Halide Ions In Solution Research Articles

Ultrafast adsorption of hexavalent chromium from aqueous effluents using covalent triazine frameworks

We have synthesized low-cost high performance covalent triazine framework (CTF) through Schiff base reaction of melamine and terephthalaldehyde with different proportions of the reactants. The synthesized adsorbents showed excellent capacity for adsorption of Cr (VI) at acidic pH while almost negligible adsorption at higher pH. The adsorbent displays excellent reusability, with a little decrease in adsorption capacity with the increasing number of cycles. Moreover, Cr (VI) the adsorption is unaffected by the presence of 50–500 times higher concentration of alkali metal and halide ions in solution, while sulphate ions demonstrate shielding behavior decreasing the adsorption capacity. Mechanistic studies indicate electrostatic attractions, ion exchange and reduction being responsible for the adsorption mediated by abundant nitrogen sites that also imbibes the adsorbent with high capacity. The adsorbent was also utilized to recover chromium from an industrial electroplating effluent, which demonstrates applicability of material for practical applications.

Poly-pnictogen bonding: trapping halide ions by a tetradentate antimony(iii) Lewis acid.

A highly halide affine, tetradentate pnictogen-bonding host-system based on the syn-photodimer of 1,8-diethynylanthracene was synthesized by a selective tin-antimony exchange reaction. The host carries four C[triple bond, length as m-dash]C-Sb(C2F5)2 units and has been investigated regarding its ability to act as a Lewis acidic host component for the cooperative trapping of halide ions (F-, Cl-, Br-, I-). The chelating effect makes this host-system superior to its bidentate derivative in competition experiments. It represents a charge-reversed crown-4 and has the ability to dissolve otherwise poorly soluble salts like tetra-methyl-ammonium chloride. Its NMR-spectroscopic properties make it a potential probe for halide ions in solution. Insights into the structural properties of the halide adducts by X-ray diffraction and computational methods (DFT, QTAIM, IQA) reveal a complex interplay of attractive pnictogen bonding interactions and Coulomb repulsion.

Role of Solid-State Miscibility during Anion Exchange in Cesium Lead Halide Nanocrystals Probed by Single-Particle Fluorescence.

In this Letter, we used fluorescence microscopy to image the reversible transformation of individual CsPbCl3 nanocrystals to CsPbBr3, which enables us to quantify heterogeneity in reactivity among hundreds of nanocrystals prepared within the same batch. We observed a wide distribution of waiting times for individual nanocrystals to react as has been seen previously for cation exchange and ion intercalation. However, a significant difference for this reaction is that the switching times for changes in fluorescence intensity are dependent on the concentration of substitutional halide ions in solution (i.e., Br- or Cl-). On the basis of the high solid-state miscibility between CsPbCl3 and CsPbBr3, we develop a model in which the activation energy for anion exchange depends on the density of exchanged ions in the nanocrystal. The heterogeneity in reaction kinetics observed among individual nanocrystals limits the compositional uniformity that can be achieved in luminescent CsPbCl3-xBrx nanocrystals prepared by anion exchange.

Specific Ion Effects on Hydrogen-Bond Rearrangements in the Halide-Dihydrate Complexes.

Small aqueous ionic clusters represent ideal systems to investigate the microscopic hydrogen-bonding structure and dynamics in ion hydration shells. In this context, halide-dihydrate complexes are the smallest systems where the interplay between halide-water and water-water interactions can be studied simultaneously. Here, quantum molecular dynamics simulations unravel specific ion effects on the temperature-dependent structural transition in X-(H2O)2 complexes (X = Cl, Br, and I), which is induced by the breaking of the water-water hydrogen bond. A systematic analysis of the hydrogen-bonding rearrangements at low temperature provides fundamental insights into the competition between halide-water and water-water interactions depending on the properties of the halide ion. While the halide-water hydrogen-bond strength decreases going from Cl-(H2O)2 to I-(H2O)2, the opposite trend in observed in the strength of the water-water hydrogen-bond, suggesting that nontrivial many-body effects may also be at play in the hydration shells of halide ions in solution, especially in frustrated systems (e.g., interfaces) where the water molecules can have dangling OH bonds.

Base-free non-noble-metal-catalyzed hydrogen generation from formic acid: scope and mechanistic insights.

The iron-catalyzed dehydrogenation of formic acid has been studied both experimentally and mechanistically. The most active catalysts were generated in situ from cationic Fe(II) /Fe(III) precursors and tris[2-(diphenylphosphino)ethyl]phosphine (1, PP3 ). In contrast to most known noble-metal catalysts used for this transformation, no additional base was necessary. The activity of the iron catalyst depended highly on the solvent used, the presence of halide ions, the water content, and the ligand-to-metal ratio. The optimal catalytic performance was achieved by using [FeH(PP3 )]BF4 /PP3 in propylene carbonate in the presence of traces of water. With the exception of fluoride, the presence of halide ions in solution inhibited the catalytic activity. IR, Raman, UV/Vis, and EXAFS/XANES analyses gave detailed insights into the mechanism of hydrogen generation from formic acid at low temperature, supported by DFT calculations. In situ transmission FTIR measurements revealed the formation of an active iron formate species by the band observed at 1543 cm(-1) , which could be correlated with the evolution of gas. This active species was deactivated in the presence of chloride ions due to the formation of a chloro species (UV/Vis, Raman, IR, and XAS). In addition, XAS measurements demonstrated the importance of the solvent for the coordination of the PP3 ligand.

Understanding of Ion Transport in a Na–Mordenite Membrane: Use of Numerical Modeling To Estimate Surface–Solute Interactions in the Pore

A mordenite membrane was prepared and surface characterizations were performed on the synthesized mordenite (as powder form). The surface charge remained constant when mordenite powder was in contact with the studied solutions. A pore diameter of 5.8 × 10–9 m was estimated. Filtration tests of single salt–water solutions (NaCl, NaF, and Na2SO4) were carried with the mordenite membrane. No rejection was observed. After an alkaline treatment, the rejections were observed: NaF = Na2SO4 = 5–6%, while NaCl = 0%. New filtration tests of mixed salt–water solutions were carried out (Na2SO4 + NaCl and Na2SO4 + NaF). The sulfate ion was retained by a majority (up to 16%) whatever the halide ion in solution. The rejection rate of sulfate ion in mixtures decreases with the applied pressure, which actually cannot be explained (no observable polarization layer effect). A preferential transport is observed for chloride ions and the rejection rate of the fluoride ions remained constant. A numerical modeling (Nernst–Planc...

Determination of Halide Impurities in Ionic Liquids by Total Reflection X-ray Fluorescence Spectrometry

The determination and quantification of halide impurities in ionic liquids is highly important because halide ions can significantly influence the chemical and physical properties of ionic liquids. The use of impure ionic liquids in fundamental studies on solvent extraction or catalytic reactions can lead to incorrect experimental data. The detection of halide ions in solution by total reflection X-ray fluorescence (TXRF) has been problematic because volatile hydrogen halide (HX) compounds are formed when the sample is mixed with the acidic metal standard solution. The loss of HX during the drying step of the sample preparation procedure gives imprecise and inaccurate results. A new method based on an alkaline copper standard Cu(NH3)4(NO3)2 is presented for the determination of chloride, bromide, and iodide impurities in ionic liquids. The 1-butyl-3-methylimidazolium ([C4mim]) ionic liquids with the anions acetate ([C4mim][OAc]), nitrate ([C4mim][NO3]), trifluoromethanesulfonate ([C4mim][OTf]), and bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]) were synthesized via a halide-free route and contaminated on purpose with known amounts of [C4mim]Cl, [C4mim]Br, [C4mim]I, or potassium halide salts in order to validate the new method and standard.

Determination of Halide Ions in Solution by Total Reflection X-ray Fluorescence (TXRF) Spectrometry

An accurate quantitative determination of halide ions X (X = Cl, Br, I) in aqueous solution by total reflection X-ray fluorescence (TXRF) is not possible using the traditional acidic internal standards. In general, the standard solutions are highly acidic (e.g., Ga(NO3)3 in HNO3) to avoid precipitation of hydroxides of the standard element and to obtain a stable and reliable standard. In acidic solutions, dissolved halide salts can exchange their cation for a proton. The resulting volatile HX compounds can evaporate during the drying procedure of the TXRF sample preparation. In this technical note, we show that an alkaline Cu(NH3)4(NO3)2 standard can be used for the determination of chlorine, bromine and iodine without facing problems of HX evaporation.

Modeling the hydration of mono-atomic anions from the gas phase to the bulk phase: The case of the halide ions F−, Cl−, and Br−

In this work, we investigate the hydration of the halide ions fluoride, chloride, and bromide using classical molecular dynamics simulations at the 10 ns scale and based on a polarizable force-field approach, which treats explicitly the cooperative bond character of strong hydrogen bond networks. We have carried out a thorough analysis of the ab initio data at the MP2 or CCSD(T) level concerning anion/water clusters in gas phase to adjust the force-field parameters. In particular, we consider the anion static polarizabilities computed in gas phase using large atomic basis sets including additional diffuse functions. The information extracted from trajectories in solution shows well structured first hydration shells formed of 6.7, 7.0, and 7.6 water molecules at about 2.78 Å, 3.15 Å, and 3.36 Å for fluoride, chloride, and bromide, respectively. These results are in excellent agreement with the latest neutron- and x-ray diffraction studies. In addition, our model reproduces several other properties of halide ions in solution, such as diffusion coefficients, description of hydration processes, and exchange reactions. Moreover, it is also able to reproduce the electrostatic properties of the anions in solution (in terms of anion dipole moment) as reported by recent ab initio quantum simulations. All the results show the ability of the proposed model in predicting data, as well as the need of accounting explicitly for the cooperative character of strong hydrogen bonds to reproduce ab initio potential energy surfaces in a mean square sense and to build up a reliable force field.

A Deep Cavitand with a Fluorescent Wall Functions as an Ion Sensor

The synthesis and characterization of a deep cavitand bearing a fluorescent benzoquinoxaline wall is reported. Noncovalent host-guest recognition events are exploited to sense small charged molecules including acetylcholine. The cavitand also exhibits an anion dependent change in fluorescence that is used to differentiate halide ions in solution.

Calculations of the intrinsic constants of the complexation between Cu(II) and halide ions in solution

Experimental curves of spectrophotometric titration for systems containing mononuclear homoleptic complexes were interpreted in an alternative way involving calculation of the intrinsic constants of binding of the ligand by a central ion with fixed coordination sites. This matrix approach allows one to reduce the number of variables in least-squares optimization of titration curves, describing the formation of complexes [MXn] (n = 1–4) via three independent variables (\( \bar K \), ωcis and ωtrans) for a square planar geometry and via two variables (\( \bar K \) and ω) for a tetrahedral geometry. Differences in the mutual cis-and trans-influences of coordinated ligands were quantitatively estimated for labile complexes in solution. The method proposed was used to calculate the intrinsic constants of complexation between Cu2+ and the chloride ion in methanol from spectrophotometric titration data.

Solute–Solvent Charge Transfer in Aqueous Solution

H bonds as main electron-transfer vehicles: DFT molecular dynamics simulations on the GlyGly peptide in water indicate that solute–-solvent interactions appear to involve a significant amount of intermolecular charge transfer at the charged termini (see picture). Similar results are obtained for alkali halide ions in solution. The electronic charge mostly distributes uniformly throughout the H bonds, and it arranges electrostatically when they are absent.

The electrochemical halogenation of benzene: an in situ confocal microprobe Raman study

The electrochemical substitution of benzene on Pt and Rh electrodes has been studied by a confocal microprobe Raman technique. The results showed that chlorination or bromination of benzene could occur with the positive-shift of the electrode potential. The two processes are significantly influenced by the roughness of the electrodes, the relative concentration of benzene and halide ion in solution and the entity of the substrates. The possible mechanism of the electrochemical halogenation of benzene has been proposed.

Electron Photodetachment from Halide Ions in Solution: Excited-State Dynamics in the Polarization Well

The electronic relaxation and photodetachment dynamics of an electron originating from an aqueous iodide ion have been studied using femtosecond absorption spectroscopy. The results indicate the importance of an upper excited charge transfer to solvent (CTTS) state, of odd parity, in the potential well of the solvated ion. The upper excited CTTS state, which is accessed by two-photon excitation, relaxes in <50 fs to the lowest excited CTTS, which in turn relaxes to the ground state of the I-in 80 fs. It is found that most of the solvated electrons are produced by a three-photon excitation to a photoionized state, rather than from the CTTS excitation. 25 refs., 4 figs.

Influence of the Anodic Oxide Film on Pitting of Iron

The fundamental processes leading to the initiation of pitting on pure Fe in acetate and borate solutions containing halide ions are discussed. The results of potentiostatic step experiments show that pit initiation is associated with a critical stage in the development of the passive oxide film, likely corresponding to a certain critical oxide thickness. The critical oxide thickness depends on the identity (chloride or bromide) and the concentration of the halide ion in solution, and on the supporting electrolyte, but not on the anodic potential. Acetate is shown to inhibit pitting. The critical oxide film characteristics have been investigated using galvanostatic cathodic reduction techniques. Scanning electron microscopy with computerized image analysis has been used to study the size distribution of the pits formed in these experiments. The results can be used to support the proposed model for pitting.

Effect of γ-radiation on some physicochemical properties of polystyrene strong base anion exchangers

The effect of γ-radiation up to 1 MGy dose on the ion-exchange capacity and moisture content of polystyrene resins in the chloride, bromide and iodide forms containing 8% DVB and either N +(CH 3) 2 · CH 2 · CH 2OH or N +(CH 3) 3 group was investigated. For the iodide form of the resins the changes were minimum and the equilibrium coefficient values with respect to other halide ions in solution decreased slightly.

Studies On The Use Of Halide Ion Selective Electordes In Salt Media And The Extension Of The Generalized Standard Addition method To Determine The Concentration Of Halide Ions In Geothermal Brins

Abstract The effect of chloride on the bromide and iodide solid state precipitate electrodes is studied and selectivity constants calculated. The use of multiple linear regression analysis to determine the initial concentration of halide ions in solutions is studied and the resulting technique is used to determine fluoride, iodide and bromide in a geothermal-geopressured brine.

Solid-state halide ion-selective electrodes: studies of quaternary ammonium halide solutions and determination of surfactants

The feasibility of using homogeneous membrane-type halide ion-selective electrodes in solutions containing cationic surfactant compounds was examined. The results established the applicability of these electrodes for monitoring halide ions in solution without interference by the surfactants. The data also provided a basis for estimation of the surfactant in solution through the halide content. Two typical plating-bath compositions containing CTAB have been successfully analysed for their surfactant content by this procedure.

Preferential solvation of ions and solvent transport

Abstract

Convenient synthesis of aryl halides from arylamines via treatment of 1-aryl-3,3-dialkyltriazenes with trimethylsilyl halides

Treatment of 1-aryl-3,3-diethyltriazenes with trimethylsilyl halides in acetonitrile at 60/sup 0/C resulted in the rapid and quantitative evolution of nitrogen and in the formation of aryl halides. 1-Aryl-3,3-diethyltriazenes were prepared by a conventional route in high yields, and trimethylsilyl iodide and bromide were produced in site by the reaction of trimethylsilyl chloride with sodium iodide or lithium bromide, respectively. The high reactivity of trimethylsilyl halides toward 1-aryl-3,3-diaklytriazenes may be explained in terms of their strong electrophilicity and the marked affinity of the trimethylsilyl group toward nitrogen. The reaction rate seemed to be markedly dependent on the nature of the free halide ion in solution; iodide ion reacted faster than bromide ion, and chloride ion was only converted to the aryl chloride after an extended reaction period. In addition, in the absence of trimethylsilyl chloride, neither iodide not bormide ion reacted with the aryldialkyltriazenes under our experimental conditions. Since the trimethylsilyl chloride with sodium iodide or lithium bromide, this method is applicable to the preparation of aromatic radiohalide compounds. For example aromatic radiohalide derivatives may be prepared from bromide (/sup 75/Br or /sup 77/Br) and iodide (/sup 123/I, /sup 125/I, or /sup 131/I) with high radiochemical purity and yields which makesmore » this synthetic method useful for the preparation of radiopharmaceuticals of medicinal interest.« less