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A new type of core–shell composite material was prepared and applied as a hydrophilic interaction liquid chromatography (HILIC) stationary phase. In this work, silica spheres were first modified with a bimetallic central metal–organic framework (ZnCoMOF) by a new strategy of static self-assembled in situ growth. This strategy was beneficial for increasing the electrostatic interaction between the MOF ligand and silica via introducing a sodium dodecylbenzenesulfonate (SDBS) group. The ZnCoMOF@silica stationary phase was characterized and evaluated in comparison with amino-modified and bare silica columns in terms of various polar analytes including eight nucleosides and nucleobases, seven carbohydrates, and multiple sulfonamides and antibiotics. The effects of organic solvent concentration, water content, the concentration of the salt and the pH of the buffer solution on the retention time were studied, which demonstrated the typical retention behavior of HILIC on the ZnCoMOF@silica column. Compared with most reported MOF-based stationary phases, the new composite material showed excellent hydrophilic properties and separation efficiency for various polar analytes. Moreover, the obtained stationary phase showed good reproducibility and stability. The relative standard deviation (RSD) of the retention time for repeatability was found to range from 0.1% to 0.6%, and the RSD of the retention time for stability was found to range from 0.3% to 0.7%. Furthermore, the column batch-to-batch reproducibility showed excellent preparation reproducibility, which few reported in most previous MOF@silica composite materials. This specific preparation method offers an easy and novel way to manipulate the amount of MOF particles on silica, which extends a universal way to produce various MOF@silica stationary phases by the method of static self-assembled in situ growth. [ABSTRACT FROM AUTHOR]

• A functionalized MOFs-based composite with dispersed hierarchical pores was fabricated. • It was applied as mixed-mode stationary phase for fast and efficient separation. • It exhibited superior selectivity for separation of various analytes. • It highlighted the role of the defect of MOFs and function of L-Cysteine. The micropores of the metal-organic frameworks (MOFs) endow with the advantages of size selectivity and large specific surface area, etc., but they limit their applications toward the control of diffusion and transport processes. Here, we report a strategy to prepare the hierarchical porous material, functional defect, which allows incorporation of L-Cysteine in the MOF by defect-loading. Silica microspheres were modified with these materials to form core-shell composites and used as mixed-mode stationary phases for chromatographic separations. Compared with the traditional MOFs-based stationary phase, it exhibited superior efficiency and selectivity for separation of various analytes and highlighted the role of defect of MOFs and function of L-Cysteine. In addition to the rapid separation of hydrophobic compounds, the stationary phase showed great potential in the separation of hydrophilic analytes, especially for separation of ten carbohydrates and eight sulfonamides. It showed excellent chromatographic reproducibility and stability, and the repeatability of preparation was investigated by relative standard deviations of retention time and/or column efficiency of objective compounds, which was among different batches less than 1.81%. This demonstration provided deep understanding of separation mechanism between MOF-based composites with functional defect and analytes, and stimulated the wide applications of such defective MOFs complexes in separations and analysis. [ABSTRACT FROM AUTHOR]

The nickel organic framework capped with polyvinylpyrrolidone was prepared and synergistically immobilized onto porous silica surface as the mixed-mode stationary phase for high-performance liquid chromatography. Here, polyvinylpyrrolidone firstly was chosen as functional molecules to change morphology and size of the metal organic framework. The silica microspheres were then modified by them via a simple bonding method rather than in-situ growth method with the aid of electrostatic interaction commonly used before. The stationary phase showed flexible selectivity for separation of both hydrophilic and hydrophobic compounds, especially for hydrophilic compounds such as carbohydrates, alkaloids and sulfonamides etc. The chromatographic behaviors were evaluated by investigating various factors, and a typical mixed-mode retention feature of the column was observed. The composites could be prepared repetitively, and relative standard deviations of retention time of objective compounds among different batches were less than 1.75%. It also showed excellent chromatographic reproducibility, stability and potentiality for application in real samples. In short, the composites can be used for a feasible option for analysis of multiple compounds as the mixed-mode stationary phase and it provides a general approach for preparing MOFs-based composites by changing morphology and size of MOFs. [Display omitted] • The polyvinylpyrrolidone was chosen as functional molecules to change morphology and size of the Ni-MOF. • The silica microspheres were modified by Ni-MOF capped with PVP via a simple bonding method. • The new composites showed flexible selectivity for separation of both hydrophilic and hydrophobic compounds. [ABSTRACT FROM AUTHOR]

A novel mosaic structure Silica@C/Co@ZIF-67 composite was synthesized by successfully embedding Co nanoparticles on the surface of silica spheres with the help of thermoplastic polyethyleneimine by carbon-reduction. The ZIF-67 half-shell layer structure was synthesized by the in-situ growth of ZIF-67 on the surface of silica spheres through the coordination of 2-methylimidazole with Co metal nodes. The composite was used as a magnetic solid-phase extraction adsorbent combined with high performance liquid chromatography-ultraviolet detector (HPLC–UV) for the extraction and determination of benzoylurea insecticides (BUs) in vegetables and tea. Based on the presence of π-π, hydrophobic and hydrogen bonding interactions between Silica@C/Co@ZIF-67 and BUs, the BUs were rapidly captured by the composites resulting in high adsorption performance. Under the optimal extraction parameters, the linear ranges were 0.3–200 µg L−1 for diflubenzuron, 0.6–200 µg L−1 for chlorbenzuron, and 1.0–200 µg L−1 for triflumuron, teflubenzuron, and flufenoxuron, with correlation coefficients (R2) greater than 0.9991. The limits of detection (LODs) of the method were 0.1–0.3 μg L−1, and the relative standard deviations (RSDs) were 1.2–3.0% for intra-day and 2.6–4.6% for inter-day. In the spiked recovery experiments of vegetables and tea, the recoveries of the five kinds of BUs ranged from 75.8 to 112.9%. In addition, after 10 repetitions using Silica@C/Co@ZIF-67, the recoveries of the five kinds of BUs were still as high as 78.4 to 83.9%. [ABSTRACT FROM AUTHOR]

A zirconium(IV)‐based metal organic framework, composed of 4,4′‐biphenyldicarboxylic acid ligands and Zr6O4(OH)4 clusters, was successfully fabricated. Characterizations were performed on fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, Brunauer‐Emmett‐Teller, and thermogravimetric analysis, which confirmed that it possessed large specific surface area, high pore volume, and strong acid resistant stability. Furthermore, the prepared material containing biphenyl skeleton and a large number of Zr‐O bonds, can grasp acid herbicides especially phenoxyacetic acid herbicides with aromatic structures through π‐π interaction, hydrophobic interaction and Zr‐O‐H+ bonds. Based on these advantages, a method was developed for the determination of four phenoxyacetic acid herbicides from vegetable samples. Under the optimal conditions, wide linearities from 0.3 to 250 μg/L and low limits of detection from 0.1 to 0.5 μg/L were obtained. The intra‐ and interday relative standard deviations were 1.56‐3.92 and 5.01‐7.65%, respectively. The proposed method was applied to analyze phenoxyacetic acid herbicides residues in the tomato, cucumber, and white gourd samples. The satisfactory recoveries (86.12–103.44%) for the spiked samples in vegetable samples were achieved which demonstrated the method was an efficient pretreatment procedure and has a potential application for the trace determination of phenoxyacetic acids from a complex matrix. [ABSTRACT FROM AUTHOR]

A general method was developed for preparing a metal–organic framework–polymer composite coated silica core–shell stationary phase. Silica microspheres were comodified with metal–organic framework and polyvinylpyrrolidone rather than the in situ method of silica modification by original metal–organic framework particles. Metal–organic framework particles and polyvinylpyrrolidone on silica surface were beneficial to suppress silanol activity and enhance composite material tolerance, as well as increasing the water compatibility of the original metal–organic framework-based stationary phases. The stationary phase exhibited superior hydrophilic and hydrophobic performance in terms of separation for various analytes including seven alkaloids, six sulfonamides, five antibiotics, and five polycyclic aromatic hydrocarbons. Moreover, the composite material also showed excellent stability with the relative standard deviation of the retention time of 0.4 to 0.7%. The separation performance with real samples proved that the column has good practical application potential. In summary, the poposed method provides a general way for preparing metal–organic framework–polymer composite material and changed the current status of original metal–organic framework particles modified silica as a single mode chromatographic stationary phase. [ABSTRACT FROM AUTHOR]

Magnetic hierarchical nickel/nickel oxide/carbon nanorods (Ni/NiO@C) were prepared via the pyrolysis of a metal-organic framework containing nickel(II) nickel (Ni-MOF; Ni3(BTC)2) under argon atmosphere. In this material, magnetic Ni/NiO@C nanoparticles are embedded in porous carbon nanorods, and the morphology is similar to that of the original Ni-MOF precursor. The synthesized nanorods were applied as magnetic sorbents in the solid-phase extraction of five benzoylurea insecticides (flufenoxuron, chlorbenzuron, teflubenzuron, diflubenzuron and triflumuron), and their performance was evaluated under optimized conditions. The results show that the material exhibits high extraction recoveries from spiked samples (82.9%–107.6%) and linear response in the range of 0.2–450 μg·L−1. It is also characterized by relatively low limits of detection (50–100 ng·mL−1) at a signal-to-noise ratio of 3. The sorbent is chemically stable and can be repeatedly recycled, with little decline in extraction capacity after 20 cycles of reuse. The method was successfully applied to the quantification of benzoylureas in tea, wolfberry, millet, and oat samples, and it showed high extraction efficiency. [ABSTRACT FROM AUTHOR]

A metal organic framework (MOF-235) was fabricated by a simple solvothermal method and utilized as an adsorbent for the selective removal of electron-rich conjugated dyes. Parameters that influenced the adsorption process were investigated and the excellent adsorption properties of MOF-235 toward Congo red (CR) and lemon yellow (LY) are also exhibited in a wide range of pH 3–9. Moreover, the adsorption kinetics and thermodynamics were determined, indicating that the Langmuir model can well describe the adsorption isotherm and the pseudo-second order model can satisfactorily describe the adsorption kinetics. Thanks to the large hydrophobic effect between electron-deficient MOF and electron-rich conjugated dye molecules, the ultrahigh maximum adsorption capacity for CR and LY calculated by the Langmuir model is up to 1250 and 250 mg g−1, respectively, which surpass that of most reported adsorbents. Notably, the maximum adsorption capacity of adsorption of CR and LY is up to 1131 and 209 mg g−1 in fruit juice, respectively. Additionally, the synthesized MOF-235 has a high adsorptive selectivity and fast adsorption rate and can be regenerated for removal by washing with ethanol containing NaOH solution. These results demonstrated that MOF-235 would be an effective and easily reusable adsorbent for the adsorptive removal of CR and LY from fruit juice. [ABSTRACT FROM AUTHOR]

Herein, a novel, fusiform-like magnetic metal–organic framework material (Fe3O4-NH2@MOF-235) was fabricated by a facile two-step solvothermal approach. Then, Fe3O4-NH2@MOF-235 was applied as an adsorbent in magnetic solid-phase extraction (MSPE) coupled with high-performance liquid chromatography (HPLC) for the simultaneous extraction and determination of five kinds of benzoylurea insecticides (flufenoxuron, chlorbenzuron, teflubenzuron, diflubenzuron and triflumuron) from honey, fruit juice and tap water samples. Moreover, potential variables influencing the MSPE efficiency were optimized. Under the optimized conditions, an excellent linearity was achieved in the range of 1.0–300.0 μg L−1 for teflubenzuron and flufenoxuron and 2.0–300.0 μg L−1 for diflubenzuron, chlorbenzuron and triflumuron, with the correlation coefficients of 0.9991–0.9995. The limits of detection for the analytes were 0.25–0.5 μg L−1, and the recoveries at three fortified concentration levels ranged from 76.45% to 90.74% for the honey samples, 79.95–95.27% for the fruit juice samples, and 84.02–99.62% for the tap water samples. The π–π stacking and hydrophobic interactions between Fe3O4-NH2@MOF-235 and the analytes played an important role in the adsorption process. Moreover, maximum adsorption could be achieved within 5 minutes with very little adsorbent for all the samples. Therefore, the magnetic Fe3O4-NH2@MOF-235 composite combined with MSPE is a convenient approach to detect benzoylurea insecticides in actual samples. [ABSTRACT FROM AUTHOR]

A zirconium(IV)‐based metal–organic framework material (MOF‐808) has been synthesized in a simple way and used for the extraction of phenoxyacetic acids in complex samples. The material has good thermal and chemical stability, large specific surface area (905.36 m²/g), and high pore size (22.18 Å). Besides, it contains a large amount of Zr‐O groups, easy‐to‐form Zr‐O‐H bond with carboxyl groups of phenoxyacetic acids, and possesses biphenyl skeleton structure, easy to interact with compounds through π‐π and hydrophobic interactions. These characteristics make the material very suitable for the extraction of certain compounds with a high extraction efficiency and excellent selectivity. The extraction conditions were optimized, and then an analytical method was successfully established and applied for analysis of actual samples. The solid‐phase extraction method based on prepared material had a wide linear range of 0.2–250 μg/L and a low detection limit of 0.1–0.5 μg/L for four phenoxyacetic acid compounds including 2,4‐dichlorophenoxyacetic acid, 2‐(2,4‐dichlorophenoxy) propionic acid, 4‐chlorophenoxyacetic acid, and dicamba. The relative standard deviations of intra‐ and interday precision were 1.8–3.8 and 4.3–6.9%, and the recoveries after spiking were between 77.1 and 109.3%. The results showed that the material is a desired substituent for the extraction of compounds with benzene ring structure containing carboxyl groups. [ABSTRACT FROM AUTHOR]

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. • The synthetic strategies of MOF/COF composites is systematically outlined. • The highlight of the synergistic effects between MOFs and COFs. • Analytical and other applications of MOF/COF composites are systematically presented. • Issues and perspectives of MOF/COF composites were discussed. [ABSTRACT FROM AUTHOR]

• The hydrogel@SiO 2 column has an acceptable degree of swelling in LC. • The hydrogel@SiO 2 column has flexible selectivity for many polar analytes. • The double network structure is composed of hydrogel and metal organic framework. • A kind of hydrogel-MOF composite functionalized silica column was used in LC. Hydrogel is a kind of three-dimensional network structure polymer that can absorb water and swell in water. It has been widely used in many fields due to its flexible functionality. We proposed the design strategy of dual-network hydrogel assisted by a metal-organic-framework (MOF) and modified them on the surface of silica (with average particle diameter of 5 μm and average pore diameter of 76 Å). On the basis of effectively avoiding shortcomings such as osmotic pressure caused by swelling, abundant mesh types of composite material also improves the separation selectivity of the stationary phase. A variety of analytes such as nucleosides/bases, antibiotics, organic acids, carbohydrates, alkylbenzenes, polycyclic aromatic hydrocarbons, pesticides and anions can be selectively separated. The research on the retention behavior and the interaction mechanism proves that the column can be used in mixed mode liquid chromatography. By comparing with the optimized chromatographic conditions of commercial HILIC column and C18 column, this new type of stationary phase also has some significant advantages in the selective separation of mixed analytes. This new stationary phase also has excellent acid/base stability. The intraday relative standard deviation of their retention time under acidic conditions is 0.05%-0.26% (n = 10), and the intraday relative standard deviation under basic conditions is 0.11–0.14% (n = 10). After optimizing the chromatographic conditions, the efficiency of this new type of chromatographic column can reach 90,300 plates/m (sucrose). In short, a new strategy for applying hydrogel to liquid chromatography with high selectivity and chromatographic separation performance is proposed. [ABSTRACT FROM AUTHOR]

• 2D bimetallic magnetic mesoporous carbon (Ni/ZnO@C) were fabricated. • The Ni/ZnO@C nanosheet was gained by calcining 2D bimetallic Ni-ZIF-8. • The materials were used as magnetic solid phase extraction adsorbents. • The method was used to analyze nitroimidazoles from real water samples. We prepared two-dimensional (2D) bimetallic metal-organic frameworks (Ni-ZIF-8) nanosheets by a simple solvent-free method at room temperature. The morphology and composition of Ni-ZIF-8 can be controlled through adding different amounts of Ni. And then, the 2D magnetic mesoporous nanosheets (Ni/ZnO@C) were synthesized by directly pyrolyzing Ni-ZIF-8 under argon atmosphere and explored as magnetic solid phase extraction (MSPE) adsorbents for the determination of nitroimidazole antibiotics (NIABs). Magnetic Ni nanoparticles embedded in carbon nanosheets uniformly resulted in high magnetization saturation of Ni/ZnO@C for easy separation. The Ni/ZnO@C can form hydrogen bond and π-π interaction with three NIABs resulting from their rich N-H containing imidazole, π-electron. Due to the high specific surface area and high mass transfer rate of 2D Ni/ZnO@C, the materials showed satisfactory adsorption capacity and rapid adsorption kinetics for NIABs. A rapid and effective method of Ni/ZnO@C-MSPE combined with high-performance liquid chromatography was proposed for the determination of NIABs. Several main parameters affecting MSPE were investigated. Under the optimal conditions, wide linear was achieved ranging from 0.1 to 500 µg⋅L−1 with a low detection limit of 0.025-0.05 µg⋅L−1. The established method has been successfully applied to analyze NIABs from environmental water samples with satisfactory recovery from 74.33 to 105.71%. [ABSTRACT FROM AUTHOR]

The core-shell composites were first prepared by surface modification of silica spheres with two-dimensional MOF-FDM-23 nanosheets via a simple approach. The successful immobilization of 2D MOF-FDM-23 on the silica (2D MOF-FDM-23@silica) was confirmed by series of method including elemental analysis, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and the Brunauer–Emmett–Teller (BET). The obtained material showed excellent separation performance for multiple polar compounds such as sulfonamides, alkaloids, antibiotic and amino acid compounds etc. In addition, it was found to be superior to most reported MOF-based stationary phases in terms of separation performance, preparative reproducibility and chromatographic stability. The reproducibility of material preparation was demonstrated by the difference in retention time of the same mixture on three batches of the material at different times. The relative standard deviation (RSD) of the retention time for preparation repeatability was found to range from 0.5% to 1.4%. In short, the core-shell composite material prepared by this method broadened the application of MOF-based composites as chromatography stationary phase, and significantly developed the field of 2D MOF nanosheets in chromatography. Image 1 • A simple synthetic method for 2D MOFs nanosheets functional silica microspheres was established. • The obtained material showed excellent separation performance in HILIC mode. • The reproducibility of material was demonstrated by the difference in retention time of on the same material on time several time intervals on several days. [ABSTRACT FROM AUTHOR]

• A novel Fe 2 O 3 @C was synthesized by carbonizing MOF-235 under Ar atmosphere. • The magnetic Fe 2 O 3 particles were evenly embedded in porous carbon matrix. • The Fe 2 O 3 @C was used to extract benzoylurea insecticides from tea drink samples. • This work studied the removal effect of three washing on residues from tea leaf. • This method showed satisfactory recovery, wide linear range and low LODs. Ferric oxide/carbon (Fe 2 O 3 @C) was fabricated via direct carbonization of metal-organic framework of iron (MOF-235) under argon atmosphere. The magnetic Fe 2 O 3 nanoparticles are evenly embedded in porous carbon matrix, while original morphology of MOF-235 was well-maintained. The synthesized Fe 2 O 3 @C was used as magnetic sorbent for extracting five benzoylurea insecticides (BUs). The materials exhibited excellent extraction performance, which benefited not only from the strong π-π interaction and hydrophobic interaction (π-conjugated system), but also to the abundant adsorption sites and flexible transport channel (the interconnected 3D porous structure). A three-factor-three-level Box-Behnken design (BBD) was selected to optimize three greatly influential parameters: amount of adsorbent (A), desorption time (B) and volume of desorption solvent (C) by response surface methodology. The established method coupled to HPLC-UV detection showed wide linearity with the range of 0.2–450 μg•L−1, relatively low limits of detection (0.05–0.10 μg•L−1) with the relative standard deviation (RSD) (n = 7) lower t than 5.47%. Moreover, the proposed method was successfully applied to analyze BUs in tea samples and investigate the removal effect of different washing on BUs residues from tea leaf. These results indicated that the synthesized Fe 2 O 3 @C is a promising adsorbent material for magnetic solid phase extraction of BUs at trace concentrations from tea samples. [ABSTRACT FROM AUTHOR]