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     

Studies on the synthesis of electrospun PAN‐Ag composite nanofibers for antibacterial application

We have successfully synthesized polyacrylonitrile (PAN) nanofibers impregnated with Ag nanoparticles by electrospinning method at room temperature. Briefly, the PAN‐Ag composite nanofibers were prepared by electrospinning PAN (10% w/v) in dimethyl formamide (DMF) solvent containing silver nitrate (AgNO₃) in the amounts of 8% by weight of PAN. The silver ions were reduced into silver particles in three different methods i.e., by refluxing the solution before electrospinning, treating with sodium borohydride (NaBH₄), as reducing agent, and heating the prepared composite nanofibers at 160°C. The prepared PAN nanofibers functionalized with Ag nanoparticles were characterized by field emission scanning electron microscopy (FESEM), SEM elemental detection X‐ray analysis (SEM‐EDAX), transmission electron microscopy (TEM), and ultraviolet‐visible spectroscopy (UV‐VIS) analytical techniques. UV‐VIS spectra analysis showed distinct absorption band at 410 nm, suggesting the formation of Ag nanoparticles. TEM micrographs confirmed homogeneous dispersion of Ag nanoparticles on the surface of PAN nanofibers, and particle diameter was found to be 5–15 nm. It was found that all the three electrospun PAN‐Ag composite nanofibers showed strong antibacterial activity toward both gram positive and gram negative bacteria. However, the antibacterial activity of PAN‐Ag composite nanofibers membrane prepared by refluxed method was most prominent against S. aureus bacteria. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Antimicrobial properties of silver nanoparticles synthesized by bioaffinity adsorption coupled with TiO2 photocatalysis

BACKGROUND: On the basis of effective bioaffinity adsorption of Ag⁺, silver nanoparticles (Ag NPs) were synthesized on the surface of chitosan‐TiO₂ adsorbent (CTA) by TiO₂ photocatalysis for crystal growth. RESULTS: Among the microstructure characterizations of the resulting silver nanoparticles‐ loaded chitosan‐TiO₂ adsorbent (Ag‐CTA), X‐ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive X‐ray (EDX) revealed the formation of metallic Ag on the CTA, which was further confirmed by the surface plasmon resonance of Ag NPs in the UV‐visible absorption spectrum. The underlying mechanism behind the formation of Ag NPs on the CTA by TiO₂ photoreduction was studied by Fourier transform infrared (FTIR) spectroscopy. The distinctive feature of Ag‐CTA after adsorption was the highly efficient antimicrobial activity in inactivating different test strains. In the case of Escherichia coli, 1.50 mg 1.67 wt% Ag‐CTA could totally inhibit 1.0–1.2 × 10⁷ colony forming units (CFU) in 100 mL nutrient medium, which was superior to that previously reported. CONCLUSIONS: CTA effectively adsorbed the precious metal ion Ag⁺ onto active imprinting sites on the adsorbent and then exerted efficient antimicrobial effects against diverse microbes. This research will be useful for designing a novel CTA‐based wastewater treatment for multi‐functional performance. Copyright © 2010 Society of Chemical Industry     

In situ preparation,electrospinning, and characterization of polyacrylonitrile nanofibers containing silver nanoparticles

Silver nanoparticles were prepared from a polyacrylonitrile (PAN)/N,N‐dimethylformamide solution of silver nitrate (0.05–0.5 wt %) with light treatment (xenon arc) to reduce Ag⁺ ions into Ag⁰. The formation of silver nanoparticles in the PAN solution and the effect of treatment time on the numbers of silver nanoparticles, their average diameter and size distribution were investigated by UV–visible spectroscopy. In addition, the average size of silver nanoparticles and their shapes in colloidal solution were determined by transmission electron microscopy images and found to be on the order of 10 nm. The resulting solution was electrospun into PAN nanofibers. An increase in the salt concentration led to decreases in the nanofiber diameter and bead numbers (determined by scanning electron microscopy images) and an increase in the crystallinity (confirmed by X‐ray diffraction patterns). A continuous rate of silver release from the nanofiber web was monitored by the atomic absorption technique. These nanofibers showed strong antibacterial activity against Pseudomonas aeruginosa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

Photocatalytic Deposition of Silver Nanoparticles onto Organic/Inorganic Composite Nanofibers

Summary: In this work, silver nanoparticles were embedded in electrospun organic/inorganic composite nanofibers consisting of PAN and TiO₂ through photocatalytic reduction of the silver ions in silver nitrate solutions under UV irradiation. The morphology and diameter of PAN/TiO₂ composite nanofibers could be controlled by varying the initial contents of TiO₂ in the spinning solution. From TEM images and UV‐Vis spectra, it has been confirmed that monodisperse silver nanoparticles with a diameter of ≈2 nm were deposited selectively upon the titania of the as prepared composite nanofibers. The amount of Ag nanoparticles embedded on composite nanofibers was greatly influenced by the amount of TiO₂ in composite nanofibers, reflecting the role of titania as the inorganic stabilizer and photocatalyst.

Morphology of silver nanoparticles embedded on PAN/TiO₂ composite nanofibers.     

Synthesis and intercalation of silver nanoparticles in kaolinite/DMSO complexes

Ag nanoparticles were synthesized in the interlamellar space of a layered kaolinite. Disaggregation of the lamellae of the nonswelling kaolinite was achieved by the intercalation of dimethyl sulfoxide (DMSO). The kaolinite was suspended in aqueous AgNO₃ solution and the adsorbed Ag⁺ ions were reduced on the surface of kaolinite lamellae with NaBH₄ or UV light irradiation. The silver nanoparticles formed were characterized by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). We studied the effects of the two reduction methods on the size and the size distribution of Ag nanoparticles and how clay mineral structure is altered as a consequence of particle formation. It was established that the size of Ag nanoparticles depends on both silver content and the reduction method. Photoreduction of silver led to the formation of relatively large Ag nanoparticles (diameter 8–14 nm).     

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.     

A novel shape-controlled synthesis of dispersed silver nanoparticles by combined bioaffinity adsorption and TiO2 photocatalysis

Shape-controlled silver nanoparticles (Ag NPs) were prepared in a well-dispersed mode on the active imprinting sites of chitosan-TiO₂ adsorbent (CTA) by means of bioaffinity adsorption and TiO₂ photocatalysis. Nontoxic hydrogen peroxide (H₂O₂) was used as a suitable etching reagent in our production of shape-controlled Ag NPs, since it could regulate the TiO₂ photocatalysis and accelerate the generation of O₂. With the same amount of H₂O₂ addition, silver nanocubes, nanospheres and truncated triangular nanoplates were individually obtained on the surface of CTA under UV irradiation by facilely adjusting the initial Ag⁺ concentration. The FE-SEM, XRD and UV-visible characterizations confirmed single crystal Ag NPs with different shapes loaded on CTA. The mechanism for the formation of shape-controlled Ag NPs was discussed based on a photocatalytic reaction system. As an example of applications of the Ag NPs, we tested the biocidal properties, and silver nanocubes exhibited the highest antibacterial activity. Our research provided a simple synthesis for shape-regulated Ag NPs steadily loaded on CTA. It might moreover be a guide in preparing metal nanocrystals monodispersely immobilized on chemical substrates.     

In situ preparation of Au or Ag nanoparticles in the presence of hyperbranched poly(amidoamine)s with hydrophobic end‐groups as nanoreactors and reductants

Hyperbranched poly(amidoamine)s with methyl ester terminals (HPAMAM‐COOCH₃) were used as nanoreactors and reductants to prepare gold or silver nanoparticles (Au NPs or Ag NPs). HPAMAM‐COOCH₃ could bind AuCl₄ ⁻ (or Ag⁺) and then reduce AuCl₄ ⁻ (or Ag⁺) into Au NPs (or Ag NPs) through their internal amines, while the external methyl ester groups prevented the aggregation of polymers. The formation of Au NPs or Ag NPs was verified using transmission electron microscopy (TEM), ultraviolet‐visible spectroscopy (UV‐Vis), X‐Ray powder diffraction (XRD), Fourier‐transform infrared spectroscopy (FT‐IR), and thermogravimetric analysis (TGA), confirming the formation of Au NPs or Ag NPs with small particle size and low size distribution.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

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).     

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.     

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     

Polyamide/silver antimicrobials: effect of crystallinity on the silver ion release

Polyamide/silver (PA/Ag) composite materials are regarded as potential antimicrobials by virtue of their efficacy to release the Ag⁺ ions in an aqueous medium. The effects of the matrix crystallinity on the Ag⁺ ion release characteristics of PA/Ag composites are discussed. It is found that matrix crystallinity is very decisive for the silver ion releasing properties and hence the antimicrobial efficacy of silver‐based antimicrobial polyamides. The crystallinities of the composites were evaluated using differential scanning calorimetry. The silver ion release characteristics of these composites were measured by anode stripping voltammetry. Silver ion release was higher in systems possessing lower degrees of crystallinity. Water‐diffusion characteristics of the composites control the silver ion release. The effect of crystallinity on silver ion release rate depends on the time of soaking of the specimens in water. Copyright © 2005 Society of Chemical Industry     

Ag and Si Codoped Phosphate Glasses: Plasmonic Nanocomposites with Enhanced UV Transparency

The use of silicon powder to produce plasmonic Ag nanocomposite phosphate glasses which also exhibit improved transparency in the ultraviolet (UV) is proposed. Ag₂O/Si codoped glasses were prepared in a barium‐phosphate matrix by a simple melt‐quench method in ambient atmosphere. The as‐prepared glasses exhibit enhanced UV transparency, whereby the surface plasmon resonance of Ag nanoparticles (NPs) is manifested for the glasses with higher Ag₂O contents. ³¹P nuclear magnetic resonance spectroscopy is consistent with the formation of P–O–Si bonds, thus suggesting their possible role on the improved UV light transmission. Consequently, a model was presented accounting for the influence of silicon on the polymerization of the phosphate network concomitant with the creation of highly reactive oxygen species. Further exploiting the proposed reactive species, a real‐time spectroscopic study of the plasmonic response of Ag NPs in Ag/Si codoped glass samples was carried out during an in situ thermal processing. The temperature dependence of the Ag particle precipitation was studied in the 400°C–430°C range, from which an Arrhenius‐type plot allowed for estimating the activation energy of the process at 3.42 (±0.38) eV. Ultimately, the vanishing of the luminescence ascribed to Ag⁺ ions was observed in a heat‐treated sample, consistent with the high reactivity acquired by the glass matrix. Silicon thus appears promising for producing UV transparent glasses for high‐performance optics and for the reduction of Ag⁺ ions to produce Ag nanocomposites valuable for photonic (nanoplasmonic) applications.     

Preparation of antimicrobial poly(ϵ‐caprolactone) electrospun nanofibers containing silver‐loaded zirconium phosphate nanoparticles

Antimicrobial nanofibers of poly(?‐caprolactone) (PCL) were prepared by electrospinning of a PCL solution with small amounts of silver‐loaded zirconium phosphate nanoparticles (nanoAgZ) for potential use in wound dressing applications. The electrospun nanoAgZ‐containing PCL nanofibers were characterized using field emission scanning electron microscopy, energy dispersive X‐ray spectrum (EDX), X‐ray diffraction analysis (XRD), antimicrobial tests, and biocompatibility tests. The SEM, EDX, and XRD investigations of the electrospun fibers confirmed that silver‐containing nanoparticles were incorporated and well dispersed in smooth and beadless PCL nanofibers. The results of the antimicrobial tests showed that these fibers have maintained the strong killing abilities of Ag⁺ existed in the nanoAgZ against the tested bacteria strains and discoloration has not been observed for the nanofibers. To test the biocompatibility of nanofibers as potential wound dressings, primary human dermal fibroblasts (HDFs) were cultured on the nanofibrous mats. The cultured cells were evaluated in terms of cell proliferation and morphology. The results indicated that the cells attached and proliferated as continuous layers on the nanoAgZ‐containing nanofibers and maintained the healthy morphology of HDFs. The earlier results suggested that nanoAgZ‐containing fibers may be expected to be a novel material for potential wound dressing applications because of the significant bacteriostatic activities and good biocompatibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Silver/poly(N‐vinyl‐2‐pyrrolidone) hydrogel nanocomposites obtained by electrochemical synthesis of silver nanoparticles inside the polymer hydrogel aimed for biomedical applications

Silver nanoparticles were produced inside a poly(N‐vinyl‐2‐pyrrolidone) hydrogel (PVP) by an innovative method based on the electrochemical reduction of Ag⁺ ions within the swollen PVP hydrogel. UV‐visible spectroscopy showed the highest value of the absorbance intensity and the lowest values of the wavelength of the absorbance maximum and the full width at the half‐maximum absorbance for the Ag/PVP nanocomposite obtained at 200 V during 4 min. Cyclic voltammetry results suggested an adequate entrapment of the silver nanoparticles. The mechanical properties under bioreactor conditions of the Ag/PVP nanocomposite suggested the possibility of wound dressing application. Silver release from Ag/PVP nanocomposites was confirmed under static conditions as well as by their antimicrobial activity against Staphylococcus aureus. POLYM. COMPOS., 35:217–226, 2014. © 2013 Society of Plastics Engineers     

TiO<Subscript>2</Subscript> porous ceramic/Ag–AgCl composite for enhanced photocatalytic degradation of dyes under visible light irradiation

TiO₂ porous ceramic/Ag–AgCl composite was prepared by incorporating AgCl nanoparticles within the bulk of TiO₂ porous ceramic followed by reducing Ag⁺ in the AgCl particles to Ag⁰ species under visible light irradiation. The porous TiO₂ ceramic was physically robust and chemically durable, and the porous structure facilitated the implantation of AgCl NPs. Compared with the bare TiO₂ ceramic, TiO₂ porous ceramic/Ag–AgCl composite exhibited higher photocatalytic performance for the degradation of MO and RhB under visible light irradiation. The reaction rate constants k of MO and RhB degradation over TiO₂ porous ceramic/Ag–AgCl composite was respectively 6.25 times and 3.62 times higher than those recorded over the bare TiO₂ porous ceramic. The photocatalytic activity showed virtually no decline after four times cyclic experiments under visible light irradiation. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectra and X-ray photoelectron spectroscopy were used to characterize the TiO₂ porous ceramic/Ag–AgCl composite.     

Morphological and thermal properties of photodegradable biocomposite films

Biocomposites containing ultraviolet (UV) radiation absorbing inorganic nanofillers are of great interest in food packaging applications. The biodegradable polylactide (PLA) composite films were prepared by solvent casting method by incorporating 1 wt % of titanium dioxide (TiO₂) and Ag‐TiO₂ (silver nanoparticles decorated TiO₂) nanoparticles to impart the photodegradable properties. The films were exposed to UV radiation for different time periods and morphology of the composite films before and after UV exposure were investigated. The results showed that homogenous filler distribution was achieved in the case of Ag‐TiO₂ nanoparticles. The thermal properties and thermomechanical stability of the composite film containing Ag‐TiO₂ nanoparticles were found to be much higher than those of neat PLA and PLA/TiO₂ composite films. The scanning electron microscopy and X‐ray diffraction studies revealed that the photodegradability of PLA matrix was significantly improved in the presence of Ag‐TiO₂ nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013