation of the dispersed phase (spherical silver nanoparticles, 2–50 nm in diameter) by hydrogen peroxide was studied for the first time. The well-pronounced correlation between the oxidative dissolution rate and the biological activity of silver dispersions was revealed with respect to the inhibition of the growth of the Saccharomyces cerevisiae yeast. The biological activity of nanosilver dispersions was found to be primarily controlled by the rate of generation of silver ions while the chemical nature of the capping agent defined the rate of generation of silver ions, thus showing an effective way to control the biological action of medications based on silver nanoparticles by varying the nature of the capping agent. [ABSTRACT FROM AUTHOR]