Various Amounts Of Ag Research Articles

Antibacterial Activity of Visible Light Responsive‐Silver‐Nanoparticle/Titania Composite Thin Films with Unprecedently Higher Amounts of Silver

AbstractTo study the antibacterial efficacy of metallic Ag nanoparticle/titania (Ag‐NP)/TiO2 composite thin films against Escherichia coli (ATCC 25922), COMP‐Agn with various amounts of Ag (10 mol% ≤ n ≤ 80 mol%) are fabricated on a quartz glass substrate at 600 °C using the molecular precursor method. The films are characterized by X‐ray diffraction, X‐ray photoelectron, scanning electron microscopy, transmission electron microscopy, photoluminescence, and UVvis techniques. The analysis reveals that the films are composed of metallic Ag‐NPs embedded in a mixture of anatase and rutile matrix, with a volumetric fraction of Ag ranging from 0.18 to 0.68. The antibacterial activity of the TiO2 thin film and COMP‐Agn are determined by disk diffusion and viable cell count methods. Neither pure TiO2 nor pure Ag films exhibit any discernible antibacterial under dark and visible light. The antibacterial of Ag content in composite films is observed to persist for a maximum increase of 70%. The model is proposed on the basis of photoexcited electron transfer from Ag NPs to the TiO2 conduction band of COMP‐Agn, which clarifies the main factors affecting the photoresponse and the excellent response to visible light via surface plasmon resonance.

Synthesis of Ag and Mn/ZnO nanoparticles using a hydrothermal method - A brief study and their role in the electrocatalytic oxidation of glucose in alkaline media

Ag and Mn/ZnO were synthesized via a low-temperature hydrothermal process and applied as glucose oxidation reaction (GOR) catalysts. The sample characterization was performed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), which revealed homogenous clustered nanoparticles for synthesized materials. The various amounts of Ag and Mn were loaded in ZnO nanostructure and their electrocatalytic effect on GOR was investigated by electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy in an alkaline solution containing 3 mM glucose and 0.1 M NaOH. The Ag/ZnO and Mn/ZnO with 50% and 60% loading, respectively, were identified as the best electrocatalysts. The experimental data showed that the larger effective surface area of Ag/ZnO-50 (6.9 cm2) and Mn/ZnO-60 (9.25 cm2) accompanied by faster glucose diffusion coefficient due to the effective impact of Ag and Mn loading on the ZnO nanostructure improved the GOR for Ag/ZnO-50 and Mn/ZnO-60 compared to the ZnO.

Silver-doped ZnO for photocatalytic degradation of methylene blue

Removal of organic dyes from wastewater has become an important issue because of their carcinogenic and mutagenic effects. In this study, we prepared Ag-doped ZnO (Ag_ZnO) photocatalysts containing various amounts of Ag (0.05-0.5mol%) by a hydrothermal process followed by calcination at 500 °C and evaluated the photocatalytic degradation of methylene blue (MB) under sunlight irradiation. The incorporation of Ag into the ZnO lattice and the hexagonal wurtzite structure of the prepared catalysts could be confirmed by X-ray photoelectron spectroscopy and powder Xray diffraction analysis. BET analysis shows that the pore volume and pore size was increased with doping Ag into ZnO. The photocatalytic degradation of methylene blue followed a pseudo-first-order kinetics and the rate constant for dye degradation with 0.1% mol Ag was almost three-times bigger than that with bare ZnO. Our study shows that the photocatalytic activity of ZnO toward MB degradation under sunlight can be effectively enhanced by doping with Ag.

On the importance of the structure in the catalytic reactivity of Au-based catalysts

Au-based materials are remarkably efficient catalysts in the domain of partial oxidation reactions. Nonetheless, questions remain about the physico-chemical phenomena involved at the molecular level. In this work, the catalytic properties of Au-Ag samples, in the form of ultrathin Ag layers on a Au(1 1 1) surface and Au-based model nanoparticles, have been investigated with different microscopy techniques. Using photoemission electron microscopy (PEEM), the exposure of a Au(1 1 1) single crystal doped with various amounts of Ag (0 to 3 monolayers) to O2/H2 and O2/CH3OH gas mixtures did not lead to any specific spatiotemporal pattern formation. In contrast, the use of curved nanoscopic Au and Au-8.8 at.% Ag tip-samples analysed by field emission microscopy (FEM) under similar experimental conditions indicates the presence of catalytic activity. The influence of the silver concentration and of the morphology on the reactivity is discussed. This work highlights the necessity of different experimental approaches aimed at bridging the materials gap often encountered between surface science studies and applied catalysis.

Ag-incorporated macroporous CeO2 catalysts for soot oxidation: Effects of Ag amount on the generation of active oxygen species

A series of CeO2-based catalysts were investigated for soot oxidation with O2. The macroporous CeO2 catalyst (M-CeO2) showed higher soot oxidation activity than mesoporous CeO2 due to the enhanced contact between catalyst and soot caused by the large pore size of M-CeO2. Moreover, various amounts of Ag (2–20 wt.%) were introduced to M-CeO2 to increase the activity, and the Ag-incorporated macroporous CeO2 catalysts (Ag(x)_M-CeO2) were characterized. Raman spectra showed that the ratio of active oxygen species (Oxn−) were different according to amount of Ag. The ratio of highly reactive superoxide (O2−) was largest for the Ag(5)_M-CeO2 catalyst, and then it was decreased as the Ag amount increased further. In addition, XPS analysis showed that the difference in Oxn− generation could be attributed to diverse surface oxygen vacancies in the catalysts. Hence, the amount of loaded Ag affected the surface oxygen vacancies of Ag(x)_M-CeO2 and consequently the ratio of Oxn− was different according to the surface oxygen vacancies of the catalysts. Ag(5)_M-CeO2 with the appropriate surface oxygen vacancies induced the promotion of O2− generation, resulting in the best soot oxidation activity. It was concluded that the amount of Ag on CeO2 has a great influence on the catalytic soot oxidation activity, and proper surface oxygen vacancies facilitated O2− generation, whereas excessive surface oxygen vacancies hindered the formation of highly reactive Oxn−.

Structural and Solar Cell Properties of a Ag-Containing Cu2ZnSnS4 Thin Film Derived from Spray Pyrolysis.

A silver (Ag)-incorporated kesterite Cu2ZnSnS4 (CZTS) thin film was fabricated by a facile spray pyrolysis method. Crystallographic analyses indicated successful incorporation of various amounts of Ag up to a Ag/(Ag + Cu) ratio of ca. 0.1 into the crystal lattice of CZTS in a homogeneous manner without formation of other impurity compounds. From the results of morphological investigations, Ag-incorporated films had larger crystal grains than the CZTS film. The sample with a relatively low Ag content (Ag/(Ag + Cu) of ca. 0.02) had a compact morphology without appreciable voids and pinholes. However, an increase in the Ag content in the CZTS film (Ag/(Ag + Cu) ca. 0.10) induced the formation of a large number of pinholes. As can be expected from these morphological properties, the best sunlight conversion efficiency was obtained by the solar cell based on the film with Ag/(Ag + Cu) of ca. 0.02. Electrostructural analyses of the devices suggested that the Ag-incorporated film in the device achieved reduction in the amounts of unfavorable copper on zinc antisite defects compared to the bare CZTS film. Moreover, the use of a Ag-incorporated film improved band alignment at the CdS(buffer)-CZTS interface. These alterations should also contribute to enhancement of device properties.

Rapid Degradation of Methyl Orange by Ag Doped Zeolite X in the Presence of Borohydride

A series of Ag nanoparticles impregnated on zeolite X (Ag-ZX) containing various amounts of Ag (in wt%) were prepared via impregnation method. The pristine zeolite X and Ag-ZX catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption desorption analyses and atomic absorption spectroscopy (AAS). The prepared catalysts were employed for the decolourization of methyl orange (MO) in the presence of potassium borohydride (KBH4). Various parameters such as the amount of Ag impregnated, MO concentration, KBH4: MO mole ratios, pH and catalyst reusability were investigated. It was found that the best decolourization efficiency was obtained when 0.06g of Ag-ZX (6.7) catalyst was employed using a KBH4: MO mole ratio of 731: 1 at pH 5. The degradation process obeyed pseudo first-order kinetics.

Influence of Ag Additive to the Spacer Layer on the Structure and Giant Magnetoresistance of Electrodeposited Co/Cu Multilayers

In order to explore the possible surfactant effect of Ag on the formation of electrodeposited multilayers, Co/Cu(Ag) multilayers were prepared by this technique and their structure and giant magnetoresistance (GMR) were investigated. The multilayers were deposited from a perchlorate bath with various amounts of Ag+ ions in the solution for incorporating Ag atoms into the multilayer stack. Without Ag addition, secondary neutral mass spectroscopy (SNMS) indicated a well-defined composition modulation of the undermost Co/Cu bilayers. However, already at an Ag content as low as 1.8 at.% incorporated, SNMS showed a deterioration of the periodic multilayer structure. In agreement with the SNMS results, superlattice satellites were visible in the X-ray diffraction (XRD) patterns of the multilayers with up to 0.3 at.% Ag. The satellites were, however, very faint even for multilayers without Ag addition, indicating that the multilayers have high interface roughness and/or poor periodicity. In the absence of Ag and at the smallest Ag content investigated by XRD, a strong central multilayer peak and the weak superlattice satellites were complemented by weak diffraction maxima from non-periodic Co and Cu domains. In the Co/Cu(Ag) multilayer containing about 25 at.% Ag, i.e., nearly as much as Cu, XRD found a separate Ag(Cu) phase. In spite of the imperfect layered structure, a multilayer-type GMR behavior was observed in all samples up to about 10 at.% Ag incorporated in the multilayer stack. The GMR magnitude increased for Ag contents up to about 1 at.%, which implies that a small amount of Ag may have a beneficial effect through a slight modification of the layer growth and/or interface formation. However, for higher Ag contents beyond this level, the GMR was reduced in line with the structural degradation revealed by XRD and SNMS. For the highest Ag contents (above about 10 at.%), the GMR exhibited a behavior characteristic of a granular magnetic alloy, in agreement with the results of the structural study.

Photocatalytic Activity of Vis-Responsive Ag-Nanoparticles/TiO2 Composite Thin Films Fabricated by Molecular Precursor Method (MPM)

The Ag-nanoparticles (Ag-NP)/TiO2 composite thin films with various amounts of Ag (10 mol% ≤ n ≤ 80 mol%) were examined as a potential photocatalyst by decoloration reaction of methylene blue (MB) in an aqueous solution. These composite thin films of ca. 100 nm thickness were fabricated by the MPM at 600 °C in air. The decoloration rates monitored by the absorption intensity of the MB solution indicated that the composite thin films of Ag with an amount less than 40 mol% are not effective under vis-irradiation, though they can work as a photocatalyst under UV-irradiation. Further, the UV-sensitivity of the composite thin films gradually decreased to almost half the level of that of the TiO2 thin film fabricated under the identical conditions when the Ag amount increased from 10 to 40 mol%. Contrarily, the composite thin films of Ag content larger than 50 mol% showed the vis-responsive activity, whose level was slightly lower than the decreased UV-sensitivity. Diffuse reflectance spectra suggested that the vis-responsive activity of the composite thin films is due to the conductivity, localized surface plasmon resonance and surface plasmon resonance of Ag-NP. It was also elucidated that the vis-responsive level of the composite thin films corresponds to their electrical conductivity that depends on the Ag content.

Absorption spectra and photocurrent densities of Ag nanoparticle/TiO2 composite thin films with various amounts of Ag

To study the absorption spectra and photocurrent densities of metallic Ag nanoparticle/titania (Ag NP)/TiO2 composite thin films, COMP-Agn, with various amounts of Ag (10 mol% ≤n ≤80 mol%) were fabricated on a quartz glass substrate at 600 °C using the molecular precursor method. Respective precursor solutions for Ag-nanoparticles and titania were prepared from Ag salt and a titanium complex. Apart from a surface plasmon resonance (SPR) peak around 400 nm, additional wide-range absorption spread in the wide vis-region at wavelengths greater than 400 nm was observed in the composite thin films. The wide-range absorption is due to a tip–tip plasmon mode, intraparticle plasmonic coupling of tip and cavity resonances (LSPR). The absorption spectral patterns could be categorized into three types, depending on the Ag NP content. The photocurrent density of the TiO2 thin film and COMP-Agn was measured under natural potential by a conventional three-electrode method using a Ag plate as a counter electrode. The photocurrent densities of COMP-Agn were comparable to those of the three patterns categorized according to their absorption spectra. The cathodic photocurrent densities generated by COMP-Agn with Ag content greater than 45 mol% could be observed under both UV- and visible (vis-) light irradiation. The enhanced photocurrent density was observed till the Ag content was increased up to 70 mol%. Under dark conditions, cathodic current densities were 1/5–1/20 of those under vis-light irradiation probable due to chemical redox reactions that may occur to the system. On the basis of photoexcited electron transfer from Ag NPs to the TiO2 conduction band and the electrical conductivity of COMP-Agn, the excellent response to vis-light and major factors affecting the photoresponse and photocurrent polarity were clarified by LSPR.

Nano-sized Ag–BaTiO3 composite powders with various amount of Ag prepared by spray pyrolysis

The preparation of precursors of BaTiO 3 nanopowders with various amounts of Ag by spray pyrolysis is reported. The precursor powders obtained with hollow and thin-wall particles are composed of uniformly dispersed Ba, Ti, and Ag components. After post-treatment and a simple milling process, the precursor powders, irrespective of the amount of Ag, are transformed into Ag–BaTiO 3 composite nanoparticles. The mean particle size of the Ag (10 mol%)–BaTiO 3 powders is 142 nm. BaTiO 3 pellets containing Ag exhibit dense structures even at a low sintering temperature of 1000 °C. BaTiO 3 pellets with 10 mol% Ag show the highest dielectric constant of 2950, as opposed to the pure BaTiO 3 pellets (without Ag), whose dielectric constant is 1827.

Effect of Cu and Ag solute segregation on βSn grain boundary diffusivity

We investigate the effect of various amounts of Ag and Cu solute atoms on the self-diffusivity of Sn in the (101) symmetric tilt βSn grain boundary. Using molecular dynamics simulations over a temperature range of 300 K to 450 K, we show that both Ag and Cu decrease the grain boundary self-diffusivity of Sn as the amount of solute in the interface increases. Additionally, the presence of Ag at the grain boundary interface causes a greater reduction in the self-diffusivity of Sn when compared to Cu. We also analyze the solute effect on the diffusive width of the interface and find that low concentrations of both Ag and Cu shrink the width relative to the pure βSn interface. However, adding Cu in excess density greater than 5 × 10−3 atoms/Å2 causes the interface to expand to values almost twice the original width, possibly caused by the larger cohesive energy of Cu-Sn versus Sn-Sn.

Solute Effects on β-Sn Grain Boundary Energy and Shear Stress

The excess enthalpy and shear strain behavior of the β-Sn (101) grain boundary containing various amounts of Ag and Cu solute atoms was investigated using molecular simulation. An increase in either type of solute at the interface lowers the excess enthalpy of the grain boundary. The enthalpies of segregation for both solute types are computed as the slope of excess enthalpy of the grain boundary per area versus interfacial solute concentration per area. For Ag, ΔHSEG=0.64(9) eV/atom , and for Cu, ΔHSEG=0.45(8) eV/atom , indicating a preference for grain boundary segregation. These results agree with other simulation work that attributes a larger decrease in grain boundary energy to a solute with a larger atomic radius. A (301) special boundary of β-Sn was also investigated and found ΔHSEG=0.12(9) eV/atom for Ag and ΔHSEG=0.06(9) eV/atom for Cu. Statistically, this shows the possibility for excess enthalpy increase when Cu is present at the (301) boundary. Under constant shear strain, addition of solu...

Influence of Ag on the Composition and Electromagnetic Properties of Low‐Temperature Cofired Hexaferrites

We have studied the compatibility of Ag and (Co,Cu)Z‐hexaferrite with the composition Ba3Co1.4Cu0.6Fe24O41 (Z). In order to do this, the (Co,Cu)Z‐hexaferrite was cofired with various amounts of Ag at 900°C. The degradation of the (Co,Cu)Z‐hexaferrite to Y‐ and U‐hexaferrite occurred during the cofiring and was confirmed by X‐ray diffraction as well as by thermomagnetic measurements. The permeability and permittivity of the cofired ceramics were measured in the range 1 MHz to 10 GHz. For the (Co,Cu)Z‐hexaferrite, both these properties were significantly influenced by the Ag when the amount of Ag exceeded a minimum of 4.5 wt%. The influence of the Ag and the degradation of the (Co,Cu)Z‐hexaferrite on the permeability were evaluated using the Bruggeman effective media theory.

Heterogeneous growth of metal clusters from solutions of seed nanoparticles.

We describe the solution growth of a series of discrete sized generations of Au nanoparticles by the heterogeneous deposition of atoms onto monodisperse seed nanocrystals. The growth process was studied using size-exclusion chromatography (SEC) and transmission electron microscopy (TEM). The size dispersion of each generation was determined from the SEC elution line widths and the spectral homogeneity of the elution peaks. The heterogeneous deposition of various amounts of Ag on Au nanocrystals and Au on Ag nanocrystals using the same synthetic protocol is also described. The effect of such deposition on the optical absorbance of each generation of larger clusters was measured during SEC using an on-line photodiode array absorbance detector.

The reliability study of selected Sn–Zn based lead-free solders on Au/Ni–P/Cu substrate

Since both Ag and In are important melting point depressants in Sn–Zn based solders, a series Sn–Zn based solders with various amounts of Ag and In additions was studied in the experiment. The melting behavior of solder alloys, wetting characteristics, coefficients of thermal expansion, microstructural evolution and long-term reliability of the selected Sn–Zn based solder on Au/Ni–P metallized copper substrate were examined. Based on the experimental result, there is little change in the melting range of Sn–Zn based solder alloys by minor addition of Ag. On the contrary, the melting point of Sn–Zn based alloys can be effectively decreased by In additions. However, the difference between solidus and liquidus temperature is broadened as the increment of In into Sn–Zn based solders. 76Sn–9Zn–15In has the lowest liquidus temperature among all alloys, and it can effectively bond the Au/Ni–P metallized copper substrate. The microstructure of 76Sn–9Zn–15In alloy soldered at 200 °C for 20 min is primarily comprised of Sn–In γ phase and needle-like ZnO 2. Since there is no flux usage during soldering, zinc oxide cannot be avoided even the process performed under 2×10 −2 mbar vacuum environment. It is also noted that there is no interfacial reaction layer between 76Sn–9Zn–15In and Au/Ni–P metallized copper substrate after soldering. However, there is a reaction layer between 76Sn–9Zn–15In and substrate as the soldered specimen aged at 90 °C for 168 h. Its chemical composition is close to Zn-rich γ phase (NiZn 3) alloyed with minor Sn, In, Cu and P. For the specimen further aged at 90 °C for 336 h, there are cracks along the interface between solder alloy and electroless Ni–P layer. The oxidation of the interfacial Zn-rich γ phase plays an important role in deterioration of the bonding between 76Sn–9Zn–15In and Au/Ni–P metallized copper substrate.

CH4 Deep Oxidation on Ag Promoted Manganese Oxide Catalysts

Manganese oxide modified by various amounts of Ag was prepared and used for CH

Improvement of mechanical properties of YBCO-Ag composite superconductors made by mixing with metallic Ag powder and solution

The role of Ag additions in the microstructural evolution and related mechanical properties of YBCO has been studied. Various amounts of Ag have been added to YBCO by two different mixing techniques, i.e. in the form of metallic Ag powder and solution. The strength and fracture toughness of YBCO specimen increased with increasing Ag content, probably because of strengthening mechanisms resulting from Ag addition. In addition, YBCO-Ag composites showed higher values of strength and fracture toughness when Ag was added in the form of solution compared with those when it was added in the form of metallic Ag powder. Specifically, an addition of 10 vol% Ag, made by mixing with metallic Ag powder, increased strength from 88 to 116 MPa and fracture toughness from 1.6 to . Corresponding improvements in strength and fracture toughness were 128 MPa and , respectively, when YBCO was mixed with solution. The better mechanical properties of the YBCO-Ag specimen mixed by the solution method are believed to be due to the microstructure of more finely and uniformly distributed Ag particles. Furthermore, addition of Ag did not have an adverse effect on the critical current density of YBCO superconductors.

Formation of metal/superconducting oxide composites by oxidation of melt spun metallic precursors

Melt spinning was used to produce homogeneous, melt-spun ribbons of Yb/sub 1/Ba/sub 2/Cu/sub 3/ and Yb/sub 1/Ba/sub 2/Cu/sub 3/ plus various amounts of Ag. While none of these alloys was completely glassy, they did contain glassy alloy and they were homogeneous. Metallic precursors as long as 12 m were produced; the widths were typically 1 to 2 mm, and the thicknesses ranged from 25 to 170 mu m. The dimensions of the specimens varied with the alloy composition and the processing conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Photoemission studies of the initial adsorption and growth of Ag and Au on Ge and Si.

High-resolution core-level and valence-band photoemission studies have been performed to investigate the initial phases of growth of Ag on Si(111)-(7 x 7) and Ge(111)-c(2 x 8), and Au on Ge(111)-c(2 x 8). These systems were also studied with electron diffraction. Upon the deposition of various amounts of Ag or Au on the Si and Ge substrates, the photoemission spectra exhibited selective modifications of surface states and individual core-level components corresponding to different atomic sites. The results establish correlations between the electronic and structural properties of the substrate surfaces and have implications for possible growth models of Au and Ag upon them.