Adsorption Of Silver Research Articles

Tris(2‐Aminoethyl)Amine‐Functionalized Fe3O4 Magnetic Nanoparticles as a Selective Sorbent for Separation of Silver and Gold Ions in Different pHs

The usage of tris(2‐aminoethyl)amine‐functionalized Fe3O4 nanoparticles as a novel magnetic sorbent for rapid extraction, preconcentration, and determination of trace amounts of silver and gold ions was investigated. The optimum conditions for sample pH, eluent parameters (type, concentration and volume) were obtained. The effect of various cationic interferences on the adsorption of silver and gold was evaluated. The analytical efficiency values of both silver and gold ions were higher than 98.0% in the optimum conditions. The limits of detection (LOD) were less than 0.8 and 0.5 ng mL−1 for silver and gold, respectively. The linear ranges for silver and gold were 1.5–1000 ng mL−1 and 1.0–1000 ng mL−1 respectively. The maximum capacity of the modified magnetic nanoparticles was more than 97.3 mg g−1 and 167 mg g−1 for silver, and gold ions, respectively. The presented method was used to determine silver and gold ions in real samples. Finally, the method accuracy was confirmed by standard reference materials.

Molecular-Ion-Imprinted Chitosan Hydrogels for the Selective Adsorption of Silver(I) in Aqueous Solution

Chitosan hydrogels were prepared and imprinted by AgI with different mass ratios. Compared with the native chitosan hydrogel sample, the optimally imprinted sample (Agim75) presents a significantly enhanced AgI adsorption capacity as well as a high selectivity. This is attributed to the specific cavities formed by the template AgI ions in the polymer matrix. The effect of the adsorption conditions and desorption process were also studied.

Potential of Rice Husk for the Decontamination of Silver Ions from Aqueous Media

The sorption behavior of silver ions on rice husk has been investigated in detail. Various physico-chemical parameters were optimized to simulate the best conditions in which this material can be used as an adsorbent. Maximum adsorption was observed at 0.001 mol L−1 of acid solutions (HNO3, H2SO4 and HClO4) using 0.5 g of adsorbent for 9.27 × 10−5 mol L−1 silver concentration in fifteen minutes equilibration time. The adsorption of silver was decreased with the increase in the concentrations of all the acids used. The kinetic data indicated an intraparticle diffusion process with sorption being pseudo-second order. The determined rate constant k2 was 14.707 ± 1.832 mol g−1 min−1. The adsorption data obeyed the Freundlich, Langmuir, and Dubinin-Radushkevich isotherms over the silver concentration range of 1.85 × 10−4 to 1.16 × 10−3 mol L−1. The characteristic Freundlich constants, that is, 1/n = 0.38 ± 0.033 and K = 0.271 ± 0.104 m mol g−1 whereas the Langmuir constants Q = (1.504 ± 0.054) × 10−2 m mol g−1 and b = (16.582 ± 2.227) × 103 dm3 mol−1 have been computed for the sorption system. The sorption mean free energy from the Dubinin-Radushkevich isotherm is 12.16 ± 0.82 kJ mol−1 indicating ion-exchange mechanism of chemisorption. The uptake of silver increases with the rise in temperature (283–333 K). Thermodynamic quantities, namely, ΔG, ΔS, and ΔH have also been calculated for the system. The sorption process was found to be endothermic. The effect of other cations and anions on the adsorption of silver has also been studied.

Influence of interfacial water layer on surface properties of silver halides: Effect of pH on the isoelectric point

The hypothesis that pH dependent charge of interfacial water affects electrokinetic charge and electrokinetic potential of hydrophobic colloids, but not the (inner) surface potential was tested. It was found that isoelectric points of silver chloride, bromide and iodide shift to the higher pAg values in the acidic solutions, but that surface potential did not depend on pH. Isoelectric points of water at inert surfaces lie in the range 2<pH<4. In the neutral environment around pH≈7, the interfacial water is negatively charged due to preferential accumulation of OH− ions, with respect to H+ ions, thus increasing the negative electrokinetic charge of silver halide particles. In the acidic region, the isoelectric points of silver halides were shifted to the higher pAg values by 0.5–1.0pAg units depending on the type of silver halide, as well on the ionic strength of the solution. At pH≈3, the interfacial water is almost uncharged so that electrokinetic charge of silver halide particles is due to adsorption of silver and halide ions only. The conclusion was supported by mass titration experiments. Consequently, the electroneutrality points of silver halide surfaces correspond to values obtained in the acidic media. For silver chloride, pAgeln=5.3; for silver bromide, pAgeln=5.5; and for silver iodide, pAgeln=4.8.

Silver nano particle formation on Ar plasma – treated cinnamyl alcohol

Metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy are employed to study the adsorption of silver on cinnamyl alcohol films prepared on Au(111) substrates by thermal evaporation. Additionally, the impact of an Ar atmosphere dielectric barrier discharge plasma applied to the cinnamyl alcohol film preliminary to the Ag adsorption is investigated. In both cases silver nano particles with an average diameter of 9 nm are formed. These particles do not interact chemically with the underlying cinnamyl alcohol film. We do not find any influence of the preliminary Ar plasma-treatment on the adsorption behavior at all.

Electrooxidation of d- and l-Glucose at Well-Defined Chiral Bimetallic Electrodes

The electrooxidation of d- and l-glucose at chiral Pt{321}r/s single crystal electrodes modified with Au, Ag and Bi adatoms up to a coverage of one monolayer (ML) is reported. All adatoms investigated are found to selectively decorate kink and step sites. Only at higher coverages is adsorption onto the narrow {111} terrace sites observed for Bi, Ag and Au, consistent with previously reported adsorption behaviour on stepped surfaces vicinal to the {111} plane for chemisorbates exhibiting a lower work function than platinum. However, silver is found to block {111} terrace sites even when Pt step sites are still available on Pt{321}. This behaviour is ascribed to the propensity of silver to undergo place-exchange to form a surface alloy. The selective decoration of chiral kink sites has a profound influence on the voltammetric response of Pt{321} towards glucose electrooxidation. For bismuth adsorption, the electrooxidation current density initially increases and reaches a maximum when bismuth adsorption at {111} terraces commences. This is because the reaction pathways at step/kink sites leading to the formation of adsorbed CO (a surface poison for the clean surface reaction) and other strongly adsorbed intermediates, are either blocked by adsorbed bismuth or their electrooxidation and subsequent removal promoted. Once all step/kink sites are blocked by bismuth, hardly any chiral discrimination can be discerned between r-/s-electrodes towards d-/l-glucose. Silver adsorption does not cause any increase in glucose electrooxidation current density but rather induces a continual attenuation in glucose electrooxidation activity, particular (in contrast to bismuth) electrooxidation current at potentials in excess of 0.35 V. Therefore, unlike for bismuth, the initial glucose adsorption and electrooxidation processes associated with chiral kink sites appear to be preserved even though silver adsorbs at these sites. It is speculated that spontaneous place-exchange of silver with platinum to form a PtAg surface alloy at steps is responsible for this difference in behaviour between silver and bismuth. Finally, gold neither promotes reaction rate nor preserves chiral discrimination and is therefore deduced to act as an inert site blocker (no alloying, no promotion of CO electrooxidation) leading to complete attenuation of glucose electrooxidation current at a coverage of one ML.

Adsorption of Cu, Ag, and Au atoms on graphene including van der Waals interactions

We performed a systematic density functional (DF) study of the adsorption of copper, silver, and gold adatoms on pristine graphene, especially accounting for van der Waals (vdW) interactions by the vdW-DF and PBE + D2 methods. In particular, we analyze the preferred adsorption site (among top, bridge, and hollow positions) together with the corresponding distortion of the graphene sheet and identify diffusion paths. Both vdW schemes show that the coinage metal atoms do bind to the graphene sheet and that in some cases the buckling of the graphene layer can be significant. Only the results for silver are qualitatively at variance with those obtained with the generalized gradient approximation, which gives no binding in this case. However in all three cases, we observe some quantitative differences between the vdW-DF and PBE + D2 methods. For instance the adsorption energies calculated with the PBE + D2 method are systematically higher than the ones obtained with vdW-DF. Moreover, the equilibrium distances computed with PBE + D2 are shorter than those calculated with the vdW-DF method.

Determination of Trace Silver in Polymetallic Ore Samples by Flame Atomic Absorption Spectrometry after Solid‐Phase Extraction Using a Microcolumn Comprising Eggshell Membrane

A rapid and inexpensive method was developed for the determination of trace silver in polymetallic ore samples by use of eggshell membrane (ESM), a natural biomaterial, as the solid‐phase extraction (SPE) adsorbent coupled with flame atomic absorption spectrometry (FAAS). The ESM was used for the separation/pre‐concentration of silver, and the parameters affecting sensitivity, such as pH, sample flow rate, eluent volume and eluent flow rate, were carefully investigated. ESM was found to be an effective solid phase extractant for the adsorption of trace silver over a wide range of acidity from 0.02 to 0.50 mol l−1 HNO3. The sample solution in 0.4 mol l−1 HNO3 was pumped through an ESM microcolumn at the rate of 1.0 ml min−1. Silver was absorbed, and then eluted with a solution of 1.0% m/v thiourea–0.5% v/v HCl. Under these optimal conditions, ESM exhibited a good enrichment efficiency for silver with a dynamic adsorption capacity of 1.7 mg g−1. The proposed method was applied to the FAAS determination of trace silver in polymetallic ores and geological reference materials, GSO‐2, 3 and 5, and GSD‐11, GSD‐12, and the determined values were in good agreement with certified values.

Adsorption of Silver(I) from Aqueous Solution by Chelating Resins with 3-Aminopyridine and Hydrophilic Spacer Arms: Equilibrium, Kinetic, Thermodynamic, and Mechanism Studies

The equilibrium, kinetics, thermodynamics, and mechanism of two novel chelating resins with 3-aminopyridine and hydrophilic spacer arms (denoted as PS-DEG-3-AP and PS-TEG-3-AP) for Ag(I) were investigated in detail. The Boyd, Langmuir, Freundlich, and Dubinin−Radushkevich (D-R) models were applied to describe the adsorption of the resins for Ag(I). The saturated adsorption capacities of PS-DEG-3-AP and PS-TEG-3-AP for Ag(I) were (0.21 and 0.30) mmol·g−1 at pH 4, respectively. The results showed that the adsorption processes were governed by film diffusion and followed the pseudo second-order model well. The Langmuir model was better than the Freundlich model to describe the isotherm process. The E values obtained from the D−R model indicated that the adsorption of Ag(I) ions onto the resins occurred by chemical ion exchange. The adsorption mechanism of the resins for Ag(I) was confirmed by X-ray photoelectron spectroscopy (XPS). The XPS results clarified that not only 3-aminopyridine but also S atoms exis...

Stimulated adsorption and capillary condensation

The joint adsorption of silver and water vapors on an ideal substrate is studied in a numerical experiment using a modified Langmuir adsorption model. The calculations reveal a number of previously unknown phenomena. It is established that the adsorption and condensation of silver vapor stimulate the adsorption of water vapor, resulting in its capillary condensation at the molecular level even at low saturation. It is shown that the rate of capillary condensation depends on the wetting angle of water on silver, and there is a characteristic wetting angle at which the rate of capillary condensation changes radically. It is also found that water vapor has a significant effect on the adsorption of silver vapor and the structure of its condensate on the substrate: the presence of water vapor reduces the adsorption of silver atoms on the substrate and weakens the adhesion of silver condensate to the substrate. The results can be used to study two-component adsorption and capillary condensation and to develop technologies for growing thin films in a gas phase.

Adsorption of silver from aqueous solution onto fly ash and phosphogypsum using full factorial design

AbstractThe aim of this research is to analyze the role of experimental factors on the adsorption of silver from an aqueous solution by using 24 factorial design. The experimental factors and their respective levels that were selected include an initial silver concentration of 50–250 mg/L, an adsorbent dosage of 1.25–10 g/L, a temperature of 20–60°C, and material types that consist of fly ash and phosphogypsum. The results were statistically analyzed by using the student's t‐test, analysis of variance (ANOVA), and an F‐test to define important experimental factors and their levels. A regression model that considers the significant main and interaction effects was suggested. The selected experimental factors were determined to influence the adsorption process but their importance varied according to the sequence: initial concentration (50 mg/L) &gt; waste material type (fly ash) &gt; adsorbent dosage (10 g/L) &gt; temperature (60°C). © 2010 American Institute of Chemical Engineers Environ Prog, 2010

Powerful adsorption of silver(I) onto thiol-functionalized polysilsesquioxane microspheres

The strong adsorbability of Ag(I) ions onto poly(3-mercaptopropylsilsesquioxane) (PMPSQ) microspheres synthesized through a two-step acid–base catalyzed sol–gel process method was systematically examined. The effect of adsorption time, initial Ag(I) concentration, and solution pH was studied to optimize the Ag(I) adsorbability of PMPSQ microspheres. The PMPSQ microspheres demonstrate a powerful Ag(I) adsorbability with an adsorptivity above 99.99% when the initial Ag(I) concentration is lower than 10 mM and the highest Ag(I) adsorbance of 1140 mg/g at an initial Ag(I) concentration of 150 mM. Adsorption phenomena appeared to follow Langmuir isotherm. The kinetic studies indicated that the adsorption process well fits the pseudo-second-order kinetics with a very rapid initial adsorption rate of 15.28 mg g −1 min −1. The appropriate solution pH for Ag(I) adsorption is around 2.0–5.4. The PMPSQ microspheres demonstrate a promising application in the removal of Ag(I) ions from aqueous solutions.

Ag on Cu(110)-(2*1)O: Desorption of Oxygen versus Diffusion of Ag

The adsorption of silver on the Cu(110)-(2×1)O surface was studied by Auger electron spectroscopy and scanning tunneling microscopy. For deposition at room temperature the CuO layer is overgrown by a highly stressed and therefore rough silver layer. If the sample is annealed, the oxygen will desorb via formation of temporary Ag-O compounds. At the same time silver will diffuse into the copper bulk. The situation is quite different if silver is deposited at 660 K: For the deposition of up to one monolayer of silver no significant desorption of oxygen is observed by Auger electron spectroscopy. It is found that domains of a Ag rich Ag/Cu alloy and the bare CuO phase are spatially separated. Only upon further Ag deposition, oxygen desorption takes place. [DOI: 10.1380/ejssnt.2010.32]

The preg-robbing of gold and silver by clays during cyanidation under agitation and heap leaching conditions

Abstract Laboratory scale leaching tests were carried out in different experimental conditions, with monitoring of gold and silver recovery, the concentration of cyanide used in leaching, solution pH, and precious metal adsorption onto clay. Evidence for the adsorption or re-precipitation of gold from cyanide solutions onto clay minerals is conclusive and indicates that adsorption contributes to the total gold loss from conventional cyanidation. The loss is related to the type of clay, and appears to be affected by the extent of time cyanidation. It was observed that silver adsorption capacity was above 80% and that the degree of adsorption for gold oscillated between 1.68% and 7.49%, depending on the type and characteristics of the evaluated clay.

Quantum chemical study of adsorption of Ag 2, Ag 4 and Ag 8 on stoichiometric TiO 2 (1 1 0) surface

A density functional theory (DFT) calculations have been carried out to study the adsorption of silver di-, tetra- and octamers on stoichiometric rutile (1 1 0) surface. In order to determine the most reliable model of adsorption, two different approaches have been used: a cluster model and a periodic one. Comparison of the calculation results with the experimental data revealed that the periodic model exhibits better results than the cluster one. The most stable adsorption sites for each silver cluster have been found. It has been shown that hollow-sites are preferable to adsorption over chain oxygen atoms. Population and charge analysis have been carried out to determine the binding mechanisms for the most stable structures. The adsorbed clusters are coupled with the surface through two types of binding in case of the hollow-sites. The first type is the overlap between HOMO of the cluster and unfilled surface level which consists mostly of Ti atom 3d-orbitals. The charge is partly transferred from cluster to the surface, thus all adsorbed clusters have positive charges. The value of charge correlates with binding energies. The second binding type is the interaction of MOs of the cluster with surface eigenstates localized on chain oxygen atoms. This interaction is equally strong as compared to that of the first type and leads to deformation of silver clusters structure during adsorption. The second type of binding only occurs during the adsorption over chain oxygen atoms. Thus, the binding energies are smaller in this case. The presence of filled levels in the band gap has been revealed for some structures. It can be one of the reasons of high photocatalytic activity typical for Ag/TiO 2 systems.

Silver: a novel growth catalyst for Ge nanoislands on Si(113)

The impact of silver pre-adsorption on germanium growth on Si(113) was investigated using in-situ low-energy electron microscopy (LEEM) as well as low-energy electron diffraction (LEED). The adsorption of silver leads to the formation of a regular pattern of nanofacets along the [10] direction. The periodicity of this pattern in [33] direction was determined to (44 ± 4) nm. From LEED series at different energies the facets were identified to be of (111) and (115) orientation. While the (111) facets show a (√3 × √3)-R30° reconstruction, the (115) facets exhibit a (2 × n) superstructure. The subsequent growth of Ge results in the formation of nanoislands that are aligned along the facets. These Ge islands have an anisotropic shape with typical sizes of about 100 nm in [33] direction and 400 nm in [10] direction. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of a novel dithiooxamide–formaldehyde resin and its application to the adsorption and separation of silver ions

In this study, a new chelating resin of dithiooxamide (rubeanic acid)–formaldehyde (DTOF) has been synthesized by the reaction of dithiooxamide and formaldehyde. Also a well-known chelating resin of thiourea (thiooxamide)–formaldehyde (TUF) has been prepared by the reaction of thiourea and formaldehyde. DTOF and TUF chelating resins were used in the adsorption, separation and concentration of silver ions by batch and column techniques. These resins were characterized using FTIR and elemental analysis. It was found that DTOF resin has silver adsorption capacity of 3333.3 mg g −1 or 30.86 mmolg g −1 and TUF resin has the capacity of 1428.6 mg g −1 or 13.22 mmol g −1. DTOF resin showed more affinity to silver ions according to Cu(II), Zn(II), Ni(II) and Co(II) base metal ions than TUF resin. It was also demonstrated that DTOF resin can be used in the separation and concentration of silver ions.

Determination of Silver by Flame Atomic Absorption Spectrometry after Preconcentration on Naphthalene Modified with Dithizone

AbstractA solid‐phase extraction method for preconcentration of silver and consequent determination by atomic absorption spectrometry is described. The method is based on the adsorption of silver on naphthalene modified with dithizone in a column. The adsorbed silver is eluted from the column with a thiourea solution and determined by flame atomic absorption spectrometry. The adsorption conditions including pH, reagent concentration, eluent volume, flow rate and interfering ions were investigated. The calibration graph was linear in the range 10–1000 ng mL−1 of Ag in the initial solution with r = 0.9998. The limit of detection based on 3Sb was 3.9 ng mL−1. The relative standard deviation for ten replicate measurements of 40 and 600 ng mL−1 of Ag was 4.4% and 0.9%, respectively. The method was applied to the determination of silver in mineral, radiology film and wound dressing samples.

Adsorption of silver(I) on synthetic chelating polymer derived from 3-amino-1,2,4-triazole-5-thiol and glutaraldehyde

New types of polymer condensation adducts were synthesized through the reaction of 3-amino-1,2,4-triazole-5-thiol (AZ) with glutaraldehyde in the absence and in the presence of thiourea at different molar ratios. The adsorption behavior of the chelating polymers towards Ag(I) from aqueous solutions was studied. Better adsorption behavior was achieved for Ag(I) by thiourea polymeric adducts. The chelating matrix obtained from a molar ratio of 2:1:3 of AZ, thiourea and glutaraldehyde, respectively, showed uptake capacity of 3.6 mmol/g. These polymers were evaluated for their recovery of Ag(I) from aqueous solutions using batch methods. The obtained polymers achieved promising results in the selective separation of Ag(I) from other metal ions. Both kinetics and thermodynamic parameters of the adsorption process were obtained. The data indicated that the adsorption process is an endothermic reaction and kinetically proceeds according to pseudo-first-order model. These parameters indicated that the polymers can be applied in the recovery of Ag(I).

Bacillus Spore Classification via Surface-Enhanced Raman Spectroscopy and Principal Component Analysis

Surface-enhanced Raman spectroscopy (SERS) can provide rapid fingerprinting of biomaterial in a nondestructive manner. The adsorption of colloidal silver to biological material suppresses native biofluorescence while providing electromagnetic surface enhancement of the normal Raman signal. This work validates the applicability of qualitative SER spectroscopy for analysis of bacterial species by utilizing principal component analysis (PCA) to show discrimination of biological threat simulants, based upon multivariate statistical confidence limits bounding known data clusters. Gram-positive Bacillus spores (Bacillus atrophaeus, Bacillus anthracis, and Bacillus thuringiensis) are investigated along with the Gram-negative bacterium Pantoea agglomerans.