Covalent organic frameworks for environmental analysis

Facile preparation of covalent-organic framework composites for magnetic solid-phase extraction of naphthaleneacetic acid in food prior to HPLC-UV analysis

Novel magnetic covalent organic frameworks (COFs) were prepared by one-pot synthetic strategy and employed as an efficient adsorbent for magnetic solid-phase extraction (MSPE) of naphthaleneacetic acid (NAA) in food samples. Depending on the predesigned the hydrogen bonding, π-π and hydrophobic interactions of magnetic COFs, the efficient and selective extraction process for NAA was achieved within 15 min. The magnetic COFs adsorbent combined with HPLC-UV was devoted to develop a novel quantitative method for NAA in complex food. The method afforded good coefficient in range of 0.002-10.0 µg mL-1 and low limit of detection was 0.0006 µg mL-1. And the newly established method afforded less adsorbent consumption, wider linearity and lower LODs than the reported analytical methods. Ultimately, the method was successfully applied to determine NAA in fresh pear, tomato and peach juice. The magnetic COFs based MSPE coupled with HPLC-UV method provided a simple, efficient and dependable alternative to monitor trace NAA in food samples.

Magnetic covalent organic frameworks as sorbents in the chromatographic analysis of environmental organic pollutants

Covalent organic frameworks (COFs) are featured with large specific surface areas, good thermal stability, and abundant pores. These properties are exactly what the sorbents used for extraction or adsorption of interest substances are desired with. While, the low density and hydrophobicity of COFs often makes them difficult to be dispersed evenly and recovered from the aqueous solution. Magnetic covalent organic frameworks (MCOFs) inherit magnetic property of the magnetic particles and porous structure of COFs. They have improved dispersity in aqueous solution and phase separation can be rapidly achieved via external magnetic fields. This review summarized the synthesis strategies for MCOFs, and their application in trace environmental organic pollutants analysis by chromatography techniques. The selection of COFs types and modification with active groups for a certain adsorption purpose is discussed, along with the exploration of adsorption mechanisms, which is beneficial for the design and synthesis of MCOFs.

Internal Superwettability Inversion of a COF-Encapsulated Melamine Sponge Prepared by a One-Step Synthesis at Room Temperature

Superwettable materials have been attracting attention due to their unique properties, showing great application prospects in a variety of fields including oil-water separation. Herein, a kind of covalent organic framework (COF)-encapsulated melamine sponge (MS) capable of internal superwettability inversion is prepared by a one-step synthesis at room temperature. COF is produced in situ on the skeleton of MS, which is favorable for practical application, and the prepared COF-encapsulated sponge (MS@COF) exhibits superhydrophobicity (water contact angle of about 157.0°) due to the rough surface provided by the micro/nanostructure of COF. More importantly, MS@COF displays reversibly superhydrophilicity by simple prewetting, achieving superwettability inversion conveniently, unlike the previous switchable materials that rely on external conditions. This facile intrinsic superwettability inversion greatly enriches the application prospects of this kind of smart sponge.

Construction of a Bifunctional Redox-Site Conjugated Covalent-Organic Framework for Photoinduced Precision Trapping of Uranyl Ions

The performance of covalent-organic frameworks (COFs) for the photocatalytic extraction of uranium is greatly limited by the number of adsorption sites. Herein, inspired by electronegative redox reactions, we designed a nitrogen-oxygen rich pyrazine connected COF (TQY-COF) with multiple redox sites as a platform for extracting uranium via combining superaffinity and enhanced photoinduction. The preorganized bisnitrogen-bisoxygen donor configuration on TQY-COF is entirely matched with the typical geometric coordination of hexavalent uranyl ions, which demonstrates high affinity (tetra-coordination). In addition, the presence of the carbonyl group and pyrazine ring effectively stores and controls electron flow, which efficaciously facilitates the separation of e-/h+ and enhances photocatalytic performance. The experimental results show that TQY-COF removes up to 99.8% of uranyl ions from actual uranium mine wastewater under the light conditions without a sacrificial agent, and the separation coefficient reaches 1.73 × 106 mL g-1 in the presence of multiple metal ions, which realizes the precise separation in the complex environment. Importantly, DFT calculations further elucidate the coordination mechanism of uranium and demonstrate the necessity of the presence of N/O atoms in the photocatalytic adsorption of uranium.

Supramolecular Materials as Solid-Phase Microextraction Coatings in Environmental Analysis

Solid-phase microextraction (SPME) has been widely proposed for the extraction, clean-up, and preconcentration of analytes of environmental concern. Enrichment capabilities, preconcentration efficiency, sample throughput, and selectivity in extracting target compounds greatly depend on the materials used as SPME coatings. Supramolecular materials have emerged as promising porous coatings to be used for the extraction of target compounds due to their unique selectivity, three-dimensional framework, flexible design, and possibility to promote the interaction between the analytes and the coating by means of multiple oriented functional groups. The present review will cover the state of the art of the last 5 years related to SPME coatings based on metal organic frameworks (MOFs), covalent organic frameworks (COFs), and supramolecular macrocycles used for environmental applications.

Sustainable remediation of pesticide pollutants using covalent organic framework - A review on material properties, synthesis methods and application

Covalent organic frameworks (COF) have emerged as a potential class of materials for a variety of applications in a wide number of sectors including power storage, environmental services, and biological applications due to their ordered and controllable porosity, large surface area, customizable structure, remarkable stability, and diverse electrical characteristics. COF have received a lot of attention in recent years in the field of environmental remediation, It also find its way to eliminate the emerging pollutant from the environment notably pesticide from polluted water. This review more concentrated on the application of COF in pesticide removal by modifying COF structure, COF synthesis and material properties. To increase the adsorption ability and selectivity of the material towards certain pesticides removal, the synthesis of COF involves organic linkers with various functional groups such as amine, carboxylic acid groups etc. The COF have a high degree of stability and endurance make them suitable for intermittent usage in water treatment applications. This review manifests the novel progress where modified COFs employed in a prominent manner to remove pesticides from polluted water. Some examples of COF application in the eradication of pesticides are triformyl phenylene framework functionalized with amine groups has capacity to remove up to 50 mg/l of Organophosphorus - chlorpyrifos. COF modified to improve their photocatalytic capacity to breakdown the pesticide under visible light irradiation. COF tetraphenyl ethylene linked with carboxylic acid group shows efficient photocatalytic degradation of 90% of organochlorine insecticide endosulfan when subjected to visible light. Atrazine and imidacloprid are reduced from 100 ppm to 1 ppm in aqueous solutions by COF based on high adsorption capacity. In addition, the strategies, technique, synthesis and functional group modification design of COF are discussed.

A simple AIE probe to pesticide trifluralin residues in aqueous phase: Ultra-fast response, high sensitivity, and quantitative detection utilizing a portable platform

The threat from pesticide trifluralin residues to ecological environment and public health is becoming a growing problem. Thus, rapid and sensitive detection, particularly a simple and portable detected platform for trifluralin residues, are highly desired. Here, a small organic aggregation-induced emission (AIE) molecule (TPETPy) is facilely synthesized and applied to detect trifluralin both in lab and in actual water systems. Based on the photo-induced electron transfer (PET) mechanism, the emissive peak of TPETPy located at 475 nm in tetrahydrofuran (THF)/water mixture (ƒw = 90 %) under the excitation of 340 nm, decreases dramatically upon trace trifluralin addition and exhibits ultra-fast response (3 s), high sensitivity and selectivity, and good anti-interference ability. The fluorescence sensing correlation with the concentration of trifluralin shows good linearity in the range of 20-90 μg L-1 with the limit of detection of 6.28 μg L-1. Moreover, a portable smartphone-integrated detected platform based on fluorescent pattern Red/Green/Blue (RGB) values is first employed to realize the real-time and on-site quantitative fluorescent detection of trifluralin in actual water sources, featuring good accuracy and reproducibility. Hereby, this work provides not only a highly efficient trifluralin residues fluorescent probe but also a portable and straightforward operating platform to detect trifluralin pesticides quantitatively.

A novel deep eutectic solvent modified magnetic covalent organic framework for the selective separation and determination of trace copper ion in medicinal plants and environmental samples

BACKGROUND

Pretreatment techniques should be introduced before metal ion determination because there is very low content of heavy metals in Chinese medicinal plants and environmental samples. Magnetic dispersive micro solid phase extraction (MDMSPE) has been widely used for the separation and adsorption of heavy metal pollutants in medicinal plants and environmental samples. However, the majority of MDMSPE adsorbents have certain drawbacks, including low selectivity, poor anti-interference ability, and small adsorption capacity. Therefore, modifying currently available adsorption materials has gained attention in research.

RESULTS

In this study, a novel adsorbent MCOF-DES based on a magnetic covalent organic framework (MCOF) modified by a new deep eutectic solvent (DES) was synthesized for the first time and used as an adsorbent of MDMSPE. The MDMSPE was combined with inductively coupled plasma optical emission spectrometry (ICP-OES) for selective separation, enrichment, and accurate determination of trace copper ion (Cu2+) in medicinal plants and environmental samples. Various characterization results show the successful preparation of new MCOF-DES. Under the optimal conditions, the enrichment factor (EF) of Cu2+ was 30, the limit of detection (LOD) was 0.16 μg L-1, and the limit of quantitation (LOQ) was 0.54 μg L-1. The results for the determination of Cu2+ were highly consistent with those of inductively coupled plasma mass spectrometry (ICP-MS), which verified the accuracy and reliability of the method.

SIGNIFICANCE

The established method based on a new adsorption material MCOF-DES has achieved the selective separation and determination of trace Cu2+ in medicinal and edible homologous medicinal materials (Phyllanthus emblica Linn.) and environmental samples (soil and water), which provides a promising, selective, and sensitive approach for the determination of trace Cu2+ in other real samples.

A miniaturized stir bar sorptive dispersive microextraction method for the determination of bisphenols in follicular fluid using a magnetic covalent organic framework

BACKGROUND

Bisphenols, particularly bisphenol A (BPA), are the primary monomers used as additives in the manufacturing of many consumer products. The exposure to these compounds is related to endocrine-disrupting and reproductive effects, among others. For this reason, the development of analytical methods for their determination in biological matrixes is needed to monitor the population exposure to these compounds. Their quantification at ovarian level (i.e., follicular fluid) is interesting for the assessment of the bisphenol content to draw conclusions about infertility problems. However, the background does not meet all requirements by focusing mainly on BPA.

RESULTS

In this work, a miniaturized stir bar sorptive dispersive microextraction (mSBSDME) approach has been developed for the determination of BPA and eight analogues in follicular fluid. In the proposed method, the sample is previously cleaned-up using a zirconia-based solid-phase extraction cartridge, removing proteins and phospholipids, and then subjected to the mSBSDME for the preconcentration of the analytes. For this purpose, a magnetic covalent organic framework was used as sorbent. A Plackett-Burman design was applied to select the significant variables affecting the mSBSDME. Afterwards, the only significant variable (i.e., sorbent amount) was optimized. Under the optimized conditions, the proposed method was properly validated, and satisfactory analytical parameters in terms of linearity (up to 50 ng mL-1), enrichment factors (8.5-14.3), limits of detection in the low ng mL-1 range, and precision (relative standard deviations below 11.5 %) were obtained. Finally, the method was successfully applied to five samples, detecting BPA and other two analogues.

SIGNIFICANCE

This method expands the potential applicability of the mSBSDME to other low-availability complex matrixes, which would otherwise be difficult to analyze. Moreover, it offers a valuable tool for monitoring the female population's exposure to bisphenols with the final aim of evaluating if infertility problems of women might be associated to the exposure to these highly endocrine disrupting compounds.

Recent progress of covalent organic frameworks as attractive materials for solid-phase microextraction: A review

Solid-phase microextraction (SPME) is a green, environmentally friendly, and efficient technique for sample pre-treatment. Covalent organic frameworks (COFs), a class of porous materials formed by covalent bonds, have gained prominence owing to their remarkable attributes, including large specific surface area, tunable pore size, and robust thermal/chemical stability. These characteristics have made COFs highly appealing as potential coatings for SPME fiber over the past decades. In this review, various methods used to prepare SPME coatings based on COFs are presented. These methods encompass physical adhesion, sol-gel processes, in situ growth, and chemical cross-linking strategies. In addition, the applications of COF-based SPME coating fibers for the preconcentration of various targets in environmental, food, and biological samples are summarized. Moreover, not only their advantages but also the challenges they pose in practical applications are highlighted. By shedding light on these aspects, this review aims to contribute to the continued development and utilization of COF materials in the field of sample pretreatment.

Magnetic covalent organic frameworks for extraction and determination of endocrine-disrupting chemicals in beverage and water samples

BACKGROUND

Phenolic endocrine-disrupting chemicals (EDCs) are widespread and easily ingested through the food chain. They pose a serious threat to human health. Magnetic solid-phase extraction (MSPE) is an effective sample pre-treatment technology to determine traces of phenolic EDCs.

RESULTS

Magnetic covalent organic framework (COF) (Fe3 O4 @COF) nanospheres were prepared and characterized. The efficient and selective extraction of phenolic EDCs relies on a large specific surface and the inherent porosity of COFs and hydrogen bonding, π-π, and hydrophobic interactions between COF shells and phenolic EDCs. Under optimal conditions, the proposed magnetic solid-phase extraction-high-performance liquid chromatography-ultra violet (MSPE-HPLC-UV) based on the metallic covalent organic framework method for phenolic EDCs shows good linearities (0.002-6 μg mL-1 ), with R2 of 0.995 or higher, and low limits of detection (6-1.200 ng mL-1 ).

CONCLUSION

Magnetic covalent organic frameworks (Fe3 O4 @COFs) with good MSPE performance for phenolic EDCs were synthesized by the solvothermal method. The magnetic covalent organic framework-based MSPE-HPLC-UV method was applied successfully to determine phenolic EDCs in beverage and water samples with satisfactory recoveries (90.200%-123%) and relative standard deviations (2.100%-12.100%). © 2023 Society of Chemical Industry.

Embedding Mixed Sorbents in Binder: Solid-Phase Microextraction Coating with Wide Extraction Coverage and Its Application in Environmental Water Analysis

Solid-phase microextraction (SPME) is a simple and highly effective sample-preparation technique for water analysis. However, the extraction coverage of a given SPME device with a specific coating can be an issue when analyzing multiple environmental contaminants. Therefore, instead of synthesizing one sorbent material with dual or multiple functions, we investigated a new strategy of preparing SPME blades using a homogeneous slurry made by mixing three different sorbent particles─namely, hydrophobic/lipophilic balanced (HLB), HLB-weak cationic exchange (HLB-WCX), and HLB-weak anionic exchange (HLB-WAX)─with a polyacrylonitrile (PAN) binder. The developed coating is matrix compatible, as the binder functions not only as a glue for immobilizing the sorbent particles but also as a porous filter, which only allows small molecules to enter the pores and interact with the particles, thus avoiding contamination from large elements. The results confirmed that the proposed mixed-coating SPME device provides good extraction performance for polar and nonpolar as well as positively and negatively charged compounds. Based on this device, three comprehensive analytical methodologies─high-throughput SPME-LC-MS/MS (for the quantitative analysis of targeted drugs of abuse and artificial sweeteners), in-bottle SPME-LC-high resolution MS (HRMS) (for the untargeted screening of organic contaminants), and on-site drone sampling SPME-LC-HRMS (for on-site sampling and untargeted screening)─were developed for use in environmental water analysis. The resultant data confirm that the proposed strategies enable comprehensive water quality assessment by using a single SPME device.

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.

Applications of covalent organic frameworks for the elimination of dyes from wastewater: A state-of-the-arts review

Covalent organic frameworks (COFs) are class of porous coordination polymers made up of organic building blocks joined together by covalent bonding through thermodynamic and controlled reversible polymerization reactions. This review discussed versatile applications of COFs for remediation of wastewater containing dyes, emphasizing the advantages of both pristine and modified materials in adsorption, membrane separation, and advanced oxidations processes. The excellent performance of COFs towards adsorption and membrane filtration has been centered to their higher crystallinity and porosity, exhibiting exceptionally high surface area, pore size and pore volumes. Thus, they provide more active sites for trapping the dye molecules. On one hand, the photocatalytic performance of the COFs was attributed to their semiconducting properties, and when coupled with other functional semiconducting materials, they achieve good mechanical and thermal stabilities, positive light response, and narrow band gap, a typical characteristic of excellent photocatalysts. As such, COFs and their composites have demonstrated excellent potentialities for the elimination of the dyes.

Mixed-Linkage Donor-Acceptor Covalent Organic Framework as a Turn-On Fluorescent Sensor for Aliphatic Amines

Amine determination is crucial to our daily life, including the prevention of pollution, the treatment of certain disorders, and the evaluation of food quality. Herein, a mixed-linkage donor-acceptor covalent organic framework (named DSE-COF) was first constructed by the polymerization between 2,4-dihydroxybenzene-1,3,5-tricarbaldehyde (DTA) and 4,4'-(benzo[c][1,2,5]selenadiazole-4,7-diyl)dianiline (SEZ). DSE-COF displayed superior turn-on fluorescent responses to primary, secondary, and tertiary aliphatic amines, such as cadaverine, isopropylamine, sec-butylamine, cyclohexylamine, hexamethylenediamine, di-n-butylamine, and triethylamine in absolute acetonitrile than other organic species. Further experiments and theoretical calculations demonstrated that the combination of intramolecular charge transfer (ICT) and photoinduced electron transfer (PET) effects between the DSE-COF and aliphatic amines resulted in enhanced fluorescence. Credibly, DSE-COF can quantitatively detect cadaverine content in actual pork samples with satisfactory results. In addition, DSE-COF-based test papers could rapidly monitor cadaverine from real pork samples, manifesting the potential application of COFs in food quality inspection.

Efficient capture and highly sensitive analysis of okadaic acid by three-dimensional covalent organic frameworks with hydroxyl surface engineering

A novel three-dimensional covalent organic framework (3D-COF) with content-tunable and active hydroxyl groups (OH) on the pore walls was developed and adopted for the high-performance capture of okadaic acid (OA) marine toxins. Using pore-surface engineering, the integration of linear building blocks (4,4'-diamino-3,3'-biphenyldiol, BD(OH)2 and benzidine, BD) with the 3D structural building block backbone (4,4',4'',4'''-methane-tetrayltetrabenzaldehyde, TFPM) was achieved. By adjusting the ratio of BD(OH)2, functional multicomponent-COFs [OH]x-BD-TFPM COFs (X = 25%) were synthesized, which offered ideal access to convert a conventional COF into a functional platform with multiple-mode interactions of hydrophobic and hydrophilic groups for OA capture. [OH]x-BD-TFPM was characterized using SEM, XRD, FT-IR, and BET. The adsorption features and analytical performance of OA were screened and evaluated. Optimization of dispersive solid-phase extraction using [OH]25-BD-TFPM was accomplished, and the method was verified for sensitive quantitative detection of OA in clam and mussel samples. Coupled with LC-MS/MS, the resultant [OH]25-BD-TFPM COF demonstrated the ability to analyze OA, and the limit of detection for OA in shellfish was determined to be 0.005 μg/kg. A significant improvement in trace OA detection was observed compared to previously reported SPE materials without adjustable hydrophilic interactions. The recoveries of OA in the fortified clam and mussel samples were in the ranges of 93.9‒105.1% and 96.7‒110.2%, respectively. This study highlights that OH-group surface engineering in channel walls is a facile and powerful strategy for developing functional 3D-COFs with multiple interactions for high-performance target capture.

Boost of Gas Adsorption Kinetics of Covalent Organic Frameworks via Ionic Liquid Solution Process

Adsorption, storage, and conversion of gases (e.g., carbon dioxide, hydrogen, and iodine) are the three critical topics in the field of clean energy and environmental mediation. Exploring new methods to prepare high-performance materials to improve gas adsorption is one of the most concerning topics in recent years. In this work, an ionic liquid solution process (ILSP), which can greatly improve the adsorption kinetic performance of covalent organic framework (COF) materials for gaseous iodine, is explored. Anionic COF TpPaSO3 H is modified by amino-triazolium cation through the ILSP method, which successfully makes the iodine adsorption kinetic performance (K80% rate) of ionic liquid (IL) modified COF AC4 tirmTpPaSO3 quintuple compared with the original COF. A series of experimental characterization and theoretical calculation results show that the improvement of adsorption kinetics is benefited from the increased weak interaction between the COF and iodine, due to the local charge separation of the COF skeleton caused by the substitution of protons by the bulky cations of ILs. This ILSP strategy has competitive help for COF materials in the field of gas adsorption, separation, or conversion, and is expected to expand and improve the application of COF materials in energy and environmental science.

In-situ immobilization of covalent organic frameworks as stationary phase for capillary electrochromatography

A new kind of covalent organic framework (COF) was first utilized as an stationary phase for open-tubular electrochromatography (OT-CEC) by in situ synthesis immobilized method at room temperature. On the basis of our previous work, 4,4',4″-(1,3,5-Triazine-2,4,6-triyl)trianiline (TZ) and 2,5-bis(2-propyn-1-yloxy)-1,4-benzenedicarboxaldehyde (BPTA) were employed as building blocks for the synthesis of COF TZ-BPTA. The coated capillary and COF TZ-BPTA were characterized by scanning electron microscopy (SEM). Then, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were also applied to characterize COF TZ-BPTA and the modified column. In SEM, it can be seen that COF TZ-BPTA was the spherical shape and the modified capillary was covered with globular particles equably. The COF TZ-BPTA coated column exhibited good separation resolution and efficiency towards two antiepileptic drugs and other kinds of small organic molecules involving alkylbenzene, sulfonamides, polycyclic aromatic hydrocarbon (PAH), parabens, amino acids and herbicides. The maximum column efficiency was over 2.8 × 105 plates·m-1. In addition, the precisions (RSDs) of the retention times for the alkylbenzenes of intra-day runs (n = 3), inter-day runs (n = 3) and column-to-column runs (n = 3) were all less than 1.70% and separation performance was without obvious change within 100 times run. In addition, the real sample was tested on COF TZ-BPTA coated column. Hence, COF TZ-BPTA showed great potential in the separation domain.

Irreversible fluorine covalent organic framework based probe nanoelectrospray ionization mass spectrometry for direct and rapid determination of perfluoroalkyl carboxylic acids

Probe nanoelectrospray ionization mass spectrometry (PESI-MS) is practically desirable for rapid and ultra-sensitive analysis of trace contaminants in environment, but limited with the stable and selective probe coating. Herein, we show the design and preparation of irreversible fluorine-based covalent organic framework (TFPPA-F₄) covalently bonded probe to couple with ESI-MS (TFPPA-F₄-PESI-MS) for direct and rapid determination of perfluoroalkyl carboxylic acids (PFCAs) in environmental water. Chemical bonding coating of irreversible crystalline TFPPA-F₄ not only improved stability of the probe, but also offered accessible multiple interactions including hydrophobic, hydrogen bonding and F-F interactions to promote the kinetics and selectivity for PFCAs. The proposed TFPPA-F₄-PESI-MS realized rapid determination of PFCAs (about 4 min) with low limits of detection of 0.06-0.88 ng L^-1 and wide linear range of 1-5000 ng L^-1 (R² of 0.9982-0.9998). Recoveries for the spiked lake and pond water were 85.9-111.1 %. TFPPA-F₄ based probe can maintain the extraction performance after 100 times of extraction. This work shows the great potential of the irreversible covalent organic framework based PESI-MS in rapid and ultra-sensitive determination of contaminants in environmental samples.

Methacrylate bonded covalent organic framework monolithic column online coupling with high-performance liquid chromatography for analysis of trace estrogens in food

Covalent organic frameworks (COFs) are a burgeoning class of crystalline porous materials with unique properties and have been considered as a promising functional extraction medium in sample pretreatment. In this study, a new methacrylate-bonded COF (TpTh-MA) was well designed and synthesized via the aldehyde-amine condensation reaction, and the TpTh-MA was incorporated into poly (ethylene dimethacrylate) porous monolith by a facile polymerization reaction inside capillary to prepare a novel TpTh-MA monolithic column. The fabricated TpTh-MA monolithic column was characterized with scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction, and N₂ adsorption-desorption experiments. Then, the homogeneous porous structure, good permeability and high mechanical stability of TpTh-MA monolithic column was used as separation and enrichment media of capillary microextraction, which was coupled with high-performance liquid chromatography fluorescence detection for online enrichment and analysis of trace estrogens. The main experimental parameters influencing the extraction efficiency were systematically investigated. The adsorption mechanism for three estrogens was also explored and discussed based on hydrophobic effect, π-π affinity and hydrogen bonding interaction, which contributed to its strong recognition affinity to target compounds. The enrichment factors of the TpTh-MA monolithic column micro extraction method for the three estrogens were 107-114, indicating a significant preconcentration ability. Under optimal conditions, a new online analysis method was developed and exhibited good sensitivity and wide linearity range of 0.25-100.0 µg·L^-1 with a coefficient of determination (R²) higher than 0.9990 and a low limit of detection with 0.05-0.07 µg·L^-1. The method was successfully applied for online analysis of three estrogens of milk and shrimp samples and the recoveries obtained from spiking experiments were in range of 81.4-113% and 77.9-111%, with the relative standard deviations of 2.6-7.9% and 2.1-8.3% (n = 5), respectively. The results revealed the great potential for the application of the COFs-bonded monolithic column in the field of sample pretreatment.

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.

Magnetic covalent organic frameworks for rapid solid-phase extraction of phthalate esters and bisphenol A in beverage samples

Phthalate esters (PAEs) and bisphenol A (BPA) are endocrine-disrupting chemicals (EDCs), which are widely used in the production of food plastic packaging and easily migrate to food. Continuous exposure to EDCs may cause harm to human health. Herein, magnetic covalent organic framework TFP-NDA/Fe₃O₄ was synthesized by magnetizing covalent organic framework TFP-NDA through a facile coprecipitation method, and used as an adsorbent for rapid solid-phase extraction of PAEs (diethyl phthalate (DEP), diisobutyl phthalate (DIBP) and dibutyl phthalate (DBP)) and BPA. The extraction equilibrium can be reached within 12 min. By combination with a gas chromatography-flame ionization detector, the limits of detection were 0.7-2.3 μg L^-1 and the linear ranges were 10-500 μg L^-1 for diethyl phthalate (DEP) and 10-1000 μg L^-1 for diisobutyl phthalate (DIBP), dibutyl phthalate (DBP) and BPA with R² > 0.9916. In beverage samples (plastic bottled drinking water, juice and carbonated drink), the developed method was successfully applied to extract and quantify PAEs and BPA with recoveries ranging from 81.7% to 114.2%.

Covalent organic frameworks (COFs): a promising CO2 capture candidate material

Covalent organic frameworks (COFs) are an emerging kind of porous crystal material.

Covalent organic framework in situ grown on Fe3O4 hollow microspheres for stir bar sorptive-dispersive microextraction of triazole pesticides

Based on covalent organic framework (COF) 1,3,5-tris-(4-formylphenyl)benzene-benzidine (TFPB-BD) in situ grown on Fe₃O₄ hollow microspheres and combined with gas chromatography-flame thermionic detector, a rapid and simple stir bar sorptive-dispersive microextraction method was developed for the determination of five triazole pesticides (paclobutrazol, hexaconazole, flusilazole, propiconazole, and tebuconazole). The synthesized TFPB-BD/Fe₃O₄ microspheres were characterized by transmission electron microscope, vibrating sample magnetometer, and thermogravimetric analysis, which showed that the material has strong magnetism and higher load capacity of COF. Under optimal conditions, the extraction equilibrium could be achieved within 9 min with detection limits of 0.17-1.48 μg L^-1 (S/N = 3) and a linear range of 5-1000 μg L^-1. The developed method was applied to the determination of trace triazole pesticides in apples, pears, and cabbages with recoveries from 81 to 117%.

Covalent organic framework-loaded silver nanoparticles as robust mimetic oxidase for highly sensitive and selective colorimetric detection of mercury in blood

Covalent organic frameworks (COFs) were fabricated with a hierarchical flower-like hollow structure, possessing a large specific surface area, high porosity, and excellent environmental stability. In situ growth of noble silver nanoparticles (AgNPs) onto COFs was conducted yielding COF-Ag nanozymes. The structural advantages of COFs can ensure the uniform dispersion and effective size control of AgNPs. More interestingly, the oxidase-like catalytic activity of the obtained COF-Ag nanozymes could be enhanced in the presence of Hg²⁺ ions, which could specifically interact with AgNPs to form Ag-Hg alloys. A COF-Ag catalysis-based colorimetric platform was thereby constructed for highly selective and sensitive analysis of Hg²⁺ ions, showing a linear concentration range from 0.050 to 10.0 μM, with a limit of detection of about 3.7 nM. Besides, the developed colorimetric strategy was successfully applied for detecting Hg²⁺ ions in human blood with favorable detection recoveries, indicating its potential for applications in the biomedical analysis, environmental monitoring, and food safety fields.

Core-shell-structured magnetic covalent organic frameworks for effective extraction of parabens prior to their determination by HPLC

Covalent organic framework (COF)-decorated magnetic nanoparticles (Fe₃O₄@DhaTab) with core-shell structure have been synthesized by one-pot method. The prepared Fe₃O₄@DhaTab was well characterized, and parameters of magnetic solid-phase extraction (MSPE) for parabens were also investigated in detail. Under optimized conditions, the adsorbent dosage was only 3 mg and extraction time was 10 min. The developed Fe₃O₄@DhaTab-based MSPE-HPLC analysis method offered good linearity (0.01-20 μg mL^-1) with R² (0.999) and low limits of detection (3.3-6.5 μg L^-1) using UV detector at 254 nm. The proposed method was applied to determine four parabens in environmental water samples with recoveries in the range 64.0-105% and relative standard deviations of 0.16-7.8%. The adsorption mechanism was explored and indicated that porous DhaTab shell provided π-π, hydrophobic, and hydrogen bonding interactions in the MSPE process. The results revealed the potential of magnetic-functionalized COFs in determination of environmental contaminants.

Efficient and selective solid-phase microextraction of polychlorinated biphenyls by using a three-dimensional covalent organic framework as functional coating

Developing functional fiber coating for selective solid phase microextraction (SPME) of trace pollutants is critical in environmental analysis. Herein, the novel covalent organic frameworks (COFs) with three-dimensional (3D) frameworks and multiple interactions were designed and presented for the selective SPME of polychlorinated biphenyls (PCBs). Using tetra (p-aminophenyl) methane (TAM) and 1,3,5-triformylphloroglucinol (Tp) as the monomers, the 3D TpTAM-COF was synthesized and possessed a large specific surface area, high thermal stability, and spatial selectivity toward PCBs. Characterizations such as morphology, XPS, XRD, thermal stability, and enhancement factors (EFs) were studied. Multiple interactions including π-π conjugation, hydrophobic interaction, and selectivity toward non-planar structure were adopted, which resulted in a superior adsorption affinity toward PCBs on TpTAM-COF. Under the optimal conditions, the spatial selectivity toward PCBs, organic analogs (o-dichlorobenzene, biphenyl) and polycyclic aromatic hydrocarbons (naphthalene, pyrene, and anthracene)) was achieved. Efficient and selective adsorption of fifteen PCBs was fulfilled with the highest EF up to 10305. Using the HS-SPME-GC-MS method, the recoveries of PCBs in the river water and soil samples were determined to be 84.8 ± 7.8% ∼ 117.2 ± 8.5% (n = 3) and 84.4 ± 8.6% ∼ 114.7 ± 7.6% (n = 3), respectively. Compared with most commercial SPME fibers and other COFs-based fibers, the resultant TpTAM-COF-coated fibers possessed higher selectivity and EFs of PCBs. It proposed a promising approach for selective SPME of trace PCBs by multiple interactions in the steric structure of 3D COFs.

Integrating Ordered Two-Dimensional Covalent Organic Frameworks to Solid-State Nanofluidic Channels for Ultrafast and Sensitive Detection of Mercury

Grafting specific recognition moieties onto solid-state nanofluidic channels is a promising way for selective and sensitive sensing of analytes. However, the time-consuming interaction between recognition moieties and analytes is the main hindrance to the application of nanofluidic channel-based sensors in rapid detection. Here, we show the integration of ordered two-dimensional covalent organic frameworks (2D COFs) to solid-state nanofluidic channels to achieve rapid, selective, and sensitive detection of contaminants. As a proof of concept, a thiourea-linked 2D COF (JNU-3) as the recognition unit is covalently bonded on the stable artificial anodic aluminum oxide nanochannels (AAO) to fabricate a JNU-3@AAO-based nanofluidic sensor. The rapid and selective interaction of Hg(II) with the highly ordered channels of JNU-3 allows the JNU-3@AAO-based nanofluidic sensor to realize ultrafast and precise determination of Hg(II) (90 s) with a low limit of detection (3.28 fg mL^-1), wide linear range (0.01-100 pg mL^-1), and good precision (relative standard deviation of 3.8% for 11 replicate determination of 10 pg mL^-1). The developed method was successfully applied to the determination of mercury in a certified reference material A072301c (rice powder), real water, and rice samples with recoveries of 90.4-99.8%. This work reveals the great potential of 2D COFs-modified solid-state nanofluidic channels as a sensor for the rapid and precise detection of contaminants in complicated samples.

Application of a novel hydroxyl functionalized fluorescent covalent organic framework for turn-off ultrasensitive Zn2+ ion detection

In this research, a novel hydroxyl functionalized covalent organic framework (COF) with fluorescence properties was rationally designed based on the reaction between 2,5-dihydroxy-terephthalic-dihydrazide (DHTPz) and 1,3,5-benzenetricarboxaldehyde (Bt) for Zn²⁺ detection. The prepared DHTPz-Bt exhibited strong fluorescence, while the apparent quenching of fluorescence was observed after the introduction of Zn²⁺. Meanwhile, DHTPz-Bt exhibited high sensitivity and promising selectivity during the detection of Zn²⁺. Additionally, the recognition process was revealed to be attributed to the coordination between the hydroxyl groups on the phenyls of DHTPz-Bt and Zn²⁺ ions, as verified by using Fourier-transform infrared spectra and X-ray photoelectron spectra. This work demonstrates the great potential of fluorescent probes by rationally introducing metal ligands, which will lead to a suite of new COF materials for metal ion sensing in a practical manner.

Building-block exchange synthesis of amino-based three-dimensional covalent organic framework for gas chromatographic separation of isomers

The thermally stable three-dimensional covalent organic framework (3D COFs) with rich pore of channels and cages are promising as stationary phase for gas chromatography (GC), which has not been explored....