Mei-Ling Feng

Efficient Removal and Recovery of Uranium by a Layered Organic–Inorganic Hybrid Thiostannate

Uranium is important in the nuclear fuel cycle both as an energy source and as radioactive waste. It is of vital importance to recover uranium from nuclear waste solutions for further treatment and disposal. Herein we present the first chalcogenide example, (Me2NH2)1.33(Me3NH)0.67Sn3S7·1.25H2O (FJSM-SnS), in which organic amine cations can be used for selective UO2(2+) ion-exchange. The UO2(2+)-exchange kinetics perfectly conforms to pseudo-second-order reaction, which is observed for the first time in a chalcogenide ion-exchanger. This reveals the chemical adsorption process and its ion-exchange mechanism. FJSM-SnS has excellent pH stability in both strongly acidic and basic environments (pH = 2.1-11), with a maximum uranium-exchange capacity of 338.43 mg/g. It can efficiently capture UO2(2+) ions in the presence of high concentrations of Na(+), Ca(2+), or HCO3(-) (the highest distribution coefficient Kd value reached 4.28 × 10(4) mL/g). The material is also very effective in removing of trace levels of U in the presence of excess Na(+) (the relative amounts of U removed are close to 100%). The UO2(2+)···S(2-) interactions are the basis for the high selectivity. Importantly, the uranyl ion in the exchanged products could be easily eluted with an environmentally friendly method, by treating the UO2(2+)-laden materials with a concentrated KCl solution. These advantages coupled with the very high loading capacity, low cost, environmentally friendly nature, and facile synthesis make FJSM-SnS a new promising remediation material for removal of radioactive U from nuclear waste solutions.

A magnesium MOF as a sensitive fluorescence sensor for CS2 and nitroaromatic compounds

Presented here are the hydrothermal synthesis, structural characterization, and luminescent and gas adsorption properties of a magnesium metal–organic framework compound, namely Mg5(OH)2(BTEC)2(H2O)4·11H2O (1, H4BTEC = 1,2,4,5-benzenetetracarboxylic acid). The structure of 1 features a three-dimensional network constructed from the linkage of BTEC ligands and rare pentanuclear magnesium clusters as secondary building units, giving rise to the 1D channels along the a axis. Luminescence studies revealed that compound 1 demonstrated high fluorescence sensing of carbon disulfide (CS2) and nitroaromatic compounds, that is, the fluorescence intensities were almost completely quenched only at the concentrations of 0.8 vol% of CS2 and 0.04 vol% of nitrobenzene.

A two-dimensionally microporous thiostannate with superior Cs+ and Sr2+ ion-exchange property

The removal of highly radioactive and long-lived 137Cs+ and 90Sr2+ from solution is of significance for radionuclide remediation. Herein we prepared a two-dimensionally microporous thiostannate, namely (Me2NH2)4/3(Me3NH)2/3Sn3S7·1.25H2O (FJSM-SnS), and systematically investigated its Cs+ and Sr2+ ion-exchange performance in different conditions. The structural stabilities and variation, ion-exchange kinetic and isothermal behavior, pH-dependent distribution coefficients (Kd), ion-exchange in simulated groundwater and ion-exchange applied to chromatography have been investigated. The results indicated that the maximum Cs+ and Sr2+ ion-exchange capacities of FJSM-SnS were 408.91 mg g−1 and 65.19 mg g−1, respectively. In particular, FJSM-SnS showed quick ion-exchange ability and wide pH resistance (0.7–12.7) which make it outstanding among the ion-exchangers. An ion-exchange chromatographic column was firstly studied for chalcogenido ion-exchange materials, that is, a column filled with 3.0 g FJSM-SnS could remove 96–99% of Cs+ ion and near 100% of Sr2+ ion at low ionic concentrations in 900 bed volumes solutions. Furthermore, the title material could be synthesized on a large scale by a facile, one-pot and economical solvothermal method. The relatively low cost but remarkable ion-exchange performance makes it promising for radionuclide remediation.

Layered indium chalcogenidoantimonates [Me2NH2]2In2Sb2S7-xSex (x = 0, 2.20, 4.20, 7) with tunable band gaps and photocatalytic properties

Two novel indium chalcogenidoantimonates and their quaternary mixed solid solutions with a layered structure of [In2Sb2S7-xSex]n2n− are successfully synthesized under mild solvothermal conditions. The compounds show a red-shift of their optical absorption edges and exhibit tunable photocatalytic activity for degradation of methyl orange (MO) with a shift of optical response from UV to the visible light region, as the proportions of Se increase.

Two Gallium Antimony Sulfides Built on a Novel Heterometallic Cluster

Two gallium antimony sulfides, [Ni(en)(3)][Ga(2)Sb(2)S(7)] (1) and [(Me)(2)NH(2)](2)[Ga(2)Sb(2)S(7)] (2), have been prepared under mild solvothermal conditions. Both structures feature a two-dimensional network in which two GaS(4) tetrahedra and two SbS(3) trigonal pyramids are combined to form a heterometallic cluster of {Ga(2)Sb(2)S(9)} as a new secondary building unit. The thermal properties of 1 and 2 have been studied by thernogravimetric analysis, and the optical properties of 1 and 2 have been characterized by UV-vis spectra.

Ionothermal syntheses, crystal structures and properties of three-dimensional rare earth metal–organic frameworks with 1,4-naphthalenedicarboxylic acid

Twelve isostructural rare earth metal-organic frameworks, namely, [Hmim][RE(2)Cl(1,4-NDC)(3)] (RE = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Y (12), Hmim = 1-hexyl-3-methylimidazolium, 1,4-NDCH(2) = 1,4-naphthalenedicarboxylic acid), have been ionothermally synthesized and structurally characterized. The structures feature three-dimensionally anionic frameworks of [RE(2)Cl(1,4-NDC)(3)](n)(n-) with channels in which the Hmim(+) cations are located. The current results are the first ionothermal synthesis of rare earth metal-organic frameworks based on 1,4-NDCH(2) which possess a previously unknown (4,7)-connected 3-nodal network with the Schläfli symbol of (3(2)·4(2)·5(2))(3(2)·4(9)·5(2)·6(8))(2)(4(3)·6(3))(2). Luminescent and magnetic properties of some of the title compounds have been studied. Thermogravimetric analyses indicated that all these compounds were thermally stable up to ca. 250 °C.

[NH3CH3]4[In4SbS9SH]: a novel methylamine-directed indium thioantimonate with Rb+ ion-exchange property

The protonated methylamine was successfully used to direct the formation of one novel indium thioantimonate compound, namely, [NH3CH3]4[In4SbS9SH] (1), whose structure features a three-dimensionally microporous framework based on the linkage of a T2 {In4S9SH} cluster and a {SbS3} pyramid. Detailed ion-exchange reactions performed on the sample of 1 demonstrated its high selectivity for Rb+ ion adsorption, as well as the significant role of the pore size directed by the organic amine cation on ion-exchange selectivity. Under the time-dependent Rb+-exchange treatments, compound 1 exhibited framework flexibility, in which the increasing exchange yields accompanied the gradual contraction of its unit cell.

A series of novel organically templated germanium antimony sulfides.

A series of novel organically templated germanium antimony sulfides have been solvothermally synthesized and structurally, thermally, and optically characterized. The compound [Me(2)NH(2)](6)[(Ge(2)Sb(2)S(7))(Ge(4)S(10))] (1) features two distinct tetranuclear [Ge(2)Sb(2)S(7)](2-) and [Ge(4)S(10)](4-) isolated clusters. The compound [(Me)(2)NH(2)][DabcoH](2)[Ge(2)Sb(3)S(10)] (2) (Dabco = triethylenediamine) features a 1D-[Ge(2)Sb(3)S(10)](n)(3n-) ribbon constructed with two [GeSbS(5)](n)(3n-) chains bridged by Sb(3+) ion in psi-SbS(4) configuration. Compounds [M(en)(3)][GeSb(2)S(6)] (M = Ni (3), Co (4) en = ethylenediamine) feature the unique 2D grid layer structures of [GeSb(2)S(6)](n)(2n-). The compound [(Me)(2)NH(2)](2)[GeSb(2)S(6)] (5) previously reported by us features a 3D chiral microporous structure with the chiral channels. The optical absorption spectra indicate that all the compounds are wide bandgap semiconductors. Thermal stabilities of these compounds have been investigated by thermogravimetric analyses (TGA).

[Ni(phen)3]2Sb18S29: A Novel Three-Dimensional Framework Thioantimonate(III) Templated by [Ni(phen)3] Complexes

A novel thioantimonate(III), namely, [Ni(phen)(3)](2)Sb(18)S(29) (1; phen = 1,10-phenanthroline), has been solvothermally synthesized. Its structure features a three-dimensional framework with the largest channels in thioantimonates. The chiral [Ni(phen)(3)](2+) cations and the Sb:S ratio (1:1.611) in 1 are unique among those in the reported thioantimonates. The thermal stability, optical properties, and electric conductivity as well as the theoretical band structure and density of state of 1 have also been studied.

Assembly of novel organic-decorated quaternary TM–Hg–Sb–Q compounds (TM = Mn, Fe, Co; Q = S, Se) by the combination of three types of metal coordination geometries

Four organic-decorated quaternary TM-Hg-Sb-Q compounds, namely, [Mn(phen)](2)HgSb(2)S(6) (phen = 1,10-phenanthroline) (1) and isomorphic [TM(tren)]HgSb(2)Se(5) (TM = Mn (2), Fe (3), Co (4); tren = tris(2-aminoethyl)amine) have been solvothermally prepared, and structurally characterized by single crystal X-ray diffraction analyses. 1 and 2 (3, 4) feature distinct one-dimensional neutral infinite ribbon-like structures constructed by the combination of Sb(3+), Hg(2+) and TM(2+), the latter two of which adopt different coordination modes. In compound 1, organic-decorated {[Mn(phen)](2)Sb(2)S(6)} clusters assembled by {MnS(4)N(2)} octhedra and {SbS(3)} pyramids are bridged by the {HgS(2)} groups in a linear fashion. Differently, the {SbSe(3)} pyramids, {HgSe(4)} tetrahedra and {TMSeN(4)} trigonal-bipyramids in 2 (3, 4) are combined to form novel {[TM(tren)](2)Hg(2)Sb(4)Se(12)} clusters, which are interconnected to form {[TM(tren)]HgSb(2)Se(5)}(n) ribbons. The results of optical diffuse-reflectance measurements and band structure calculations based on DFT methods indicate that 1 and 2 (3, 4) are indirect and direct semiconductors, respectively. Photocatalytic experiments have shown the ability of 2 in photodegradation of Rhodamine B (RhB).