Selective Crystallization of Phosphoester Coordination Polymer for the Separation of Neodymium and Dysprosium: A Thermodynamic Approach.

Thermodynamics of the formation of coordination polymers (CPs) or metal-organic frameworks (MOFs) has not been focused on, whereas many CPs or MOFs have been synthesized in a solution. With a view of separating Nd3+ and Dy3+ in an aqueous solution, we demonstrate that crystallization of the CPs of Nd3+ and Dy3+ based on dibutyl phosphoric acid (Hdbp) can be thermodynamically described; crystallization yields of [Ln(dbp)3] (Ln = Nd or Dy) complex are predicted well using a simple calculation, which takes the apparent solubility products (Kspa) for [Ln(dbp)3] and the acid dissociation constant of Hdbp into account. The Kspa values of [Nd(dbp)3] and [Dy(dbp)3] are experimentally determined to be (1.3 ± 0.1) × 10-14 and (2.9 ± 0.4) × 10-18 M4, respectively, at 20 °C. The ratio of these Kspa values, that is, ca. 4500, is significantly larger than the ratio of the solubility products for inorganic salts of Nd3+ and Dy3+. Therefore, Nd3+ and Dy3+ are selectively crystallized in an aqueous solution via the formation of CPs. Under optimized conditions, Dy3+ crystallization is preferable, whereas Nd3+ remains in the solution phase, where the ratio of the Dy molar content to the total metal content (i.e., Nd + Dy) in the crystal is higher than 0.9. The use of acids, such as HCl or HNO3, has no practical impact on the separation in an aqueous solution.

Direct Synthesis of Unilamellar MgAl-LDH Nanosheets and Stacking in Aqueous Solution.

Two-dimensional (2D) materials, such as graphene, inorganic oxides, and hydroxides, are one of the most extensively studied classes of materials due to their unilamellar crystallites or nanosheet structures. In this study, instead of using the universal exfoliation method of the bulky crystal precursor, 2D crystals/nanosheets of MgAl-layered double hydroxides (LDHs) were synthesized in formamide. We propose that the obtained crystals are unilamellar according to the XRD, TEM, and AFM observations. The HRTEM and fast Fourier transform images confirm that the crystal structures are the same as those of the exfoliated MgAl-LDH nanosheets. The directly synthesized sheets can stack into a 3D crystal structure, which is the same as that of typical LDHs except for the disordered orientation of the a-/b- crystal axis of each sheet. This result provides not only a novel approach to the preparation of 2D crystals but also insight into the formation mechanism of LDHs.

Lithium recovery from salt lake brine by H2TiO3.

The details of the ion exchange properties of layered H2TiO3, derived from the layered Li2TiO3 precursor upon treatment with HCl solution, with lithium ions in the salt lake brine (collected from Salar de Uyuni, Bolivia) are reported. The lithium adsorption rate is slow, requiring 1 d to attain equilibrium at room temperature. The adsorption of lithium ions by H2TiO3 follows the Langmuir model with an adsorptive capacity of 32.6 mg g(-1) (4.7 mmol g(-1)) at pH 6.5 from the brine containing NaHCO3 (NaHCO3 added to control the pH). The total amount of sodium, potassium, magnesium and calcium adsorbed from the brine was <0.30 mmol g(-1). The H2TiO3 was found capable of efficiently adsorbing lithium ions from the brine containing competitive cations such as sodium, potassium, magnesium and calcium in extremely large excess. The results indicate that the selectivity order Li(+) ≫ Na(+), K(+), Mg(2+), Ca(2+) originates from a size effect. The H2TiO3 can be regenerated and reused for lithium exchange in the brine with an exchange capacity very similar to the original H2TiO3.

Lanthanide ion exchange properties of a coordination polymer consisting of di(2-ethylhexyl) phosphoric acid and trivalent metal ions (Ce3+, Fe3+, or Al3+).

Three kinds of coordination polymers ([M(dehp)3], M = Ce, Fe, or Al) were prepared by mixing the sodium form (Na(dehp)) of di(2-ethylhexyl) phosphoric acid and MCl3 in an ethanol-water binary mixture. They have monoclinic crystalline structure with similar lattice parameters. The lanthanide ion (Ln(3+) = La(3+), Sm(3+), Dy(3+), or Yb(3+)) exchange properties were studied in a 20 : 80 vol% ethanol-water binary mixture containing 2 mM Ln(NO3)3 at room temperature. The rate of Ln(3+) adsorption is relatively slow; it requires over 3 weeks to reach equilibrium. [M(dehp)3] has different Ln(3+) affinities depending on the kind of central metal ions: the affinity order at 3 week adsorption is Yb(3+) < La(3+) < Dy(3+) < Sm(3+) for [Ce(dehp)3], La(3+) < Sm(3+) < Dy(3+) < Yb(3+) for [Fe(dehp)3], and La(3+) < Sm(3+), Dy(3+), Yb(3+) for [Al(dehp)3]. The difference in affinity order can be explained by two factors: the coordination preference and steric strain caused by the polymeric structure. The chemical and structural analyses suggested that the Ln(3+) adsorption progresses first by the central M(3+)/Ln(3+) exchange, followed by a morphological change to a rod-like or fibrous form by a solid phase reaction. In the case of [Fe(dehp)3], the eluted Fe(3+) may be hydrolyzed and precipitated as amorphous iron hydroxide.

Central metal ion exchange in a coordination polymer based on lanthanide ions and di(2-ethylhexyl)phosphoric acid: exchange rate and tunable affinity.

In this paper the exchange of lanthanide(III) ions (Ln(3+)) between a solution and a coordination polymer (CP) of di(2-ethylhexyl)phosphoric acid (Hdehp), [Ln(dehp)3], is studied. Kinetic and selectivity studies suggest that a polymeric network of [Ln(dehp)3] has different characteristics than the corresponding monomeric complex. The reaction rate is remarkably slow and requires over 600 h to reach in nearly equilibrium, and this can be explained by the polymeric crystalline structure and high valency of Ln(3+). The affinity of the exchange reaction reaches a maximum with the Ln(3+) possessing an ionic radius 7% smaller than that of the central Ln(3+), therefore, the affinity of the [Ln(dehp)3] is tunable based on the choice of the central metal ion. Such unique affinity, which differs from the monomeric complex, can be explained by two factors: the coordination preference and steric strain caused by the polymeric structure. The latter likely becomes predominant for Ln(3+) exchange when the ionic radius of the ion in solution is smaller than the original Ln(3+) by more than 7%. Structural studies suggest that the incoming Ln(3+) forms a new phase though an exchange reaction, and this could plausibly cause the structural strain.

Steric effect involved in Ln3+/Ce3+ exchange in a coordination polymer based on di(2-ethylhexyl)phosphoric acid.

Coordination polymers can be attractive ion exchange materials because of their crystallinity and semi-flexibility, which are rather opposing properties, and play integral and synergistic roles in introducing unique ion-exchange behavior. In this paper, Ln(3+)/Ce(3+) exchange (Ln(3+) = Nd(3+), Gd(3+), Dy(3+), or Lu(3+)) in a coordination polymer, [Ce(dehp)3], based on di(2-ethylhexyl)phosphoric acid (Hdehp) is studied by distribution coefficient measurements, ion-exchange isotherms, Kielland plot analysis, and morphology observation. The ion-exchange selectivity is in the order Nd(3+) < Gd(3+) < Dy(3+) < Lu(3+) when a small amount of Ln(3+) is loaded, but Lu(3+) ≈ Nd(3+) < Gd(3+) ≈ Dy(3+) for a high loading ratio. The Kielland plot suggests that a steric effect is involved in the reactions, which becomes stronger in the order of Nd(3+)/Ce(3+) < Gd(3+)/Ce(3+) < Dy(3+)/Ce(3+) < Lu(3+)/Ce(3+) for exchange systems. This trend is attributable to the differences in the ionic sizes between an incoming Ln(3+) and original Ce(3+). Scanning electron microscopy observations reveal the generation of a new phase via the Ln(3+)/Ce(3+) exchange. Such a phenomena results from solid-solid transformation, rather than dissolution-recrystallization. The small steric strain in the Nd(3+)/Ce(3+) system leads to the formation of a Nd(3+)-and-Ce(3+) solid-solution, whereas the morphological change is possibly restrained by the strong strain caused by loaded Ln(3+) with an ionic size significantly smaller than the original Ce(3+).

Tunable selectivity of lanthanide ion exchange within a coordination polymer.

The exchange of lanthanide(III) ions (Ln(3+)) between a solution and a coordination polymer (CP) formed by cerium(III) or samarium(III) ion and an organophosphorous ligand has been studied. The CPs exhibit distinctive Ln(3+) affinity that varies with a small change in its framework, depending on the central Ln(3+).

Structural adjustment during intercalation of macrocyclic crown ether into LDH via swelling/restoration reaction: staging formation and mechanism insights.

The structural control involving staging formation was studied in the nanocomposites of macrocyclic tetraazacrown ether carboxylic acid derivative (TECA) and layered double hydroxide (LDH) obtained by an osmotic swelling/restoration process. After NO(3)-type MgAl-LDH was osmotically swollen in formamide, TECA was added, leading to a restoration of the LDH sheets and formation of TECA-LDH nanocomposites. In the wet state, the structure of the composites was homogenous, and the basal spacings of ∼2.0 or 1.8 nm were not changed by the water-washing process that removed formamide and caused the replacement of NO(3)(-) by CO(3)(2-). However, in the drying process, both the orientation of TECA in the interlayer and the formed staging structure varied with the TECA content. The TECA orientation changed from horizontal to tilted/twisted and finally to vertical with interlayer TECA density. The staging structure occurred for samples with both TECA and small inorganic guests coexisting in the interlayer. Third-staging, second-staging, and homogenous structures were observed at TECA/LDH weight ratios of low (0.125 and 0.25), medium (0.5) and large (1 and 2) values, respectively. The decrease of negative charge of TECA ions from -4 to -1 led to the co-existence of small ions (NO(3)(-)) with TECA in the gallery and the formation of a NO(3)(-)-containing staging structure, even at a high TECA/LDH ratio of 2. The study of the influence of CO(3)(2-) on the composite structure indicates that a TECA/CO(3)(2-) ion exchange progressed reversibly and the staging structure formed is thermodynamically stable, depending mainly on the chemical composition of the interlayer guests. The staging formation could be explained by the Daumas-Hérold model, which differs markedly from the Rüdorff model previously proposed for the LDH system. The treatment in formamide of the composite such as T2L+Na(2)CO(3) with staging structure shows that the transformation process is reversible, and these kinds of composites may be used as an adsorbent for some harmful organic solvents.

Uptake properties of phosphate on a novel Zr-modified MgFe-LDH(CO(3)).

We prepared a novel Zr-modified MgFe-LDH(CO(3)) composite by adding a mixed solution of MgCl(2), FeCl(3), and ZrOCl(2) and another mixed solution of 1mol/dm(3) NaOH and 1mol/dm(3) Na(2)CO(3) to distilled water at a constant pH of 10. The composite exhibited only a poorly crystalline structure, resembling that of layered double hydroxides (LDH) from X-ray diffraction. The phosphate uptake is dependent on pH, decreasing with an increase in pH. This composite shows a much greater uptake of phosphate ions in P-enriched seawater (0.33mg-P/dm(3)) than amorphous zirconium oxide and MgFe-LDH(CO(3)). The uptake isotherm was fitted with a Freundlich relation. These phosphate-uptake behaviors closely resemble those of the relevant Zr-MgAl-LDH, which is estimated to be a composite of MgAl-LDH with amorphous zirconium hydroxide on the surface from X-ray absorption spectroscopy. Therefore, a similar structure of Zr-modified MgFe-LDH(CO(3)) composite probably causes the marked increase in phosphate uptake from P-enriched seawater.

Topotactic intercalation of a bulky organic anion (thiacalix[4]arene) into LDH through an osmotic swelling/restoration reaction in formamide.

Utilizing the osmotic swelling of LDH in formamide, for the first time, the bulky thiacalix[4]arene anion is introduced, leading to the recovery of LDH layers, and the hexagonal prism morphology of the precursor is well retained.

Synthesis and phosphate uptake behavior of Zr4+ incorporated MgAl-layered double hydroxides.

We synthesized Zr(4+) incorporated MgAl-layered double hydroxides, Mg(AlZr)-LDH(A) (where A denotes a counteranion in the interlayer space and is expressed as CO(3) for carbonate and Cl for chloride ions), with different molar ratios of Mg/(Al+Zr). Then we characterized their uptake behavior toward phosphate ions. CO(3)-type tertiary LDH materials synthesized at room temperature show low crystallinity, whereas the highly crystalline Cl-type tertiary LDH, [Mg(0.68)Al(0.17)Zr(0.14)(OH)(2)][Cl(0.26)(CO(3))(0.04)1.24H(2)O], was synthesized for the first time using a hydrothermal treatment at 120 degrees C. The distribution coefficients (K(d)) of oxo-anions were measured with a mixed solution containing trace amounts of the anions. The selectivity sequences were Cl(-), NO(-)(3)

IR spectra of manganese oxides with either layered or tunnel structures.

Four kinds of manganese oxides with either layered or tunnel structures were prepared by different methods. The structural features of the prepared materials were characterized by power X-ray diffraction, IR spectra and SEM observation. A compare analysis of IR spectra for these materials before and after the acid treatment was carried out. Band around 761 cm(-1) could be assigned to a characteristic adsorbent band of tunnel-type manganese oxides; while it was not observed in layer-type manganese oxides. After the acid treatment, the position and relative intensity of the bands in 300-1200 cm(-1) region showed an obvious change for layered manganese oxides in compare with tunnel-type manganese oxides. The variation of IR spectra could be used to distinguish layered manganese oxides from tunnel manganese oxides.

Preparation and structural evolution of SiO(2)-TiO(2) pillared layered manganese oxide nanocomposite upon intercalating reaction.

SiO(2)-TiO(2) pillared layered manganese oxide nanohybrid was successfully synthesized by preliminarily expanding the interlayer of H-type layered manganese oxide using dodecylamine, followed by reacting it with a mixture solution of titanium isopropoxide and tetraethylorthosilicate. The basal spacing and the pillared agent content of the obtained materials connected with the length of intercalated n-alkylamine, incorporated Si/Ti molar ratios and the solvothermal treatment temperature. The structural evolution of SiO(2)-TiO(2) pillared layered manganese oxide nanohybrid was characterized by XRD, DSC-TGA, SEM, IR, N(2) adsorption-desorption and element analyses. TiO(2) particles exhibited a stronger affinity for the negatively charged manganese layers, and the TiO(2) particles incorporated were independently intercalated without any distinct chemical bonding with the co-intercalated SiO(2) particles. SiO(2)-TiO(2) pillared layered manganese oxide nanohybrid had a BET surface area of 98 m(2)/g with a gallery height of about 1.43 nm between layers. The obtained SiO(2)-TiO(2) co-pillared layered manganese oxide nanohybrid is expected as a selective catalyst, or an improved battery material.

Preparation of cerium-loaded Y-zeolites for removal of organic sulfur compounds from hydrodesulfurizated gasoline and diesel oil.

Ce(IV)-loaded Y-zeolites (CeY) were prepared for selective removal of the trace amount of organic sulfur compounds from hydrodesulfurization (HDS)-treated diesel oil. The CeY samples can be obtained from NH4-Y-zeolite (NH4Y) using liquid-phase ion-exchange and solid-state ion-exchange methods. The ion-exchange reactions, structures, and selective adsorptions of organic sulfur compounds of the CeY samples were investigated using XRD, IR, XPS, TEM, and GC sulfur analyzer. The organic sulfur compound uptakes strongly depend on the amount and the valency of Ce in the zeolite structure. Ce(IV) shows much higher adsorptive ability than Ce(III). A CeY-S sample prepared by solid-state ion-exchange reaction of NH4Y and Ce(NO3)3 with Ce/NH4 mole ratio of 0.63 at 250 degrees C showed a maximum sulfur uptake from a model solution of HDS-treated gasoline containing thiophene [S = 5 ppm (ppm = mg/L)]. A desulfurization from a HDS-treated diesel oil containing organic sulfur compounds (S = 1.87 ppm) and H2S (S = 0.73 ppm) was investigated with a combination of the CeY-S and a CuO adsorbent for removal of H2S by a batch method. The sulfur content was reduced to below 0.01 ppm for the first time. This method provides a promising desulfurization process to prepare a clean fuel for fuel cells.

Phosphate adsorption on synthetic goethite and akaganeite.

Low crystalline iron hydroxides such as goethite (alpha-FeOOH) and akaganeite (beta-FeOOH) were synthesized, and the selective adsorption of phosphate ions from phosphate-enriched seawater was examined. The results of the distribution coefficients (K(d)) of oxoanions in mixed anion solutions at pH 8 follow the selectivity order Cl-, NO3-, SO4(2-) << CO3(2-), HPO4(2-) for goethite, and Cl-, CO3(2-) < NO3- < SO4(2) << HPO4(2-) for akaganeite. In seawater, both adsorbents show high selectivity for phosphate ions despite the presence of large amounts of major cations and anions in seawater. The adsorption isotherms fitted better with the Freundlich equation and the maximum uptake of phosphate from phosphate-enriched seawater was 10 mg P/g at an equilibrium phosphate concentration of 0.3 mg P/L on both adsorbents. The phosphate adsorption/desorption cycles show that akaganeite is an excellent adsorbent even after 10 cycles and its chemical stability is good.

Selective adsorption of phosphate from seawater and wastewater by amorphous zirconium hydroxide.

Phosphate adsorption from single electrolyte (NaH2PO4), phosphate-enriched seawater, and model wastewater was studied using amorphous zirconium hydroxide, ZrO(OH)2(Na2O)0.05 1.5H2O, as an adsorbent. Batch experiments were carried out to investigate the adsorption of phosphate. The effect of pH on phosphate adsorption from seawater showed that the uptake of phosphate increased with an increase in pH up to 6, and then decreased sharply with a further increase in pH of the solution. The equilibrium data of phosphate adsorption were followed with a Freundlich isotherm. The uptake of phosphate at the adsorbent/solution ratio 0.05 g/2 L was 10 and 17 mg-P/g for the phosphate-enriched seawater and the model wastewater, respectively. A much higher adsorptivity toward phosphate ions in seawater was observed on ZrO(OH)2(Na2O)0.05 1.5H(2)O than on other representative adsorbents based on layered double hydroxides of Mg(II)-Al(III), Mg(II)-Fe(III), and Ni(II)-Fe(III). The effective desorption of phosphate ions on ZrO(OH)2(Na2O)0.05 1.5H2O could be achieved using a 0.1 M NaOH solution. The usefulness of experimental data for practical applications in removing phosphate in seawater and wastewater is discussed.

Adsorption of phosphate from seawater on calcined MgMn-layered double hydroxides.

Adsorptive properties of MgMn-3-300 (MgMn-type layered double hydroxide with Mg/Mn mole ratio of 3, calcined at 300 degrees C) for phosphate were investigated in phosphate-enriched seawater with a concentration of 0.30 mg-P/dm3. It showed the highest phosphate uptake from the seawater among the inorganic adsorbents studied (hydrotalcite, calcined hydrotalcite, activated magnesia, hydrous aluminum oxide, manganese oxide (delta-MnO2)). The phosphate uptake by MgMn-3-300 reached 7.3 mg-P/g at an adsorbent/solution ratio of 0.05 g/2 dm3. The analyses of the uptakes of other constituents (Na+, K+, Ca(+, Cl-, and SO(2-)4) of seawater showed that the adsorbent had a markedly high selectivity for the adsorption of phosphate ions. Effects of initial phosphate concentration, temperature, pH, and salinity on phosphate uptake were investigated in detail by a batch method. The phosphate uptake increased slightly with an increase in the adsorption temperature. The adsorption isotherm followed Freundlich's equation with constants of logK(F)=1.25 and 1/n=0.65, indicating that it could effectively remove phosphate even from a solution of markedly low phosphate concentration as well as with large numbers of coexisting ions. The pH dependence showed a maximum phosphate uptake around pH 8.5. The pH dependence curve suggested that selective phosphate adsorption progresses mainly by the ion exchange of HPO(2-)4. The study on the effect of salinity suggested the presence of two kinds of adsorption sites in the adsorbent: one nonspecific site with weak interaction and one specific site with strong interaction. The effective desorption of phosphate could be achieved using a mixed solution of 5 M NaCl + 0.1 M NaOH (1 M = 1 mol/dm3), with negligible dissolution of adsorbent. The adsorbent had high chemical stability against the adsorption/desorption cycle; it kept a good phosphate uptake even after the repetition of the seventh cycle.

Selective adsorption of thiophene and 1-benzothiophene on metal-ion-exchanged zeolites in organic medium.

Adsorption of the organic sulfur compounds thiophene (TP) and 1-benzothiophene (1-BTP) in an organic model solution of hydrodesulfurizated gasoline (heptane with 1 wt% toluene and 0.156 mM (5 ppmw as sulfur) TP or 1-BTP) was studied by a batch method at 80 degrees C using metal-ion-exchanged Y-zeolites. Although NaY-zeolite or its acid-treated material rarely adsorbed the organic sulfur compounds, NaY-zeolites exchanged with Ag+, Cu2+, and Ce3+ ions and NH(4)Y-zeolites exchanged with Ce3+ ions showed markedly high adsorptive capacities for TP and 1-BTP. The sulfur uptake increased in the order CuY-zeolite(Na)

Studies on the formation of todorokite-type manganese oxide with different crystalline birnessites by Mg2+-templating reaction.

The formation of todorokite-type manganese oxide (TodMO) by hydrothermal soft chemical reaction (Mg2+ exchange followed by hydrothermal treatment) was studied using three kinds of Na-type birnessite (Na-BirMO) with different crystallinities. Buserite (BusMO) formation by Mg2+ exchange and TodMO formation by hydrothermal treatment progressed in a similar manner regardless of the crystallinity of the initial Na-BirMO, but the crystallinity of the synthesized TodMO depended on that of the initial Na-BirMO. Particle morphology of the synthesized TodMO was related to the crystallinity of the initial Na-BirMO. The amounts of fibrous morphology were gradually increasing, accompanied by increased crystallinity of the initial Na-BirMO. TodMO with a neat fibrous morphology was obtained using a high crystalline Na-BirMO as precursor. Most of the interlayer metal ions (Na+ and Mg2+) were extracted from Na-BirMO and BusMO by treatment with a 0.1 M HCl solution, while only 37% of Mg2+ was extracted from TodMO. Both the acid treatment and the particle morphology may be the most convenient method to distinguish TodMO from BusMO.

Theoretical studies on the structure of hydration in perfluorinated lithium salt membranes.

Using an ab initio molecular orbital (MO) method, the normal frequencies are calculated for perfluorinated lithium sulfonate and carboxylate membranes by construction of a cluster model, which severs the ion core from the polymer chain, and then analysis of the experimentally observed infrared (IR) spectra is carried out. During the process of dehydration, small sharp peaks at about 3650 and 3700 cm(-1) appeared on the shoulder of the broad band at about 3500 cm(-1). These sharp peaks are identified as the symmetric and asymmetric stretching modes of the free water molecule. Furthermore, by estimation of the evaporation ratio based on thermochemical analysis, it can be assumed that the first hydration shells are naked in some part of the ion core, thereby allowing evaporation to take place within the external hydration shell during the dehydration process.