Adsorption Of Ag Research Articles

Removal and reutilization of metal ions on ZIF-67/GO membrane via synergistic photocatalytic-photothermal route

The serious problem from pollution of metal ions placed great pressure to global water ecosystem and human beings. Herein, a synergistic photocatalytic-photothermal system of integrated membrane for the removal and reutilization of aqueous Ag+ ions was designed. The crystal of zeolitic imidazolate frameworks-67 (ZIF-67) stably grew on the graphene oxide (GO) membrane with the uniform distribution. In the ZIF-67/GO membrane, the adsorption and photo-reduction of Ag+ ions on ZIF-67 crystals led to the deposition of Ag nanoparticles on the membrane surface, which facilitated the capture of visible light, suppressed the recombination of the electron-hole pairs and promoted the photothermal effect. Meanwhile, the high efficiency of photothermal conversion on GO substrate realized the water evaporation to concentrate the Ag+ solution and inhibited the separation of photo-induced charges. The synergistic photocatalytic-photothermal route on ZIF-67/GO membrane provides a new sight for the recycle of metal ions for the future practical applications.

Preparation and properties of a dual-function cellulose nanofiber-based bionic biosensor for detecting silver ions and acetylcholinesterase

A dual-function cellulose nanofiber (CNF)-based bionic biosensor with good biocompatibility was developed for detecting Ag+ and acetylcholinesterase (AChE) by grafting deoxyribonucleic acid (DNA) onto CNF. The Ag+ ions captured by the biosensor acted as recognition sites for the detection of AChE. The CNF-based bionic biosensor (CNF-DNA) could detect Ag+ concentrations as low as 10−6 nM in the presence of interference metal ions (Hg2+, Ba2+, Cd2+, Mg2+, Mn2+, Pb2+, and Zn2+). DNA-template silver nanoclusters (DNA-AgNCs) were formed on the surface of CNF-DNA during the detection of Ag+ (CNF-DNA-AgNCs). This new strategy yielded CNF-DNA-AgNCs through the adsorption of Ag+ ions onto the cytosine base of the single-stranded DNA in CNF-DNA without the use of any additional reducer. Meanwhile, the CNF-DNA-AgNCs exhibited excellent sensitivity and selectivity for trace levels (0.053 mU/mL) of AChE in the presence of interference reagents. The novel strategy proposed in this paper may establish a foundation for further research on DNA-template AgNCs for developing biosensors and biomarkers for in vivo and in vitro detection.

Understanding the adsorption mechanism of Ag+ and Hg2+ on functionalized layered double hydroxide via statistical physics modeling

Modeling analysis based on a statistical physics theory was used to explain the adsorption of Ag+ and Hg2+ on layered double hydroxides (LDH) functionalized with anions CO32−, NO3−, S52− and MoS42−. Theoretical adsorption models assuming different types of functional groups on LDH surface were tested and compared. A statistical physics model based on two active sites for the adsorbate binding was the best option to characterize and interpret the removal of investigated heavy metals on LDH. Modeling results showed that the total adsorption capacities at saturation ranged from 112 to 631 mg/g and from 110 to 638 mg/g for Ag+ and Hg2+, respectively. LDH functionalized with anion MoS42− was the best adsorbent for the removal of both metal ions. It was also demonstrated that the anionic functionalities and the oxygen-containing groups of LDH contributed in different extent for the adsorption of Ag+ and Hg2+. Statistical physics parameters suggested a multi-ionic and endothermic adsorption caused by physical and chemical interactions. Finally, the adsorption mechanism was macroscopically explained via the calculation and analysis of thermodynamic potentials.

Oxygen adsorption of molten Ag[sbnd]Cu eutectic alloy and its associated surface modification

The surface tension of liquid AgCu eutectic alloy has been measured in a wide range of oxygen partial pressures using two different methods: the constrained drop method and the electromagnetic levitation method. In order to investigate the influence of oxygen potential on the surface tension of the Ag40Cu (at.%) eutectic alloy, the oxygen partial pressure was varied between 8.62 × 10−15 and 2.42 Pa. At low oxygen partial pressure, the surface tension of the AgCu eutectic alloy measured in the temperature range of 1223–1476 K, shows temperature dependence in a good agreement with previously reported results. At higher oxygen partial pressures, the decrease in surface tension is more pronounced and the oxygen adsorption on the surface accordingly increases. Moreover, at high oxygen partial pressure, the oxygen adsorption on the AgCu eutectic alloy was found to be far greater than the expected saturation limit taking into account the theoretically calculated surface concentration of Cu in the AgCu eutectic alloy and the surface excess of oxygen on the molten Cu at saturation. This phenomenon can be explained with a model where the surface of the AgCu eutectic alloy undergoes Cu-substitution at the Ag sites during the oxygen adsorption process.

Using MgO nanoparticles as a potential platform to precisely load and steadily release Ag ions for enhanced osteogenesis and bacterial killing

Bio-functional fillers including bio-ceramic, degradable metallic and composite particles are commonly introduced into bone tissue engineering (BTE) scaffolds to endow the materials with specific biological functions for enhanced bone defect therapy. In this work, MgO nanoparticles (NPs) were employed as a potential platform for precise loading and sustained release of Ag+. The results showed that MgO NPs possessed strong adsorption capacity (almost 100%) towards Ag+ in AgNO3 solutions with different concentrations (0.1, 1 and 10 mM). After the adsorption of Ag+ in AgNO3 solutions, cube-shaped MgO NPs transformed to lamella-structured nano-composites (NCs) composed of Mg(OH)2 and Ag2O, which were referred as MgO-xAg (x = 0.1, 1 or 10) NCs depending on the employed concentration of AgNO3 solution. After being suspended in distilled water, as-prepared positively charged NCs underwent a fast degradation process during the initial 4 days. From day 4 and 14, steady release behaviors of Mg2+ and/or Ag+ from the NCs were noticed. With the lowest loading amount of Ag+, MgO-0.1Ag NCs did not exhibit significant modulatory effect on SaOS-2 cell response. On the contrary, MgO-10Ag NCs loaded with the highest amount of Ag+ showed significant cyto-toxicity towards SaOS-2 cells. With appropriate amount of Ag+ loading, MgO-1Ag NCs showed significantly stimulatory effects on SaOS-2 cell proliferation and differentiation. This is evidenced by the enhanced cell viability, alkaline phosphatase (ALP) activity and collagen (COL) production as well as the gene expressions of ALP, COL and osteoprotegerin (OPG) in MgO-1Ag group. Moreover, MgO-1Ag exhibited strong bactericidal capacity against both Escherichia coli and Staphylococcus aureus. Together, the results indicate that MgO could be employed as a potential platform for precise loading and sustained release of Ag+. MgO-1Ag NCs are promising to be used as bio-functional fillers in BTE scaffolds for simultaneously promoted osteogenesis and bacterial killing.

DFT study of gas adsorption and sensing based on noble metal (Ag, Au and Pt) functionalized boron selenide nanosheets

Adsorption of transition metal atoms on the surface of 2D layered nanomaterials plays a significant role in modulating the electronic properties of the metal functionalized systems. In this work, we examined the adsorption of Ag, Au and Pt adatoms on the surface of BSe monolayer based on the DFT method. Our band structure calculations reveal that perfect BSe monolayer displays indirect gap semiconductor property. The adsorption performance of the Au-adsorbed BSe monolayer upon NO, NH3 and NO2 gas molecules was examined to evaluate its potential use for highly efficient gas sensor devices. The Au adatom is adsorbed on the BSe monolayer with considerable adsorption energy, which indicates the strength and stability of the substrate for adsorption processes. Thus, the Au-adsorbed BSe monolayer behaves as an excellent adsorbent for sensing NO, NH3 and NO2 gas molecules. Interestingly, all the gas molecules are strongly chemisorbed on the Au site of Au–BSe system. NO2 molecule presents the most favorable adsorption on the surface with oxygen atoms coordinated to the Au atom. Our results also suggest that gas molecules adsorption on the Au–BSe monolayer can lead to remarkable variations in the electronic properties of the systems. The greatly enhanced electron overlaps between the projected density of states of the interacting atoms confirm the chemical interaction between the gas molecules and Au–BSe monolayer.

Comparison of Monovalent and Divalent Ions Removal from Aqueous Solutions Using Agricultural Waste Biochars Prepared at Different Temperatures—Experimental and Model Study

Copper (Cu) and silver (Ag) occur naturally in the environment but have toxic effects on organisms at elevated concentrations. This paper discussed the removal of Cu and Ag from aqueous solutions using biochars obtained at different pyrolysis temperatures. Three biomass sources—sunflower husks (SH), a mixture of sunflower husks and rapeseed pomace (SR) and wood waste (WW)—were pyrolyzed at 300, 400 and 500 °C. Biochars produced at 500 °C exhibited a higher specific surface area, lower variable surface charge and lower contents of surface functional groups than those obtained at 400 or 300 °C. The pseudo-second-order model and intra-particle diffusion (IPD) model well-described the Cu and Ag adsorption kinetics. The Cu adsorption was about 1.48 times slower than the Ag adsorption on the biochars obtained at 500 °C. The model of Langmuir-Freundlich well-described the equilibrium adsorption. Agricultural biochars obtained at >500 °C had a surface with a higher affinity to attract Ag than Cu and were able to remove a larger amount of heavy metals from aqueous media than those prepared at lower pyrolysis temperatures.

Silver Adsorption on Calcium Niobate(001) Nanosheets: Calorimetric Energies That Explain Sinter-Resistant Support.

Metal nanoparticles deposited on oxide supports are essential to many technologies, including catalysts, fuel cells, and electronics. Therefore, understanding the chemical bonding strength between metal nanoparticles and oxide surfaces is of great interest. The adsorption energetics, adhesion energy, and adsorbate structure of Ag on dehydrated HCa2Nb3O10(001) nanosheets at 300 K have been studied using metal adsorption calorimetry and surface spectroscopies. These dehydrated ("dh") calcium niobate nanosheets (dh-HCa2Nb3O10(001)) have the stoichiometry Ca4Nb6O19. They impart unusual stability to metal nanoparticles when used as catalyst supports and are easy-to-prepare by Langmuir-Blodgett (LB) techniques, highly ordered, and essentially single-crystal surfaces of mixed oxides with a huge ratio of terrace to edge sites. Below the monolayer coverage, Ag grows on dh-HCa2Nb3O10(001) as 2D islands of thickness ∼2 layers. The differential heat of Ag adsorption is initially ∼303 kJ/mol, increasing slowly to ∼338 kJ/mol by 0.8 ML. At higher coverages, Ag atoms mainly add on top of these 2D islands, growing 3D nanoparticles of increasing thickness, as the heat decreases asymptotically toward silver's heat of sublimation (285 kJ/mol). The adhesion energy of Ag(s) to this Ca niobate surface is estimated to be 4.33 J/m2, larger than that on any oxide surface previously measured. This explains the sinter resistance reported for metal nanoparticles on this support. Electron transfer from Ag into the calcium niobate is also measured. These results demonstrate an easy way to do single-crystal-type surface science studies-and especially thermochemical measurements-on the complex surfaces of mixed oxides: using LB-deposited perovskite nanosheets and ultrahigh-vacuum annealing in O2.

Efficient recovery of Ag(I) from aqueous solution using MoS2 nanosheets: Adsorption study and DFT calculation

An attempt was made to recover Ag(I) using MoS2 nanosheets as adsorbent. The adsorption process was investigated through adsorption kinetics and isotherm tests, and the adsorption mechanism was revealed by XPS and DFT calculations. The results indicated that adsorption process was well consistent with Langmuir isotherm model. The high Ag(I) adsorption capacity of MoS2 (780 mg/g) could be attributed mainly to the complexation of Ag-S, along with insignificant complexation of Ag-O. The interaction between Ag(I) and MoS2 surface was in the form of orbital hybridization of Ag(I) with S and O.

The effects of transition metal adatoms on the electronic properties of stanene

Abstract The electronic characteristics of transition metal adatoms (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt and Au) adsorbed on monolayer stanene have been investigated by using the first-principles calculations. The results show that the transition metal atoms are energetically favorable at the hollow and top sites of the stanene. Stanene has good adsorption capacity to foreign adsorbed atoms, and the adsorption energy is up to 6.241 eV, which is stronger than that of phosphorene and graphene. For Ni-, Ru- and Pd-adatoms, a narrow bandgap is opened in the monolayer stanene with the bandgap of 109.4 meV, 69.6 meV and 32.4 meV, respectively. The adsorption of Fe, Co, Cu, Ag, and Au adatoms upshifts the Fermi level to the conduction band and causing n-type doping. For the Fe-, Co-, Ru-, Rh- and Os-adsorbed stanene, it can be found that the magnetic moments are 3.144 μ B , 2.024 μ B , 2.028 μ B , 1.007 μ B and 1.995 μ B , respectively. Interestingly, for Os-adsorbed stanene, the spin upward is a metal, and the spin down is a semiconductor with 215.5 meV, namely, it shows the half-metallicity. The remaining (Fe-, Co-, Cu-, Ag-, Pt-) adsorbed stanene all exhibit metallic character. Our results indicate that the transition metal adsorption may be pave the way for the study of nanoelectronics and spintronics of stanene.

Adsorption behaviors and mechanism of graphene oxide for silver complex anion removal

Graphene oxide (GO) is an outstanding material for water treatment, their film structure and functional groups may play crucial roles in anion removal. Herein, the removal of silver complex anion Ag(CN)2− by GO was conducted to study the behavior and mechanism of GO in silver exceeded system. The work was carried out by the adsorption of Ag(CN)2− on GO as functions of pH, adsorption time and adsorbate concentration. The results, based on XRD, SEM, TEM, AFM, XPS, FT-IR, presented that the prepared GO has a film structure and amount of oxygenous functional groups. Further studies found that GO exhibits big adsorption capacity (100.7 mg/g) and high adsorption rate (0.0084 min−1) in accordance with the adsorption kinetics and isotherm, implying the GO might be a good potential adsorbent for Ag(CN)2− removal. The adsorption progress was found fits well with second-order adsorption model meanwhile follows Langmuir adsorption model well. The silver was confirmed adsorbed in form of Ag(CN)2− and distributed uniformly on GO. The adsorption performance and mechanism was ascribed to the film structure and the interactions between Ag(CN)2− and oxygenous functional groups, and the DFT calculation implied the groups contribute for adsorption in order of epoxy > hydroxyl > carboxyl.

Selective adsorption for Ag (I) from wastewater by carbon-magnetic fly ash beads modified with polydopamine and thiourea

A magnetic adsorbent was prepared by polydopamine coating and thiourea grafting on carbon-modified discarded fly ash magnetic beads (TPCMFA). The successfully preparation of the TPCMFA was supported by SEM image, XRD, FT-IR and Raman spectroscopy. Batch adsorption experiments reveal that the adsorption of silver ions on this magnetic sorbent TPCMFA agreed with the Langmuir isotherm model, with a maximum absorbability of 94.94 mg g-1. Kinetics data revealed that the adsorption of silver ions on TPCMFA conform to a pseudo-second-order. The TPCMFA achieved remarkable selectivity for Ag (I) that was almost five times higher than that for ions of copper, zinc and nickel. After three cycles, the adsorption capacity of TPCMFA remained at 93.5% of the adsorption capacity of the initial material. These results show that this new magnetic adsorbent prepared from discarded fly ash magnetic beads has promising commercial prospects.

Pseudo-SILAR assisted unique synthesis of ZnO/Ag2O nanocomposites for improved photocatalytic and antibacterial performance without cytotoxic effect

The combination of silver (I) oxide (Ag2O) with zinc oxide (ZnO) evolves the magnificent response of composite for antimicrobial and photocatalytic applications concomitantly. A novel, cost-effective and facile wet-chemical recipe for developing ZnO/Ag2O nanocomposites is realized by customizing pseudo-successive ionic layer adsorption and reaction (p-SILAR) process. Quantitatively as well as qualitatively controlled Ag2O was deposited on flower-like ZnO, termed as ZnO NFs, by carrying out 1–4 cycles of customized p-SILAR. It was affirmed that the cationic adsorption of Ag+ from AgNO3 solution instigates the formation of Ag2O over ZnO NFs via a simple heat-treatment process. Followed by the customary material characterizations including SEM, TEM, XPS etc., the ZnO/Ag2O nanocomposites were tested for controlling the toxic organic dye (Rhodamine B) and harmful bacterial species i.e. E. coli and B. subtilis. A significant increase in the photocatalytic performance of ZnO NFs under ultra-violet (UV) as well as visible (vis) irradiation was obtained by incorporating 2 cycles of Ag2O deposition. Consequently, the degradation rate constant of optimal ZnO/Ag2O-2C was increased to 0.1077 and 0.0104 from 0.0235 and 0.0011 min−1, under UV and vis light respectively. Similarly, ZnO/Ag2O evolved a significant increase in the inhibition zones without exhibiting a considerable decrease in the cell viability of HepG2, which further avowed the bio-compatibility of ZnO NFs having Ag2O.

Biomass type effect on biochar surface characteristic and adsorption capacity relative to silver and copper

Copper (Cu) and silver (Ag) have toxic effects on the environment at elevated concentrations, and thus, the effective removal of these elements from aqueous media is of great importance. This paper describes a study of the sorption properties of biochars in aqueous solutions relative to Cu and Ag. The biochars used in the experiment were produced through pyrolysis of sunflower husks (BC1), a mixture of sunflower husks and rapeseed pomace (BC2) and wood waste (BC3) at 600 °C. BC2 exhibited the highest specific surface area, value of surface charge and content of functional groups of the three biochars. The pseudo-second-order model and IPD model best described adsorption kinetics, and the Langmuir-Freundlich model accounted for the adsorption data. BC2 had the highest adsorption capacity and was conductive to the fastest rate of adsorption, and this biochar thus enabled the removal of a largest quantity of heavy metals from aqueous media. In the BC2 trial, the rate of Ag sorption was approximately 1.2 times faster than that of Cu, and the Ag adsorption amount was about 34.3 times greater than that observed for Cu.

Effect of undercoordinated Ag(111) defect sites on the adsorption of ethanol

In recent years, the use of silver-based materials for selective and highly active ethanol reactivity in single atom catalysis and the ethanol oxidation reaction in direct fuel cells highlights the importance of silver (Ag) in an ethanol economy. Understanding the interaction of ethanol with Ag(111) and the natural defects found on extended Ag(111) is critical to the overall understanding of more complex catalytic processes including ethanol activation over Ag-based catalysts. The research herein aims to characterize the interaction of ethanol molecules on undercoordinated defect sites of Ag(111) to mimic active sites found on Ag nanoparticle catalysts. The interaction between ethanol and Ag(111) was studied using temperature programed desorption (TPD), x-ray photoelectron spectroscopy, and density functional theory (DFT). Molecular ethanol adsorption and desorption from Ag(111) and the distinction between undercoordinated Ag(111) adsorption sites were determined using TPD in correlation with DFT. Complete analysis of TPD data for ethanol adsorbed to terrace sites was used to calculate a kinetic prefactor (3.4 × 1015) and desorption energy (0.54 eV). A better understanding of defect-dependent behavior for ethanol on silver can lead to a greater insight into high surface area nanoparticle catalysts used in industries, catalytic converters, and photo-, electro-, and heterogeneous catalysis. The results suggest that ethanol preferentially adsorbs to undercoordinated sites on Ag(111), resulting in higher binding energies for these molecules (Redhead first order approximation for desorption energies is terrace, 0.54 eV; step edge, 0.57 eV; and kink sites, 0.61 eV). Furthermore, alteration of the silver surface can lead to a redistribution of these sites.

Enhanced Gold(III) adsorption using glutaraldehyde-crosslinked chitosan beads: Effect of crosslinking degree on adsorption selectivity, capacity, and mechanism

Recovery of gold from electronic waste (e-waste) has received significant attention due to its high economic value. This study reports glutaraldehyde-crosslinked chitosan (GCC) beads as highly efficient bioadsorbents for the separation of auric ions (Au(III)) from acidic e-waste leaching solutions. With increasing extent of glutaraldehyde-crosslinking, the GCC beads showed enhanced adsorption selectivity and capacity toward Au(III). The Au(III) adsorption capacity, however, was saturated with a further increase in the crosslinking time due to increasing self-oligomerization of glutaraldehyde. High adsorption selectivity was also observed for other precious metals such as Pd(II), Pt(IV), Ir(III), Os(IV), and Ag(I), but negligible adsorption was found for most other metals. The high Au(III) adsorption capacity and selectivity of GCC beads was attributed to multiple mechanisms such as electrostatic attraction, chelation, and reduction of Au(III), based on a range of spectroscopic evidence (FTIR, XRD, XPS, SEM, and TEM) and Au(III) adsorption behavior. The adsorbed Au(III) was reduced to Au(I) and then to Au(0), forming Au-nanoparticles as the main Au species with increasing adsorption time. The GCC beads showed a good reusability in repeated Au(III) adsorption–desorption cycle tests and were used to successfully separate high purity gold (96.7%) from an acidic e-waste leaching solution.

Adsorption behavior of Ag(I) onto elemental sulfur-encapsulated silica nanocapsules for industrial applications

Pure silica nanocapsules (SiNC-P) and elemental sulfur-encapsulated silica nanocapsules (SiNC-ES) as Ag(I) adsorbents were successfully synthesized by a one-step water-in-oil microemulsion polymerization process. The characterization of the synthesized materials, such as surface morphology, surface area, porosity, functional groups and thermal characteristics, was carried out using various analytical techniques. The SiNC-P and SiNC-ES have nearly similar morphology, but the surface area and pore size of the SiNC-ES are higher than SiNC-P. The Ag(I) adsorption study showed that it increased with increasing elemental sulfur (ES) amount in the SiNC-ES. The SiNC-ES shows high adsorption capacity, independent of pH, and higher adsorption rate as compared to SiNC-P. The maximum Ag(I) adsorption capacity of SiNC-P and SiNC-ES was 50.49 mg g−1 and 98.51 mg g−1, respectively. The adsorption isotherm data were best described by the Langmuir model. The diffusion modeling analysis of the kinetic data indicated that film diffusion is the controlling step, while chemical reaction modeling obeys the pseudo-second-order kinetic model. The SiNC-ES was reusable and good adsorption performance up to four adsorption cycles was observed. The practical capability of the SiNC-ES to adsorb Ag(I) was successfully demonstrated using an industrial waste solution in which a high removal efficiency was observed (η>90%). This demonstrates that the SiNC-ES can be a potential adsorbent for Ag(I) recovery from industrial wastes.

A DFT study of the adsorption of noble metal adatoms (Pd, Pt, Ag, Au) on 2D tin disulfide monolayers: Potential towards nanoscale electronic devices

Abstract We examined the structural characteristics and electronic properties of various transition metals (Pd, Pt, Ag, and Au) adsorption on the SnS2 monolayers and elucidated their possibility for utilization in next generation electronic devices. Our obtained results confirmed the strong interactions between the different noble metal adatoms and the hollow site of SnS2 monolayers. Our calculated binding energies suggested that the noble metal adsorbed SnS2 monolayers are energetically stable. The electronic properties analysis demonstrated that the electronic charges were drastically distributed over the adsorbed noble metal adatoms. Moreover, among all noble metal adatoms, embedded Pd atom has the strongest interaction with SnS2 monolayers because of its higher binding energy. In contrast, the weakest interaction corresponds to the embedding of Au adatom on the surface. Our calculated results propose new routes for the design and the development of highly talented noble metal embedded SnS2 based 2D materials.

Adsorption of silver ion from the aqueous solution using a polyvinylidene fluoride functional membrane bearing thiourea groups

A novel polyvinylidene fluoride (PVDF)-based functional membrane was fabricated with the incorporation of thiourea groups for removal of Ag(I) from the aqueous solution. The morphology, hydrophilicity, chemical groups and components of the membrane were characterized, and its trapping performance of Ag(I) was evaluated. Effects of conventional parameters (such as pH and initial Ag(I) concentration) on Ag(I) uptake and the adsorption characteristics were investigated. The adsorption equilibrium can be obtained about 6 h with a removal efficiency of 99 % for this metal. The adsorption kinetic and isotherm adsorption of Ag(I) can be described by the pseudo-second-order equation and the Langmuir model; the breakthrough curves can be described by Thomas model. This process exhibits the spontaneous and exothermic nature. The coexisting substances decrease the Ag(I) uptake, Co(II) and Na2S2O3 show a more remarkable disturbance than Cu(II), Ni(II), TA, and EDTA. The analysis of adsorption-diffusion equations ascertains the distribution gradient of Ag(I) along the longitudinal filtration direction of the membrane stack. This membrane shows a noticeable antifouling property and an excellent reusability (< 4.15 % loss in Ag(I) uptake over 8 runs). The eluent (0.3 mol L−1 thiourea and 0.1 mol L−1 HNO3 mixed solution) can be reused without apparent loss in regeneration performance after 8 cycles. In addition, a promising issue should be noted that the black silver and silver sulfide particles can be harvested during the regeneration process.

Fast recovery of Au (III) and Ag(I) via amine‐modified zeolitic imidazolate framework‐8

In this paper, zeolitic imidazolate framework‐8 modified by the ethanediamine (NH2‐ZIF‐8) was employed for adsorbing Au (III) and Ag(I) from aqueous solutions. The adsorption capacities of NH2‐ZIF‐8 towards Au (III) and Ag(I) were found to be significantly affected by the pH values of the solution. The adsorption kinetics studies show that NH2‐ZIF‐8 presents a fast adsorption property towards metals, attaining 93% of adsorption equilibrium uptake for Au (III) within the first 30 min. This phenomenon can be ascribed to the coordination interaction between the amino group and Au (III). The thermodynamic data suggest that the adsorption of NH2‐ZIF‐8 towards Au (III) is endothermic process, while that for Ag(I) is exothermic. The maximum adsorption capacities of NH2‐ZIF‐8 toward Au (III) and Ag(I) can be achieved to 357 mg·g−1 and 222.25 mg·g−1, respectively. The metal ions interference results show that Cu (II) and Ni (II) hardly have no interference on Au (III) adsorption in e‐waste containing 1500 mg·l−1 Cu (II),100 mg·l−1 Ni (II) and 10 mg·l−1 Au (III); while for Ag(I), Cd (II) and Zn (II) have little interference on Ag(I) adsorption in the hybrid solutions containing Ag(I), Ni (II), Cd (II) and Zn (II) with equal concentration (50 mg·l−1), but Ni (II) interference most. The XPS study shows that partial Au (III) was reduced to Au(I), and that Ag(I) was completely reduced to Ag(0) during the adsorption process. The abundant of active sites of NH2‐ZIF‐8 containing C=N, N‐H, and Zn‐OH groups play a key role in the adsorption of Au (III) and Ag(I). In addition, electrostatic interaction can be responsible for the adsorption of Au (III) by NH2‐ZIF‐8. The regeneration experiments results show that the adsorption capacities of NH2‐ZIF‐8 towards Au (III) and Ag(I) can maintain after three cycles. This work provides a reliable method to improve the adsorption kinetics for metal ions.