Ion Exchange In Solution Research Articles

Catalytic oxidation of trichloroethylene over Fe-ZSM-5: Influence of the preparation method on the iron species and the catalytic behavior

Fe-ZSM-5 zeolite was synthesized by following different routes namely ion exchange from solution, impregnation and solid state ion exchange. All the catalysts were tested in the oxidation of trichloroethylene (TCE) in vapor phase. The catalysts were characterized using different physico-chemical technique which included BET surface area analysis, NH3-TPD analysis, H2-TPR analysis, XRD analysis, TEM analysis, DRS UV–vis, EPR, and XPS. The characterization results gave significant insight on the active sites responsible for the oxidation. It was found that Fe nanoparticles present in the extra framework of the zeolite were largely responsible for oxidation rather than the acidic sites. The catalysts prepared by impregnation or solid state ion exchange method were found to be active in the oxidation of TCE; however, comprehensively less active than the catalyst synthesized by ion exchange method. The activity of Fe-ZSM-5 was also compared with H-ZSM-5, and it was found that the activity and stability of Fe-ZSM-5 catalyst was much higher than the protonic form. Studies on the deactivation mechanism of the catalysts showed that the major reason for loss in activity was due to formation of FeCl3 rather than coke deposition.

Ion-imprinted chitosan gel beads for selective adsorption of Ag+ from aqueous solutions

In this study, the Ag+-imprinted chitosan gel beads were synthesized to selectively adsorb Ag+ from bimetallic aqueous solutions containing the same molar concentration of Ag+ and Cu2+. The Ag+-imprinting not only helps to achieve extremely high selectivity of Ag+, but also enhances the uptake capacity of the target Ag+ by protecting some amine groups, the primary binding sites of metal ions from cross-linking. The maximum uptake of Ag+ by the ion-imprinted chitosan beads was found to be 89.20mgg−1 at 25.0°C with an initial Ag+ concentration of 352.95mgL−1 and the biosorbent dosage of 1.0gL−1. The adsorption equilibrium and kinetics of Ag+ by the ion-imprinted chitosan beads can be better described by Langmuir isotherm and the intraparticle diffusion model. FTIR and XPS analyses suggested that amine functional groups involve the binding of Ag+ via complexation at higher solution pH (3.0≤pH≤5.0) and ion exchange at lower solution pH (1.0≤pH<3.0).

Delithation, Exfoliation, and Transformation of Rock-Salt-Structured Li2TiO3 to Highly Exposed {010}-Faceted Anatase.

{010}-Facet-exposed anatase TiO2 crystals exhibit the highest photoreactivity among the exposed facets. To obtain a higher exposure rate of this facet, the work investigated the transformation of the nanosheets with cavities within the layers derived from a rock-salt-structured Li2TiO3 precursor. All the lithium ions were extracted from the precursor by H+/Li+ ion exchange in HCl aqueous solutions, and after tetramethylammonium ions were intercalated, the precursor can delaminated into the nanosheets. The [TiO3]2- nanosheets were hydrothermally treated under different temperatures and pH values. The results showed that the anatase phase was formed in a wider range of pH and temperature, compared with using nanoribbons of [Ti4O9]2- and nanosheets of [Ti1.73O4]1.07-. At low pH, [111]-faceted nanorod-shaped anatase nanocrystals were formed preferentially, and the nanocrystals preferentially grow along the [001] direction with the increase of solution pH, leading to a large percentage of {010} facets on their surface. The photocatalytic activity increases with the increase of exposure rate of {010} facets.

Fabrication of spinel Li4−xTi5O12 via ion exchange for high-rate lithium-ion batteries

The present work demonstrates that lithium ions can be stepwise substituted by protons from spinel Li4Ti5O12 crystalline particles though simple ion-exchange in aqueous HCl solution with the aid of heat treatment. This enables us to continuously tune the Li-to-Ti stoichiometric ratios from 0.80 to 0.59, 0.41, 0.21, 0.15, and 0.09, thus transforming Li4Ti5O12 to Li4−xTi5O12 nanocrystals. The resulting nanocrystals maintain the spinel crystal structure when x becomes smaller than 3. Among as-prepared the Li4−xTi5O12 crystalline particles, Li1Ti5O12 shows the highest capacity of 193 mAh g−1 at 1C and 148 mAh g−1 at 20C, lower current impedance (47 Ω), significantly improved rate capability and fairly long cycle life. This excellent electrochemical performance makes spinel Li4−xTi5O12 particles as a promising anode candidate for lithium ion batteries superior.

Single-crystal structures of Zn2+-exchanged zeolite A: dependence on Zn2+ concentration of aqueous solution during exchange

To study the tendency of Zn2+ exchange into zeolite A, two single-crystals of fully dehydrated Zn2+-and Na+-exchanged zeolite A were prepared by the static ion-exchange method using a mixed ion-exchange solution whose Zn(NO3)2:NaNO3 mol ratios were 1:4 (crystal 1) and 3:2 (crystal 2), respectively, with a total concentration of 0.05 M, followed by vacuum dehydration at 623 K. Their single-crystal structures and chemical compositions were determined by single-crystal synchrotron X-ray diffraction techniques and electron probe microanalysis. Their structures were refined to the final error indices R 1/wR 2 = 0.0678/0.2154 and 0.0619/0.1938 for crystals 1 and 2, respectively. In both structures, the 4 Zn2+ ions are located in sodalite unit, whereas, the remaining 4 Na+ ions are located in large cavity. Unit-cell formula of two single-crystal structures is approximately |Zn4Na4|[Si12Al12O48]-LTA. This work shows that the degree of Zn2+ exchange by increasing the initial Zn2+ concentration and decreasing the initial Na+ concentration in given ion-exchange solution does not differ significantly.

A combined ion exchange–nanofiltration process for water desalination: I. sulphate–chloride ion-exchange in saline solutions

Removal of chloride ions from saline water with seven different ion-exchange (IX) resins in sulphate form has been studied both on laboratory and pilot scales. It was found that sulphate–chloride exchange is very fast in aqueous solutions and that the feed salt concentration and the nature of the functional group of the resin play an important role in this process. It was shown that the chloride/sulphate separation factor depends on salt content in feed water and the higher the substitution of hydrogen atoms in amine functional group of anion exchange resin the higher chloride over sulphate selectivity. Exhausted IX resins were successfully regenerated using 0.2M Na2SO4 solution and multiple regeneration/saturation cycles proved that this did not affect the resin's performance on chloride ion removal. It was shown that the osmotic pressure of sea water was significantly reduced after SO4/Cl ion exchange. Due to the drop of osmotic pressure lower energy consuming nanofiltration membranes compared with reverse osmosis membranes might be used for salty water desalination after IX treatment.

An intrinsically magnetic biomaterial with tunable magnetic properties.

Many magnetic materials lack intrinsic biocompatibility and require surface functionalization for in vivo applications. In this study, we fabricated an intrinsically biocompatible, biodegradable magnetic material through iron substitution into hydroxyapatite (FeHA) via ion-exchange. Controlling the oxidation state of iron in the ion exchange solution resulted in 'tunable' magnetic properties. Superparamagnetic behavior was observed in Fe2+HA and Fe2+3+HA and paramagnetism in Fe3+HA. FeHA powders were characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infra-red (FTIR) and X-ray photoelectron spectroscopy (XPS) with no detection of iron oxide phases. The as-synthesized HA and Fe2+3+HA samples were characterized in vitro using MC3T3-E1 cells. Cellular proliferation of Fe2+3+HA was found comparable to HA, while our cytotoxicity results from a lactate dehydrogenase assay showed Fe2+3+HA to be less toxic than pure HA, a widely used implantable biomaterial. Thus, these results collectively suggest that we have fabricated a magnetic biomaterial with intrinsic biocompatibility.

Understanding ammonia selective catalytic reduction kinetics over Cu/SSZ-13 from motion of the Cu ions

Cu/SSZ-13 catalysts with Si/Al=6 and various Cu/Al ratios are synthesized with solution ion exchange. Catalysts are characterized with surface area/pore volume measurements, Temperature Programmed Reduction (TPR), and Electron Paramagnetic Resonance (EPR) spectroscopy. Catalytic properties are examined using NO oxidation, ammonia oxidation, and standard ammonia selective catalytic reduction (NH3-SCR) reactions. Prior to full dehydration of the zeolite catalysts, hydrated Cu2+ ions are found to be very mobile as judged from EPR. NO oxidation is catalyzed by O-bridged Cu-dimer species that form at relatively high Cu loadings and in the presence of O2. For NH3 oxidation on samples with low to intermediate Cu loadings, transient Cu-dimers are the low-temperature (⩽300°C) active centers, while these dissociate to monomers at 350°C and above and become active centers. For the much more complex standard SCR reaction, transient Cu-dimers are the active sites for reaction temperatures <250°C at very low Cu loadings (Cu/Al⩽0.016). Between ∼250 and 350°C, these Cu-dimers become less stable causing SCR reaction rates to decrease. At temperatures ⩾350°C, Cu2+ monomers that had migrated to faces of 6-membered rings are the active sites. At intermediate Cu loadings, monomeric Cu2+ ions are also active in SCR in the low-temperature regime; these are proposed to be located within CHA cages and next to 8-membered rings, likely in the form of [Cu(OH)]+. At high Cu loadings (i.e., more than one Cu2+ ion in each unit cell), stable Cu-dimers form and these do not dissociate at temperatures above 350°C. These moieties effectively occupy CHA cage space and block pore openings causing decreased efficiency of the catalysts. Also these moieties are highly active in catalyzing the NH3 oxidation reaction thus causing SCR selectivities to decrease above ∼450°C. Finally, our kinetics results strongly support a redox mechanism for standard SCR.

Synthesis, supramolecular self-organization, and thermal behavior of the heteropolynuclear complex ([H3O][Au{S2CN(CH2)6}2][Au2{S2CN(CH2)6}4][ZnCl4]2) n

The interaction of binuclear zinc cyclo-hexamethylenedithiocarbamate [Zn2{S2CN(CH2)6}4] with [AuCl4]− anions in the 2M HCl medium is studied. The result of a heterogeneous reaction involving the chemisorption binding of gold(III) from a solution and partial ion exchange, was the formation of a heteropolynuclear gold(III)-zinc complex as an individual form of gold(III) binding. The crystal and molecular structure of the polymeric complex of the composition ([H3O][Au{S2CN(CH2)6}2][Au2{S2CN(CH2)6}4][ZnCl4]2)n (I) is determined by single crystal X-ray diffraction. The structure of the complex contains three isomeric complex [Au{S2CN(CH2)6}2]+ cations: centrosymmetric A with the Au(1) atom and two non-centrosymmetric B with Au(2) and C with Au(3). Due to the pairs of non-symmetric secondary Au⋯S interactions of the non-valence type, the noncentrosymmetric cations form a binuclear [Au2{S2CN(CH2)6}4]2+ cation of the B⋯C type. The subsequent structural self-organization of the complex at the supramolecular level also proceeds due to Au⋯S interactions between the binuclear B⋯C and mononuclear A cations, as a result of which zigzag polymeric chains (⋯ [B⋯C]⋯A⋯)n are formed. The hydronium ion participates in the pairwise binding of [ZnCl4]2− anions by Cl⋯O hydrogen bonds. The multistage process of the thermal destruction of I includes the dehydration of the complex, thermolysis of the dithiocarbamate moiety and [ZnCl4]2− (with releasing metallic gold, ZnCl2, and partial formation of ZnS). The final products of thermal transformations are metallic gold and ZnS.

Theoretical and experimental investigation of diffusion permeability of hybrid MF-4SC membranes with silica nanoparticles

The diffusion permeability through hybrid materials based on a Nafion-type membrane and hydrated silica is investigated using the Nernst–Planck approach. A method of quantitative evaluation of physicochemical parameters (averaged and individual diffusion coefficients and averaged distribution coefficients of ion pairs in the membrane) of system “electrolyte solution–ion-exchange membrane–water” is developed. The parameters of hybrid membranes on the base of MF-4SC and hydrated silica are obtained from experimental data on diffusion permeability of HCl and NaCl solutions using theoretical calculations.It is shown that the dependence of computed diffusivities of sodium cation and proton upon SiO2 content has a minimum at 5% and 7%, respectively. At the same time experimental values of distribution coefficients of HCl and NaCl molecules reach the maximum at 1.5–3% of SiO2 content. The results obtained are in a good correlation with the physicochemical model of the limited elasticity of the membrane pore walls.

Recovery of molybdenum and vanadium with high purity from sulfuric acid leach solution of spent hydrodesulfurization catalysts by ion exchange

Valuable metals, such as Mo, V, Co and Ni together with base metals (Fe and Al) are present in the sulfuric acid leaching solutions of spent hydrodesulfurization catalysts. In order to develop a process to recover pure Mo and V from the solution, batch and continuous ion exchange experiments with strong anionic resin (AG1-x8) have been performed by employing a synthetic sulfuric acid solution. Batch experimental results indicated that the separation of molybdenum and vanadium from the solution with AG1-x8 was possible by adjusting the pH of the solution to 0.5 and 1.6, respectively. Column experimental results verified the complete separation and recovery of molybdenum and vanadium from the solution at the specified pH conditions. Molybdenum and vanadium in the loaded resin was eluted by using NaOH solution. The purity of Mo and V solution after elution was found to be higher than 99%. After elution, AG1-x8 was successfully regenerated by converting its form from hydroxide to chloride by using NaCl solution.

Single-Crystal Structures of Sr2+ and Cs+-Exchanged Zeolites X and Y, |Sr40Cs12|[Si100Al92O384]-FAU and |Sr29Cs17|[Si117Al75O384]-FAU

Two single-crystals of fully dehydrated, Sr2+-and Cs+-exchanged zeolites X (|Sr40Cs12|[Si100Al92O384]-FAU (Si/Al = 1.09, crystal 1)) and Y (|Sr29Cs17|[Si117Al75O384]-FAU (Si/Al = 1.56, crystal 2)) were prepared by the flow method using a mixed ion-exchange solution whose Sr(NO3)2:CsNO3 mol ratio was 1:1 with a total concentration of 0.1 M. The crystals were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group $$Fd\overline{ 3}$$ and $$Fd\overline{ 3} m,$$ respectively, and were refined to the final error indices R 1/wR 2 = 0.070/0.209 and 0.052/0.155 for crystals 1 and 2, respectively. In the structure of |Sr40Cs12|[Si100Al92O384]-FAU, 40 Sr2+ ions per unit cell occupy three different equipoints; 16, 1.5, and 22.5 are at sites I, II′, and II, respectively. The 12 Cs+ ions per unit cell occupy three equipoints; 1, 6, and 5 are at sites II′, II, and IIIa, respectively. In the structure of |Sr29Cs17|[Si117Al75O384]-FAU, 29 Sr2+ ions per unit cell occupy four equipoints; 15, 1.5, 2.5, and 10 are at sites I, I′, II′, and II, respectively. The 17 Cs+ ions per unit cell are found at four different sites; 2.5, 9, 4, and 1.5 are at sites II′, II, IIIa, and IIIb, respectively. The Sr2+ ions occupy smaller pore size such as the centers of the double 6-rings and the positions near the center of single 6-rings planes, whereas, Cs+ ions preferentially occupy large-cavity sites in the supercage. Two single-crystals of fully dehydrated, Sr2+-and Cs+-exchanged zeolites X (|Sr40Cs12|[Si100Al92O384]-FAU (Si/Al = 1.09, crystal 1)) and Y (|Sr29Cs17|[Si117Al75O384]-FAU (Si/Al = 1.56, crystal 2)) were determined by single-crystal synchrotron X-ray diffraction techniques.

An ion adsorption–diffusion process for preparing YVO4:Eu3+@SiO2 core–shell nanoparticles with strong luminescence

In this work, YVO4:Eu3+@SiO2 core–shell nanoparticles with strong luminescence were successfully prepared using an ion adsorption–diffusion process. Undoped YVO4 nanoparticles with a size about 7nm were synthesized using a solvothermal method, and they were then coated with SiO2 shell using a facile sol–gel method to form the YVO4@SiO2 core–shell nanoparticles with a size about 10nm. Eu3+ ions were adsorbed onto the YVO4@SiO2 nanoparticles to prepare the YVO4:Eu3+@SiO2 core–shell nanoparticles. For the same Eu3+ concentration in the ion-exchange solution, luminescence of the as-prepared YVO4:Eu3+@SiO2 nanoparticles decreased with the amount of SiO2. For the same amount of SiO2, luminescence of the as-prepared YVO4:Eu3+@SiO2 nanoparticles increased with the Eu3+ concentration before a quenching concentration was reached. Upon thermal annealing, the adsorbed Eu3+ ions were doped into the YVO4 matrix via diffusion to form the annealed YVO4:Eu3+@SiO2 core–shell nanoparticles with a size about 11nm. It was found that luminscence of the YVO4:Eu3+@SiO2 core–shell nanoparticles can be considerably enhanced by annealing. The effect of the SiO2 shell, Eu3+ concentration and annealing temperature on the luminescence of the YVO4:Eu3+@SiO2 nanoparticles was investigated in detail.

ChemInform Abstract: Ion‐Exchange Synthesis, Crystal Structure, and Physical Properties of Hydrogen Titanium Oxide H2Ti3O7.

AbstractThe title compound is synthesized from Na2Ti3O7 by Na+/H+ ion exchange in HCl solution at 333 K for 5 d.

Preparation of high-purity 68Ga solutions by ion exchange in mixed acetone-hydrochloric acid medium

Ion-exchange behavior of 68Ga in the mixed HCl-acetone medium on cation and anion exchangers was studied. The equilibrium gravimetric distribution coefficients of 68Ga on Dowex AG 50W×8 strongly acidic cation exchanger in the H+ form and on Dowex AG 1×8 strongly basic anion exchanger in the Cl− form in mixed HCl-acetone solutions at HCl concentrations in the range 0.1–3 M and acetone volume fractions in the range 0–90% were determined. The dynamic characteristics of the 68Ga ion exchange in mixed HCl-acetone solutions were studied. A process based on the data obtained was developed for preparing 68Ga solutions in 0.1 MHCl of high chemical and radiochemical purity, suitable for producing 68Ga radiopharmaceuticals of required quality (radiochemical purity 98.1 ± 1.4%).

Biodiesel Produced from Catalyzed Transesterification of Triglycerides Using ion-Exchanged Zeolite Beta and MCM-22

In this work, biodiesel production from catalyzed transesterification of triglycerides with excess methanol was studied by using ion-exchanged Zeolite Beta and MCM-22 as heterogeneous catalysts. Zeolite Beta and MCM-22 were synthesized with hydrothermal processes and, subsequently, modified by ion-exchanged with alkali ions. These as-obtained zeolite catalysts could yield a high conversion of triglycerides to biodiesel. The conversion efficiency was largely affected by crystallinity and frameworks of zeolite support, pH value of alkali ion-exchange solutions and alkali loadings onto the zeolite support. Furthermore, the effects of the duration of the sodium ion-exchange process on the final conversion efficiency of triolein to biodiesel, both the as-prepared Zeolite MCM-22 and Zeolite Beta catalysts were used. The effect of the duration of the sodium ion-exchange process is insignificant in transesterification using Na-ion-exchanged Zeolite MCM-22 catalysts from 0.5 to 4h. In contrast, the conversion efficiency of triolein to biodiesel reached ca. 95% in 0.5hours of transesterification using Zeolite Beta ion-exchanged with 3 mmol-eq. Na+/g cat for 0.5hours.

Preparation of AgY zeolite and study on its adsorption equilibrium and kinetics

Adsorbents with Ag-doped AgY zeolite were prepared by introducing silver into the framework of NaY zeolite using a liquid-phase ion exchanged method. Adsorbents were characterized by X-ray diffraction, ICP elemental analysis, diffuse-reflectance UV/Vis spectra, scanning electron microscope, X-ray photoelectron spectroscopy, and N2-adsorption specific surface area measurements (Brunauer–Emmett–Teller). The effects of concentration of ion exchange solution and volume, ion exchanged time, and calcination temperature on AgY adsorbents activities were investigated. The adsorptive desulfurization activity of the AgY adsorbent exchanged with AgNO3 solution of 0.25 mol L−1 volume of 20 mL, ion exchanged time of 24 h, and calcined at 500 °C exhibited the best performance. Using 10 ml of model oil, 0.2 g of AgY adsorbent and an adsorption temperature of 40 °C for 30 min, the desulfurization rate reached 93.8 %. The Langmuir isotherm best represented the equilibrium adsorption data and kinetics of adsorptive desulfurization followed a pseudo-second-order model. The thiophene adsorption was found to be controlled by external mass transfer at earlier stages and by intra-particle diffusion at later stages.

Ion-Exchange Synthesis, Crystal Structure, and Physical Properties of Hydrogen Titanium Oxide H2Ti3O7

Hydrogen titanium oxide H2Ti3O7 was prepared from Na2Ti3O7 as a parent compound via Na(+)/H(+) ion exchange in acidic solution at 333 K. It crystallizes in the monoclinic system, space group C2/m, and the lattice parameters of a = 16.0380(8) Å, b = 3.7533(1) Å, c = 9.1982(3) Å, and β = 101.414(3)°. The crystal structure of H2Ti3O7 was refined to the conventional values of Rwp = 2.60% and Rp = 1.97% with a fit indicator of GOF = Rwp/Re = 1.90 by Rietveld analysis using powder neutron diffraction data. The basic (Ti3O7)(2-) framework in H2Ti3O7 was changed from that in the parent Na2Ti3O7. The atomic coordinate of hydrogen atoms were determined by this study for the first time. The hydrogen site in the layer space was refined with a strict H1-O3 distance of 0.80(2) Å and H2-O4 distance of 0.86(2) Å in H2Ti3O7, respectively. The structural stability of H2Ti3O7 was confirmed by bond valence sums. From these results, protons were suggested as the ordered occupation in the crystal structure.

Preparation of Li4Ti5O12 by solution ion-exchange of sodium titanate nanotube and evaluation of electrochemical performance

Nano-sized spinel lithium titanate (Li4Ti5O12) was synthesized using sodium titanate nanotube as precursor via a facile solution ion-exchange method in association with subsequent calcination treatment at relatively low temperature. The influences of precursors, ion-exchange condition, and calcination temperature on the microstructure and electrochemical performance of the products were studied. Results indicate that pure-phase Li4Ti5O12 can be harvested from sodium titanate nanotube precursor through an ion-exchanging at room temperature and calcination at 500 °C. The products exhibit a better performance as Li-ion battery anode material than the counterparts prepared from protonic titanate nanotube (H-titanate) precursor. The reason may lie in that sodium titanate nanotube is easier than protonic titanate nanotube to synthesize lithium titanate without TiO2 impurity, resulting in reduced electron transfer ability and Li-ion transport ability. The capacity of Li4Ti5O12 prepared from sodium titanate nanotube is 146 mAh/g at 10 C, and it has only 0.7 % decay after 200 charge/discharge cycles.

Biochemical characteristics of a fibrinolytic enzyme purified from a marine bacterium, Bacillus subtilis HQS-3

A fibrinolytic enzyme isolated from marine Bacillus subtilis HQS-3 was purified to electrophoretic homogeneity using ammonium sulphate precipitation, alkaline solution treatment, membrane concentration, dialysis, ion exchange, and gel filtration chromatography. SDS-PAGE and gel filtration chromatography showed that it was a monomeric protein with an apparent molecular weight of 26kDa. The purified enzyme was active at pH 6.0–10.0 with an optimum pH of 8.0. It was stable at temperatures ranging from 25 to 37°C, exhibiting maximum activity between 45°C and 50°C. The isoelectric point of the enzyme was 9.0–9.2, which was higher than those of other known fibrinolytic enzymes from Bacillus species. PMSF, EDTA, Cu2+, Zn2+, and Co2+ inhibited the enzyme activity significantly. This enzyme did not cause hemolysis in vitro and preferred direct degradation of fibrin in the following order: α, β, and γ–γ chains. Thus, these results suggest that the marine-derived enzyme is a plasmin-like serine metalloprotease, which is distinct from other fibrinolytic enzymes from genus Bacillus.