Double-Walled Metal-Organic Framework with Regulable Pore Environments for Efficient Removal of Radioactive Cesium Cations

Effect of incorporated transition metals on the adsorption mechanisms of radioactive cesium in Prussian blue analogs

Extensive efforts were made to remove radioactive cesium (137Cs) from the environment, with Prussian blue analogs (PBAs) emerging as highly selective and efficient materials for 137Cs removal. However, limited studies systematically compared Cs+ adsorption across different transition metals in PBA. This study investigates the influence of the choice of transition metal ion (Co, Cu, Fe, Mn, Ni, Zn) on Cs+ adsorption mechanisms and efficiency. PBAs were synthesized and characterized based on their specific surface area, ion exchange capacity, lattice parameter, and defect sites (as indicated by water molecule content). Cs+ adsorption mechanisms varied significantly with transition metals. In CoFe and FeFe PBAs, ion exchange with K+ dominated, while CuFe and MnFe PBAs, with more defect sites primarily used ion exchange between H+ and Cs+. NiFe and ZnFe exhibited enhanced Cs+ adsorption under light irradiation, likely due to their light-absorbing properties facilitating a reduction reaction. The Langmuir adsorption isotherm was applied to model the adsorption behavior, confirming that each performance of PBA depends on the transition metal used. These findings suggest that PBAs with various transition metals can efficiently remove 137Cs under diverse environmental conditions by using distinct adsorption mechanisms.

Advanced porous materials and emerging technologies for radionuclides removal from Fukushima radioactive water

Japan recently announced the plan to discharge over 1.2 million tons of radioactive water into the Pacific Ocean, which contained hazardous radionuclides such as 60Co, 90Sr, 125Sb, 129I, 3H, 137Cs, and 99TcO4-, etc. The contaminated water will pose an enormous threat to global ecosystems and human health. Developing materials and technologies for efficient radionuclide removal is highly desirable and arduous because of the extreme conditions, including super acidity or alkalinity, high ionic strength, and strong ionizing radiation. Recently, advanced porous material, such as porous POPs, MOFs, COFs, PAFs, etc., has shown promise of improved separation of radionuclides due to their intrinsic structural advantages. Furthermore, emerging technologies applied to radionuclide removal have also been summarized. In order to better deal with radionuclide contamination, higher requirements for the design of nanomaterials and technologies applied to practical radionuclide removal are proposed. Finally, we call for comprehensive implementation of strategies and strengthened cooperation to mitigate the harm caused by radioactive contamination to oceans, atmosphere, soil, and human health.

Metal-organic frameworks for wastewater treatment: Recent developments, challenges, and future prospects

Wastewater treatment is critically important for the existence of life on earth; however, this approach involves the removal of toxic metal contaminants and organic pollutants, requiring efficient adsorbent materials. Within this agenda, metal-organic frameworks (MOFs) appear to be potential materials due to their unique properties as efficient adsorbents, effective photocatalysts, and reliable semi-permeable membranes. Therefore, MOFs have undergone various modifications over the years without desirable success to improve adsorption capacity, hydro-stability, reaction kinetics, and reusability. Therefore, scientists around the world got engaged in MOF research for novel modifications, including defect engineering, carbonization, and membrane fabrication, at the laboratory scale. This review focuses on developing MOF-based adsorbents, photocatalysts, and semi-permeable membranes for wastewater treatment since 2015, emphasizing their structural-functional relationships. Finally, the challenges and opportunities with MOFs in wastewater treatment are also underlined for future efforts.

Enhanced Separation Performance of Radioactive Cesium and Cobalt in Graphene Oxide Membrane via Cationic Control

The great applications of nuclear power for the most promising clean energy sources have been challenged by a large amount of radioactive wastewater generated, specifically the Cs⁺/Co²⁺ separation for nuclear waste storage, retreatment or recycling of radioactive wastewater, because of their wide difference in half-life and high heat release. In this work, graphene oxide membranes (GOMs) with interlayer spacing controlled by cations were used to separate mixed Cs⁺/Co²⁺ ions. The separation factors of Cs⁺/Co²⁺ for K⁺-controlled graphene oxide membranes (K-GOMs) was 2∼3 times higher than that of GOMs without treatment. In addition, the separation factors of Cs⁺/Co²⁺ for K-GOMs can be further enhanced with the increase of membranes thickness and change the initial ratios of the two ions. Typically, the separation factors of K-GOMs with a thickness of ∼300 nm reached up to 73.7 ± 3.9. Moreover, the K-GOM showed outstanding stability of the separation performance under long-term operation within 7 days. First-principles calculation revealed that the enhanced ionic selectivity of controlled GOM is induced by the difference of adsorption energies between the hydrated cations and aromatic rings, resulting in a significant increase in the mobility differences between Cs⁺ and Co²⁺ through a fixed narrow interlayer spacing. This study demonstrated excellent separation performances of GO-based membranes based on their size-exclusion effect rather than electrostatic repulsion effect, and we believe this work can enable potential efficient treatment technologies for radioactive wastewater needed urgently.

Rapid Cs+ Capture via Multiple Supramolecular Interactions in Anionic Metal-Organic Framework Isomers

Metal-organic frameworks (MOFs) provide an ideal platform for ion exchange due to their high porosity and structural designability; however, developing MOFs that have the essential characteristics for ion exchange remains a challenge. These crucial features include fast kinetics, selectivity, and stability. We present two anionic isomers, DGIST-2 (2D) and DGIST-3 (3D), comprising distinctly arranged 5-(1,8-naphthalimido)isophthalate ligands and In³⁺ cations. Interestingly, in protic solvents, DGIST-2 transforms into a hydrolytically stable crystalline phase, DGIST-2'. DGIST-2' and DGIST-3 exhibit rapid Cs⁺ adsorption kinetics, as well as high Cs⁺ affinity in the presence of competing cations. The mechanism for rapid and selective sorption is explored based on the results of single-crystal X-ray diffraction analysis of Cs⁺-incorporated DGIST-3. In Cs⁺-containing solutions, the loosely incorporated dimethylammonium countercation of the anionic framework is replaced by Cs⁺, which is held in the hydrophobic cavity by supramolecular ion-ion and cation-π interactions.

Four Keggin-type polyoxometalate-based complexes derived from bis(pyrazine)–bis(amide) ligands for electrochemical sensing of multiple analytes and adsorbing dye molecules

Four new Keggin-based complexes derived from bis(pyrazine)–bis(amide) ligands are used to detect multiple analytes (BrO3− NO2−, Cr(vi) and Fe(iii) ions) and adsorb organic dye molecules from aqueous solution.

A Li-based MOF-derived multifunctional PEO polymer solid-state electrolyte for lithium energy storage

A Li-based MOF has been successfully synthesized and applied in a solid-state lithium energy storage system. The MOF filler is added into the PEO-LiTFSI electrolyte, which exhibits both the mechanical strength and the ionic conductivity increase.