Preparation and antibacterial activity of polyvinyl alcohol/regenerated silk fibroin composite fibers containing Ag nanoparticles

Polyvinyl alcohol (PVA)/regenerated silk fibroin (SF)/AgNO₃ composite nanofibers were prepared by electrospinning. A large number of nanoparticles containing silver were generated in situ and well‐dispersed nanoparticles were confirmed by transmission electron microscopy (TEM) intuitionally. Ultraviolet (UV)‐visible spectroscopy and X‐ray diffraction (XRD) patterns indicated that nanoparticles containing Ag were present both in blend solution and in composite nanofibers after heat treatment and after subsequent UV irradiation. By annealing the nanofibers, Ag⁺ therein was reduced so as to produce nanoparticles containing silver. By combining heat treatment with UV irradiation, Ag⁺ was transformed into Ag clusters and further oxidized into Ag₃O₄ and Ag₂O₂. Especially size of the nanoparticles increased with heat treatment and subsequent UV irradiation. This indicated that the nanoparticles containing silver could be regulated by heat treatment and UV irradiation. The antimicrobial activity of heat‐treated composite nanofibers was evaluated by Halo test method and the resultant nanofibers showed very strong antimicrobial activity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A Novel Approach to Prepare Poly(Vinyl Acetate)/Ag Nanocomposite for Effective Antimicrobial Coating Applications

Polyvinyl acetate nanocomposites were successfully prepared based on silver nanoparticles. First, silver nanoparticles were directly prepared during the in situ emulsion polymerization of vinyl acetate monomer using AgNO₃ as a source of Ag⁺ ions and poly(vinyl alcohol) was used for dual functions as emulsifier for emulsion polymerization and as a stabilizing agent, trisodium citrate (C₆H₅O₇Na₃) was used as reducing agent for Ag⁺ ions during the polymerization process. The prepared polyvinyl acetate/Ag nanocomposites were assessed using X-ray diffraction, scanning electron microscopy, Fourier transform infrared, transmission electron microscopy, and ultraviolet spectra. The antibacterial properties of the prepared polyvinyl acetate/Ag nanocomposites were investigated as antimicrobial activity against pathogenic bacteria, i.e., Staphylococcus aureus (G^+ve bacteria) and Escherichia coli (G^?ve bacteria). These polyvinyl acetate nanocomposites could be used as a promising material for enhanced and continuous antibacterial applications as coating and packaging materials.     

Electrodeposition of Ag and Pd on a reconstructed Au(1 1 1) electrode surface studied by in situ scanning tunneling microscopy

Electrochemical deposition of Ag and potential-induced structural change of the deposited Ag layer on a reconstructed surface of Au(1 1 1) electrode were followed by in situ scanning tunneling microscope (STM). A uniform Ag monolayer was formed on a reconstructed Au(1 1 1) surface in a 50-mM H₂SO₄ solution at +0.3 V (vs. Ag/AgCl) after adding a solution containing Ag₂SO₄ so that the concentration of Ag⁺ in the STM cell became ca. 2 μM. No characteristic height corrugation such as the Au reconstruction was observed on the surface, indicating that the lifting of the substrate Au reconstruction occurred by Ag deposition. The formed Ag monolayer was converted to a net-like shaped Ag nano-pattern of biatomic height when the potential was stepped from +0.3 to −0.2 V in the solution containing 2 μM Ag⁺. This result indicates that the substrate Au(1 1 1)-(1 × 1) surface was converted to the reconstructed surface even in the presence of Ag adlayer. Quite different structure was observed for Pd deposition on a reconstructed surface of Au(1 1 1) electrode at +0.3 V and the origin for this difference between Ag and Pd deposition is discussed.     

Synthesis and characterization of novel silver/L‐phenylalanine‐based optically active polyacrylate nanocomposite

Novel bioactive and optically active poly(N‐acryloyl‐L ‐phenylalanine) (PAPA) was synthesized by atom transfer radical polymerization. PAPA‐silver (Ag) nanocomposites have been successfully prepared via in situ reducing Ag⁺ ions anchored in the polymer chain using hydrazine hydrate as reducing agent in an aqueous medium. By controlling of the amount of Ag⁺ ions introduced, we have produced an organic/inorganic nanocomposite containing Ag nanoparticles with well controlled size. Nanocomposites were characterized by X‐ray diffraction (XRD), UV–Vis spectrophotometry, transmission electron microscopy, and Fourier transform infrared. XRD pattern showed presence of Ag nanoparticles. The PAPA/Ag nanocomposites with 1 : 10 silver nitrate (AgNO₃) : PAPA ratio revealed the presence of well‐dispersed Ag nanoparticles in the polymer matrix. All of these Ag nanoparticles formed are spherical and more than 80% of them are in the range of 15–25 nm. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrochemical behavior of poly(3-hexylthiophene). Controlling factors of electric current in electrochemical oxidation of poly(3-hexylthiophene)s in a solution

Electrochemical response of regio-random and regio-controlled poly(3-hexylthiophene), P3HexTh, was investigated by cyclic voltammetry. P3HexTh underwent electrochemical oxidation at about 0.4 V vs. Ag⁺/Ag in a THF solution, and the peak anode electric current, i_pa, was proportional to the sweeping rate v; i_pa=const×v^1/2. These data indicated that diffusion of the P3HexTh molecule in the solution was important to determine i_pa. Application of a Matsuda's equation with assumptions gave a diffusion coefficient, D, of about 1×10⁻⁷ cm² s⁻¹ at molecular weight of about 5000, and the D value steeply decreased with increase in the molecular weight.     

Comportement electrochimique et reactivite du systeme Ag(II)-Ag(I)-bipyridine dans le carbonate de propylene

The electrochemical behaviour of silver(I)- and silver(II)-bipyridyl complexes has been investigated using voltammetry, cyclic voltammetry and coulometry in propylene carbonate. In unbuffered non-acidic medium, when the stoichiometry of the solutions is C_L/C_Ag = 2, the Ag^I(bipy)⁺ concentration is low; the preponderant species is Ag^I(bipy)₂⁺. Under such conditions, the Ag^II(bipy)₂²⁺/Ag^I(bipy)₂⁺ couple hs a reversible behaviour and is one of the must powerful oxidants used in the solvent (E^′° = 0.790 V vsE_Fc^′° + _Fc). As a function of the acidity level of the solutions, one observes the oxidation of either Ag^I(bipy)⁺ or Ag⁺ in the presence of the protonated ligand to complexed Ag(II). The silver(II) species produced oxidizes water and the excess of ligand (C_L/C_Ag > 2).     

Calculation of chloride concentration at color change boundary of AgNO3 colorimetric measurement

AgNO₃ colorimetric measurement of chloride in cement-based materials can be implemented owing to chemical reactions between Ag⁺ and Cl⁻ or OH⁻ ions, which result in the precipitation of AgCl and Ag₂O. When the mass ratio of AgCl to precipitated AgCl + Ag₂O reaches a critical value (P_crit-AgCl), a color change boundary appears. In this paper, chloride concentrations required for the formation of the critical mass ratio of AgCl to precipitated AgCl + Ag₂O derived from the AgNO₃–NaCl–NaOH system were calculated based on the solubility products of silver hydroxide and silver chloride, and mass conservation of the chemical reactions. P_crit-AgCl was determined as 0.65 through a series of AgNO₃ colorimetric measurements on cement-based materials. Calculated results indicated that if Ag⁺ could react with all OH⁻ and Cl⁻, there existed a linear relationship between the critical chloride concentration for color change (C_crit-Cl^–) and OH⁻ concentration (C_OH^–), namely C_crit-Cl^– = 1.6C_OH^–. If Ag⁺ could react with only partial OH⁻ and Cl⁻, there existed an exponential relationship among C_crit-Cl^– and C_OH^–, Ag⁺ concentration (C_Ag⁺), volume of AgNO₃ solution (V_Ag⁺) as well as the volume of NaCl + NaOH solution (V_{OH^–+ Cl^–}), namely C_crit-Cl^– = 0.00695C_OH^– + 0.608C_Ag⁺V_Ag⁺/V_{OH^–+ Cl^–}. It can be concluded that the alkalinity of cement-based materials, concentration and volume of sprayed AgNO₃ solution and volume of pore solution have effects on chloride concentration at the color change boundary (C_d). Calculated C_d values ranged between 0.03 and 0.96 mol/L (in pore solution) or 0.011% to 2.27% (by the mass of binder), respectively. This explains why reported range of chloride concentration at the color change boundary in publications varied in a broad range.     

Self-assembly Ag2O nanoparticles into nanowires with the aid of amino-functionalized silica nanoparticles

This paper describes a novel self-assembly behavior of Ag₂O nanoparticles to Ag₂O nanowires. In the alkaline water-alcohol solution, Ag⁺ ions reacted with OH⁻ ions on silica nanoparticles functionalized by N-(2-aminoethyl)-3-aminopropyl-trimethoxy-silane (AEAPTS) to form Ag₂O nanoparticles. The Ag₂O nanoparticles further self-assembled into Ag₂O nanowires. The morphology of Ag₂O nanowires could be controlled by adjusting Ag/Si molar ratios in the systems. With low Ag/Si molar ratio, uniform Ag₂O nanowires were obtained with diameter of about 50 nm and length of tens micrometers. With the increase of Ag/Si molar ratio, Ag₂O nanowires became thicker, shorter and irregular. It was shown by high-resolution transmission electron microscopy (HRTEM) that all Ag₂O nanowires consisted of tiny Ag₂O nanoparticles with diameter of 10-20 nm. The self-assembly of Ag₂O nanoparticles into Ag₂O nanowires was observed by transmission electron microscopy (TEM) and the corresponding growth mechanism was proposed.     

In situ green synthesis of Ag nanoparticles on graphene oxide/TiO2 nanocomposite and their catalytic activity for the reduction of 4-nitrophenol,congo red and methylene blue

The Ag/RGO/TiO₂ nanocomposite was synthesized through an environmentally benign, simple, cost efficient, surfactant-free and green method using Euphorbia helioscopia L. leaf extract as a stabilizing and reducing agent. The E. helioscopia L. leaf extract was used for the reduction of Ag⁺ ions and GO to Ag NPs and RGO, respectively. The GO/TiO₂ and Ag/RGO/TiO₂ nanocomposites were characterized by FT-IR, UV–vis, TEM, XRD, SEM, EDS and ICP techniques. The Ag/RGO/TiO₂ nanocomposite was highly active for the reduction of 4-nitrophenol (4-NP), congo red (CR) and methylene blue (MB) in aqueous media at an ambient temperature. The Ag/RGO/TiO₂ nanocomposite was easily separated and recovered from the reaction mixture by centrifugation and reused for several cycles without any significant loss of catalytic activity.     

Preparation and characterization of poly(styrene)/metal composites via reversible addition-fragmentation chain transfer (RAFT) polymerization

The expectant dithiocarbamate group end-functional poly(styrene) (PS) with a controlled molecular weight and low molecular weight distribution was synthesized conveniently via reversible addition-fragmentation chain transfer (RAFT) polymerization and was used to prepare polymer/metal composites with coordination chemistry. By the self-assembly technique, PS coordinated with the rare earth metal in N,N-dimethylformamide (DMF) to generate the fluorescent Eu–PS and Sm–PS complexes. Furthermore, PS-coated spherical silver nanoparticles (AgNPs) were prepared by reducing Ag⁺ to Ag⁰ under ultrasound irradiation in the presence of DMF and H₂O. The well core/shell structure of the AgNPs was characterized by transmission electron microscopy (TEM).     

Comportement electrochimique et reactivite dy systeme Ag(II)/Ag(I)-bipyridine dans le carbonate de propylene—II. Etude du couple carbonate de propylene—II. Etude du couple AgII(bipy)2+/AgI(bipy)+

Due to the reactivity expected in the presence of an excess Ag⁺ with respect to the 1–2 stoichiometry (Ag-bipy), the electrochemical behaviour of the Ag(II)/Ag(I)-bipyridine system has been investigated using voltammetry and coulometry. The change in the current-potential curves has been rationalized taking into account an equilibrium between different species of Ag(I) in neutral or acidic media. Changes of the solution nature (ratio C_bipy/C_Ag) or pH actually led to the formation of reactive species.     

Tuned interactions of silver nanoparticles with ZSM-5 zeolite by adhesion-promoting poly(acrylic acid) deposited by electrospray ionization (ESI)

The electrospray ionization (ESI) method was used for deposition of thin films of poly(acrylic acid) (PAA) on Cu/ZSM-5 (5 wt.% Cu) and Ag–Cu/ZSM-5 (1 wt.% Ag and 4 wt.% Cu) composites. For comparative purposes, the ZSM-5 zeolite was synthesized under hydrothermal conditions and loaded with PAA under the same treating conditions as the composites. This method allowed the formation of uniform polymer films of controlled thickness on conductive substrates. The structural characteristics were characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, atomic force microscopy and X-ray diffraction (XRD). The deposited PAA layer over ZSM-5 acts as a common dispersing and stabilizing agent through coordination-driven guest-templated polymer via interaction of Ag⁺ and Cu²⁺ with carboxylic acid groups, thus increasing and controlling the adhesion and the release of metallic species. A short exposure to light and temperature has reduced the metal ions to Cu⁰ and Ag⁰ metallic nanoparticles. The results of XRD analysis let suggest that the interaction of Cu and Ag with carboxylic groups of PAA inhibits the formation of large metallic silver particles. These samples were being studied for their potential as antibacterial agents toward the bacterial strains such as Staphylococcus pneumonia, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa as Gram positive and Gram negative bacteria, respectively. Aspergillus fumigatus and Candida albicans as Fungi were also evaluated. The Cu/ZSM-5 and Ag–Cu/ZSM-5 nanocomposites coated with a 10 nm thick PAA layer exhibit significant antibacterial activity.     

Development of silver nanoparticles‐loaded calcium alginate beads embedded in gelatin scaffolds for use as wound dressings

Silver nanoparticles (AgNPs)‐loaded calcium alginate beads embedded in gelatin scaffolds were developed to sustain and maintain the release of silver (Ag⁺) ions over an extended time period. The UV irradiation technique was used to reduce Ag⁺ ions in alginate solution to AgNPs. The average sizes of AgNPs ranged between ca 20 and ca 22 nm. The AgNPs‐loaded calcium alginate beads were prepared by electrospraying of a sodium alginate solution containing AgNPs into calcium chloride (CaCl₂) solution. The AgNPs‐loaded calcium alginate beads were then embedded into gelatin scaffolds. The release characteristics of Ag⁺ ions from both the AgNPs‐loaded calcium alginate beads and the AgNPs‐loaded calcium alginate beads embedded in gelatin scaffolds were determined in either deionized water or phosphate buffer solution at 37 °C for 7 days. Moreover, the AgNPs‐loaded calcium alginate beads embedded in gelatin scaffolds were tested for their antibacterial activity and cytotoxicity. © 2014 Society of Chemical Industry     

Microwave enhanced synthesis of chitosan-graft-polyacrylamide

Chitosan-graft-polyacrylamide (Ch-g-PAM) was synthesized without any radical initiator or catalyst using microwave (MW) irradiation. Under optimal grafting conditions, 169% grafting was observed at 80% MW power in 1.16 min. Conventionally under similar conditions a maximum grafting of 82% could be achieved in 1 h using K₂S₂O₈/ascorbic acid as redox initiator coupled with Ag⁺ ions as catalyst and atmospheric oxygen as co-catalyst on a thermostatic water bath at 35±0.2 °C. The representative microwave synthesized graft copolymer was characterized by Fourier transform-infrared spectroscopy, thermo gravimetric analysis and X-ray diffraction measurement, taking chitosan as a reference. The effects of reaction variables as monomer/chitosan concentration, MW power and exposure time on the graft co-polymerization were studied. A probable free radical mechanism for grafting under microwaves has been proposed. The solubility pH for the grafted samples with different extent of grafting was monitored. The adsorption capacity of chitosan was much enhanced after grafting. The microwave synthesized Ch-g-PAM in comparison to that prepared conventionally was found to have much more adsorption ability for Ca²⁺ and Zn²⁺ ions in aqueous solution.     

Determination potentiometrique des constantes de stabilite des complexes entre l'argent(I) et quelques heterocycles azotes en milieu neutre et acide dans le carbonate de propylene

The formation of AgL⁺_n (n = 1–4) (L = pyridine), AgL′⁺ and AgL′₂⁺ [L′ = 2,2′ bipyridine, 2,2′ biquinoline, 2-(2-pyridyl)benzimidazole] complexes has been studied using potentiometry with a silver electrode. The acidity constants of the ligands have been measured potentiometrically with the hydrogen electrode. The silver distribution between the Ag⁺ and AgL_n⁺ species has been computed by means of the so obtained β_n. In acidic medium, the metallic complexes are destroyed by the ligand protonation.     

Reaction of Ozone with Ag(I)—Mechanistic Considerations

Ozone reacts slowly with Ag⁺ (circumneutral pH, k = (11 ± 3) × 10^?2 M^?1 s^?1). After some time, ozone decay kinetics may suddenly become faster with the concomitant formation of silver sol. As primary process, an O-transfer from O₃ to Ag(I) is suggested, whereby Ag(III) is formed [Ag⁺ + O₃ + 2 H₂O → Ag(OH)₃ + O₂ + H⁺]. This conproportionates with Ag(I), which is in large excess, leading to Ag(II) [Ag⁺ + Ag(OH)₃ ? 2 Ag(OH)⁺ + HO^?]. Further, Ag(II) reacts with ozone in a high exergonic reaction [Ag(OH)⁺ + O₃ → Ag + 2 O₂ + H⁺], where ozone acts as a reducing agent. Thereby, a single silver atom, Ag, is formed that can be oxidized by O₂ and O₃ or can aggregate to a silver sol. Aggregation slows down the rate of oxidation. When Ag⁺ is complexed by acetate ions, ozone decay and silver sol formation are speeded up by enhancing Ag(II) formation [Ag(I)acetate + O₃ → Ag(III)acetate → Ag(II) + CO₂ + ?CH₃]. In the presence of oxalate, the formed complex reacts faster with ozone than Ag⁺, and Ag(III)oxalate decarboxylates rapidly [Ag(I)oxalate + O₃ → Ag(III)oxalate → Ag⁺ + 2 CO₂]. This enhances ozone decay but prevents silver sol formation. Quantum chemical calculations have been carried out for substantiating mechanistic suggestions.     

Conductance measurements of some electrolytes in N, N-dimethylformamide and in binary mixtures of N, N-dimethylformamide containing some organic bases and acetonitrile

Equivalent conductances of Bu₄ NBPh₄ Bu₄ NNO₃ NI, KI, NaBPh₄, Ph₄ PCl and AgNO₃ in N, N-dimethylformamide (DMF) and in binary mixtures of DMF containing 1 mol % of pyridine (Py), α-picoline (α-Pic), β-picoline (β-Pic), γ-picoline (γ-Pic) and acetonitrile (AN) have been measured at 25°C. Limiting ion conductances have been obtained by the method of Fuoss and coworkers [J. Solution Chem. 3, 45 (1974); ibid. 4 (1975)]. The actual solvated radii of ions, calculated using limiting ion conductances show that Ag⁺ possesses very strong preferential solvation by all the bases and by AN, while Na⁺ and K⁺ do not have preferential solvation by these solvents. DMF, though, is more basic than AN, but it does not show preferential solvation for Ag⁺ while AN does.     

Thioether‐Functionalized Corn Oil Biosorbents for the Removal of Mercury and Silver Ions from Aqueous Solutions

Heavy‐metal contamination is one of the most important environmental problems faced in the world, particularly in developing countries. Metals such as silver and mercury from drinking water, food, and air sources can accumulate in living organisms and present significant health concerns. Meanwhile, the demand for these metals in many industries continues to increase. In the present study, thioether‐functionalized corn oil (TFCO) from a photoinitiated thiol‐ene synthesis was utilized to remove Ag⁺ and Hg²⁺ ions from an aqueous solution. An aqueous solution containing AgNO₃ and Hg[NO₃]₂ was prepared and contacted directly with TFCO. After vortex mixing for 60 s, the experiment ran for 351 min with the aqueous phase being periodically sampled for the analysis of metal ions (M ⁿ⁺). Results showed that 88.9% of Ag⁺ and 99.6% of Hg²⁺ ions were removed from the aqueous phase by the TFCO. Mass balances indicated that the total M ⁿ⁺ concentration in the oil phase was 13.890 g kg^?1 under the conditions studied. TFCO exhibited higher selectivity for removing Hg²⁺ than for Ag⁺ ions. Analysis of the adsorption kinetics showed that a pseudosecond‐order model may be used to determine the rate of Ag⁺ ion sorption by the oil phase. The presence of the Hg²⁺ ions interfered with the adsorption of Ag⁺ ions from the aqueous solution.     

Adsorptive removal of tetrahydrothiophene (THT) and tert-butylmercaptan (TBM) using Na-Y and AgNa-Y zeolites for fuel cell applications

Adsorptive removal of tetrahydrothiophene (THT) and tert-butylmercaptan (TBM) that are widely used sulfur odorants in pipeline natural gas was studied using AgNa-Y zeolites at ambient temperature and atmospheric pressure. The AgNa-Y were obtained via Ag⁺-exchange with Na⁺ of Na-Y at various exchange levels, and the contributions of formed adsorption sites (Ag⁺, Na⁺, Ag⁰, H⁺, and Ag₂O) in the THT and TBM adsorption uptake and selectivity were characterized. THT adsorption strength on these sites followed an order of Ag⁺ > Na⁺ ∼ Ag⁰ > H⁺ > Ag₂O. The adsorption strength of THT on Na⁺ sites was sufficiently high, thus an increase in the Ag⁺-exchange level did not lead to a notable increase in the breakthrough THT uptake. Differently, adsorption of TBM on Na⁺ sites was weak, whereas that on Ag⁺ sites was strong. This resulted in a marked increase in the breakthrough TBM uptake with an increase in the Ag⁺-exchange level, showing an order of magnitude higher uptake on AgNa-Y compared with that on Na-Y. Noticeably, the adsorption strength of THT on these adsorption sites was higher than that of TBM. This resulted in an almost 100% adsorption selectivity for THT over TBM, when these two sulfur species coexisted in the feed stream.     

A hybrid microreactor/microwave high-pressure flow system of a novel concept design and its application to the synthesis of silver nanoparticles

This article reports on a microreactor/microwave high-pressure flow hybrid apparatus of a novel concept design, which includes both the microreactor and a spiral reactor, and its efficient use in the synthesis of silver nanoparticles of relatively uniform sizes (4.3 ± 0.7 nm) under microwave irradiation. By contrast, under otherwise identical experimental conditions but with conventional heating, the nanoparticle size was non-uniform (8.3 ± 2.7 nm) and the spiral reactor walls were covered with a silver mirror deposit. Formation of the nanoparticles was monitored by UV–visible spectroscopy (plasmonic absorption band; LSPR), TEM and by small-angle X-ray scattering (SAXS). Both the spiral microreactor and the spiral quartz reactor of the hybrid system played an important role in the synthesis, with the microreactor providing the environment wherein mixing of the aqueous solution of [Ag(NH₃)₂]⁺ and the solution of glucose (the reducing agent) and poly(N-vinyl-2-pyrrolidone) (PVP; stabilizer/dispersing agent) occurred. The microwaves provided the thermal energy to effect a uniform growth of the silver nanoparticles at temperatures above 120 °C. Mixing the two solutions by conventional methods (no microreactor) failed to yield such nanoparticles even under microwave irradiation and no formation of a silver mirror occurred in the inner walls of the spiral reactor.