Increasing Ag Content Research Articles

Synthesis and characterization (optical and antibacterial) of silver doped zinc oxide nanoparticles

In the present work, Zn1-xAgxO (x = 0, 0.03, 0.05, and 0.07) nanoparticles were synthesized by the sol-gel synthesis method. Microstructural, morphological, optical, and antibacterial characterizations were performed. The wurtzite crystalline structure was confirmed through XRD analysis. The maximum crystallite size was found for Zn0.93Ag0.07O (∼22.36 nm). Rietveld refinement was performed to understand better crystal symmetry. The optical band gap property exhibited a decremental pattern with the increasing Ag content. The lowest band gap was achieved by Zn0.93Ag0.07O (∼3.26 eV). The Fourier transform infrared spectroscopy (FTIR) analysis ensured the bond stretching of Zn–O and Ag–O near the absorbance band of 490 cm−1. Further, the Thermogravimetric analysis (TGA) was performed to determine the samples' weight loss, and the minimum weight loss was observed for Zn0.93Ag0.07O (∼9–11%). Finally, the antibacterial characterization was performed using Escherichia coli (gram-negative bacteria), and again Zn0.93Ag0.07O exhibited better performances than other synthesized nanoparticles.

In-situ electrodeposited Ag/Cu for electrochemical reduction of acetic acid to nanodiamond under ambient conditions

Carbon nanostructured materials such as nanodiamonds and graphene are useful for various applications, but their low-energy production technologies remain an important challenge to overcome. Herein, the electrochemical reduction of acetic acid using in-situ electrodeposited Ag/Cu to nanocrystalline carbon products was investigated as a function of AgNO3 concentrations in the presence of water and [BMIM]+[BF4]- ionic liquid. Under the conditions used, the deposited Ag clusters could become negatively charged and were responsible for the reduction of acetic acid and the consequent crystalline carbon growth. Increasing Ag concentrations did not only result in higher amounts of Ag being deposited but also created significant local pressure on the atomistic level, where the crystalline carbon was formed, resulting in the re-ordering of carbon atoms into nanodiamond structure. The presence of nanodiamond with average crystallite size 27 nm was clearly evidenced by XRD, Raman, XPS, and TEM-EDX-SAED. The in-situ electrochemical reduction has shown to be an effective ultra-low energy strategy to produce crystalline solid carbon under ambient conditions.

Experimental investigation on fracture toughness of Cu-based shape memory alloys with silver addition

An attempt is made in the present work to determine the fracture toughness of shape memory alloys by the addition of Ag as a quaternary element. Cu-Al-Mn-Ag shape memory alloys are synthesized by using a bottom pouring type casting machine. Three samples are prepared by varying the Ag concentration by 2%, 4%, and 6% (wt.%) and keeping the Mn content constant (2 wt%). After preparing the samples, they are homogenized in a muffle furnace at 850 °C to achieve the required strength and homogeneity. Single-edged crack specimens are prepared and a three-point bend test was conducted on Universal Testing Machine (UTM) as per ASTM standards. The stress Intensity Factor (KIC) is calculated using an empirical formula. It is observed from the experimental results that Stress Intensity Factor increases with an increase in Ag concentration. Microstructural analysis is conducted using Image Analyzer Microscope. It is observed there is a decrease in grain size with an increase in Ag concentration. According to XRD data, a change in Ag concentration does not significantly alter the size of the crystallites.

Mechanical properties and failure mechanisms of Zr-based amorphous alloys with various element compositions under different strain rates

This study investigated the mechanical properties, glass-forming ability (GFA), and microstructural evolution of ZrCuAlNi amorphous alloys with various niobium (Nb) and silver (Ag) additions under static (1 × 10–1 – 1 × 10–3 s−1) and dynamic (3 × 103 – 5 × 103 s−1) loading conditions. The x-ray diffraction (XRD) results revealed that all of the alloys had an amorphous structure, and the GFA improved with an increasing Ag content. The Zr56Cu24Al9Ni7Nb1Ag3 alloy showed the highest flow stress among the various alloys under both strain rate ranges. For all of the alloys, the fracture strain increased with an increasing Ag content. Moreover, the strain rate sensitivity increased with increasing strain rate. The scanning electron microscopy observations showed that the fracture surfaces had a dimple structure. As the Ag content increased, the dimple structure changed from a smooth to molten appearance. In addition, the dimple structure density increased with an increasing strain rate. The results present that the ductility of the ZrCuAlNi amorphous alloys could be improved by increasing the Ag element content.

Effects of Cu and Ag Elements on Corrosion Resistance of Dual-Phase Fe-Based Medium-Entropy Alloys.

The effect of adding elements to promote phase separation on the functional properties of medium-entropy alloys has rarely been reported. In this paper, medium-entropy alloys with dual FCC phases were prepared by adding Cu and Ag elements, which exhibited a positive mixing enthalpy with Fe. Dual-phase Fe-based medium-entropy alloys were fabricated via water-cooled copper crucible magnetic levitation melting and copper mold suction casting. The effects of Cu and Ag elements microalloying on the microstructure and corrosion resistance of a medium-entropy alloy were studied, and an optimal composition was defined. The results show that Cu and Ag elements were enriched between the dendrites and precipitated an FCC2 phase on the FCC1 matrix. During electrochemical corrosion under PBS solutions, Cu and Ag elements formed an oxide layer on the alloy's surface, which prevented the matrix atoms from diffusing. With an increase in Cu and Ag content, the corrosion potential and the arc radius of capacitive resistance increased, while the corrosion current density decreased, indicating that corrosion resistance improved. The corrosion current density of (Fe63.3Mn14Si9.1Cr9.8C3.8)94Cu3Ag3 in PBS solution was as high as 1.357 × 10-8 A·cm-2.

Determination of critical resolved shear stresses associated with slips in pure Zn and Zn-Ag alloys via micro-pillar compression

The room-temperature plastic deformation behavior of pure Zn and Zn-Ag (0–2.2 at.%) biodegradable alloys has been investigated via uniaxial in situ micro-pillar compression tests performed within a scanning electron microscope. The critical resolved shear stresses (CRSS) were quantified as a function of micro-pillar diameter. The compression of single crystal micro-pillars was performed at various strain rates in carefully selected grains, the crystallographic orientation of which facilitates deformation either via basal 0001〈112¯0〉 or prismatic 101¯0〈112¯0〉 slip. The CRSS values increased with decreased micro-pillar diameter, revealing a more pronounced size effect in pure Zn deformed via basal slip. The observed solid solution strengthening effect in Zn-Ag alloys with increasing Ag content was associated with a CRSS increase from 26.6 MPa to 37.0 MPa (by ∼ 40 %) in the basal slip system and from 99.1 MPa to 188.4 MPa (by ∼ 104 %) in the prismatic slip system. The extraordinarily high CRSS values for basal slip activated in pure Zn and Zn-0.14Ag alloy compared to the solid solution strengthening model was attributed to the critically low dislocation density. In the Zn-Ag alloy with Ag content > 0.5 at.% higher dislocation densities are expected, which result in a more predictable plastic deformation behavior.

Effect of Ag content on friction and wear properties of TiCN/Ag films in different service environments

Thin-film materials require improved performance to withstand complex and harsh environments as the modern industry evolves. In this study, a series of TiCN/Ag films were fabricated to enhance the frictional properties of the films and extend the lifetime of friction sliding components. The microstructure, mechanical properties, friction, and wear properties of the films were investigated in different service environments. The results showed that the film comprised fcc-TiN, fcc-Ag, amorphous carbon, and amorphous carbon nitride. As the Ag content increased, the hardness of the film first increased, then decreased rapidly, after which the decreasing trend became stable. When the Ag content was 1.8 at%, the optimal hardness and elastic modulus of the films were 29.7 GPa and 228.09 GPa, respectively. Under oil lubrication conditions, Ag atoms can catalyze the formation of a highly graphitized carbon-based friction film on the TiCN/Ag worn surface, thereby enhancing the friction and wear properties of the films. In the air friction, the soft-phase Ag with a low shear modulus acts as a lubricant, and the friction coefficient decreases with an increase in Ag content; however, the consumption of Ag during friction increases the wear rate. In the 3.5 wt% NaCl solution, as the Ag content increased, the surface roughness and corrosion current of the film increased, while the corrosion potential and resistance of the film decreased, resulting in an increase in the friction coefficient and wear rate.

First Approach to ZrB2 Thin Films Alloyed with Silver Prepared by Magnetron Co-Sputtering

Hexagonal ZrB2 belongs to the group of ultra-high temperature ceramics representing an important class of materials with the potential to meet the high demands of today’s industry. However, this potential is limited by inherent brittleness and poor tribological properties. Here, the combination of density functional theory and experiment is used to investigate the effect of silver alloying on the mechanical and tribological properties of hexagonal ZrB2 thin films. Calculations indicate strong insolubility of Ag atoms in the ZrB2 metal sublattice and a significant effect on the mechanical properties, pointing out an improvement in ductility and tribological properties but at the cost of reduced hardness. The experiments confirmed the theoretical predictions of the strong insolubility of silver, where the magnetron-sputtered Zr1−xAgxB2+Δ films form a segregated nanostructure consisting of separated hexagonal ZrB2 and cubic Ag phases. With increased Ag content, values of Young’s modulus decrease from EZrB2.31 = 375 GPa to EZr0.26Ag0.74B0.89 = 154 GPa, followed by a decrease in hardness from HZrB2.31 = 30 GPa to a value of HZr0.26Ag0.74B0.89 = 4 GPa. The suppression of crack formation is also shown with the material flow around cube corner indents, indicating enhanced ductility. The improvement of tribological properties was also confirmed when the coefficient of friction (COF) was reduced from COFZrB2.31 ~0.9 to a value of COFZr0.26Ag0.74B0.89 ~0.25 for all counterpart materials—steel (100Cr6), Si3N4, and WC/Co.

Transport and thermoelectric properties of crystalline Cu2−xAgxSe alloys prepared by facile method

Crystalline alloys of Cu2−Se containing a transition metal, Earth-abundant and eco-friendly element, are studied in this article as promising eco-friendly thermoelectric materials. Thermoelectric and transport properties of Cu2−xAgxSe (x = 0.00, 0.01, 0.03, 0.05, 0.07) bulk alloys were studied in the temperature range 273–473 K. Crystal structure and surface morphology were tested by X-ray diffraction analysis and scanning electron microscope. Electrical conductivity measurements showed metallic conduction behaviour besides a tremendous decrease in its values with increasing Ag content (x). In contrast, Ag-doping increased the Seebeck coefficient to a large extent. Calculations of the electronic thermal conductivity showed that phonon scattering is increased due to the Ag-doping. The incorporation of Ag-atoms resulted in existence of point defects, introduced secondary phases which significantly reduced the thermal conductivity. Such effects resulted in enhanced ZT, specially at higher Ag-content. The largest ZT value was recorded at 0.25, achieved for Cu1.93Ag0.07Se at 473 K, which is about two times of that observed for the pristine Cu2Se sample. The overall findings of the current study clearly demonstrates that the increasing of the Ag content helps to obtain good TE properties of the cubic Cu2−xAgxSe system, specially at higher temperatures.

Laser surface alloying of titanium alloy with silver: Microstructure, hardness and corrosion property

In this study, silver (Ag) was surface-alloyed in TC4 alloy (Ti6Al4V) with a high-power diode laser (HPDL). The Ag content in the alloyed layers were controlled to be 5 to 24 wt%. The microstructure, hardness and corrosion properties of the alloyed layers are affected by the Ag content. The hardness of TC4 alloy, when laser surface-alloyed with 14 wt% Ag increased from 381 HV0.2 to a maximum value of 569 HV0.2, caused by the formation of hard intermetallic phases (Ti2Ag and TiAg) in the α-Ti matrix. However, with the increase of Ag content to 24 wt% the hardness of the alloy was lowered to 456 HV0.2, result of the formation of a soft Ag-rich phase. In addition, observing a decrease in corrosion resistance of the laser surface-alloyed TC4 with a high Ag content, which is attributed to micro-galvanic effect between the α-Ti and Ti2Ag, TiAg and Ag-rich phase.

Biocompatible Ti3Au–Ag/Cu thin film coatings with enhanced mechanical and antimicrobial functionality

BackgroundBiofilm formation on medical device surfaces is a persistent problem that shelters bacteria and encourages infections and implant rejection. One promising approach to tackle this problem is to coat the medical device with an antimicrobial material. In this work, for the first time, we impart antimicrobial functionality to Ti3Au intermetallic alloy thin film coatings, while maintaining their superior mechanical hardness and biocompatibility.MethodsA mosaic Ti sputtering target is developed to dope controlled amounts of antimicrobial elements of Ag and Cu into a Ti3Au coating matrix by precise control of individual target power levels. The resulting Ti3Au-Ag/Cu thin film coatings are then systematically characterised for their structural, chemical, morphological, mechanical, corrosion, biocompatibility-cytotoxicity and antimicrobial properties.ResultsX-ray diffraction patterns reveal the formation of a super hard β-Ti3Au phase, but the thin films undergo a transition in crystal orientation from (200) to (211) with increasing Ag concentration, whereas introduction of Cu brings no observable changes in crystal orientation. Scanning and transmission electron microscopy analysis show the polyhedral shape of the Ti3Au crystal but agglomeration of Ag particles between crystal grains begins at 1.2 at% Ag and develops into large granules with increasing Ag concentration up to 4.1 at%. The smallest doping concentration of 0.2 at% Ag raises the hardness of the thin film to 14.7 GPa, a 360% improvement compared to the ∼4 GPa hardness of the standard Ti6Al4V base alloy. On the other hand, addition of Cu brings a 315—330% improvement in mechanical hardness of films throughout the entire concentration range of 0.5—7.1 at%. The thin films also show good electrochemical corrosion resistance and a > tenfold reduction in wear rate compared to Ti6Al4V alloy. All thin film samples exhibit very safe cytotoxic profiles towards L929 mouse fibroblast cells when analysed with Alamar blue assay, with ion leaching concentrations lower than 0.2 ppm for Ag and 0.08 ppm for Cu and conductivity tests reveal the positive effect of increased conductivity on myogenic differentiation. Antimicrobial tests show a drastic reduction in microbial survival over a short test period of < 20 min for Ti3Au films doped with Ag or Cu concentrations as low as 0.2—0.5 at%.ConclusionTherefore, according to these results, this work presents a new antimicrobial Ti3Au-Ag/Cu coating material with excellent mechanical performance with the potential to develop wear resistant medical implant devices with resistance to biofilm formation and bacterial infection.Graphical

Ag Alloying in Cu2−yAgyBa(Ge,Sn)Se4Films and Photovoltaic Devices

Trigonal Cu2BaGe1−xSnxSe4(CBGTSe) has recently gained interest as a potential photovoltaic absorber to target mitigation of antisite defect formation in Cu2ZnSn(S,Se)4. This study examines partial substitution of Cu by Ag as a potential approach to tune the properties of Ag‐incorporated CBGTSe in the following aspects: 1) phase stability and crystal structure as a function of Ag content; 2) film morphology and grain structure; 3) charge carrier properties; 4) band positions; and 5) charge carrier kinetics and recombination. Up to 20% of Cu can be substituted by Ag in CBGTSe, while above 20% a phase mixture appears. Increasing Ag content induces larger average grain size and reduced hole carrier densities. In contrast, photoelectron spectroscopy and photoluminescence measurements reveal negligible impact of Ag substitution on ionization potential (≈5.4 eV) and electron affinity (≈3.7 eV). Also, Ag content offers negligible impact on carrier lifetimes (few ns). Consistent with these fundamental properties, solar cells based on two different Ag/(Ag + Cu) ratios (≈0% and ≈20%) show comparable power conversion efficiencies (≈2.7–2.8%). These results indicate that CBGTSe films and solar cells may be less sensitive to Ag substitution compared to Cu2ZnSn(S,Se)4, at least at the current level of absorber and device optimization.

The effect of Ag content on the electronic structure and optical property of α-Fe2O3

The electronic structure and optical properties of Ag-doped α-Fe2O3 with different Ag contents (1.67 mol%, 3.33 mol%, 5.00 mol% and 6.67 mol%) were studied by density-functional theory (DFT). α-Fe2O3 has the characteristics of semimetal after Ag doping, and the semimetal property increases with increasing Ag contents. Doped Ag loses less electrons for Ag-doped α-Fe2O3 than corresponding Fe (replaced iron) for pure α-Fe2O3, which led the weaker Ag-O bond than Fe-O bond before Ag doping. However, the number of losing electrons for Ag increases gradually with the increase of Ag content. For optical properties, it is found that the peaks of imaginary parts of dielectric function and extinction coefficient for Ag-doped α-Fe2O3 shift to low energy (red shift) relative to those of pure α-Fe2O3. In the ultraviolet range (200 nm-380 nm), Ag doping reduces the optical absorption intensity. However, the optical absorption is enhanced steeply with the increase of Ag contents in the wavelength of 420 nm to 1400 nm. The optical absorption intensity of 3Ag-doped and 4Ag-doped α-Fe2O3 is similar in the visible range, suggesting that excessive Ag concentration (over 3 Ag) has little effect on the optical absorption property.

Microstructure, mechanical and tribological behaviors of hard-yet-tough Hf-Ag-N coating

Hafnium nitride (HfN) possesses excellent mechanical properties such as high hardness and wear resistance, and is usually used as a protective coating on high-end equipment and precision instruments. Nevertheless, the high coefficient of friction of HfN coating poses a serious threat to equipment and instruments, so doping modifications are imperative. Here, HfN coatings doping with different Ag contents were prepared by magnetron sputtering. It was found in the experiments that the introduction of a trace amount of Ag atoms (∼1.85 at.%) could replace the Hf atoms in the HfN sublattice, resulting in a solid solution Hf-Ag-N. As compared with the pure HfN coating (20.3 GPa), the solid solution Hf-Ag-N coating has higher hardness (25.5 GPa), lower coefficient of friction (μ = 0.28) and lower wear rate (3.03 × 10−8 mm3/(N·mm). With increasing Ag content, solid solution structure disappears and a nanocomposite structure forms, leading to a sharp decrease in hardness of Hf-Ag-N coating due to the precipitation of soft Ag phase. Additionally, X-ray photoelectron spectroscopy and Raman spectrum analysis revealed that the reason for the low coefficient of friction of Hf-Ag-N solid solution coating is mainly due to the large number of tribo-oxidation products (HfO2, Ag2O) and self-lubricating phase (Ag) on the worn surface. The density functional theory further confirms that Ag atoms in solutes promote spontaneous oxidation of Hf-Ag-N which is important for causing tribo-oxidation. The results of this study expect to provide new idea as well as certain theoretical basis for designing new protective coatings.

Revisiting Alloy Design of Al-Base Alloys for Potential Orthotics and Prosthetics Applications

The primary objective of this research was to open a promising avenue for designing new low-cost precipitation-hardened Al base alloys in semblance with the desired mechanical properties that can be exploited in the fabrication of lightweight exoskeleton frames, prosthetics, and wheelchair components. In multicomponent Al-Cu-based systems (2xxx), the substitution of elements such as copper (Cu), magnesium (Mg), and akin Cu/Mg ratio are mainly manipulated to improve the mechanical strength of these alloys. Nonetheless, these kinds of alloying optimizations are not well suited from the cost and sustainability points of view. The starting point of the present work is to screen out the optimum value of the Ag/Sn ratio, which can be a potential substitute for the conventional Cu/Mg alloy ratio in Al-Cu-Mg-based ternary alloys without sacrificing its key features of mechanical properties. Based on our microstructural and mechanical results, it was found that the chemical composition and microstructure were the most important variables influencing the mechanical properties. The increase in the mechanical strength of our alloys was mainly attributed to the precipitation hardening phenomenon. Typically, at peak-aged conditions, the correlation between the mechanical and subsequent microstructural analysis revealed that the synergistic increase in Ag and Sn content in the Al-Cu-Mg-based alloy led to an improvement in the mechanical strength and its trade-offs by changing the shape and distribution of the micron-scaled second phase in the matrix. From optical microscopy and subsequent scanning electron microscopy analyses, this continuous precipitated phase in the matrix is identified as the Mg2Sn phase, which is mainly elicited from the solid-state reaction during artificial aging treatment. Indeed, the presence of suitable microstructure at the peak aged condition that has uniformly dispersed, micron-scale Mg2Sn phase proved to be very useful in blocking the dislocation glide and increasing the mechanical strength of the alloys during tensile testing. This combination of precipitation-hardening phases has not been previously observed in alloys with higher or lower Cu/Mg ratios. Among the studied alloys, the alloy having Ag/Sn ratio of 23 (and chemical composition of Al-4 Cu-0.5 Mg-0.7 Ag-0.03 Sn (wt.%)-T6 (denoted as Al-loy-4) exhibited an average ultimate tensile strength of 450 MPa which is almost four times larger than the pure aluminum having an ultimate tensile strength of 90 MPa currently used in healthcare and medical industries.

Silver nanoparticle toxicity to the larvae of oyster Crassostrea angulata: Contribution of in vivo dissolution

Understanding the toxic mechanism of silver nanoparticles (AgNPs) is crucial for it risk assessment in marine environment, but the role of Ag+ release in the AgNP toxicity to marine biota is not yet well addressed. This study investigated the toxicity of AgNPs to the veliger larvae of oyster Crassostrea angulata, with a specific focus on the possibility of the involvement of in vivo dissolution of AgNPs in the toxicity via an aggregation-induced emission luminogen (AIEgen)-based imaging technique. AgNO3 exhibited significantly greater toxicity than AgNPs based on the total Ag, as indicated by lower 50 % growth inhibition concentration (EC50). The average concentration of soluble Ag in seawater at the EC50 of AgNPs was far lower than the EC50 of AgNO3, indicating that the AgNP toxicity could not be fully explained by the dissolved Ag in the medium. Despite the comparable soluble Ag concentration in seawater for both treatments, more Ag was accumulated in the larvae exposed to AgNPs, suggesting their ability to directly ingest particulate Ag, which was further confirmed by the presence of AgNPs aggregates in the esophagus and stomach. With the application of AIEgen-based imaging technique, in vivo dissolution of AgNPs in oyster larvae was thoroughly verified by an increase in Ag(I) content in the larvae exposed to AgNPs after depuration. The results collectively implied that apart from the Ag released in the medium, the Ag dissolved from the ingested AgNPs may also greatly contribute to the toxicity of AgNPs toward the oyster larvae. The findings of this work shed new light on the bioavailability and toxicity of AgNPs in marine environment.

Shape-stable Bi-Sn-In alloy/Ag/copper foam composite phase change material for thermal storage and management

With the increasing challenge of heat dissipation in electronic device, the development of rapid thermal storage and management materials with high thermal conductivity becomes an important topic. This study developed a novel low melting point metal composite phase change material composed of Bi-Sn-In alloy, Ag particles (1–4 wt%) and copper foam (apertures 0.25–0.64 mm) using high thermal conductivity synergetic enhanced effect. The Ag particles were uniformly distributed in Bi-Sn-In alloy and they changed to Ag strips with high Ag content, and Bi-Sn-In alloy/Ag can be evenly filled in apertures of copper foam. Bi-Sn-In alloy/Ag/copper foam composite with optimal aperture of 0.42 mm exhibited highest shape stability, because it avoided molten alloy leakage for larger apertures and residual alloy which was not pressed into copper foam for small apertures. As Ag content increases, the melting points of Bi-Sn-In alloy/Ag and Bi-Sn-In alloy/Ag/copper foam with Ag content of 4 wt% respectively increased by 4.91 % and 2.46 %, while their enthalpy slightly decreases by 10.9 % and 2.49 %. More importantly, the synergistic effect of Ag strips and copper skeleton addition formed continuous channels for heat transfer. The thermal conductivities of alloy/Ag (4 wt%) and alloy/Ag (4 wt%)/copper foam were respectively 22.4 and 42.7 Wm−1 °C−1, and they were remarkably higher than that of Bi-Sn-In alloy (16.4 Wm−1 °C−1). Furthermore, thermal management test showed that Bi-Sn-In alloy/Ag/foam copper had the most prominent endothermic and exothermic properties. The outstanding performance of present Bi-Sn-In alloy/Ag/copper foam demonstrates a promising prospect for solving the thermal management problems of contemporary electronic devices.

Short- and medium range order in GeTe4-Ag glasses

Short- and medium range order glasses of GeTe4-Ag approximate composition have been studied by neutron diffraction, X-ray diffraction and extended X-ray absorption fine structure spectroscopy. Chemical correlations have been determined by fitting multiple datasets simultaneously with the reverse Monte Carlo simulation technique. It has been found that Ge atoms remain basically fourfold coordinated by Te while Te atoms have mostly two Ge/Te neighbours. The topology of the GeTe4 host network does not change upon adding Ag. Similarly to binary Ge-Te glasses, neighbouring GeTe4 tetrahedra are predominantly in corner sharing configuration in all investigated GeTe4-Ag compositions. Ag atoms bind mostly to Te and the average total coordination number of Ag does not change significantly with increasing Ag content.

Effect of Ag-Decorated BiVO4 on Photoelectrochemical Water Splitting: An X-ray Absorption Spectroscopic Investigation.

Bismuth vanadate (BiVO4) has attracted substantial attention on account of its usefulness in producing hydrogen by photoelectrochemical (PEC) water splitting. The exploitation of BiVO4 for this purpose is yet limited by severe charge recombination in the bulk of BiVO4, which is caused by the short diffusion length of the photoexcited charge carriers and inefficient charge separation. Enormous effort has been made to improve the photocurrent density and solar-to-hydrogen conversion efficiency of BiVO4. This study demonstrates that modulating the composition of the electrode and the electronic configuration of BiVO4 by decoration with silver nanoparticles (Ag NPs) is effective in not only enhancing the charge carrier concentration but also suppressing charge recombination in the solar water splitting process. Decoration with a small number of Ag NPs significantly enhances the photocurrent density of BiVO4 to an extent that increases with the concentration of the Ag NPs. At 0.5% Ag NPs, the photocurrent density approaches 4.1 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (RHE) under solar simulated light illumination; this value is much higher than the 2.3 mA cm−2 of pure BiVO4 under the same conditions. X-ray absorption spectroscopy (XAS) is utilized to investigate the electronic structure of pure BiVO4 and its modification by decoration with Ag NPs. Analytical results indicate that increased distortion of the VO4 tetrahedra alters the V 3d–O 2p hybridized states. Additionally, as the Ag concentration increases, the oxygen vacancy defects that act as recombination centers in BiVO4 are reduced. In situ XAS, which is conducted under dark and solar illumination conditions, reveals that the significantly enhanced PEC performance is attributable to the synergy of modulated atomic/electronic structures and the localized surface plasmon resonance effect of the Ag nanoparticles.

Crystal shape and size of CdTe colloidal quantum dots controlled by silver doping for enhanced quantum dots sensitized solar cells performance

Pristine and silver (Ag) doped (0–5 at. %) CdTe QDs were synthesized by the colloidal process in an aqueous medium. The red shift in absorption and emission peak positions was observed with respect to Ag doping concentrations due to a change in composition (Cd1-xAgxTe). During the synthesis, the concentrations of silver doping played a significant role in controlling the shape and size of CdTe QDs. XRD studies indicate the crystal undergoes a series of shapes from octahedron to truncated octahedron followed by truncated cube to cube in CdTe QDs with respect to silver doping concentrations. The morphologies and elemental compositions of CdTe and Cd1-xAgxTe QDs were studied by HRTEM and EDX analysis. The photovoltaic efficiency of fabricated devices using CdTe QDs was increased from 0.85% to 1.66% with increasing Ag concentrations. The JSC of the J-V measurement and the integrated JSC of IPCE follow the same trend. Thus, silver doping manipulates the crystal shape and size of CdTe QDs and is quite efficient for visible light utilization, separation of charges, and enhances the solar cell efficiency.