Cationic Covalent Organic Nanosheets for Rapid and Selective Capture of Perrhenate: An Analogue of Radioactive Pertechnetate from Aqueous Solution

Multiple-component covalent organic frameworks for simultaneous extraction and determination of multitarget pollutants in sea foods

Persistent organic pollutants (POPs), such as perfluoroalkyl and polyfluoroalkyl substances (PFASs), polychlorinated biphenyls (PCBs), and bisphenols (BPs), have been raising global concerns due to their toxic effects on environment and human health. The monitoring of residues of POPs in seafood is crucial for assessing the accumulation of these contaminants in the study area and mitigating potential risks to human health. However, the diversity and complexity of POPs in seafood present significant challenges for their simultaneous detection. Here, a novel multi-component fluoro-functionalized covalent organic framework (OH-F-COF) was designed as SPE adsorbent for simultaneous extraction POPs. On this basis, the recognition and adsorption mechanisms were investigated by molecular simulation. Due to multiple interactions and large specific surface area, OH-F-COF displayed satisfactory coextraction performance for PFASs, PCBs, and BPs. Under optimized conditions, the OH-F-COF sorbent was employed in a strategy of simultaneous extraction and stepwise elution (SESE), in combination with HPLC-MS/MS and GC-MS method, to effectively determined POPs in seafood collected from coastal areas of China. The method obtained low detection limits for BPs (0.0037 -0.0089 ng/g), PFASs (0.0038 -0.0207 ng/g), and PCBs (0.2308 -0.2499 ng/g), respectively. This approach provided new research ideas for analyzing and controlling multitarget POPs in seafood. ENVIRONMENTAL IMPLICATIONS: Persistent organic pollutants (POPs), such as perfluoroalkyl and polyfluoroalkyl substances (PFASs), polychlorinated biphenyls (PCBs), and bisphenols (BPs), have caused serious hazards to human health and ecosystems. Hence, there is a need to develop a quantitative method that can rapidly detect POPs in environmental and food samples. Herein, a novel multi-component fluorine-functionalized covalent organic skeletons (OH-F-COF) were prepared at room temperature, and served as adsorbent for POPs. The SESE-SPE strategy combined with chromatographic techniques was used to achieve a rapid detection of POPs in sea foods from the coastal provinces of China. This method provides a valuable tool for analyzing POPs in environmental and food samples.

Dipole moment regulation for enhancing internal electric field in covalent organic frameworks photocatalysts

Covalent organic frameworks (COFs) have recently emerged as a kind of promising photocatalytic platform in addressing the growing threat of trace pollutants in aquatic environments. Along this, we propose a strategy of constructing internal electric field (IEF) in COFs through the dipole moment regulation, which intrinsically facilitates the separation and transfer of photogenerated excitons. Two COFs of BTT-TZ-COF and BTT-TB-COF are developed by linking the electron-donor of benzotrithiophene (BTT) block and the electron-acceptor of triazine (TZ) or tribenzene (TB) block, respectively. DFT calculations demonstrate TZ block with larger dipole moment can achieve more efficient IEF due to the stronger electron-attractive force and hence narrower bandgap. Moreover, featuring the highly-order crystalline structure for accelerating photo-excitons transfer and rich porosity for facilitating the adsorption, BTT-TZ-COF exhibited an excellent universal performance of photocatalytic degradations of various dyes. Specifically, a superior photodegradation efficiency of 99% Rhodamine B (RhB) is achieved within 20 min under the simulated sunlight. Therefore, this convenient construction approach of enhanced IEF in COFs through rational regulation of the dipole moment can be a promising way to realize high photocatalytic activity.

Covalent organic frameworks: spotlight on applications in the pharmaceutical arena

Covalent organic frameworks (COFs) have much potential in the field of analytical separation research due to their distinctive characteristics, including easy modification, low densities, large specific surface areas and permanent porosity. This article provides a historical overview of the synthesis and broad perspectives on the applications of COFs. The use of COF-based membranes in gas separation, water treatment (desalination, heavy metals and dye removal), membrane filtration, photoconduction, sensing and fuel cells is also covered. However, these COFs also demonstrate great promise as solid-phase extraction sorbents and solid-phase microextraction coatings. In addition to various separation applications, this work aims to highlight important advancements in the synthesis of COFs for chiral and isomeric compounds.

Development of novel ionic covalent organic frameworks composite nanofiltration membranes for dye/salt separation

Covalent organic frameworks (COF) have desirable properties such as high porosity, low mass density, excellent heat resistance and regulatable structure, making them an ideal candidate for membrane material. Traditional methods for preparing covalent organic framework composite membranes, such as interfacial polymerization, vacuum filtration, and covalent organic framework abrasive coating. Stand-alone COF membranes produced by the above methods usually suffer from problems such as poor mechanical properties. Here, we fabricated high performance COF composite membranes by modified casting-precipitation-evaporation method. The designed composite membranes consisted of the ionic COF (iCOF) selective layer and the support layer are applied in dye/salt separation. The high permeability (∼ 68 L h-1 m-2 bar-1), high dyes rejection (97% for Rose Bengal), and low salts rejection (∼ 2.86% for NaCl) are achieved by the iCOF functional layer. The as-prepared composite membranes have a hydrophilic and highly smooth surface, making them have good anti-fouling performance. In addition, the rigid pore structure of iCOF selective layer endows the composite membranes with excellent stability, the composite membranes maintain original structure under high pressure (6 bar) and ultrasonic treatment (16 kHz for 60 min). This work may open up a novel path to fabricate iCOF composite membranes, which exhibit great potential in dye/salt separation.

Always positive covalent organic nanosheet enabling pH-independent adsorption and removal of Cr(Ⅵ)

Rapid and highly effective removal of hexavalent chromium (Cr(Ⅵ)) is extremely vital to water resources restoration and environmental protection. To overcome the pH limitation faced by most ionic absorbents, an always positive covalent organic nanosheet (CON) material was prepared and its Cr(VI) adsorption and removal capability was investigated in detail. As-prepared EB-TFB CON (TFB = 1,3,5-benzaldehyde, EB = ethidium bromide) shows strong electropositivity in the tested pH range of 1 ∼ 10, display a pH-independent Cr(VI) removal ability, and work well for Cr(VI) pollution treatment with good anti-interference capability and reusability in a wide pH range covering almost all Cr(VI)-contaminated real water samples, thus eliminating the requirement for pH adjustment. Moreover, the nanosheet structure, which is obtained by a facile ultrasonic-assisted self-exfoliation, endows EB-TFB CON with fully exposed active sites and shortened mass transfer channels, and the Cr(VI) adsorption equilibrium can be reached within 15 min with a high adsorption capacity of 280.57 mg·g-1. The proposed Cr(VI) removal mechanism, which is attributed to the synergetic contributions of electrostatic adsorption, ion exchange and chemical reduction, is demonstrated by experiments and theoretical calculations. This work not only provides a general Cr(VI) absorbent without pH limitation, but also presents a paradigm to prepare ionic CONs with relatively constant surface charges.

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.

Ultrafast and selective capture of 99TcO4-/ReO4- from wastewater by hyper-branched quaternary ammonium group-functionalized resin

99Tc primarily exists high mobility in the natural aqueous environment due to its extremely high solubility and non-complexing features, which can easily cause radioactive pollution. We herein report a general strategy for constructing a novel resin (SiPAN-PEI) with multiple positive charges nitrogen, exhibiting ultrafast adsorption kinetics (< 3 min), superior adsorption capacities (463.96 mg g-1), and excellent selectivity in the presence of excess competitive anions, which exceed those of most commercial resins. Moreover, based on impressive structure stability in extreme conditions, SiPAN-PEI can still maintain superior adsorption abilities after suffering irradiation, calcination, and immersion in strong acid. In addition, the separation performance kept excellently after five loading-washing-eluting cycles and the total adsorption ratio can still reach 97 %. Outstandingly, SiPAN-PEI can remove most of ReO4- from simulated nuclear wastewater through a sequential injection automatic separation system and can reduce the concentration of ReO4- to the maximum concentration standard set by the World Health Organization (WHO) in a short time. Leveraging density functional theory calculations and other characteristics clearly elucidated adsorption mechanism of anion-exchange between Cl- and TcO4-/ReO4-. In terms of superior adsorption property, SiPAN-PEI is demonstrated to be a pretty candidate for 99Tc elimination from wastewater.

Synthesis and performance of guanidinium-based cationic organic polymer for the efficient removal of TcO4-/ReO4. JOURNAL OF HAZARDOUS MATERIALS 2024;466:133602. [PMID: 38286051 DOI: 10.1016/j.jhazmat.2024.133602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Cationic organic polymers have found relatively extensive utility for TcO4-/ReO4- removal, but the harsh preparation conditions constrain their practical application. The bifunctional guanidinium-based cationic organic polymer (GBCOP) was successfully and facilely synthesized in benign conditions within 1 h. Batch experiments showed that GBCOP exhibited rapid removal kinetics (1 min, >98.0%) and a substantial removal capacity of 536.8 mg/g for ReO4-. Even in 1000-fold co-existing NO3- anions, the removal efficiency of GBCOP for ReO4- was 74.0%, indicating its good selectivity. Moreover, GBCOP had high removal efficiencies for ReO4- across a wide pH (3.0-10.0) range and presented remarkable stability under the conditions of strong acid and base. GBCOP could be reused four times while removing 80.8% ReO4- from simulated Hanford wastewater. SEM and XPS results revealed that the mechanism of ReO4- removal involved Cl- ion exchange within the channels of GBCOP. Theoretical calculation results supported that existing the strong electrostatic interaction between guanidinium and ReO4-. This dual-function GBCOP material is cost-effective and holds significant potential for large-scale preparation, making it a promising solution for TcO4- removal from nuclear wastewater.

Removal of radionuclide 99Tc from aqueous solution by various adsorbents: A review

Technetium isotope 99Tc is a main radioactive waste produced in the process of nuclear reaction, which has the characteristics of long half-life and strong environmental mobility, and can be bio-accumulated in organisms, resulting in serious threat to human health and ecosystem. Adsorption method is widely used in the field of removing radionuclides from water due to the advantages of high treatment rate, simple and mature industrial application. In this review paper, the recent advances in research and application of various adsorption materials for 99Tc pollution treatment were summarized and analyzed for the first time, including inorganic adsorbents, such as activated carbon, zero-valent iron, metallic minerals, clay minerals, layered double hydroxides (LDHs), tin-based materials, and sulfur-based materials; organic adsorbents, such as porous organic polymers (POPs), covalent-organic frameworks (COFs), metal-organic frameworks (MOFs), and ion exchange resin; and biological adsorbents, such as biopolymers (chitosan, cellulose, alginate), and microbial cells. The performance characteristics and the adsorption kinetics and isotherms of various adsorption materials were discussed. This review could deepen the understanding of the adsorptive removal of 99Tc from aqueous solution, and provide a reference for the future research in this field.

Selective capture of palladium from acid wastewater by thiazole-modified activated carbon: Performance and mechanism

As a kind of scarce metal, palladium is widely used in many chemical industries. It essential to recover palladium from secondary resources, especially acidic media, owing to high content of palladium in secondary wastes and widespread extraction of palladium via strong acids. Chemically modified carbon materials not only have the advantage of activated carbon but also achieve the precise removal of specific pollutants, which is a kind of adsorption material with broad application prospects. In this direction, we report a solid carbon material named AT-C, which is obtained by one-step synthesis of 2-aminothiazoles grafted to the carbon surface by amidation. The present adsorbent delivers a high palladium adsorption capacity of 178.9 mg g-1, and desirable thermal and chemical stability. The uniform presence of abundant sulfur atoms and CO in the porous network enables AT-C to achieve selective absorption and rapid adsorption kinetics of Pd2+ in the complex water mixture containing many competing ions in the acidic pH range. For the strongly acidic leachates of catalysts, AT-C exhibits outstanding stability in cyclic experiments. Meanwhile, the fixed-bed column test indicates that 1076 bed volumes of the feeding streams can be effectively treated. In addition, AT-C exhibits superior adsorption selectivity, and the recovery efficiency of Pd2+ in actual industrial wastewater is 96.6%. This work realizes an efficient, rapid, and selective removal of palladium under acidic conditions, and provides a reference for complex industrial water treatment and resource recovery of precious metals.

Post-Modification of a Robust Covalent Organic Framework for Efficient Sequestration of 99 TcO4 - /ReO4. Chemistry 2023;29:e202302168. [PMID: 37534580 DOI: 10.1002/chem.202302168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Nuclear industry spent fuel reprocessing and some radioactive contamination sites often involve high acidity and salinity environments. Currently developed and reported sorbents in 99 TcO4 - sequestration from the nuclear waste are unstable and show low adsorption efficiency in harsh conditions. To address this issue, we developed a post-synthetic modification strategy by grafting imidazole-based ionic liquids (ILs) onto the backbone of covalent organic framework (COF) via vinyl polymerization. The resultant COF-polyILs sorbent exhibits fast adsorption kinetics (<5 min) and good sorption capacity (388 mg g-1 ) for ReO4 - (a nonradioactive surrogate of 99 TcO4 - ). Outstandingly, COF-polyILs composite shows superior ReO4 - removal even under highly acidic conditions and in the presence of excess competing ions of Hanford low-level radioactive waste stream, benefiting from the stable covalent bonds between the COF and polyILs, mass of imidazole rings, and hydrophobic pores in COF.

A novel cationic covalent organic framework as adsorbent for simultaneous removal of methyl orange and hexavalent chromium

The simultaneous removal of toxic, carcinogenic organic dyes and metal ions from water by one material offers significant advantages when fast, facile, and robust water purification is required. Ionic covalent organic frameworks (ICOFs) have the combined properties of COFs and ion exchange resins and are expected to achieve simultaneous capture of heavy metal ions and organic dyes from water. Herein, a novel guanidinium-based ICOF was synthesized using a solvothermal method. Benefitting from the cationic character, porosity and nanoscale pore size of ICOFs, the adsorbent exhibited high simultaneous adsorption capacities of 290 mg g-1 and 158 mg g-1 for methyl orange (MO) and Cr(vi), respectively, and retained more than 90% adsorption capacity after six adsorption-desorption cycles. In addition, based on dual control of size-exclusion and charge-selection, precisely selective adsorption is achieved towards diverse mixed anionic and cationic pollutants. This strategy offers a practical solution for COFs to confront environmental pollution issues.

Ionic covalent organic framework for selective detection and adsorption of TcO4-/ReO4. Chem Commun (Camb) 2023. [PMID: 37455640 DOI: 10.1039/d3cc02429f]

Herein, a novel fluorescent ionic covalent organic framework (BTTA-BDNP) based on a linked carbazole unit was constructed for the synchronous monitoring and capture of TcO₄^-/ReO₄^-. BTTA-BDNP has a fast fluorescence response time with a low detection limit (66.7 nM) for ReO₄^- (a non-radioactive substitute for TcO₄^-). Meanwhile, the high charge density and hydrophobic skeleton of BTTA-BDNP enable it to exhibit rapid and selective trapping of ReO₄^- in complex environments.

Trifluoromethyl-Functionalized 2D Covalent Organic Framework for High-Resolution Separation of Isomers

Development of novel functional materials for effective isomer separation is of great significance in environmental science, chemical industry, and life science due to the different functions of isomers. However, the similar physicochemical properties of isomers make their separation greatly challenging. Here, we report the fabrication of trifluoromethyl-functionalized 2D covalent organic framework (COF) TpTFMB with 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 1,3,5-triformylphloroglucinol (Tp) for the separation of isomers. TpTFMB was in situ-grown on the inner surface of a capillary for the high-resolution separation of isomers. The introduction of hydroxyl and trifluoromethyl functional groups with uniform distribution in 2D COFs is a powerful tactic to endow TpTFMB with various functions such as hydrogen bonding, dipole interaction, and steric effect. The prepared TpTFMB capillary column enabled the baseline separation of positional isomers such as ethylbenzene and xylene, chlorotoluene, carbon chain isomers such as butylbenzene and ethyl butanoate, and cis-trans isomers 1,3-dichloropropene. The hydrogen-bonding, dipole, and π-π interactions as well as the structure of COF significantly contribute to the isomer separation. This work provides a new strategy for designing functional 2D COFs for the efficient separation of isomers.

Leaf-like ionic covalent organic framework for the highly efficient and selective removal of non-steroidal anti-inflammatory drugs: Adsorption performance and mechanism insights

In recent years, ionic covalent organic frameworks (iCOFs) have become popular for the removal of contaminants from water. Herein, we employed 2-hydroxybenzene-1,3,5-tricarbaldehyde (TFP) and 1,3-diaminoguanidine monohydrochloride (Dg_Cl) to develop a novel leaf-like iCOF (TFP-Dg_Cl) for the highly efficient and selective removal of non-steroidal anti-inflammatory drugs (NSAIDs). The uniformly distributed adsorption sites, suitable pore sizes, and functional groups (hydroxyl groups, guanidinium groups, and aromatic groups) of the TFP-Dg_Cl endowed it with powerful and selective adsorption capacities for NSAIDs. Remarkably, the optimal leaf-like TFP-Dg_Cl demonstrated an excellent maximum adsorption capacity (1100.08 mg/g) for diclofenac sodium (DCF), to the best of our knowledge, the largest adsorption capacity ever achieved for DCF. Further testing under varying environmental conditions such as pH, different types of anions, and multi-component systems confirmed the practical suitability of the TFP-Dg_Cl. Moreover, the prepared TFP-Dg_Cl exhibited exceptional reusability and stability through six adsorption-desorption cycles. Finally, the adsorption mechanisms of NSAIDs on leaf-like TFP-Dg_Cl were confirmed as electrostatic interactions, hydrogen bonding, and π-π interactions. This work significantly supplements to our understanding of iCOFs and provides new insights into the removal of NSAIDs from wastewater.

CTAB assisted evaporation-induced self-assembly to construct imidazolium-based hierarchical porous covalent organic polymers for ReO4-/TcO4- removal

Evaporation-induced self-assembly method (EISA) was a facile and reliable method to synthesize porous materials. Herein, we report a kind of hierarchical porous ionic liquid covalent organic polymers (HPnDNH₂) under cetyltrimethylammonium bromide (CTAB) assisted by EISA for ReO₄^-/TcO₄^- removal. Unlike covalent organic frameworks (COFs), which usually needed to be prepared in a closed environment or with a long reaction time, HPnDNH₂ in this study was prepared within 1 h in an open environment. It was worth noting that CTAB not only served as a soft template for forming pore, but also induced ordered structure, which was verified by SEM, TEM, and Gas sorption. Benefit from its hierarchical pore structure, HPnDNH₂ exhibited higher adsorption capacity (690.0 mg g^-1 for HP1DNH₂ and 808.7 mg g^-1 for HP1.5DNH₂) and faster kinetics for ReO₄^-/TcO₄^- than 1DNH₂ (without employing CTAB). Additionally, the material used to remove TcO₄^- from alkaline nuclear waste was seldom reported, because combining features of alkali resistance and high uptake selectivity was not easy to achieve. In this study, in the case of HP1DNH₂, it displayed outstanding adsorption efficiency toward aqueous ReO₄^-/TcO₄^- in 1 mol L^-1 NaOH solution (92%) and simulated Savannah River Site High-level waste (SRS HLW) melter recycle stream (98%), which could be a potentially excellent nuclear waste adsorbing material.

Super-hydrophilic sulfonate-modified covalent organic framework nanosheets for efficient separation and enrichment of glycopeptides

Highly efficient extraction of glycopeptides prior to mass spectrometry detection is extremely crucial for glycoproteomic research, especially in disease biomarker research. Reported here is the first time by applying two-dimensional (2D) covalent organic framework (COFs) nanosheets for highly efficient enrichment of glycopeptides. Particularly, by incorporating hydrophilic monomers through a bottom-up strategy, the 2D COF nanosheets (denoted as NUS-9) displayed an ultra-high graft density of sulfonic groups and super-hydrophilicity. In addition, because of the large surface area, low steric hindrance, high chemical stability, and abundant accessibility sites of 2D COF nanosheets, NUS-9 exhibited remarkable efficiency for glycopeptide enrichment, involving excellent detection sensitivity (0.01 fmol μL^-1), outstanding enrichment capability, and good enrichment selectivity (1:1500, horseradish peroxidase (HRP) tryptic digest to bovine serum albumin (BSA) tryptic digest), and recovery (92.2 ± 2.0%). Moreover, the NUS-9 was able to unambiguously detect 631 endogenous glycopeptides from human saliva, demonstrating an unparalleled high efficiency in glycopeptide enrichment. Gene ontology analyses of proteins from human saliva enriched by NUS-9 demonstrated its potential for comprehensive glycoproteome analysis.

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

Efficient extraction of radioactive ⁹⁹TcO₄^- from strong acid/base solutions by porous adsorbents is extremely desirable but remains a great challenge. To overcome the challenge, here we report the first example of an olefin-linked cationic covalent organic framework (COF) named BDBI-TMT with excellent acid, base and radiation stability is synthesized by integrating robust imidazolium salt-based linkers with triazine building blocks. BDBI-TMT shows an ultra-fast adsorption kinetics (equilibrium is reached within 1 min) and an excellent ReO₄^- (a non-radioactive surrogate of ⁹⁹TcO₄^-) capture capacity of 726 mg g^-1, which can be attributed to the abundance of precisely tailored imidazolium salt-based units on the highly accessible pore walls of the ordered pore channels. Furthermore, the formation of the highly conjugated bulky alkyl skeleton enhances the hydrophobicity of BDBI-TMT, which significantly improves not only the affinity toward ReO₄^-/⁹⁹TcO₄^- but also the chemical stability, allowing selective and reversible extraction of ReO₄^-/⁹⁹TcO₄^- even under extreme conditions. This work demonstrates the great potential of olefin-linked cationic COFs for ReO₄^-/⁹⁹TcO₄^- extraction, providing a new avenue to construct high-performance porous adsorbents for radionuclide remediation.

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.

Porous Covalent Organic Framework Based Hydrogen-Bond Nanotrap for the Precise Recognition and Separation of Gold

Utilizing weak interactions to effectively recover and separate precious metals in solution is of great importance but the practice remains a challenge. Herein, we report a novel strategy to achieve precise recognition and separation of gold by regulating the hydrogen-bond (H-bond) nanotrap within the pore of covalent organic frameworks (COFs). It is found that both COF-HNU25 and COF-HNU26 can efficiently capture Au^III with fast kinetics, high selectivity, and uptake capacity. In particular, the COF-HNU25 with the high density of H-bond nanotraps exhibits an excellent gold uptake capacity of 1725 mg g^-1 , which is significantly higher than that (219 mg g^-1 ) of its isostructural COF (COF-42) without H-bond nanostrap in the pores. Importantly, the uptake capacity is strongly correlated to the number of H-bonds between phenolic OH in the COF and [AuCl₄ ]^- in water, and multiple H-bond interactions are the key driving force for the excellent gold recovery and reusability of the adsorbent.

Synthesis of cationic polymer decorated with halogen for highly efficient trapping 99TcO4-/ReO4. JOURNAL OF HAZARDOUS MATERIALS 2023;443:130325. [PMID: 36372023 DOI: 10.1016/j.jhazmat.2022.130325]

The elimination of anion is of great importance from radioactive nuclear waste containing ⁹⁹TcO₄^- by rationally designing anion-scavenging materials with high density of charge and more accessible adsorption sites. Herein, a tailor-made cationic organic polymer with donor-acceptor (D-A) structure, namely TrDCPN, was successfully synthesized by rationally modifying the benzimidazole unit for efficient trapping the perrhenate (ReO₄^-) as a ⁹⁹Tc surrogate. Systematic control of the skeleton affect enables the material to integrate a variety of features, surmounting the long-term challenge of ⁹⁹TcO₄^-/ReO₄^- remediation under extreme conditions of high acid/base and high ionic strength. Furthermore, the TrDCPN shows excellent affinity toward ReO₄^- in the existence of large excess of competitive anions (SO₄^2-, NO₃^- and PO₄^3-etc.) as well as promising reusability for trapping ReO₄^-. The excellent stability and separation were derived from the introduction of large conjugated modules, triazine core and hydrophobic. More importantly, the synthetic cationic organic polymer with D-A feature was first proved that the introduction of halogen can effectively enhance the backbone charge, and increase the adsorption capacity by synergy of ion exchange, electrostatic interaction and δ hole-anion interaction. The adsorption capacity of TrDCPN can be up to 420.3 mg/g and reach equilibrium within 20 min. It is noteworthy that TrDCPN successfully immobilizes ReO₄^- from simulated Hanford waste with a high separation efficiency of 93 %, providing a new paradigm for material design to dispose of the problem of radioactive pollutants in the environment.

Advanced Covalent Organic Framework-Based Membranes for Recovery of Ionic Resources

Membrane technology has shown a viable potential in conversion of liquid-waste or high-salt streams to fresh waters and resources. However, the non-adjustability pore size of traditional membranes limits the application of ion capture due to their low selectivity for target ions. Recently, covalent organic frameworks (COFs) have become a promising candidate for construction of advanced ion separation membranes for ion resource recovery due to their low density, large surface area, tunable channel structure, and tailored functionality. This tutorial review aims to analyze and summarize the progress in understanding ion capture mechanisms, preparation processes, and applications of COF-based membranes. First, the design principles for target ion selectivity are illustrated in terms of theoretical simulation of ions transport in COFs, and key properties for ion selectivity of COFs and COF-based membranes. Next, the fabrication methods of diverse COF-based membranes are classified into pure COF membranes, COF continuous membranes, and COF mixed matrix membranes. Finally, current applications of COF-based membranes are highlighted: desalination, extraction, removal of toxic metal ions, radionuclides and lithium, and acid recovery. This review presents promising approaches for design, preparation, and application of COF-based membranes in ion selectivity for recovery of ionic resources.

Fabricating Industry-Compatible Olefin-Linked COF Resins for Oxoanion Pollutant Scavenging

Large-scale and low-cost synthesis of covalent organic frameworks (COFs) to meet the demands of industrial application remains formidably challenge. Here we report using 2,4,6-collidine as monomer to produce a series of highly crystalline olefin-linked COFs by a melt polymerization method. This method enables the kilogram-scale fabrication of self-shaped monolithic robust foams. The afforded COFs possess extremely low cost (<50 USD/kg), superior to all the reported COFs. Furthermore, using one-pot or post-modification methods can conveniently transform neutral COFs to ionic COFs, which can be applied as highly efficient ion-exchange sorbents for scavenging oxoanion pollutants. Remarkably, the superior adsorption capacity of a model oxoanion (ReO₄ ^- ) is the highest among crystalline porous materials reported so far. This work not only expands the scopes of olefin-linked COFs but also enlightens the route for the industrial production of crystalline ion exchange sorbents.

An ionic vinylene-linked three-dimensional covalent organic framework for selective and efficient trapping of ReO4- or 99TcO4. Nat Commun 2022;13:7621. [PMID: 36494388 PMCID: PMC9734744 DOI: 10.1038/s41467-022-35435-7]

The synthesis of ionic olefin linked three-dimensional covalent organic frameworks (3D COFs) is greatly challenging given the hardness of the formation of stable carbon-carbon double bonds (-C = C-). Herein, we report a general strategy for designing porous positively charged sp² carbon-linked 3D COFs through the Aldol condensation promoted by quaternization. The obtained 3D COFs, namely TFPM-PZI and TAPM-PZI, showed impressive chemical stability. Furthermore, the positively charged frameworks with regular porosity endow 3D ionic COFs with selective capture radioactive ReO₄^-/TcO₄^- and great removal efficiency in simulated Hanford waste. This research not only broadens the category of 3D COFs but also promotes the application of COFs as efficient functional materials.

Aqueous Two-Phase Interfacial Assembly of COF Membranes for Water Desalination

Aqueous two-phase system features with ultralow interfacial tension and thick interfacial region, affording unique confined space for membrane assembly. Here, for the first time, an aqueous two-phase interfacial assembly method is proposed to fabricate covalent organic framework (COF) membranes. The aqueous solution containing polyethylene glycol and dextran undergoes segregated phase separation into two water-rich phases. By respectively distributing aldehyde and amine monomers into two aqueous phases, a series of COF membranes are fabricated at water-water interface. The resultant membranes exhibit high NaCl rejection of 93.0-93.6% and water permeance reaching 1.7-3.7 L m^-2 h^-1 bar^-1, superior to most water desalination membranes. Interestingly, the interfacial tension is found to have pronounced effect on membrane structures. The appropriate interfacial tension range (0.1-1.0 mN m^-1) leads to the tight and intact COF membranes. Furthermore, the method is extended to the fabrication of other COF and metal-organic polymer membranes. This work is the first exploitation of fabricating membranes in all-aqueous system, confering a green and generic method for advanced membrane manufacturing.

Covalent Organic Frameworks with Ionic Liquid-Moieties (ILCOFs): Structures, Synthesis, and CO2 Conversion

CO₂, an acidic gas, is usually emitted from the combustion of fossil fuels and leads to the formation of acid rain and greenhouse effects. CO₂ can be used to produce kinds of value-added chemicals from a viewpoint based on carbon capture, utilization, and storage (CCUS). With the combination of unique structures and properties of ionic liquids (ILs) and covalent organic frameworks (COFs), covalent organic frameworks with ionic liquid-moieties (ILCOFs) have been developed as a kind of novel and efficient sorbent, catalyst, and electrolyte since 2016. In this critical review, we first focus on the structures and synthesis of different kinds of ILCOFs materials, including ILCOFs with IL moieties located on the main linkers, on the nodes, and on the side chains. We then discuss the ILCOFs for CO₂ capture and conversion, including the reduction and cycloaddition of CO₂. Finally, future directions and prospects for ILCOFs are outlined. This review is beneficial for academic researchers in obtaining an overall understanding of ILCOFs and their application of CO₂ conversion. This work will open a door to develop novel ILCOFs materials for the capture, separation, and utilization of other typical acid, basic, or neutral gases such as SO₂, H₂S, NOx, NH₃, and so on.

3D Ionic Olefin-Linked Conjugated Microporous Polymers for Selective Detection and Removal of TcO4-/ReO4- from Wastewater

Technetium (⁹⁹Tc) is a highly toxic radioactive nuclear wastewater contaminant. Real-time detection of ⁹⁹Tc is very difficult due to its difficult-to-complex nature. Herein, a novel three-dimensional ionic olefin-linked conjugated microporous polymer (TFPM-EP-Br) is constructed using tetrakis(4-aldehyde phenyl)methane (TFPM) as the central monomer. The unique cationic cavity and highly hydrophobic framework enable TFPM-EP-Br to act as a fluorescent sensor for TcO₄^-. The fluorophores of TFPM-EP-Br can be quenched due to electron transfer from TFPM-EP-Br to TcO₄^- and the formation of strongly nonfluorescent complexes. Meanwhile, the regular pore channels are beneficial for the fast mass transfer of TcO₄^-, resulting in an ultrafast response time (less than 2 s) with an ultralow detection limit (33.3 nM). In addition, the ultrahigh specific surface area enables TFPM-EP-Br to combine the ability to synergistically detect and remove radioactive ⁹⁹Tc. From this perspective, the novel conjugated microporous polymer has made a breakthrough in the detection and extraction of radioactive contaminants.

Fluorescence turn on amine detection in a cationic covalent organic framework

Ionic covalent organic frameworks (iCOFs) are new examples of porous materials and have shown great potential for various applications. When functionalized with suitable emission sites, guest uptake via the ionic moieties of iCOFs can cause a significant change in luminescence, making them excellent candidates for chemosensors. In here, we present a luminescence sensor in the form of an ionic covalent organic framework (TGH⁺•PD) composed of guanidinium and phenanthroline moieties for the detection of ammonia and primary aliphatic amines. TGH⁺•PD exhibits strong emission enhancement in the presence of selective primary amines due to the suppression of intramolecular charge transfer (ICT) with an ultra-low detection limit of 1.2 × 10^‒7 M for ammonia. The presence of ionic moieties makes TGH⁺•PD highly dispersible in water, while deprotonation of the guanidinium moiety by amines restricts its ICT process and signals their presence by enhanced fluorescence emission. The presence of ordered pore walls introduces size selectivity among analyte molecules, and the iCOF has been successfully used to monitor meat products that release biogenic amine vapors upon decomposition due to improper storage.

Ionic covalent organic frameworks (iCOFs) are new examples of porous materials and show great potential for various applications. Here, the authors demonstrate functionalization of an iCOFs with suitable emission sites and application as chemosensor for amine detection with high sensitivity which can be used to monitor meat spoilage.

Aminomethylpyridine isomers functionalized cellulose microspheres for TcO4-/ReO4- uptake: Structure-properties relationship and their application in different aquatic systems

Technetium-99 (⁹⁹Tc) is a long-lived radioactive nuclide that poses great threat to environment, hence selective removal of ⁹⁹Tc from aquatic system is always an issue. Aminomethylpyridine (AMP) equipped with pyridine and amino, is a promising receptor for TcO₄^- and its surrogate ReO₄^-, thus it is of interest to explore and understand the structure-properties relationship of ReO₄^- adsorption related to n-AMP structure that differ in amino methyl position. In this work, three n-AMP functionalized cellulose microspheres (n-AMPR, n = 2, 3, 4) were synthesized and employed for TcO₄^-/ReO₄^- uptake. The effect of aminomethyl position on adsorption properties of n-AMPR for ReO₄^- were investigated and compared. Adsorption kinetics and adsorption isotherm showed that adsorption speed and adsorption capacity were in order of 3-AMPR > 2-AMPR > 4-AMPR. DFT calculation verified that the adsorption of ReO₄^- by n-AMPR was attributed to electrostatic interaction and hydrogen bonding interaction, the order of adsorption abilities of n-AMPR was due to that steric effect and hydrogen bond collaborated in stabilizing n-AMPR-ReO₄^- complexes. The column experiments demonstrated that 3-AMPR can be selectively remove ReO₄^- from simulated groundwater. More importantly, ⁹⁹Tc column experiments showed that 3-AMPR had a better ability for actual radioactive TcO₄^-.

A Novel Functionalized Ionic Liquid for Highly Selective Extraction of TcO4. Inorg Chem 2022;61:10609-10617. [PMID: 35758888 DOI: 10.1021/acs.inorgchem.2c01775]

Due to the highly acidic and high-salinity nature of the high-level radioactive waste liquid (HLLW), selective extraction of TcO₄^- from HLLW remains to be a challenging task. Traditional anion exchangers show low selectivity and unsatisfactory extraction performance due to the lack of functional groups that can interact strongly with TcO₄^-. In this work, a tailor-made binding site was constructed by decorating two acetamide functional groups on imidazolium cation to fabricate a new Tc separation material, which exhibits high selectivity. Unlike most reported Tc separation materials, which can only perform well under low acidic, neutral, or alkaline conditions, this material still has good extraction performance in highly acidic solutions. In the simulated high-level waste liquid of 3 M nitric acid, the extraction efficiency of 0.5 mol/L organic phase for Tc can reach 96.5% through the first-stage extraction. Our theoretical simulations suggest that ReO₄^-/TcO₄^- anions were adsorbed on the top of the imidazolium ring during the extraction process, with p-π and p-p interactions acting as the driving forces.

Covalent Organic Frameworks-Based Membranes as Promising Modalities from Preparation to Separation Applications: An Overview

Covalent organic frameworks (COFs) are a promising class of porous crystalline materials made up of covalently connected and periodically protracted network topologies through organic linkers. The tailorability of organic linker and intrinsic structures endow COFs with a tunable porosity and structure, low density, facilely-tailored functionality, and large surface area, attracting increasing amount of interests in variety of research areas of membrane separations. COF-based membranes have spawned a slew of new research projects, ranging from fabrication methodologies to separation applications. Herein, we tried to emphasis the major developments in the synthetic approaches of COFs based membranes for a variety of separation applications such as, separation of gaseous mixtures, water treatment as well as separation of isomeric and chiral organic compounds. The proposed methods for fabricating COF-based continuous membranes and columns for real world applications are also thoroughly explored. Finally, a viewpoint on the future directions and remaining challenges for COF research in the area of separation is provided.

Efficient Selective Removal of Radionuclides by Sorption and Catalytic Reduction Using Nanomaterials

With the fast development of industry and nuclear energy, large amounts of different radionuclides are inevitably released into the environment. The efficient solidification or elimination of radionuclides is thereby crucial to environmental pollution and human health because of the radioactive hazardous of long-lived radionuclides. The properties of negatively or positively charged radionuclides are quite different, which informs the difficulty of simultaneous elimination of the radionuclides. Herein, we summarized recent works about the selective sorption or catalytic reduction of target radionuclides using different kinds of nanomaterials, such as carbon-based nanomaterials, metal–organic frameworks, and covalent organic frameworks, and their interaction mechanisms are discussed in detail on the basis of batch sorption results, spectroscopy analysis and computational calculations. The sorption-photocatalytic/electrocatalytic reduction of radionuclides from high valent to low valent is an efficient strategy for in situ solidification/immobilization of radionuclides. The special functional groups for the high complexation of target radionuclides and the controlled structures of nanomaterials can selectively bind radionuclides from complicated systems. The challenges and future perspective are finally described, summarized, and discussed.

Enhanced removal of Cr(VI) by cation functionalized bamboo hydrochar

Chemical modification on hydrochars can significantly improve their ability of removing heavy metal ions from wastewater, but so far no research has focused on the chemical modification through free radical reaction. In this work, a cation functionalized hydrochar (CFHC) bearing - N⁺H₂R was synthesized by grafting-polymerization of glycidyl methacrylate (GMA) onto bamboo hydrochar under initiation by benzoyl peroxide, followed by the amination with the introduced epoxy group and diethylenetriamine and a subsequent hydrochloric acid treatment. The resulted CFHC exhibited a superior removal capacity of 424.09 mg·g^-1 for Cr(VI), and the highest sorption occurred at pH of 2. Combining a series of characterizations and tests, it was concluded that the sorption conformed to the pseudo-second-order and Freundlich equations, indicating a multilayer chemisorption process that mainly driven by electrostatic reaction, reduction, and surface complexation. This research proved that a free radical polymerization treatment could effectively transform hydrochars into super adsorbents for wastewater treatment.