Biosynthesis and stabilization of Au and Au–Ag alloy nanoparticles by fungus,Fusarium semitectum

Abstract

Crystallized and spherical-shaped Au and Au–Ag alloy nanoparticles have been synthesized and stabilized using a fungus, F . semitectum in an aqueous system. Aqueous solutions of chloroaurate ions for Au and chloroaurate and Ag⁺ ions (1 : 1 ratio) for Au–Ag alloy were treated with an extracellular filtrate of F . semitectum biomass for the formation of Au nanoparticles (AuNP) and Au–Ag alloy nanoparticles (Au–AgNP). Analysis of the feasibility of the biosynthesized nanoparticles and core–shell alloy nanoparticles from fungal strains is particularly significant. The resultant colloidal suspensions are highly stable for many weeks. The obtained Au and Au–Ag alloy nanoparticles were characterized by the surface plasmon resonance (SPR) peaks using a UV-vis spectrophotometer, and the structure, morphology and size were determined by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and transmission electron microscopy (TEM). Possible optoelectronics and medical applications of these nanoparticles are envisaged.     

Optical spectroscopy of arrays of Ag–Au nanoparticles obtained by vacuum-thermal evaporation

The possibility of creating irregular arrays of bimetallic Ag–Au nanoparticles is investigated. The ability to manipulate their optical properties based on the simple engineering processes of thermal spraying followed by low-temperature annealing is demonstrated.     

Theoretical study of the optical absorption behavior of Au/Ag core–shell nanoparticles

The dependence of linear optical response properties of bimetallic core–shell spherical nanoparticles is investigated as a function of size and relative composition. Two kinds of schematic models have been tested for describing the dielectric behavior of bimetallic particles and the related linear electromagnetic response: (i) Drude model, in conjunction with bulk dielectric data relative to the pure metals, in the assumption of a simple combination law; (ii) DFT-based approach to the dynamic polarizability of a binary particle, with the nature of the metals involved taken into account through their Wigner–Seitz radius.     

Preparation and plasmonic properties of polymer-based composites containing Ag–Au alloy nanoparticles produced by vapor phase co-deposition

Nanocomposite (NC) thin films with noble metal nanoparticles (NPs) embedded in a dielectric material show very attractive plasmonic properties due to dielectric and quantum confinement effects. For single component NPs, the plasmon resonance frequency can only be tuned in a narrow range. Much interest aroused in bimetallic NPs, however, many wet chemical approaches often lead to core shell particles, which exhibit multiple plasmon resonances or do not allow large variation of the NPs alloy composition and filling factor. Here, we report a vapor phase co-deposition method to produce polymer–metal NCs with embedded homogeneous Ag–Au alloy particles showing a single plasmon resonance. The method allows production of NPs with controlled alloy composition (x), metal filling (f), and nanostructure in a protecting Teflon AF matrix. The nanostructure size and shape were characterized by transmission electron microscope. Energy dispersive X-ray spectroscopy was used to determine x and f. The optical properties and the position of surface plasmon resonance were studied by UV–Vis spectroscopy. The plasmon resonance can be tuned over a large range of the visible spectrum associated with the change in x, f, and nanostructure. Changes upon annealing at 200 °C are also reported.     

Dynamic light scattering and UV–vis spectroscopy of gold nanoparticles solution

Gold nanoparticles solution prepared in water by laser ablation at 1064 nm of a gold metal plate was characterized by dynamic light scattering and UV–vis spectroscopy. Polarized dynamic scattering allows the measurement of translational diffusivity of Au nanoparticles, while depolarized scattering yields simultaneously the characterization of translational and rotational diffusivities. From these measurements the size and shape of Au nanoparticles are determined. Dynamic light scattering yields an average radius of 32 nm for the spherical nanoparticles in as prepared solution. The same measurements performed in an aged solution reveal the formation of ellipsoidal nanoparticles with minor and major semi-axis of 36 nm and 69 nm, respectively. The measured values allow to fit the UV–vis spectra with the Mie-Gans model and to measure the concentration of Au nanoparticles obtaining a complete characterization of their nanostructure. Dynamic light scattering results a powerful technique to characterize the size and shape of gold nanoparticles.     

Achieving excellent tunability of magnetic property and microwave absorption performance of FeZn-C core–shell nanoparticles by designing the Fe/Zn ratio

Composition design is vital for the excellent microwave absorption (MA) of core–shell nanoparticles (NPs). In this work, FeZn-C core–shell NPs were synthesized by metal organic chemical vapor deposition with the mixture of zinc (II) acetylacetonate and iron acetylacetonate as precursor. The Fe/Zn ratio of the nanocores could be facilely tuned by adjusting the Zn/Fe ratio in the mixture precursor, and their magnetic behavior could therefore be tuned from super-paramagnetic to ferromagnetic. The Fe/Zn ratio might change the resonance intensity and peak position of the nanoparticle absorbers, and thus be able to tune the attenuation property and improve the thickness matching, leading to double reflection loss peaks and broad effective bandwidth. The optimal reflection loss value of ?58.0 dB and effective bandwidth of 8.3 GHz have been achieved from the NP absorbers. These results demonstrated that the introducing of non-magnetic metal atom in C-coated core–shell ferromagnetic NPs endowed them with excellent tunability in magnetic and MA performance, and could also provide a bench for the design of other core–shell NPs.     

Green synthesis of bimetallic copper–silver nanoparticles and their application in catalytic and antibacterial activities

Clean Technologies and Environmental Policy - The present research is focused on the synthesis of copper–silver bimetallic nanoparticles using the extracts from the date palm tree (Phoenix...     

Effect of strain on the I–V characteristics of discontinuous silver films and determination of their gauge factor

Three films (A, B and C) of discontinuous silver films whose mass thicknesses (d _m ) are 6, 12 and 18 Å, respectively were deposited onto Corning 7059 glass substrates at ambient temperature using a thermal evaporation technique. The increase in dc resistance (R _dc ), in air, with time (time-ageing) was monitored till short-term stability was achieved. The effect of strain on the I–V characteristics of discontinuous silver films and determination of their gauge factor (v) was studied and it was found that; (1) a deviation from linearity is observed at higher voltages (>60 V) and at particular voltage, the electric current increases as d _m increases (2) R _dc increases as the tensional strain (?) increases and the dependence of fractional change of resistance on ε is linear with no hysteresis (3) v decreases as d _m increases and the high values of ν for these films candidates them to be miniature strain sensors. The data of this work are discussed on the ground that the thermally activated tunneling is the mechanism responsible for the electrical conduction in discontinuous silver films.     

Synthesis,characterization and bactericidal activity of silica/silver core–shell nanoparticles

Silica/silver core–shell nanoparticles (NPs) were synthesized by coating silver NPs on silica core particles (size ~300 ± 10 nm) via electro less reduction method. The core–shell NPs were characterized for their structural, morphological, compositional and optical behavior using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and UV–Visible spectroscopy, respectively. The size (16–35 nm) and loaded amount of silver NPs on the silica core were found to be dependent upon reaction time and activation method of silica. The bactericidal activity of the NPs was tested by broth micro dilution method against both Bacillus subtilis (gram positive) and Escherichia coli ATCC25922 (gram negative) bacterium. The bactericidal activity of silica/silver core–shell NPS is more against E. coli ATCC25922, when compared to B. subtilis. The minimal inhibitory concentration of the core–shell NPs ranged from 7.8 to 250 μg/mL and is found to be dependent upon the amount of silver on silica, the core. These results suggest that silica/silver core–shell NPs can be utilized as a strong substitutional candidate to control pathogenic bacterium, which are otherwise resistant to antibiotics, making them applicable in diverse medical devices.     

Synthesis of Au@CdS core–shell nanoparticles and their photocatalytic capacity researched by SERS

High-quality Au@CdS core–shell nanoparticles (CSNs) have been synthesized to improve photo-conversion efficiency in photocatalysis. They demonstrate higher photocatalytic activity in the experiment of photocatalytic degradation of rhodamine 6G (R6G) solution than that of CdS counterparts. Au@CdS CSNs can broaden the absorption range in visible region compared to CdS counterparts. The heterojunction interface between Au and CdS facilitates the separation of photo-generated electron–hole pairs, and transfers electrons from CdS region to Au core. The two advantages are crucial to improve the photocatalytic activity of Au@CdS CSNs. Charge transfer mechanism between metal and semiconductor is efficient that can be used to guide the design of photocatalysts, photovoltaics, and other optoelectronic devices to effectively utilize the solar power. In this paper, we research the photocatalytic process by surface-enhanced Raman scattering (SERS). The combination of photocatalysis and SERS not only can show the change in concentration of R6G solution, but also can provide the information of the change of R6G molecular structure in photocatalytic process.     

Synthesis of nanoparticles composed of silver and copper for metal–metal bonding

A metal–metal bonding technique is described that uses nanoparticles composed of silver and copper. Colloid solutions of nanoparticles with an Ag content of 0–100?mol% were prepared by simultaneous reduction of Ag⁺ and Cu²⁺ using hydrazine with polyvinylpyrrolidone and citric acid as stabilisers. The nanoparticles ranged in size from 34 to 149?nm depending on the Ag content. Copper discs were strongly bonded at 400°C for 5?min under 1.2?MPa pressure in hydrogen gas; the maximum shear strength was as high as 23.9?MPa. The dependence of shear strength on the Ag content was explained by a mismatch between the d-spacings of Cu metal and Ag metal.     

Characterization of Cu–Ni alloy electrodeposition and synthesis of nanoparticles by pulsed sonoelectrochemistry

Binary alloy Cu–Ni nanoparticles were synthesized by sonoelectrochemical technique from aqueous bath in presence of Na-citrate as complexing agent, to allow co-deposition of Cu and Ni. Alloy Pulsed Electro-Deposition (PED) was carried out to study nucleation kinetic and the effects of pH and surfactant on the final product physical and chemical properties, with the aim to determine optimized parameters for subsequent sonoelectrosyntheses of nanoparticles. Role of pH and Na-citrate in the synthesis process was investigated and it was found that i) pH is the main parameter affecting the stability of synthesis solutions, ii) Na-citrate content influences the sonoelectrochemical process efficiency but at the same time iii) the complexing agent is necessary to obtain Cu and Ni co-deposition; iv) produced nanoparticles are made of CuNi alloy with a fcc crystalline structure and v) pH is weakly responsible of increase in mean grain size of produced nanoparticles.     

Synthesis of Sn–Ag binary alloy powders by mechanical alloying

Sn–Ag binary powders of 2–5 wt%Ag were synthesized by mechanical alloying. Structural evolutions, morphologies, particle size distributions and melting points of the milled Sn–Ag powders were studied. The results show that the milled Sn–Ag powders consist of a supersaturated solid solution of Ag in Sn, Sn(Ag), and Ag₃Sn. During ball milling, Sn, Ag particles in the Sn–3.5Ag powders are deformed, overlapped and cold-welded together to form the Sn/Ag composite particles with a lamellar structure, and then the composite particles are fractured into small spherical particles. When increasing the Ag content from 2 to 5 wt%, the average particle sizes of the 60 h milled Sn–Ag powders are changed from 2.2 to 5.7 μm, and the morphologies of them are changed from spherical shape to irregular shape, respectively. It indicates that the cold-welding and agglomeration of the Sn–Ag powders increases with the Ag content during MA. The melting point of the 60 h milled Sn–3.5Ag powders was detected to be 224.23 °C, near to the eutectic point of the Sn–Ag binary system (221 °C).     

Microstructure of alumina ceramic/Ag–Cu–Ti brazing alloy/Kovar alloy joint

Abstract

The microstructure of the alumina ceramic/Kovar alloy joint brazed with Ag–35·2Cu–1·8Ti (wt-%) was studied. The effects of brazing temperature on the microstructure were also discussed. It was found that the microstructure of the joint brazed at 1173 K for 5 min was TiO + TiNi₃ + TiFe/eutectic Ag–Cu/TiFe₂ + TiNi₃/TiFe₂ + Cu (s.s) +Ag (s.s). When the brazing temperature was >1193 K, there was no TiO formed on the alumina ceramic/brazing alloy interface.     

Development and antibacterial performance of silver nanoparticles incorporated polydopamine–polyester-knitted fabric

Metallization is one of the finishing processes in textile treatment that can produce multifunctional effects. The present study dealt with the development of an antibacterial polyester-knitted fabric via facile and green impregnation of silver nanoparticles (SNPs). This was done by applying a polymeric foundation on the polyester-knitted fabric by simply dip-coating in the aqueous solution of dopamine. Then the SNPs were in situ fabricated and impregnated on the surface of polydopamine-modified polyester-knitted fabric in an aqueous solution of AgNO₃ at room temperature. Thus, a multi-functional finishing of polyester-knitted fabric was done. The Fourier transform infrared spectroscopy was done to confirm the polymer attachment. Scanning electron microscopy equipped with energy dispersive X-ray was done to confirm the presence of SNPs on treated fabric. The crystallography of the treated surface was examined by X-ray diffraction. The antibacterial properties of treated fabrics against broad spectrum bacterial strains were investigated and found significant.     

Rapid and green synthesis of bimetallic Au–Ag nanoparticles using an otherwise worthless weed Antigonon leptopus

We demonstrate a simple, straightforward, clean-green, single pot approach for the synthesis of bimetallic Ag/Au nanoparticles (BNPs) by using a highly invasive terrestrial weed coral vine (Antigonon leptopus). Aqueous extracts of the weed were found to reduce the metal ions to form nanosised aggregates and then stabilise them by preventing further aggregation. The efficacy of the extracts of all its parts was explored by varying the stoichiometry of reactants, temperature, pH and reaction time. The electron micrographs of the synthesised BNPs indicated the presence of particles of predominantly spherical shapes in sizes ranging from 10 to 60 nm. The presence of gold and silver atoms was confirmed from the energy dispersive X-ray, X-ray photoelectron and X-ray diffraction studies. The Fourier transform infra-red spectroscopic spectral study indicated that the phenolics (including flavonoids) and proteins contained in the plant extract could have been responsible for the formation and stabilisation of the BNPs.     

In-situ preparation of epoxy/silver nanocomposites by thermal decomposition of silver–imidazole complex

A novel method for the preparation of epoxy/silver nanocomposites was developed by in-situ formation of silver nanoparticles within the epoxy matrix. The silver–imidazole complex was synthesized by silver acetate and 2-ethyl-4-methylimidazole (2E4MZ). During the cure of epoxy resin, silver nanoparticles were in-situ generated through thermal decomposition of the silver–imidazole complex which was capable of reducing Ag⁺ to Ag⁰ by itself. The simultaneously released imidazole could cure the epoxy. In addition, the in-situ generated silver nanoparticles could be stabilized by the formed epoxy network. Therefore, by using the thermal decomposition method, uniformly dispersed silver nanoparticles of size of around 11.6 nm were in-situ generated in epoxy matrix.     

Ascorbic acid-mediated synthesis and characterisation of iron oxide/gold core–shell nanoparticles.

The current article reports on providing surface modification of magnetic nanoparticles with gold to provide stability against aggregation. Gold-coated magnetite nanoparticles were synthesised to combine both magnetic as well as surface plasma resonance (SPR) properties in a single moiety. The nanocomposites were produced by reduction (using ascorbic acid) of gold chloride on to the surface of iron oxide nanoparticles. Ascorbic acid not only acts as a reducing agent, but also the oxidised form of ascorbic acid i.e. Dehydro-ascorbic acid acts as a capping agent to impart stability to as synthesised gold-coated iron oxide nanocomposites. The synthesised nanocomposite was monodispersed with a mean particle size of around 16 nm and polydispersity index of 0.190. X-ray diffraction analysis confirms presence of gold on the surface of magnetite nanoparticles. The synthesised nanocomposites had a total organic content of around 3.2% w/w and also showed a shifted SPR peak at 546 nm as compared to gold nanoparticles (528 nm). Both uncoated and gold-coated magnetite exhibited superparamagnetic behaviour at room temperature. Upon coating with gold shell, saturation magnetisation of iron oxide nanoparticles decreases from 42.806 to 3.54 emu/gram.     

Enhancement of creep resistance and thermal behavior of eutectic Sn–Cu lead-free solder alloy by Ag and In-additions

The eutectic Sn–0.7Cu solder alloy is widely used in electronic packaging in which the creep property of the solder joint is essential to meet the global demand for longer operating lifetime in their applications. In this study, the influence of Ag and In additions on tensile creep behavior and thermal properties of bulk eutectic Sn–Cu solder alloy is reported. Results show that addition of Ag and In resulted not only in the formation of new Ag₃Sn and γ-SnIn₄ intermetallic compounds (IMCs), but also in the refinement of grain size of Sn–0.7Cu solder from ∼0.50 to ∼0.15 μm. Accordingly, the creep properties of the Ag or In-containing solder alloys are notably improved. The creep strain rate increases and creep lifetime decreases as the applied stress level and temperature increase. Room and elevated-temperature creep rate of bulk Sn–Cu solder was reduced by 521.0% after Ag addition, but for In addition the reduction was about 200.7%. These differences are attributed to the presence of new Ag₃Sn and γ-SnIn₄ precipitates and their rules in classical dispersion strengthening as a separate phases. Moreover, the eutectic temperature of Sn–0.7Cu is decreased from 227.4 to 217.8 and 224.0 °C with the addition of Ag and In, respectively.