Preparation and characterization of polyoxometalate-modified poly(vinyl alcohol)/polyethyleneimine hybrids as a chemical and biological self-detoxifying material

Nanohybrid membranes based on the Keggin-type polyoxometalate (POM) H₅PV₂Mo₁₀O₄₀ and a poly(vinyl alcohol)/polyethyleneimine (PVA/PEI) blend were prepared as a chemical and biological protective material. The objective of the study was to develop and evaluate permeable membranes (PVA/PEI) impregnated with reactive nanoparticulates (POM) that can protect against simulants of chemical and biological warfare agents. The physical properties of the PVA/PEI–POM hybrids were examined using SEM, TEM, TGA, and UV–Vis spectroscopy, the results of which indicated that the POM was incorporated in the PVA/PEI matrix after impregnation. The redox properties against 2-chloroethyl-ethyl sulfide (CEES) were investigated based on significant color changes and UV absorption in the POM upon reduction by CEES. The antibacterial effects of the PVA/PEI–POM hybrids were assessed by the zone of inhibition, minimum inhibitory concentration (MIC), and plate-counting methods. The results of this study showed that PVA/PEI–POM hybrids that act against simulants of chemical and biological weapons while retaining their ability to transmit moisture vapor could be obtained.     

Antibacterial ultrafiltration membrane with silver nanoparticle impregnation by interfacial polymerization for ballast water

Interfacial polymerization technology was employed to immobilize silver (Ag) nanoparticles on the surface of commercial polyethersulfone (PES) membrane to develop antibacterial and antifouling ultrafiltration membrane. Ag nanoparticles were prepared from the reduction of silver nitrate (AgNO₃) by sodium borohydride in the presence of polyethyleneimine (PEI) as the stabilizer. The encapsulated Ag nanoparticles in the PEI solution were embedded into the PEI membrane when trimesoyl chloride solution was used to crosslink the PEI solution with the PES membrane, forming Ag-polyamide (PA) networks through the interfacial polymerization reaction. Experimental results showed that the membrane prepared with 50 mmol/L of AgNO₃ and 20 mmol/L of PEI had the optimized antibacterial effect against Escherichia coli. Bacterial concentration and species were also investigated. Exiguobacterium aestuarii and Staphylococcus aureus which are gram-positive bacteria, needed significantly more time for the Ag-PA/PES membrane to kill the bacteria completely when compared to E.coli and Vibrio coralliilyticus which are gram-negative bacteria. This study showed that Ag nanoparticles impregnated in membrane surfaces were 100% effective in killing various types of marine bacteria and bacteria in the seawater collected off Sentosa Island in Singapore. These membranes exhibit excellent antibacterial and antifouling properties which can be used to kill bacteria in ballast water and seawater.     

Structure and coordination properties of facilitated olefin transport membranes consisting of crosslinked poly(vinyl alcohol) and silver hexafluoroantimonate

The high selectivity of solid‐state crosslinked poly(vinyl alcohol) (CPVA) membranes containing silver hexafluoroantimonate (AgSbF₆), with respect to olefin/paraffin mixtures, was previously reported. The structure and coordination properties of CPVA/AgSbF₆ complexes were investigated in this study with wide‐angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), X‐ray photoelectron spectroscopy (XPS), and theoretical ab initio calculations, and they were compared with those of poly(vinyl alcohol) (PVA)/AgSbF₆ complexes. Contrary to expectations, the measurements of the intersegmental d‐spacings and glass‐transition temperatures indicated that the chain mobility in the PVA/AgSbF₆ membranes was lower than that in the CPVA/AgSbF₆ membranes. The different extents of transient crosslinking in the two systems were attributed mostly to their different coordination structures; silver ions in PVA/AgSbF₆ were coordinated with hydroxyl oxygens located near the polymer main chains, whereas those in CPVA/AgSbF₆ were coordinated with aldehyde oxygens located far from the main chains. According to WAXS spectra, AgSbF₆ was completely dissolved in both PVA and CPVA, and this disrupted the crystallinity of the polymers. However, our DSC study showed that the silver ions dissolved in both polymer matrices recrystallized into silver oxide at elevated temperatures. The binding energy of Ag3d_5/2, as determined from XPS spectra, shifted to lower values with the addition of increasing amounts of the polymer matrix, indicating the increasing coordination of silver ions with polymer chains. The presence of various oxygen species with and without coordination to silver ions was confirmed from O1s XPS spectra of CPVA membranes containing silver ions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 621–628, 2004     

Self-assembled polyelectrolyte multilayer membranes with highly improved pervaporation separation of ethanol/water mixtures

Ethanol/water pervaporation through ultrathin polyelectrolyte multilayer membranes is described. The membranes were prepared by the layer-by-layer technique, i.e. by alternating sequential adsorption of cationic and anionic polyelectrolytes on a porous support. The separation capability was optimized by variation of the chemical structure of the polyelectrolytes, by variation of pH and ionic strength of the polyelectrolyte solutions used for membrane preparation and by annealing of the polyelectrolyte membranes. It was found that the separation is mainly affected by the charge density of the polyelectrolytes which is controlled by the chemical structure and the degree of ionisation of the polar groups. Selectivity for water was highest, if polyelectrolytes of high charge density such as polyethyleneimine (PEI), polyvinylamine (PVA) and polyvinylsulfate (PVS) were used and if the pH of the polyelectrolyte solutions was equal to the mean of the pK_a values of the corresponding cationic and anionic polyelectrolyte. Best results were obtained for PVA/PVS and PEI/PVS membranes which are characterized in detail with regard to their separation behavior.     

Poly(vinylalcohol)/poly(ethyleneglycol)/poly(ethyleneimine) blend membranes - structure and CO2 facilitated transport

Poly(vinylalcohol) (PVA)/poly(ethyleneimine) (PEI)/poly(ethyleneglycol) (PEG) blend membranes were prepared by solution casting followed by solvent evaporation. The effects of the blend polymer composition on the membrane structure and CO₂/N₂ permeation characteristics were investigated. IR spectroscopy evidenced strong hydrogen bonding interactions between amorphous PVA and PEI, and weaker interactions between PVA and PEG. DSC studies showed that PVA crystallization was partially inhibited by the interactions between amorphous PVA and PEI blend, in which PEG separated into nodules. The CO₂ permeability decreased with an increase in CO₂ partial pressure in feed gas, while the N₂ permeability remained constant. This result indicated that only CO₂ was transported by the facilitated transport mechanism. The CO₂ and N₂ permeabilities increased monotonically with the PEI content in the blend membranes, whereas the ideal selectivity of CO₂ to N₂ transport showed a maximum. When CO₂ is humidified, its permeability through the blend membranes is much higher than that of dry CO₂, but the change in permeability due to the presence of humidity is reversible.     

Preparation and Antibacterial Effect of Bamboo Charcoal/Ag on Staphylococcus Aureus and Pseudomonas Aeruginosa

Bamboo charcoal supporting silver (BC/Ag) was prepared by activation and chemical reduction. The BC/Ag composites were characterized by silver particle size and distribution, silver ion (Ag⁺) release and antibacterial properties. Scanning and transmission electron microscopy (SEM and TEM) showed that the Ag particles were distributed uniformly on the BC matrix. The Ag particle size was found to be less than 150 nm based on TEM. The Ag⁺ release increased initially which was followed by a marginal increase between the 8th and 24th hour. Composites contained higher amounts of silver exhibited a further rise in Ag⁺ release from the 24‐hours of storage in water. The antibacterial effects of the BC/Ag composite powders against Pseudomonas aeruginosa and Staphylococcus aureus were assessed from the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) method, and an excellent antibacterial performance was discovered.     

A Simple and Fast Aqueous‐Phase Synthesis of Ultra‐Highly Concentrated Silver Nanoparticles and Their Catalytic Properties

A simple and fast synthetic route to ultra‐highly concentrated silver nanoparticles with long‐term stability by reducing AgNO₃ with ascorbic acid in the presence of polyethyleneimine (PEI) as a stabilizer in an aqueous phase is reported. The concentration of silver precursor was as high as 2000 mm (200 g of Ag nanoparticle per liter of water) and the reaction time was less than 10 min. The resulting silver nanoparticles show long‐term stability after two months of storage at room temperature without any signs of particle aggregation or precipitation in an aqueous phase. The successful ligand exchange of PEI‐stabilized silver nanoparticles to polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) without particle aggregation is also demonstrated. In addition, the catalytic activities of silver nanoparticles stabilized by various stabilizers prepared by the ligand exchange method was investigated. The PEI‐stabilized silver nanoparticles exhibited a higher stability than those of PEG‐ and PVP‐stabilized silver nanoparticles in the diffusion‐controlled catalytic reduction of 4‐nitrophenol to 4‐aminophenol by NaBH₄.     

Electrospinning fabrication and characterization of poly(vinyl alcohol)/montmorillonite/silver hybrid nanofibers for antibacterial applications

Poly(vinyl alcohol) (PVA)/montmorillonite clay (MMT)/silver (Ag) nanoparticles have been electrospun for fabricating PVA/MMT/Ag nanofiber in aqueous solutions. Since PVA is a water-soluble and biocompatible polymer, it is one of the best materials for preparation of antibacterial nanofiber. MMT has been used as an inorganic filler to enhance properties of homopolymeric nanofiber. The PVA/MMT/Ag nanofiber diameter increases with increasing contents of MMT clay and Ag nanoparticles. In preservation test, the PVA/MMT/Ag nanofiber confirms an excellent antibacterial performance, elucidating for practical uses as a new preservative. Moreover, the PVA/MMT/Ag nanofiber shows improved thermal properties.     

Synthesis of Ultrastable Ag Nanoplates/Polyethylenimine–Reduced Graphene Oxide and Its Application as a Versatile Electrochemical Sensor

Investigations on Ag nanostructures/reduced graphene oxide composites have been frequently reported, yet the morphology control of those loaded Ag nanocrystals is still challenging. We herein develop a facile method to grow triangular Ag nanoplates (AgP) on polyethylenimine‐modified reduced graphene oxide (AgP/PEI‐rGO). The AgP/PEI‐rGO hybrids show unexpected high stability against chloride ions (Cl^?) and hydrogen peroxide (H₂O₂), which is possibly due to the strong interaction between surface Ag atoms with the amine groups of PEI. In the chronoamperometry measurements for detecting H₂O₂, N₂H₄, and NaNO₂, the AgP/PEI‐rGO hybrid shows very wide linear ranges (usually 10^?6–10^?2 mol L^?1 for H₂O₂, N₂H₄, and NaNO₂) and low detection limits (down to ≈1×10^?7 mol L^?1), which demonstrate the promising electrochemical sensor applications of these metal/graphene hybrids with well‐defined morphologies and facets. In addition, this strategy could be extended to the deposition of other noble metals on rGO with controlled morphologies.     

Metal nanocomposite films prepared in situ from PVA and silver nitrate. Study of the nanostructuration process and morphology as a function of the in situ routes

Cast‐hybrid films composed of polyvinyl alcohol (PVA) and silver nitrate were treated according to three different ways, thermal annealing, UV‐irradiation, and chemical reduction by a borohydride solution, to obtain PVA/silver nanocomposite films. The nanostructuration process was studied as a function of the treatment conditions, and discussed as a function of the mobility state of the polymer chains in the nanocomposite matrix during treatment. A homogeneous dispersion of crystalline silver nanoparticles was obtained by thermal annealing above T_g and below T_m and UV‐lamp irradiation below T_g. For these two treatments, the major processing parameters were the annealing temperature and time and the UV‐exposure time, respectively. For low‐conversion rate in Ag(0), the films evolved upon ageing at room temperature. Totally different morphology and Ag(0) conversion were achieved by chemical reduction in a borohydride solution. All the silver ions were reduced into Ag(0), and crystalline silver nanoparticles layers parallel to the film surface were observed after the treatment. This morphology was related to the high‐swollen state of the polymer matrix during treatment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2062–2071, 2008     

Synthesis of silver nanoparticles in an aqueous suspension of graphene oxide sheets and its antimicrobial activity

A solution-based approach to the synthesis of silver (Ag) nanoparticles by chemical reduction of AgNO(3) in a graphene oxide (GrO) suspension is demonstrated. X-ray diffraction and transmission electron microscopy indicate that the Ag nanoparticles, of size range 5-25nm, were decorated on the GrO sheets. The size and shape of the Ag nanoparticles are dependent on the concentration of the AgNO(3) solution. Antimicrobial activity of such hybrids materials is investigated against the Gram negative bacteria Escherichia coli and Pseudomonous aeruginosa. The bacterial growth kinetics was monitored in nutrient broth supplemented with the Ag nanoparticle-GrO suspension at different conditions. It was observed that P. aeruginosa is comparatively more sensitive to the Ag nanoparticle-GrO suspension.     

Ultrasonic green synthesis of silver nanoparticles mediated by Pectin: Characterization and evaluation of the cytotoxicity,antioxidant, and colorectal carcinoma properties

Regarding applicative, facile, green chemical research, a bio-inspired approach is being reported for the synthesis of Ag nanoparticles by pectin as a natural reducing and stabilizing agent without using any toxic and harmful reagent. The biosynthesized Pectin/Ag NPs were characterized by advanced physicochemical techniques like ultraviolet–visible (UV–Vis), Fourier Transformed Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HR-TEM), Energy Dispersive X-ray spectroscopy (EDX), and X-ray Diffraction (XRD) study. It has been established that pectin-stabilized silver nanoparticles have a spherical shape with a mean diameter from 15 to 20 nm. After that, the biological performance of those biomolecules functionalized Ag NPs was investigated. In the MTT assay, human colorectal carcinoma (HCT-8 [HRT-18], Ramos.2G6.4C10, HT-29, and HCT 116) and normal cell lines (HUVEC) were used to study the cytotoxicity and anticancer potential of human colorectal over the AgNO₃ and Pectin/Ag NPs. The cell viability of Pectin/Ag NPs was very low against human colorectal carcinoma cell lines without any cytotoxicity on the normal (HUVEC) cell line. The best anti-human colorectal carcinoma properties of Pectin/Ag NPs against the above cell lines was in the case of the HCT 116 cell line. The antioxidant properties of the AgNO₃ and Pectin/Ag NPs were calculated against DPPH free radicals. The IC50 of Pectin/Ag NPs was 167 µg/mL. According to the above results, the Pectin/Ag NPs may be administrated to treat human colorectal carcinoma in humans.     

Preparation and characterization of Ag‐deposited aminosilane‐modified silicate by chemical reduction method

Nanocomposites based on silver (Ag) and organically modified silicate (Ormosil) were prepared by an in situ reduction method, in which silver nitrate, tetraethoxysilane and N‐[3‐(trimethoxysilyl)propyl]diethylenetriamine (ATS) acted as precursor, linker, and colloidal suspension stabilizer, respectively. The objective of the study was to produce silver nanoparticles through AgNO₃ chemical reduction in a continuous media, in which aminosilanes act as superficial modifiers of Ag nanoparticles, inhibiting their growth and preventing aggregation. The physical properties of the Ormosil/Ag composites were examined using NMR, electron spin resonance, scanning electron microscope, transmission electron microscope, and thermal gravimetric analysis spectroscopy, the results of which indicated that Ag was incorporated in the Ormosil matrix after impregnation. The Ag content and surface morphology of the Ormosil/Ag composites depended on the initial concentration of AgNO₃. The antibacterial effects of the Ormosil/Ag composites were assessed by the zone of inhibition and plate‐counting methods, and an excellent antibacterial performance was discovered. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Antiproliferative Homoleptic and Heteroleptic Phosphino Silver(I) Complexes: Effect of Ligand Combination on Their Biological Mechanism of Action

A series of neutral mixed-ligand [HB(pz)₃]Ag(PR₃) silver(I) complexes (PR₃ = tertiary phosphine, [HB(pz)₃]⁻ = tris(pyrazolyl)borate anion), and the corresponding homoleptic [Ag(PR₃)₄]BF₄ compounds have been synthesized and fully characterized. Silver compounds were screened for their antiproliferative activities against a wide panel of human cancer cells derived from solid tumors and endowed with different platinum drug sensitivity. Mixed-ligand complexes were generally more effective than the corresponding homoleptic derivatives, but the most active compounds were [HB(pz)₃]Ag(PPh₃) (5) and [Ag(PPh₃)₄]BF₄ (10), both comprising the lipophilic PPh₃ phosphine ligand. Detailed mechanistic studies revealed that both homoleptic and heteroleptic silver complexes strongly and selectively inhibit the selenoenzyme thioredoxin reductase both as isolated enzyme and in human ovarian cancer cells (half inhibition concentration values in the nanomolar range) causing the disruption of cellular thiol-redox homeostasis, and leading to apoptotic cell death. Moreover, for heteroleptic Ag(I) derivatives, an additional ability to damage nuclear DNA has been detected. These results confirm the importance of the type of silver ion coordinating ligands in affecting the biological behavior of the overall corresponding silver complexes, besides in terms of hydrophilic–lipophilic balance, also in terms of biological mechanism of action, such as interaction with DNA and/or thioredoxin reductase.     

Electrospun PVA Nanofibrous Membranes Reinforced with Silver Nanoparticles Impregnated Cellulosic Fibers: Morphology and Antibacterial Property

To enhance the mechanical and antibacterial properties of silver nanoparticle impregnated cellulosic fibers, carboxy-cellulose nanocrystals(CCNs) were grafted with chitooligosaccharide(COS), which was used as a stabilizer for silver nanoparticles (AgNPs). Nanofibrous membranes reinforced with silver nanoparticle impregnated cellulosic fibers(CCN-COS-AgNP) were prepared via electrospinning using polyvinyl alcohol(PVA) as a matrix. The effects of CCN-COS-AgNP contents on the morphology, surface composition, mechanical properties, and antibacterial performances of the prepared CCN-COS-AgNP/PVA membranes were examined. The addition of CCN-COS-AgNP certainly improved the mechanical properties and antibacterial performances of the PVA nanofibers. The tensile strength was significantly increased from 4.40 MPa to 8.60 MPa when 8% CCN-COS-AgNP(mass ratio) was introduced. When 10%(mass ratio) CCN-COS-AgNP was added, the nanofibers showed an excellent antibacterial activity for S. aureus(Staphylococcus aureus) and E. coli(Escherichia coli), with the maximum inhibition zones of 2.30 and 1.60 cm, respectively. Moreover, the 2%(mass ratio) CCN-COS-AgNP/PVA fibrous membrane showed 126% cell viability for mg63 human osteoblasts. The electrospun PVA membrane has great potential application in biomedical field.     

Structure and morphology controllable synthesis of Ag/carbon hybrid with ionic liquid as soft-template and their catalytic properties

Ag/carbon hybrids were fabricated by the redox of glucose and silver nitrate (AgNO₃) in the presence of imidazolium ionic liquid ([C₁₄mim]BF₄) under hydrothermal condition. Monodisperse carbon hollow sub-microspheres encapsulating Ag nanoparticles and Ag/carbon cables were selectively prepared by varying the concentration of ionic liquid. Other reaction parameters, such as reaction temperature, reaction time and the mole ratio of silver nitrate to glucose, play important roles in controlling the structures of the products. The products were characterized by XRD, TEM (HRTEM), SEM, energy-dispersive X-ray spectroscopy (EDX), FTIR spectroscopy and a Raman spectrometer. The possible formation mechanism was proposed. The catalytic property of the hybrid in the oxidation of 1-butanol by H₂O₂ was also investigated.     

Polyethyleneimine-capped silver nanoclusters as a fluorescence probe for sensitive detection of hydrogen peroxide and glucose

In this work, we utilized polyethyleneimine-capped silver nanoclusters (PEI-Ag nanoclusters) to develop a new fluorometric method for the determination of hydrogen peroxide and glucose with high sensitivity. The PEI-Ag nanoclusters have an average size of 2 nm and show a blue emission at 455 nm. The photostable properties of the PEI-Ag nanoclusters were examined. The fluorescence of the PEI-Ag nanoclusters could be particularly quenched by H₂O₂. The oxidization of glucose by glucose oxidase coupled with the fluorescence quenching of PEI-Ag nanoclusters by H₂O₂ can be used to detect glucose. Under optimum conditions, the fluorescence intensity quenched linearly in the range of 500 nM–100 μM with high sensitivity. The detection limit for H₂O₂ was 400 nM. And a linear correlation was established between fluorescence intensity (F₀ − F) and concentration of glucose in the range of 1.0 × 10⁻⁶ to 1.0 × 10⁻⁵ M and 1.0 × 10⁻⁵ to 1.0 × 10⁻³ M with a detection limit of 8.0 × 10⁻⁷ M. The method was used for the detection of glucose in human serum samples with satisfactory results. Furthermore, the mechanism of sensitive fluorescence quenching response of Ag nanoclusters to glucose and H₂O₂ has been discussed.     

Textile with silver silica spheres: its antimicrobial activity against <Emphasis Type="Italic">Escherichia coli and Staphylococcus aureus</Emphasis>

The aim of this study was to investigate antimicrobial activity of textiles doped with silver in different forms. Three types of textiles were prepared and examined: textiles doped with commercially available Ag nanoparticles, textiles doped with commercial colloidal silver and textiles doped with silver silica SiO₂/Ag spheres. The specimens of silica submicron spheres were synthesized by the sol–gel method as a matrix for biological active silver. The results of microbiological tests revealed that among three kinds of Ag doped textiles only these doped with SiO₂/Ag spheres are bacteriostatically active. During the experiments minimal inhibiting bacteria growth concentration of active SiO₂/Ag spheres added to textiles was determined.     

Preparation and characterization of activated carbon fibers supported with silver metal for antibacterial behavior

In this work, the effect of immersion in silver nitrate solution on activated carbon fibers (ACFs) was investigated in relation to adsorption behavior and antibacterial activity of ACFs supported with silver (ACF/Ag). The pore and surface properties were studied in terms of BET volumetric measurement with nitrogen adsorption, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The antibacterial activities of ACF/Ag were studied in broth dilution tests against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) from a point of view of water purification. As an experimental result, the silver content of ACF/Ag increased with increasing concentration of silver nitrate. It was found that the micropore structure slightly decreased as the silver nitrate concentration increased. Otherwise, it was revealed that the ACF/Ag possessed a strong antibacterial activity and an inhibitory effect for the growing of E. coli and S. aureus, respectively. Silver content on ACF/Ag decreased rapidly because of rough morphology of silver particles in water erosion.     

Transport properties of PVA/PEI/PEG composite membranes: sorption and permeation characterizations

Poly(vinylalcohol)/poly(ethyleneglycol)/poly(ethyleneimine) blend membranes were prepared by solution casting followed by solvent evaporation. The chemical structure of the prepared membranes was analyzed by FTIR and DSC. The sorption behavior as well as the permeabilities of the membranes for pure CO₂ and N₂ were investigated. The results show that the PVA/PEI/PEG membranes possess a higher permeability of CO₂ and a lower permeability of N₂. The membrane displays a CO₂ permeability of 27 Barrer, and a N₂ permeability of 3 Barrer at 25°C and 1 bar. CO₂ sorption behavior of the composite membrane, which can be classified as a dual-mode sorption model, and N₂ sorption behavior of the copolymeric membrane is in agreement with the Fickian diffusion model.