Cu-Co bimetallic organic framework as effective adsorbents for enhanced adsorptive removal of tetracycline antibiotics.

In this study, the removal effect of a new MOF-on MOF adsorbent based on Cu-Co bimetallic organic frameworks on tetracycline antibiotics (TCs) in water system was studied. The adsorbent (Cu-MOF@Co-MOF) were synthesized by solvothermal and self-assembly method at different concentrations of Co2+/Cu2+. The characterization results of SEM, XRD, XPS, FTIR and BET indicated that the MOF-on MOF structure of Cu-MOF@Co-MOF exhibited the best recombination and physicochemical properties when the molar ratio of Co2+: Cu2+ is 5:1. In addition, the Cu-MOF@Co-MOF have a high specific surface area and bimetallic clusters, which can achieve multi-target synergistic adsorption of TCs. Based on above advantages, Cu-MOF@Co-MOF provided a strong affinity and could efficiently adsorb more than 80% of pollutants in just 5 to 15 min using only 10 mg of the adsorbent. The adsorption capacity of tetracycline and doxycycline was 434.78 and 476.19 mg/g, respectively, showing satisfactory adsorption performance. The fitting results of the experimental data were more consistent with the Langmuir isotherm model and pseudo-second-order kinetic model, indicating that the adsorption process of TC and DOX occurred at the homogeneous adsorption site and was mainly controlled by chemisorption. Thermodynamic experiments showed that Cu-MOF@Co-MOF was thermodynamically advantageous for the removal of TCs, and the whole process was spontaneous. The excellent adsorption capacity and rapid adsorption kinetics indicate the prepared MOF-on MOF adsorbent can adsorb TCs economically and quickly, and have satisfactory application prospects for removing TCs in practical environments. The results of the study pave a new way for preparing novel MOFs-based water treatment materials with great potential for efficient removal.

Ionic liquid-enhanced silica aerogels for the specific extraction and detection of aflatoxin B1 coupled with a smartphone-based colorimetric biosensor.

The polymer ionic liquid (1-allyl-3-butylimidazolium bromide) enhanced silica aerogel was modified onto the surface of stainless-steel mesh to immobilize aptamer-1 for the specific recognition of AFB1. The porous channels of silica aerogel could prevent the interference of macromolecules in food samples. Enzyme kinetic analysis showed that the MoS2/Au was an effective peroxidase mimic with a relatively low Michaelis constant (Km) value of 0.17 mM and a high catalytic rate of 3.87 × 10-8 mol (L·s)-1, which exhibited obvious superiority compared with horseradish peroxidase. The established "sandwich-structure" biosensor was coupled with the smartphone "Color Picker" application was used to detect AFB1 with a wide linear range (1-100 ng mL-1) and low detection limit (0.25 ng mL-1). The anti-interference ability of the established biosensor was evaluated by adding different concentrations of standards in corn, peanut, and wheat and matrix effects were 90.84-106.11 %. The results showed that this method demonstrated high specificity, sensitivity, rapidity and low interference in food samples.

Magnetic mesoporous carbon nanosheets derived from two-dimensional bimetallic metal-organic frameworks for magnetic solid-phase extraction of nitroimidazole antibiotics.

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%.

Metal-organic frameworks derived magnetic porous carbon for magnetic solid phase extraction of benzoylurea insecticides from tea sample by Box-Behnken statistical design.

Ferric oxide/carbon (Fe2O3@C) was fabricated via direct carbonization of metal-organic framework of iron (MOF-235) under argon atmosphere. The magnetic Fe2O3 nanoparticles are evenly embedded in porous carbon matrix, while original morphology of MOF-235 was well-maintained. The synthesized Fe2O3@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 Fe2O3@C is a promising adsorbent material for magnetic solid phase extraction of BUs at trace concentrations from tea samples.

Magnetic 3D hierarchical Ni/NiO@C nanorods derived from metal-organic frameworks for extraction of benzoylurea insecticides prior to HPLC-UV analysis.

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. Graphical abstractSchematic representation of the synthesis of magnetic hierarchical nickel/nickel oxide/carbon nanorods derived from Ni-MOF. The material is employed as a sorbent for the magnetic solid-phase extraction of benzoylurea insecticides.

Solid-phase extraction of phenoxyacetic acid herbicides in complex samples with a zirconium(IV)-based metal-organic framework.

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.

Unusual Hypochlorous Acid (HClO) Recognition Mechanism Based on Chlorine-Oxygen Bond (Cl-O) Formation.

One of the most important endogenous reactive oxygen species, hypochlorous acid (HClO), is involved in numerous pathological and physiological processes. Herein, a near-infrared fluorescence probe (CyHR) was designed and synthesized for ultrafast (within 0.2 s), sensitive (limit of detection=39.44 nm), and selective response to HClO. The reaction mechanism was systematically analyzed by MS, 1 H NMR spectroscopy, HPLC-MS techniques, and theoretical calculations. The results indicated that HClO can be recognized by CyHR, which is based on chlorine-oxygen (Cl-O) bond formation. To the best of our knowledge, this study is the first to find Cl-O bonds among organic aromatic compounds, given that Cl-O bonds are common among inorganics. Through biological experiments, CyHR was successfully applied to image exogenous and endogenous HClO in macrophage cells (RAW 264.7). Thus, CyHR is a promising tool for HClO-related physiological and pathological studies and may provide a means for designing HClO-specific fluorescence probes.

Zirconium(IV)-based metal-organic frameworks (UiO-67) as solid-phase extraction adsorbents for extraction of phenoxyacetic acid herbicides from vegetables.

A zirconium(IV)-based metal organic framework, composed of 4,4'-biphenyldicarboxylic acid ligands and Zr6 O4 (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.