Preparation and properties of electrospun poly(vinyl alcohol)/silver fiber web as wound dressings

A novel wound dressing material was prepared by electrospinning poly(vinyl alcohol) (PVA)/AgNO₃ aqueous solution into nonwoven webs and then treating the webs by heat or UV radiation. Through SEM, TEM, and XPS analyses, it was observed that the silver (Ag) nanoparticles were generated and existed in the near surface of the electrospun nanofibers. It was found that heat treatment as well as UV radiation reduced the Ag⁺⁺⁺ ions in the electrospun PVA/AgNO₃ fiber web into the Ag nanoparticles. Also the heat treatment improved the crystallinity of the electrospun PVA fiber web and so it made the web unsolved in moisture environment. Therefore, it was concluded that the only heat treated electrospun PVA/AgNO₃ fiber web was a good material as wound dressings because it had structural stability in moisture environment as well as excellent antimicrobial ability and, quick and continuous release of the effectiveness. POLYM. ENG. SCI., 47:43–49, 2007. © 2006 Society of Plastics Engineers     

Silver-Doped Organic-Inorganic Hybrid Silica Membranes by Sol-Gel Method: Preparation and Hydrothermal Stability

Silver-doped methyl-modified silica membranes (Ag/M-SiO₂) have been prepared using the sol-gel method by adding AgNO₃ solution to a methyl-modified silica sol. The influence of silver-doping on the physical and chemical structures, thermal stability of –CH₃ groups, and gas permeation performance for the silica membranes were investigated. The metallic silver results from the reduction of AgNO₃ which can be completely transformed after calcined above 200°C. The Si–CH₃ vibrational bands disappear completely when the calcination temperature is increased to 600°C, which mineralized when the calcination temperature is further increased to 750°C. The doping of silver nanoparticles has nearly no influence on the chemical structure of the methyl-modified silica materials and the thermal stability of –CH₃ groups, but can make the mean pore size, total pore volume, H₂ permeability, and H₂/CO₂ selectivities of the silica membranes increase. When operated at 200°C and a pressure difference of 0.35 MPa, the H₂ permeance and H₂/CO₂ selectivity of Ag/M-SiO₂ membrane with the AgNO₃/tetraethylorthosilicate molar ratio of 0.08 is 8.99 × 10^?6 mol · m^?2 · Pa^?1 · s^?1 and 10.22, respectively. After hydrothermal treatment and regeneration, the Ag/M-SiO₂ membranes show a smaller change in gas permeances and H₂/CO₂ permselectivities than the methyl-modified silica membranes without silver-doping.     

Infusion of Ag‐Ion from Aqueous Solution into Solid Calcium Phosphate of Hydroxyapatite (HA) Crystal Structure

In contrast to extensive literature concerning Ag incorporation in hydroxyapatite, HA, while the phosphate approximated to stoichiometry of Ca₁₀(PO₄)₆(OH)₂, with added Ag has been precipitating from an aqueous solution, the paper presents Ag incorporation through Ag ion infusion from AgNO₃ solution into solid HA pressed in pellet and ignited at 800°C. After Ag ions infused into the HA‐solid (crossed the interfacial solution‐solid boundary), they diffused across the crystal structure to a depth of time‐dependent several mm. The path of Ag diffusion in the solid HA was recorded using SEM‐EDS point analyses of Ag, Ca, P, EDS‐linear analyses of those elements, and elemental mapping. Time‐dependent concentrations of Ag⁺, Ca²⁺, and PO₄^3? in AgNO₃ solutions were also analyzed. The appearance of Ag in the crystalline HA with simultaneous local depletion in Ca and phosphate recorded as P, observed by EDS with simultaneous appearance of Ca²⁺ and PO₄^3? ions and a decrease in Ag⁺ concentration in AgNO₃ solution led the authors to a conclusion that Ag⁺ for Ca²⁺ substitution supported by PO₄^3? charge balancing in the crystalline HA was in process. The HA particles in the section of the pellet without Ag had a uniform shape and size approximated to 300–400 nm. SEM image of the HA solid section, where Ag ions appeared was characterized by irregular aggregates of smaller crystals with sporadically present large, shaped in prism blocks identified by the XRD as Ag₃PO₄.     

The thermal‐electrical properties of polyvinyl alcohol/AgNO3 films

In this article, one cast technique to fabricate 20–40 wt %AgNO₃‐doped polyvinyl alcohol (PVA) composite films of which electrical resistance sharply dropped (4–5 order) in a certain temperature range was reported. The phase, structure thermal, and electrical resistivity properties of films at different heat treatment temperatures were studied by X‐ray diffraction (XRD), scanning electrical microscopy (SEM) and differential scanning calorimetry (DSC). The results showed that all the AgNO₃ (20–40 wt %) doped PVA films presented an exothermic peak at 182°C. And the temperature of exothermic peak kept constant for various contents of AgNO₃. Meanwhile, the phase composition of the films was greatly affected by the heat treatment temperature. Ag particles were generated during the heat treatment process, and the content of Ag particles increased with increasing the temperature. The resistivity of PVA/AgNO₃ films decreased with increasing the temperature. And a sharp decrease appeared at 155–165°C due to the generation and contact of a mass of Ag particles at this temperature. The thermal‐electrical results suggested the applicability of these materials in temperature sensor, for example, critical temperature resistor thermistor. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Hydrothermal synthesis,crystal structure and fluorescent properties of a novel 1D polymer: VO2(C7H3O4N)Ag(C10H8N2)·H2O

The hydrothermal synthesis of V₂O₅, AgNO₃, pyridine-2,6-dicarboxylic acid (H₂pdc) and 2,2′-bipyridine (bpy) in water at 160 °C for 4 days yields a novel 1D coordination polymer VO₂(C₇H₃O₄N)Ag(C₁₀H₈N₂)·H₂O (1). Each V center chelates to a tridentate ligand pdc^2? and coordinates to two O atoms, while the square based pyramid conformation of Ag center consists of three O atoms and a bpy molecular. V and Ag polyhedra alternate by either carboxyl or oxo bridges to further form a unique 3d–4d heterometal-based 1D double-chain ribbon.     

Complex formation in molten salts - IV: Association constants of silver-bromo complexes in molten KNO3Ba(NO3)2 eutectic as solvent

Potentiometric measurements on the molten salt concentration cell: Ag/AgNO₃, KNO₃Ba(NO₃)₂//AgNO₃, KBr, KNO₃Ba(NO₃)₂/Ag were carried out over a wide range of solute concentration and at temperatures in the range 350–410°C to study the association equilibria in dilute solutions of Ag⁺ and Br^? in molten KNO₃Ba(NO₃)₂(89:11 mole %). The results indicated formation of the species AgBr, AgBr^?₂; Ag₂Br⁺ was not formed under the experimental conditions employed. The temperature-dependence of the association constants were, within limits of experimental precision, predictable from the quasi-lattice model.     

Selective preparation of Ag species on photoluminescence of Sm3+ in borosilicate glass via Ag+-Na+ ion exchange

Photoluminescence (PL) of rare earth ion-doped glasses could be enhanced by diverse Ag species such as Ag⁺ ions, Ag⁺-Ag⁺ pairs, Ag nano-clusters (NCs), and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ion-doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, Ag⁺ ions and Ag NCs were selectively prepared in the Sm³⁺-doped borosilicate glass via the Ag⁺-Na⁺ ion exchange. The influence of AgNO₃/NaNO₃ ratio in the molten salt on the Ag existing states was investigated. The results demonstrate that the isolated Ag⁺ ions exist in the Sm³⁺-doped borosilicate glass when the ratio of AgNO₃/NaNO₃ is 1/1000. The Ag NCs are formed in the Sm³⁺-doped borosilicate glass when the AgNO₃/NaNO₃ ratio is 1/10. The influence of Ag⁺ ions or Ag NCs on the PL of Sm³⁺ was systematically investigated. The results show that the PL of Sm³⁺ was enhanced by the energy transfer from Ag⁺ ions or Ag NCs to Sm³⁺.     

A mononuclear complex of norfloxacin with silver(I) and its properties

Reaction of norfloxacin (H-Norf) with AgNO₃ yields an unusual mononuclear complex [Ag(H-Norf)₂]NO₃ (1) in which the local coordination environment around Ag⁺ ion is approximately linear with a N–Ag–N angle of 162.1(2)°. Larger concentration of Ag⁺ ions was found in water solution of 1. The unique bonding in 1 may lead to the readily release of Ag⁺ ion from 1, and leads to better antibacterial action in topical burn treatments. Strong blue fluorescent emission of 1 was also observed.     

Preparation and Characterization of Polypyrrole Silver Nanocomposites via Interfacial Polymerization

Conducting polypyrrole silver (Ppy-AgNC) nanocomposite was synthesized by an interfacial polymerization method. Ag⁺ ions from the AgNO₃ solution were taken in the formation of Ppy-AgNC. The incorporated silver was confirmed by X-ray diffraction (XRD). During the polymerization in a nitrate ion-containing solution, the impregnation leads to the formation of metallic silver. The size distribution of Ag into the polymer is confirmed by transmission electron microscopy (TEM), and proves the formation of a uniform species with spherical particles of Ag (mean diameter of 8-12 nm) branching at the border of Ppy. The thermal behavior of the material was studied by thermogravimetric measurements.     

Structural and thermoelectric properties of hydrothermal-processed Ag-doped Fe2O3

Fe_2-xAg_xO₃ (0?≤?x?≤?0.04) nanopowders with various Ag contents were synthesized at different hydrothermal reaction temperatures (150?°C and 180?°C). Their structural properties were fully investigated through an X-ray diffraction, a Fourier transform infrared spectroscopy, and an X-ray photoelectron spectroscopy. The hydrothermal reaction temperature, time, and Ag content remarkably affected the morphological characteristics and crystal structure of the synthesized powders. The Fe_2-xAg_xO₃ (0?≤?x?≤?0.04) powders synthesized at 150?°C for 6?h and the Fe_2-xAg_xO₃ (0.02?≤?x?≤?0.04) powders synthesized at 180?°C for 12?h formed the orthorhombic α-FeOOH phase with a rod-like morphology, whereas the Fe_2-xAg_xO₃ (0?≤?x?≤?0.01) powders synthesized at 180?°C for 12?h formed the rhombohedral α-Fe₂O₃ phase with a spherical-like morphology. The Fe_1.98Ag_0.02O₃ fabricated by utilizing Fe_1.98Ag_0.02O₃ powders synthesized at 180?°C showed the largest power factor (0.64?×10^?5 Wm^?1 K^?2) and dimensionless figure-of-merit (0.0036) at 800?°C.     

Synthesis and characterization of Ag nanoparticles embedded in PVA via UV-photoreduction technique for synthesis of Prussian blue pigment

Silver nanoparticles doped in polyvinyl alcohol (AgNps/PVA) were synthesized via polymer-promoted reductive reaction of AgNO₃ and PVA under time-dependent exposure to UV radiation. The AgNps/PVA composites were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, UV–Vis spectroscopy, and transmission electron microscopy to describe the structure, nuclearity, and distribution of Ag Nps within the PVA matrix. The UV–Vis spectrum of AgNps/PVA exhibited a broad surface plasmon absorption around 425–443 nm which originated from the formation of Ag NPs. Surface analysis by XPS indicated that the Ag NPs were grown solely on the PVA surface at UV exposure time of 2 h (2.0AgNPs/PVA). Increasing the UV exposure time to 4 h will cause the transformation of metallic nanosilver to oxidized nanosilver. UV–Vis absorption spectra were in situ recorded to follow the synthesis of Prussian blue (PB) on 2.0AgNPs/PVA (PB@2.0AgNPs/PVA). The colloidal dispersion of 2.0AgNPs/PVA in an acidic medium containing free Fe(III) ions and potassium hexacyanoferrate(III) revealed an additional band centered at 720 nm due to the intermetal charge-transfer absorbance of the polymeric Fe(II)-C-N-Fe(III) of the PB@2.0AgNPs/PVA nanocomposite. Control experiments were shown to involve a spontaneous electron transfer reaction between 2.0AgNPs/PVA and Fe(III) ions, with a concomitant decomposition of hexacyanoferrate(III) and formation of PB was observed. Moreover, IR gave clear cut evidence for the synthesis of PB@2.0AgNPs/PVA from the appearance of a band for the cyano group at 2090 cm^?1.     

Conductivity and kinetic studies of silver-sensing electrodes

The mixed conductivity (ionic and electronic) of Ag₂S was measured at room temperature by a square wave method. Various types of cells were used. They allowed blocking of either the ionic or electronic current in the steady state. The electronic conductivity was very different depending upon whether the Ag₂S was contacted with metallic silver or not, the ratio of electronic to ionic conductivity being 3·22 or 0·015, respectively. The ionic conductivity was the same in both cases, in agreement with theoretical expectations for a system with high ionic disorder and relatively small electronic disorder. The measurements yielded also information about the kinetics of the exchange of Ag⁺ -ions at the interface Ag₂S Ag_aq. It was estimated that the exchange current density is at least 100 mA cm² for a 0·1 M AgNO₃ solution. In contrast to this the kinetics of a redox process (Fe^3?_aq + e → Fe²⁺_aq) were found to be very slow. These two features are favourable from the viewpoint of the use of Ag₂S as an ion selective electrode.The kinetics of the Ag/Ag⁺_aq interface were also studied. Especially with AgNO₃ solutions the polarisation resistance is extremely high near the equilibrium potential (at cd's of the order of μA/cm²) and drops suddenly at potentials above about 5–10 mV. The phenomena observed are probably due to adsorption effects. The difference between the behaviour of the Ag and Ag₂S interfaces is discussed.     

Photocatalytic Activity of AgBr as an Environmental Catalyst

The photocatalytic activity of AgBr has been investigated. AgBr(N₂) was prepared by solid(AgNO₃)–solid(KBr) reaction at different temperatures in a stream of N₂. AgBr(N₂) prepared at 250 °C showed the highest H₂ generation activity although the larger crystallites of Ag were observed. When the preparation was carried out under air [AgBr(air)] at 250 °C, the photoactivity and the crystallization of Ag were lowered by the formation of silver oxides species in AgBr(air) probably during the natural cooling under air. It is pointed out however that the amount of hydrogen of both AgBr(N₂) and AgBr(air) increased linearly increasing with reaction time regardless of the formation of large Ag crystallites even after UV irradiation for 50 h. This suggests that the behavior of Ag formed might be different from that of the latent image in the photographic process.     

The role of silver species on Ag/Al2O3 catalysts for the selective catalytic oxidation of ammonia to nitrogen

The role of Ag species on Ag/Al₂O₃ catalyst for the selective catalytic oxidation (SCO) of NH₃ to N₂ was studied using 10 wt% Ag/Al₂O₃ catalysts prepared with impregnation, incipient wetness impregnation and sol–gel methods. The catalyst characterization was preformed using N₂ adsorption–desorption, UV/Vis, TEM and XRD. O₂-chemisorption and H₂–O₂ titration were measured to confirm the metal dispersion on the catalyst. The Ag species state and Ag particle size have significant influence on the Ag/Al₂O₃ activity and N₂ selectivity of the SCO of NH₃ at low temperature. Ag⁰ is proposed to be an active species on the H₂ pretreated catalyst at low temperature (<140 °C). It is evident that well-dispersed and small particle Ag⁰ enhances catalytic activity at low temperature, whereas large particle Ag⁰ is relate to a high N₂ selectivity. In contrast, Ag⁺ could also be the active species at temperatures above 140 °C.     

Fast synthesis and morphology control of silicalite-1 in the presence of polyvinyl alcohol

Silicalite-1 crystals with various morphologies were prepared by addition of polyvinyl alcohol (PVA) in silicalite-1 synthesis solution at 180 °C for 6?C40 h. The samples were characterized by X-ray diffraction, scanning electron microscopy, FT-IR, thermogravimetric analysis and N₂ sorption. PVA in the synthesis solution promoted the fast crystallization of silicalite-1 within 6 h due to its adsorption on the surface of silicalite-1 precursors and the hydrogen bonding effect. The addition of PVA would produce silicalite-1 without aggregation because PVA served as temporary physical barriers. However, more PVA in the system (weight ratio of PVA/SiO₂ = 1.75) slowed down the nucleation rate of silicalite-1 as the high viscosity of PAV hindered the selectivity between PVA and crystal facet. PVA also changed the surface energy of silicalite-1 precursors, and resulted in silicalite-1 crystals with sizes from 6 × 2 × 0.6 to 15 × 10 × 3 ??m³. Silicalite-1 crystals exhibited coffin-, plate-, and rod-like structure when different weight ratios of PVA/SiO₂ were applied, and the silicalite-1 crystals had high BET surface areas of 485?C513 m²/g.     

Preparation and Characterization of Gelatin Nanofibers Containing Silver Nanoparticles

Ag nanoparticles (NPs) were synthesized in formic acid aqueous solutions through chemical reduction. Formic acid was used for a reducing agent of Ag precursor and solvent of gelatin. Silver acetate, silver tetrafluoroborate, silver nitrate, and silver phosphate were used as Ag precursors. Ag⁺ ions were reduced into Ag NPs by formic acid. The formation of Ag NPs was characterized by a UV-Vis spectrophotometer. Ag NPs were quickly generated within a few minutes in silver nitrate (AgNO₃)/formic acid solution. As the water content of formic acid aqueous solution increased, more Ag NPs were generated, at a higher rate and with greater size. When gelatin was added to the AgNO₃/formic acid solution, the Ag NPs were stabilized, resulting in smaller particles. Moreover, gelatin limits further aggregation of Ag NPs, which were effectively dispersed in solution. The amount of Ag NPs formed increased with increasing concentration of AgNO₃ and aging time. Gelatin nanofibers containing Ag NPs were fabricated by electrospinning. The average diameters of gelatin nanofibers were 166.52 ± 32.72 nm, but these decreased with the addition of AgNO₃. The average diameters of the Ag NPs in gelatin nanofibers ranged between 13 and 25 nm, which was confirmed by transmission electron microscopy (TEM).     

Three Ag(I)–cyanide coordination polymers with metal bonds tuned by N-heterocyclic ligands

Hydrothermal reactions of AgNO₃, K₃[Fe(CN)₆] with N-heterocyclic ligands afforded three novel Ag(I)–cyanide coordination polymers, [Ag₂(CN)₂(tpt)]_n (1), {[Ag(CN)(bpe)_0.5][Ag(CN)]}_n (2) and [Ag(CN)(btmb)_0.5]_n (3) (tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine, bpe = 1,2-bis(4-pyridyl)ethane, btmb = 1,2-bis(1,2,4-triazol-1-ylmethyl)benzene). In complex 1, two Ag(CN) linear chains are bridged by bidentate tpt ligand to form a ladder-like structure, which are further connected by AgAg metal bond to generate a 2D polymeric network. Complex 2 is an interesting 3D supramolecular architecture assembled by 2D [Ag¹(CN)(bpe)_0.5]_n network and linear [Ag²(CN)]_n chain combined by strong AgAg metal bond. Complex 3 is a 1D ladder-like double-chain polymer constructed from Ag–cyanide linear chains and btmb spacer, which is further extended to a 2D supramolecular network by Ag–Ag weak interaction. The Ag–Ag metal interactions play important roles in the construction of three coordination polymers. Complexes 1 and 2 are respectively thermally stable at 300 and 180 °C. Complexes 1 and 3 emit strong blue luminescence.     

Transport numbers and ionic mobilities in nitrate melts by EMF-measurements on concentration cells with transference

The transport numbers of the cation constituents, referred to the common anion constituent, have been measured for the molten systems KNO₃ + AgNO₃, RbNO₃ + AgNO₃, and CsNO₃ + AgNO₃ over the entire range of compositions at temperatures varying from 230° to 350°C by the use of concentration cells with transference. The ionic mobilities have been calculated from the existing data of the densities and electric conductivities for these systems. For all three systems, the mobility of Ag⁺ is higher than that of the other cation in the region rich in silver nitrate while the opposite is true for the region rich in alkali nitrate. This is equivalent to the statement that the curve representing the transport numbers as a function of composition crosses the diagonal (“inversion point”). This inversion varies systematically with the temperature and the ion diameter of the alkali ion.     

In vitro silver ion release kinetics from nanosilver/poly(vinyl alcohol) hydrogels synthesized by gamma irradiation

A nanosilver (nano‐Ag)/poly(vinyl alcohol) (PVA) hydrogel device was synthesized with γ irradiation because it is a highly suitable tool for enhanced nano‐Ag technologies and biocompatible controlled release formulations. The amount of the Ag⁺ ions released in vitro by the nano‐Ag/PVA hydrogel device was in the antimicrobial parts per million concentration range. The modeling of the Ag⁺ ion release kinetics with the elements of the drug‐delivery paradigm revealed the best fit solution (R² > 0.99) for the Kopcha and Makoid–Banakar's pharmacokinetic dissolution models. The term A/B, derived from the Kopcha model, indicated that the nano‐Ag/PVA hydrogel was mainly an Ag⁺‐ion diffusion‐controlled device. Makoid–Banakar's parameter and the short time approximated Ag⁺‐ion diffusion constant reflected the importance of the size of the Ag nanoparticles. However, it appeared that the cell oxidation potential of the Ag nanoparticles depended on the diffusion characteristics of the fluid penetrating into the Ag/PVA nanosystem. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40321.