Ion‐imprinted PHEMA based monolith for the removal of Fe3+ ions from aqueous solutions

Molecular recognition based Fe³⁺ imprinted monolith was prepared for selective removal of Fe³⁺ ions from aqueous solutions. The precomplexation was achieved by the coordination of Fe³⁺ ions with N‐methacryloyl‐(L )‐cysteine methyl ester (MAC) to form the complex monomer (MAC‐Fe³⁺). The polymerization step was then carried out in the presence of MAC‐Fe³⁺ complex and hydroxyethyl methacrylate (HEMA) monomer by bulk polymerization to constitude a Fe³⁺‐imprinted polymer (PHEMAC‐Fe³⁺). The specific surface area of PHEMAC‐Fe³⁺ monolith was found to be 35.2 m²/g, with a swelling ratio of 60.2% after the template was removed from the monolith by 0.1M EDTA solution. The maximum adsorption capacity of PHEMAC‐Fe³⁺ monolith for Fe³⁺ ion was 0.76 mg/g. The adsorption behavior of the monolith has been successfully described by the Langmuir isotherm. It was determined that the relative selectivity of PHEMAC‐Fe³⁺ monolith was 59.7 and 37.0 times greater than that of the nonimprinted PHEMAC monolith as compared with the Cd²⁺ and Ni²⁺ ions, respectively. The PHEMAC‐Fe³⁺ monolith was recovered and reused many times without any significant decrease in its adsorption capacity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Separation and Recovery of Silver(I) Ions from Base Metal Ions by Melamine‐formaldehyde‐thiourea (MFT) Chelating Resin

Abstract

Melamine‐formaldehyde‐thiourea (MFT) chelating resin were prepared using melamine (2,4,6‐triamino‐1,3,5‐triazine), formaldehyde, and thiourea and this resin has been used for separation and recovery of silver(I) ions from copper(II) and zinc(II) base metals and calcium(II) alkaline‐earth metal in aqueous solution. The MFT chelating resin was characterized by elemental analysis and FT‐IR spectra. The effect of pH, adsorption capacity, and equilibrium time by batch method and adsorption, elution, flow rate, column capacity, and recovery by column method were studied. The maximum uptake values of MFT resin were found as 60.05 mg Ag⁺/g by batch method and 11.08 mg Ag⁺/g, 0.052 mg Zn²⁺/g, 0.083 mg Cu²⁺/g and 0.020 mg Ca²⁺/g by column method. It was seen that MFT resin showed higher uptake behavior for silver(I) ions than base and earth metals due to chelation.     

Use of electrodialysis to remove silver ions frommodel solutions and wastewater

The feasibility of the removal of Ag⁺ ions in a model solution and a sample of rinse water provided from an industrial plating plantwas investigated in a batch electrodialysis system. The experiments were carried out using two different types of ion-exchange membranes. The effects of applied potential, pH value and initial silver concentration on the duration of electrodialysis and energy consumption were examined. Full removal of Ag+ ions was achieved from model solutions and the sample of rinse water. The most convenient applied voltage and energy consumption values to remove silver ions are reported. These results will be useful for designing and operating different capacities of electrodialysis plants for recovering Ag⁺ ions.     

Synthesis of lysozyme imprinted column with macroporous structure and enhanced selectivity: Utilization of cryogelation technique and electrostatic functional monomers

Applicability of molecularly imprinted polymers (MIP) in conventional protein separation processes demands monolithic construction of columns with macroporous structure in addition to the high specificity and adsorption capacity. In this study, therefore, lysozyme (Lyz) imprinted monolithic cryogel columns were synthesized using electrostatic functional monomers (EFMs) to provide strong interactions between template and polymer, leading to specific recognition and capture of Lyz. SEM images and FTIR spectroscopy analysis confirmed the macroporous structure and presence of EFMs in the samples. Adsorption isotherms, heterogeneity, and breakthrough curves as well as selectivity of the molecularly imprinted cryogels (EFMs‐MIC) and non‐imprinted cryogels (EFMs‐NIC) were investigated. Results showed effective imprinting with a maximum adsorption capacity of 211 mg/g and a high imprinting factor (IF) of 4.2 at low Lyz concentrations. A high relative selectivity coefficient of 7.24 was obtained for Lyz over cytochrome c, a competing protein, indicating that the imprinted sites could well distinguish Lyz. Reusability of MICs was also examined, where insignificant changes were observed in the cryogel adsorption/desorption characteristics after four cycles. Therefore, it is suggested to use EFMs and cryogelation in the synthesis of imprinted monolithic cryogels column for application in conventional protein separation processes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42880.     

Influence of nitrate ions on silver electrocrystallization

The influence of nitrate anions on the reduction of silver ions on a silver cathode from a silver nitrate solution was studied with three different experimental methods: potentiokinetic curves, chronopotentiometry and impedance measurements. It was concluded that charge transfer of the Ag⁺ ions is certainly not the rate determining step of the reaction. It was clearly shown with the three methods that an increase in the nitrate ion concentration activates the reduction of the Ag⁺ ions; the overvoltage of the reaction decreases markedly. With the aid of an equivalent circuit it is possible to quantify the activation of the electrode, in particular through the determination of the charge transfer resistance and the resistance and the capacity of adsorbed species.     

Synthesis of ion‐imprinting chitosan/PVA crosslinked membrane for selective removal of Ag(I)

A novel ion‐imprinted membranes were synthesized for selective removal and preconentration for Ag(I) ions from aqueous solutions. The membranes were obtained via crosslinking of chitosan (CS), PVA, and blend chitosan/PVA using glutaraldehyde (GA) as crosslinker. The FTIR spectra were used to confirm the membrane formation. Comparing with the nonimprinted membranes, Ag(I)‐imprinted CS and CS/PVA has higher removal capacity and selectivity for Ag⁺ ions. An enhancement in the Ag⁺ removal capacity by ～ 20% (from 77.8 to 94.4 mg g^–1) and ～ 50% (from 83.9 to 125 mg g^–1) was found in the Ag(I)‐imprinted CS and Ag(I)‐imprinted CS/PVA membranes, respectively, when compared with the nonimprinted membranes. Removal equilibra was achieved in about 40 min for the non‐ and ion‐imprinted CS/PVA. The pH and temperature significantly affected the removal capacity of ion‐imprinted membrane. The relative selectivity coefficient values of Ag⁺/Cu²⁺ and Ag⁺/Ni²⁺ are 9 and 10.7 for ion‐imprinted CS membrane and 11.1 and 15 for ion‐imprinted CS/PVA membrane when compared with nonimprinted membranes. The imprinted membranes can be easily regenerated by 0.01M EDTA and therefore can be reused at least five times with only 15% loss of removal capacity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Immunoglobulin G recognition with Fab fragments imprinted monolithic cryogels: Evaluation of the effects of metal-ion assisted-coordination of template molecule

In this study, we applied the epitope imprinting approach to prepare molecularly imprinted monolithic cryogels for immunoglobulin G (IgG) recognition. In this respect, we imprinted F_ab fragments of IgG molecules instead of intact protein molecules via two different non-covalent interactions. In the first approach, we directly coordinated F_ab fragments with N-methacryloyl-L-histidine (MAH), polymerizable derivative of L-histidine, but for the second, we used cupric ions [Cu(II)] as mediator between MAH and F_ab fragments. The monolithic cryogels were characterized by Fourier transform infrared (FTIR) spectroscopy, swelling test, and scanning electron microscopy. Then, the monolithic cryogels were used for F_ab fragment adsorption from aqueous solution while evaluating the factors such as pH and F_ab fragment concentration affecting on adsorption process in continuous set-up. After that, monolithic cryogels were used for IgG adsorption by varying pH, IgG concentration, flowrate, and temperature in appropriate ranges. Maximum IgG adsorption capacities were determined as 32.4 mg/g and 49.0 mg/g for directly coordinated cryogel (MIP_Direct) and Cu(II) assisted cryogel (MIP_{Cu(II) assisted}), respectively. Non-imprinted monolithic cryogels were also prepared for control purposes. In addition to F_ab fragments and IgG molecules, albumin and F_c fragment of IgG molecules were used as competitor biomolecules in order to investigate the selectivity gained by imprinting process. Relative selectivity constants were calculated as 1.47, 2.64 and 3.89 for MIP_Direct and 2.90, 8.98, and 11.51 for MIP_{Cu(II) assisted} for F_ab/IgG, F_ab/F_c, and F_ab/albumin as biomolecule pairs, respectively. The desorption efficiency and reusability of MIP_{Cu(II) assisted} cryogel were better than that of MIP_Direct. The results reported here showed that the metal ion assistance improved the selectivity features of the imprinted cryogels and allowed to study under milder conditions with enhanced adsorptive properties.     

Electrochemical behavior of pyrite in sulfuric acid solutions containing silver ions

A systematic electrochemical study of pyrite in H₂SO₄ solutions containing dissolved silver was undertaken to gain more information about the transfer of silver ions to pyrite and their role in enhancing the direct oxidation of pyrite. The results of cyclic voltammetry experiments provide additional evidence of the formation of metallic silver on the FeS₂ surface under open-circuit conditions. A pyrite electrode held at the open-circuit potential for 2 h in the presence of 10^–3 m Ag⁺ exhibits a large and sharp anodic peak at about 0.7V. The current associated with this peak is the result of the dissolution of metallic silver deposited during the initial conditioning period. There is no evidence of silver deposition without preconditioning until the potential drops below about 0.6V for Ag⁺ concentrations ranging from 10^–4 to 10^–2 m. However, subsequent silver deposition appears to be very sensitive to the dissolved silver concentration in this range. There is also evidence that the state of the pyrite surface has a pronounced influence on its interaction with silver ions. Agitation has also been found to have a significant effect on the electrochemistry of the Ag–FeS₂ system.     

Molecularly imprinted smart cryogels for selective nickel recognition in aqueous solutions

Smart polymers with fast response to slight changes show high practicability in separation and removal applications, such as water and wastewater treatment. Molecular imprinted polymers (MIPs) are designed to possess specific binding sites enabling the recognition of the target analytes. In this article, the newly synthesized smart adsorbents were used for the selective removal of nickel [Ni(II)] ions from aqueous solutions, which have dual (pH and temperature) memory for the recognition of Ni(II) ions due to the self-assembled recognition sites in MIP structure. The Ni(II)-MIP smart cryogels were prepared by cryopolymerization of N-isopropylacrylamide (NIPAm) and N-methacryloyl-l -histidine (MAH) monomers to incorporate their smart features for removal of Ni(II) ions in a selective and temperature-modulated way. The maximum binding capacity of Ni(II) ions onto MIP smart cryogel was determined at pH 6 as 414 μg g⁻¹ at 20°C and only 104.5 μg g⁻¹ at 40°C, respectively. The adsorption reached an equilibrium within 30 min, while 85% of the bound amount of Ni(II) ions was achieved in only 15 min. This unique MIP cryogel as a smart and selective adsorbent was able to remove Ni(II) ions immediately by a significant temperature and pH change as an alternative application for water and wastewater treatment.     

Thioether‐Functionalized Corn Oil Biosorbents for the Removal of Mercury and Silver Ions from Aqueous Solutions

Heavy‐metal contamination is one of the most important environmental problems faced in the world, particularly in developing countries. Metals such as silver and mercury from drinking water, food, and air sources can accumulate in living organisms and present significant health concerns. Meanwhile, the demand for these metals in many industries continues to increase. In the present study, thioether‐functionalized corn oil (TFCO) from a photoinitiated thiol‐ene synthesis was utilized to remove Ag⁺ and Hg²⁺ ions from an aqueous solution. An aqueous solution containing AgNO₃ and Hg[NO₃]₂ was prepared and contacted directly with TFCO. After vortex mixing for 60 s, the experiment ran for 351 min with the aqueous phase being periodically sampled for the analysis of metal ions (M ⁿ⁺). Results showed that 88.9% of Ag⁺ and 99.6% of Hg²⁺ ions were removed from the aqueous phase by the TFCO. Mass balances indicated that the total M ⁿ⁺ concentration in the oil phase was 13.890 g kg^?1 under the conditions studied. TFCO exhibited higher selectivity for removing Hg²⁺ than for Ag⁺ ions. Analysis of the adsorption kinetics showed that a pseudosecond‐order model may be used to determine the rate of Ag⁺ ion sorption by the oil phase. The presence of the Hg²⁺ ions interfered with the adsorption of Ag⁺ ions from the aqueous solution.     

Using probe beam deflection (PBD) to investigate the electrochemical oxidation of silver in perchlorate media in the presence and absence of chloride ions

The electrochemical oxidation of silver in 0.1 M KClO₄ solutions containing KCl were investigated by cyclic voltammetry (CV) and electrochemical probe beam deflection (PBD). Ag⁺_(aq) ions were the main product of the silver oxidation in the absence of the halide. The formation of Ag⁺_(aq) provoked a beam deflection towards the electrode surface. A beam deflection away from the electrode surface was then observed during the reduction of the Ag⁺_(aq) ions. A convolution analysis yielded a diffusion coefficient of 1.2×10⁻⁹ m² s⁻¹ for Ag⁺_(aq) in this medium. An anodic peak due to the formation of AgCl_(s) film was observed for the oxidation of silver in solutions containing Cl⁻_(aq). As the applied potentials were made more positive in media containing chloride (after the peak due to the AgCl_(s) formation), a flux of ions away from the electrode surface was clearly detected by PBD. This was assigned to the formation of Ag⁺_(aq) ions through the porous AgCl_(s) film structure. Oscillations on the position of the laser beam were present during the oxidation at high chloride concentrations, due to the precipitation of AgCl_(s) from the solution phase. The electrochemical and PBD data were consistent with a dissolution-precipitation mechanism for the AgCl_(s) film formation.     

Ion imprinted beads embedded cryogels for in vitro removal of iron from β-thalassemic human plasma

Molecular recognition based Fe³⁺ imprinted poly(GMA-MAC) (MIP) beads embedded PHEMA composite cryogel was prepared for selective removal of Fe³⁺ ions from β-thalassemia patient plasma. The precomplexation was achieved by the coordination of Fe³⁺ ions with N-methacryloyl-(L )-cysteine methyl ester (MAC-Fe³⁺). MIP beads were prepared by dispersion polymerization in the presence of MAC-Fe³⁺ complex and glycidyl methacrylate (GMA) monomer. Then the MIP beads were embedded into poly(hydroxyethyl methacrylate) (PHEMA) cryogel. The specific surface area and the swelling degree of the PHEMA-MIP composite cryogel were found to be 76.8 m²/g and 7.7 g H₂O/g cryogel, respectively. The maximum adsorption amount of Fe³⁺ ions was 2.23 mg/g. The relative selectivity of PHEMA-MIP composite cryogel towards the Fe³⁺ ions was 135.0, 61.4, and 57.0 times greater than that of the PHEMA-NIP cryogel as compared with the Ni²⁺, Zn²⁺, and Fe²⁺ ions, respectively. PHEMA-MIP composite cryogel was recovered and reused many times without any significant decrease in its adsorption capacity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of the Eu2+ on the Silver Aggregates Formation in Ag+–Na+ Ion‐Exchanged Eu3+‐Doped Sodium–Aluminosilicate Glasses

Europium‐doping sodium–aluminosilicate glasses are prepared by melt‐quenching method, in which europium ions were spontaneously reduced from their trivalent to divalent state. The silver was introduced into glasses by Ag⁺–Na⁺ ion exchange and the interactions between europium ions and silver species were investigated. Owing to energy transfer (ET) from Ag⁺/silver aggregates to Eu³⁺, significant enhancements of Eu³⁺ emission were observed for 285/350‐nm excitation, respectively. The divalent europium ions promote the formation of silver aggregates in the process of ion exchange.     

Novel antibacterial composite of coal/LLDPE loaded with silver ions

A novel antibacterial composite of coal/LLDPE (linear low density polyethylene) loaded with silver ions (ACCPE) was prepared by means of solid–liquid phase adsorption and extrusion. The composite was characterized by IR, XRD and SEM, and the mechanical, rheological, and Ag⁺‐releasing, and antibacterial properties of the composite were investigated. We discover that the ACCPE shows favorable mechanical properties, features a higher processability and antibacterial activity, and the coal and silver ion possess superimposed effect on antibacterial activity against Escherichia coli. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Selective preparation of Ag species on photoluminescence of Sm3+ in borosilicate glass via Ag+-Na+ ion exchange

Photoluminescence (PL) of rare earth ion-doped glasses could be enhanced by diverse Ag species such as Ag⁺ ions, Ag⁺-Ag⁺ pairs, Ag nano-clusters (NCs), and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ion-doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, Ag⁺ ions and Ag NCs were selectively prepared in the Sm³⁺-doped borosilicate glass via the Ag⁺-Na⁺ ion exchange. The influence of AgNO₃/NaNO₃ ratio in the molten salt on the Ag existing states was investigated. The results demonstrate that the isolated Ag⁺ ions exist in the Sm³⁺-doped borosilicate glass when the ratio of AgNO₃/NaNO₃ is 1/1000. The Ag NCs are formed in the Sm³⁺-doped borosilicate glass when the AgNO₃/NaNO₃ ratio is 1/10. The influence of Ag⁺ ions or Ag NCs on the PL of Sm³⁺ was systematically investigated. The results show that the PL of Sm³⁺ was enhanced by the energy transfer from Ag⁺ ions or Ag NCs to Sm³⁺.     

Preparation and characterization of poly(vinyl alcohol) cryogel‐silver nanocomposites and evaluation of blood compatibility,cytotoxicity, and antimicrobial behaviors

In this investigation, cryogels composed of poly(vinyl alcohol) (PVA) were prepared by repeated freeze‐thaw method. The prepared cryogels served as templates for producing highly stable and uniformly distributed silver nanoparticles via in situ reduction of silver nitrate (AgNO₃) using alkaline formaldehyde solution as reducing agent. The structure of the PVA/Ag cryogel nanocomposites was characterized by a Fourier transform infrared and Raman spectroscopy. The morphologies of pure PVA cryogels and PVA/Ag nanocomposites were observed by a scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The SEM analysis suggested that cryogels show a well defined porous morphology whereas TEM micrographs revealed the presence of nearly spherical and well separated Ag nanoparticles with diameter about 100 nm. XRD results showed all relevant Bragg's reflections for crystal structure of silver nanoparticles. The amount of silver in cryogel nanocomposites and thermal stability were determined by inductively coupled plasma atomic emission spectrometry (ICP‐AES) and thermogravimetric analysis measurements. Mechanical properties of nanocomposites were observed in terms of tensile strength. The antibacterial studies of the synthesized nanosilver containing cryogels showed good antibacterial activity against both gram‐negative and gram‐positive bacteria. The prepared PVA/Ag nanocomposites were also investigated for swelling and deswelling behaviors. The results reveal that both the swelling and deswelling process depends on the chemical composition of the cryogel silver nanocomposites, number of freeze‐Thaw cycles and pH and temperature of the swelling medium. The biocompatibility of the prepared nanocomposites was judged by in vitro methods of percent hemolysis and protein (BSA) adsorption. POLYM. COMPOS., 36:1983–1997, 2015. © 2014 Society of Plastics Engineer     

Effect of hydroxyl ions on chloride penetration depth measurement using the colorimetric method

In this paper, the effect of hydroxyl ions on chloride penetration depth measurement using the colorimetric method was studied. Equivalent silver nitrate solution (i.e. Ag⁺ = Cl⁻) was added to the NaCl + NaOH solution with different concentrations, then the amount of precipitated silver chloride and silver oxide were determined by chemical methods, and the color of the precipitated products was examined. Results show that the amount of silver chloride formed decreases linearly as OH⁻ to Cl⁻ ratio (r) increases. Thus, the chloride concentration at color change boundary changes with the pH value of the concrete. AgCl has a white color, while Ag₂O has a dark brown color. When the value of r exceeds 4, the color of the mixture looks brown, and color change boundary cannot be easily distinguished.     

Preparation of Cr(VI)-imprinted polypropylene nonwoven fibers using plasma polymerization-assisted grafting

Polypropylene (PP) fibers were grafted with glycidyl methacrylate (GMA) using plasma polymerization and then aminated, imprinted, and crosslinked to prepare Cr(VI)-imprinted fibers. The plasma polymerization conditions were optimized by single factor experiment and response surface methodology, and various properties and adsorption mechanism of the fibers were analyzed. The results showed that at pH 3, the imprinted fibers had a maximum Cr(VI) adsorption capacity of 173.36 mg/g, and the adsorption equilibrium could be reached within 40 min. In the presence of competing ions (SO₄²⁻, NO₃⁻ and PO₄³⁻) each at a concentration of 5 times of that of Cr(VI), the Cr(VI) adsorption rate of the fibers could be maintained at around 50%, which indicates that the imprinted fibers have high selectivity towards Cr(VI). The results also showed that the imprinted fibers had good reusability and enrichment ability, thus can be a good candidate for treating actual Cr(VI)-contaminated water.     

Spontaneous and Electrochemical Reduction of Silver by Polypyrrole Deposits

Abstract

Polypyrrole (ppy) coatings doped with p-toluene sulfonate sodium on stainless steel mesh (SSM) have been electrosynthesized in aqueous solution. The removal of Ag⁺ ions from acidic solutions was investigated through spontaneous reduction (SR) and electrochemical reduction (ER) procedures using reduced composite ppy-SSM. Higher removal efficiencies and current efficiencies were obtained by ER process for ppy-SSM rather than SR process for ppy-SSM and ER process for SSM under comparable conditions. Due to its high efficiency and simplicity, ER was supposed to be an alternative advantageous method for the recovery of low-level silver concentration in industrial wastewater. Cyclic voltammetry was carried out to characterize the electrochemical behavior of ppy-SSM in acid solutions containing Ag⁺. Metallic silver deposited on ppy-SSM has been evidenced by scanning electron microscopy (SEM) analysis.     

Competitive Adsorption of Ag+, Pb2+, Ni2+, and Cd2+ Ions on Vermiculite

Competitive adsorption of Ag⁺, Pb²⁺, Ni²⁺, and Cd² ions on vermiuculite in a binary, ternary, and quaternary mixture was investigated in batch experiments. The effects of the presence of Ag⁺, Ni²⁺, and Cd²⁺ ions on the adsorption of Pb²⁺ ions were investigated in terms of the equilibrium isotherm. Experimental results indicated that Pb²⁺ ions always favorably adsorbed on vermiculite over Ag⁺, Ni²⁺, and Cd²⁺ ions. The adsorption equilibrium data of Pb²⁺ ions better fitted the Langmuir model than the Freundlich model. The results showed that the pseudo-second-order kinetics model was in good agreement with the experimental results for all metal ions, and the adsorption rate among the metal ions followed Ag⁺ > Pb²⁺ > Ni²⁺ > Cd²⁺. The desorption and regenration study indicated that vermiculite can be used repeatedly and be suitable for the design of a continuous process.