Silver Ion Exchange Research Articles

Flexible, foldable and transparent SERS film with high sensitivity and signal homogeneity via silver ion exchange and in-situ reduction

The adhesion between metal plasma and substrate was the key of surface-enhanced Raman scattering (SERS) technology. The preparation of ideal SERS substrate with multiple advantages such as high sensitivity and good signal reproducibility was still the focus of research. A flexible foldable and transparent fluorinated polyimide/silver NPs (FPI@Ag) SERS film was fabricated by the ion exchange and in-situ reduction method in this work. The effects of KOH hydrolysis time, AgNO3 ion exchange time and concentration, the type and concentration of reducing agents on the SERS performance of the FPI@Ag film were systematically discussed. As a result, the hydrolysis time of KOH affected the thickness of the metallic silver layer, the concentration of AgNO3 affected the size and spacing of Ag NPs, and the Raman signal of was remarkably enhanced when borane dimethylamine complex (DMAB) was used as reducing agent. When the detection limit of 4-Aminothiophenol was as low as 1 × 10−11 mol·L−1, the obvious Raman characteristic peak still appeared. The enhancement factor (EF) was up to 9.4 × 107. The linear quantification range was achieved in the range from 10−3–10−11 mol·L−1, R2 = 0.9987. In addition, we also performed multi-cycle bending and torsion test on the FPI@Ag film, and obtained stable Raman signals. The prepared FPI@Ag film can be attached to the surface of uneven samples, which can be used for on-site Raman detection and analysis.

Preliminary evaluation of zeolite-based platforms as potential dual drug delivery systems against microbial infections in the tumor microenvironment

Several zeolite-based delivery systems (ZDS) built with faujasite structure were prepared containing silver (Ag+) and 5-Fluorouracil (5-FU) as antimicrobial and antineoplastic agents, respectively. The idea behind this drug combination is an answer to the increasing evidence of colonization of tumor microenvironments by pathogenic microorganisms and their active role in tumor growth. Two ZDS with a fixed load of 5-FU and different silver loads, Ag7(5-FU)@Y and Ag4(5-FU)@Y, were prepared through ion-exchange of silver followed by 5-FU encapsulation in liquid phase. The developed ZDS were characterized in-depth by scanning microscopy (SEM), thermogravimetric analysis (TGA), N2 adsorption analysis, ICP-AES analyses and X-ray photoelectron spectroscopy (XPS), and successfully confirmed the incorporation of both drug-active species into the zeolite framework without inducing structural alteration. Finally, the antimicrobial properties of the ZDS were investigated against various strains of bacteria. ZDS containing both drug-active species - Ag and 5-FU - displayed lower Minimum Inhibitory Concentration (MIC) values than AgxY, indicating higher effectiveness in inhibiting bacterial growth. Ag4(5-FU)@Y resulted to be the most favourable combination exhibiting efficient encapsulation of 5-FU while containing an efficient amount of silver.

Effect of potassium and silver ion-exchange on the strengthening effect and properties of aluminosilicate glass

In this work, the aluminosilicate glass was subjected to ion-exchange using the KNO3-AgCl mixed molten salt in order to strengthen the glass while imparting antimicrobial properties. The concentration distribution of K+ ions and Ag+ ions of the ion-exchanged glasses was characterized by EDS, the effects of ion-exchange temperature (460-500 °C), ion-exchange time (0.5-3 h) and AgCl concentration (0–2.5 wt%) in the mixed molten salt on the strengthening effect and properties of the glass were investigated. The results showed that Ag+-Na+ ion-exchange, K+-Na+ ion-exchange existed simultaneously, and Ag+-Na+ ion-exchange occurred preferentially. Due to the presence of metallic silver, the appearance of the Ag+ ion-exchanged glass was light yellow and its transmittance showed a decrease. The surface compressive stress trended up and then down with increasing temperature and time because of the stress relaxation effect. The Vickers hardness of ion-exchanged glass increased by 15%, and the densities and chemical stability were also increased. Ions leaching experiments showed that the Ag+ ions release concentration of silver-loaded glass in aqueous environment can reach the bactericidal level. It has been shown that ion-exchange of glass in KNO3-AgCl mixed molten salts allowed the glass to be strengthened and incorporated with antimicrobial active ions, its chemical stability was improved, too.

Antimicrobial and mechanical properties of silver ion-exchanged transparent lithium-mica glass-ceramics

This study investigates silver ion-exchange of the transparent lithium-mica glass-ceramic in a molten mixture of AgNO3 and Ag2SO4 to realize the glass-ceramic antibacterial activity and improved mechanical properties. The ion-exchanged glass-ceramic was heated at 700 °C. Li+ ions in the interlayers of mica near surface of the glass-ceramic were exchanged for Ag+ ions in the molten salt. Ag+ ions intruded deeper inside from surface as the soaking time of the ion-exchange increased, disturbing the layer structure of the mica. Heating also diffused Ag+ ions deeper inside the glass-ceramic, reducing the concentration of Ag+ ions near the surface and realizing a uniform distribution of Ag+ ions to create a regular layer structure of mica. Both the ion-exchanger and the heated ion-exchanger showed antibacterial activity against Escherichia coli. However, their activities decreased in repeated antimicrobial tests. Because ion-exchange generated compressive stress near the surface, the Vickers hardness and fracture toughness increased, whereas heating lowered the heightened hardness. Although ion-exchange and subsequent heat treatment improved the machinability of the glass-ceramic, ion-exchange alone did not.

How Activity Series Governs Transformation of Metal Nanoparticles in Glasses.

It has been experimentally shown for the first time that metallic copper in glasses can play the role of a reducing agent for other metallic ions, in particular, resulting in the formation of metal nanoparticles. Silver ions have been introduced into an alkali silicate glass containing copper nanoparticles by ion exchange. This has resulted in the formation of silver nanoparticles accompanied by the disappearance of copper nanoparticles initially contained in the glass. Such a process has never been observed and described anywhere. The process has been explained by the redox reaction Cu0 + Ag+ → Cu+ + Ag0 taking place in silver ion exchange. It has been shown that this reaction can go only in one direction (from left to right) as a result of the relative positions of copper and silver in the activity series.

Analysing Regulatory Framework for Silver Exchange Traded Funds, Prepaid Payment Instruments, Digital Banks, Etc.

Analysing Regulatory Framework for Silver Exchange Traded Funds, Prepaid Payment Instruments, Digital Banks, Etc.

Forecasting financial signal for automated trading: An interpretable approach

Traders can now use online trading applications to increase their capital by benefiting from financial markets fluctuations. The foreign exchange (forex) market, the silver and gold exchange markets, and stock indices (e.g. S&P 500) are among the most famous financial markets. Traders must identify the correct trends in any given market and take appropriate actions to increase their earnings. High levels of knowledge and competency are required to conduct profitable transactions. Deep learning and data clustering were employed in this study to propose an interpretable automated financial market trading model. In the proposed method, feature vectors are first extracted from the market price index and the values of useful indicators (e.g., RSI and MA). Data labeling is then performed through clustering. After that, a dataset is created to train a deep learning model in order to identify and adopt the best action (buy, sell, or no action). In financial markets, prices may change drastically and disrupt the performance of learning models. Therefore, an autoencoder network was designed to identify drastic fluctuations (outliers) in the market and avoid trading at such cases. This could prevent a steep drawdown. Experiments were performed on different markets to compare the proposed approach with the state-of-the-arts. The results indicate higher profitability with respect to the trading risk in comparison with other methods.

Using silver exchange to achieve high uptake and selectivity for propylene/propane separation in zeolite Y

Adsorptive separation of propylene and propane, an important step of polypropylene production, is more energy-efficient than distillation. However, the challenge lies in the design of an adsorbent which exhibits both high selectivity and uptake. Herein, we hypothesise that enhancing the propylene affinity of the adsorption sites while keeping a suitable pore size can address this challenge. To do so, we performed silver exchange of a commercial zeolite Y, thereby making the adsorbent design easily scalable. We characterised the adsorbent using analytical, spectroscopic and imaging tools, tested its equilibrium and dynamic sorption properties using volumetric and gravimetric techniques and compared its performance to those of state-of-the-art adsorbents as well as other silver-functionalised adsorbents. The silver-exchanged zeolite Y (Ag-Y) exhibited one of the best selectivity vs uptake performances reported so far. Ag-Y also displayed fast adsorption kinetics and reversible propylene sorption, making it a promising new benchmark for propylene/propane separation. Synchrotron-based pair distribution function analyses identified the silver cations’ location which confirmed that the silver sites are easily accessible to the adsorbates. This aspect can, in part, explain the propylene/propane separation performance observed. The overall design strategy proposed here to enhance sorption site affinity and maintain pore size could be extended to other adsorbents and support the deployment of adsorption technology for propylene/propane separation.

Predicting Gold and Silver Price Direction Using Tree-Based Classifiers

Gold is often used by investors as a hedge against inflation or adverse economic times. Consequently, it is important for investors to have accurate forecasts of gold prices. This paper uses several machine learning tree-based classifiers (bagging, stochastic gradient boosting, random forests) to predict the price direction of gold and silver exchange traded funds. Decision tree bagging, stochastic gradient boosting, and random forests predictions of gold and silver price direction are much more accurate than those obtained from logit models. For a 20-day forecast horizon, tree bagging, stochastic gradient boosting, and random forests produce accuracy rates of between 85% and 90% while logit models produce accuracy rates of between 55% and 60%. Stochastic gradient boosting accuracy is a few percentage points less than that of random forests for forecast horizons over 10 days. For those looking to forecast the direction of gold and silver prices, tree bagging and random forests offer an attractive combination of accuracy and ease of estimation. For each of gold and silver, a portfolio based on the random forests price direction forecasts outperformed a buy and hold portfolio.

Solid state field-assisted silver ion exchange in porcelain stoneware: A new route toward antimicrobial tiles?

The development of tiles possessing antimicrobial activity is of great technological and scientific interest to improve the functionality of a very widely used article. Also the current SARS-CoV-2 pandemic is drawing the attention towards materials or compounds able to inactivate the virus, silver being among all the most promising one.In the present work, field-assisted ion exchange process was used to functionalize porcelain stoneware by introducing silver into the material surface using a solid silver electrode. The application of a small direct electric current (10 mA cm−2) at 380 °C allowed to fasten silver diffusion. The penetration of silver into stoneware appears homogeneous and primarily involves an exchange between silver and sodium ions under the effect of the external electric current. Penetration depths approaching 120 μm can be obtained in only 5 min. Preliminary characterization revealed that the Ag-exchanged stoneware possesses a strong biocidal action against Staphylococcus aureus.

Near-infrared photoluminescence enhancement and radiative energy transfer in RE-doped zinc-silicate glass (RE = Ho, Er, Tm) after silver ion exchange

Co-doping of rare-earth-doped glasses with silver is a promising option to enhance the photoluminescence of rare-earth (RE) ions. The enhancement of the emission of erbium has been demonstrated with great effect, but the research on the effect of silver on the near-infrared luminescence of holmium- and thulium-doped glass has been scarce. We have prepared a set of zinc-silicate glass samples doped by Ho3+/Yb3+, Er3+/Yb3+ and Tm3+/Yb3+ ions and co-doped them with silver to clarify the mechanisms behind luminescence enhancement and explore the possibility of enhancing the luminescence of holmium- and thulium-doped glass. Our results show that silver dimers increase the luminescence of RE-doped glass upon excitation in the visible range via the energy-transfer mechanism. Moreover, the photoluminescence enhancement has been observed upon excitation at 975 nm due to a combination of effects such as the structural changes of a silicate matrix and the SPR effect of silver nanoparticles.

Mechanistic investigation of elemental mercury adsorption over silver-modified vanadium silicate: A DFT study

Ag-modified vanadium silicate (EVS-Ag) has been regarded as a superior sorbent for elemental mercury (Hg0) capture from coal-fired flue gas. However, the atomic-level reaction mechanism which determines Hg0 adsorption capacity of EVS-Ag sorbent remains elusive. Reaction mechanism and active sites of Hg0 adsorption over EVS-Ag sorbent were studied using density functional theory (DFT) calculations systematically. DFT calculation results indicate that silver exchange shows little effects on the geometric structure of EVS-10 sorbent. Hg0 adsorption on EVS-10 and EVS-Ag surfaces is controlled by the physisorption and chemisorption mechanisms, respectively. Ag2 cluster is determined to be the most active site of Hg0 adsorption over Ag-modified EVS sorbent. The adsorption energy of Hg0 on Ag2 cluster is −51.93 kJ/mol. The orbital hybridization and electron sharing between Ag and Hg atoms are responsible for the strong interaction between EVS-Ag surface and Hg0. HgO prefers to adsorb on Ag2 cluster of EVS-Ag sorbent, and yields an energy release of 306.21 kJ/mol. HgO desorption from EVS-Ag sorbent surface needs a higher external energy, and occurs at the relatively higher temperatures. O2 molecule promotes Hg0 adsorption over EVS-Ag sorbent. HgO species can be easily formed during Hg0 adsorption over EVS-Ag sorbent in the presence of O2.

Distance-dependent visual fluorescence immunoassay on CdTe quantum dot-impregnated paper through silver ion-exchange reaction.

Apaper-based visual fluorescence immunoassay is presentedfor the detection of matrix metalloproteinase-7 (MMP7) that is related to renal cancer. The method is based on thedistance-dependent fluorescence quenching of CdTe quantum dots (QDs) on a nitrocellulose membrane by Ag+ followinga sandwich-type immunoreaction on microtiter wells using silver nanoparticle (AgNP)-labeled secondary antibody- and primary antibody-coated microtiter wells. The silver nanoparticles captured in the well are dissolved with HNO3, while the quenching effect of QDs is based on silver ion-exchange reaction under 365-nm excitation light irradiation. Increasingconcentration of released Ag+, thus higher concentration of the protein, leads to an increased distance of quenching on the nitrocellulose membrane. The paper-based immunoassay by combination of AgNP-assisted ion-exchange reaction with QD gives good distance-dependent responses and allows the detection of MMP7 at a concentration as low as 7.3pgmL-1. The coefficients of variation are less than 6.9% and 12.4% for intra-assay and inter-assay, respectively. High specificity and long-term stability are achieved during the assay. Importantly, the testing of human serum samples using our strategy shows well-matched results with commercial human MMP7 ELISA kits. Graphical abstract A distance-dependent visual immunoassay is developed for the determination of serum matrix metalloproteinase-7 on CdTe quantum dot-impregnated paper with silver ion-exchange reaction.

Novel dental adhesive containing silver exchanged EMT zeolites against cariogenic biofilms to combat dental caries

Abstract Secondary caries often occurs due to acids produced by biofilms at the tooth-restoration bonded interface, and is considered as one of the primary reasons for dental restoration failure. The objective of this study was (1) to synthesize nanosized EMT zeolites with silver ion exchanging, (2) to incorporate them into a commercial dental adhesive and (3) investigate the inhibition of biofilm formation at the tooth-restoration margin. The template-free zeolite nanocrystals are synthesized and stabilized in water suspensions and directly used for silver ion-exchange. Streptococcus mutans, Streptococcus gordonii, Streptococcus sanguinis were selected as representative strains of cariogenic pathogens and to form single-species biofilms. Colony-forming units (CFU), live/dead and metabolic activity were measured. The Ag+-EMT zeolites addition would not compromise the color and esthetics of dental restoration. EMT zeolites with longest exchanging time (40 min) in the adhesives achieved the greatest reduction in early attachment, bacterial biomass, biofilm growth and metabolic activity. Biofilm CFU counts were reduced by nearly 2 orders of magnitude for all three cariogenic pathogens. Therefore, the adhesives containing Ag+ exchanged zeolites had remarkable antibacterial properties to serve as “bioactive” adhesive materials and revealed its potential value for anti-biofilm and anti-caries clinical applications.

A silver transformation: Chinese monetary integration in times of political disintegration, 1898–1933†

AbstractThis article provides the first systematic econometric study on the evolution of Chinese silver exchange and monetary regimes during the period 1898–1933. Using high‐quality datasets of monthly and daily prices of silver dollars, we apply the threshold autoregressive models to estimate the silver points between Shanghai and 18 other cities in northern and central China. We find a noticeable improvement in monetary integration between Shanghai and Tianjin from the 1910s, which then spread to other cities in our sample throughout the 1920s and 1930s. We supplement our analysis with new datasets on volumes and costs of silver flows and with an in‐depth historical narrative. This article re‐evaluates the efficiency of the silver regime and China's economic performance in the Republican era.

An immunosensor for sensitive photoelectrochemical detection of Staphylococcus aureus using ZnS–Ag2S/polydopamine as photoelectric material and Cu2O as peroxidase mimic tag

We report here sensitive photoelectrochemical immunosensing of Staphylococcus aureus (S. aureus) using ZnS–Ag2S/polydopamine (PDA) as a novel photoelectric material and Cu2O as the peroxidase mimic tag. ZnS–Ag2S heterojunctions were prepared on indium tin oxide (ITO) via electrodeposition of ZnS nanoparticles, followed by silver ion exchange. To prepare a PDA/ZnS–Ag2S/ITO, the ZnS–Ag2S/ITO electrode was coated with PDA by self-polymerization of dopamine. The photocurrent of the PDA/ZnS–Ag2S/ITO is 1.55 times that of the ZnS–Ag2S/ITO and 7.87 times that of the ZnS/ITO, indicating a high-performance photoelectric material. A sandwiched-type photoelectrochemical immunosensor was constructed by using PDA/ZnS–Ag2S/ITO as the photoelectrode and Cu2O nanocubes as the labels. Cu2O nanocubes can serve as peroxidase mimic to generate catalytic precipitates on the immunoelectrodes, and both the Cu2O nanocubes and the generated precipitates can decrease the photocurrents of the immunoelectrodes, so a photoelectrochemical immunosensor for detecting S. aureus was constructed, showing a linear range between 10 and 107 CFU mL−1 and a low detection limit of 2 CFU mL−1. Owing to the signal amplification of Cu2O labeling, the sensitivity of the Cu2O-labeled immunosensor is 4 times that of a label-free immunosensor for detecting S. aureus, and the detection limit (2 CFU mL−1) is lower than that of a label-free immunosensor (10 CFU mL−1). This work not only provides a new and efficient photoelectric material but also demonstrated an efficient signal-amplification strategy for photoelectrochemical biosensing.

Electric field assisted ion exchange of silver in soda-lime glass: A study of ion depletion layers and interactions with potassium

The introduction of silver ions into glass by diffusion from an external source is of interest in modifying the optical and electrical properties of glass for device applications. Silver is introduced to fabricate in-glass waveguides, while potassium ions are introduced to pattern the silver diffusion by locally impeding the diffusion. Electric fields assist the silver diffusion, leading to faster diffusion rates of ions and allowing greater concentrations of silver without a metallic cluster formation. However, ion depletion layers are formed in the glass as a result of the application of electric field. Here, we study the nature of these depletion layers using depth profiles of composition after electric field diffusion, using cross-sectional energy dispersive x-ray spectroscopy analysis and infrared spectroscopy (Fourier transform infrared attenuated total reflection spectroscopy). We confirm the accelerated diffusion of silver by an electric field and show that potassium impedes the diffusion of silver even when a field is present. We find that an ion depletion layer is formed below the glass surface by the applied electric field which leads to a thermal relaxation and depolarization process when the samples are reheated. Observation of this process enables activation energies and threshold temperatures for the diffusion of Ag, K, and Na to be evaluated and compared with values obtained by composition profiles. Potassium was found to increase the initially low temperature threshold for silver diffusion, increase the activation energy, and also impede sodium diffusion.

Preparation of AgNPs/saponite nanocomposites without reduction agents and study of its antibacterial activity

A simple method for preparing AgNPs/clay nanocomposites using an adsorption process without any reducing agent was developed in which saponite iron-rich clay was both the solid inorganic support and reducing agent. Silver adsorption by ion exchange of silver ions and saponite ferrous ions resulted in simultaneous silver reduction and silver nanoparticle formation. The maximum loading of silver was determined as 48 mg/g (4.8 mass %). Microscopy showed a homogeneous distribution of sphere-like silver nanoparticles which are composed from smaller crystallites in the form of twinned triangular prisms. The silver particle sizes ranged from 1 nm to 50 nm but predominantly between 8 and 10 nm. The optimum pH range for silver immobilization on saponite support was between 4 and 8. Characterization of the clay samples and synthesized AgNPs/saponite nanocomposites was performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), porosimetry (low temperature nitrogen adsorption-desorption) and zeta potential measurements. The antibacterial activities of raw saponite and AgNPs/saponite nanocomposite samples were tested against clinical relevant Gram-positive Staphylococcus aureus, Staphylococcus epidermidis, and Gram-negative Escherichia coli, Pseudomonas aeruginosa and Proteus mirabilis bacteria by the well diffusion method.

Facile and ultrasensitive electrochemical impedance sensing for formaldehyde based on silver ions doped in controllable and homogeneous silica microspheres

Formaldehyde is a highly reactive and toxic compound in air pollutants, exposure to even a low concentration of formaldehyde will do harm to human health. Herein, a novel electrochemical impedance sensor for formaldehyde has been developed based on Ag+-SiO2 microspheres prepared by the exchange of silver ions with trapped ammonium ions. The probe of silver ion is easily and selectively reduced by formaldehyde, then the silver nanoparticles would be generated. Exposure to more concentration of formaldehyde, more proportionate silver nanoparticles would be loaded on the surface of silica microspheres, and then the decrement of interface charge transfer resistance (Rct) would be obtained accordingly. The decrement of Rct was linear with the concentration of formaldehyde in the range from 2 to 6000 pmol L−1 with a detection limit of 0.5 pmol L−1. Enabled by such a unique sensing mechanism, the fabricated sensor has been successfully applied for the detection of formaldehyde in real samples with high performance in selectivity, low power consumption, sensitivity, cost-effectiveness, facility, and portability.

Hydrolysis of cellulose to glucose by supercritical water and silver mesoporous zeolite catalysts

The hydrolysis of cellulose into glucose is a critical step for the conversion of lignocellulosic biomass into fuels and chemical products. The combination of supercritical water hydrolysis in ultrafast reactors, with the subsequent hydrolysis of the cello-oligosaccharides on silver-exchanged mesoporous mordenite zeolite, offers the possibility of a clear enhancement in the conversion of cellulose and in glucose formation. Complete dissolution of cellulose is achieved in the supercritical step and 81.8% of formed oligosaccharides are hydrolyzed in the catalytic step, with a yield into glucose of 77.0%. A fraction of Al is octahedrally coordinated, indicating a distribution of acid sites after the silver exchange. A deactivation of the catalyst between the first and third reaction cycle is observed, with a reduction in hydrolyzed carbon from 81.8% up to 45.6%. However, the selectivity to glucose only varies from 94.1 to 81.8%. Afterwards, the activity remains constant up to the fifth cycle. The presence of Ag(0) particles, together with the formation of coke, are responsible for the partial blockage of the pores of the support and loss of catalytic activity.