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     

In vitro anticancer activity and comparative green synthesis of ZnO/Ag nanoparticles by moringa oleifera,mentha piperita,and citrus lemon

This study proposes a simple, effective, and environmentally friendly approach for the synthesis of zinc oxide/silver nanoparticles (ZnO/Ag NPs) using three different plant extracts. The plants used in this study were moringa oleifera (MO), mentha piperita (MP), and citrus lemon (CL). Characterizations of ZnO/Ag NPs were done using ultraviolet–visible spectroscopy (UV vis), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) along with energy dispersive spectroscopy (EDX), and fourier transform infrared spectroscopy (FTIR). In accordance with size distribution findings, ZnO/Ag NPs synthesized with MO have a narrow size distribution, with the average particle size being 119 ± 36 nm. Among these three reducing agent MO act as the best reducing agent. Moreover, the anticancer activity of silver nanoparticles (Ag NPs), zinc oxide nanoparticles (ZnO NPs) and ZnO/Ag NPs synthesized with MO were demonstrated in human cervical cancer cells (HeLA). The results revealed that ZnO/Ag NPs demonstrate in vitro cell viability of 72%, 81%, and 84% using 2.5, 5, and 10 μgml^?1of ZnO/Ag NPs for 24 h. While Ag NPs and ZnO NPs prepared with MO showed 50% and 60% cell viability using 2.5 μgml^?1concentration for 24 h. This showed that the ZnO/Ag NPs act as a strong anticancer agent compared to Ag NPs and ZnO NPs. Overall, this research proposes a green synthesis approach for ZnO/Ag NPs with a wide range of potential uses, particularly in biomedicine.     

Lithium insertion in ultra-thin nanobelts of Ag2V4O11/Ag

In this study, ultra-thin nanobelts of Ag₂V₄O₁₁/Ag were successfully synthesized. The synthesized ultra-thin nanobelts of Ag₂V₄O₁₁/Ag are highly crystalline and the thickness is found to be about 5 nm. A lithium battery using ultra-thin nanobelts of Ag₂V₄O₁₁/Ag as the active materials of the positive electrode exhibits a high initial discharge capacity of 276 mAh g⁻¹, corresponding to the formation of Li_xAg₂V₄O₁₁ (x = 6). With increased cycling, the electrode made of ultra-thin nanobelts of Ag₂V₄O₁₁/Ag tends to loose electrochemical activity due to Ag⁺ ions in the ultra-thin nanobelts of Ag₂V₄O₁₁ were reduced and new phase was formed.     

Dual Z-scheme heterojunction g-C3N4/Ag3PO4/AgBr photocatalyst with enhanced visible-light photocatalytic activity

Recently, there has been a significant interest in developing high-performance photocatalysts for removing organic pollutants from water environment. Herein, a ternary graphitic C₃N₄ (g-C₃N₄)/Ag₃PO₄/AgBr composite photocatalyst is synthesized using an in-situ precipitation-anion-exchange process and characterized by several spectroscopic and microscopic techniques. During the photocatalytic reaction, X-ray photoelectron spectroscopy clearly illustrated the formation of metallic Ag on the g-C₃N₄/Ag₃PO₄/AgBr composite surface. The ternary composite photocatalyst demonstrated an increased photoactivity under visible light (>420 nm), achieving a complete decolorization of methyl orange (MO) in 5 min. The ternary g-C₃N₄/Ag₃PO₄/AgBr hybrid was also applied to the 2-chlorophenol degradation under visible light, further confirming its excellent photocatalytic activity. In addition, quenching experiments revealed that holes (h⁺) and O₂^?– were the major attack species in the decolorization of MO. The enhanced photoactivity of g-C₃N₄/Ag₃PO₄/AgBr results from the efficient transfer/separation of photoinduced charges with the dual Z-scheme pathway and the charge recombination sites on the formed Ag particles.     

Electrical and optical properties of Al-doped ZnO and ZnAl2O4 films prepared by atomic layer deposition

ZnO/Al₂O₃ multilayers were prepared by alternating atomic layer deposition (ALD) at 150°C using diethylzinc, trimethylaluminum, and water. The growth process, crystallinity, and electrical and optical properties of the multilayers were studied with a variety of the cycle ratios of ZnO and Al₂O₃ sublayers. Transparent conductive Al-doped ZnO films were prepared with the minimum resistivity of 2.4 × 10⁻³ Ω·cm at a low Al doping concentration of 2.26%. Photoluminescence spectroscopy in conjunction with X-ray diffraction analysis revealed that the thickness of ZnO sublayers plays an important role on the priority for selective crystallization of ZnAl₂O₄ and ZnO phases during high-temperature annealing ZnO/Al₂O₃ multilayers. It was found that pure ZnAl₂O₄ film was synthesized by annealing the specific composite film containing alternative monocycle of ZnO and Al₂O₃ sublayers, which could only be deposited precisely by utilizing ALD technology.     

Silver Cluster Interactions with Tyrosine: Towards Amino Acid Detection

Tyrosine (Tyr) is involved in the synthesis of neurotransmitters, catecholamines, thyroid hormones, etc. Multiple pathologies are associated with impaired Tyr metabolism. Silver nanoclusters (Ag NCs) can be applied for colorimetric, fluorescent, and surface-enhanced Raman spectroscopy (SERS) detection of Tyr. However, one should understand the theoretical basics of interactions between Tyr and Ag NCs. Thereby, we calculated the binding energy (E_b) between Tyr and Ag_n^q (n = 1–8; q = 0–2) NCs using the density functional theory (DFT) to find the most stable complexes. Since Ag NCs are synthesized on Tyr in an aqueous solution at pH 12.5, we studied Tyr⁻¹, semiquinone (SemiQ⁻¹), and Tyr⁻². Ag₃²⁺ and Ag₅⁺ had the highest E_b. The absorption spectrum of Tyr⁻² significantly red-shifts with the attachment of Ag₃²⁺, which is prospective for colorimetric Tyr detection. Ag₃²⁺ interacts with all functional groups of SemiQ⁻¹ (phenolate, amino group, and carboxylate), which makes detection of Tyr possible due to band emergence at 1324 cm⁻¹ in the vibrational spectrum. The ground state charge transfer between Ag and carboxylate determines the band emergence at 1661 cm⁻¹ in the Raman spectrum of the SemiQ⁻¹–Ag₃²⁺ complex. Thus, the prospects of Tyr detection using silver nanoclusters were demonstrated.     

Fabrication and NO2 gas sensing performance of TeO2-core/CuO-shell heterostructure nanorod sensors

TeO₂-nanostructured sensors are seldom reported compared to other metal oxide semiconductor materials such as ZnO, In₂O₃, TiO₂, Ga₂O₃, etc. TeO₂/CuO core-shell nanorods were fabricated by thermal evaporation of Te powder followed by sputter deposition of CuO. Scanning electron microscopy and X-ray diffraction showed that each nanorod consisted of a single crystal TeO₂ core and a polycrystalline CuO shell with a thickness of approximately 7 nm. The TeO₂/CuO core-shell one-dimensional (1D) nanostructures exhibited a bamboo leaf-like morphology. The core-shell nanorods were 100 to 300 nm in diameter and up to 30 μm in length. The multiple networked TeO₂/CuO core-shell nanorod sensor showed responses of 142% to 425% to 0.5- to 10-ppm NO₂ at 150°C. These responses were stronger than or comparable to those of many other metal oxide nanostructures, suggesting that TeO₂ is also a promising sensor material. The responses of the core-shell nanorods were 1.2 to 2.1 times higher than those of pristine TeO₂ nanorods over the same NO₂ concentration range. The underlying mechanism for the enhanced NO₂ sensing properties of the core-shell nanorod sensor can be explained by the potential barrier-controlled carrier transport mechanism.

PACS

61.46. + w; 07.07.Df; 73.22.-f     

Synthesis and characterization of LiMn2O4/Ag composite by citrate gel and combustion method

The powder of LiMn₂O₄/Ag composite was prepared by citrate gel and combustion technique using lithium acetate, manganese acetate and silver nitrate as starting materials. Phase identification, surface morphology and electrochemical properties were studied by X-ray diffraction, scanning electron microscopy, galvanostatic charge–discharge experiments, and electrochemical impedance spectroscopy. The results show that the powder is the composite of LiMn₂O₄ and Ag metal, and silver disperses homogeneously in LiMn₂O₄ particles. Compared with LiMn₂O₄, LiMn₂O₄/Ag composite has higher specific capacity, higher columbic efficiency and lower polarization. The additive of Ag improves the cycleability of LiMn₂O₄ powders, especially at higher charge–discharge rate.     

Bimetallic Zn/Ag doped polyurethane spider net composite nanofibers: A novel multipurpose electrospun mat

The objective of this study was to develop a new class of bimetallic ZnO/Ag embedded polyurethane multi-functional nanocomposite by a straightforward approach. Bimetallic nanomaterials, composed of two unlike metal elements, are of greater interest than the monometallic materials because of their improved characteristics. In the present study the bimetallic composite was prepared using sol–gel via the facile electrospinning technique. The utilized sol–gel was composed of zinc oxide, silver and poly(urethane). The physicochemical properties of as-spun composite mats were determined by X-ray diffraction pattern, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. The antibacterial activity was tested using Escherichia coli as model organism. The antibacterial test showed that ZnO:Ag/polyurethane composite possesses superior antimicrobial activity than pristine PU and ZnO/PU hybrids. Furthermore, our results illustrate that the synergistic effect of ZnO and Ag resulted in the advanced antimicrobial action of bimetallic ZnO/Ag composite mat. The viability and proliferation properties of NIH 3T3 mouse fibroblast cells on the ZnO:Ag/polyurethane composite nanofibers were analyzed by in vitro cell compatibility test. Our results indicated the non-cytotoxic behavior of bimetallic ZnO:Ag/polyurethane nanofibers towards the fibroblast cell culture. In summary, novel ZnO:Ag/polyurethane composite nanofibers which possess large surface to volume ratio with excellent antimicrobial activity were fabricated. The unique combination of ZnO and Ag nanoparticles displayed potent bactericidal effect due to a synergism. Hence the electrospun bimetallic composite indicates the huge potential in water filtration, clinical and biomedical applications.     

Decomposition of ozone on Ag/SiO2 catalyst for abatement of waste gases emissions

A silica-supported Ag system made by the incipient wetness impregnation method was investigated in the reaction of heterogeneous catalytic decomposition of ozone. It was established that the catalytic ozone decomposition on Ag/SiO₂ proceeded in the temperature interval −40 °C to 25 °C as a first order reaction with activation energy of 65 kJ/mol (pre-exponential factor 5.0 × 10¹⁴ s⁻¹). Based on the results from the instrumental methods (SEM, XRD, XPS, EPR, TPD) it can be concluded that in presence of ozone the silver is oxidized to a complicated mixture of Ag₂O₃ and AgO. Due to the high activity and stability of the Ag/SiO₂ catalyst, it is promising for neutralization of waste gases containing ozone.     

Microplasma illumination enhancement of vertically aligned conducting ultrananocrystalline diamond nanorods

Vertically aligned conducting ultrananocrystalline diamond (UNCD) nanorods are fabricated using the reactive ion etching method incorporated with nanodiamond particles as mask. High electrical conductivity of 275 Ω·cm⁻¹ is obtained for UNCD nanorods. The microplasma cavities using UNCD nanorods as cathode show enhanced plasma illumination characteristics of low threshold field of 0.21 V/μm with plasma current density of 7.06 mA/cm² at an applied field of 0.35 V/μm. Such superior electrical properties of UNCD nanorods with high aspect ratio potentially make a significant impact on the diamond-based microplasma display technology.     

Highly sensitive C2H2 gas sensor based on Ag modified ZnO nanorods

The sliver (Ag) modified zinc oxide (ZnO) nanorods were successfully obtained with a simplified and environmentally friendly solvothermal method. Materials characterization indicated that the metallic Ag was located on the outside of ZnO nanorods after annealing. In comparison with ZnO nanorods, Ag modified ZnO (Ag–ZnO) nanorods exhibited a considerably enhanced response to C₂H₂. The response of the 3 at% Ag–ZnO based sensor operating at 175 °C is 539 (R_a/R_g), which is the highest value among all the sensors in detecting 100 ppm C₂H₂. The Ag–ZnO based sensors exhibited fast response speed, lower operation temperature and higher selectivity.     

Antibacterial and photocatalytic properties of Ag/TiO2/ZnO nano-flowers prepared by facile one-pot hydrothermal process

In this paper, a simple and efficient strategy of one-pot synthesis of Ag doped TiO₂/ZnO photocatalyst was developed using hydrothermal process. Simultaneous crystallization of Ag and ZnO crystals from their precursor solution containing P25 (TiO₂) NPs could form effectively bonded Ag/TiO₂/ZnO composite photocatalyst during hydrothermal treatment. Several analytical techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), FT-IR spectroscopy, and photoluminescence spectroscopy have been used to characterize the resulting Ag/TiO₂/ZnO photocatalyst. Results showed that ZnO nano-flowers doped with TiO₂ and Ag NPs were formed by this simple facile one-step process. The unique properties of Ag NPs on binary semiconductor composite not only provide the decreased rate of electron–hole separation but also prevent from the loss of photocatalyst during recovery due to the fixed attachment of Ag and TiO₂ NPs on the surface of flower shaped large ZnO particles. Therefore, as-synthesized composite is an economically and environmentally friendly photocatalyst.     

One-pot hydrothermal synthesis of Mn3O4 nanorods grown on Ni foam for high performance supercapacitor applications

Mn₃O₄/Ni foam composites were synthesized by a one-step hydrothermal method in an aqueous solution containing only Mn(NO₃)₂ and C₆H₁₂N₄. It was found that Mn₃O₄ nanorods with lengths of 2 to 3 μm and diameters of 100 nm distributed on Ni foam homogeneously. Detailed reaction time-dependent morphological and component evolution was studied to understand the growth process of Mn₃O₄ nanorods. As cathode material for supercapacitors, Mn₃O₄ nanorods/composite exhibited superior supercapacitor performances with high specific capacitance (263 F · g^-1 at 1A · g^-1), which was more than 10 times higher than that of the Mn₃O₄/Ni plate. The enhanced supercapacitor performance was due to the porous architecture of the Ni foam which provides fast ion and electron transfer, large reaction surface area, and good conductivity.     

Preparation and characterization of Ag/MnOx/perovskite catalysts for CO oxidation

The spray decomposition method with lanthanum nitrate, manganese nitrate, silver nitrate and citric acid was used to synthesize Ag- and Mn-incorporated perovskites. The resulting samples were characterized by X-ray diffraction, BET adsorption measurement, X-ray photoelectron spectroscopy, and temperature-programmed oxygen desorption (O₂-TPD) measurement. The obtained composite Ag/MnO_x/perovskites catalysts exhibit higher activity by a few orders of magnitude at 338 K than that of LaMnO₃. From the O₂-TPD measurement, the high activity of the Ag/MnO_x/perovskites may result from the increase of weak oxygen adsorption below 373 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Role of vanadium ions,oxygen vacancies,and interstitial zinc in room temperature ferromagnetism on ZnO-V2O5 nanoparticles

In this work, we present the role of vanadium ions (V⁺⁵ and V⁺³), oxygen vacancies (V_O), and interstitial zinc (Zn_i) to the contribution of specific magnetization for a mixture of ZnO-V₂O₅ nanoparticles (NPs). Samples were obtained by mechanical milling of dry powders and ethanol-assisted milling for 1 h with a fixed atomic ratio V/Zn?=?5% at. For comparison, pure ZnO samples were also prepared. All samples exhibit a room temperature magnetization ranging from 1.18?×?10⁻³ to 3.5?×?10⁻³ emu/gr. Pure ZnO powders (1.34?×?10⁻³ emu/gr) milled with ethanol exhibit slight increase in magnetization attributed to formation of Zn_i, while dry milled ZnO powders exhibit a decrease of magnetization due to a reduction of V_O concentration. For the ZnO-V₂O₅ system, dry milled and thermally treated samples under reducing atmosphere exhibit a large paramagnetic component associated to the formation of V₂O₃ and secondary phases containing V⁺³ ions; at the same time, an increase of V_O is observed with an abrupt fall of magnetization to σ?~?0.7?×?10⁻³ emu/gr due to segregation of V oxides and formation of secondary phases. As mechanical milling is an aggressive synthesis method, high disorder is induced at the surface of the ZnO NPs, including V_O and Zn_i depending on the chemical environment. Thermal treatment restores partially structural order at the surface of the NPs, thus reducing the amount of Zn_i at the same time that V₂O₅ NPs segregate reducing the direct contact with the surface of ZnO NPs. Additional samples were milled for longer time up to 24 h to study the effect of milling on the magnetization; 1-h milled samples have the highest magnetizations. Structural characterization was carried out using X-ray diffraction and transmission electron microscopy. Identification of V_O and Zn_i was carried out with Raman spectra, and energy-dispersive X-ray spectroscopy was used to verify that V did not diffuse into ZnO NPs as well to quantify O/Zn ratios.     

Highly Efficient Room Temperature Synthesis of Silver‐Doped Zinc Oxide (ZnO:Ag) Nanoparticles: Structural,Optical, and Photocatalytic Properties

Synthesis of silver‐doped zinc oxide (ZnO:Ag) nanoparticles through precipitation method has been reported. The synthesis was conducted at room temperature and no subsequent thermal treatment was applied. ZnO nanoparticles were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), fourier transmission infrared spectroscopy (FTIR), and ultraviolet‐visible (UV–Vis) spectroscopy. Detailed crystallographic investigation was accomplished through Rietveld refinement. The effect of silver content on structural and optical properties of resultant ZnO nanoparticles has been reported. It was found that silver doping results in positional shifts for the XRD peaks and the absorption band edge of ZnO. These were attributed to the substitutional incorporation of Ag⁺ ions into Zn²⁺ sites within the ZnO crystal. In addition, higher silver incorporation resulted in smaller size for ZnO nanoparticles. The photocatalytic activity of the ZnO:Ag nanoparticles was also determined by methylene orange (MO) degradation studies and compared to that of undoped ZnO. Improved photocatalytic activity was obtained for ZnO:Ag nanoparticles. It has been shown that an optimum amount of silver dopant is required to obtain maximum photocatalytic activity.     

Green synthesis of Ag/ZnO nanohybrid using sodium alginate gelation method

Mesoporous Ag/ZnO nanohybrid material has been successfully synthesized using simple and green route via sodium alginate media. The as-synthetized nanomaterial was structurally characterized using various techniques such as X-ray powder diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA) and N₂ adsorption-desorption measurements (BET). The Ag/ZnO nanoparticles were quasi-spherical, crystalline with a size ranging from 40 to 50 nm. In addition, characterization results confirmed that calcined Ag/ZnO nanomaterial sample was stable and mainly consisting of both hexagonal ZnO and cubic silver nanoparticles.     

Vanadium pentoxide: Synthesis and characterization of nanorod and nanoparticle V2O5 using CTAB micelle solution

Using a surfactant-mediated method (surfactant based on cetyltrimethyl ammonium bromide, CTAB) V₂O₅ nanorod and nanoparticles have been successfully prepared. Morphologies of V₂O₅ nanostructures can be controlled by applying different precursors and by varying reaction conditions within the CTAB soft template. With ammonium metavanadate and sulfuric acid as precursors, nanoparticles are synthesized in the size range of 45–160 nm. Precursors of vanadyl sulfate hydrate and sodium hydroxide yield vanadium pentoxide nanorods with diameters of 30–90 nm and lengths of 260–600 nm. The resulting products are characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), variable pressure scanning electron microscopy (VPSEM) and X-ray photoelectron spectroscopy (XPS). Temperature programmed reduction (TPR) is included to test catalytic performance. The results show that V₂O₅ nanoparticles and nanorods achieve better catalytic performance compared to bulk V₂O₅, i.e. lower onset temperature, workability at lower temperatures, and higher H₂ consumption (μmol/g).     

Electrochemical window of molten LiCl-KCl-CaCl2 and the Ag/Ag reference electrode

The electrochemical window of an LiCl-KCl-CaCl₂ eutectic melt (52.3:11.6:36.1 mol%) was determined by cyclic voltammetry and open-circuit potentiometry at 723-873 K. The reaction at the anodic limit was confirmed to be Cl₂ gas evolution. The reaction at the cathodic limit was found to be a liquid Ca-Li alloy formation on the basis of ICP analysis of the deposits. An Ag⁺/Ag reference electrode separated with a Pyrex membrane showed good stability for more than 1 week. The standard electrode potential of Ag⁺/Ag was determined in the temperature range of 723-823 K by measuring the potential of a silver electrode in different concentrations of Ag⁺ ions.