Facile preparation of Ag/ZnO nanoparticles via photoreduction

Ag/ZnO nanoparticles can be obtained via photocatalytic reduction of silver nitrate at ZnO nanorods when a solution of AgNO₃ and nanorods ZnO suspended in ethyleneglycol is exposed to daylight. The mean size of the deposited sphere like Ag particles is about 5 nm. However, some of the particles can be as large as 20 nm. The ZnO nanorods were pre-prepared by basic precipitation from zinc acetate di-hydrate in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. They are about 50–300 nm in length and 10–50 nm in width. Transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDS), X-ray powder diffraction (XRD), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) were used to characterize the resulting Ag/ZnO nanocomposites.     

Multiplexed dot immunoassay using Ag nanocubes,Au/Ag alloy nanoparticles,and Au/Ag nanocages

We report the first application of Ag nanocubes, Au/Ag alloy nanoparticles, and Au/Ag nanocages in a multiplexed dot immunoassay. The assay principle is based on the staining of analyte drops on a nitrocellulose membrane strip by using multicolor nanoparticles conjugated with biospecific probing molecules. Nanoparticles were prepared by a galvanic replacement reaction between the Ag atoms of silver nanocubes and Au ions of tetrachloroauric acid. Depending on the Ag/Au conversion ratio, the particle plasmon resonance was tuned from 450 to 700 nm and the suspension color changed from yellow to blue. The particles of yellow, red, and blue suspensions were functionalized with chicken, rat, and mouse immuno gamma globulin (IgG) molecular probes, respectively. The multiplex capability of the assay was illustrated by a proof-of-concept experiment involving simultaneous one-step determination of target molecules (rabbit anti-chicken, anti-rat, and anti-mouse antibodies) with a mixture of fabricated conjugates. Under naked eye examination, no cross-colored spots or nonspecific bioconjugate adsorption were observed, and the low detection limit was about 20 fmol.      

Efficient green photocatalyst of Ag/ZnO nanoparticles for methylene blue photodegradation

Journal of Materials Science: Materials in Electronics - Ag/ZnO nanoparticles photocatalysts with various Ag concentrations were synthesized through the hydrothermal treatment. The as-prepared...     

Synthesis,characterization, and voltammetric hydrogen peroxide sensing on novel monometallic (Ag,Co/MWCNT) and bimetallic (AgCo/MWCNT) alloy nanoparticles

Multiwall carbon nanotube supported (MWCNT) Ag, Co, and Ag-Co alloy nanocatalysts were synthesized at varying metal loadings by borohydride reduction methods without stabilizers to obtain enhanced hydrogen peroxide sensitivity. The resulting materials were characterized employing Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). For electrochemical measurements carried out cyclic voltammetry (CV) and differential pulse voltammetry (DPV), glassy carbon electrode (GCE) was modified with Ag/MWCNT, Co/MWCNT, and Ag-Co/MWCNT alloy nanoparticles. Ag-Co/MWCNT/GCE exhibited the highest performance toward electrochemical oxidation of H₂O₂ in 0.1 M phosphate buffered solution (PBS). Furthermore, the sensitivity and the limit of detection values for Ag-Co/MWCNT/GCE were obtained as 57.14 µA cm^?2 mM^?1and 0.74 µM, respectively. However, the sensitivity values for Ag/MWCNT/GCE, and Co/MWCNT/GCE are 41.66 and 13.88 µA cm^?2 mM^?1, respectively. The LOD values were predicted as 1.84 µM for Ag/MWCNT/GCE and 3.3 µM for Co/MWCNT/GCE.

In addition, the interference experiment indicated that the Ag-Co/MWCNT alloy nanoparticles have good selectivity toward H₂O₂.     

Magnetic, optical and structural studies on Ag doped ZnO nanoparticles

The influences of annealing effects have been explored on the crystallinity, morphology, optical and magnetic properties of Ag–ZnO nanostructures prepared by a simple sol–gel method. X-ray powder diffraction, scanning electron microscope, high resolution transmission electron microscope (HRTEM), vibrating sample magnetometer and photoluminescence spectroscopy (PL) have been used to characterize the crystal structures, surface morphology, magnetic and optical properties of the pure ZnO and Ag–ZnO nanostructures respectively. The synthesized Ag–ZnO nanostructures are found to have hexagonal wurtzite crystal structures and their grain size increases while lattice strain decreases on annealing. From HRTEM observation, it is found that the annealed samples show nanorod like structures with Ag nanoparticles (NPs) embedded on the surface. Due to annealing effect, Ag–ZnO shows higher saturation magnetization at room temperature.     

Influence of Ag thickness of aluminum-doped ZnO/Ag/aluminum-doped ZnO thin films

Highly conducting aluminum-doped ZnO (30 nm)/Ag (5-15 nm)/aluminum-doped ZnO (30 nm) multilayer thin films were deposited on glass substrate by rf magnetron sputtering (for top/bottom aluminum-doped ZnO films) and e-beam evaporation (for Ag film). The transmittance is more than 70% for wavelengths above 400 nm with the Ag layer thickness of 10 nm. The resistivity is 3.71 × 10^− 4 Ω-cm, which can be decreased to 3.8 × 10^− 5 Ω-cm with the increase of the Ag layer thickness to 15 nm. The Haacke figure of merit has been calculated for the films with the best value being 8 × 10^− 3 Ω^− 1. It was shown that the multilayer thin films have potential for applications in optoelectronics.     

DNA-encoded morphological evolution of bimetallic Pd@Au core-shell nanoparticles from a high-indexed core

DNA-mediated synthesis of nanoparticles is a powerful method to access exclusive shapes and surface properties. Previous studies employed seeds containing low-energy facets, such as a simple cubic palladium seed, in the synthesis of Pd-Au bimetallic nanoparticles; however, few studies have investigated whether DNA molecules are influential when a seed containing high-energy facets is used. Seeds enclosed by high-energy facets act as facile nucleation sites in nanoparticle growth and could suppress the effect of DNA. We report the DNA-encoded control of the morphological evolution of bimetallic Pd@Au core-shell nanoparticles from a concave palladium nanocube seed containing high-indexed facets. Based on detailed spectroscopic and microscopic studies of time-dependent growth of bimetallic nanoparticles, we found that the DNA molecules containing 10 repeating units of thymine, guanine, cytosine, or adenine (referred to as T10, G10, C10, and A10, respectively) show a unique interaction with the surface of the seed and the precursor. The most important factor is the binding affinity of the nucleobase to the Pd surface; A10 shows the highest binding affinity and can stabilize the high energy surfaces of the seed. Initially, the growth of bases with lower binding affinities (T10, G10, and C10) is completely dictated by the seed’s surface energy, but later growth can be influenced by different DNA sequences, providing four Pd@Au bimetallic nanoparticles with unique morphologies. The effect of these DNA molecules with medium or low binding affinities can only be observed when more Au is deposited. We propose a scheme for DNA-controlled growth. These results provide insights into the factors governing the DNA-mediated growth of core-shell structures using seeds with high-energy sites, and the insights can be readily applied to other bimetallic systems.

Open image in new window

     

Plasmonic Au x Ag y bimetallic alloy nanoparticles enhanced photoluminescence upconversion of Er3+ ions in antimony glass hybrid nanocomposites

Er³⁺ ions and spherical (3–23?nm) Au _x Ag _y bimetallic alloy (where x?=?18–96 and y?=?4–82, atom %) nanoparticles incorporated novel antimony oxide based reducing dielectric (glass) matrix, K₂O–B₂O₃–Sb₂O₃ (KBS), has been synthesized by a new single step methodology involving selective thermochemical reduction. Their absorption spectra show a single tunable (536–679 nm) surface plasmon resonance band along with the typical absorption peaks of the Er³⁺ ion. X-ray and SAED indicate the formation of (111) and (200) planes of Au _x Ag _y alloy. The luminescence intensity of two prominent emission bands of Er³⁺ ions centered at 536 (green) and 645 (red) nm due to ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions were observed to be strongly dependent on the Au _x Ag _y nanoparticle composition. Both the bands undergo a maximum of 1.5- and 4.5-fold intensity enhancement respectively in the presence of the Ag₅₆Au₄₄ alloy (atom %) due to plasmon induced local field enhancement.     

A simple approach for facile synthesis of Ag,anisotropic Au and bimetallic (Ag/Au) nanoparticles using cruciferous vegetable extracts

We present a simple and straightforward approach for the synthesis and stabilization of relatively monodisperse Ag, Au and bimetallic (Ag/Au) nanoparticles by using cruciferous vegetable (green/red) extracts by simply adjusting the pH environment in the aqueous medium. The vegetable extracts act both as reducing and capping agents. The monometallic and bimetallic nanoparticles of Ag and Au so obtained were characterized by UV–visible spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS) and transmission electron microscopy (TEM). It is shown that red cabbage extract can be used for the preparation of anisotropic Au nanoparticles. The formation of Au anisotropic nanoparticles was found to depend on a number of environmental factors, such as the pH of the reaction medium, reaction time, and initial reactant concentrations. Additionally, it is shown that these extract-stabilized Au and Ag nanoparticles can be used as a seed for preparation of bimetallic Au/Ag nanoparticles. For bimetallic alloy nanoparticles the absorption peak was observed between the two maxima of the corresponding metallic particles. The surface plasmon absorption maxima for bimetallic nanoparticles changed linearly with increasing Au mole ratio content in various alloy compositions. It has been shown that the formation of hollow Au spheres depends on the experimental conditions.     

Design of ZnO/Ag/ZnO multilayer transparent conductive films

We have studied the properties of ZnO/Ag/ZnO multilayers prepared on glass substrates by simultaneous RF magnetron sputtering of ZnO and dc magnetron sputtering of Ag. The electrical and optical performance of Ag and ZnO single layer films was also investigated. Different optimization procedures were used for good transparent conductive film. Several analytical tools such as spectrophotometer, scanning electron microscope (SEM), four-point probes were used to explore the causes of the changes in electrical and optical properties. Low sheet resistance of 3 Ω/sq. and transmittance over 90% at 580 nm was achieved. The results of optimization condition of both oxide layers and metallic Ag layers were illustrated.     

纤维基ZnO/Ag/ZnO多层膜的制备、结构及性能研究

利用射频磁控溅射法,室温下通过交替溅射ZnO和Ag,在PET纤维基材上制备ZnO／Ag／ZnO纳米结构多层膜。运用扫描电镜和原子力显微镜对薄膜表面形貌进行分析,用分光光度计测试其透光性能,用四探针电阻测试仪测试其方块电阻。结果表明：纤维基Zno／Ag／ZnO多层膜致密、均匀,对紫外光表现为较强的吸收能力;Ag膜厚度的改变可以调控多层膜的光电性能;ZnO（40nm）／Ag（20nm）／ZnO（40m）多层膜呈现多晶结构,方块电阻为4．4Ω;透光率接近30％。     

Fabrication of silica nanocapsules containing Ag/Au alloy nanoparticles by galvanic replacement reaction

A straightforward method has been developed to generate silica nanocapsules containing Ag/Au alloy nanoparticles (Ag/Au@silica) by in-situ galvanic replacement reaction between the silica-coated silver (Ag@silica) nanoparticles with aqueous chloroauric acid (HAuCl4). Ag/Au@silica exhibits an optical absorbance derived from the surface Plasmon resonance of the encapsulated Ag/Au alloy nanoparticle. The behaviour of chemical diffusion across the silica shells of Ag/Au@silica is also investigated. It is worthy to noting that this facile synthetic strategy could be amenable to the other systems that involve the use of different combination of materials for the core (Pd/Ag, Pt/Ag alloy nanoparticles) and for the shell (titania).     

Preparation of Ag nanoparticles coated tetrapod-like ZnO whisker photocatalysts using photoreduction

Ag/tetrapod-like ZnO whisker (T-ZnOw) photocatalysts with different Ag loadings were synthesized by photoreduction of Ag⁺ on the surface of T-ZnOw. The chemical composition, morphology and photocatalytic properties of Ag/T-ZnOw photocatalysts were characterized and studied in detail. It is found that metal Ag can exist either as nanoparticles or as agglomerates through varying the Ag/ZnO molar ratio (MR). In photodegradation of methyl orange, enhanced degradation rates are achieved by all Ag/T-ZnOw photocatalysts due to increased separation efficiency of photogenerated electron and hole pairs. Specifically, the photocatalytic activities of Ag/T-ZnOw photocatalysts increase with increasing Ag/ZnO MR from 2.4 to 12%. However, further increasing the Ag/ZnO MR to 14.4% induces the formation of more agglomerates, which can act as recombination centers of photogenerated electron and hole pairs, leading to decreased photocatalytic activity of the photocatalyst.     

Optical studies of ZnO/Ag nanojunctions

Ag/ZnO nano-hetero-junctions were synthesized by an electrochemical route. The optical absorption spectroscopy and photoluminescence studies reveal the reaction mechanism at the junction. Optical absorption spectra indicate presence of well-defined ZnO excitonic feature along with the Ag surface plasmon absorption feature at 400 nm. Moreover, ZnO green photoluminescence appears on junction formation with Ag. Detailed analysis of emission and excitation processes indicate that efficient charge transfer is taking place from ZnO to Ag. Ag is also responsible for creation of levels in the HOMO-LUMO gap of ZnO. This finding may be of relevance so far as p-type doping in ZnO is concerned.     

Seed germination and biochemical profile of Silybum marianum exposed to monometallic and bimetallic alloy nanoparticles

In recent years nanotechnology has become increasingly important in almost every field. The new and improved physical, chemical and biological properties of material at nanoscale have far reaching implications in the fields of science and technology. Nanoparticles’ effect on various plant species must be investigated to develop a comprehensive toxicity profile for nanoparticles. The current study strives to evaluate the effects of nine types of metal nanoparticles including monometallic and bimetallic alloy nanoparticles [Ag, Au, Cu, AgCu (1:3), AgCu (3:1), AuCu (1:3), AuCu (3:1), AgAu (1:3), AgAu (3:1)] on seed germination, root and shoot growth and biochemical profile of Silybum marianum plant. Seed germination was greatly affected and increased significantly upon treatment with nanoparticles’ suspensions and was recorded highest for Ag nanoparticle suspension. Metal nanoparticles also had a significant effect on the biochemical profile of S. marianum. For the first week, the effect on DPPH, total phenolics content, total flavonoids content, total protein content, peroxidase activity and superoxide dismutase activity was enhanced, but declined as the time progressed. Among the nanoparticles being used, the effect of Ag nanoparticle was mostly enhancing. The results obtained are significant in mapping the effects of different monometallic and bimetallic nanoparticles on medicinal plant species.Inspec keywords: silver, gold, copper, silver alloys, gold alloys, copper alloys, nanoparticles, nanofabrication, nanobiotechnology, biochemistry, bimetals, enzymes, molecular biophysics, suspensions, toxicologyOther keywords: Au, Cu, AgCu, AuCu, AgAu, Ag, medicinal plant species, superoxide dismutase activity, peroxidase activity, total protein content, total flavonoids content, DPPH, total phenolics, nanoparticle suspensions, shoot growth, root growth, comprehensive toxicity profile, plant species, nanoparticle effect, nanoscale material, biological properties, chemical properties, physical properties, nanotechnology, bimetallic alloy nanoparticles, monometallic alloy nanoparticles, Silybum marianum, biochemical profile, seed germination     

Physical and magnetic properties of (Co, Ag) doped ZnO nanoparticles

Undoped and (Co, Ag) co-doped ZnO nanostructure powders are synthesized by chemical precipitation method without using any capping agent and annealed in air ambient at 500 °C for 1 h. Here, the Ag concentration is fixed at 5 mol% and Co concentration is increased from 0 to 5 mol%. The X-ray diffraction studies reveal that undoped and doped ZnO powders consist of pure hexagonal structure and nano-sized crystallites. The novel Raman peak at 530 cm^?1 has corroborated with the Co doped ZnO nanoparticles. Moreover, the PL studies reveal that as the Co doping concentration increases and it enters into ZnO lattice as substitutional dopant, it leads to the increase of oxygen vacancies (Vo) and zinc interstitials (Zn_i). From the magnetization measurements, it is noticed that the co-doped ZnO nanostructures exhibit considerably robust ferromagnetism i.e. 4.29 emu g^?1 even at room temperature. These (Co, Ag) co-doped ZnO nanopowders can be used in the fabrication of spintronic and optoelectronic device applications.     

Synthesis of Au-Ag alloy nanoparticles with Au/Ag compositional control in SiO2 film matrix

Au-Ag alloy nanoparticles with tunable atomic ratios have been generated in SiO2 film matrix using a new two layer (TL) approach. Two successive overlapping coating layers of similar thickness were deposited on silica glass substrates using Au- and Ag-incorporated inorganic-organic hybrid silica sols, respectively. The Au and Ag concentrations in the individual layers were varied to obtain the desired Au-Ag alloys of different compositions. Four sets of such TL coating assemblies were prepared from the following pair of sols: (i) 4 equivalent mol.% Au-96% SiO2 and 2 equivalent mol.% Ag-98% SiO2, (ii) 3 equivalent mol.% Au-97% SiO2 and 2 equivalent mol.% Ag-98% SiO2, (iii) 3 equivalent mol.% Au-97% SiO2 and 3 equivalent mol.% Ag-97% SiO2, and (iv) 2 equivalent mol.% Au-98% SiO2 and 3 equivalent mol.% Ag-97% SiO2 and subjected to UV (2.75 J/cm2) and heat-treatments (450-550 degrees C) in air and H2-N2 atmospheres for the generation of Au-Ag alloy nanoparticles of approximate compositions Au.66Ag0.33, Au0.6Ag0.4, Au0.5Ag0.5, and Au0.4Ag0.6, respectively. After UV-treatment, individual Au and Ag nanoparticles were formed in the respective layers. The heat-treatment (450-550 degrees C) induces interlayer diffusion of Au and Ag to each other with the generation of Au-Ag alloy nanoparticles, and as a result, Au-Ag alloy surface plasmon resonance (SPR) absorptions were observed in between the Ag- and Au-SPR absorption positions in the visible spectra. The expected alloy compositions are formed through several intermediate alloy nanoparticles, which can also be arrested by controlling the annealing parameters. The alloy formations were monitored by UV-VIS, FTIR, XRD, EDAX, and TEM studies.     

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.