Olefin-linked cationic covalent organic frameworks for efficient extraction of ReO4-/99TcO4. J Hazard Mater 2023;446:130603. [PMID: 36580784 DOI: 10.1016/j.jhazmat.2022.130603]

Efficient capture of 99TcO4-/ReO4- via node and linker bifunctional anion exchange covalent organic frameworks

In nuclear wastewater treatment, ion-scavenging materials designed to trap 99TcO4- is urgently needed. However, strong acid/base, high radiation and high salt concentration of nuclear wastewater usually result in inadequate stability and adsorption capacity of the adsorbent. Herein, we report a new class of bifunctional anion-exchange olefin-linked COF (BPDC-MTMP) prepared via Knoevenagel condensation reactions, the first example exploring the synergistic integration of positively charged fragments at both nodes and linkers. Surprisingly, BPDC-MTMP exhibits a record ReO4- (a non-radioactive surrogate of 99TcO4-) adsorption capacity up to 1593.21 mg g-1, its outstanding adsorption capacity can be attributed to the synergistic enhancement of the positively charged fragments of the nodes and linkers leading to a significant increase in the positive charge density and the number of anion exchange sites. BPDC-MTMP's hydrophobicity is enhanced by the highly conjugated bulky alkyl skeleton, the affinity toward ReO4- and chemical stability are therefore significantly improved, ReO4- can be selectively and reversibly extracted even under strong acid/base and high salt concentration solutions. This study illustrates that the node and linker bifunctional anion exchange COF is of great potential for ReO4-/99TcO4- trapping, which provides a new method to design high-performance adsorbents for the treatment of nuclear wastewater.

Covalent organic frameworks as superior adsorbents for the removal of toxic substances

Developing new materials capable of the safe and efficient removal of toxic substances has become a research hotspot in the field of materials science, as these toxic substances pose a serious threat to human health, both directly and indirectly. Covalent organic frameworks (COFs), as an emerging class of crystalline porous materials, have advantages such as large specific surface area, tunable pore size, designable structure, and good biocompatibility, which have been proven to be a superior adsorbent design platform for toxic substances capture. This review will summarize the synthesis methods of COFs and the properties and characteristics of typical toxicants, discuss the design strategies of COF-based adsorbents for the removal of toxic substances, and highlight the recent advancements in COF-based adsorbents as robust candidates for the efficient removal of various types of toxicants, such as animal toxins, microbial toxins, phytotoxins, environmental toxins, etc. The adsorption performance and related mechanisms of COF-based adsorbents for different types of toxic substances will be discussed. The complex host-guest interactions mainly include electrostatic, π-π interactions, hydrogen bonding, hydrophobic interactions, and molecular sieving effects. In addition, the adsorption performance of various COF-based adsorbents will be compared, and strategies such as reasonable adjustment of pore size, introduction of functionalities, and preparation of composite materials can effectively improve the adsorption efficiency of toxins. Finally, we also point out the challenges and future development directions that COFs may face in the field of toxicant removal. It is expected that this review will provide valuable insights into the application of COF-based adsorbents in the removal of toxicants and the development of new materials.

Gram-scale green synthesis of a highly stable cationic covalent organic framework for efficient and selective removal of ReO4 -/99TcO4. JOURNAL OF MATERIALS CHEMISTRY. A 2024;13:214-219. [PMID: 39554595 PMCID: PMC11566665 DOI: 10.1039/d4ta06442a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Covalent organic frameworks (COFs) have developed as efficient and selective adsorbents to mitigate 99TcO4 - contamination. However, the eco-friendly and scalable production of COF-based adsorbents for the removal of 99TcO4 - has not yet been reported. This study explores the potential of a cationic COF (TpDB-COF) synthesized via a green hydrothermal method, achieving gram-scale yields per batch, thereby addressing a significant limitation of existing COF production methods. The TpDB-COF demonstrates an exceptional stability in strongly acidic conditions (2 weeks in 3 M HNO3), as well as in various organic solvents, making it suitable for harsh nuclear waste environments. Adsorption experiments using ReO4 - as a surrogate for 99TcO4 - show rapid adsorption kinetics, reaching nearly 100% removal efficiency within 1 min (with initial concentration of 28 ppm at a solid-to-liquid ratio of 1 g L-1), a maximum adsorption capacity of 570 mg g-1 and excellent stability. Moreover, the COF maintains high selectivity for ReO4 - even in the presence of competing anions such as SO4 2- and NO3 -. These findings highlight that the hydrothermal synthesis is an effective method to synthesize COF adsorbents for efficient removal of 99TcO4 - and offers a sustainable approach for practical applications.

A robust amphiphilic ionic covalent organic framework intercalated into functionalized graphene oxide hybrid membranes for ultrafast extraction uranium from wastewater

The efficient capture of uranium from wastewater is crucial for environmental remediation and the sustainable development of nuclear energy, yet it poses considerable challenges. In this study, amphiphilic ionic covalent organic framework intercalated into graphene oxide (GO) nanosheets functionalized with polyethyleneimine (PEI) were used to construct hybrid membranes with ultrafast uranium adsorption. These hybrid membranes achieved equilibrium in just 10 min and the adsorption capacity was as high as 358.8 mg g-1 at pH = 6. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analyses revealed that the strong interaction between sulfonic acid groups and uranyl ions was the primary reason for the high adsorption capacity and selectivity. The extended transition state and natural orbitals for chemical valence (ETS-NOCV) analysis revealed that the interaction between the 7 s and 5f orbitals of uranyl and the 2p orbitals of S and O in the sulfonate was the primary reason for the strong interaction between the sulfonate and the uranyl ion. This research presents an effective method for the rapid extraction of uranium from wastewater.

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-.

Efficient removal of perrhenate/pertechnetate by a pyridinium-based porous polymer

The extraction of 99TcO4- from radioactive effluents is extremely crucial for the purposes of nuclear disposal and environmental remediation. Herein, utilizing a facile and low-cost synthesis method, we report a pyridinium-based cationic polymer network, CPP-Cl, with impressive adsorption performance and ultrafast adsorption kinetics towards ReO4-. The structure featuring highly density of charged pyridinium units was synthesized, making it an effective adsorbent for capturing ReO4-. The material showed fast ReO4- adsorption kinetics reaching adsorption equilibrium within 30 s, an excellent capture capability of 1069.7 mg/g, and exceptional separation efficiency of 94.3% for removing 1000 ppm ReO4-. Furthermore, it possessed excellent reusability in multiple sorption/desorption trials and good uptake capacity within a widely ranging pH values. It is noteworthy that the extraction efficiency of CPP-Cl for ReO4- from simulated nuclear waste can be up to 94.2%. The favorable performance of the material in multiple tests revealed that CPP-Cl has tremendous potential as a high-efficiency sorbent for capturing 99TcO4-/ReO4- in complex nuclear associated environmental systems.

Unveiling the Role of Cationic Pyridine Sites in Covalent Triazine Framework for Boosting Zinc-Iodine Batteries Performance

Rechargeable Zinc-iodine batteries (ZIBs) are gaining attention as energy storage devices due to their high energy density, low-cost, and inherent safety. However, the poor cycling performance of these batteries always arises from the severe leakage and shuttle effect of polyiodides (I3 - and I5 -). Herein, a novel cationic pyridine-rich covalent triazine framework (CCTF-TPMB) is developed to capture and confine iodine (I2) species via strong electrostatic interaction, making it an attractive host for I2 in ZIBs. The as-fabricated ZIBs with I2 loaded CCTF-TPMB (I2@CCTF-TPMB) cathode achieve a large specific capacity of 243 mAh g-1 at 0.2 A g-1 and an exceptionally stable cyclic performance, retaining 93.9% of its capacity over 30 000 cycles at 5 A g-1. The excellent electrochemical performance of the ZIBs can be attributed to the pyridine-rich cationic sites of CCTF-TPMB, which effectively suppress the leakage and shuttle of polyiodides, while also accelerating the conversion reaction of I2 species. Combined in situ Raman and UV-vis analysis, along with theoretical calculations, clearly reveal the critical role played by pyridine-rich cationic sites in boosting the ZIBs performances. This work opens up a promising pathway for designing advanced I2 cathode materials toward next-generation ZIBs and beyond.

Advanced Porous Materials as Designer Platforms for Sequestering Radionuclide Pertechnetate

Technetium-99 (99Tc), predominantly present as pertechnetate (99TcO4 -), is a challenging contaminant in nuclear waste from artificial nuclear fission. The selective removal of 99TcO4 - from nuclear waste and contaminated groundwater is complex due to (i) the acidic and intricate nature of high-level liquid wastes; (ii) the highly alkaline environment in low-activity level tank wastes, such as those at Hanford, and in high-level wastes at locations like Savannah River; and (iii) the potential for 99TcO4 - to leak into groundwater, risking severe water pollution due to its high mobility. This Review focuses on recent developments in advanced porous materials, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and their amorphous counterparts, porous organic polymers (POPs). These materials have demonstrated exceptional effectiveness in adsorbing 99TcO4 - and similar oxyanions. We comprehensively review the adsorption mechanisms of these anions with the adsorbents, employing macroscopic batch/column experiments, microscopic spectroscopic analyses, and theoretical calculations. In conclusion, we present our perspectives on potential future research directions, aiming to overcome current challenges and explore new opportunities in this area. Our goal is to encourage further research into the development of advanced porous materials for efficient 99TcO4 - management.

Creation of Cationic Polymeric Nanotrap Featuring High Anion Density and Exceptional Alkaline Stability for Highly Efficient Pertechnetate Removal from Nuclear Waste Streams

There is an urgent need for highly efficient sorbents capable of selectively removing 99TcO4- from concentrated alkaline nuclear wastes, which has long been a significant challenge. In this study, we present the design and synthesis of a high-performance adsorbent, CPN-3 (CPN denotes cationic polymeric nanotrap), which achieves excellent 99TcO4- capture under strong alkaline conditions by incorporating branched alkyl chains on the N3 position of imidazolium units and optimizing the framework anion density within the pores of a cationic polymeric nanotrap. CPN-3 features exceptional stability in harsh alkaline and radioactive environments as well as exhibits fast kinetics, high adsorption capacity, and outstanding selectivity with full reusability and great potential for the cost-effective removal of 99TcO4-/ReO4- from contaminated water. Notably, CPN-3 marks a record-high adsorption capacity of 1052 mg/g for ReO4- after treatment with 1 M NaOH aqueous solutions for 24 h and demonstrates a rapid removal rate for 99TcO4- from simulated Hanford and Savannah River Site waste streams. The mechanisms for the superior alkaline stability and 99TcO4- capture performances of CPN-3 are investigated through combined experimental and computational studies. This work suggests an alternative perspective for designing functional materials to address nuclear waste management.

Rapid and selective removal of aristolochic acid I in natural products by vinylene-linked iCOF resins

Rapid, efficient, and selective removal of toxicants such as aristolochic acid I (AAI) from complex natural product systems is of great significance for the safe use of herbal medicines or medicine-food plants. Addressing this challenge, we develop a high-performance separation approach based on ionic covalent organic frameworks (iCOFs) to separate and remove AAI. Two vinylene-linked iCOFs (NKCOF-46-Br- and NKCOF-55-Br-) with high crystallinity are fabricated in a green and scalable fashion via a melt polymerization synthesis method. The resulting materials exhibit a uniform morphology, high stability, fast equilibrium time, and superior affinity and selectivity for AAI. Compared to conventional separation media, NKCOF-46-Br- and NKCOF-55-Br- achieve the record high adsorption capacities of 246.0 mg g-1 and 178.4 mg g-1, respectively. Various investigations reveal that the positively charged framework and favorable pore microenvironment of iCOFs contribute to their high selectivity and adsorption efficiency. Moreover, the iCOFs exhibit excellent biocompatibility by in vivo toxicity assays. This study paves a new avenue for the rapid, selective and efficient removal of toxicants from complex natural systems.

Ultra-stable 3D pyridinium salt-based polymeric network nanotrap for selective 99TcO4-/ReO4- capture via hydrophobic and steric engineering

Selective capture of radioactive ⁹⁹TcO₄^- from highly alkaline nuclear waste is highly desirable for environmental remediation and waste disposal. However, the combined features of adsorbents with excellent chemical stability and high capture selectivity for ⁹⁹TcO₄^- have not yet been achieved. Herein, we report an ultra-stable 3D pyridinium salt-based polymeric network (TMP-TBPM) nanotrap with remarkable radiation, acid and base stability for selective capture of ReO₄^- via hydrophobic engineering and steric hindrance, a non-radioactive surrogate of ⁹⁹TcO₄^-. The batch capture experiments show that TMP-TBPM has high capture capacity (918.7 mg g^-1) and fast sorption kinetics (94.3 % removal in 2 min), which can be attributed to the high density of pyridinium salt-based units on the highly accessible pore channels of 3D interconnected low-density skeleton. In addition, the introduction of abundant alkyl and tetraphenylmethane units into the 3D framework not only greatly enhanced the hydrophobicity and stability of TMP-TBPM, but also significantly improved the affinity toward ⁹⁹TcO₄^-/ReO₄^-, enabling reversible and selective capture of ⁹⁹TcO₄^-/ReO₄^- even under highly alkaline conditions. This study exhibits the great potential of 3D pyridinium salt-based polymeric network nanotrap for ⁹⁹TcO₄^-/ReO₄^- capture from highly alkaline nuclear waste, providing a new strategy to construct high-performance cationic polymeric sorbents for radioactive wastewater treatment.

Constructing an ultrastable imidazole covalent organic framework for concurrent uranium detection and recovery

Uranium is one of the most important strategic resources for the development of the nuclear industry, but its unintended release has created potential environmental and health risks. It is highly desired to explore new methods that enable concurrent uranium monitoring and recovery for environmental protection and sustainable development of the nuclear industry. Here, for the first time, an imidazole fluorescent covalent organic framework (named PyTT-Tp) with ultrastable skeleton and open nanopore channel is synthesized by condensing ammonium acetate, 1,3,5-triformylphloroglucinol and pyrene-4,5,9,10-tetrone. By precisely tailoring complexing ligands, PyTT-Tp shows an excellent uranium recovery capacity of 941.27 mg g^-1 and reached equilibrium within 60 min, which can be attributed to dense selective uranium binding sites on the highly accessible open skeleton. In addition, due to the signal amplification of the pyrene-imidazole skeleton, it has an ultra-low detection limit of 4.92 nM UO₂²⁺ and an ultra-fast response time (2 s) suitable for on-site monitoring the uranium content of the extracted water. By modulating target complexing ligands, this approach can be extended to the monitoring and recovery of other strategic nuclides.