Facile preparation of uniform-sized covalent organic framework nanoflowers as versatile sample-pretreatment platforms for sensitive and specific determination of hazardous substances

Tuning the planarity of molecularly imprinted covalent organic frameworks for selective extraction of ochratoxin A in alcohol samples

Here, we report a monomer planarity modulation strategy for room-temperature constructing molecularly imprinted-covalent organic frameworks (MI-COFs) for selective extraction of ochratoxin A (OTA). 2,4,6-triformylphloroglucinol (Tp) was used as basic building block, while three amino monomers with different planarity were employed as modulators to explore the effect of planarity on the selectivity of MI-COFs. The MI-TpTapa constructed from Tp and the lowest planarity of monomer Tapa gave the highest selectivity for OTA, and was further used as the adsorbent for dispersed-solid phase extraction (DSPE) of OTA in alcohol samples. Coupling MI-TpTapa based DSPE with high-performance liquid chromatography allowed the matrix-effect free determination of OTA in alcohol samples with the limit of detection of 0.023 μg kg-1 and the recoveries of 91.4-97.6%. The relative standard deviation (RSD, n = 6) of intra and inter day was <3.2%. This work provides a new way to construct MI-COFs for selective extraction of hazardous targets.

Engineering of molecularly imprinted cavity within 3D covalent organic frameworks: An innovation for enhanced extraction and removal of microcystins

The scarcity of selective adsorbents for efficient extraction and removal of microcystins (MCs) from complex samples greatly limits the precise detection and effective control of MCs. Three-dimensional covalent organic frameworks (3D COFs), characterized by their large specific surface areas and highly ordered rigid structure, are promising candidates, but suffer from lack of specific recognition. Herein, we design to engineer molecularly imprinted cavities within 3D COFs via molecularly imprinted technology, creating a novel adsorbent with exceptional selectivity, kinetics and capacity for the efficient extraction and removal of MCs. As proof-of-concept, a new CC bond-containing 3D COF, designated JNU-7, is designed and prepared for copolymerization with methacrylic acid, the pseudo template L-arginine and ethylene dimethacrylate to yield the JNU-7 based molecularly imprinted polymer (JNU-7-MIP). The JNU-7-MIP exhibits a great adsorption capacity (156 mg g-1) for L-arginine. Subsequently, the JNU-7-MIP based solid-phase extraction coupled with high performance liquid chromatography-mass spectrometry achieves low detection limit of 0.008 ng mL-1, wide linear range of 0.025-100 ng mL-1, high enrichment factor of 186, rapid extraction of 10 min, and good recoveries of 92.4%-106.5% for MC-LR. Moreover, the JNU-7-MIP can rapidly remove the MC-LR from 1 mg L-1 to levels (0.26-0.35 μg L-1) lower than the WHO recommended limit for drinking water (1 μg L-1). This work reveals the considerable potential of 3D COF based MIPs as promising adsorbents for the extraction and removal of contaminants in complex real samples.

High-Performance enrichment and sensitive analysis of bisphenol and its analogues in water and milk using a novel Ni-Based cationic Metal-Organic framework

A novel cationic metal-organic framework (iMOF-Ni) was designed and synthesized by a solvothermal method. It was fabricated as a solid-phase extraction (SPE) cartridge and exhibited high adsorption performance for Bisphenols (BPs). The theoretical simulation demonstrated that the adsorption mechanism between iMOF-Ni and BPs was attributed to cation-π bonding, π-π interaction, and electrostatic interactions. Under optimized SPE, a method for analyzing BPs was established by combining high-performance liquid chromatography-diode array detection (HPLC-DAD). The developed method has good linearity (R2 ≥ 0.994), low detection limits (0.07-0.16 ng/mL), and good reproducibility (1.72-6.35 %, n = 6). The applicability of the method was further evaluated by analyzing water and milk samples. Recoveries of four BPs in spiked samples were from 72.2 % to 96.6 %.

Length-controlled hydrophobic CF3-COF as a highly efficient absorbent coating for dual-mode solid-phase microextraction of sixteen polycyclic aromatic hydrocarbons in water samples

Polycyclic aromatic hydrocarbons (PAHs), a group of seriously hazardous environmental contaminants, have attracted extensive attention due to their carcinogenicity, genotoxicity, mutagenicity, and ubiquity. In this work, the excellent hydrophobic trifluoromethyl-enriched covalent organic framework (CF3-COF) was designed and synthesized as coating of solid-phase microextraction (SPME). The CF3-COF offered a high adsorption selectivity for PAHs, which could be attributed to the multiple interactions between the CF3-COF and PAHs, including hydrophobicity interaction, π-π and H bond interactions. Furthermore, headspace (HS) and direct immersion (DI) dual-mode solid-phase microextraction (HS/DI-SPME) were innovatively integrated as a dual-mode extraction by varying the length of SPME coating on stainless-steel, which could simultaneously and efficiently extract 16 PAHs with different volatile. Amazingly, the proposed strategy achieved fast adsorption for PAHs and shortened the adsorption equilibrium time to 15 min. By further integrating with gas chromatography tandem mass spectrometry (GC-MS/MS), PAHs could be detected in the range of 0.008-0.16 ng mL-1 with a quantitative limit of 0.029-0.47 ng mL-1, respectively. The recoveries of PAHs in water samples ranged from 80.84 to 117.67 %. This work indicates that the dual-mode CF3-COF-SPME is a promising candidate for the enrichment of multiple hazardous substances in complicated samples.

Hydroxylated hierarchical flower-like COF for solid-phase extraction of adrenergic receptor agonists in milk

A new detection platform based on a hydroxylated covalent organic framework (COF) integrated with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was constructed and used for detecting adrenergic receptor agonists (ARAs) residues in milk. The hydroxylated COF was prepared by polymerization of tris(4-aminophenyl)amine and 1,3,5-tris(4-formyl-3-hydroxyphenyl)benzene and applied to solid-phase extraction (SPE) of ARAs. This hydroxylated COF was featured with hierarchical flower-like morphology, easy preparation, and copious active adsorption sites. The adsorption model fittings and molecular simulation were applied to explore the potential adsorption mechanism. This detection platform was suitable for detecting four α2- and five β2-ARAs residues in milk. The linear ranges of the ARAs were from 0.25 to 50 µg·kg-1; the intra-day and the inter-day repeatability were in the range 2.9-7.9% and 2.0-10.1%, respectively. This work demonstrates this hydroxylated COF has great potential as SPE cartridge packing, and provides a new way to determine ARAs residues in milk.

Imprinted covalent organic frameworks solid-phase microextraction fiber for in vivo monitoring of acidic per- and polyfluoroalkyl substances in live aloe

Per- and polyfluoroalkyl substances (PFASs) can lead to risks associated with animal and human health through the transfer along food chains. It is confirmed that PFASs can be transported to each part of plants after taken up by the roots. To better elucidate the underlying mechanisms for such exposure, it is highly valuable to develop analytical capabilities for in vivo monitoring of PFASs in live plants. In this work, a novel imprinted covalent organic frameworks (CMIP) solid-phase microextraction coupled with ultra-performance liquid chromatography-tandem mass spectrometry was developed with low limits of detection for six acidic PFASs (0.1-0.3 ng g-1) and used for in vivo monitoring in live aloe. The CMIP coating shows good precision (RSD of intra and inter ≤9.6 % and 10.2 %, respectively) and possesses much higher extraction efficiency than the commercial coatings. After cultivating aloe in soil spiked PFASs, the in vivo assays gave a wealth of information, including steady-state concentrations, translocation factors, elimination rate constants, and half-life of PFASs. The in vivo tracing method for live plants can provide much needed and unique information to evaluate the risk of PFASs, which are very important for the safety of agriculture production.

Pore Size Adjustment Strategy for the Fabrication of Molecularly Imprinted Covalent Organic Framework Nanospheres at Room Temperature for Selective Extraction of Zearalenone in Cereal Samples

Covalent organic frameworks (COFs) are attractive adsorbents for sample pretreatment due to their unique structure and properties. However, the selectivity of COFs for the extraction of hazardous compounds is still limited due to the lack of specific interactions between COFs and targets. Herein, we report a pore size adjustment strategy for room-temperature synthesis of molecularly imprinted COF (MICOF) for selective extraction of zearalenone (ZEN) in complex food samples. The three-dimensional building block tetra(4-aminophenyl) methane was used as a functional monomer, while dialdehyde monomers with different numbers of benzene ring were used to adjust the pore size of MICOF to match with the size of ZEN molecules. The prepared MICOF gave the largest adsorption capacity of 177.2 mg g-1 and the highest imprinting factor of 10.1 for ZEN so far. MICOF was used as the adsorbent for dispersed solid-phase extraction in combination with high-performance liquid chromatography for the determination of trace ZEN in cereals. The high selectivity of the developed method allows simple aqueous standard calibration for the matrix effect-free determination of ZEN in food samples. The limit of detection and the recoveries of the developed method were 0.21 μg kg-1 and 93.7-101.4%, respectively. The precision for the determination of ZEN was less than 3.8% (RSD, n = 6). The developed method is promising for the selective determination of ZEN in complex matrices.

Fluorine-functionalized covalent organic framework as efficient solid phase extraction sorbent for adsorption of aflatoxins in nuts

In this study, a new fluorine-functionalized covalent organic framework (F-COF) was designed and fabricated by the direct polycondensation of tris(4-aminophenyl)amine and 2,3,5,6-tetra-fluoroterephthaldehyde for the first time. F-COF exhibited a remarkably enhanced adsorption capability compared with that of the fluorine-free COF. The favorable adsorption of aflatoxins was attributed to multiple interactions including pseudo hydrogen bond, F-O, π-π, F-π interactions and hydrophobic interactions between F-COF and aflatoxins. By coupling F-COF based solid phase extraction with high-performance liquid chromatography equipped with fluorescence detector, a rapid and sensitive method for determining aflatoxins (aflatoxin B1, B2, G1 and G2) in nuts (peanuts and pistachios) was established. Under optimal conditions (35 mg F-COF, 100 mL sample solution, 3 mL min-1 as sample loading rate, pH<7, 0.2 mL acetonitrile as desorption solvent), the limits of detection for aflatoxins were 0.02-0.30 ng g-1. The linear range was 0.08-16.0 ng g-1 and the recoveries of the F-COF-based method were 83.5-114 % with relative standard deviations less than 8.0 %.

Controllable synthesis of uniform flower-shaped covalent organic framework microspheres as absorbent for solid-phase extraction of trace 2,4-dichlorophenol

Controllable synthesis of micro-flower covalent organic frameworks (MFCOFs) with controllable size, monodisperse, spherical, and beautiful flower shape was realized by using 2,5-diformylfuran (DFF) and p-phenylenediamine (p-PDA) as building blocks at room temperature. High-quality MFCOFs (5 - 7 μm) were synthesized by controlling the kind of solvent, amounts of monomers, catalyst content, and reaction time. The synthesized MFCOFs possessed uniform mesopores deriving from the intrinsic pores of frameworks and wide-distributed pores belonging to the gap between the petals. The MFCOFs-packed solid-phase extraction (SPE) column shows adsorption capacity of about 8.85 mg g-1 for 2,4-dichlorophenol (2,4-DCP). The MFCOF-based SPE combined with the HPLC method was established for the determination of 2,4-DCP in environmental water. The linear range of this method is 20-1000 ng mL-1 (R2 > 0.9994), and limit of detection (S/N = 3) is 10.9 ng mL-1. Spiked recoveries were 94.3-98.5% with relative standard deviations lower than 2.3%.

Synthesis of composite materials combining magnetic metal-organic frameworks and conjugated organic frameworks for selective extraction of carbendazim and thiabendazole residues from Chinese herbal medicine samples

A magnetic metal-organic framework MIL-68(Al) and a covalent organic framework were used as magnetic solid-phase extraction (MSPE) adsorbents in combination with high-performance liquid chromatography ultraviolet detection (HPLC-UV) to detect carbendazim (CBZ) and thiabendazole (TBZ). The main parameters affecting the extraction in the MSPE process were studied and optimized. Fe3O4@MIL-68(Al) coated with 1,3,5-tris(4-aminophenyl)benzene and terephthaldehyde (Fe3O4@MIL-68(Al)@TAPB-PDA-COF) was analyzed and verified. The material was proven to be suitable for adsorbing CBZ and TBZ. Various adsorption models were used to study its adsorption mechanism. The adsorption results were in good agreement with the pseudo-second-order kinetic model and Langmuir isotherm model. The maximum adsorption capacities of Fe3O4@MIL-68(Al)@TAPB-PDA-COF over CBZ and TBZ were 54.24 and 67.87 mg g-1, respectively, and the equilibrium adsorption time was 200 min. Fe3O4@MIL-68(Al)@TAPB-PDA-COF with excellent recyclability showed higher adsorption capacity and selectivity. A method based on Fe3O4@MIL-68(Al)@TAPB-PDA-COF combined with HPLC-UV was established under the optimal extraction conditions and used to separate and detect trace imidazole drugs in Chinese herbal samples, achieving a low limit of detection (0.65-1.30 μg L-1) with excellent linear correlation (r > 0.999). The recovery rate and relative standard deviation were 86.05-99.78 % and 0.15-4.90 %, respectively. Therefore, the Fe3O4@MIL-68@TAPB-PDA-COF can be regarded as an effective adsorbent for the pretreatment of CBZ and TBZ drugs in Chinese herbal samples.

Surface imprinted-covalent organic frameworks for efficient solid-phase extraction of fluoroquinolones in food samples

Molecularly imprinting on covalent organic frameworks (MI-COF) is a promising way to prepare selective adsorbents for effective extraction of fluoroquinolones (FQs). However, the unstable framework structure and complex imprinting process are challenging for the construction of MI-COF. Here, we report a facile surface imprinting approach with dopamine to generate imprinted cavities on the surface of irreversible COF for highly efficient extraction of FQs in food samples. The irreversible-linked COF was fabricated from hexahydroxytriphenylene and tetrafluorophthalonitrile to ensure COF stability. Moreover, the introduction of dopamine surface imprinted polymer into COF provides abundant imprinted sites and endows excellent selectivity for FQs recognition against other antibiotics. Taking enrofloxacin as a template molecule, the prepared MI-COF gave an exceptional adsorption capacity of 581 mg g-1, a 2.2-fold enhancement of adsorption capacity compared with nonimprinted COF. The MI-COF was further explored as adsorbent to develop a novel solid-phase extraction method coupled with high-performance liquid chromatography for the simultaneous determination of enrofloxacin, norfloxacin and ciprofloxacin. The developed method gave the low limits of detection at 0.003-0.05 ng mL-1, high precision with relative standard deviations less than 3.5%. The recoveries of spiked FQs in food samples ranged from 80.4% to 110.7%.

Magnetically driven nanorobots based on peptides nanodots with tunable photoluminescence for rapid scavenging reactive α-dicarbonyl species and effective blocking of advanced glycation end products

The present work constructed magnetically driven nanorobots by conjugating the photoluminescent β-alanine-histidine (β-AH) nanodots to superparamagnetic nanoparticles (SPNPs) for simultaneously sensitive determination and fast trapping RDS in food processing, achieving efficient regulation of advanced glycation end products (AGEs) risk. Bio-derivative β-AH nanodots with orderly self-assembly nanostructure and tunable photoluminescent properties served as both biorecognition elements to effectively bind and scavenge the reactive α-dicarbonyl species (RDS), as well as the indicator with sensitive fluorescence response in the food matrix. The magnetically driven nanorobots with excellent biosafety of endogenous dipeptides displayed a high binding capacity of 80.12 mg g^-1 with ultrafast equilibrium time. Furthermore, the magnetically driven nanorobots achieved rapid removal of the RDS with the manipulation of the external magnetic field, which enabled intercepting AGEs generation without byproducts residual as well as ease-of-operation. This work provided a promising strategy with biosafety and versatility for both accurate determination and efficient removal of hazards.

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.

Rational design, structure properties, and synthesis strategies of dual-pore covalent organic frameworks (COFs) for potent applications: A review

Dual-pore covalent organic frameworks (COFs) offer a molecular scaffold for introducing building blocks into periodically organized polygonal skeletons to produce fascinating structural features. The rapid development of this material has attracted intensive interest from researchers with diverse expertise. This review selects the leading scientific findings about dual-pore COFs and highlights their functions and perspectives on design, structure properties, and synthesis strategies. Dual-pore COFs, as newly hetero-pore COFs by integrating particular pores into one polygonal skeleton, have been compared to conventional COFs. Dual-pore COFs display hierarchical/heterogeneous porosities and homogeneous porosity, which endow them with exceptional features involving mass diffusion, charge transfer, and large surface area with abundant active sites. Additionally, the strategic dual-pore design by opting for different approaches, such as integration of [D_2h + C₂] symmetries, kagome-type lattices, and other symmetric arrangements of monomers, are inclusively discussed. Identification and construction of dual-pores in COFs via optimal synthetic methods, such as desymmetrization, multiple linking sites, and orthogonal reactions, are highlighted as the primary pore engineering routes to simultaneously regulate the growth and alter the characteristics of COFs for promising applications. Lastly, a focused discussion on various challenges and critical fundamentals of dual-pore engineering is successfully outlined, with potential prospects of introducing dual-pore in COFs.