Fabrication and photoluminescence properties of Ag0 and Ag0–Er3+ containing plasmonic glass nanocomposites in the K2O–ZnO–SiO2 system

Here, we report the preparation of nano silver (Ag) and nano Ag-erbium (Ag–Er) co-embedded potassium–zinc-silicate based monolithic glass nanocomposites by a controlled heat-treatment process of precursor glasses. The nanocomposites were characterized by differential scanning calorimeter, dilatometer, UV–Visible absorption spectrophotometer, X-ray diffractometer and transmission electron microscope and spectroflurimeter. A strong surface plasmon resonance (SPR) band is observed around 430 nm in all the heat-treated glass nanocomposite samples due to the formation of Ag⁰ nanoparticles (NP). The Ag-glass nanocomposite samples display nearly 2-fold enhanced photoluminescence (PL) at 470 nm upon excitation at 290 nm until the size of the NP increases to the value equals to the mean free path of conduction electrons inside the particles. On contrary to this, the photoluminescence spectra of Er³⁺ ions exhibit a gradual decrease of NIR emission at 1540 nm due to ⁴I_13/2 → ⁴I_15/2 transition under excitation at 523 nm in the heat-treated glass nanocomposites which happened due to excitation energy transfer of Er³⁺ ions to the Ag NP, acting as ‘plasmonics diluents’ for Er³⁺ ions. These nanocomposites have huge potential for various nanophotonic applications.     

γ-Ray induced catalytic properties of the silica nanoparticles dispersed in the aerated aqueous solution

Silica nanoparticles (NPs) dispersed in an aerated aqueous solution containing Ag⁺ were irradiated to a dose of 10 kGy using ⁶⁰Co γ-rays. The typical surface plasmon band of Ag NPs was observed around 400 nm, indicating that even in the presence of dissolved oxygen the reduction of Ag⁺ occurred by silica NPs. Transmission electron microscopy images indicated that Ag NPs formed on the surface of the silica NPs. The subtraction spectra showed broad absorption around 500 nm with the absorbance depending on the dose. The electrons generated by charge separation from silica NPs with a size of about 12 nm reduce Ag⁺ to Ag⁰ and form (Ag⁰) _n species on the silica NPs, and the type of (Ag⁰) _n species formed depended on the silica NP, and Ag⁺ contents, and the dose. In the co-presence of organic molecules on the silica NP such as rhodamine, the absorbance of the surface plasmon band of both Ag NPs and rhodamine decreased, indicating the electrons to participate in the reductive decomposition of rhodamine molecules adsorbed on the silica NP. Furthermore, in the case when the silica NPs contained fluorescein molecules, the fluorescein molecules were also decomposed, indicating that the fluorescein molecules adsorbed on the inner surface of the silica NPs. The addition of I₂ as an oxidative reagent prevented the decomposition of the fluorescein molecules, indicating that electrons are the main species emitted from irradiated silica NPs.     

Nanosecond probing of the early nucleation steps of silver atoms in colloidal zeolite by pulse radiolysis and flash photolysis techniques

The process of formation and the subsequent aggregation of silver atoms (Ag⁰) in nanosized zeolite beta (BEA) are studied by transient absorption spectroscopy. The zeolite nanocrystals are stabilized in aqueous colloidal suspensions with a narrow particle size distribution in the range 30–60 nm. The reduction of silver cations is initiated either by pulse radiolysis of the aqueous suspension or by photoinduced electron transfer using an organic electron donor adsorbed in the zeolite framework. The silver atom in BEA nanosized crystals is found to be stable on the microsecond timescale.     

Preparation of antimicrobial poly(vinyl alcohol) nanofibers containing silver nanoparticles

Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO₃) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO₃ nanofibers became insoluble, while the Ag⁺ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag⁺ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag⁺ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006     

Controlled synthesis and self-assembly of highly monodisperse Ag and Ag(2)S nanocrystals

A facile method to control the synthesis and self‐assembly of monodisperse Ag and Ag₂S nanocrystals with a narrow‐size distribution is described. Uniform Ag nanoparticles of less than 4 nm were obtained by thermolysis of Ag–oleate complexes in the presence of oleic acid and dodecylamine, and monodisperse Ag nanoparticles of less than 10 nm were also prepared in one step by using dodecylamine and oleic acid as capping agents. Moreover, the surface‐enhanced Raman scattering (SERS) properties of the Ag substrates have also been investigated. It is worth mentioning that these Ag nanoparticles and assemblies show great differences in the SERS activities of Rhodamine B dye. In addition, the superlattices of Ag₂S nanocrystals were synthesized with Ag–oleate complexes, alkanethiol, and sulfur as the reactants. The resulting highly monodisperse nanocrystals can easily self‐assemble into interesting superstructures in the solution phase without any additional assembly steps. This method may be extended to the size‐controlled preparation and assembly of many other noble‐metal and transition‐metal chalcogenide nanoparticles. These results will aid the study of the physicochemical properties of the superlattice assemblies and construction of functional macroscopic architectures or devices.     

Discrete Silver(I)‐Palladium(II)‐Oxo Nanoclusters, {Ag4Pd13} and {Ag5Pd15}, and the Role of Metal–Metal Bonding Induced by Cation Confinement

We introduce the class of discrete silver(I)‐palladium(II)‐oxo nanoclusters with the preparation of {Ag₄Pd₁₃} and {Ag₅Pd₁₅}. Both polyanions represent the first examples of noble metal‐capped polyoxo‐noble‐metalates in a fully inorganic assembly, featuring an unprecedented host–guest mode containing hetero‐ and homometallic Ag–Pd and Ag–Ag bonding interactions. Comprehensive theoretical calculations suggest that the Ag–Pd metallic bonds originate partially from surface confinement of Ag^I guest ions onto the anionic polyoxopalladate host that is induced by strong electrostatic forces. This work opens the field of fully inorganic silver‐palladium‐oxo nanoclusters, which can be considered as discrete mixed noble metal precursors for the formation of monodisperse core–shell nanoparticles, with high relevance for catalysis.     

<Emphasis Type="Italic">In situ</Emphasis> XPS study of the size effect in the interaction of NO with the surface of the model Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/FeCrAl catalysts

The interaction of NO with the surface of model Ag/Al₂O₃/FeCrAl catalysts containing Ag nanoparticles of different size (1 and 3 nm) was studied. The use of the Auger parameter α_Ag (E _b(Ag3d_5/2) + E _kin(Ag MVV)) made it possible to reliably identify the change in the chemical state of silver cluster upon their interaction with О₂ and NO. The oxygen treatment leads to the oxidation of small Ag nanoparticles (1 nm) and formation of AgO _x clusters resulted in the intensive formation of nitrite—nitrate structures on the step of the interaction with NO. These structures are localized on both the silver clusters and Al₂O₃ surface. An increase in the size of Ag⁰ nanoparticles to 3 nm results in an increase in the stability of these structures and impedes the Ag⁰ → AgO _x transition, due to which the formation of surface groups NO₂ ^–/NO₃ ^– is suppressed. The data obtained make it possible to explain the dependence of the activity of the Ag/Al₂O₃ catalysts in the selective reduction of NO on the Ag nanoparticle size.     

Olefin Recovery by *BEA-Type Zeolite Membrane: Affinity-Based Separation with Olefin−Ag+ Interaction

Ag⁺ was introduced into *BEA-type zeolite membrane by an ion-exchange method to enhance olefin selectivity. Ag−*BEA membrane exhibited superior olefin separation performance for both ethylene/ethane and propylene/propane mixtures. Particularly, the separation factor for ethylene at 373 K reached 57 with the ethylene permeance of 1.6×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹. Adsorption properties of olefin and paraffin were evaluated to discuss contribution of Ag⁺ to separation performance enhancement. A strong interaction between olefin and Ag⁺ in the membrane caused preferential adsorption of olefin against paraffin, leading to selective permeation of olefin. Ag−*BEA membrane also exhibited high olefin selectivities from olefin/N₂ mixtures. The affinity-based separation through Ag−*BEA membrane showed a high potential for olefin recovery and purification from various gas mixtures.     

Preparation of Ag nanocrystals embedded silicate glass by field-assisted diffusion and its properties of optical absorption

Ag nanocrystals embedded silicate glass was successfully prepared by solid-state field-assisted diffusion, combined with post-annealing process. The changes of glass structure, the chemical states of Ag and O species, the microstructures of Ag nanocrystals, as well as the properties of optical absorption were studied for the as-diffused and post-annealed samples. The result showed that after the field-assisted diffusion process, some Ag⁺ ions replaced the alkaline ions in the glass matrix. Meanwhile, other Ag⁺ ions were reduced to Ag⁰ atoms occupying the interspaces of the network and Ag⁰ atoms clusters with small size were formed. This caused the relaxation of the glass network and the deceasing of force constant for Si–O linkage. After post-annealing process, bigger size of Ag nanoparticles were formed, which caused the peak corresponding to the surface plasmon resonance (SPR) observed.     

Redox reactions of arabinogalactan with silver ions and formation of nanocomposites

Formation of silver nanoparticles in the course of chemical reduction of AgNO₃ with arabinogalactan in aqueous alkaline solution was studied by electronic absorption spectroscopy and X-ray diffraction analysis. The pH of the solution was found to be the major factor affecting the degree of reduction of Ag⁺ ions. The probable reaction mechanism was discussed. Composites containing up to 58% Ag, with the metal particle size of 7–16 nm, were prepared. The nanoparticle size can be controlled by varying the reactant ratio AgNO₃: arabinogalactan. Chemical modification of arabinogalactan was confirmed by IR and ¹³C NMR spectroscopy and by TLC.     

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.     

Silver nanoparticles active as surface-enhanced Raman scattering substrates prepared by high energy irradiation

In surface-enhanced Raman scattering (SERS) technique the preparation of metal substrates containing minimum hindrance from impurities is an important issue. The synthesis of silver nanoparticles (Ag NPs) active as SERS substrates and having the above-mentioned advantage, were obtained by electron beam irradiation of Ag⁺ aqueous solutions. Ag⁺ ions were reduced by free radicals radiolytically generated in solution without the addition of chemical reductants or stabilizing agents.The metal colloids were characterised by UV-Vis spectroscopy and scanning electron microscopy, monitoring the nanoparticles’ growth process that depends on the irradiation dose and the initial AgNO₃ concentration. Nanoparticles of long-time stability and with different size and shape, included silver nanocubes, were synthesised by varying the irradiation dose. Different tests on the SERS activity of Ag NPs obtained by electron beam irradiation were performed by using benzenethiol as a probing molecule, achieving a good magnification of the adsorbate Raman bands.     

Enhancement on the structural,functional, optical and morphological properties of temperature treated silver sulfide nanostructures

The Silver Sulfide (Ag₂S) nanostructures were synthesized via the facile co-precipitation method. Thorough study and analysis were carried out to reveal and compare the structural, optical, functional, and morphological characteristics of as-synthesized samples annealed at various temperatures. The XRD analysis characterized the structural properties of Ag₂S nanoparticles, which unveiled the excellent crystallinity and monoclinic structure. The as-synthesized samples show an average crystallite size of 52 nm–41.7 nm. The modes of vibration and peak position of metal sulfides in Ag₂S nanoparticles were investigated through the FTIR technique. The optical attributes of prepared samples were scrutinized using UV–Vis analysis, which portrays the cut-off wavelength in the range of 1192–1223 nm for non-annealed and annealed Ag₂S nanoparticles, alongside the optical band gap is about 0.86 eV–0.96 eV. This work elucidates a novel approach to synthesis and scrutinises the characteristics of Ag₂S nanoparticles by subjecting them to distinct annealing temperatures precisely, as-prepared, 200 °C and 400 °C.     

A comparative studyof heat‐treated Ag:SiO2 nanocomposites synthesized by cosputtering and sol‐gel methods

In this work, we compared formation and properties of heat‐treated Ag nanoparticles in silica matrix synthesized by RF‐reactive magnetron cosputtering and sol–gel methods separately. The sol–gel and sputtered films were annealed at different temperatures in air and in a reduced environment, respectively. The optical UV‐visible spectrophotometry have shown that the absorption peak appears at 456 and 400 nm wavelength indicating formation of silver nanoparticles in SiO₂ matrix for both the sol–gel and sputtering methods at 100 and 800 °C, respectively. XPS measurements showed that the metallic Ag⁰ nanoparticles can be obtained from both the techniques at these temperatures. According to XPS and AFM analysis, by increasing annealing temperature, the concentration of the Ag nanoparticles on the surface decreased and the nanoparticles diffused into the substrate for the sol–gel films, while for the films deposited by cosputtering method, the Ag surface concentration increased by increasing the temperature. Based on AFM observations, the size of nanoparticles on the surface were obtained at about 25 and 55 nm for sputtered and sol–gel films, respectively, supporting our optical data analysis. In comparison, the sputtering technique can produce Ag metallic nanoparticles with a narrower particle size distribution relative to the sol–gel method. Copyright © 2008 John Wiley & Sons, Ltd.     

XPS study of silver and copper nanoparticles demonstrated selective anticancer,proapoptotic, and antibacterial properties

Silver and copper nanoparticles were produced by an ecologically safe metal vapor synthesis (MVS) method using acetone as an organic dispersion medium. Transmission electron microscopy (TEM) showed that the specimens are spherical and polydisperse, and their average size is 2.5 nm for silver nanoparticles (Ag NPs) and 2.6 nm for copper nanoparticles (Cu NPs). X-ray photoelectron spectroscopy analyses showed that the state of silver in the nanoparticles is close to that of silver in the Ag⁰ state, whereas copper black contains two oxidized states of the metal—Cu⁺ and Cu²⁺. Biological in vitro studies demonstrated that the nanoparticles have antibacterial activity against Gram-positive and Gram-negative bacterial species. Cu NPs exhibited more prominent antibacterial effects and induced significant growth inhibition of Bacillus cereus and Escherichia coli. Both types of nanoparticles showed anticancer properties in vitro. Cu NPs induced intense cytotoxicity in cancer and normal fibroblasts in vitro cultures, but their inhibitory effect against noncancerous cells was milder compared with cancer cell lines. Ag NPs demonstrated selective cytotoxicity against human lung and cervical adenocarcinoma cell lines. Further in vitro studies indicated that the mechanism of Ag NPs and Cu NPs anticancer effects involves induction of apoptosis. The present study describes a green synthesis approach for production of biologically active silver and copper nanoparticles and highlights their potential for medical application.     

Y2O3:Eu (5 mol%) with Ag nanoparticles prepared by citrate precursor

Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) and Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) containing 1 mol% of Ag nanoparticles were prepared by heat treatment of a viscous resin obtained via citrate precursor. TEM and EDS analyses showed that Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) is formed by nanoparticles with an average size of 12 nm, which increases to 30 nm when Ag is present because the effect of metal induced crystallization occurs. Ag nanoparticles with a size of 9 nm dispersed in Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) were obtained and the surface plasmon effect on Ag nanoparticles was observed. The emission around 612 nm assigned to the Eu³⁺ (⁵D₀→⁷F₂) transition enhanced when the Ag nanoparticles were present in the Y₂O₃:Eu³⁺ luminescent material.     

Formation mechanism of nanostructured Ag films from Ag2O particles using a sonoprocess

Nanostructured Ag films composed of nanoparticles and nanorods can be formed by the ultrasonication of ethanol solutions containing Ag₂O particles. The present work examined the formation process of these films from ethanol solutions by two different agitation methods, including ultrasonication and mechanical stirring. The mass-transfer process from Ag₂O particles to ethanol solvent is accelerated by the mechanical effects of ultrasound. Ag⁺ ions and intermediately reduced Ag clusters were released into the ethanol. These Ag⁺ ions and Ag clusters provide absorption bands at 210, 275 and 300 nm in UV-vis spectra. These bands were assigned to the absorption of Ag⁺, Ag ₄ ²⁺ and Ag_n (n?≈?3). The Ag_n clusters that readily grow to become Ag nanoparticles were formed due to the surface reaction of Ag₂O particles with ethanol under ultrasonication. The reactions of Ag⁺ ions in ethanol to form Ag nanomaterials (through the formation of Ag ₄ ²⁺ clusters) were also accelerated by ultrasonication.     

Photochemical properties of Ag ion clusters included within ZSM-5 zeolites prepared by an ion-exchange method

Photoluminescence investigations of the Ag ion-exchanged ZSM-5 (Ag⁺ /ZSM-5) zeolite revealed that a Ag ion cluster (Agⁿ _m ⁺) exists in the pore structure of ZSM-5 exhibiting photoluminesm cence at 380 nm upon excitation at 332 nm. UV irradiation ( = 285 nm) of Ag⁺ /ZSM-5 at 77 K leads to the transformation of Agⁿ _m ⁺ into a different Ag ion cluster (Ag_m ^(n-1)+) which exhibits photoluminescence at 465 nm upon excitation at 315 nm. This photo-transformation of the Ag ion clusters was found to be thermally reversible under vacuum. It was demonstrated that an electron transfer from the photo-excited Al³⁺ -O^2- to Agⁿ _m ⁺ plays a significant role in this process. In the presence of oxygen, UV irradiation of Ag⁺ /ZSM-5 leads to the formation of O₂- instead of an Ag ion cluster (Ag_m ^(n-1)+), suggesting that oxygen acts as an efficient electron scavenger, which interferes with the electron capture of Agⁿ _m ⁺ under UV irradiation at 285 nm.     

Au–Ag Nanoflower Catalysts with Clean Surfaces for Alcohol Oxidation

Shape‐controlled metal nanocrystals, such as nanowires and nanoflowers, are attractive owing to their potentially novel catalytic properties and bimetallic nanocrystals composed of two distinct metals are expected to act as highly active catalysts. However, their catalytic activities are limited because of the capping agents adsorbed on the metal surfaces, which are necessary for the preparation and dispersion of these nanocrystals in solvents. Therefore, the preparation of bimetallic shape‐controlled noble metal nanocrystals with clean surfaces, devoid of almost all capping agents, are expected to have high catalytic activity. Herein, we report the preparation of bimetallic Au–Ag nanoflowers using melamine as the capping agent. The bimetallic Au–Ag nanoflowers with a clean surface were subsequently obtained by a support and extraction method. The bimetallic nanoflowers with a clean surface were then used for the aerobic oxidation of 1‐phenylethyl alcohol and they exhibited high rates for the formation of acetophenone compared to Au nanoflowers and spherical nanoparticles with almost the same size and Au/Ag ratio. We also show that Au–Ag nanoflowers containing only 1 % Ag (Au₉₉–Ag₁NFs) exhibit the highest rate of acetophenone formation among Au–Ag nanoflowers with different Au/Ag ratios owing to an increase in the electron density of the Au atoms that act as active sites for the oxidation of 1‐phenylethyl alcohol.     

Electron Transfer in Peptides: On the Formation of Silver Nanoparticles

Some microorganisms perform anaerobic mineral respiration by reducing metal ions to metal nanoparticles, using peptide aggregates as medium for electron transfer (ET). Such a reaction type is investigated here with model peptides and silver as the metal. Surprisingly, Ag⁺ ions bound by peptides with histidine as the Ag⁺‐binding amino acid and tyrosine as photoinducible electron donor cannot be reduced to Ag nanoparticles (AgNPs) under ET conditions because the peptide prevents the aggregation of Ag atoms to form AgNPs. Only in the presence of chloride ions, which generate AgCl microcrystals in the peptide matrix, does the synthesis of AgNPs occur. The reaction starts with the formation of 100 nm Ag@AgCl/peptide nanocomposites which are cleaved into 15 nm AgNPs. This defined transformation from large nanoparticles into small ones is in contrast to the usually observed Ostwald ripening processes and can be followed in detail by studying time‐resolved UV/Vis spectra which exhibit an isosbestic point.