Facile preparation of silver/reduced graphene oxide/chitosan colloid and application of the nanocomposite in antibacterial and catalytic activity

Reduced graphene oxide (RGO) decorated with silver nanoparticles (AgNPs) was synthesized by a facile solution‐based approach in chitosan (CS) solution. The morphology and elemental composition of as‐prepared Ag/RGO/CS colloid were characterized by SEM and energy dispersive X‐ray spectroscopy, respectively. TEM images show that most of the AgNPs are uniformly dispersed in the CS matrix while the other nanoparticles are decorated on the RGO nanosheets. XRD indicates that the interlayer distance of RGO is between 0.34 and 1.87 nm while the diameter of face‐centered cubic AgNPs is no more than 30 nm. Fourier transform infrared spectroscopy of the Ag/RGO/CS colloid confirms the formation of AgNPs and RGO. X‐ray photoelectron spectroscopy proves that both the Ag ? O bond and the C ? N bond exist in the nanocomposite. Antimicrobial assays were performed using the most common species of Gram bacteria. The inhibitory effect indicates that the incorporation of AgNPs and RGO significantly improves the antimicrobial activity of CS colloid. In addition, the nanocomposite colloid exhibits significant catalytic activity toward the reduction of 4‐nitrophenol by NaBH₄. © 2018 Society of Chemical Industry     

Fabrication of paper based carbon/graphene/ZnO aerogel composite decorated by polyaniline nanostructure: Investigation of electrochemical properties

The cellulose derived carbon/graphene/ZnO aerogel composite was prepared as an electrode in order to investigate the electrochemical properties. Carbon aerogel was synthesized using paper as an available cellulose source, and the composite was obtained through a new and simple preparation method including the immersion of monolithic carbon aerogel in graphene oxide/Zn²⁺ suspension and subsequent chemical reduction and freeze drying. The morphology, functional groups and crystalline structure of the samples were studied with Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction Spectroscopy (XRD), respectively. Electrochemical performance of the prepared binder free electrodes was examined using Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The data revealed that flexible carbon/graphene/ZnO composite resulted in a low density (0.035 g cm⁻³) electrode with the capacitance of 900 mF cm⁻² at a high current density of 10 mA cm⁻², lower IR drop and high cyclic stability (capacitance retention of 96%) after 1000 cycles, at 10 mA cm⁻². These features were due to the presence of 3D porous conductive network, highly reduced graphene oxide, and the formation of ZnO nanoparticles on graphene sheets. Moreover, polyaniline (PANI) was introduced to carbon/graphene/ZnO composite electrode using electro-oxidation method at different reaction time and aniline concentration in order to achieve remarkably improved capacitance of 2500 mF cm⁻² (at 10 mA cm⁻²) and low charge transfer resistance. Also, after the supercapacitor device assembly, the capacitance was retained. Based on the results, the synthesized composite is a promising material for new generation of lightweight freestanding electrodes with the high electrochemical performance.     

Comparative voltammetric behaviour of the silver/silver oxide electrode prepared on vitreous carbon and silver substrates

The voltammetric behaviour of vitreous carbon/chemically precipitated silver hydroxide layer and silver/electrochemically formed silver oxide layer electrodes are compared. As the former type of electrode is free from silver substrate contributions during the oxidation-reduction cycles (ORC) the voltammetric data indicate the occurrence of soluble Ag(I) species in the gel-like silver hydroxide matrix. Soluble species can be formed during the ORC as a consequence of AgOH formation at the early stages of the oxidation and reduction processes. Nucleation and growth of new phases produce a non-homogeneous layer structure and a decrease in the amount of active material participating in the ORC under preset conditions.     

Nanocomposite of chitosan and silver oxide and its antibacterial property

An aqueous emulsion of chitosan nanoparticles encapsulating silver oxide is prepared from silver nitrate and chitosan. The nanoparticles are positively charged with an average diameter of 300 nm. The dried particle has a spherical shape with a 100 nm diameter. The emulsion is applied onto cotton and delivers a durable antibacterial activity against S. aureus and E. coli, after 20 washings. The coefficient of friction of the treated fabric is similar to that of the untreated cotton fabric. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Electrochemical synthesis of silver oxide nanowires,microplatelets and application as SERS substrate precursors

We describe the electrochemical synthesis of silver oxide nanowires and nanowire bundles, filled platelets and hollow microplatelets in either basic or acidic N,N-dimethylformamide solution. We propose that these nanostructures are formed at the electrode surface via two competing reactions namely, silver dissolution off the electrode in the presence of NH₃ or HF during the anodization of silver, and silver oxide precipitation. Results show that the precipitated silver oxide nanoparticles aggregate into nanowires as well as into filled and hollow microscale platelets, depending upon the nuclei concentration and the anodization current density. X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and Raman scattering spectroscopy show that the nanowires and microplatelets are mainly composed of Ag₂O. Nanowire bundles are used as substrates for surface-enhanced Raman scattering (SERS) where single molecule detection is achieved and evidenced using a bianalyte Raman technique.     

Enhanced photoluminescence property and mechanism of Eu3+‐doped tellurite glasses by the silver and gold nanoparticles

In this work, the silver or gold nanoparticle single‐existing and co‐existing tellurite glasses doped with Eu³⁺ were prepared, and the influence of gold or silver nanoparticles on the photoluminescence of tellurite glasses doped with Eu³⁺ were investigated. The photoluminescence of tellurite glasses doped with Eu³⁺ was enhanced by the surface plasmon absorption of gold or silver nanoparticles, and the maximum luminescence enhancement factors caused by the silver and gold nanoparticles are 4.8 and 3.5 factors, respectively. The differentiation of luminescence enhancement mechanisms caused by the gold or silver nanoparticles was demonstrated. The enhanced luminescence mechanism of the Au nanoparticle single‐existing tellurite glasses doped with Eu³⁺ was from the increasing of radiative decays rate caused by the Au nanoparticles. The excitation field enhancement caused by the Ag nanoparticles was responsible for the luminescence enhancement of the Ag single‐existing tellurite glasses doped with Eu³⁺. About 4.2‐factor luminescence enhancement was observed in the Ag and Au nanoparticle co‐existing tellurite glasses doped with Eu³⁺, which is attributed to the increasing of radiative decays rate and excitation field enhancement caused by the Au and Ag nanoparticles.     

The effect of pulse-reverse electroplating bath temperature on the wear/corrosion response of Ni-Co/tungsten carbide nanocomposite coating during layer deposition

In this article, the effect of bath temperature during layer deposition on the electrochemical/abrasion responses of Ni-Co/tungsten carbide nanocomposite coating has been investigated. The Ni-Co/tungsten carbide nanocomposite coating was obtained using simultaneous deposition of tungsten carbide nanoparticles in three Ni-Co bath temperatures of 20, 40, and 60?°C. Afterwards, in order to characterize the obtained coatings, Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM), X-Ray diffraction (XRD), MAP analysis, potentiodynamic polarization and electrochemical impedance spectroscopy methods in 3.5?wt% NaCl, and also abrasion test using a pin on disc method were carried out. The results of this study revealed that the deposition obtained from Ni-Co bath contains tungsten carbide nanoparticles and results in strong (200) and hard (111) textures in the coating at different temperatures. Also increasing the bath temperature from 20 to 40?°C results in the absorption of cobalt and tungsten carbide nanoparticles, as well as reducing the nickel content and corrosion resistance in the coating, and on one hand it increases the abrasion resistance of the coating. However, a bath-temperature increase from 40 to 60?°C results in reducing the absorption of cobalt and tungsten carbide nanoparticles, and increasing the nickel content and corrosion resistance in the coating as well as reducing the abrasion resistance of the coating.     

Sintering behavior and effect of silver nanoparticles on the resistivity of electrically conductive adhesives composed of silver flakes

In this paper, silver nanoparticles with size of 30–50 nm were synthesized by reducing silver nitrate with sodium borohydride and sodium citrate and using PVP as an adsorption agent in the ethanol solution. The experimental results indicate that the morphologies and sintering behaviors of both kinds of silver nanoparticles are impacted by glutaric acid and sintering temperature. The electrically conductive adhesives (ECAs) filled with micro-sized silver flakes and silver nanoparticles as hybrid fillers were fabricated and the electrical properties were investigated based on the fraction of the silver nanoparticles of the total of silver flakes and the curing temperature, etc. The incorporation of the untreated/treated silver nanoparticles into the polymer matrix with 65?wt% silver filler the resistivity increased in almost all cases, especially the high fraction and the low curing temperature. The curing temperature has influence on the resistivity of the ECAs filled with micro-sized silver flakes and the silver nanoparticles due to the sintering of the silver nanoparticles. The addition of 10% treated silver nanoparticles into the ECAs with 60?wt% silver fillers, the resistivity is slightly lower than that of the ECAs with micro-sized silver flakes. In the system of the ECAs with the high loading of silver fillers, the untreated/treated silver nanoparticles have little effect on the electrical conductivity. The results suggest that the morphology and distribution of silver fillers are the key to affect the conductivity of ECAs when nanoparticles are included in the system.     

Shell-isolated nanoparticle-enhanced Raman spectroscopy of pyridine on smooth silver electrodes

The invention of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) extends the study of Raman spectroscopy into surface electrochemistry on the SERS-inactive smooth electrodes. This work aims to investigate the electrochemical system perturbation brought about by spreading Au–core silica–shell nanoparticles (Au@SiO₂ NPs) over the electrode surface for SHINERS. The differential capacitance measurements have shown SHINERS to cause the minimum of disturbance in the electrochemical system. The spectral features of SHINERS of pyridine adsorbed at smooth silver electrodes differs from that of SERS on the electrochemically roughened surface because pyridine interacts with silver much more strongly on the roughened electrode with many heterogeneous adsorption sites. Since most electrochemical data about surface adsorption are based on mechanically polished surface, the spectral information provided by the in situ SHINERS could be more reliable and better correlation.     

Electrochemical oxidation of glucose on silver nanoparticle-modified composite electrodes

Silver nanoparticle-modified composite electrodes were prepared by electroless forming silver nanoparticles in carbon black dispersed electroless silver plating solution, and then incorporating the silver nanoparticle/carbon black mixture in a polystyrene matrix. The electrooxidation of glucose in 0.1 M NaOH was studied by using cyclic voltammetry. The electrode has surface-confined nanoparicles showing effective catalytic behavior in the studies of glucose oxidation. It showed stepwise electrocatalytic oxidation behavior clearly without suppression by high background redox current caused by inner layer silver of disk-type silver electrodes. Initially the glucose was catalytically oxidized by AgO, and then the reaction glucose oxidation intermediates with Ag₂O were followed stepwisely. Based on the cyclic voltammetric results, pulsed amperometric detection parameters for flow injection analysis were optimized for sensitive detection of glucose.     

Reproduction of Jun‐red glazes with nano‐sized copper oxide

Nano sized copper oxide was firstly employed for producing Jun‐red glazes. A series of Jun‐red glazes were prepared by adjusting the copper oxide nanoparticle content and the valance state of elemental copper in the glaze matrix. The coloring and microstructure of each glaze was investigated by spectrophotometer, X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectrometer, and transmission electron microscope. Under reducing conditions, the red glaze color gradually darkens with increasing CuO content from 0.5 to 1.0 wt%. Interestingly, the coloring of the samples fired under reducing atmosphere turned to be green‐blue, when the content of nanosized CuO was increased to 1.5 wt%. We also found that increased CuO content increases the size of phase separation in the glazes. As comparison, the coloring of samples fired without nanosized CuO are slightly blue under reducing atmosphere, which is attributed to the structural color generated owing to the Rayleigh scattering. Red color of the Jun glazes may arise from elemental copper nanoparticles. The current research utilizing modern nanotechnology provides a new insight into both the “furnace transmutation” and “color regulating” of the ancient Jun‐red glazes.     

Influence of surface chemical structure of active carbon on its electrochemical behaviour in the presence of silver

Cyclic voltammetric studies of the influence of surface chemistry on the electrochemical behaviour of powdered active carbon electrodes were carried out in the presence of silver both in bulk solution and pre-adsorbed on carbon. Surfaces with a variety of chemical properties were obtained through the modification of carbon samples by heat treatment under vacuum, oxidation with concentrated nitric acid and annealing in an ammonia atmosphere. The surface area (BET), acid–base neutralization capacities and sorption capacity towards Ag+ ions were estimated in the samples obtained. The states and relative amounts of deposited Ag species were estimated using XPS. The influence of the surface chemistry of the powdered carbon material in terms of its electrochemical properties and the mechanism of silver adsorption and deposition is discussed.     

Effect of Supercritical Ethanol Drying on the Properties of Zinc Oxide Nanoparticles

The synthesis, characterization, and application as polymers and anti-wear additives of nanosized zinc oxide particles obtained by conventional and supercritical ethanol drying are reported in this study. The nanaoparticles of ZnO produced by the two different drying techniques were characterized using Fourier Transform Infrared (FT-IR) spectrophotometry, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Thermogravimetric analysis (TGA) to elucidate the shape, size, composition, and stability of the nanoparticles. ZnO nanoparticles were then applied to poly (vinyl chloride) (PVC) powder and light mineral oil to assess their effectiveness and suitability as additives in diverse areas. XRD analysis revealed ZnO crystalline structure with average particle size of 24.7 nm for zinc oxide nanoparticles prepared by supercritical ethanol drying while SEM showed well-isolated and monodisperse particles with average size of 61.08 nm.     

Si/VGCF复合材料的储锂性能

以纳米硅颗粒为原料,采用液相法制备了硅纳米粒子与气相生长碳纤维(VGCF)复合的材料(Si/VGCF)。考察了Si/VGCF制备工艺和VGCF的最佳含量,分别采用SEM和TEM表征了Si/VGCF材料形貌和晶体结构,测试和计算了材料电导、BET比表面积和孔尺寸数据。采用循环伏安、恒流充放电和交流阻抗等测试了Si/VGCF复合电极的电化学性能,并与其他碳材料进行了对比分析。结果表明,Si与VGCF形成了多级框架结构,丰富了离子和电子传输网络;同时发达的孔结构也缓解了Si粒子在嵌/脱锂过程中的体积效应,使电极活性材料的利用率和电化学稳定性显著提高。当m(Si)∶m(VGCF)为1:0.5时,Si/VGCF复合电极在500 mA/g的电流密度下,充放电循环100次后,可逆容量高达1470 mA·h/g。     

Surface activation of manganese oxide electrode for oxygen evolution from seawater

Utilizing the fact that the equilibrium potential of oxygen evolution is lower than that of chlorine evolution, oxygen evolution in seawater electrolysis was enhanced by decreasing the polarization potential under galvanostatic conditions through increasing the effective surface area of manganese oxide electrodes. Electrodes were prepared by a thermal decomposition method. IrO2-coated titanium (IrO2/Ti electrode) was used as the substrate on which manganese oxide was coated (MnOX/IrO2/Ti electrode). Subsequently, oxide mixtures of manganese and zinc were coated (MnOX–ZnO/MnOX/IrO2/Ti electrode). The effective surface area of the MnOX–ZnO/MnOX/IrO2/Ti electrodes was increased by selective dissolution of zinc (leaching) into hot 6M KOH. The oxygen evolution efficiency of the MnOX/IrO2/Ti electrode was 68–70%. Leaching of zinc from the MnOX–ZnO/MnOX/IrO2/Ti electrodes with 25mol% or less zinc led to a significant increase in the oxygen evolution efficiency. The maximum efficiency attained was 86% after leaching of zinc from the MnOX–25mol%ZnO/MnOX/IrO2/Ti electrode. However, large amounts of zinc addition, such as 40mol% or more are detrimental because of a decrease in the oxygen evolution efficiency. This is due to the formation of a double oxide, ZnMnO3, which is hardly dissolved in hot 6M KOH.     

Synthesis of antimicrobial silver nanoparticles on silk fibers via γ‐radiation

Antimicrobial silver nanoparticles (NPs) were successfully synthesized on the surface of silk fibers via γ‐ray irradiation. The products were characterized with scanning electron microscope (SEM), energy dispersion spectrum, and X‐ray diffraction. The results revealed that the silver particles with a diameter of less than 20 nm were immobilized and well dispersed on the surface of silk fibers. The antimicrobial capability against the gram positive bacterium Staphylococcus aureus and the washing stability of the silk fibers produced with different conditions were tested and found to be excellent. The silk fibers treated with 1 mM solution and 10 kGy γ‐radiation showed 96% antimicrobial activity and still kept above 85% antibacterial activity after 10 washing cycles. Moreover, a mechanism for the formation of silver NPs on silk fibers under γ‐radiation was generally discussed. The resulting silk fibers coated with silver NPs can be useful as functional fabrics in a range of applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Surface Modification of Graphene Oxide and Investigation of Its Effects on Surface Properties of Aramid Membranes

To manufacture aramid thin-film-composite membrane for desalination application (reverse osmosis) via in situ interfacial polymerization, the different weight percents of modified graphene oxide were applied into the aramid layer during interfacial polymerization. The dispersion of the modified graphene oxide was investigated by X-ray Diffraction (XRD) and Transition Electron Microscopy (TEM) methods. Also, the effect of the modified graphene oxide on the surface chemical composition and surface morphology of aramid membrane was investigated by Attenuated Total Reflectance-Infrared Spectroscopy (ATR-IR), scanning electron microscopy, and atomic force microscopy, respectively. The results showed that in the presence of the modified graphene oxide, the interfacial polymerization reaction is transferred between the nanoparticles so the depth of surface porosity is increased strongly. In addition, the hydrophilic value of aramid layer in the presence of the modified graphene oxide firstly increased up to 0.15 wt% but with an increase in the modified graphene oxide percent at 0.2 wt%, the surface hydrophilicity decreased gradually. As a result, the optimum hydrophilic and morphological properties were observed in samples containing 0.15 wt% of modified graphene oxide.     

Deposition of platinum on the outer surface of carbon-encapsulated silver nanoparticles

Investigations of the morphological and phase characteristics of silver nanoparticles encapsulated in amorphous carbon shell (Ag@C) during heating, acid treatment and galvanic replacement reactions were carried out. It was found that upon heating of Ag@C nanoparticles up to 800 °C the silver sublimes resulting in the formation of hollow carbon nanocapsules. Washing of Ag@C nanoparticles with nitric or hydrochloric acid solutions also leads to dissolution of encapsulated silver core and formation of hollow carbon nanocapsules. Electron microscopic investigations showed that, for short treatment times of Ag@C nanoparticles with a H₂PtCl₆ solution, nanoparticles of metallic platinum, several nanometers in diameter, are deposited on the outer surface of the carbon shells. With increasing treatment time or concentration of H₂PtCl₆ solution, increasing numbers of noble metal nanoparticles on the surface of the carbon shells, and almost complete dissolution of the metal core, were observed. This process opens broad possibilities for the design and direct preparation of modified by noble metal carbon-based nanomaterials of different compositions for a wide variety of practical applications.     

Fabrication and characterization of zinc oxide nanoparticle coated magnetic iron oxide: Effect of S-layers adsorption on surface of oxide

Mixed zinc oxide nanoparticle coated magnetic iron oxide has been prepared by a sol–gel and co-precipitation routes. Magnetic iron oxide nanoparticles were synthesized by co-precipitation of ferric and ferrous ions with ammonia, and then zinc oxide was coated onto the surface of magnetic iron oxide by hydrolysis of zinc precursors. As a result, zinc oxide coated magnetic iron oxide nanoparticles with an average size of 68 nm were obtained. The crystalline bacterial cell surface layer)S-layer (used in this study was isolated from Lactobacillus helveticus ATCC 12046. The S-layer was adsorbed onto the surface of zinc oxide nanoparticle coated magnetic iron oxide. The nanoparticles were analyzed by X-ray powder diffractometry (XRD), infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM) were used to characterize the structural and the chemical features of the nanocomposites. The infrared spectra indicate that the S-layer-nanoparticle interaction occurs. This novel nanoparticle showed admirable potential in adsorption of S-layers on the surface of oxides for drug delivery.     

Electrodeposition of macroporous silver films from ionic liquids and assessment of these films in the electrocatalytic reduction of nitrate

Macroporous silver films, ordered or fragmented, were fabricated by electrodeposition of silver into the interstitial spaces of templates formed by polystyrene (PS) latex spheres that had been self-assembled onto bare indium tin oxide (ITO) electrodes or onto gold-coated ITO (ITO/Au) electrodes (in which the electrode had been coated by gold sputtering deposition) from two room-temperature ionic liquids (ILs): N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP-TFSI) and N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA), respectively, under normal atmospheric conditions. After electrodeposition of silver, the PS spheres were removed by dissolution in tetrahydrofuran (THF) to leave a macroporous silver structure. The higher wettability of ILs onto PS spheres leads to improved penetration of the ILs into the cavities of the PS templates. Electrodeposition is easier if an electrolyte that has a good penetration into the interstitial spaces between the PS spheres. The macroporous silver electrode exhibited much better electrocatalytic performance with respect to nitrate reduction than a regular silver wire electrode. Quantitative determination of nitrate was also examined.