All-Inorganic Open-Framework Chalcogenides, A₃Ga₅S₉·xH₂O (A = Rb and Cs), Exhibiting Ultrafast Uranyl Remediation and Illustrating a Novel Post-Synthetic Preparation of Open-Framework Oxychalcogenides

Abstract

Fast and effective uranyl sequestration is of interest to the nuclear industry. Recently, layered chalcogenide materials have demonstrated fast, selective, and efficient sorption properties toward uranyl cations, and the development and investigation of new types of chalcogenide materials continues to be of interest and represents an intriguing option for uranyl remediation. Three new all-inorganic A 3 Ga 5 S 9 •xH 2 O (A = Rb, Rb/Cs, and Cs) open-framework chalcogenides were obtained via an in situ alkali carbonate to alkali sulfide conversion process achieved under mild hydrothermal conditions. The structures of the all-inorganic openframework chalcogenides consist of a twofold interpenetrated diamond-like 3D framework containing pseudo-T 3 [Ga 10 S 20 ] 10− supertetrahedra. Forty-eight percent of the structural volume is occupied by A + cations and water species, as established by single-crystal X-ray diffraction (SCXRD), infrared (IR) spectroscopy, and energy-dispersive spectroscopy (EDS). The dynamic nature of the A + cations and water molecules within the pores was investigated via SCXRD as well as by IR spectroscopy-monitored H 2 O-to-D 2 O exchange experiments. Framework stability was probed with post-synthetic treatment of A 3 Ga 5 S 9 •xH 2 O (A = Rb and Cs) samples in acidic solutions that resulted in the formation of the oxysulfide (A/H) 3 Ga 5 S 9−y O y •xH 2 O (A = Rb and Cs; y = 0−1), as shown by SCXRD and IR. Ion-exchange studies on A 3 Ga 5 S 9 •xH 2 O (A = Rb and Cs) samples were carried out utilizing a uranyl acetate solution. The presence of the UO 2 2+ species in the ion-exchange product was supported by IR spectroscopy and EDS. Batch method ion-exchange experiments on Cs 3 Ga 5 S 9 •xH 2 O powder demonstrated fast kinetics with 95% uranyl removal from the uranyl acetate solution during the first minute, a maximum uranyl uptake capacity of 15 mg/g, and the subsequent elution of uranyl species with KCl solution. The porous and dynamic nature of the A 3 Ga 5 S 9 •xH 2 O framework coupled with effective UO 2 2+ •••S 2− bonding interactions makes it a good potential sorbent for uranyl remediation from aqueous media.

Advances in Chalcogenide Crystal Growth: Flux and Solution Syntheses, and Approaches for Postsynthetic Modifications

“…For example, the solvothermal or hydrothermal reactions of indium metal with sulfur in the presence of different organic molecules, 1,3,4,6,7,8-hexahydro-2 H -pyrimido­[l,2-a]­pyrimidine, dipiperidinomethane, or hexamethylenimine, resulted in a completely different arrangement of indium-sulfide-based clusters (Figure a,b). , Furthermore, open-framework chalcogenides offer an opportunity for nonzero organic–inorganic connectivity: pyridine- and imidazoline-containing organic molecules demonstrated the ability to bind chalcogenide clusters (Figure a,b), i.e., chalcogenide clusters are connected not through chalcogens or metals but via organic building blocks. Therefore, open-framework chalcogenides are a well-studied material class with an expansive application library in photocatalysis, ion-exchange materials, ionic conductors, and semiconductors. − Recent review articles on open-framework chalcogenide materials classification, design, synthesis, and applications can be found elsewhere. ,, …”

“…Transformation of the pseudo-T 3 supertetrahedral cluster [Ga 10 S 20 ] 10– of the open-framework chalcogenide Cs 3 Ga 5 S 9 · x H 2 O to [Ga 10 S 16 O 4 ] 10– as a function of pH . Green, orange, and red ellipsoids represent Ga, S, and O atoms, respectively.…”

“…Therefore, the class of open-framework chalcogenides is not limited to organic–inorganic hybrids. In fact, there are some examples of all-inorganic Ga- and In-based open-framework chalcogenides with Li + , Na + , Ca 2+ , Rb + , Sr 2+ , and Cs + ions, which were obtained using the hydrothermal technique. ,,, However, in this case, there is no structure-directing organic molecule; alkali metals successfully substituted for them and produced a wide variety of open-framework chalcogenides with clusters ranging from pseudo-T 2 ( M 4 Q 10 ) up to pseudo-T 5 ( M 35 Q 56 ) supertetrahedral clusters. The Li + -containing open-framework chalcogenides exhibited excellent ionic conductivity influenced by the relative humidity .…”

Tunable Salt-Inclusion Chalcogenides for Ion Exchange, Photoluminescence, and Scintillation

“…Advances in synthetic chalcogenide chemistry have accelerated the discovery of functional materials as well as stimulated the development of numerous technological applications for these materials, all helped by an increased understanding of composition–property relationships. , Chalcogenide-based compounds occupy a unique position in material chemistry due to the soft nature of the chalcogen elements and emerging covalent metal chalcogenide bonding, which results in a rich and diverse crystal chemistry. , In fact, the electronic structure of chalcogenide materials favors their applications as quantum materials, catalysts, ion-exchange materials, ion-conductors, luminophores, thermoelectric materials, and semiconductors. − Recent advances in developing convenient synthetic approaches have enabled the rational synthesis of new functional chalcogenide-based materials containing a wide range of elements, resulting in various material types, ranging from nanoparticles to large single crystals of pure inorganic compositions and hybrid structures. − Another new material type that has emerged from these investigations is salt-inclusion chalcogenide materials (SICs) , that exhibit novel framework topologies and possess ionic inserts (salt-inclusions).…”

Flux-assisted polytypism in the [Na2Cl]GaQ2 heterolayered salt-inclusion chalcogenide family

“…40 In general, layered chalcogenide materials are known to be excellent sorbents for uranyl species due to effective UO 2 2+ ⋯S 2− bonding interactions. [41][42][43][44] Therefore, we probed the ion-exchange properties of the salt-inclusion layered chalcogenides. For the ion exchange experiments, we used single crystals of [Na 2 Cl]GaS 2 materials and soaked them in uranyl nitrate solutions of different concentrations, ranging from 0.001 M to 0.01 M (see ESI † for more information).…”