Strong Cation Anion Research Articles

Ion Pairing Limits Crystal Growth in Metal–Oxygen Batteries

Aprotic alkali metal–oxygen batteries are promising high specific energy alternatives to Li-ion batteries. Growth and dissolution of alkali metal oxides such as Li2O2 in Li–O2 batteries and NaO2 and KO2 in Na–O2 and K–O2 batteries, respectively, are central to the discharge and charge processes in these batteries. However, crystal growth and dissolution of the discharge products is poorly understood, especially in aprotic electrolytes. In this work, we chose the growth of NaO2 in Na–O2 batteries as a model system and show a strong correlation between the electrolyte salt concentration and the NaO2 crystal size. With a combination of experiments and theory, we argue that the correlation is a direct manifestation of the strong cation–anion interactions, leading to decreased crystal growth rate at high salt concentrations. Furthermore, we propose and experimentally demonstrate that cation-coordinating crown molecules are electrochemically stable electrolyte additives that weaken ion pairing and enhance discharge capacities in metal–oxygen batteries.

(Invited) Ultrasound Application and Multi-Step Reactions in Electrodeposition of Refractory Metals

This contribution discusses the application of ultrasound in ionic liquids (ILs) and its effect on refractory metal deposition as well as the particular electrochemistry of NbCl5 in TFSI based ILs. While ILs have enabled the electrodeposition of materials not accessible from aqueous solutions [1, 2], the transfer to technological applications is still hampered by high costs, stringent requirements on humidity and oxygen levels, and aspects of integration into industrial scale processes. Further, there are metals that are difficult to deposit, particularly the refractory metals: The deposition of tantalum [3] and niobium [4, 5] has been accomplished, but not yet in the form of thick, crack-free layers with good adhesion and low impurity level. Titanium was only deposited in ultrathin layers [6, 7]. Research into fundamental properties of ILs and especially the interfacial properties has shed light on some causes for these difficulties, like the presence of strong cation-anion multilayers at the interface and partial reduction of the metal precursors, especially halides, resulting in subhalide precipitation [3, 8]. The application of ultrasound leads to strongly improved mass transport and thus can counteract the accumulation of halide ions and the depletion of metal precursor close to the interface. It also might disturb the interfacial IL layers by cavitation, facilitating thereby refractory metal deposition. In aqueous solutions, the application of ultrasound can significantly enhance the deposition rate and influence the morphology and grain size of deposited films [9]. ILs with their negligible vapor pressure represent a very different environment. Nevertheless, ultrasound has been applied in ILs [10-12], cavitation was reported [13, 14] and is also associated with locally extreme temperatures [13]. This induces the risk of electrolyte decomposition. Therefore a systematic study was carried out in order to study electrochemical reactions and electrolyte decomposition in the presence of ultrasound. Extended application of ultrasound induced partial IL decomposition and formation of solid precipitates. Changes in background current and conductivity were observed and the electrolytes characterized by different spectroscopic techniques. The enhancement of electrochemical reactions in ILs by ultrasound application was demonstrated for model reactions and by application to Ta deposition from BMP TFSI. Especially the application of short ultrasound pulses at elevated temperatures increased electrochemical reaction rates. The reduction of Ta and Nb precursors requires the transfer of five electrons for each ion. The exact speciation in the IL (complexation) and thus the counter ion of the metal precursor influence the redox potentials of these individual reduction steps. (Apparent) multi-electron transfer reactions may facilitate the deposition, sequential one or two-electron transfer steps increase the risk to form sparingly soluble intermediates and can lead to corrosion of as-deposited layers [15]. The reduction of NbCl5 from BMP and OMP TFSI ILs [15] is characterized by five separate distinct reduction and corresponding oxidation steps. This system was studied in depth using the electrochemical quartz crystal microbalance technique, among others, and revealed strong changes in the electrolyte properties close to the interface.

(Invited) Constructing Efficient Photocatalysts Based on the Bonding Difference

Solar-driven photocatalysis represents a promising pathway of utilizing intermittent solar energy to produce storable chemical fuels from water splitting/CO2 reduction or to decompose pollutants in air/water environment. Photocatalysis can be divided into three basic steps, namely light absorption, charge separation and surface catalysis. Most stable photocatalysts suffer from the narrow visible light absorption range and/or high recombination probability of photogenerated charge carriers. Various strategies have been developed to address these challenges in the past decades. Controlling the compositions/defects of photocatalysts is an essential way of changing band structure of materials for a wide visible light absorption. Our ongoing studies on this topic demonstrate the substantial role of homogeneous distribution of electronic structure modifiers (dopants, defects, or disordering) in realizing band-to-band redshift of the absorption edge towards visible light region. Besides taking advantage of the natural diffusion pathways of some materials for electronic structure modifiers, another strategy we developed is weakening strong cation-anion bonds for an easy substitutional doping or introduction of anion vacancies. Some progress in producing a series of red anatase TiO2 and graphitic carbon nitride with strong visible light absorption has achieved. Constructing heterostructures of photocatalysts represents an important way of promoting the separation of photogenerated charge carriers. On the basis of the different bonding nature of different bonds in complex oxides, a series of complex oxide-binary oxide heterostructures were prepared by an in-situ process. As a consequence, the promoted charge separation is responsible for the enhanced photocatalytic activity.

Applying neutron diffraction with isotopic substitution to the structure and proton-transport pathways in protic imidazolium bis{(trifluoromethyl)sulfonyl}imide ionic liquids.

Neutron diffraction with isotopic substitution has been applied to examine the potential for complex-ion formation in protic imidazolium bis{(trifluoromethyl)sulfonyl}imide ionic liquids. Strong cation-anion hydrogen-bonding in the 1 : 1 base : acid ionic liquid results in a high population of anions adopting a cis-conformation and, on adding excess imidazole (2 : 1 base : acid stoichiometry), cation-base and base-base correlations were identified, however, persistent hydrogen-bond associations were not observed.

Amphiphilic Mesoporous Poly(Ionic Liquid) Immobilized Heteropolyanions Towards the Efficient Heterogeneous Epoxidation of Alkenes with Stoichiometric Hydrogen Peroxide

AbstractNew mesoporous poly(ionic liquid)s (MPILs) that feature a pure polycationic framework and tunable hydrophobicity were synthesized through the free‐radical polymerization of alkyl‐functionalized ionic liquids (ILs) and bisvinylimidazolium salt. Phosphotungstic (PW) anions were immobilized firmly on these MPILs with a high dispersion and density. The obtained catalyst was effective in the epoxidation of cis‐cyclooctene with stoichiometric hydrogen peroxide (H2O2) to give a high yield (>98 %) and a remarkable H2O2 efficiency (>98 %). The maximum turnover number and turnover frequency was 2375 and 685 h−1, respectively. The catalyst can be recovered easily by filtration and reused with stable activity. Other alkenes can be converted with high yields. The extraordinary performance was attributed to the pure ionic porous framework with an enhanced hydrophobicity that not only provides strong cation–anion interactions towards the stable immobilized PW anions with a high dispersion but also enables the strong affinity of the catalyst with both the substrate and oxidant.

Counterintuitive Adsorption of [PW11O39]7- on Au(100).

Understanding the interaction between charged species and surfaces is one of the most challenging topics in chemistry, given its wide involvement in several fields such as electrocatalysis, stabilization of metal nanoparticles, preparation of devices, etc. In general, these systems are particularly complex to model because of the elevated number of factors that must be taken into account. Here, we report a robust strategy based on density functional theory for studying these interactions, which has been applied to the highly charged lacunary [PW11O39]7- (PW11) adsorbed on gold and silver surfaces. In this context, we find that, unlike the modeling of polyoxoanions in solution, the incorporation of counterions in the computational models is crucial for accurately reproducing the properties of the system, even if an implicit solvent is used. Most interestingly, we find that the PW11 cluster does not preferentially adsorb to the gold surface via its more nucleophilic monodefect face but, rather, through less negatively charged terminal oxygen ligands, with an orientation similar to that found for the nondefective Keggin anion [SiW12O40]4-, induced by the strong anion-cation interactions from the same and neighboring units. This counterintuitive result is important for ongoing efforts to understand and utilize the properties of polyoxometalate monolayers on gold and other reactive metal surfaces.

FT-Raman spectroscopy study of solvent-in-salt electrolytes**Project supported by the National Basic Research Program of China (Grant No. 2014CB932300), the National Natural Science Foundation of China (Grant Nos. 51222210, 51472268, and 11234013), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA09010300).

Cation–anion interaction with different ratios of salt to solvent is investigated by FT-Raman spectroscopy. The fitting result of the C–N–C bending vibration manifests that the cation–anion coordination structure changes tremendously with the variation of salt concentration. It is well known that lithium-ion transport in ultrahigh salt concentration electrolyte is dramatically different from that in dilute electrolyte, due to high viscosity and strong cation–anion interaction. In ultrahigh salt concentrated “solvent-in-salt” electrolyte (SIS-7#), we found, on one hand, that the cation and anion in the solution mainly formed cation–anion pairs with a high Li+ coordination number (≥ 1), including intimate ion pairs (20.1%) and aggregated ion pairs (79.9%), which not only cause low total ionic conductivity but also cause a high lithium transference number (0.73). A possible lithium transport mechanism is proposed: in solvent-in-salt electrolytes, lithium ions’ direct movement presumably depends on Li-ion exchange between aggregated ion pairs and solvent molecules, which repeats a dissolving and re-complexing process between different oxygen groups of solvent molecules.

The tricyanomethanide anion favors low viscosity of the pure ionic liquid and its aqueous mixtures.

Ionic liquids (ILs) constitute a broad research interest. One of the serious drawbacks of ILs is their high shear viscosity, which originates from bulky particles and strong cation-anion coordination. A continuous molecular design is being done to develop low-viscosity ILs. Low-viscosity ILs are also expected to exhibit an increased ionic conductivity. We investigate such an IL composed using a new anion (to the IL field) tricyanomethanide [C(CN)3](-) and the cation 1-ethyl-3-methylimidazolium [EMIM](+). Having developed the force field for [EMIM][C(CN)3], we simulate molecular dynamics (MD) of the pure IL and its mixtures with water over an entire range of compositions. According to MD simulations, [EMIM][C(CN)3] exhibits unusually low shear viscosity (for the imidazolium family) and high ionic conductivity. This is achieved thanks to weak cation-anion coordination and no hydrogen bonding between them. Furthermore, cation-water and anion-water hydrogen bonds were detected in the [EMIM][C(CN)3]/water mixtures. We correlate the structure and dynamics of [EMIM][C(CN)3] in aqueous mixtures to provide guidelines for future development of low-viscosity and highly conductive ILs.

Formation of indium(III) 1,3-dithiole-2-thione-4,5-dithiolate anions, [In(dmit)2]1− and [In(dmit)]3−. Crystal structure of Cs[In(dmit)2]: Strong cation–anion interactions

The preparations of [InIII(dmit)n]m− (m,n=1,2 or 3,3) salts, using [Na]2[dmit] and [Cs]2[dmit] as dmit sources, are reported ([dmit]2−=1,3-dithiole-2-thione-4,5-dithiolate). Characterizations were generally achieved via elemental analyses and IR spectroscopy. Compounds, [Q][InIII (dmit)2] (Q=NMe4, PPh4 and AsPh4) were generally obtained using mole ratios of [Na]2[dmit]:QX (X=halide):InCl3 of 2:1:1. However, using [Cs]2[dmit] with the same addition sequence of reagents and a similar mole ratio of reagents, mixed cation salts, [Q]y[Cs]1−y[In(dmit)2] (e.g., Q, y=NBu4, 0.323; PPh4, 0.437), were isolated. Tris(dmit) salts, [InIII(dmit)3]3−, were invariably obtained using reagent mole ratios of [Cs]2[dmit]:[Q]X:InCl3=3:3:1 in MeOH solution. However only with the bulkiest cations, (Q+=[AsPh4]+ or [PPh4]+), were single salts, [Q]3[In(dmit)3], obtained. For less bulky cations, such as (Q+=[NBu4]+ or [NMe4]+), compounds isolated had mixed cations, [Q]x[Cs]3−x[InIII(dmit)3].The crystal structure of [Cs][InIII(dmit)2] was determined from data collected at 120K. Primary coordination to indium is through the thiolato sulfurs of two chelating dmit ligands, which provides four equal bonds of length 2.4678(7)Å, in a distorted tetrahedral array. Strong cation–anion interactions are present, providing four Cs–S bonds of length 3.6433(3) and four of length 3.6828(7)Å to thione and thiolato sulfurs, respectively, and a three dimensional array. Thus caesium is eight coordinate in [Cs][InIII(dmit)2].

Plasma estrone sulfate, clinical biochemistry, and milk yield of dairy cows carrying a fetus from a bull or its clone

The aim of this article was to compare plasma estrone sulfate (E1SO4), clinical biochemistry, and milk yield of dairy cows carrying a female fetus from a bull (BULL) or from its clone (CLONE), evaluating also the relationship between the former variables and the birth weight of the newborn. Sixteen recipient dairy Friesian heifers (10 BULL and 7 CLONE) received a female embryo, obtained by in vitro embryo production and sexing by polymerase chain reaction with the semen of the BULL or the CLONE. Blood samples on all cows were obtained before feed distribution in the morning from jugular vein from 4 weeks before to 4 weeks after calving, to be analyzed for metabolic profile. The samples from late gestation were also analyzed for E1SO4 concentration. To separately assess the effect of calf birth weight (CBW), data were categorized as follows: low (<39 kg; BWT-A), mid (39–46 kg; BWT-B), and high (>46 kg; BWT-C). The plasma concentrations of β-hydroxybutyric acid (BHB, P = 0.019), Na (P = 0.002), Cl (P = 0.026), strong cation–anion balance (P = 0.020), total bilirubin (P = 0.054), and α1-globulin (P = 0.044) were higher in prepartum BULL recipients than those in CLONE, whereas BHB (P = 0.021) and Mg (P = 0.090) were higher in postpartum BULL recipients, while no differences were recorded in the remaining postpartum parameters. The CBW class had significant interaction with week of gestation on antepartum plasma estrone sulfate (P = 0.021), whereas CBW per se affected antepartum plasma BHB (P = 0.021), and nonesterified fatty acids (NEFA; P = 0.011) being higher in BWT-C which also had the lower NEFA concentration during postpartum. Milk yield was unaffected by the sire used, both for quantitative and qualitative aspects. Cows carrying heavier fetus (BWT-C) had a different lactation affected by month compared with the other 2 CBW groups. From these results, there were no differences between BULL and CLONE recipients. Estrone sulfate, BHB, and NEFA may be used to predict CBW and provide different nutritional management during gestation.

Low dilution hydration boundary in liquid–liquid phase equilibria of 1-methyl-3-alkyl (hexyl/octyl) imidazolium chloride ionic liquids

We report observation of low dilution hydration boundary in room temperature liquids (RTILs), 1-methyl-3-octylimidazolium chloride and 1-methyl-3-hexylimidazolium chloride ([C8mim][Cl] and [C6mim][Cl]), homologous members differing by two methylene units, were diluted with water at very low concentration (xw<0.08). The liquid–liquid phase equilibria were probed systematically using data obtained from rheology and Raman studies. Viscoelastic studies revealed binding of water to ILs was predominantly driven by hydrogen bonding, and was concentration specific, with maximum IL–water interaction occurring at mole fractions of water xw=0.024 and 0.044 for [C6mim][Cl] and [C8mim][Cl] respectively. [C8mim][Cl], though more hydrophobic, was found to be more selectively hydrated as compared to [C6mim][Cl]. Change in packing fraction (ΔΦm) was estimated from Kreigher–Dougherty dispersion model, ηIL−w=ηw(1−ΦIL/Φm)−2 where ΦIL is the volume fraction of IL (ΦIL<maximum packing fraction, Φm). ηIL-w and ηw are viscosity of IL–water solution and water respectively. [C8mim][Cl] molecules experienced twice as much change in packing due to higher dilution as compared to [C6mim][Cl] molecules. No discernible blue shift in Raman bands was noticed indicating the presence of strong cation–anion pairs in the explored samples. The identified bands were: (CH2)asym, (2895cm−1), CH3–FR (2930cm−1), (CH3)asym (2956cm−1) and (C4–C5)asym (3086cm−1) modes. These bands selectively got affected in presence of water due to formation of H-bonds. Unique hydration phase diagrams depicting the liquid–liquid phase equilibria of the ILs are presented.

Luminescence induced by strong cation–anion π–π interactions in crystals of viologen analogues

The crystal structures of bis[2-(1-alkyl-pyridinium-4-yl)vinyl]benzenes and their unusual structure-luminescence dependence are reported and discussed. It has been found that luminescence of viologen analogues can be activated by tuning their molecular and crystal structure (via modification of the N-alkyl substituents, exchange of anion, including or excluding the solvent molecules) in an unusual way. The formation of π-stacked close ionic pairs leads to a significant increase in luminescence intensity, which is attributed to strong π–π interactions.

Hydrogen Bonding Interactions between a Representative Pyridinium-Based Ionic Liquid [BuPy][BF4] and Water/Dimethyl Sulfoxide

Infrared spectroscopy and density functional theory calculations have been applied to elucidate the hydrogen bonding interactions between water/dimethyl sulfoxide (DMSO) and a representative pyridinium-based ionic liquid, 1-butylpyridinium tetrafluoroborate ([BuPy][BF(4)]). It has been found that both solvents can interact with the BuPy(+) cation through the aromatic C-H. The strength of the H-bonds involving the aromatic C-H in water is similar to that in pure [BuPy][BF(4)], but is much stronger in DMSO. For DMSO, when it forms H-bonds with the BuPy(+) cation through its S=O group, its back-side methyl groups act as electron donors, while the butyl group of the cation acts as an electron acceptor. For water, when it forms the strong anion-HOH-anion complex, it can also form H-bonds with the aromatic C-H on the BuPy(+) cation. This is different from the imidazolium-based ionic liquid, where the strong anion-cation interaction and steric hindrance from the alkyls prevent water molecules from H-bonding with the aromatic C-H other than with the anion.

Salts and Ionic Liquids of Resonance Stabilized Amides

The synthesis, structure, and bonding of alkali salts of resonance stabilized amides, such as diformylamide (dfa), formylcyanoamide (fca), nitrocyanoamide (nca), and for comparision, the well-known dicyanoamide (dca), are discussed on the basis of experimental and theoretical data. The first structural reports of K(18-crown-6)+dfa-, K(18-crown-6)+fca-, Na+nca-, and Li(TMEDA)+dca- are presented. Examination of the X-ray data reveals almost planar anions with strong cation-anion interactions resulting in network-like structures in the solid state. For comparison, the X-ray structures of covalently bound phenyldicyanoamide and diformamide are also discussed. The thermal behavior of the alkali salts of these amides is studied by thermoanalytical experiments. Moreover, several novel ionic liquids based on resonance stabilized amides have been prepared and were fully characterized, namely the dfa, fca, and nca salts of EMIM (1-ethyl-3-methyl-imidazolium), BMIM (1-butyl-3-methyl-imidazolium), and HMIM (1-hexyl-3-methyl-imidazolium). Most of them are liquid at room temperature, except BMIM+fca- that melts at 32 degrees C. These ionic liquids are neither heat nor shock sensitive, are thermally stable up to over 200 degrees C, and can be prepared easily in large quantities.

Dl-Asparaginium nitrate.

In the title compound, C4H9N2O3 +·NO3 −, alternatively called (1RS)-2-carbamoyl-1-carboxy­ethanaminium nitrate, the asymmetric unit comprises one asparaginium cation and one nitrate anion. The strongest cation–cation O—H⋯O hydrogen bond in the structure, together with other strong cation–cation N—H⋯O hydrogen bonds, generates a succession of infinite chains of R 2 2(8) rings along the b axis. Additional cation–cation C—H⋯O hydrogen bonds link these chains into two-dimensional layers formed by alternating R 4 4(24) and R 4 2(12) rings. Connections between these layers are provided by the strong cation–anion N—H⋯O hydrogen bonds, as well as by one weak C—H⋯O inter­action, thus forming a three-dimensional network. Some of the cation–anion N—H⋯O hydrogen bonds are bifurcated of the type D—H⋯(A 1,A 2).

Octanuclear Copper(I) Clusters Inscribed in a Se12Icosahedron: Anion-Induced Modulation of the Core Size and Symmetry

Synthesis and structural characterization of an octanuclear Cu(I) cluster [Cu(8){Se(2)P(O(i)Pr)(2)}(6)](PF(6))(2) (1) with an empty Cu(8) cubic core involving diisopropyl diselenophosphate (dsep) ligand has been demonstrated despite its high tendency to abstract anions even from the traces of impurities in the solvent. Reaction of 1 with anion sources (Bu(4)NF for F(-); NaBH(4) for H(-), and NaSH for S(2-)) in a 1:1 ratio produced anion-centered Cu(8) clusters with a formula [Cu(8)(X){Se(2)P(O(i)Pr)(2)}(6)](PF(6)) (X = F, 2a; H, 3a; D, 3a') and [Cu(8)(S){Se(2)P(O(i)Pr)(2)}(6)] (4) in high yields. In addition, fluoride- and hydride-centered Cu(8)(I) clusters [Cu(8)(X){Se(2)P(OEt)(2)}(6)](PF(6)) (X = F, 2b; H, 3b) could be generated in approximately 80% yield by direct reaction of [Cu(CH(3)CN)(4)](PF(6)), NH(4)Se(2)P(OEt)(2), and the anion sources (Bu(4)NF for F(-); NaBH(4) for H(-)) in 8:6:1 ratio. Whereas the structural elucidation of complexes 2 and 4 revealed an anion-centered cubic Cu(8) core surrounded by six dsep ligands, it was a tetracapped tetrahedral copper framework with a hydride in the center in compounds 3. All Cu...Cu distances along either the edge of the cube in 2 and 4 or the tetracapped tetrahedron in 3 are shorter than those identified in 1. Although the cubic (or spherical) contraction of the copper framework that was identified in a series of closed-shell anion-centered (except a hydride) Cu(8) cube having T(h) symmetry could be explained by the existence of strong anion-cation attractions, it was definitely a surprise that the hydride, which is the smallest closed-shell anion and spherical too, induced a tetrahedral contraction of four out of the eight Cu atoms in the empty cube 1, resulting in a tetracapped-tetrahedral geometry and reducing the symmetry to T from T(h). Furthermore the fact that the encapsulated anion induced modulation of the copper core size and symmetry was fully reproduced by DFT calculations on model compounds. To the best of our knowledge, this demonstrated the first example of the reduction of molecular symmetry (from T(h) to T) simply by changing the encapsulated species without altering the general bonding pattern of the surrounding ligands. We also demonstrated that the hydride can easily replace other anions (Cl(-), Br(-), F(-), S(2-), Se(2-)) in a very facile manner to produce hydride-centered species. Eventually, compounds 3 were stable in the presence of other anions, and hydride/deuteride exchange could not be achieved.

Application of strong ion difference theory to urine and the relationship between urine pH and net acid excretion in cattle

To develop an equation expressing urine pH in terms of independent variables, derive an equation relating urine pH to net acid excretion (NAE), and apply this new knowledge to determine the role that monitoring urine pH should play when diets with low cationanion difference are fed to dairy cattle. 11 Holstein-Friesian cows. A physicochemical strong ion approach was used to develop a general electroneutrality equation for urine that involved urine pH and strong ion difference (SID [difference between strong cation and strong anion concentrations]), PCO(2), the concentration of ammonium ([NH(4)(+)]) and phosphate ([PO(4)]), and 3 constants. The general electroneutrality equation was simplified for use in bovine urine and applied to 321 data points from 11 cows fed different diets. Urine pH was dependent on 4 independent variables (urine SID, [NH(4)(+)], PCO(2), and [PO(4)]) and 3 constants. The simplified electroneutrality equation for bovine urine was pH approximately {pK(1)' - log(10)(S PCO(2))} + log(10)([K(+)] + [Na(+)] + [Mg(2+)] + [Ca(2+)] + [NH(4)(+)] - [Cl(-)] - [SO(4)(2-)]). The relationship between urine pH and NAE (in mEq/L) for cattle fed different diets was pH = 6.12 + log(10)(-NAE + [NH(4)(+)] + 2.6). A change in urine SID, [NH(4)(+)], PCO(2), or [PO(4)] independently and directly led to a change in urine pH. Urinary [K(+)] had the greatest effect on urine pH in cattle, with high urine [K(+)] resulting in alkaline urine and low urine [K(+)] resulting in acidic urine. Urine pH provided an accurate assessment of NAE in cattle when pH was > 6.3.

Structural and dynamical properties of ionic liquids: The influence of ion size disparity

The influence of ion size disparity on structural and dynamical properties of ionic liquids is systematically investigated employing molecular dynamics simulations. Ion size ratios are varied over a realistic range (from 1:1 to 5:1) while holding other important molecular and system parameters fixed. In this way we isolate and identify effects that stem from size disparity alone. In strongly size disparate systems the larger species (cations in our model) tend to dominate the structure; the anion-anion distribution is largely determined by anion-cation correlations. The diffusion coefficients of both species increase, and the shear viscosity decreases with increasing size disparity. The influence of size disparity is strongest up to a size ratio of 3:1, then decreases, and by 5:1 both the diffusion coefficients and viscosity appear to be approaching limiting values. The conventional Stokes-Einstein expression for diffusion coefficients holds reasonably well for the cations but fails for the smaller anions as size disparity increases likely due to the neglect of strong anion-cation correlations. The electrical conductivity is not a simple monotonic function of size disparity; it first increases up to size ratios of 2:1, remains nearly constant until 3:1, then decreases such that the conductivities of the 1:1 and 5:1 systems are similar. This behavior is traced to the competing influences of ion diffusion (enhancing) and ion densities (reducing) on conductivities at constant packing fraction. The temperature dependence of the transport properties is examined for the 1:1 and 3:1 systems. In accord with experiment, the temperature dependence of all transport properties is well represented by the Vogel-Fulcher-Tammann equation. The dependence of the diffusion coefficients on the temperature/viscosity ratio is well described by the fractional Stokes-Einstein relation D proportional to (T/eta)(beta) with beta approximately = 0.8, consistent with the exponent observed for many molten inorganic salts.

Uptake of Iodine and Bromine by Ion-Exchange Resins in Aqueous Solution

The uptakes of molecular iodine and bromine by both strong acid cation (Dowex 50W-X4 and X8) and strong base anion (Dowex 1-X4 and X8) exchange resins have been studied in aqueous solutions at 25 degrees C. An empirical formula for the amount of solute taken up by the resin in mmol per gram of dry resin, Q, as a function of the solute concentration in M (mol dm(-3)), C, was derived. Direct proportional relationships between Q and C have been found, except for the bromine-anion exchanger system. In contrast to the cation-exchange resin, the anion exchanger exhibits extremely high affinity for I(2) and Br(2).

Characteristic Performance of Deionized Columns

The reclamation of makeup water is studied in terms of breakthrough time (i.e., the leakage of the cations). Makeup water was subjected to lab-scale ion exchangers of two types: strong acid cation and weak base anion exchanger. The experimental investigation was directed to study the ion exchanger performance in terms of four different parameters (i.e., copper concentration, total dissolved solids (TDS), feed rate and bed depth). Box-Wilson composite rotatable design was adopted in designing the experiments. Breakthrough times of the effluent stream are measured in terms of copper concentration of 2 to 25 ppm, TDS concentration of 250 to 1250 ppm, feed rate of 0.38 to 5.34 l/h and bed depth of 5 to 70 cm. Simulation the effect of the studied variables through their pre-designed ranges in terms of breakthrough time was done by 2nd order polynomial equation. In general, the performance and characteristic of adopting two bed deionizers (cation and anion beds) was efficiently recommended to remove the ionic contaminants and not less than 95 % of wastewater is recycled.