Preparation of magnetic metal-organic framework MIL-101(Fe) and its application in the extraction of anthraquinones in rhubarb

In this work, a magnetic octahedral metal-organic framework (Fe₃O₄@NH₂-MIL-101(Fe)) was synthesized for the magnetic solid-phase extraction of three anthraquinones, including aloe-emodin, emodin, and physcion, in rhubarb. The Fe₃O₄@NH₂-MIL-101(Fe) exhibits a high specific surface area of 259.2 m²/g with an average pore size of 6.0 nm and high magnetic responsivity of 23.4 emu/g, which may be used as an adsorbent for rapid preconcentration and separation of target analytes. The main parameters for magnetic solid-phase extraction of anthraquinones, including the amount of adsorbent, extraction time, extraction temperature, extraction pH, elution solvent, and elution time, were systematically optimized. The whole extraction process requires a very low amount of adsorbent and a small volume of the sample. Besides, under the optimized conditions, the method shows satisfactory spiked recovery for anthraquinones in the range of 93.3–109.1% and the limits of detection are 1.7–3.4 ng/mL. The relative standard deviations for intra- and inter-day precision are 0.2–1.3% and 0.2–0.6%, respectively. The experimental results indicate that the developed method is feasible for the analysis of anthraquinones in rhubarb.     

Preparation and characterization of metal-organic framework MIL-101(Cr)-coated solid-phase microextraction fiber

Metal-organic frameworks (MOFs) have received great attention as novel sorbents due to their fascinating structures and intriguing potential applications in various fields. In this work, a MIL-101(Cr)-coated solid-phase microextraction (SPME) fiber was fabricated by a simple direct coating method and applied to the determination of volatile compounds (BTEX, benzene, toluene, ethylbenzene, m-xylene and o-xylene) and semi-volatile compounds (PAHs, polycyclic aromatic hydrocarbons) from water samples. The extraction and desorption conditions of headspace SPME (HS-SPME) were optimized. Under the optimized conditions, the established methods exhibited excellent extraction performance. Good precision (<7.7%) and low detection limits (0.32–1.7 ng L⁻¹ and 0.12–2.1 ng L⁻¹ for BTEX and PAHs, respectively) were achieved. In addition, the MIL-101(Cr)-coated fiber possessed good thermal stability, and the fiber can be reused over 150 times. The fiber was successfully applied to the analysis of BTEX and PAHs in river water by coupling with gas chromatography–mass spectrometry (GC–MS). The analytes at low concentrations (1.7 and 10 ng L⁻¹) were detected, and the recoveries obtained with the spiked river water samples were in the range of 80.0–113% and 84.8–106% for BTEX and PAHs, respectively, which demonstrated the applicability of the self-made fiber.     

Highly chemiluminescent metal-organic framework of type MIL-101(Cr) for detection of hydrogen peroxide and pyrophosphate ions

The authors describe a highly chemiluminescent metal-organic framework (MOF) that was obtained by loading the pores of MIL-101(Cr) with luminol. Immobilization is based on Lewis acid-base interactions between the coordinatively unsaturated metal sites of MIL-101(Cr) and the amino groups of luminol. The luminol-loaded MOF displays strong chemiluminescence (CL) in the presence of hydrogen peroxide (H₂O₂) in alkaline solution. Pyrophosphate (PPi), in turn, acts as a quencher of this CL. These findings have been exploited in the design of a CL based method for the determination of either H₂O₂ or PPi. The assays for H₂O₂ works in the 3 to 100 μM concentration range and has a detection limit of 0.5 μM. The quenchometric assay for PPi works in the 5 to 70 μM concentration range and has a 1.2 μM detection limit.

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Graphical abstract Luminol-embedded metal-organic frameworks (MOFs) with high chemiluminescent activity were prepared and used for the sensitive determination of either H₂O₂ or pyrophosphate ions.

     

金属-有机骨架MIL-101(Cr)掺杂聚合物整体柱的制备及其用于酚类化合物的在线固相萃取

制备了金属-有机骨架（MOF）MIL-101（Cr）掺杂聚合物整体柱，建立了在线固相萃取-高效液相色谱检测水中4-硝基苯酚、2-硝基苯酚、3-甲基苯酚和2，4-二氯苯酚的方法。考察了样品溶液pH值、上样时间、上样流速和解吸时间对酚类化合物萃取效果的影响。在最优萃取条件下，采用制备的整体柱检测水中酚类化合物，其富集因子高，线性范围宽，精密度好，检出限低，适用于水中酚类化合物的检测。制备掺杂聚合物整体柱是促进和拓宽MOFs在线固相萃取应用的有效方法之一。     

五乙烯六胺改性金属有机骨架材料MIL-101(Cr)对CO_2的吸附性能

采用溶剂热法合成金属有机骨架材料MIL-101(Cr),用回流法将五乙烯六胺(PEHA)负载到MIL-101(Cr)孔道中的不饱和金属位点上,使用扫描电镜、粉末X射线衍射、氮气物理吸附、元素分析和傅里叶变换红外光谱等表征手段考察材料的结构和形貌,测试氨基改性前后的MIL-101(Cr)在25℃、不同压力下对CO_2的吸附效果。结果表明,负载0.24 m L五乙烯六胺后的MIL-101(Cr)对CO_2的吸附效果最好,在25℃、常压下对CO_2的饱和吸附量可达58.944 mg/g,相比未负载五乙烯六胺的MIL-101(Cr)吸附量(CO_2饱和吸附量为44.208 mg/g)增加了33%。随着吸附压力的增加,MIL-101(Cr)和0.24PEHAM IL-101(Cr)对CO_2的饱和吸附量逐渐增加,当吸附压力为1.1 MPa时,两者的吸附量分别为1 147.59和1 256.74 mg/g,表明该类材料在高压下对CO_2有着良好的吸附效果。     

Thermodynamics of adsorption of aromatic compounds from non-aqueous solutions by MIL-53(Al) metal-organic framework

The thermodynamics of adsorption of mono-, di-, and tricyclic aromatic compounds by MIL-53(Al) metal-organic framework from their solutions in MeCN, MeOH and n-C₆H₁₄–PrⁱOH was studied for the first time. It was found that the adsorption of the test substances from solutions in MeCN and MeOH is characterized by positive values of enthalpy and entropy changes, and the adsorption from n-C₆H₁₄–PrⁱOH medium is characterized by negative enthalpy and entropy changes. Upon adsorption by MIL-53(Al) framework from polar media, aromatic compounds were proposed to transfer from the liquid phase with a higher degree of association into the solvent medium with a lower degree of association, molecules of which are disordered due to the strong interaction with the hydrophobic walls of the framework pores. It was concluded that the driving force of adsorption by MIL-53(Al) from MeCN and MeOH is increase in entropy of the system, while the factor of adsorption from n-C₆H₁₄–PrⁱOH medium is decrease in enthalpy of the adsorption system. The compensation effect in liquid-phase adsorption of aromatic compounds by MIL-53(Al) framework was discovered. The effect of the liquid phase nature on selectivity of adsorption from solutions onto investigated metal-organic framework was demonstrated.     

Fluorescent metal-organic framework for selective sensing of nitroaromatic explosives

Highly luminescent micrometre-sized fine particles of a Zn(II) metal-organic framework (MOF) of a new π-electron rich tricarboxylate dispersed in ethanol is demonstrated as a selective sensory material for the detection of nitroaromatic explosives via a fluorescence quenching mechanism.     

Ligand controlled structure of cadmium(II) metal-organic frameworks for fluorescence sensing of Fe3+ ion and nitroaromatic compounds

2-Fold interpenetrating 3D framework for selective adsorption of CO₂ over CH₄ and fluorescence detection of Fe³⁺ ions and nitroaromatic compounds through fluorescence quenching.     

Microwave-assisted synthesis of mesoporous metal-organic framework NH<Subscript>2</Subscript>—MIL-101(Al)

The possibility of formation of the mixed matrix membranes NH₂—MIL-101(Al) under the conditions of microwave activation of the reaction mixture at atmospheric pressure is studied. Microwave irradiation affects the morphology and crystallite size and significantly shortens the synthesis time (from tens of hours to 10—30 min). The obtained samples of NH₂—MIL-101(Al) with a crystallite size of 100 nm were used as nanofillers for polymer matrix based on the PIM-1 polymer with intrinsic microporosity for the preparation of hybrid membrane materials. Gas permeability for a series of gases was measured on the synthesized membranes.     

Study of selective adsorption of aromatic compounds from solutions by the flexible MIL-53(Al) metal-organic framework

The dynamic method under conditions close to equilibrium was applied to study the liquid-phase adsorption in the Henry region for a series of aromatic compounds on the MIL-53(Al) metal-organic framework at different temperatures. The interpretation of the obtained experimental adsorption data was based on the TOPOS analysis of the structure of the cavities in the MIL-53(Al) framework using the Voronoi—Dirichlet polyhedra concept. It is shown that the adsorption activity of the investigated material under the liquid-phase conditions is governed by a possible expansion of the channels and cavities in the structure and by a breathing effect of the structure caused by the temperature variation. The selectivity of adsorption shown by MIL-53(Al) for a series of the studied compounds is due to the adsorbate—adsorbent π—π-interaction and hydrogen bonding of adsorbate molecules with Brönsted acid sites of the metal-organic framework. High adsorption selectivity of the MIL-53(Al) framework were found for compounds differed in the number of aromatic rings in the molecule and the presence of the methyl substituent, as well as for aromatic hydrocarbons and their sulfur-containing heterocyclic analogs.     

A luminescent nanoscale metal-organic framework for sensing of nitroaromatic explosives

The first nanoscale luminescent metal-organic framework has been realized for the straightforward and highly sensitive sensing of nitroaromatic explosives in enthanol solution.     

Adsorption separation of CO2 and N2 on MIL-101 metal-organic framework and activated carbon

In this work, the CO₂ and N₂ adsorption properties of MIL-101 metal-organic framework (MOF) and activated carbon (AC) were investigated using a standard gravimetric method within the pressure range of 0–30 bar and at four different temperatures (298, 308, 318 and 328 K). The dual-site Langmuir–Freundlich (DSLF) model was used to describe the CO₂ adsorption behaviors on these two adsorbents. The diffusion coefficients and activation energy E _a for diffusion of CO₂ in the MIL-101 and AC samples were estimated separately. Results showed that the isosteric heat of CO₂ adsorption on the MIL-101 at zero loading was much higher than that on the AC due to a much stronger interaction between CO₂ molecule and the unsaturated metal sites Cr³⁺ on MIL-101. Meanwhile, the dramatically decreased isosteric heats of CO₂ adsorption on MIL-101 indicated a more heterogeneous surface of MIL-101. Furthermore, the adsorption kinetic behaviors of CO₂ on the two samples can be well described by the micropore diffusion model. With the increase of temperature, the diffusion coefficients of CO₂ in the two samples both increased. The activation energy E _a for diffusion of CO₂ in MIL-101 was slightly lower than that in AC, suggesting that MIL-101 was much favorable for the CO₂ adsorption. The CO₂/N₂ selectivities on MIL-101 and AC were separately estimated to be 13.7 and 9.2 using Henry law constant, which were much higher than those on other MOFs.     

Remarkable adsorptive performance of a metal-organic framework, vanadium-benzenedicarboxylate (MIL-47), for benzothiophene

Liquid-phase adsorption of benzothiophene over isotypic MOFs such as MIL-47 and MIL-53(Al, Cr) has shown that a metal ion of a MOF-type material has a dominant role in adsorptive desulfurization and MIL-47 has a remarkable performance.     

A competitive microcystin-LR immunosensor based on Au NPs@metal-organic framework (MIL-101)

A porous metal organic frameworks (MOFs) material (MIL-101) based on trivalent chromium skeleton were synthesized by hydrothermal synthesis method, and loaded with Au nanoparticles (Au NPs) to prepare Au NPs@MIL-101 composite materials which were used as a marker to label anti microcystin-LR (Anti-MC-LR). The composite materials have strong catalytic properties to the oxidation of ascorbic acid. Anti-MC-LR was immobilized on glassy carbon electrode surface using electrodeposition graphene oxide (GO) as a fixed matrix to construct a competitive microcystin-LR immunosensor.     

金属有机框架MIL-101(Fe)对水中微囊藻毒素-LR的吸附

通过溶剂热法制备了性质稳定的金属有机框架材料MIL-101(Fe),并用于吸附去除水中的微囊藻毒素-LR。采用电子显微镜、傅立叶变换红外光谱(FT-IR)、Zeta电位和N_2吸附-脱附等方法对制备的纳米材料进行了表征。MIL-101(Fe)具有多孔结构和较高的比表面积(375.2 m~2/g),尺寸约为500 nm。考察了pH值、离子强度、温度、吸附时间、浓度等参数对吸附剂吸附能力的影响。结果表明,静电作用和配位作用是主要的作用机理。MIL-101(Fe)对微囊藻毒素-LR的吸附速度很快(20 min内达到吸附平衡),吸附过程符合准二级动力学模型;MIL-101(Fe)对微囊藻毒素-LR表现出良好的吸附性能,其最大吸附量为256.4 mg/g。溶液中存在的腐植酸对MIL-101(Fe)的吸附性能产生一定的影响。受腐殖酸、盐类的影响,相同条件下MIL-101(Fe)对江水中微囊藻毒素-LR的吸附性能有所下降,但仍可达到68.1 mg/g。因此,该方法简便、高效,适用于快速除去污染水体中的微囊藻毒素-LR。     

A new luminescent metal-organic framework for selective sensing of nitroaromatic explosives

A microporous luminescent metal-organic framework [Zn_4L_2(H_2O)_2].(H_2O)_m(DMA)_n(1)(H_4L=5,5'-((1H-pyrazole-3,5-dicarbonyl)bis(azanediyl))diisophthalic acid, DMA=N,N-dimethylacetamide) was synthesized and characterized by infrared radiation(IR), thermogravimetric analyses(TGA), powder X-ray diffraction spectra(PXRD) and X-ray diffraction. Complex 1has a three dimensional(3D) framework, which can be simplified as 5,5,5,5-c net with the Schlfi symbol of {43.64.83}{44.65.8}{45.65}2. This luminescent metal-organic framework(MOF) shows selectively sensitive to nitrobenzene and series of nitroaromatic explosives such as 4-nitrotoluene, 1,4-dinitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene, and exhibits well recyclability. So complex 1 could be used to detect nitroaromatic explosives as a selective sensing material.     

Facile magnetization of metal-organic framework MIL-101 for magnetic solid-phase extraction of polycyclic aromatic hydrocarbons in environmental water samples

The unusual properties such as high surface area, good thermal stability, uniform structured nanoscale cavities and the availability of in-pore functionality and outer-surface modification make metal-organic frameworks (MOFs) attractive for diverse analytical applications. However, integration of MOFs with magnets for magnetic solid-phase extraction for analytical application has not been attempted so far. Here we show a facile magnetization of MOF MIL-101(Cr) for rapid magnetic solid-phase extraction of polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. MIL-101 is attractive as a sorbent for solid-phase extraction of pollutants in aqueous solution due to its high surface area, large pores, accessible coordinative unsaturated sites, and excellent chemical and solvent stability. In situ magnetization of MIL-101 microcrystals as well as magnetic solid-phase extraction of PAHs was achieved simultaneously by simply mixing MIL-101 and silica-coated Fe(3)O(4) microparticles in a sample solution under sonication. Such MOF-based magnetic solid-phase extraction in combination with high-performance liquid chromatography gave the detection limits of 2.8-27.2 ng L(-1) and quantitation limits of 6.3-87.7 ng L(-1) for the PAHs. The relative standard deviations for intra- and inter-day analyses were in the range of 3.1-8.7% and 6.1-8.5%, respectively. The results showed that hydrophobic and π-π interactions between the PAHs and the framework terephthalic acid molecules, and the π-complexation between PAHs and the Lewis acid sites in the pores of MIL-101 play a significant role in the adsorption of PAHs.