Anion Exchange Properties Research Articles

Silver Coordination Polymers Based on Newly Designed Bis(cyanobenzyl)bipiperidine Ligand: Synthesis, Anion Exchange, Guest Inclusion, Electrochemical, and Photoluminescence Properties

A new flexible ligand, bis(cyanobenzyl)bipiperidine (L), has been synthesized and structurally characterized. Nine novel silver(I) coordination polymers (CPs), the dimensionality of which depends on the counteranion, [Ag2(L)(NO3)2]n (1), [Ag2(L)(NO3)2]n (2), {[Ag2(L)(NO3)2)](C16H10)}n (3), {[Ag2(L)(NO3)2)](C20H12)}n (4), [Ag2(L)(ClO4)2]n (5), [Ag2(L)(CF3SO3)2(C4H8O)2]n (6), [Ag2(L)(CF3SO3)2(C3H6O)2]n (7), {[Ag2(L)2]·(BF4)·2(C3H6O)}n (8), and [Ag2(L)3(PF6)2]·x(C3H6O) (9), have been prepared by self-assembly of L with AgX (X = NO3–, ClO4–, CF3SO3–, BF4–, and PF6–) and aromatic guest molecules. Reactions of L with AgNO3 in acetone in either 1:2 or 1:1 stoichiometric ratio occurred rapidly at room temperature, yielding topologically different structural isomers of the three-dimensional (3D) CPs 1 and 2. Additional reactions of linker L with AgNO3 in the presence of aromatic guest molecules (pyrene, perylene) formed CPs of 3 and 4 with the inclusion of the corresponding guest in the crystal lattice associated ...

Enhanced sequestration of Cr(VI) by nanoscale zero-valent iron supported on layered double hydroxide by batch and XAFS study

Herein, the reduction of nanoscale zero-valent iron (NZVI) and adsorption of layered double hydroxides (LDH) to sequester Cr(VI) were well combined by the immobilization of NZVI onto LDH surface (NZVI/LDH). The characterization results revealed that LDH decreased NZVI aggregation and thus increased Cr(VI) sequestration. The batch results indicated that Cr(VI) sequestration by NZVI/LDH was higher than that of NZVI, and superior to the sum of reduction and adsorption. The LDH with good anion exchange property allowed the adsorption of Cr(VI), facilitating interfacial reaction by increasing the local concentration of Cr(VI) in the NZVI vicinity. X-ray absorption near edge structure (XANES) results indicated that Cr(VI) was almost completely reduced to Cr(III) by NZVI/LDH, but Cr(VI) was partly reduced to Cr(III) by NZVI with a trace of Cr(VI) adsorbed on corrosion products. The coordination environment of Cr from extended X-ray absorption fine structure (EXAFS) analysis revealed that LDH could be a good scavenger for the insoluble products produced during reaction. So, the insoluble products on NZVI could be reduced, and its reactivity could be maintained. These results demonstrated that NZVI/LDH exhibits multiple functionalities relevant to the remediation of Cr(VI)-contaminated sites.

An arsenicniobate-based 3D framework with selective adsorption and anion-exchange properties

An arsenicniobate-based cationic framework shows a high adsorption selectivity of water and ethanol and effectively removes toxic SCN− anions.

Synthesis of layered double hydroxide coatings with an oriented structure and controllable thickness on aluminium substrates

Layered double hydroxides (LDHs) are applied in environmental purification and biomedicine because of their anion intercalation and exchange properties. This study investigates the formation of LDH layers on aluminium substrates, through the reaction of substrates in solution containing magnesium ions at 30–90 °C. The resulting LDH layer was constructed from many plate-shaped crystals. The LDH crystal size increased with increasing reaction temperature. The LDH layer was preferentially oriented perpendicular to the substrate, thus the LDH crystal orientation was out-of-plane. The oriented structure was formed by crystal-growth-controlled geometrical selection. The LDH layer growth rate also increased with increasing reaction temperature. A high reaction temperature (90 °C) resulted in rapid formation of an approximately 10 μm-thick LDH layer. Milder temperatures (30 and 60 °C) resulted in a moderate LDH layer growth rate, which allowed the LDH layer thickness to be precisely controlled. The LDH layer removed toxic fluoride anions from aqueous solution without damaging the layer. These findings promote the development of oriented LDH coatings with precisely controlled microstructures and thickness.

Microsystems for Anion Exchange Separation of Radionuclides in Nitric Acid Media

An efficient and reproducible photopolymerized poly(ethylene glycol methacrylate methacrylate-co- allyl methacrylate) monolith was synthesized and a photografting process based on the ene-thiol click-chemistry has been performed to give anion exchange properties to the monolith. Since their introduction in the early 1990s polymethacrylate monoliths have emerged as a powerful alternative for microscale separations or sample treatment. Their relatively simple implementation in columns with small internal diameters makes them particularly attractive for the new chromatographic challenges of complex matrices analysis and on-chip separations. Despite their relatively poor ion-exchange capacity due to their highly porous structure, their use as anion exchangers is of large interest for nuclear analysis as numerous separations are based on this process. This paper presents a systematic study of the synthesis of the polymeric porous monolith and the versatile and robust functionalization method developed for the specific strong acidic media used in radiochemical procedures. The robustness of the stationary phase was tested in concentrated nitric acid.

Periodic stacking of 2D charged sheets: Self-assembled superlattice of Ni–Al layered double hydroxide (LDH) and reduced graphene oxide

Vertically stacked artificial 2D materials, such as van der Waals heterostructures, hold great scientific and technological promise. Stacking 2D atomic layers with stronger electrostatic forces in a controlled fashion could be more challenging. Positively charged atomic sheets of layered double hydroxide (LDH) such as hydrotalcite mineral with weakly bound anions have known intercalation and anion exchange properties, while reduced graphene oxide (rGO) are known to be negatively charged. So self-assembly of periodic (LDH/rGO)n superlattice is possible, although true periodicity at atomic scale has never been demonstrated for Ni–Al LDH. This work introduces a new protocol for the synthesis of true Ni–Al LDH/GO superlattice and the corresponding reduced product Ni–Al LDH/rGO, by systematically optimizing various key experimental parameters in chemical exfoliation, dispersion and self-assembly by co-feeding. This method is further applied to the successful synthesis of more complex Ni–Co–Al/GO superlattice. The Ni–Al LDH/rGO superlattice is then tested as cathode in alkaline hybrid supercapacitor, with 129Ah/kg capacity at 8-min discharge, two times that of pristine Ni–Al LDH, and maintains 72.7% of its initial capacity after 10,000 charge/discharge cycles. Our superlattice synthesis strategy and its energy applications demonstrate the potential to design artificial 2D materials.

Microwave-Assisted Hydrothermal Synthesis of Layered Europium Hydroxynynitrate, Eu2(OH)5NO3∙xH2O

A facile method of layered europium hydroxonitrate (LEuH) synthesis based on hydrothermal- microwave treatment of hexamethylenetetramine (HMT) and europium (III) nitrate mixed solutions is reported. Synthetic conditions, including microwave power, heating rate, temperature and duration of microwave treatment and filling coefficient of the hydrothermal reactor strongly affect the microstructure of LEuH. Obtained layered materials possess good anion-exchange properties. This work provides a simple and time-saving route to the europium layered hydroxides, which might represent a promising method for preparation of other layered rare-earth hydroxides. Keywords: Hexamethylenetetramine, homogeneous hydrolysis, layered rare-earth hydroxocompounds, microwave-assisted hydrothermal synthesis, nanocrystalline materials.

Study of retention and peak shape in hydrophilic interaction chromatography over a wide pH range

Retention factor and column efficiency measurements were made for 14 test compounds comprising acids, bases and neutrals on two pairs of amide and bare silica HILIC columns, each pair obtained from a different manufacturer. The columns were tested with up to 6 different mobile phases with acetonitrile–water containing formic (FA), trifluoroacetic (TFA), heptafluorobutyric acids (HFBA) and ammonium salt buffers at wwpH 3, 6 and 9. Measurements of mobile phase pH in water (wwpH) and in the aqueous–organic mixture (wspH) were performed, and calculations of ionic strength made, in order to aid interpretation of the chromatographic results. Stronger acids like TFA produced very different selectivity compared with ammonium formate buffers at similar aqueous pH. On a given column using TFA as additive, the retention of strongly acidic solutes was considerably increased relative to that of bases. Some bases even showed exclusion on both amide, and on a hybrid silica column. Conversely, in ammonium formate buffers of similar aqueous pH, bases had increased retention compared with acids, particularly on the bare silica columns. This result can be attributed to the higher pH of the salt buffers when measured in the aqueous–organic phase and interaction with negatively charged silanols. It is possible that the silica surface becomes positively charged at the low pH of TFA, leading to anion exchange properties that become competitive with the cation exchange properties normally attributed to silanol dissociation, although other explanations of these results are possible. Very marked selectivity differences were obtained by use of TFA in the mobile phase. Useful selectivity differences may also be obtained with salt buffers at different pH if the use of TFA is not desired due to its relatively unfavourable properties in mass spectrometry.

Nature and reactivity of layered double hydroxides formed by coprecipitating Mg, Al and As(V): Effect of arsenic concentration, pH, and aging

Arsenic (As) co-precipitation is one of the major processes controlling As solubility in soils and waters. When As is co-precipitated with Al and Mg, the possible formation of layered double hydroxides (LDHs) and other nanocomposites can stabilize As in their structures thus making this toxic element less available. We investigated the nature and reactivity of Mg–Al–arsenate [As(V)] co-precipitated LDHs formed in solution affected by As concentration, pH, and aging. At the beginning of the co-precipitation process, poorly crystalline LDH and non-crystalline Al(Mg)-oxides form. Prolonged aging of the samples promotes crystallization of LDHs, evidenced by an increase in As K XANES intensities and XRD peak intensities. During aging Al- and/or Mg-oxides are likely transformed by dissolution/re-precipitation processes into more crystalline but still defective LDHs. Surface area, chemical composition, reactivity of the precipitates, and anion exchange properties of As(V) in the co-precipitates are influenced by pH, aging, and As concentration. This study demonstrates that (i) As(V) retards or inhibits the formation and transformation of LDHs and (ii) more As(V) is removed from solution if co-precipitated with Mg and Al than by sorption onto well crystallized LDHs.

Tuning and Investigating the Structure of M<sup>II</sup>-Fe<sup>III</sup> Layered Double Hydroxides (M<sup>II</sup> = Ni<sup>II</sup>, Co<sup>II</sup> and Mg<sup>II</sup>) in Relation to their Composition: From Synthesis to Anionic Exchange Properties

The ease of preparation as well as the fine tuning of their chemical composition makes layered double hydroxides (LDH) very attractive for a large variety of applications. The aim of this feature article is to provide the keys that permit to finely tune the structure of the materials in controlling simple parameters involved in the synthesis procedures. In a first part, the influence of the synthesis parameters on the crystallinity and morphology of MII-FeIII LDH (MII = NiII, MgII and CoII) is studied. In a second part, further insight into the variability of composition of the layer is proposed to explain the interdependence between the cationic nature of the layer and its layer charge flexibility. The third part is devoted to the anion exchange property of LDH. We showed that a previously proposed method for anionic exchange can be successfully applied to all couple of cations in their range of composition. Finally, a molecular description of the interlayer organisation is given.

Syntheses, structures and anion exchange properties of accommodative silver chains using a positively charged and flexible ligand

Eight silver(I) coordination polymers were synthesized and structurally characterized. Direct reaction of various Ag(I) starting materials with a positively charged and flexible ligand, 1,3-di(2-picolyl)imidazolium (L) in different salts, including L-Cl, L-ClO4 and L-PF6, gave compounds [AgL(NO3)2] (1), [AgL(CH3CN)](BF4)2 (2), [Ag2L2(NO3)2](NO3)Cl (3), [AgL(CH3CN)](PF6)2·0.5CH3CN (4), [AgL(NO3)](PF6) (5), [AgL](NO3)(PF6) (6), [AgL(CH3CN)2](ClO4)(PF6)·CH3CN (7), and [AgL](ClO4)2·CH3CN (8). Structural analysis revealed that ligand L has three kinds of conformations in these structures. As benefited by the flexible feature of L, the silver chains in 1–8 are different and are depended on the shape and the size of counter anions. Anion exchange studies showed that crystals of 4, 6 and 8 had anion exchange properties, and the channel size in the corresponding solid state structures played a crucial role. These results highlighted the significance of positively charged and flexible ligand L in the construction of various silver chain structures with different conformations and thus packing diagrams for anion exchange studies.

Overview of the effect of salts on biphasic ionic liquid/water solvent extraction systems: anion exchange, mutual solubility, and thermomorphic properties.

Hydrophobic (water-immiscible) ionic liquids (ILs) are frequently used as organic phase in solvent extraction studies. These biphasic IL/water extraction systems often also contain metal salts or mineral acids, which can significantly affect the IL trough (un)wanted anion exchange and changes in the solubility of IL in the aqueous phase. In the case of thermomorphic systems, variations in the cloud point temperature are also observed. All these effects have important repercussions on the choice of IL, suitable for a certain extraction system. In this paper, a complete overview of the implications of metal salts on biphasic IL/water systems is given. Using the Hofmeister series as a starting point, a range of intuitive prediction models are introduced, supported by experimental evidence for several hydrophobic ILs, relevant to solvent extraction. Particular emphasis is placed on the IL betainium bis(trifluoromethylsulfonyl)imide [Hbet][Tf2N]. The aim of this work is to provide a comprehensive interpretation of the observed effects of metal salts, so that it can be used to predict the effect on any given biphasic IL/water system instead of relying on case-by-case reports. These prediction tools for the impact of metal salts can be useful to optimize IL synthesis procedures, extraction systems and thermomorphic properties. Some new insights are also provided for the rational design of ILs with UCST or LCST behavior based on the choice of IL anion.

Metal-organic frameworks with 1,3,5-tris(1-imidazolyl)benzene and dicarboxylate ligands: Synthesis, anion exchange and gas adsorption

Six new metal-organic frameworks [M2(tib)2(bpdc)(H2O)2]·SO4·2H2O [M = Ni (1), Co (2), Cu (3)], [Co(tib)(dnbpdc)(H2O)]·DMF·H2O (4), [M2(tib)2(bpndc)(H2O)5]·(bpndc)·5H2O [M = Ni (5), Mn (6)], [tib = 1,3,5-tris(1-imidazolyl)benzene, H2bpdc = 4,4′-biphenyldicarboxylic acid, H2dnbpdc = 2,2′-dinitro-4,4′-biphenyldicarboxylic acid, H2bpndc = 4,4′-benzophenonedicaboxylic acid, DMF = N,N-dimethylformamide] have been synthesized and characterized by single-crystal and powder X-ray diffractions, infrared spectra (IR), elemental and thermogravimetric analyses. Complexes 1, 2 and 3 are (3, 4)-connected 2-nodal three-dimensional (3D) frameworks with point (Schläfli) symbol of {4·6·8}{4·62·8·102}, while 4 is one-dimensional (1D) chain, which is further linked together by hydrogen bonding interactions to give a 3D framework. Complexes 5 and 6 are 3D frameworks with the point (Schläfli) symbol of {4·142}. Anion exchange and adsorption properties of 1 were studied.

Hybrid materials comprising trimethylglycinamide groups: immobilization consequences for anion binding affinities

A thorough binding study of three trimethylglycinamide functionalized mesoporous silica gels is reported. Anion-exchange properties of these hybrid materials were established alongside the properties of their organic analogues, to provide insight into the effects of ligand immobilization on the selectivity and effectiveness of anion binding. Chloride, benzoate, nitrate, oxalate, dichromate and phosphate salts were examined. Materials and compounds after the ion exchange were studied by potentiometric titration, FTIR and 1H NMR spectroscopy. The data acquired indicate that immobilization is a viable alternative to high preorganization of a successful host molecule.

Tuned synthesis of two coordination polymers of Cd(II) using substituted bent 3-pyridyl linker and succinate: structures and their applications in anion exchange and sorption properties.

Two new Cd(II) coordination polymers, namely [Cd(3-bpdh)2(ClO4)2]n (1) and {[Cd(3-bpdh)(suc)(H2O)]·3(H2O)}n (2), have been synthesized using a substituted bent N,N'-donor ligand 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene (3-bpdh) and aliphatic dicarboxylate disodium succinate (suc) with Cd(II) perchlorate salts at room temperature by a slow diffusion technique for the exploration of our previous reported work. Both the structures were determined by single-crystal X-ray diffraction analysis and also by other physicochemical methods. Structure analysis revealed that complex 1 is a 1D chain structure containing coordinated perchlorate with a metal centre, and complex 2 shows a porous 3D framework with encapsulation of lattice water molecules into the void along the crystallographic a-axis. The PXRD study shows the bulk purity of both the complexes and TGA analysis of 2 exhibits that the structure is thermally stable up to 250 °C. Complex 1 shows a nice anion exchange property with replacement of weakly coordinated perchlorate with the inclusion of new anions; and the anion exchanged solids were characterised by FT-IR, PXRD and photoluminescence properties. The desolvated framework of 2 exhibits sorption of CO2 and water vapor and surface adsorption of N2 corroborating with the nature of the pore environment present in 2. The photoluminescence study has been also done for both complexes in the solid state which exhibits ligand based emissions at room temperature.

Structural diversities in Cu(i) and Ag(i) sulfonate coordination polymers and their anion exchange properties

Cu(i)/Ag(i) sulfonate CPs have been synthesized and characterized. One of the CPs exhibits a reversible anion exchange for perchlorate and permanganate.

Triazole based Ag coordination clusters: synthesis, structural diversity and anion exchange properties

In this work three novel triazole based cluster-based silver(i) clusters have been isolated. 2 and 3 can effectively capturing the anion pollutants Cr2O72−, MnO4− in water solutions and Congo Red in methanol solutions.

Size-tunable LDH-protein hybrids toward the optimization of drug nanocarriers.

Layered double hydroxides (LDHs) are extensively investigated as drug nanocarriers due to their anion exchange properties and potential capacity to achieve enhanced cellular trafficking and targeted delivery. In this work, LDH-protein hybrids with controlled particle size were obtained by modulation of the charge and hydrophobicity of LDH matrixes. In order to do that, bovine serum albumin (BSA) adsorption was studied in LDH matrixes intercalated with chloride and dodecylsulfate (DS-) in different ratios and its dependence on pH and ionic strength was determined. Positively charged LDH-Cl matrixes in aqueous solution changed from micro- to nano-size when adsorbing BSA molecules at pH values higher than the isoelectric point of the protein. On the other hand, the low BSA hybridization with a negatively charged LDH-DS matrix was not enough to reduce its particle size. However, a fine tuning of the physicochemical properties of the LDH-Cl matrix by controlled DS- incorporation and pH and ionic strength conditions allowed LDH-BSA nanohybrids to be partially intercalated with the surfactant that exhibited colloidal stability at high ionic strength (similar to that of biological fluids).

Synthesis of P(NIPAM-co-Am)/Mesoporous Silica Composites and Their Temperature- Responsive Anion Exchange

The purpose of this study is to examine the structure and the temperature-responsive anion exchange property of amino-functionalized mesoporous silica coated with temperature-responsive copolymer, poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-Am)). For this purpose, the composites which contained 0, 10, or 20 wt% of Am were synthesized. From the TG results, it was found that the amounts of copolymer immobilized on the mesoporous silica were 1.6 - 2.6 wt%. XRD patterns revealed that the structures of composites were hexagonal and almost the same as that of original mesoporous silica without polymer. At low temperature the methyl orange (MO) anions adsorbed and desorbed reversibly with changing pH of the solution, while at high temperature the MO anions did not. This temperature, at which the amount of adsorbed MO anions changed considerably, shifted to the higher temperature side with increasing the amount of added Am.

High-yield microwave synthesis of layered Y2(OH)5NO3·xH2O materials

A novel, facile, and versatile microwave-assisted method of high-yield synthesis of layered rare earth hydroxo compounds (LRHs) is proposed. Layered yttrium hydroxonitrates synthesized by the microwave-assisted technique crystallize in the form of thin hexagonal plates aggregated into spheroidal particles. Depending on the conditions of microwave-assisted hydrothermal synthesis, the formation of several phases differing in interplanar spacing along the [00l] direction is possible. The materials obtained are shown to possess good anion-exchange properties. This work provides a route to large-scale synthesis of LRH-based advanced materials.