Tentative Approaches for Extraction of Lanthanides from Wastewater with Low Metal Concentration.

Lanthanides are critical elements, and their recovery from wastewater increases the availability of these elements and reduces their impacts on the environment. In this study, tentative approaches to extract lanthanides from low-concentration aqueous solutions were investigated. PVDF membranes soaked with different active compounds or synthesized chitosan-based membranes containing these active compounds were used. The membranes were immersed in 10-4 M of aqueous solutions of selected lanthanides, and their extraction efficiency was assessed using ICP-MS. The PVDF membranes showed quite poor results, with only the membrane with oxamate ionic liquid giving some positive results (0.75 mg of Yb, 3 mg of lanthanides per gram of membrane). However, the chitosan-based membranes led to very interesting results, with the maximum concentration factor for the final solution relative to the initial solution being 13 times higher for Yb, which was obtained with the chitosan-sucrose-citric acid membrane. Several of the chitosan membranes, namely the one with 1-Butyl-3-methylimidazolium-di-(2-ethylhexyl)-oxamate, could extract around 10 mg of lanthanides per gram of membrane, with the better one being the membrane with sucrose/citric acid that achieved more than 18 mg/g of membrane. The use of chitosan for this purpose is a novelty. Since these membranes are easily prepared and have a very low cost, practical applications can be envisaged after further studies to better understand the underlying mechanism.

A new krypton complex - experimental and computational investigation of the krypton sulphur pentafluoride cation, [KrSF5]+, in the gas phase.

The gas-phase reactions of noble gas (Ng) cations, namely Kr+ and Xe+, with SF6 were investigated experimentally by Fourier transform ion cyclotron resonance mass spectrometry and computationally using RI-MP2 and BCCD(T) methods. The study revealed a new interaction between Kr+ and neutral SF6 that gave rise to a new cationic, weakly bound complex of Kr, [KrSF5]+, although the major reaction channel was dissociative electron transfer to yield SF5+ and {Kr, F}. Experimental studies examined the formation and stability of the new species and computational studies addressed the energetics of the reaction and indicated that [KrSF5]+ is stable by ca. 1 kcal mol-1. The same computational approach was used to examine the reaction of Xe+ with SF6 and showed it to be thermodynamically unfavourable by ca. 35 kcal mol-1, confirming the non-observation of reaction in the mass spectrometry experiments. An analysis of the bonding in [KrSF5]+ clearly showed that it is a non-covalently bound species, while in its presumed precursor [KrSF6]+ a partially covalent Kr-F bond is present.

Luminescent Ln-Ionic Liquids beyond Europium.

Searching in the Web of Knowledge for "ionic liquids" AND "luminescence" AND "lanthanide", around 260 entries can be found, of which a considerable number refer solely or primarily to europium (90%, ~234). Europium has been deemed the best lanthanide for luminescent applications, mainly due to its efficiency in sensitization, longest decay times, and the ability to use its luminescence spectra to probe the coordination geometry around the metal. The remaining lanthanides can also be of crucial importance due to their different colors, sensitivity, and capability as probes. In this manuscript, we intend to shed some light on the existing published work on the remaining lanthanides. In some cases, they appear in papers with europium, but frequently in a subordinate position, and in fewer cases then the main protagonist of the study. All of them will be assessed and presented in a concise manner; they will be divided into two main categories: lanthanide compounds dissolved in ionic liquids, and lanthanide-based ionic liquids. Finally, some analysis of future trends is carried out highlighting some future promising fields, such as ionogels.

Chemical evidence of the stability of praseodymium(v) in gas-phase oxide nitrate complexes.

The diverse reactivity of [LnO2(NO3)2]- complexes with water in the gas phase, for Ln = Ce, Pr and Nd, examined in a quadrupole ion trap and complemented by ab initio computations, illuminates the chemical stability of Pr in the unusual +5 oxidation state.

Oxidation of Actinyl(V) Complexes by the Addition of Nitrogen Dioxide Is Revealed via the Replacement of Acetate by Nitrite.

The gas-phase complexes AnO2(CH3CO2)2(-) are actinyl(V) cores, An(V)O2(+) (An = U, Np, Pu), coordinated by two acetate anion ligands. Whereas the addition of O2 to U(V)O2(CH3CO2)2(-) exothermically produces the superoxide complex U(VI)O2(O2)(CH3CO2)2(-), this oxidation does not occur for Np(V)O2(CH3CO2)2(-) or Pu(V)O2(CH3CO2)2(-) because of the higher reduction potentials for Np(V) and Pu(V). It is demonstrated that NO2 is a more effective electron-withdrawing oxidant than O2, with the result that all three An(V)O2(CH3CO2)2(-) exothermically react with NO2 to form nitrite complexes, An(VI)O2(CH3CO2)2(NO2)(-). The assignment of the NO2(-) anion ligand in these complexes, resulting in oxidation from An(V) to An(VI), is substantiated by the replacement of the acetate ligands in AnO2(CH3CO2)2(NO2)(-) and AnO2(CH3CO2)3(-) by nitrites, to produce the tris(nitrite) complexes AnO2(NO2)3(-). The key chemistry of oxidation of An(V) to An(VI) by the addition of neutral NO2 is established by the substitution of acetate by nitrite. The replacement of acetate ligands by NO2(-) is attributed to a metathesis reaction with nitrous acid to produce acetic acid and nitrite.

Gas-phase reactions of molecular oxygen with uranyl(V) anionic complexes-synthesis and characterization of new superoxides of uranyl(VI).

Gas-phase complexes of uranyl(V) ligated to anions X(-) (X = F, Cl, Br, I, OH, NO3, ClO4, HCO2, CH3CO2, CF3CO2, CH3COS, NCS, N3), [UO2X2](-), were produced by electrospray ionization and reacted with O2 in a quadrupole ion trap mass spectrometer to form uranyl(VI) anionic complexes, [UO2X2(O2)](-), comprising a superoxo ligand. The comparative rates for the oxidation reactions were measured, ranging from relatively fast [UO2(OH)2](-) to slow [UO2I2](-). The reaction rates of [UO2X2](-) ions containing polyatomic ligands were significantly faster than those containing the monatomic halogens, which can be attributed to the greater number of vibrational degrees of freedom in the polyatomic ligands to dissipate the energy of the initial O2-association complexes. The effect of the basicity of the X(-) ligands was also apparent in the relative rates for O2 addition, with a general correlation between increasing ligand basicity and O2-addition efficiency for polyatomic ligands. Collision-induced dissociation of the superoxo complexes showed in all cases loss of O2 to form the [UO2X2](-) anions, indicating weaker binding of the O2(-) ligand compared to the X(-) ligands. Density functional theory computations of the structures and energetics of selected species are in accord with the experimental observations.

Synthesis and hydrolysis of gas-phase lanthanide and actinide oxide nitrate complexes: a correspondence to trivalent metal ion redox potentials and ionization energies.

Several lanthanide and actinide tetranitrate ions, M(III)(NO3)4(-), were produced by electrospray ionization and subjected to collision induced dissociation in quadrupole ion trap mass spectrometers. The nature of the MO(NO3)3(-) products that result from NO2 elimination was evaluated by measuring the relative hydrolysis rates under thermalized conditions. Based on the experimental results it is inferred that the hydrolysis rates relate to the intrinsic stability of the M(IV) oxidation states, which correlate with both the solution IV/III reduction potentials and the fourth ionization energies. Density functional theory computations of the energetics of hydrolysis and atoms-in-molecules bonding analysis of representative oxide and hydroxide nitrates substantiate the interpretations. The results allow differentiation between those MO(NO3)3(-) that comprise an O(2-) ligand with oxidation to M(IV) and those that comprise a radical O(-) ligand with retention of the M(III) oxidation state. In the particular cases of MO(NO3)3(-) for M = Pr, Nd and Tb it is proposed that the oxidation states are intermediate between M(III) and M(IV).

Dissociation of gas-phase bimetallic clusters as a probe of charge densities: the effective charge of uranyl.

Complementary experimental and computational methods for evaluating relative charge densities of metal cations in gas-phase clusters are presented. Collision-induced dissociation (CID) and/or density functional theory computations were performed on anion clusters of composition MM'A(m+n+1)(-), where the two metal ions have formal charge states M(m+) and M'(n+) and A is an anion, NO3(-), Cl(-), or F(-) in this work. Results for alkaline earth and lanthanide metal ions reveal that cluster CID generally preferentially produces MA(m+1)(-) and neutral M'An if the surface charge density of M is greater than that of M': the metal ion with the higher charge density takes the extra anion. Computed dissociation energies corroborate that dissociation occurs via the lowest energy process. CID of clusters in which one of the two metal ions is uranyl, UO2(2+), shows that the effective charge density of U in uranyl is greater than that of alkaline earths and comparable to that of the late trivalent lanthanides; this is in accord with previous solution results for uranyl, from which an effective charge of 3.2+ was derived.