Selective Capture of Toxic Selenite Anions by Bismuth‐based Metal–Organic Frameworks

Sulfur vacancy-rich bismuth sulfide nanowire derived from CAU-17 for radioactive iodine capture in complex environments: Performance and intrinsic mechanisms

Effective capture and immobilization of volatile radioiodine from the off-gas of post-treatment plants is crucial for nuclear safety and public health, considering its long half-life, high toxicity, and environmental mobility. Herein, sulfur vacancy-rich Vs-Bi2S3@C nanocomposites were systematically synthesized via a one-step solvothermal vulcanization of CAU-17 precursor. Batch adsorption experiments demonstrated that the as-synthesized materials exhibited superior iodine adsorption capacity (1505.8 mg g-1 at 200 °C), fast equilibrium time (60 min), and high chemisorption ratio (91.7%), which might benefit from the nanowire structure and abundant sulfur vacancies of Bi2S3. Furthermore, Vs-Bi2S3@C composites exhibited excellent iodine capture performance in complex environments (high temperatures, high humidity and radiation exposure). Mechanistic investigations revealed that the I2 capture by fabricated materials primarily involved the chemical adsorption between Bi2S3 and I2 to form BiI3, and the interaction of I2 with electrons provided by sulfur vacancies to form polyiodide anions (I3-). The post-adsorbed iodine samples were successfully immobilized into commercial glass fractions in a stable form (BixOyI), exhibiting a normalized iodine leaching rate of 3.81 × 10-5 g m-2 d-1. Overall, our work offers a novel strategy for the design of adsorbent materials tailed for efficient capture and immobilization of volatile radioiodine.

Scavenging Radionuclide by Shapeable Porous Materials

Nuclear energy is a competitive and environmentally friendly low-carbon energy source. It is seen as an important avenue for satisfying energy demands, responding to the energy crisis, and mitigating global climate change. However, much attention has been paid to achieving the effective treatment of radionuclide ions produced in nuclear waste. Initially, advanced adsorbents were mainly available in powder form, which meant that additional purification processes were usually required for separation and recovery in industrial applications. Therefore, to meet the practical requirements of industrial applications, materials need to be molded and processed into forms such as beads, membranes, gels, and resins. Here, we summarize the fabrication of porous materials used for capturing typical radionuclide ions, including UO2 2+, TcO4 -, IO3 -, SeO3 2-, and SeO4 2-.

Understanding the cascade heterojunction of CuPc/Bi-MOF for photoelectrochemical nitrate reduction

Herein, a CuPc/Bi-MOF cascade heterojunction is synthesized exhibiting an excellent NH3 yield (7.13 μg h-1 cm-2) and stability. Characterization studies show that the cascade heterostructure with a unique morphology and oxygen vacancies offers new insights into future photoelectrocatalytic material design.

Construction of BiOCl/bismuth-based halide perovskite heterojunctions derived from the metal-organic framework CAU-17 for effective photocatalytic degradation

The designed synthesis of an S-scheme heterojunction has possessed a great potential for improving photocatalytic wastewater treatment by demonstrating increased the photoredox capacity and improved the charge separation efficiency. Here, we introduce the fabrication of a heterojunction-based photocatalyst comprising bismuth oxychloride (BiOCl) and bismuth-based halide perovskite (BHP) nanosheets, derived from metal-organic frameworks (MOFs). Our composite photocatalyst is synthesized through a one-pot solvothermal strategy, where a halogenation process is applied to a bismuth-based metal-organic framework (CAU-17) as the precursor for bismuth sourcing. As a result, the rod-like structure of CAU-17 transforms into well-defined plate and nanosheet architectures after 4 and 8 h of solvothermal treatment, respectively. The modulation of the solvothermal reaction time facilitates the establishment of an S-scheme heterojunction, resulting in an increase in the photocatalytic degradation efficiency of rhodamine B (RhB) and sulfamethoxazole (SMX). The optimized BiOCl/BHP composite exhibits superior RhB and SMX degradation rates, achieving 99.8% degradation of RhB in 60 min and 75.1% degradation of SMX in 300 min. Also, the optimized BiOCl/BHP composite (CAU-17-st-8h sample) exhibited the highest rate constant (k = 3.48 × 10-3 min-1), nearly 6 times higher than that of the bare BHP in the photocatalytic degradation process of SMX. The enhanced photocatalytic efficiency can be endorsed to various factors: (i) the in-situ formation of two-components BiOCl/BHP photocatalyst, derived from CAU-17, effectively suppresses the aggregation of pristine BHP and BiOCl particles; (ii) the S-scheme heterostructure establishes a closely-knit interfacial connection, thereby facilitating efficient pathways for charge separation/transfer; and (iii) the BiOCl/BHP heterostructure enhances its capacity to absorb visible light. Our investigation establishes an effective strategy for constructing heterostructured photocatalysts, offering significant potential for application in photocatalytic wastewater treatment.

A microporous bismuth-based MOF for efficient separation of acetylene from carbon dioxide

The separation of acetylene from carbon dioxide is challenging due to their almost identical molecular sizes and volatilities. Metal-organic frameworks (MOFs) in general are strong candidates for the separation of gas mixtures owing to the presence of functional pore surfaces that can selectively capture specific target molecules. Herein, we report a stable and easily synthesized bismuth-based MOF, Bi-BTC, which can achieve the separation of acetylene and carbon dioxide. We performed a detailed analysis of the sorption properties of the Bi-MOF. Bi-BTC shows good adsorption capacities for C2H2 with a capacity of 53.8 cm3 g-1 at 298 K and 1.0 bar, and C2H2/CO2 selectivity of 5.14/7.69 at 298 K and 1.0/0.1 bar. IAST selectivity calculations indicate that Bi-BTC possesses good separation capacity, and dynamic breakthrough experiments were performed to prove the separation of C2H2 and CO2. Bi-MOFs as a group of relatively less studied types of MOFs have interesting adsorption characteristics, and this study on Bi-based MOF will enrich three-dimensional Bi-MOF adsorbents for gas adsorption and separation applications.

Achieving ultrafast and highly selective capture of radiotoxic tellurite ions on iron-based metal-organic frameworks through coordination bond-dominated conversion

Chemically durable and effective adsorbents for radiotoxic TeOx2- (TeIV and TeVI) anions remain in great demand for contamination remediation. Herein, a low-cost iron-based metal-organic framework (MIL-101(Fe)) was used as an adsorbent to capture TeOx2- anions from contaminated solution with ultrafast kinetics and record-high adsorption capacity of 645 mg g-1 for TeO32- and 337 mg g-1 for TeO42-, outperforming previously reported adsorbents. Extended X-ray absorption fine structure (EXAFS) and density functional theory (DFT) calculations confirmed that the capture of TeOx2- by MIL-101(Fe) was mediated by the unique C-O-Te and Fe-O-Te coordination bonds at corresponding optimal adsorption sites, which enabled the selective adsorption of TeOx2- from solution and further irreversible immobilization under the geological environment. Meanwhile, MIL-101(Fe) works steadily over a wide pH range of 4-10 and at high concentrations of competing ions, and it is stable under β-irradiation even at high dose of 200 kGy. Moreover, the MIL-101(Fe) membrane was fabricated to efficiently remove TeO32- ions from seawater for practical use, overcoming the secondary contamination and recovery problems in powder adsorption. Finally, the good sustainability of MIL-101(Fe) was evaluated from three perspectives of technology, environment, and society. Our strategy provides an alternative to traditional removal methods that should be attractive for Te contamination remediation.

In situ growth of Bi-MOF on cotton fabrics via ultrasonic synthesis strategy for recyclable photocatalytic textiles

Bismuth-based metal-organic framework (Bi-MOF) materials have shown potential for treating organic pollutants. In this work, multifunctional textiles were produced by in situ synthesis of CAU-17 on carboxymethylated cotton fabrics by solvothermal and ultrasonic strategies and employed as recyclable photocatalysts. The compositional and structural features of the dense MOF crystal coatings on cotton fibers were confirmed by scanning electron microscopy, X-ray diffraction, and other characterization approaches. Under optimized conditions, the developed functionalized cotton fabrics achieved a photodegradation efficiency of 98.8% under visible light for RhB in water, as well as good recyclability. The described results have provided the basis and reference for the fabrication of MOF-functionalized textiles.

Surfactant-Mediated Crystalline Structure Evolution Enabling the Ultrafast Green Synthesis of Bismuth-MOF in Aqueous Condition

Green synthesis of stable metal-organic frameworks (MOFs) with permanent and highly ordered porosity at room temperature without needing toxic and harmful solvents and long-term high-temperature reactions is crucial for sustainable production. Herein, a rapid and environmentally friendly synthesis strategy is reported to synthesize the complex topological bismuth-based-MOFs (Bi-MOFs), [Bi9(C9H3O6)9(H2O)9] (denoted CAU-17), in water under ambient conditions by surfactant-mediated sonochemical approach, which could also be applicable to other MOFs. This strategy explores using cetyltrimethylammonium bromide (CTAB) amphiphilic molecules as structure-inducing agents to control the removal of non-coordinated water (dehydration) and enhance the degree of deprotonation of the ligands, thereby regulating the coordination and crystallization in aqueous solutions. In addition, another two new strategies for synthesizing CAU-17 by crystal reconstruction and one-step synthesis in binary solvents are provided, and the solvent-induced synthesis mechanism of CAU-17 is studied. The as-prepared CAU-17 presents a competitive iodine capture capability and effective delivery of the antiarrhythmic drug procainamide (PA) for enteropatia due to the broad pH tolerance and the unique phosphate-responsive destruction in the intestine. The findings will provide valuable ideas for the follow-up study of surfactant-assisted aqueous synthesis of MOFs and their potential applications.

In Situ Multicolor Imaging of Photocatalytic Degradation Process of Permanganate on Single Bismuth-Based Metal-Organic Frameworks

Bismuth-based metal-organic frameworks (Bi-MOFs) have emerged as important photocatalysts for pollutant degradation applications. Understanding the photocatalytic degradation mechanism is key to achieving technological advantage. Herein, we apply dark-field optical microscopy (DFM) to realize in situ multicolor imaging of the photocatalytic degradation process of permanganate (MnO4-) on single CAU-17 Bi-MOFs. Three reaction kinetic processes such as surface adsorption, photocatalytic reduction, and disproportionation are revealed by combining the time-lapsed DFM images with optical absorption spectra, indicating that the photocatalytic reduction of purple MnO4- first produces beige red MnO42- through a one-electron pathway, and then MnO42- disproportionates into yellow MnO2 on CAU-17. Meanwhile, we observe that the deposition of MnO2 cocatalysts enhances the surface adsorption reaction and the photocatalytic reduction of MnO4- to MnO42-. Unexpectedly, it is found that isopropanol as a typical hole scavenger can stabilize MnO42-, avoiding disproportionation and causing the alteration of the photocatalytic reaction pathway from a one-electron avenue to a three-electron (1 + 2) process for producing MnO2 on CAU-17. This research opens up the possibility of comprehensively tracking and understanding the photocatalytic degradation reaction at the single MOF particle level.

Wood aerogels decorated amino-functionalized MIL-101(Cr) as efficient filter for multistage purification of wastewater

Exploring novel water purifier to efficiently remove heavy metal ions from the wastewater is of vital importance. Inspired by the hierarchical structure of natural wood and the chelation of amino group, a high-efficiency water purifier with ethylenediamine functionalized MIL-101(Cr) octahedrons anchored on the wood aerogel (MIL-101(Cr)-ED/WA) was constructed. Benefiting from the two-pronged approach with the hierarchical structure of the wood aerogel frame for multistage filtration and the -NH2 that capable of chelation with metal ions, the fabricated MIL-101(Cr)-ED/WA exhibits excellent water purification performances, and its adsorption capacity of toxic Pb2+ ions could reach up to 6.46 mmol g-1. Furthermore, it demonstrates superior recyclability without secondary pollution and is also suitable for simultaneous treatment of multiple metal species. In general, this work will broaden the utilization of wood-based structural engineering materials in the treatment of heavy metal wastewater.

p-Block Bismuth Nanoclusters Sites Activated by Atomically Dispersed Bismuth for Tandem Boosting Electrocatalytic Hydrogen Peroxide Production

Constructing electrocatalysts with p-block elements is generally considered rather challenging owing to their closed d shells. Here for the first time, we present a p-block-element bismuth-based (Bi-based) catalyst with the co-existence of single-atomic Bi sites coordinated with oxygen (O) and sulfur (S) atoms and Bi nanoclusters (Biclu ) (collectively denoted as BiOSSA /Biclu ) for the highly selective oxygen reduction reaction (ORR) into hydrogen peroxide (H2 O2 ). As a result, BiOSSA /Biclu gives a high H2 O2 selectivity of 95 % in rotating ring-disk electrode, and a large current density of 36 mA cm-2 at 0.15 V vs. RHE, a considerable H2 O2 yield of 11.5 mg cm-2 h-1 with high H2 O2 Faraday efficiency of ∼90 % at 0.3 V vs. RHE and a long-term durability of ∼22 h in H-cell test. Interestingly, the experimental data on site poisoning and theoretical calculations both revealed that, for BiOSSA /Biclu , the catalytic active sites are on the Bi clusters, which are further activated by the atomically dispersed Bi coordinated with O and S atoms. This work demonstrates a new synergistic tandem strategy for advanced p-block-element Bi catalysts featuring atomic-level catalytic sites, and the great potential of rational material design for constructing highly active electrocatalysts based on p-block metals.

Synthesis of double-shelled periodic mesoporous organosilica nanospheres/MIL-88A-Fe composite and its elevated performance for Pb2+ removal in water

Herein, we report the synthesis of double-shelled periodic mesoporous organosilica nanospheres/MIL-88A-Fe (DSS/MIL-88A-Fe) composite through a hydrothermal method. To survey the structural and compositional features of the synthesized composite, a variety of spectroscopic and microscopic techniques, including FT-IR, XRD, BET, TEM, FE-SEM, EDX, and EDX-mapping, have been employed. A noteworthy point in this synthesis procedure is the integration of MOF with PMO to increase the adsorbent performance, such as higher specific surface area and more active sites. This combination leads to achieving a structure with an average size of 280 nm and 1.1 μm long attributed to DSS and MOF, respectively, microporous structure and relatively large specific surface area (312.87 m²/g). The as-prepared composite could be used as an effective adsorbent with a high adsorption capacity (250 mg/g) and quick adsorption time (30 min) for the removal of Pb²⁺ from water. Importantly, DSS/MIL-88A-Fe composite revealed acceptable recycling and stability, since the performance in Pb²⁺ removal from water remained above 70% even after 4 consecutive cycles.

MOF-Based Active Packaging Materials for Extending Post-Harvest Shelf-Life of Fruits and Vegetables

Active packaging that can extend the shelf-life of fresh fruits and vegetables after picking can assure food quality and avoid food waste. Such packaging can prevent the growth of microbial and bacterial pathogens or delay the production of ethylene, which accelerates the ripening of fruits and vegetables after harvesting. Proposed technologies include packaging that enables the degradation of ethylene, modified atmosphere packaging, and bioactive packaging. Packaging that can efficiently adsorb/desorb ethylene, and thus control its concentration, is particularly promising. However, there are still large challenges around toxicity, low selectivity, and consumer acceptability. Metal-organic framework (MOF) materials are porous, have a specific surface area, and have excellent gas adsorption/desorption performance. They can encapsulate and release ethylene and are thus good candidates for use in ethylene-adjusting packaging. This review focuses on MOF-based active-packaging materials and their applications in post-harvest fruit and vegetable packaging. The fabrication and characterization of MOF-based materials and the ethylene adsorption/desorption mechanism of MOF-based packaging and its role in fruit and vegetable preservation are described. The design of MOF-based packaging and its applications are reviewed. Finally, the potential future uses of MOF-based active materials in fresh food packaging are considered.

Bacterial cellulose flakes loaded with Bi2MoO6 nanoparticles and quantum dots for the photodegradation of antibiotic and dye pollutants

Effective strategies to improve charge separation in semiconductor particles are critical for improving the photodegradation of organic pollutants at levels sufficient for environmental applications. Herein, Bi₂MoO₆ (BMO_MOF), comprising both nanoparticles (NPs) and quantum dots (QDs), was synthesized from a bismuth-based metal-organic framework (Bi-MOF) precursor. Surface defects on BMO_MOF, the combination of NPs and QDs, and modified energy band edges improved photogenerated charge separation and facilitated redox reactions. When compared to BMO derived from uncoordinated Bi, the BMO_MOF photocatalyst (PC) was more efficient at photodegrading tetracycline hydrochloride (TCH) and ciprofloxacin (CIP), two widely-used antibiotics ubiquitous in wastewater, as well as the carcinogenic pollutant rhodamine B (RhB). BMO_MOF was then loaded on the biopolymer bacterial cellulose (BC) to further enhance photocatalytic performance and facilitate the recovery of the PC after water treatment processes. The novel BMO_MOF/BC photocatalytic flakes were significantly larger than pure BMO_MOF, and thus easier to recuperate. Furthermore, anchoring BMO_MOF on BC flakes augmented significantly the photodegradation of TCH, CIP, and RhB, mainly because hydroxyl groups in BC act as hole traps facilitating photogenerated electron-hole separation. Results obtained with BMO_MOF/BC highlight promising approaches to develop optimal PCs for aqueous pollutants degradation.

In Situ Implantation of Bi2S3 Nanorods into Porous Quasi-Bi-MOF Architectures: Enabling Synergistic Dissociation of Borohydride for an Efficient and Fast Catalytic Reduction of 4-Nitrophenol

Catalytic hydrogenation reduction based on sodium borohydride (NaBH₄) has gained attention as an appealing "one-stone-two-birds" approach for the simultaneous elimination of nitroaromatic pollutants and the production of high-value aminoaromatics under mild conditions. However, the slow kinetics of NaBH₄ dissociation on the surface of catalysts restrict the catalytic hydrogenation reduction efficiency. Herein, we report an intelligent localized sulfidation strategy for an in situ implantation of Bi₂S₃ nanorods within quasi-Bi-MOF architectures (Bi₂S₃@quasi-Bi-MOF) by fine-tuning the pyrolysis temperature. In this novel Bi₂S₃@quasi-Bi-MOF, the porous quasi-Bi-MOF enables efficient adsorption of BH₄^- and 4-nitrophenol (4-NP), while Bi₂S₃ facilitates the BH₄^- dissociation to form H_ads* species adsorbed on the catalyst surface. Benefiting from the synergistic structure, Bi₂S₃@quasi-Bi-MOF exhibits excellent performance for the catalytic reduction of 4-NP, delivering a high turnover frequency (TOF) of 1.67 × 10^-4 mmol mg^-1 min^-1 and an extremely high normalized rate constant (k_nor) of 435298 s^-1 g^-1. The kinetic analysis and electrochemical tests indicate that this catalytic hydrogenation reduction follows the Langmuir-Hinshelwood mechanism. This study enriches the synthetic strategy of MOF-based derivatives and offers a new catalytic platform for hydrogenation reduction reactions.

Rapid synthesis of bismuth-organic frameworks as selective antimicrobial materials against microbial biofilms

Antibiotic resistance is a global public health threat, and urgent actions should be undertaken for developing alternative antimicrobial strategies and approaches. Notably, bismuth drugs exhibit potent antimicrobial effects on various pathogens and promising efficacy in tackling SARS-CoV-2 and related infections. As such, bismuth-based materials could precisely combat pathogenic bacteria and effectively treat the resultant infections and inflammatory diseases through a controlled release of Bi ions for targeted drug delivery. Currently, it is a great challenge to rapidly and massively manufacture bismuth-based particles, and yet there are no reports on effectively constructing such porous antimicrobial-loaded particles. Herein, we have developed two rapid approaches (i.e., ultrasound-assisted and agitation-free methods) to synthesizing bismuth-based materials with ellipsoid- (Ellipsoids) and rod-like (Rods) morphologies respectively, and fully characterized physicochemical properties. Rods with a porous structure were confirmed as bismuth metal-organic frameworks (Bi-MOF) and aligned with the crystalline structure of CAU-17. Importantly, the formation of Rods was a 'two-step' crystallization process of growing almond-flake-like units followed by stacking into the rod-like structure. The size of Bi-MOF was precisely controlled from micro-to nano-scales by varying concentrations of metal ions and their ratio to the ligand. Moreover, both Ellipsoids and Rods showed excellent biocompatibility with human gingival fibroblasts and potent antimicrobial effects on the Gram-negative oral pathogens including Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis and Fusobacterium nucleatum. Both Ellipsoids and Rods at 50 ​μg/mL could disrupt the bacterial membranes, and particularly eliminate P. gingivalis biofilms. This study demonstrates highly efficient and facile approaches to synthesizing bismuth-based particles. Our work could enrich the administration modalities of metallic drugs for promising antibiotic-free healthcare.

Bi-MOFs with two different morphologies promoting degradation of organic dye under simultaneous photo-irradiation and ultrasound vibration treatment

For the first time, piezocatalysis activity has been observed in bismuth-based MOFs (ultrasound vibration treatment) with two different morphologies, namely FCAU-17 (flakes) and CAU-17 (rods). CAU-17 and FCAU-17 were synthesized by solvothermal and ultrasonic methods, respectively, with the same organic ligand (1,3,5-benzenetricarboxylic acid) and metal salt (Bi(NO₃)₃·5H₂O). Among these, the apparent rate constant k of CAU-17 in piezo-photocatalysis is 3.9 × 10^-2 min^-1, which is ∼3.9 and ∼ 1.5 times of those in photocatalysis and piezocatalysis, respectively. CAU-17 showed much high piezo-photocatalytic activity during degradation of RhB. Efficiently coupling between piezocatalysis and photocatalysis has been realized in rod-like CAU-17 (ultrasound vibration treatment). Our results provide a new strategy to improve catalytic performance of Bi MOFs through an efficient synergistic piezo-photocatalysis approach for environmental remediation.

Saiz P, Reizabal A, Wuttke S, Celaya-Azcoaga L, Valverde A, Fernández de Luis R. A State-of-the-Art of Metal-Organic Frameworks for Chromium Photoreduction vs. Photocatalytic Water Remediation

Hexavalent chromium (Cr(VI)) is a highly mobile cancerogenic and teratogenic heavy metal ion. Among the varied technologies applied today to address chromium water pollution, photocatalysis offers a rapid reduction of Cr(VI) to the less toxic Cr(III). In contrast to classic photocatalysts, Metal-Organic frameworks (MOFs) are porous semiconductors that can couple the Cr(VI) to Cr(III) photoreduction to the chromium species immobilization. In this minireview, we wish to discuss and analyze the state-of-the-art of MOFs for Cr(VI) detoxification and contextualizing it to the most recent advances and strategies of MOFs for photocatalysis purposes. The minireview has been structured in three sections: (i) a detailed discussion of the specific experimental techniques employed to characterize MOF photocatalysts, (ii) a description and identification of the key characteristics of MOFs for Cr(VI) photoreduction, and (iii) an outlook and perspective section in order to identify future trends.

Tunable rare-earth metal-organic frameworks for ultra-high selenite capture

Linkers and clusters with various conformations present challenges for the design and prediction of highly porous and stable rare-earth metal-organic frameworks (RE-MOFs) for trapping toxic ions in aqueous solutions. Herein, we designed and synthesized a series of RE-MOFs based on a malleable ligand to explore the effects of ligands, clusters, and configurations on structural stability. The results showed that the nonanuclear high-connected UPC-183 exhibited better stability than the hexanuclear low-connected RE-MOF (UPC-181/182 series). Due to the syngenetic effect of chemi- and physisorption, the adsorption capacity of UPC-183-Eu for selenite (SeO₃^2-) is as high as 308.39 mg/g, recorded one of the highest ever reported for MOFs. Furthermore, we accurately analyzed the adsorption site of UPC-183-Eu for SeO₃^2- through single-crystal structure and theoretical simulation. The ultra-high selenite adsorption capacity and removal efficiency endow UPC-183-Eu an excellent porous adsorbent for removing pollutants.

Chemically Stable Guanidinium Covalent Organic Framework for the Efficient Capture of Low-Concentration Iodine at High Temperatures

The capture of radioactive I₂ vapor from nuclear waste under industrial operating conditions remains a challenging task, as the practical industrial conditions of high temperature (≥150 °C) and low I₂ concentration (∼150 ppmv) are unfavorable for I₂ adsorption. We report a novel guanidinium-based covalent organic framework (COF), termed TGDM, which can efficiently capture I₂ under industrial operating conditions. At 150 °C and 150 ppmv I₂, TGDM exhibits an I₂ uptake of ∼30 wt %, which is significantly higher than that of the industrial silver-based adsorbents such as Ag@MOR (17 wt %) currently used in the nuclear fuel reprocessing industry. Characterization and theoretical calculations indicate that among the multiple types of adsorption sites in TGDM, only ionic sites can bond to I₂ through strong Coulomb interactions under harsh conditions. The abundant ionic groups of TGDM account for its superior I₂ capture performance compared to various benchmark adsorbents. In addition, TGDM exhibits exceptionally high chemical and thermal stabilities that fully meet the requirements of practical radioactive I₂ capture (high-temperature, humid, and acidic environment) and differentiate it from other ionic COFs. Furthermore, TGDM has excellent recyclability and low cost, which are unavailable for the current industrial silver-based adsorbents. These advantages make TGDM a promising candidate for capturing I₂ vapor during nuclear fuel reprocessing. This strategy of incorporating chemically stable ionic guanidine moieties in COF would stimulate the development of new adsorbents for I₂ capture and related applications.

Research progress of metal organic frameworks and their derivatives for adsorption of anions in water: A review

Anion pollution in water has become a problem that cannot be ignored. The anion concentration should be controlled below the national emission standard to meet the demand for clean water. Among the methods for removing excess anions in water, the adsorption method has a unique removal performance, and the core of the adsorption method is the adsorbent. In recent years, the emerging metal-organic frameworks (MOFs) have the advantages of adjustable porosity, high specific surface area, diverse functions, and easy modification. They are very competitive in the field of adsorption of liquid anions. This article focuses on the adsorption of fluoride, arsenate, chromate, radioactive anions (ReO₄^-, TcO₄^-, SeO₄^2-/SeO₃^2-), phosphate ion, chloride ion, and other anions by MOFs and their derivatives. The preparation methods of MOFs are introduced in turn, the application of different types of metal-based MOFs to adsorb various anions were discussed in categories with their crystal structure and functional groups. The influence on the adsorption of anions is analyzed, including the more common and special adsorption mechanisms, adsorption kinetics and thermodynamics, and regeneration performance are briefly described. Finally, the current situation of MOFs adsorption of anions is summarized, and the outlook for future development is summarized to provide my own opinions for the practical application of MOFs.

Selenite capture by MIL-101 (Fe) through FeOSe bonds at free coordination Fe sites

Selective immobilization of SeO₃^2- is highly desired for the remediation of Se-contaminated water. Thus, the irreversible sorption of SeO₃^2- ions by adsorbents through unique coordination bonds with high affinity is needed. Herein, we demonstrated that Fe-based metal-organic framework (MOF) (Fe-MIL-101) with free coordination sites (FCSs) enabled selective and irreversible capture of SeO₃^2- ions from aqueous solution with fast kinetics and a high uptake capacity of 183.7 mg∙g^-1, owing to large MOF apertures and substantial numbers of FCSs as capture sites through forming Fe-O-Se bonds. Meanwhile, Fe-MIL-101 maintained excellent performance in a broad pH range (4-11) and high selectivity for SeO₃^2- ions in the presence of excessive competitive anions (e.g., CO₃^2-, PO₄^3-). Density functional theory (DFT) calculation, extended X-ray absorption fine structure (EXAFS), and Mössbauer fittings confirmed that the capture on Fe-MIL-101 was through the Fe-O-Se coordination bonds between FCSs and SeO₃^2-. Moreover, Fe-MIL-101 could effectively remove SeO₃^2- in simulated natural water and sewage by overcoming the influence of co-existing ions and organic matters. This study highlights new opportunities for the design of MOF-based materials for removing toxic and radioactive anions with irreversibility and high selectivity from natural and waste water.

Synthesis, crystal structure, and topology of a polycatenated bismuth coordination polymer

Solvothermal reaction of Bi(NO3)3·5H2O with the flexible ligand 1,3,5-tris[4-(carboxyphenyl)oxamethyl]-2,4,6-trimethylbenzene (H3TBTC) in methanol at 120 °C for 1 h led to the formation of a novel coordination polymer (CP) with the composition of Bi(TBTC). The structure of the microcrystalline material was determined through three-dimensional electron diffraction (3DED) measurements and phase purity was confirmed by a Pawley refinement, elemental analysis, and thermal analysis. The compound crystallizes in the triclinic space group P 1 ‾ $P\overline{1}$ with one Bi3+ cation and one TBTC3− trianion in the asymmetric unit. Edge-sharing of BiO7 polyhedra leads to the formation of dinuclear Bi2O12 units, which through coordination to six TBTC3− ions form a layered two-periodic structure. Upon heating the material in air, the unit cell volume contracts by 9%, which is attributed to a shift in the inter-layer arrangement and to the flexibility of the building units of the structure. The compound starts to decompose at ∼300 °C. Topological analysis revealed layers consisting of 3-c and 6-c nodes, consistent with the two-periodic kgd net – the dual of the Kagome net (kgm). However, due to the non-planar nature of the Bi(TBTC) layers, adjacent layers are interlaced by polycatenation.

Facile interface engineering of hierarchical flower spherical-like Bi-metal-organic framework microsphere/Bi2MoO6 heterostructure for high-performance visible-light photocatalytic tetracycline hydrochloride degradation

The self-assembled Bi-based metal-organic framework microspheres (Bi-MOF-M) by nanorods were successfully constructed by the glycol-assisted solvothermal method. Using Bi-MOF-M as a homologous template, a petal-like Bi₂MoO₆ (BMO) layer was grown in situ on its surface to facilely construct a chemically bonded heterojunction interface, realizing a micro/nano hierarchical flower spherical-like Bi-MOF-M/BMO heterojunction composite photocatalyst. The as-prepared series of Bi-MOF-M/BMO-x catalysts show higher visible light catalytic performance for tetracycline hydrochloride (TC) degradation. Among them, Bi-MOF-M/BMO-0.3 has the optimal catalytic activity, and the degradation efficiency can reach 93.6% within 60 min of light irradiation with superior mineralization ability and structural stability, and the degradation kinetic constant is 6.12 times that of Bi-MOF-M and 5.69 times that of BMO, respectively. The homologously grown Bi-MOF-M/BMO chemically bonded heterojunction not only effectively broadens the spectral absorption range and enhances the absorption intensity but also promotes the efficient separation of photogenerated carriers through forming a favorable interfacial electric field and well-matched energy band alignment. A reasonable mechanism for the visible light degradation of TC by the Bi-MOF-M/BMO composite catalyst with h⁺ and ¹O₂ as the main reactive species is proposed. The micro/nano hierarchical structure of the Bi-MOF/BMO catalyst allows it to exhibit the easy recovery advantage of micron-scale materials while maintaining the high catalytic activity of the primary nano-components.

Atomically dispersed Fe/Bi dual active sites single-atom nanozymes for cascade catalysis and peroxymonosulfate activation to degrade dyes

Constructing single-atom nanozymes (SAzymes) with densely exposed and dispersed double metal-N_x catalytic sites for pollution remediation remains rare and challenging. Herein, we report a novel Fe-Bi bimetallic MOF-derived carbon supported Fe-N₄ and Bi-N₄ dual-site FeBi-NC SAzyme for cascade catalysis and peroxymonosulfate activation to degrade dye pollutants, which is synthesized from the Fe-doped Bi-MOF as a precursor. The formation of both Fe-N₄ and Bi-N₄ sites is demonstrated by XANES and EXAFS. The FeBi-NC SAzyme has high single atoms loadings of Fe (2.61 wt%) and Bi (8.01 wt%), and displays 5.9- and 9.8-fold oxidase mimicking activity enhancement relative to the Fe-NC and Bi-NC SAzymes, respectively. When integrated acetylcholinesterase (AChE) and FeBi-NC SAzyme, a cascade enzyme-nanozyme system is developed for selective and sensitive screening of AChE activity with a low detection limit of 1 × 10^-4 mU mL^-1. Both Fe-N₄ and Bi-N₄ in FeBi-NC display a strong binding energy and electron donating capability to promote peroxymonosulfate activation to generate highly active intermediates for rhodamine B degradation. 100% rhodamine B removal occurs within 5 min via FeBi-NC mediated activation of peroxymonosulfate. The DFT calculations reveal that high activity of FeBi-NC is due to the isolated Fe-N₄ and Bi-N₄ sites and their synergy.

Materials interacting with inorganic selenium from the perspective of electrochemical sensing

Inorganic selenium, the most common form of harmful selenium in the environment, can be determined using electrochemical sensors, which are compact, fast, reliable and easy-to-operate devices. Despite progress in this area, there is still significant room for developing high-performance selenium electrochemical sensors. To achieve this, one should take into account (i) the electrochemical process that selenium undergoes on the electrode; (ii) the valence state of selenium species in the sample and (iii) modification of the sensor surface by a material with high affinity to selenium. The goal of this review is to provide a knowledge base for these issues. After the Introduction section, mechanisms and principles of the electrochemical reduction of selenium are introduced, followed by a section introducing the modification of electrodes with materials interacting with selenium and a section dedicated to speciation methods, including the reduction of non-detectable Se(VI) to detectable Se(IV). In the following sections, the main types of materials (metallic, polymers, hybrid (nano)materials…) interacting with inorganic selenium (mostly absorbents) are reviewed to show the diversity of properties that may be endowed to sensors if the materials were to be used for the modification of electrodes. These features for the main material categories are outlined in the conclusion section, where it is stated that the engineered polymers may be the most promising modifiers.

Metal-organic frameworks as superior porous adsorbents for radionuclide sequestration: Current status and perspectives

Efficient separation of hazardous radionuclides from radioactive waste remains a challenge to the global acceptance of nuclear power due to complex nature of the waste, high radiotoxicities and presence of large number of interfering elements. Sorption of radioactive elements from liquid phase, gas phase or their solid particulates on various synthetic organic, inorganic or biological sorbents is looked as one of the options for their remediation. In this context, highly porous materials, termed as metal-organic frameworks (MOFs), have shown promise for efficient capturing of various types of radioactive elements. Major advantages that have been advocated for the application of MOFs in radionuclide sorption are their excellent chemical stability, and their large surface area due to abundant functional groups, and porosity. In this review, recent developments on the application of MOFs for radionuclide sequestration are briefly discussed. Focus has been devoted to address the separation of few crucial radioactive elements such as Th, U, Tc, Re, Se, Sr and Cs from aqueous solutions, which are important for liquid radioactive waste management. Apart from these radioactive metal ions, removal of radionuclide bearing gases such as I₂, Xe, and Kr are also discussed. Aspects related to the interaction of MOFs with the radionuclides are also discussed. Finally, a perspective for comprehensive investigation of MOFs for their applications in radioactive waste management has been outlined.

Rationally Tailoring Pore and Surface Properties of Metal-Organic Frameworks for Boosting Adsorption of Dy3

The adsorption and recovery of dysprosium ions (Dy³⁺) from industrial wastewater are necessary but still challenging. Herein, we constructed a series of defect-containing metal-organic frameworks (MOFs) [UiO-66-(COOH)₂] using sodium benzoate (BCNa) as a modulator. Upon the formation of defects, the porosity and surface charge properties of the MOFs were improved, leading to a higher utilization ratio of active groups and higher adsorption capacities for Dy³⁺. The synthesized UiO-66-(COOH)₂-B10 with an optimal addition of BCNa exhibited a superior adsorption capacity of 150.6 mg g^-1. Fast adsorption occurred at ∼5 min, and equilibrium was reached at ∼60 min. Higher pH and temperature were found to be beneficial for boosting Dy³⁺ adsorption, and selective adsorption over other metal ions was achieved in a multicomponent solution. Further, FTIR spectroscopy and XPS investigations indicate that free carboxyl contributes to the capture of Dy³⁺. Thus, this work provides a promising strategy to enhance the utilization ratio of active groups and further adsorption performance.

Reconstructed Bismuth-Based Metal-Organic Framework Nanofibers for Selective CO2 -to-Formate Conversion: Morphology Engineering

Electrochemical reduction of carbon dioxide (ERCO₂ ) is an attractive and sustainable approach to close the carbon loop. Formic acid is a high-value and readily collectible liquid product. However, the current reaction selectivity remains unsatisfactory. In this study, the bismuth-containing metal-organic framework CAU-17, with morphological variants of hexagonal prisms (CAU-17-hp) and nanofibers (CAU-17-fiber), is prepared at room temperature through a wet-chemical approach and employed as the electrocatalyst for highly selective CO₂ -to-formate conversion. An H₃ BTC-mediated morphology reconstruction is systematically investigated and further used to build a CAU-17-fiber hierarchical structure. The as-prepared CAU-17-fiber_400 electrodes give the best electrocatalytic performance in selective and efficient formate production with FE_HCOO- of 96.4 % and j_COOH- of 20.4 mA cm^-2 at -0.9 V_RHE . This work provides a new mild approach for synthesis and morphology engineering of CAU-17 and demonstrates the efficacy of morphology engineering in regulating the accessible surface area and promoting the activity of MOF-based materials for ERCO₂ .

Efficient three-phase electrocatalytic CO2 reduction to formate on superhydrophobic Bi-C interfaces

Bi-C catalysts with the three-phase interfaces of CO2 (gas), electrolyte (liquid) and catalyst (solid) exhibit a remarkable electrocatalytic CO2 reduction (ECR) to formate selectivity (above 95% faradaic efficiency) with a high current (100 mA cm-2) in a broad potential range.

Bi(iii) MOFs: syntheses, structures and applications

The synthesis methods, structures and applications of Bi(iii)-based MOFs in catalysis, adsorption, fluorescence, etc. are reviewed.

Synthesis and Characterization of Ru-MOFs on Microelectrode for Trace Mercury Detection

Mercury ions (Hg2+) pollution in the water environment can cause serious harm to human health. Trace Hg2+ detection is of vital importance for environmental monitoring. Herein, we report a novel design of Ru-MOFs modified gold microelectrode for Hg2+ determination. Ru-MOFs are synthesized directly by the cathodic method on gold microelectrode, with the covered area accurately controlled. Cathodic synthesized Ru-MOFs show good conductivity and are suitable to be used as the electrode surface material directly. The synergy of the pre-deposition process and the adsorption process of Ru-MOFs can effectively improves the performance of the sensor. The results show good linearity (R2 = 0.996) from 0.1 ppb to 5 ppb, with a high sensitivity of 0.583 μA ppb-1 mm-2. The limit of detection is found to be 0.08 ppb and the test process is within 6 min. Most importantly, the senor has a good anti-interference ability and the recoveries are satisfactory. This miniature electrochemical sensor has the potential for on-site detection of trace mercury in the field.

Chloroplast-like porous bismuth-based core-shell structure for high energy efficiency CO2 electroreduction

Electrochemical CO₂ reduction reaction (CO₂RR) to formate is economically viable considering the energy input and market value. Through learning nature, a series of chloroplast-like porous bismuth-based core-shell (CPBC) materials have been designed. In these materials, the porous carbon can enrich and transfer CO₂ to the core-shell Bi@Bi₂O₃ in CO₂ reduction process, during which Bi₂O₃ layer can be transformed into activated metastable layer to efficiently convert CO₂ into formate and Bi can provide abundant electrons. Based on this, superior performances for most of important parameters in CO₂RR can be achieved and best of them, CPBC-1 presents remarkable Faradaic efficiency (FE_formate > 94%) over a wide potential range (-0.65 to -1.0 V) with high catalysis durability (>72 h). Noteworthy, its maximum energy efficiency is as high as 76.7% at -0.7 V, the highest one in reported bismuth-based materials. This work opens novel perspectives in designing nature-inspired CO₂RR electrocatalysts.

Phosphate-Suppressed Selenite Biotransformation by Escherichia coli

Biotransformation of selenite to valuable elemental selenium nanoparticles (Se⁰) is a promising avenue to remediate seleniferous environments and simultaneously recover selenium (Se). However, the underlying oxyanion competition and selenite transformation mechanism in prokaryotes are poorly understood. In this work, the impacts of phosphate on selenite uptake and transformation were elucidated with Escherichia coli and its mutant deficient in phosphate transport as model microbial strains. Selenite uptake was inhibited by phosphate in E. coli. Moreover, the transformation of internalized Se was shifted from Se⁰ to toxic organo-Se with elevated phosphate levels, as evidenced by the linear combination fit analysis of the Se K-edge X-ray absorption near-edge structure. Such a phosphate-regulated selenite biotransformation process was mainly assigned to the competitive uptake of phosphate and selenite, which was primarily mediated by a low affinity phosphate transporter (PitA). Under phosphate-deficient conditions, the cells not only produced abundant Se⁰ nanoparticles but also maintained good cell viability. These findings provide new insights into the phosphate-regulated selenite biotransformation by prokaryotes and contribute to the development of new processes for bioremediating Se-contaminated environments, as well as bioassembly of Se⁰.

Efficient capture of Cr(VI) by carbon hollow fibers with window-like structure

Removal of toxic Cr(VI) from contaminated water is significant for environmental protection. High efficient adsorbents with outstanding adsorption performance are highly demanded. Herein, we reported that window-like structured carbon hollow fibers (WL-CHF) derived from Enteromorpha prolifera could capture toxic Cr(VI) from aqueous solutions with high adsorption capacity, fast adsorption rate, and excellent recyclable performance. The excellent adsorption performance could be attributed to the unique structure that combines a variety of advantages: large specific surface area, fast diffusion processes, and easy access of adsorption sites for Cr(VI). In addition, the adsorption process was fitted well with pseudo-second-order model and Langmuir isotherm model. The potential mechanism on Cr(VI) removal includes reduction-cation exchange and electrostatic interaction with surface oxygen-containing functional groups. This study highlights new opportunities for designing adsorbents for Cr(VI) removal from Cr-polluted water.