Effective Enrichment of Low-Concentration Rare-Earth Ions by Three-Dimensional Thiostannate K2Sn2S5

Construction of hierarchical nanostructured surface on an organic hybrid selenidostannate with light trapping effect to achieve sunlight-driven environmental remediation

Due to the low intensity of sunlight, it is a great challenge to realize highly efficient sunlight-driven photocatalysis. To maximize the utilization of sunlight, increasing the light capturing ability of photocatalysts is a prerequisite to attain high catalytic performances. Due to the multiple reflections of light in the hierarchical nanostructures, constructing hierarchical nanostructured surface should boost the sunlight capturing ability of a photocatalyst. Herein we used a surface oxidation etching method to construct a hierarchical nanostructure on the surface of an organic hybrid selenidostannate [Bmim]4[Sn9Se20], namely BTSe. After 24 hours of etching by ammonium persulfate, the surface of BTSe-O24 turned into a hierarchical nanostructure. FDTD simulation proved that the hierarchical nanostructure can effectively decline the loss of incident light and enhance light capturing ability of BTSe-O24. As a result, BTSe-O24 can completely reduce Cr(VI) (100 mg/L) in 8 min with a conversion rate of 750 mg/(g h) under sunlight. The catalytic performance of BTSe-O24 under sunlight is even better than those of most reported photocatalysts under high-power xenon lamps. More importantly, BTSe-O24 can maintain high photocatalytic efficiency in the whole daytime (from 8:00 to 16:00 in autumn and winter). Our research opens a new perspective on the design of sunlight-driven photocatalysts.

Advances in the Efficient Removal of the Key Radioactive Nuclide 90Sr Using Crystalline Ion-Exchange Materials: A Review

Nuclear energy, a rapidly advancing clean energy source, generates significant amounts of radioactive waste, including radioactive nuclides such as cesium (Cs+), strontium (Sr2+), and uranyl (UO2 2+). Among these, Sr2+ is particularly concerning due to its long half-life, high mobility in aqueous environments, and its toxic effects on both human health and ecosystems. Its radioactive decay produces beta particles, posing significant environmental and public health risks, especially in the context of nuclear waste disposal. Recently, ion exchange has emerged as one of the most effective methodologies to deal with this challenge. Consequently, ion-exchange materials have become a hot topic in contemporary research. This review summarizes the latest advancements in the removal of critical radioactive ions, particularly Sr2+, using ion-exchange materials. It provides a comprehensive overview of the structures and properties of various ion-exchange materials, explaining their ion-exchange characteristics and exploring the complex relationship between structure and performance. Key considerations discussed include identifying cations that are most amenable to exchange within interlayer channels, evaluating the impact of channel dimensions on material efficiency, and strategies to enhance the ion-exchange capabilities of intercalation compounds. These factors are essential for achieving high selectivity and rapid adsorption kinetics in ion-exchange processes for Sr2+.

Ultrafast and Highly Selective Sequestration of Radioactive Barium Ions by a Layered Thiostannate

As a simulant of hazardous 226Ra2+, the simultaneously selective and rapid elimination of radioactive 133Ba2+ ions from geothermal water is necessary but still challenging. In this paper, we demonstrated the usability of a layered thiostannate with facile synthesis and inexpensive cost, namely, K2xSn4-xS8-x (KTS-3, x = 0.65-1), for the remediation of radioactive 133Ba2+ in multiple conditions, including sorption isotherm, kinetics, and the influences of competitive inorganic/organic ions, pH values, and dosages. KTS-3 has a strong barium uptake ability (171.3 mg/g) and an ultrafast adsorption kinetics (about 2 min). Impressively, it can achieve a high preference for barium regardless of the excessive interference ions (Na+, K+, Mg2+, Ca2+, and humic acid) and acidic/alkaline environments, with the largest distribution coefficient Kd value reaching 6.89 × 105 mL/g. Also, the Ba2+-laden products can be easily eluted by a concentrated KCl solution, and its adsorption performances for barium resist well even after five consecutive cycles. In addition, owing to the regular appearance and excellent mechanical strength, the prepared KTS-3/PAN (PAN = polyacrylonitrile) granule displays a good removal efficiency in the flowing ion-exchange column. These advantages mentioned above render it very promising for the effective and efficient cleanup of radioactive 133Ba2+-contaminated wastewater.

Overview of Functionalized Porous Materials for Rare-Earth Element Separation and Recovery

The exceptional photoelectromagnetic characteristics of rare-earth elements contribute significantly to their indispensable position in the high-tech industry. The exponential expansion of the demand for high-purity rare earth and related compounds can be attributed to the swift advancement of contemporary technology. Nevertheless, rare-earth elements are finite and limited resources, and their excessive mining unavoidably results in resource depletion and environmental degradation. Hence, it is crucial to establish a highly effective approach for the extraction and reclamation of rare-earth elements. Adsorption is regarded as a promising technique for the recovery of rare-earth elements owing to its simplicity, environmentally friendly nature, and cost-effectiveness. The efficacy of adsorption is contingent upon the performance characteristics of the adsorbent material. Presently, there is a prevalent utilization of porous adsorbent materials with substantial specific surface areas and plentiful surface functional groups in the realm of selectively separating and recovering rare-earth elements. This paper presents a thorough examination of porous inorganic carbon materials, porous inorganic silicon materials, porous organic polymers, and metal-organic framework materials. The adsorption performance and processes for rare-earth elements are the focal points of discussion about these materials. Furthermore, this work investigates the potential applications of porous materials in the domain of the adsorption of rare-earth elements.

Cation-Intercalated Lamellar MoS2 Adsorbent Enables Highly Selective Capture of Cesium

Highly selective capture of cesium (Cs+) from complex aqueous solutions has become increasingly important owing to its (133Cs) indispensable role in some cutting-edge technologies and the environmental mobility of radioactive nuclide (137Cs) from nuclear wastewater. Herein, we report the development of cation-intercalated lamellar MoS2 as an effective Cs+ adsorbent with the advantages of facile synthesis and highly tunable layer spacing. Two types of cations, including Na+ and NH4+, were employed for the intercalations between adjacent layers of MoS2. The results demonstrated that the adsorption capacity of the NH4+-intercalated material (M-NH4+, 134 mg/g) for Cs+ clearly outperformed the others due to higher loading percentages of cations and larger layer spacing. The cesium partition coefficients for M-NH4+ in the presence of 100-fold competing ions all exceed 1 × 103 mL/g. A simulated complex aqueous solution containing 15.37 mg/L Cs+ and highly excess of competing ions Li+, Na+, K+, Mg2+, and Ca2+ (20-306 times higher) was introduced to prove the practical application potential using our best-performing M-NH4+, showing a good to excellent partition ability of Cs+ among other cations, especially for Cs/K and Cs/Na with separation factors of 58 and 212, respectively. The adsorption and selectivity mechanisms were clearly elucidated using various advanced techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. These results revealed that the good selectivity for Cs+ can be ascribed to the differences in Lewis acidities, hydration energy, cation sizes, and in particular, the divergence of coordination modes which was successfully achieved after tuning the layer distance via the cation intercalation strategy. In addition, the material has fast kinetics (<30 min), wide range of pH tolerance (4-10), and good reusability. Overall, our studies point out that the tunable lamellar MoS2-based materials are promising adsorbents for Cs+ capture and separation.

Recovering rare earth elements via immobilized red algae from ammonium-rich wastewater

Biotreatment of acidic rare earth mining wastewater via acidophilic living organisms is a promising approach owing to their high tolerance to high concentrations of rare earth elements (REEs); however, simultaneous removal of both REEs and ammonium is generally hindered since most acidophilic organisms are positively charged. Accordingly, immobilization of acidophilic Galdieria sulphuraria (G. sulphuraria) by calcium alginate to improve its affinity to positively charged REEs has been used for simultaneous bioremoval of REEs and ammonium. The results indicate that 97.19%, 96.19%, and 98.87% of La, Y, and Sm, respectively, are removed by G. sulphuraria beads (GS-BDs). The adsorption of REEs by calcium alginate beads (BDs) and GS-BDs is well fitted by both pseudo first-order (PFO) and pseudo second-order (PSO) kinetic models, implying that adsorption of REEs involves both physical adsorption caused by affinity of functional groups such as -COO- and -OH and chemical adsorption based on ion exchange of Ca²⁺ with REEs. Notably, GS-BDs exhibit high tolerance to La, Y, and Sm with maximum removal efficiencies of 97.9%, 96.6%, and 99.1%, respectively. Furthermore, the ammonium removal efficiency of GS-BDs is higher than that of free G. sulphuraria cells at an initial ammonium concentration of 100 mg L^-1, while the efficiency decreases when initial concentration of ammonium is higher than 150 mg L^-1. Last, small size of GS-BDs favors ammonium removal because of their lower mass transfer resistance. This study achieves simultaneous removal of REEs and ammonium from acidic mining drainage, providing a potential strategy for biotreatment of REE tailing wastewater.