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Pipette-tip micro solid-phase extraction (PT-µSPE) has emerged as a powerful technique for miniaturized sample preparation, not only due to its simplicity, low solvent consumption, and high efficiency, but also because it requires just a few mg of adsorbent for performing extraction. Recently, there has been growing interest in enhancing the extraction performance of PT-µSPE by incorporating metal-organic frameworks (MOFs) as sorbents due to their advantageous properties, including high surface area, tunable pore structure, and diverse functionalities. This review provides a comprehensive overview of advances in MOF-based adsorbents for PT-µSPE, focusing on their synthesis, characterization, and applications in sustainable microextraction methodologies. The key strategies for enhancing the extraction performance of MOFs, including surface modification and integration with other functional materials, are discussed. Finally, the review discusses future trends and opportunities for enhancing the performance of MOF-based PT-µSPE, such as improving selectivity, developing reusable adsorbents, and exploring new applications
Liquid–Liquid Extraction (LLE) is a venerable and widely used method for the separation of a targeted solute between two immiscible liquids. In recent years, this method has gained popularity in the supramolecular chemistry community due to the development of various types of synthetic receptors that effectively and selectively bind specific guests in an aqueous medium through different supramolecular interactions. This has eventually led to the development of state-of-the-art extraction technologies for the removal and purification of anions, cations, ion pairs, and small molecules from one liquid phase to another liquid phase, which is an industrially viable method. The focus of this perspective is to furnish a vivid picture of the current understanding of supramolecular interaction-based LLE chemistry. This will not only help to improve separation technology in the chemical, mining, nuclear waste treatment, and medicinal chemistry sectors but is also useful to address the purity issue of the extractable species, which is otherwise difficult. Thus, up-to-date knowledge on this subject will eventually provide opportunities to develop large-scale waste remediation processes and metallurgy applications that can address important real-life problems.
Although covalent organic frameworks (COFs) with high π -conjugation have recently exhibited great prospects in perovskite solar cells (PSCs), their further application in PSCs is still hindered by face-to-face stacking and aggregation issues. Herein, metal–organic framework (MOF-808) is selected as an ideal platform for the in situ homogeneous growth of a COF to construct a core–shell MOF@COF nanoparticle, which could effectively inhibit COF stacking and aggregation. The synergistic intrinsic mechanisms induced by the MOF@COF nanoparticles for reinforcing intrinsic stability and mitigating lead leakage in PSCs have been explored. The complementary utilization of π -conjugated skeletons and nanopores could optimize the crystallization of large-grained perovskite films and eliminate defects. The resulting PSCs achieve an impressive power conversion efficiency of 23.61% with superior open circuit voltage (1.20 V) and maintained approximately 90% of the original power conversion efficiency after 2000 h (30–50% RH and 25–30 °C). Benefiting from the synergistic effects of the in situ chemical fixation and adsorption abilities of the MOF@COF nanoparticles, the amount of lead leakage from unpackaged PSCs soaked in water (< 5 ppm) satisfies the laboratory assessment required for the Resource Conservation and Recovery Act Regulation.
Nanoplastics have garnered significant global attention as emerging environmental contaminants due to their susceptibility to be internalized by organisms, potentially leading to higher ecological and health risks compared to microplastics. Recently, adsorption has emerged as a promising strategy for nanoplastic removal, and new adsorbents have demonstrated impressive performance in this regard. In this study, we focused on the removal of polystyrene nanoplastics (NPs) from aqueous environments using a series of mesoporous Metal Organic Frameworks (MOFs). We synthesized mesoporous UiO-66 and its derivatives (–OH and –NH2) through direct solvothermal synthesis in the presence of cetyltrimethylammonium bromide (CTAB) or Pluronic-type triblock copolymer (P123). The resulting materials had high crystallinity and displayed a hierarchical mesoporosity. Remarkably, we found that UiO-66-NH2/P123 demonstrated exceptional efficiency in removing NPs, achieving up to 100 % removal efficiency at an initial concentration of 1 g·L-1. This indicates its potential as a highly effective adsorbent for nanoplastic removal from aqueous media.
Photocatalytic degradation under ultra-low powered light is a viable advanced oxidation process technique against extensive emerging contaminants. As a new and remarkable class of nanoporous materials, metal-organic frameworks (MOFs), attract interest for the supreme adsorptive and photocatalytic functionalities. An outstanding MOF, MIL-101(Fe) chosen as a photocatalyst template for the synthesis of α-Fe2O3 by a simple thermal modification to improve the structural properties toward methylene blue (MB) eradication. Octahedron-like α-Fe2O3 photocatalyst (Modified MIL-101(Fe), M-MIL-101(Fe)) was superior in dispersion and separation properties in aqueous medium. Moreover, the adsorptive and catalytic performance was increased for modified form by ~ 7.3% and ~ 17.1% compared to pristine MIL-101(Fe), respectively. Synergistic improvement of MB removal achieved by simultaneous adsorption/degradation under 5-W LED irradiation. Parametric study indicated an 18.1% and 44.5% improvement in MB removal was observed by increasing pH from 4 to 10, and M-MIL-101(Fe) dose from 0.2 to 1 g L⁻¹, respectively. MB removal followed the pseudo-second-order kinetics model and the process efficiency dropped by 38% as MB concentration increased from 5 to 20 mg L⁻¹. Radical trapping tests revealed the significant role of OH. and electron radicals as the major participants in dye degradation. A significant loss in the efficiency of M-MIL-101(Fe) was observed in the reusability tests that is good to study further. In conclusion, a simple thermal post-synthesis modification on MIL-101(Fe) improved its structural, catalytic, and adsorptive properties against MB.
Sulfonic acid-functionalized covalent organic frameworks (COF-SO3) as a coating of stir bar sorptive extraction (SBSE) for capturing three fluoroquinolones from milk have been developed. The COF-SO3 material was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. Milk without any typical treatments like protein precipitation and defatting was only diluted five times with water for test. Combined with high-performance liquid chromatography (HPLC), a SBSE-HPLC method was established for detecting fluoroquinolones in milk samples. The corresponding wide linear ranges (4.00–500.0 µg L⁻¹), low detection limits (1.20–2.62 µg L⁻¹), good test repeatability (RSD < 5.2%), and acceptable enrichment factors (56.2–61.5) were implemented for three fluoroquinolones. The analytical method was applied to determine trace targets and provided satisfactory results. Furthermore, the research displayed satisfied reproducibility for bar-to-bar (RSD < 6.5%) and batch-to-batch (RSD < 8.6%) tests.
Graphical abstract
Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) hybrid materials are a class of porous crystalline materials that integrate MOFs and COFs with hierarchical pore structures. As an emerging porous frame material platform, MOF/COF hybrid materials have attracted tremendous attention, and the field is advancing rapidly and extending into more diverse fields. Extensive studies have shown that a broad variety of MOF/COF hybrid materials with different structures and specific properties can be synthesized from diverse building blocks via different chemical reactions, driving the rapid growth of the field. The allowed complementary utilization of π‐conjugated skeletons and nanopores for functional exploration has endowed these hybrid materials with great potential in challenging energy and environmental issues. It is necessary to prepare a “family tree” to accurately trace the developments in the study of MOF/COF hybrid materials. This review comprehensively summarizes the latest achievements and advancements in the design and synthesis of MOF/COF hybrid materials, including COFs covalently bonded to the surface functional groups of MOFs (MOF@COF), MOFs grown on the surface of COFs (COF@MOF), bridge reaction between COF and MOF (MOF+COF), and their various applications in catalysis, energy storage, pollutant adsorption, gas separation, chemical sensing, and biomedicine. It concludes with remarks concerning the trend from the structural design to functional exploration and potential applications of MOF/COF hybrid materials.
The development of highly active carbon‐based bifunctional electrocatalysts for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is highly desired, but still full of challenges in rechargeable Zn–air batteries. Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have gained great attention for various applications due to their attractive features of structural tunability, high surface area and high porosity. Herein, a core–shell structured carbon‐based hybrid electrocatalyst (H‐NSC@Co/NSC), which contains high density active sites of MOF‐derived shell (Co/NSC) and COF‐derived hollow core (H‐NSC), is successfully fabricated by direct pyrolysis of covalently‐connected COF@ZIF‐67 hybrid. The core–shell H‐NSC@Co/NSC hybrid manifests excellent catalytic properties toward both OER and ORR with a small potential gap (∆E = 0.75 V). The H‐NSC@Co/NSC assembled Zn–air battery exhibits a high power‐density of 204.3 mW cm⁻² and stable rechargeability, outperforming that of Pt/C+RuO2 assembled Zn–air battery. Density functional theory calculations reveal that the electronic structure of the carbon frameworks on the Co/NSC shell can be effectively modulated by the embedded Co nanoparticles (NPs), facilitating the adsorption of oxygen intermediates and leading to enhanced catalytic activity. This work will provide a strategy to design highly‐efficient electrocatalysts for application in energy conversion and storage.
Liquid-liquid extraction (LLE) is the most commonly utilized technique for the extraction of odor-active esters (OAEs) in strong-aroma types of Baijiu (SAB). However, since the contents of different OAEs in SAB vary widely, it is still a puzzle to ensure that all OAEs to be thoroughly extracted by LLE without the problem of saturated adsorption. Herein, a novel approach of magnetic solid phase extraction (MSPE), based on the magnetic graphene oxide nanocomposite modified with polyacrylamide (GO/PAM/Fe3O4), was employed for the efficient extraction of six OAEs from SAB. Compared with LLE, GO/PAM/Fe3O4 exhibited highly selective recognition properties and larger adsorption capacities for OAEs (ranging from 13.68 to 39.06 mg/g), resulting in better extraction performances for OAEs. Coupled with GC–MS, six OAEs in real SAB were successfully determined, with recoveries ranged from 70.1 ∼ 90.0% and LODs at 0.08 ∼ 1.35 µg/L. Overall, the MSPE-GC/MS is a promising alternative for accurate determination of OAEs in SAB.
The search for building hierarchical porous materials with accelerated photo‐induced electrons and charge‐carrier separation is important because they hold great promise for applications in various fields. Here, a facile strategy of confining metal‐organic framework (MOF) in the 1D channel of the 2D covalent organic framework (COF) to construct a novel COF@MOF micro/nanopore network is proposed. Specifically, a nitrogen‐riched COF (TTA‐BPDA‐COF) is chosen as the platform for in‐situ growth of a Co‐based MOF (ZIF‐L‐Co) to form a TTA‐BPDA‐COF@ZIF‐L‐Co hybrid material. The hierarchical porous structure endows TTA‐BPDA‐COF@ZIF‐L‐Co with superior adsorption capacity. In addition, the integration of TTA‐BPDA‐COF and ZIF‐L‐Co forms a Z‐scheme photocatalytic system, which significantly improved the redox properties and accelerated the separation of photogenerated charges and holes, achieving great improvement in photocatalytic activity. This confinement engineering strategy provides a new idea to construct a versatile molecular‐material photocatalytic platform.
Solid-phase microextraction (SPME) is a well-established sample-preparation technique for environmental studies. The application of SPME has extended from the headspace extraction of volatile compounds to the capture of active components in living organisms via the direct immersion of SPME probes into the tissue (in vivo SPME). The development of biocompatible coatings and the availability of different calibration approaches enable the in vivo sampling of exogenous and endogenous compounds from the living plants and animals without the need for tissue collection. In addition, new geometries such as thin-film coatings, needle-trap devices, recession needles, coated tips, and blades have increased the sensitivity and robustness of in vivo sampling. In this paper, we detail the fundamentals of in vivo SPME, including the various extraction modes, coating geometries, calibration methods, and data analysis methods that are commonly employed. We also discuss recent applications of in vivo SPME in environmental studies and in the analysis of pollutants in plant and animal tissues, as well as in human saliva, breath, and skin analysis. As we show, in vivo SPME has tremendous potential for the targeted and untargeted screening of small molecules in living organisms for environmental monitoring applications.
Separating CH4/N2 mixture is challenging, and performance of the existing materials is still open to improvement. In this study, we examined both the adsorption- and membrane-based CH4/N2 separation performances of 5034 different materials, including metal organic frameworks (MOFs), covalent organic frameworks (COFs), ionic liquid (IL)/MOF composites, MOF/polymer composites, and COF/polymer composites by performing high-throughput computational screening and molecular simulations. The top performing adsorbents and membranes were identified by computing several performance evaluation metrics. Investigation of the interactions between the gas molecules, the IL, and the top MOF was performed by density functional theory (DFT) calculations. Results pointed out that the interactions between the gas molecules and the linker fragments of the MOF are stronger than their interactions with the IL. Thus, as the IL molecules are loaded into the selected top MOF, they occupy the adsorption sites of the gases, decreasing CH4 and N2 uptakes and increasing CH4/N2 selectivity. Our results revealed that MOFs offer great potential for adsorption-based CH4/N2 separation, and IL incorporation into MOFs remarkably increases their CH4/N2 selectivities. More than 25% of MOF and 70% of the COF membranes surpassed Robeson’s upper bound because of high N2 permeabilities and outperformed conventional polymeric membranes. N2 permeabilities and selectivities of MOF/polymer and COF/polymer composites were found to be significantly higher than those of pure polymers. Our results emphasize the promises of the design and development of new MOF and COF adsorbents, membranes, and their composites with ILs and polymers for efficient CH4/N2 separation.
Covalent organic frameworks (COFs) have emerged as an exciting new class of porous materials constructed by organic building blocks via dynamic covalent bonds. They have been extensively explored as potentially superior candidates for electrode materials, electrolytes, and separators, due to their tunable chemistry, tailorable structures, and well‐defined pores. These features enable rational design of targeted functionalities, facilitate the penetration of electrolytes, and enhance ion transport. This review provides an in‐depth summary of the recent progress in the development of COFs for diverse battery applications, including lithium‐ion, lithium–sulfur, sodium‐ion, potassium‐ion, lithium–CO2, zinc‐ion, zinc–air batteries, etc. This comprehensive synopsis pays particular attention to the structure and chemistry of COFs and novel strategies that have been implemented to improve battery performance. Additionally, current challenges, possible solutions, and potential future research directions on COFs for batteries are discussed, laying the groundwork for future advances for this exciting class of material. Covalent organic frameworks (COFs) are promising candidates in energy storage applications. This review summarizes the recent progress of COFs for batteries, including lithium‐ion, lithium–sulfur, sodium/potassium‐ion, lithium–CO2, zinc‐ion/–air batteries, etc. This review mainly focuses on the structure and chemistry of COFs and novel strategies implemented to improve battery performance along with current challenges, possible solutions, and potential future research directions.
There are a lot of review papers of sample pretreatment, but the comprehensive review on pipette-tip solid-phase extraction (PT-SPE) is lacking. This review (133 references) is mainly devoted to the development of different types of micro- and nanosorbent-based PT-SPE, including silica materials, carbon materials, organic polymers, molecularly imprinted polymers, and metal-organic frameworks. Each section mainly introduces and discusses the preparation methods, advantages and limitations of adsorbents, and their applications to environmental, biological, and food samples. This review also demonstrates the advantages of PT-SPE like convenience, speed, less organic solvent, and low cost. Finally, the future application and development trend of PT-SPE are prospected.
Graphical abstract
MOF‐74 is one of the most explored metal–organic frameworks (MOFs), but its functionalization is limited to the dative post‐synthetic modification (PSM) of the monodentate solvent site. Owing to the nature of the organic ligand and framework structure of MOF‐74, the covalent PSM of MOF‐74 is very demanding. Herein, we report, for the first time, the covalent PSM of amine‐tagged defective Ni‐MOF‐74, which is prepared by de novo solvothermal synthesis by using aminosalicylic acid as a functionalized fragmented organic ligand. The covalent PSM of the amino group generates metal binding sites, and subsequent post‐synthetic metalation with PdII ions affords the PdII‐incorporated Ni‐MOF‐74 catalyst. This catalyst exhibits highly efficient, size‐selective, and recyclable catalytic activity for the Suzuki–Miyaura cross‐coupling reaction. This strategy is also useful for the covalent modification of amine‐tagged defective Ni2(DOBPDC), an expanded analogue of MOF‐74.
Metal-organic frameworks (MOFs) and ionic liquids (ILs) represent promising materials for adsorption separation. ILs incorporated into MOF materials (denoted as IL/MOF composites) have been developed, and IL/MOF composites combine the advantages of MOFs and ILs to achieve enhanced performance in the adsorption-based separation of fluid mixtures. The designed different ILs are introduced into the various MOFs to tailor their functional properties, which affect the optimal adsorptive separation performance. In this Perspective, the rational fabrication of IL/MOF composites is presented, and their functional properties are demonstrated. This paper provides a critical overview of an emergent class of materials termed IL/MOF composites as well as the recent advances in the applications of IL/MOF composites as adsorbents or membranes in fluid separation. Furthermore, the applications of IL/MOF in adsorptive gas separations (CO2 capture from flue gas, natural gas purification, separation of acetylene and ethylene, indoor pollutants removal) and liquid separations (separation of bioactive components, organic-contaminant removal, adsorptive desulfurization, radionuclide removal) are discussed. Finally, the existing challenges of IL/MOF are highlighted, and an appropriate design strategy direction for the effective exploration of new IL/MOF adsorptive materials is proposed.
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%.
Acrylamide (AA) and heterocyclic aromatic amines (HAAs), as classic hazards produced during food thermal processing, have been widely concerned, but because of their polarity difference, it is very difficult to detect these contaminants simultaneously. Herein, novel cysteine (Cys)-functionalized magnetic covalent organic frameworks (Fe3O4@COF@Cys) were synthesized via a thiol-ene click strategy and then used as adsorbents for magnetic solid-phase extraction (MSPE). Benefiting from the hydrophobic properties of COFs and the modification of hydrophilic Cys, AA and HAAs could be enriched simultaneously. Then, a rapid and reliable method based on MSPE coupled with HPLC-MS/MS was developed for the simultaneous detection of AA and 5 HAAs in thermally processed foods. The proposed method showed good linearity (R2 ≥ 0.9987) with satisfactory limits of detection (0.012-0.210 μg kg-1) and recoveries (90.4-102.8%). Actual sample analysis showed that the levels of AA and HAAs in French fries were affected by frying time and temperature, water activity of samples, content and type of reaction precursors, and reuse of oils.
Herein, a covalent organic framework (COF) was grown on a magnetic metal-organic framework (MOF) by a solvothermal method for the efficient extraction of bisphenols (BPs). The magnetic solid-phase extraction (MSPE) of four bisphenols (bisphenol A, bisphenol B, bisphenol AF and bisphenol C) was carried out without adjusting the pH and salt concentration. When 30 mg Fe3O4@NH2-MIL-88(Fe)@TpPa was used to adsorb for 25 min, 6 mL methanol was used to elute for 20 min, and the extract was detected by high-performance liquid chromatography (HPLC). The proposed method has a low detection limit of 0.011-0.036 ng mL-1, a wide linear range of 0.05-100 ng mL-1, and a correlation coefficient (R2) of 0.9980-0.9998. The intra-day and inter-day precisions are 0.74-2.54% and 1.68-3.72%, respectively. Bisphenol A was determined by applying the proposed method to the determination of actual milk samples. The standard addition experiment showed that the relative recovery of the four bisphenols was 85.70-119.7%. Pseudosecond-order, first-order, Langmuir and Freundlich models were applied to explore the adsorption characteristics of Fe3O4@NH2-MIL-88(Fe)@TpPa. In general, the established Fe3O4@NH2-MIL-88(Fe)@TpPa-MSPE-HPLC-UV method exhibits attractive sensitivity, simple manipulation, and excellent reusability, and it has excellent prospects for the detection of trace BPs in complex milk matrices.
The dream to prepare well-defined materials drives the methodological evolution for molecular synthesis, structural control and materials manufacturing. Among various methods, chemical approaches to design, synthesize, control and engineer small molecules, polymers and networks offer the fundamental strategies. Merging covalent bonds and non-covalent interactions into one method to establish a complex structural composition for specific functions, mimicking biological systems such as DNA, RNA and proteins, is at the centre of chemistry and materials science. Covalent organic frameworks (COFs) are a class of crystalline porous polymers that enable the integration of organic units into highly ordered structures via polymerization. This polymerization system is unique as it deploys covalent bonds to construct the primary order structures of polymeric backbones via polycondensation and leverages on non-covalent interactions to create the high order structures of polymeric networks via supramolecular polymerization in a one-pot reaction system. This Primer covers all aspects of the field of COFs from chemistry to physics, materials and applications, and outlines the design principle, experimental methods, characterization and applications, with an aim to show a concise yet full picture of the field. The key fundamental issues to be addressed are analysed with an outlook on the future major directions from different perspectives. Covalent organic frameworks (COFs) are a class of crystalline porous polymers consisting of highly ordered organic structures formed by polymerization. In this Primer, Tan et al. discuss the design principle, experimental methods, characterization and applications of COFs.
A hydroxy-containing covalent organic framework (COF) was successfully obtained via a simple nitrogen-purge synthetic procedure for the first time. The COF favored a serrated AA-stacking arrangement, which enhanced the stability compared with common AA or AB arrangements. To validate the potential of the COF in environmental applications, we decorated the COF onto NiFe2O4 and used the NiFe2O4@COF nanocomposite for magnetic solid-phase extraction of trace bisphenols (BPs). The parameters affecting extraction efficiencies were systematically optimized. Under the optimum extraction conditions, calibration plots showed good linearity (5.0-1.0 × 103 ng mL-1) for six BPs, and limits of detection varied from 0.14 to 0.73 ng mL-1. Molecular polarity indexes and molecular dynamics simulations revealed why the COF could efficiently recognize and capture BPs. An adsorption mechanism related to the interaction between BP clusters and the COF was discovered. Ecotoxicological assessment of BPs further unraveled the significance of the developed method for the timely tracking of the concentration, distribution, and migration of BPs in environmental media.
To improve the extraction efficiency, availability, and stability of metal-organic framework (MOF) for pipette-tip solid-phase extraction (PT-SPE), a carbonized MOF-74/carbon aerogel composite (CMOF-74/CA) was developed. A carbon aerogel with a surface area of 547.7 m² g⁻¹ was prepared by carbonizing a watermelon peel. After that, via a hydrothermal reaction, the MOF-74 was in situ grown on the surface. After the pyrolysis at 700°C for 2 h, the CMOF-74/CA composite was obtained. Through regulating the concentration of reactants, a series of MOF-74/CA and CMOF-74/CA materials were prepared. These materials were used to extract hexaconazole and diniconazole in fruits and vegetables before gas chromatography-flame ionization detection (GC-FID). The adsorbent type and amount, sample pH, and the desorption solvent type and volume were optimized factor by factor. Under the optimized conditions, a PT-SPE-GC-FID method was established. Moreover, good linearity in the concentration ranges of 0.098-200.0 mg kg⁻¹ and 0.196-200.0 mg kg⁻¹, and detection limits ranging between 0.033 and 0.065 mg kg⁻¹ were achieved for two triazole fungicides (TFs). The relative standard deviations (n=3) for intra-day and inter-day tests were in the ranges of 3.1-3.2% and 3.0-3.4%, respectively. The method showed satisfactory analytical performance in different samples with good relative recoveries in the range of 72.6-116%. Compared with some methods, it displayed wider linearity, better or comparable sensitivity, and enhanced analytical precision.
A facile approach was proposed for the preparation of boric acid-functionalized core-shell structured magnetic covalent organic framework (COF) nanocomposites through employing the Fe3O4 nanoparticles as magnetic core, boric acid-functionalized COFs as the shell via sequential post-synthetic modification (denoted as Fe3O4@[email protected]). The synthesized nanocomposites showed large specific surface area, high magnetic responsiveness, and desirable chemical and thermal stability. Combined with HPLC-MS/MS, the as-prepared Fe3O4@[email protected] composite was applied as a sorbent for magnetic solid-phase extraction (MSPE) of endocrine disrupting compounds (EDCs) from meat samples. Under optimal conditions, the method displays low limits of detection (LODs, 0.08-0.72 μg kg⁻¹) and good precision with relative standard deviations (RSD) lower than 5.4%. The approach was successfully employed for the extraction and detection of EDCs in blank and spiked beef, chicken and pork samples with recovery ranging from 88.8 to 104.2%.
Recently, covalent organic frameworks (COFs) as an important class of porous frameworks have been employed in analytical applications owing to their significant inherent properties such as a high specific surface area with modifiable pore size and a robust nature that leads to great stabilities. Also, COFs are flexible in design to deliberate changes in their physical or chemical properties by generating functionalized COFs or COF-based composites. Here, we summarize some important categories of COFs from the point of view of their design and synthetic strategies. Subsequently, the synergistic combination aspects of COFs with other materials such as different types of magnetic, metal/metal oxide nanoparticles, silica, carbon nanomaterials, polymers, polyoxometalates (POMs), metal-organic frameworks (MOFs), and COFs are reviewed. Finally, the recent applications of COFs as efficient sorbents in analytical sample preparation methods including solid-phase extraction (SPE), dispersive solid-phase extraction (dSPE), magnetic solid-phase extraction (MSPE), and solid-phase microextraction (SPME) will be surveyed with emphasis on important factors that lead to increase extraction efficiency. In addition, challenges and obstacles in these approaches are discussed with perspective highlights.
A metal organic framework (MOF)-based dispersive solid phase extraction procedure was introduced using a hydrophobic sorbent for the extraction of multi class pesticides from fruit juice samples prior to their determination by high performance liquid chromatography-tandem mass spectrometry. For this purpose, NH2-UiO-66(Zr) MOF was synthesized by a hydrothermal approach. Then the sorbent was silylated and used in the extraction procedure. The extraction procedure was done by using 7 mg of the sorbent from 5 mL of a sample solution containing the analytes. After that, the extracted analytes were eluted and preconcentrated by vaporizing the elution solvent. The method was linear within the range of 0.29-500 ng mL⁻¹. The limits of detection, intra- and inter-day relative standard deviations, and extraction recoveries were in the ranges of 0.02-0.1 ng mL⁻¹, 2.9-8.8%, 6.8-14.4%, and 74-89%, respectively. Performing the method on the selected samples showed that they were free of the analytes. This method can help to monitor the studied pesticides in juice samples as well as improving the safety of foods.
Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have always been objects of interest to scientists in various fields by virtue of their prominent characteristic features, such as structural tunability, high specific surface area, and highly ordered pores. With the development of synthesis techniques between MOFs and COFs over the past several years, MOF/COF composites prepared by combining MOFs and COFs have become an emerging class of porous hybrid materials. Herein, we first comprehensive summarize advanced strategies for synthesizing MOF/COF composites. Then, the emerging applications of MOF/COF composites in diverse fields due to their synergistic effects are systematically highlighted, including analytical chemistry (membrane separation, sensing and sample pretreatment) and other fields (catalysis and energy storage). Last, the current challenges associated with future perspectives of MOF/COF composites are also briefly discussed to inspire the advancement of more MOF/COF composites with excellent properties.
Lead (Pb²⁺) pollution poses severe healthy and ecological risks to humans. In this work, sulfate polysaccharide from Enteromorpha prolifera (SPE) was utilized for Pb²⁺ adsorption from simulated intestinal fluid. In order to evaluate its adsorption behaviors comprehensively, batch adsorption of Pb²⁺ was investigated under different conditions. Results showed that SPE presents high adsorption ability for Pb²⁺ through chemical adsorption process and the maximum adsorption capacity for Pb²⁺ was 278.5 mg/g. And SPE exhibited higher removal efficiency (≥60%) for trace Pb²⁺ (<10 mg/L) compared to that of other adsorbents based on polysaccharide. Besides, its adsorption can be described by Langmuir isotherm and pseudo-second-order kinetic models. Further, XRD, FTIR, and XPS were used to characterize the possible interaction of Pb²⁺ with SPE, and the results showed that carboxyl and hydroxyl groups in SPE play more important role than that of sulfate group. Our work represents the first assessment of Pb²⁺ adsorption properties of SPE. This investigation highlights the potential application of SPE to protect the body from hazard of food-derived heavy metals.
In the present work, a novel composite [email protected]2@TpBD (CCF stands for carboxyl cotton fiber) was fabricated for the extraction and removal of BPs from aqueous samples. Both the UiO-66-NH2 (MOF) and TpBD (COF) were immobilized on CCF through feasible layer-by-layer and Schiff base reaction, and characterized using field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) techniques. The [email protected]2@TpBD was packed in pipette tip as micro-column to investigate the adsorption of BPs using a pipette tip solid-phase extraction (PT-SPE) method. Various parameters (sampling flow rate, sample pH, amount of adsorbent, ionic strength, methanol concentration, and flow rate of eluent) affecting the extraction efficiency were optimized. Based on strong π-π conjugation, hydrogen bonding, and hydrophobic interactions, the adsorbent exhibited good extraction and removal capability. A low limit of detection (0.16–0.75 ng/mL) and a high adsorption (4.3–5.6 mg/g) were obtained. Accordingly, the composite [email protected]2@TpBD material was shown to be a suitable adsorbent for the extraction and removal of BPs from aquatic samples due to excellent reusability, reproducibility, and high adsorption capacity.
[email protected] composite was fabricated for greater adsorption capacity through the utilization of corncob, which is a natural, sustainable, and cellulose-rich resource. An in-situ growth strategy was implemented to graft UiO-66-NH2 on carboxyl-terminal corncob induced by the thermal esterification of critic acid. Subsequently, [email protected]2@TpBD was constructed through the Schiff base reaction between 2,4,6-triformylphloroglucinol (Tp) and UiO-66-NH2 as well as benzidine (BD). The ratio of UiO-66-NH2 and TpBD was optimized to be 5:3 for enhancing adsorption capacity. Based on the π-π, hydrogen bonding, and -SO2-Zr-O- coordination effect, sulphonamides (SAs) were chosen to investigate the adsorption capacity of adsorbent using an in-syringe solid phase extraction (IS-SPE) method. The binding energy calculated using density functional theory (DFT) reached -37.45 Kcal/mol, which indicated the strong interactions between SAs and [email protected]2@TpBD. Combined with ultra-performance liquid chromatography (UPLC), a high sensitivity was obtained with low detection of 0.10 μg/L. The prepared [email protected]2@TpBD exhibited good reproducibility within relative standard deviations (RSDs) 3.1%-3.4% in intra-batch and 4.3%-8.4% in inter-batch. Moreover, the extraction capacity of adsorbent was not decreased in 20 recycles adsorption-desorption within RSDs 3.8%-8.5%. With features of permanent porosity, multiple active sites, and good renewability, [email protected]2@TpBD shows great potential towards industrial applications in the field of adsorption.
The conversion of metal–organic frameworks (MOFs) to porous carbon has attracted extensive attention for developing multifunctional adsorbent materials. Herein, we demonstrated a facile method to prepare magnetic porous carbon via calcinating MIL-101(Fe) precursor loaded with glucose at 700°C in an N2 atmosphere. The obtained magnetic porous carbon (MPCG) contained plenty of oxygen-containing functional groups and exhibited an enlarged specific surface area (177.7 m²/g) compared with its precursor (41.2 m²/g). In addition, MPCG can be easily separated from the matrix by a magnet. Benefitting from these advantages, the magnetic porous carbon exhibited high affinity toward four synthetic organic dyes (amaranth, ponceau 4R, sunset yellow, and lemon yellow) in an aqueous solution. Moreover, the adsorbent can be applied to quantitatively detect synthetic organic dyes in drinks coupled with chromatography. A new magnetic solid-phase extraction method for dye analysis yielded reasonable linearity (r0.99), low limits of detection (0.047–0.076 μg/L), and good precision within the analyte concentration range of 0.25–50 μg/L.
To improve the extraction efficiency of carbon fibers (CFs) toward organic pollutants, TiO2 nanorod arrays (NARs) were grown in situ on CFs. Subsequently, biochar nanospheres and covalent organic framework nanospheres were separately introduced to functionalize the NARs. A sequence of materials was produced by regulating the reactant concentrations and characterized using a scanning electron microscope, an X-ray photoelectron spectrometer, an X-ray diffractometer, a Raman spectrometer, and a specific surface area analyzer. The materials were then deposited into separate poly(etheretherketone) tubes for in-tube solid-phase microextraction (IT-SPME). These tubes were evaluated with different types of organic pollutants (polycyclic aromatic hydrocarbons (PAHs), estrogens, bisphenols, and phthalate esters) using a combination of high-performance liquid chromatography and IT-SPME, and they exhibited diverse extraction performance. The extraction mechanism of each material is carefully discussed, and the structure–performance relationship is also summarized based on the chemical structures and extraction properties of the materials. The most efficient extraction materials for different analytes were discovered and used to develop analytical methods. Three online methods were used to sensitively detect PAHs, estrogens, and bisphenols in real water samples, respectively. Satisfactory results were obtained, including enrichment factors up to 6784, detection limits as low as 0.001 μg L⁻¹, linear ranges of 0.003–15.0 μg L⁻¹, and relative standard deviations ranging from 0.2% to 15.2%. The results indicate that these methods have some advantages over previous material-based methods.
The functionalization of covalent organic frameworks (COFs) identifies significant potential for developing selective coating materials for solid-phase microextraction (SPME). Herein, a chlorine-functionalized covalent organic framework (CF-COF) was in-situ synthesized by employing triformylphloroglucinol (Tp) and 2,5-dichloro-1,4-phenylenediamine (2,5-DCA) as monomers on an amino-functionalized stainless steel wire. The obtained CF-COF coated fiber exhibited a higher enrichment capacity for polychlorinated biphenyls (PCBs) than commercial fibers and non-chlorinated COF fiber, owing to a more hydrophobic surface, size-matching effect, a large number of micropores and the π–π stacking interactions between COF coating and analytes. As a practical application, the CF-COF coated fiber was applied to the headspace extraction of 17 PCBs prior to their quantification by GC/MS. The established analytical method offered a good linearity in the range of 0.1 − 1000 ng L⁻¹, low detection limits of 0.0015-0.0088 ng L⁻¹, and satisfactory enhancement factors (EFs) of 699 - 4281. The repeatability for single fiber and the fiber-to-fiber reproducibility was lower than 9.26% and 9.33%, respectively. The proposed method was verified to be sensitive, selective, and applicable for the analysis of ultra-trace PCBs in environmental surface water samples with the recoveries ranged from 78.7% to 124.0%.
A novel mixed matrix of MOF@COF hybrid was firstly formed by coating of hexahedral cage structure MOF with lightweight porous COF, and applied in dispersive solid-phase extraction of the phenoxy carboxylic acids (PCAs) from water and vegetable samples. Combined with liquid chromatography-tandem mass spectrometry, an excellent method with low limits of detection (0.69−1.79 ng·L−1 / 0.002−0.006 ng·g-1), good reproducibility (1.32%–7.02% / 1.81%–6.71%), and excellent linearities (10–1000 ng·L−1, R≥0.9955 / 0.04–50 ng·g-1, R≥0.9966) was established. The adsorption mechanisms deduced that the π-π interaction, hydrophobic effects, hydrogen bond, and halogen bond may promote the excellent adsorption of the PCAs. Finally, the applicability of the method was verified by spiking four kinds of water and vegetable samples with PCAs, and satisfying recoveries were obtained (between 83.3% and 104.9%).
This study reports the development of a new type of Zr-based MOF by inserting copper and carboxylate into HCl modulated UiO-67 (UiO-67-vac) which gained higher surface area/vacant than UiO-67. Copper was inserted into MOF containing uncoordinated carboxylate group, to create open metal site in the form of COOCu which called
UiO-67-ox-Cu. PXRD, FTIR, BET, SEM, EDS, UV-Vis and XPS were used to characterize the obtained MOFs. As expected, UiO-67-ox-Cu exhibits the highest ammonia capacity (178.3 mg/g) among UiO-67 (104 mg/g) and UiO-67-vac (121 mg/g) at 298 K and 1 bar pressure. In fact, the significant increase in ammonia uptake of UiO- 67-ox-Cu is related to the modified binding affinity of -COOCu groups with ammonia. Moreover, UiO-67-vac with the highest surface area showed the hydrogen adsorption capacity of 18.75 mg/g at 77 K, which is comparable or even superior to the previously reported value. Interestingly, adsorption capacities were retained with slight changes around five cycles and three regeneration temperatures, 25, 60 and 120 ◦C under vacuum pressure which were proved by PXRD after ammonia adsorption/desorption. The good results obtained in the current work clearly show the role of post-synthesis functionalization approach for creation of new metal/active sites into MOFs.
Herein, we demonstrate, for the first time, that covalent organic frameworks (COFs) can be efficient adsorbents for the screening of pharmaceuticals in real water samples, obtaining highly representative data on their occurrence and avoiding the cost of carrying high volume samples and tedious and costly clean-up and preconcentration steps. Of the 23 pharmaceuticals found present in the water samples from the Tagus river estuary using state-of-the-art solid-phase extraction (SPE), 22 were also detected (adsorbed and recovered for analysis) using a COF as the adsorbent material with adsorption efficiency over 80% for nearly all compounds. In specific cases, acidification of the water samples was identified to lead to a dramatic loss of adsorption efficiency, underlining the effect of sample pre-treatment on the results. The COF efficiently adsorbed (>80%) 19 pharmaceuticals without acid treatment of the sample, highlighting the potential of this class of materials for representative in situ passive adsorption of pharmaceuticals, making this material suitable for being used in water monitoring programs as a simple and cost-efficient sample preparation procedure. In the case of α-hydroxyalprazolam and diclofenac, the COF outperformed the SPE procedure in the recovery efficiency. Although further efforts should be made in tailoring the desorption of the pharmaceuticals from the COF by using different solvents or solvent mixtures, we propose COFs as convenient adsorbent for broad-scope screening and as an efficient adsorbent material to target specific classes of pharmaceuticals. To the best of our knowledge, this is the first study on the use of COFs for contaminant screening in real, naturally contaminated water samples.
A temperature-responsive solid-phase microextraction (SPME) coating was prepared via in-situ atom transfer radical polymerization (ATRP) method. By controlling the temperature of solution below and above the lower critical solution temperature (LCST) of the coating, it can switch between hydrophilic and hydrophobic, thus providing a convenient approach for the selective extraction of analytes with different polarities. The average extraction amount of temperature-responsive coating for polar analytes is about 1.5-fold to that of non-polar ones below LCST, and vice versa. Effective extraction of three biomacromolecules was also obtained by controlling the temperature below or above LCST. The adsorption capacity of the coating for the hydrophilic biomacromolecules at 15°C is 1.5-2 fold that of 50°C, whereas the adsorption capacity of the coating to BSA at 50°C is about 3 fold that of 15°C. This approach holds great promise for SPME because it provides a simple strategy to prepare bifunctional coatings for various applications.