Ultrasound-assisted synthesis of clover-shaped nano-titania functionalized covalent organic frameworks for the dispersive solid phase extraction of N-nitrosamines in drinking water

In this study, three batches of nano-titania functionalized covalent organic frameworks were acquired depending on different solvothermal reaction stages (24 h, 48 h and 72 h), which were named as single roll-up shaped nano-titania functionalized COFs (SSTF-COFs), double roll-up shaped nano-titania functionalized COFs (DSTF-COFs) and clover-shaped nano-titania functionalized covalent organic framework (CSTF-COFs), respectively. After comparing their extraction performances, the more efficient and stable CSTF-COFs were selected as sorbent for the dispersive solid phase extraction (dSPE) of eight target N-nitrosamines in drinking water, followed by the determination with liquid chromatography-tandem quadrupole mass spectrometry (LC-MS/MS). Owing to the introduction of hydroxy groups, CSTF-COFs showed high extraction efficiency for N-nitrosamines with a wide range of polarities through hydrogen bonding interaction, hydrophobic interaction and hydrophilic interaction. Under optimum conditions, the developed method provided relatively low limits of detection (0.13-2.45 ng/L) and satisfactory recoveries (88.6-105.5%), with relative standard deviations (RSDs) less than 8.3%. Therefore, with the assistance of CSTF-COFs, trace levels of N-nitrosamines were quantitatively and sensitively determined in 31 out of 460 bottled drinking water samples in a sensitive and convenient way.

Dual crosslinked polyamidoxime/alginate sponge for robust and efficient uranium adsorption from aqueous solution

A facile, low-cost, organic solvent-free fabrication strategy is developed to prepare a seawater-stable sponge adsorbent from a water-soluble precursor for highly efficient extraction of uranium from seawater and uranium-containing wastewater.

Facile synthesis of a covalent organic framework (COF) based on the reaction of melamine and trimesic acid incorporated electrospun nanofiber and its application as an electrochemical tyrosinamide aptasensor

Schematic presentation of the COFCNF platform for the highly sensitive detection of tyrosinamide by using a solution containing [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ as a redox probe.

Synthesis of anionic ionic liquids@TpBd-(SO3)2 for the selective adsorption of cationic dyes with superior capacity

Anionic ionic liquids@covalent organic materials for the selective adsorption of cationic dyes.

Thiol-Ene Click Synthesis of Phenylboronic Acid-Functionalized Covalent Organic Framework for Selective Catechol Removal from Aqueous Medium

We report a thiol-ene click strategy for the preparation of a novel phenylboronic acid-functionalized covalent organic framework (COF) for selective removal of catechol in aqueous solution. Vinyl-functionalized 2,5-diallyloxyterephthalaldehyde (Da-V) was prepared as a building ligand. Da-V was then condensed with 1,3,5-tris(4-aminophenyl)benzene (Tab) to give a vinyl-functionalized COF DhaTab-V. Subsequently, 4-mercaptophenylboronic acid (4-MPBA) was covalently linked on DhaTab-V via thiol-ene click reaction to give phenylboronic acid-functionalized COF DhaTab-PBA. The adsorption isotherms, energetics and kinetics, and reusability of DhaTab-PBA for the adsorption and removal of catechol from aqueous solution were investigated in detail. This phenylboronic acid-functionalized COF is promising as sorbent for selective removal of catechol from aqueous medium with large adsorption capacity and good reusability.

One-step synthesis of Cu(II) metal-organic gel as recyclable material for rapid, efficient and size selective cationic dyes adsorption

Efficient removal of non-biodegradable and hazardous dyes from wastewater remains a hot research topic. Herein, a rationally designed a Cu(II)-based metal-organic gel (Cu-MOG) with a nanoporous 3D network structure prepared via a simple one-step mixing method was successfully employed for the removal of cationic dyes. The Cu-MOG exhibited high efficiency, with an adsorption capacity of up to 650.32 mg/g, and rapid adsorption efficiency, with the ability to adsorb 80% of Neutral Red within 1 min. The high adsorption efficiency was attributed to its large specific surface area, which enabled it to massively bind cationic dyes through electrostatic interaction, and a nanoporous structure that promoted intra-pore diffusion. Remarkably, the Cu-MOG displayed size-selective adsorption, based on adsorption studies concerning dyes of different sizes as calculated by density functional theory. Additionally, the adsorption performance of the Cu-MOG still maintained removal efficiency of 100% after three regeneration cycles. These results suggested that the Cu-MOG could be expected to be a promising and competitive candidate to conveniently process wastewater.

Remarkably efficient removal of toxic bromate from drinking water with a porphyrin-viologen covalent organic framework

The presence of carcinogenic bromate (BrO₃⁻) in drinking water became a global concern and efforts towards its removal mainly focused on addressing the source. Herein, we rationally designed a porphyrin-based covalent organic framework (PV-COF) with a cationic surface to provide electrostatic interactions and a porphyrin core to induce hydrogen bonding interactions for the efficient removal of BrO₃⁻ from water. Through H-bonding and electrostatic interactions, PV-COF exhibited an exceptional bromate removal efficiency (maximum adsorption capacity, Q_max: 203.8 mg g⁻¹) with the fastest uptake rate (k_ads) of 191.45 g mg⁻¹ min⁻¹. The bromate concentration was reduced to far below the allowed concentration in drinking water (10 ppb) within 20 minutes. We studied the relationship between bromate adsorption and COF surface modification by metalation of the porphyrinic core or neutralization of the viologen linkers by chemical reduction. The bromate adsorption mechanism was studied by EDAX mapping and molecular simulations, and it was found that ion exchange and hydrogen bonding formation drive the adsorption. Importantly, PV-COF could be easily recycled several times without compromising its adsorption efficiency.

A cationic COF removes carcinogenic bromate with a remarkable rate constant of 191.45 g mg⁻¹ min⁻¹.

Facile magnetization of covalent organic framework for solid-phase extraction of 15 phthalate esters in beverage samples

Phthalate esters (PAEs), a category of widely used plasticizers, are tend to migrate from plastic packaging to drinks. In this paper, we develop a simple and rapid coprecipitation method for synthesis of a magnetic covalent organic framework (COF) adsorbent. The fabricated COF-(TpBD)/Fe₃O₄ was applied to magnetic solid phase extraction (MSPE) of 15 phthalate esters (PAEs) for subsequent GC-MS/MS determination in beverage samples. The as-synthesized magnetic adsorbent exhibited great potential in PAEs analysis with a limit of detection of 15 PAEs ranged from 0.005 to 2.748 μg L^-1 (S/N = 3). The intra-day and inter-day relative standard deviations (RSD) value of the PAEs were less than 8.8% and 9.9%, respectively. The adsorbent can be reused after washing with methanol. The developed method was successfully applied for the determination of trace PAEs in eight beverages with recoveries ranging from 79.3% to 121.8% and RSDs were less than 11.9%. This work provides a simple magnetization process, which facilitates the application of COFs for enrichment and separation of PAEs in beverages with different matrices.

Core-Shell Structured Magnetic Covalent Organic Framework Nanocomposites for Triclosan and Triclocarban Adsorption

Triclosan (TCS) and triclocarban (TCC) are widely used as bactericides in personal-care products. They are frequently found in environmental water and have the potential to cause a number of environmental and human health problems. In this study, we investigated adsorption and magnetic extraction for efficient removal of TCS and TCC from water and serum samples by core-shell structured magnetic covalent organic framework nanocomposites (Fe₃O₄@COFs). The as-prepared Fe₃O₄@COFs was fabricated on the Fe₃O₄ nanoparticles in situ growth strategy at room temperature via condensation reaction of 1,3,5-tris(4-aminophenyl) benzene (TAPB) and terephthaldicarbox-aldehyde (TPA) in the presence of dimethyl sulfoxide (DMSO). The whole process of adsorption was monitored by ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) analysis with high sensitivity. The adsorption behaviors showed high adsorption capacity and fast adsorption. Furthermore, the adsorption performance through Langmuir and Freundlich isotherms showed multilayer adsorption through the interactions of space embedding effect, van der Waals forces, and benzene ring π-π stacking at a low concentration range and monolayer adsorption through strong π-π stacking at a high concentration range between the interface of TCS or TCC and Fe₃O₄@COFs at a high concentration range. Results indicated that the adsorption of TCS and TCC onto Fe₃O₄@COFs can be better represented by the pseudo-second-order model. Good removal efficiencies (82.3∼95.4%) and recoveries (92.9∼109.5%) of TCS and TCC in fetal bovine serum (FBS) and reusability at least 10 times were achieved. The Fe₃O₄@COFs exhibited high stability and excellent performance for the removal of TCS and TCC from water and biological samples. The results presented here thus reveal the exceptional potential of COFs for high-efficient environmental remediation.

Boric-Acid-Functionalized Covalent Organic Framework for Specific Enrichment and Direct Detection of cis-Diol-Containing Compounds by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Design and synthesis of a novel matrix that serves as highly selective adsorption material are significant for the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of small molecules in complicated biosamples. In this work, we presented a facile one-pot strategy for the synthesis of boric-acid-functionalized covalent organic frameworks (B-COFs) by using 2,4,6-trihydroxy-1,3,5-benzenetrialdehyde, benzidine, and 4-aminophenyl-boronic acid as ligands. Compared with bare COFs, the B-COFs have similar crystallinity, specific surface, and well-developed pore structure. The surface area and average pore size of B-COFs were 238.0 m²/g and 1.2 nm, respectively. The resulting material was used as an adsorbent for selective enrichment of cis-diol-containing compounds based on an affinity reaction between phenylboronic acid and cis-diol. Using luteolin, riboflavin, and pyrocatechol as model analytes, the enrichment ability of B-COFs as a matrix was examined by MALDI-TOF MS assay, and its high selectivity against target analytes was obtained in the presence of 100 times more anti-nonspecific compounds than that even in the complicated biosample. The limits of detection for luteolin, riboflavin, and pyrocatechol were as low as fg/mL with B-COF enrichment. The B-COFs were further employed and validated for specific enrichment and direct detection of target analytes with complex samples such as human serum, milk, and Capsicum samples. Large surface area, numerous boric-acid active sites, and super stability make B-COFs with high enrichment capacity, high selectivity and sensitivity, satisfying reproducibility, and excellent applicability in MALDI-TOF MS assays.

Covalent immobilization of covalent organic framework on stainless steel wire for solid-phase microextraction GC-MS/MS determination of sixteen polycyclic aromatic hydrocarbons in grilled meat samples

Covalent organic framework TpBD was grafted on stainless steel wire with polydopamine as a linker. The fabricated TpBD bonded stainless steel wire was used as the solid-phase microextraction fiber to extract sixteen polycyclic aromatic hydrocarbons (PAHs) for subsequent GC-MS/MS determination in grilled meat samples. The developed method gave the limits of detection (S/N = 3) from 0.02 (pyrene)-1.66 (naphthalene) ng L^-1 and enhancement factors from 1069 (naphthalene)-10879 (benz(a)anthracene). The relative standard deviations (RSDs) for intra-day and inter-day study are in the range of 2.6%-8.5% and 4.5%-9.4%, respectively. The fiber-to-fiber RSDs for three parallel prepared fibers were 5.3%-10.0%. One TpBD bonded fiber can stand at least 200 cycles without significant loss of extraction efficiency. The developed method was successfully applied for the determination of trace PAHs in grilled meat samples with recoveries from 85.1% to 102.8%.

Facile Preparation of Dual-Shell Novel Covalent-Organic Framework Functionalized Magnetic Nanospheres Used for the Simultaneous Determination of Fourteen Trace Heterocyclic Aromatic Amines in Nonsmokers and Smokers of Cigarettes with Different Tar Yields Based on UPLC-MS/MS

The facile preparation, characterization, and application of novel dual-shell TpBD (a kind of covalent-organic framework) coated magnetic nanospheres as sorbents for simple, fast, and high selectivity capture of 14 heterocyclic aromatic amines (HAAs) are reported. Quantum chemistry theory calculations were conducted to directly and quantifiably describe the multiple interactions, including π-π, hydrogen bonding, cation-π, static electricity, and ion-exchange, between TpBD and heterocyclic aromatic amines. The excellent adsorption capacity of TpBD coated magnetic nanospheres was further evaluated by extraction of 14 HAAs from nonsmokers' and smokers' urine samples. Under the optimized conditions, the magnetic solid phase extraction process can be completed with high recovery ranging from 95.4% to 129.3%. After being washed with acetonitrile and water successively, the collected sorbents can be easily recycled and reused five times without any significant difference in performance. Coupled with the ultra performance liquid chromatography-tandem mass spectrometer detection, the exposure level of HAAs in nonsmokers and smokers smoking cigarettes with different tar yields were successfully explored. And, this implied that the robust method based on the versatile TpBD coated dual-shell magnetic nanospheres sorbents represents a great potential application in the analysis of disease markers and body fluids.

Recyclable magnetic covalent organic framework for the extraction of marine biotoxins

A novel procedure for the preparation of magnetic covalent organic frameworks (COFs) is reported. In situ functionalization of Fe3O4 with dopamine rapidly afforded amino-functionalized magnetic nanoparticles, which after decoration with a COF building block and subsequent COF growth gave access to magnetic composite mTpBD-Me2. The optimized synthesis conditions yielded crystalline and superparamagnetic material with no loss in surface area as compared to bulk COF. The composite material was employed for the first time in magnetic solid-phase extraction of marine biotoxins from seawater with high efficiency, where calculated maximum adsorption capacities of 812 mg g-1 and 830 mg g-1 were found for okadaic acid (OA) and dinophysistoxin-1 (DTX-1), respectively, corresponding to an increase of ∼500-fold for OA and ∼300-fold for DTX-1 as compared to the commonly used non-magnetic macroporous resins. Nearly quantitative desorption efficiency of both biotoxins was obtained using 2-propanol as solvent, rendering the composite materials recyclable with merely minor losses in adsorption capacity after five consecutive cycles of adsorption/desorption. In addition, retention of crystallinity after the adsorption cycles highlights the stability of the composite in seawater. These results illustrate the great efficiency of the novel material in biotoxin adsorption and show great promise for its application in environmental monitoring programs.

Controlled Manipulation of Metal-Organic Framework Layers to Nanometer Precision Inside Large Mesochannels of Ordered Mesoporous Silica for Enhanced Removal of Bisphenol A from Water

Considerable attention has been paid on the design of hierarchical porous metal-organic framework (MOF) composites, which not only enhances the performance but also broadens the applications of MOFs. So far, controlled manipulation of nanometer-thick MOF layers in ordered mesochannels, while retaining their respective intrinsic properties, is still a main challenge because of the difficulty of growing MOFs in confined space. Herein, using a step-by-step coordination method, the formation of a hierarchical micro-mesoporous hybrid with a wall (channel wall and coating layer) thickness of up to 8.0 nm and open pore size down to 7.7 nm has been achieved based on large mesoporous SBA-15, and the wall thickness with nanometer precision can be controlled by adjusting the growth cycles of zeolite imidazolate framework-8 (ZIF-8) coating layers. Compared to pure ZIF-8, the obtained ZIF-8@SBA-15 composites showed more than 2-fold enhancement in adsorption capacity and approximately 20-fold improvement in the adsorption rate constant for bisphenol A in water, which could be ascribed to the synergistic effects of the high adsorption ability from ZIF-8 and the fast diffusion property from SBA-15. More importantly, the degraded ZIF-8@SBA-15 composite can be completely restored by a simple immersion into 2-methylimidazole solution. The easy restorability and good reusability further enable ZIF-8@SBA-15 as a promising adsorbent for effectively removing organic contaminants from water.

Efficient enrichment of triazole fungicides from fruit and vegetable samples by a spherical porous aromatic framework

A porous aromatic framework was synthesized and utilized as a novel SPME coating for efficient enrichment of triazole fungicides.

Large-scale synthesis of azine-linked covalent organic frameworks in water and promoted by water

A hydrothermal procedure has been developed to synthesize covalent organic frameworks in water with the advantages of large-scale production, short reaction time, catalyst-free reaction, and improved product quality.

Processing of covalent organic frameworks: an ingredient for a material to succeed

This tutorial provides a perspective on the processability of covalent organic frameworks, an emerging class of new organic polymers, towards their potential applications.

Eco-friendly and facile one-step synthesis of a three dimensional net-like magnetic mesoporous carbon derived from wastepaper as a renewable adsorbent

Millions of tons of paper and its derivatives are annually wasted without being recycled and reused. To promote the comprehensive utilization of resources and eco-friendly preparation, waste filter paper, printer paper, and napkins were chosen as carbon sources to one-step synthesize three types of three dimensional (3D) net-like magnetic mesoporous carbon (MMC) by an eco-friendly and low-cost method. These mesoporous (3.90–7.68 nm) composites have a high specific surface area (287–423 m² g⁻¹), well-developed porosity (0.24–0.74 cm³ g⁻¹) and abundant oxygen-containing functional groups. Compared to the other two composites, the adsorbent derived from filter paper showed the highest adsorption capacity towards methylene blue (MB) (q_max = 332.03 mg g⁻¹) and rhodamine B (RhB) (q_max = 389.59 mg g⁻¹) with a high adsorption rate (<5 min). According to the effect of pH value on adsorption capacity, and combining the analysis of Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy, the main adsorption mechanisms can be summarized as hydrogen bonds, electrostatic interactions, and π–π interaction. Besides, the occurrence of redox reactions between Fe²⁺/Fe⁰ and dye cannot be ignored. Finally, experiments on reusability were performed. They showed that the 3D net-like MMC could be easily regenerated and still maintained a removal efficiency of above 80% for RhB and 90% for MB after five cycles.

Millions of tons of paper and its derivatives are annually wasted without being recycled and reused.

Facile preparation of a cationic COF functionalized magnetic nanoparticle and its use for the determination of nine hydroxylated polycyclic aromatic hydrocarbons in smokers’ urine

A novel cationic-COF coated double-shell magnetic sorbent, possessing excellent dispersive capability, high stability, and desirable absorption affinity, was prepared.

Porous Organic Frameworks: Advanced Materials in Analytical Chemistry

Porous organic frameworks (POFs), a general term for covalent-organic frameworks (COFs), covalent triazine frameworks (CTFs), porous aromatic frameworks (PAFs), etc., are constructed from organic building monomers with strong covalent bonds and have generated great interest among researchers. The remarkable features, such as large surface areas, permanent porosity, high thermal and chemical stability, and convenient functionalization, promote the great potential of POFs in diverse applications. A critical overview of the important development in the design and synthesis of COFs, CTFs, and PAFs is provided and their state-of-the-art applications in analytical chemistry are discussed. POFs and their functional composites have been explored as advanced materials in "turn-off" or "turn-on" fluorescence detection and novel stationary phases for chromatographic separation, as well as a promising adsorbent for sample preparation methods. In addition, the prospects for the synthesis and utilization of POFs in analytical chemistry are also presented. These prospects can offer an outlook and reference for further study of the applications of POFs.

Covalent Organic Framework as Fiber Coating for Solid-Phase Microextraction of Chlorophenols Followed by Quantification with Gas Chromatography-Mass Spectrometry

Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry was adopted for the simultaneous determination of seven chlorophenols (CPs) from honey and canned-yellow-peach samples. A covalent organic framework made of 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD) was used as the SPME fiber coating to preconcentrate the acetylation derivatives of the CPs. The main experimental parameters including derivatization conditions, extraction temperature and time, headspace volume, salt concentration, and desorption temperature were investigated. The fiber showed a high extraction capability for the CPs. The limits of detection (LODs) for the analytes were 0.3-0.7 μg kg^-1 for honey and 0.8-1.8 μg kg^-1 for canned-yellow-peach samples, suggesting good sensitivity for the method. The response linearity was 2.4-250 μg kg^-1 for 2-CP and 3,4-CP and 1.0-150 μg kg^-1 for the other remaining analytes in the honey samples. For the canned-yellow-peach samples, the response linearity was 6.0-300 μg kg^-1 for 2-CP and 3,4-CP and 3.0-200 μg kg^-1 for the others. The correlation coefficients were higher than 0.9919. Good repeatability (RSD < 11.9%) for the method and high recoveries (70.2-113%) of the analytes were observed under the optimal conditions. The established method was satisfactorily applied for the analysis of honey and canned-yellow-peach samples.

3D cryogel composites as adsorbent for isolation of protein and small molecules

A green and promising sample pretreatment method was successfully established, which efficiently isolated proteins and small molecules in human serum. This method was achieved based on the multifunctional polymer, cryogel, as a solid phase extraction (SPE) monolith easily equipped in a syringe. The cryogel (pDC/GO-DE) was composed of diallyldimethyl ammonium chloride (DC) and 2-hydroxyethyl methacrylate (HE), which was further modified with graphene oxide (GO) and N-diethylethanamine hydrobromide (DE). Various proteins, including bovine serum albumin (BSA), lysozyme (Lys), γ-globulins, immunoglobulin G (IgG), transferrin, small molecules (ribavirin, adenosine, ofloxacin, estriol, rutin, amoxicillin, ibuprofen, 1-methyl-3-phenyl-propylamine, and benzylamine) and their mixtures were successively studied as model analytes to evaluate the new material and demonstrate the isolation mechanism, which was mainly dependent on mixed-mode ion-exchange and the hybrid hydrophobicity-hydrophilicity property of pDC/GO-DE cryogel. Moreover, the three-dimensional macroporous structure contributed to the underlying size-selective isolation. When 10 times diluted human serum was used as the sample, more than 95% of proteins were adsorbed within 10 min under physiological conditions, and the interference matrix in serum was also efficiently reduced. After recycling three times, the extraction ratio of proteins in human serum was still higher than 90%. When four small molecules (camptothecin, ribavirin, 1-methyl-3-phenylpropylamine and ofloxacin) were added to blank human serum, their recoveries were within 65.6-81.8%, and were comparable to those obtained by protein precipitation method (63.7-83.2%).

Aptamer-Functionalized Magnetic Conjugated Organic Framework for Selective Extraction of Traces of Hydroxylated Polychlorinated Biphenyls in Human Serum

A solid-phase extraction adsorbent based on an aptamer-functionalized magnetic conjugated organic framework (COF) was developed for selective extraction of traces of hydroxylated polychlorinated biphenyls. This material has advantages such as superparamagnetism of the magnetic core, high surface area and porous structure of the COF, and high specific affinity of the aptamer. In combination with HPLC-MS, the aptamer-functionalized magnetic COF was used for the capture of hydroxy-2',3',4',5,5'-pentachlorobiphenyl in human serum. The method provided a linear range of 0.01-40 ng mL^-1 with a good correlation coefficient (R² =0.9973). The limit of detection was as low as 2.1 pg mL^-1 . Furthermore, the material showed good reusability and could be applied in at least ten extraction cycles with recoveries greater than 90 %.