NaGaS 2 : An Elusive Layered Compound with Dynamic Water Absorption and Wide‐Ranging Ion‐Exchange Properties

First Potassium Fluoroaluminate Ionic Exchanger for Rapid and Selective Removal of Sr2+ with High Capacity

90Sr, as a typical artificial radionuclide, poses a serious threat to human health and the ecological environment. The selective removal of this radionuclide from industrial nuclear waste is crucial for our environment. Here we report a novel potassium fluoroaluminate, K2[(AlF5)H2O], which was synthesized by a simple low-temperature one-step method. It adopts a 1D AlF6-chain structure, which consists of exchangeable potassium ions in between the infinite chains of octahedral Al centers. As a remarkable inorganic ionic exchanger, K2[(AlF5)H2O] has a high chemical stability (resistance of pH=~3-12) and thermal stability (≥~300 °C). It possesses an excellent adsorption selectivity (Kd=~6.1×104 mL ⋅ g-1) and a maximum adsorption capacity of qm=~120.32 mg ⋅ g-1 for Sr2+. Importantly, it still keep a very good selectivity for Sr2+ ions even in the presence of competing Na+, Mg2+ and Ca2+ aqueous solutions. K2[(AlF5)H2O] is the first example of fluoroaluminate ionic exchange materials that can capture Sr2+. This result opens up a new way to design and synthesize inorganic ionic exchangers for the selective removal of Sr2+ ions from radioactive waste water.

Layered Chalcogenide Scintillators Enabled by Reversible Hydrous-Induced Phase Transformation for High-Resolution X-ray Imaging

Scintillation materials have been widely used in various fields, such as medical diagnosis and industrial detection. Chalcogenides have the potential to become a new generation of high-performance scintillation materials due to their high effective atomic number and good resistance to radiation damage. However, research on their application in radiation detection is currently very scarce. Herein, single crystals of rare earth ion-doped ternary chalcogenides NaGaS2/Eu were grown by a high-temperature solid-phase method. It exhibits unique characteristics of structure transformation by absorbing water molecules from the air. To maintain the anhydrous phase of the material, we have used a strategy of organic-inorganic composites of epoxy resin and NaGaS2/Eu to prepare devices for radiation detection and discuss the irradiation luminescence properties of the two phases. The anhydrous phase of NaGaS2/Eu demonstrates excellent sensitivity to X-rays, with a low detection limit of 250 nGy s-1, which is approximately 1/22 of the medical imaging dose. Additionally, composite flexible films were prepared, which exhibited excellent performance in X-ray imaging. These films enable clear observation of a wide range of objects with a high spatial resolution of up to 13.2 line pairs per millimeter (lp mm-1), indicating that chalcogenide holds promising prospects in the realm of X-ray imaging applications.

Open-framework hybrid zinc/tin selenide as an ultrafast adsorbent for Cs+, Ba2+, Co2+, and Ni2

Efficient adsorption of radioactive ¹³⁷Cs⁺ and ⁶⁰Co²⁺ and their decay products ¹³⁷Ba²⁺ and ⁶⁰Ni²⁺ bears significance for hazard elimination in case of nuclear emergency, which relies on the adsorption rate enhancement that takes advantages of compositional and structural optimization. Herein, we report a zinc-doped selenidostannate constructed from T2-supertetrahedral clusters, namely K_3.4(CH₃NH₃)_0.45(NH₄)_0.15Zn₂Sn₃Se₁₀·3.4 H₂O (ZnSnSe-1K). The soft Se and micro-porosity synergistically endow this material with a binding affinity to Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺ ions and ultrafast kinetics with R > 97.6% in 2-60 min. In particular, ZnSnSe-1K can remove 99.34% of Cs⁺ in 2 min ⁽K_d^Cs > 1.5 × 10⁵ mL g^-1), contributing to a record rate constant k₂ of 9.240 g mg^-1 min^-1 that surpasses all metal chalcogenide adsorbents. ZnSnSe-1K exhibits good acid/base tolerance (pH = 0-12), and the adsorption capacities at neutral are 253.61 ± 9.15, 108.94 ± 25.32, 45.76 ± 14.19 and 38.49 ± 2.99 mg g^-1 for Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺, respectively. The adsorption performances resist well co-existing cations and anions, and the removal rates can keep above or close to 90% even in sea water. ZnSnSe-1K is employed in continuous column and membrane filtration, both of which shows excellent elimination efficiency (R > 99%) for mixed Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺. Especially, the membrane with an ultrathin (70 µm) ZnSnSe-1K layer can remove 97-100% Cs⁺ in suction filtration with a short contact time of 0.33 s. Combined with the simple synthesis, facile elution and great irradiation resistance, ZnSnSe-1K emerges as a selenide adsorbent candidate for use in environmental remediation especially that involving nuclear waste disposal.

NaGaSe2: A Water-Loving Multifunctional Non-van der Waals Layered Selenogallate

A missing member of well-known ternary chalcometallates, a sodium selenogallate, NaGaSe₂, has been synthesized by employing a polyselenide flux and stoichiometric reaction. Crystal structure analysis using X-ray diffraction techniques reveals that it contains supertetrahedral adamantane-type Ga₄Se₁₀ secondary building units. These Ga₄Se₁₀ secondary building units are further connected via corners to form two-dimensional (2D) [GaSe₂]_∞^- layers stacked along the c-axis of the unit cell, and the Na ions reside in the interlayer space. The compound has an unusual ability to absorb water molecules from the atmosphere or a nonanhydrous solvent to form distinct hydrated phases, NaGaSe₂·xH₂O (where x can be 1 and 2), with an expanded interlayer space, as verified by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), desorption, and Fourier transform infrared spectroscopy (FT-IR) studies. The in situ thermodiffractogram indicates the emergence of an anhydrous phase before 300 °C with the decrease of interlayer spacings and reverting to the hydrated phase within a minute of re-exposure to the environment, supporting the reversibility of such a process. Structural transformation induced through water absorption results in an increase of Na ionic conductivity by 2 orders of magnitude compared to that of the pristine anhydrous phase, as verified by impedance spectroscopy. Na ions from NaGaSe₂ can be exchanged in the solid-state route with other alkali and alkaline earth metals in a topotactic or nontopotactic way, leading to 2D isostructural and three-dimensional networks, respectively. Optical band gap measurements show a band gap of ∼3 eV for the hydrated phase, NaGaSe₂·xH₂O, which is in good agreement with the calculated band gap using a density functional theory (DFT)-based method. Sorption studies further confirm the selective absorption of water over MeOH, EtOH, and CH₃CN with a maximum water uptake of 6 molecules/formula unit at a relative pressure, P/P₀, of 0.9.

Transuranium Sulfide via the Boron Chalcogen Mixture Method and Reversible Water Uptake in the NaCuTS3 Family

The behavior of 5f electrons in soft ligand environments makes actinides, and especially transuranium chalcogenides, an intriguing class of materials for fundamental studies. Due to the affinity of actinides for oxygen, however, it is a challenge to synthesize actinide chalcogenides using non-metallic reagents. Using the boron chalcogen mixture method, we achieved the synthesis of the transuranium sulfide NaCuNpS₃ starting from the oxide reagent, NpO₂. Via the same synthetic route, the isostructural composition of NaCuUS₃ was synthesized and the material contrasted with NaCuNpS₃. Single crystals of the U-analogue, NaCuUS₃, were found to undergo an unexpected reversible hydration process to form NaCuUS₃·xH₂O (x ≈ 1.5). A large combination of techniques was used to fully characterize the structure, hydration process, and electronic structures, specifically a combination of single crystal, powder, high temperature powder X-ray diffraction, extended X-ray absorption fine structure, infrared, and inductively coupled plasma spectroscopies, thermogravimetric analysis, and density functional theory calculations. The outcome of these analyses enabled us to determine the composition of NaCuUS₃·xH₂O and obtain a structural model that demonstrated the retention of the local structure within the [CuUS₃]^- layers throughout the hydration-dehydration process. Band structure, density of states, and Bader charge calculations for NaCuUS₃, NaCuUS₃·xH₂O, and NaCuNpS₃ along with X-ray absorption near edge structure, UV-vis-NIR, and work function measurements on ACuUS₃ (A = Na, K, and Rb) and NaCuUS₃·xH₂O samples were carried out to demonstrate that electronic properties arise from the [CuTS₃]^- layers and show surprisingly little dependence on the interlayer distance.

NaGa3Se5: An Infrared Nonlinear Optical Material with Balanced Performance Contributed by Complex {[Ga3Se5]-}∞ Anionic Network

Second-order nonlinear optical (NLO) materials are extensively applied in laser-related techniques. For developing IR NLO materials, chalcogenides are the main candidates. Here, NaGa₃Se₅ was explored as inspired by its unique anionic structure. It crystallizes with the orthorhombic chiral P2₁2₁2₁ structure, featuring 12 types of GaSe₄ tetrahedra built into a three-dimensional {[Ga₃Se₅]^-}_∞ anionic network, representing a new NLO-functional motif. NaGa₃Se₅ exhibits large and phase-matchable NLO response 1.37 × AgGaS₂. It has the largest band gap among the noncentrosymmetric A-M^III-Se (A = alkali metal; M = Ga, In) compounds. The NLO properties' origin is explored via theoretical analysis. The success of NaGa₃Se₅ contributes a practical case for exploring new NLO materials.

Ethane oxidative dehydrogenation with CO2 on thiogallates

The CO2-assisted oxidative dehydrogenation of ethane (ODH-CO2) attracts a lot of research interest since it combines greenhouse gas utilization with the production of valuable chemicals.

Na2GaS2Cl: a new sodium-rich chalcohalide with two-dimensional [GaS2]∞ layers and wide interlayer space

By introducing halogens to the A/Ga/Q (A = Na, K; Q = S, Se) system, one new chalcohalide namely Na₂GaS₂Cl was successfully obtained. It crystallizes in the orthorhombic space group Cmcm (63). Na₂GaS₂Cl has a layered structure consisting of two dimensional [GaS₂]_∞ layers which are stacked in "face to face" and "back to back" arrays and separated by Na⁺ and Cl^- ions. Interestingly, supertetrahedral building units [Ga₄S₁₀] (T2) which are rarely found in metal chalcogenides and metal chalcohalides are formed in this structure. Moreover, the distances of two adjacent layers are around four times larger than the ionic radius of the Na⁺ ion, which is very likely to provide a perfect environment for the storage and migration of Na⁺ ions. In particular, the volume concentration of the Na⁺ cations in this compound is as high as 1.54 × 10²² cm^-3. The UV-vis-NIR spectroscopy measurement reveals that the optical band gap of this title compound is 3.06 eV. The electronic structural calculations on Na₂GaS₂Cl show that the band gap is mainly determined by the [GaS₄] groups and Na-Cl ionic bonding.