Bimetallic metal-organic frameworks-based ratiometric fluorescence sensor for the quantitative detection of thiram in fruits samples

The identification of residual thiram (Tr) in foods is vital in view of its harmful effects on human health. Herein, a ratiometric fluorescence sensor (I₄₃₅/I₅₉₀) based on rhodamine B/NH₂-MIL-53(Al_0.75Fe_0.25) was constructed for the detection of Tr. Interestingly, the probe RhB/NH₂-MIL-53(Bim) assisted by Cu²⁺ could rapidly and sensitively recognize Tr with a low detection limit of 0.11 μg/mL in 10 min. The fluorescence sensing mechanism was investigated using fluorescence spectra, UV-Vis absorption spectra, the fluorescence lifetime and quantum yield. The results showed that the excellent sensing performance was attributed to fluorescence resonance energy transfer, electrostatic interaction, and photoinduced electron transfer. In addition, the practical application of this platform showed acceptable relative recoveries for Tr (84.03-107.81 %), and precisions were also achieved (relative standard deviation ≤ 8.69 %, n = 3). These results show that the presented herein can be applied to monitor the Tr content in real fruit samples.

Different strengthening effects of amino and nitro groups on the bisphenol A adsorption of an aluminum metal-organic framework in aqueous solution

In recent years, metal-organic frameworks (MOFs) have been employed in numerous applications for adsorption. Researchers synthesize new MOFs by various methods, including the introduction of functional groups. In this study, three different aluminum-based MOFs (with non-functionalized, amino-functionalized, nitro-functionalized) were produced by hydrothermal synthesis and used for investigating typical endocrine disrupting chemicals (EDCs), namely for bisphenol A (BPA) adsorption. We used several methods to characterize the MOFs and conducted batch adsorption experiments to investigate their adsorption properties, and explore the influence of different functional groups on adsorption materials. The specific surface area of Al-MOF-NH₂ is 6 times larger than that of Al-MOF according to the N₂ adsorption and desorption isotherms of the material, that is, the BET of Al-MOF, Al-MOF-NH₂, and Al-MOF-NO₂ were 109.68, 644.03, and 146.60 m²/g. Note that although the same synthesis method is used, pore size is greatly changed because of the different functional groups. Al-MOF and Al-MOF-NO₂ have more mesopores, and Al-MOF-NH₂ is mainly microporous. The BPA adsorption capacities of Al-MOF, Al-MOF-NH₂, and Al-MOF-NO₂ were 46.43, 227.78, and 155.84 mg/L. The outcomes can also be explained by the improved adsorption performance from the addition of amino functional groups. In this research, the adsorption isotherms and adsorption kinetics of the three Al-MOFs for BPA were also investigated to explain the different adsorption properties of various functional groups. The results show that the amino-functionalized materials have remarkable characterization morphologies, uniform particle distributions, appropriate particle sizes, excellent specific surface areas, and superior adsorption effects.

Fluorescence turn-off sensing strategy based on Al-based MOF for selective detection of tricresyl phosphate

Tricresyl phosphate (TCP), a notable emerging pollutant with a high bioconcentration factor and biotoxicity, is a typical representative of aryl-organophosphorus flame retardants. The electrochemical and chromatographic technologies used in conventional TCP detection have a variety of drawbacks. Hence, it is crucial to suggest an easy, accurate, and selective method for detecting TCP. In this study, we presented a brand-new method based on NH₂-MIL-53(Al) nanoprobe for the direct luminescence assay of TCP. NH₂-MIL-53(Al) possessed an excellent crystal structure and superior optical qualities. Notably, the introduction of TCP caused a considerable dampening of the photoluminescence signal of the nanoprobe. The fluorescence response based on static quenching was verified by fluorescence lifetime decay curves. The thermodynamic analysis further concluded that TCP and nanoprobe spontaneously produced non-fluorescent complexes due to hydrophobic interaction. The quenching efficiency (F₀-F)/F₀ of the nanoprobe and the TCP concentration displayed good linearity in the scope of 0.3-3.0 μM (R² = 0.996), and the LOD was 0.058 μM under the ideal detection conditions. More significantly, the technique was effectively used to identify TCP in lake and tap water (RSD ≤5.79%), which provided a fresh perspective on how to recognize OPFRs in environmental water.

An ultralow concentration of Al-MOFs for turn-on fluorescence detection of aflatoxin B1 in tea samples

A turn-on fluorescent sensing platform based on an ultralow concentration of Al-metal organic frameworks for the detection of aflatoxin B₁ has been developed for the first time. This fluorescence turn-on sensor exhibits the largest fluorescence enhancement (or quenching) constant value of 179404 M^-1 among all luminescence-based chemical sensors reported till date. Moreover, the sensor afforded a rapid detection of aflatoxin B₁, with a linear response in the concentration range of 0.05-9.61 μM and a low detection limit of 11.67 ppb. Additionally, the fabricated sensor showed good repeatability, reproducibility, stability, and selectivity. Most importantly, the practical application of this sensor has been demonstrated by detecting aflatoxin B₁ in complex tea samples with low relative standard deviation (≤7.72%; n = 3) and satisfactory recoveries. In summary, the proposed method has great potential as a simple, sensitive and selective strategy for monitoring aflatoxin B₁ in food samples.

Convenient synthesis of polymetallic metal–organic gels for efficient methanol electro-oxidation

Novel Ni-based AlNiCu-MOG and AB&AlNiCu-MOG composite materials were successfully fabricated, which exhibited superior MOR activities with a current density of 17.1 and 33.24 mA cm⁻², respectively.

Amino-Functionalized Al-MOF for Fluorescent Detection of Tetracyclines in Milk

A fluorescent method for detection of tetracyclines (TCs) in milk was developed by using the NH₂-MIL-53(Al) nanosensor synthesized via a one-pot hydrothermal method. The nanosensor had a crystalline nanoplates structure with rich groups of -NH₂ and -COOH. The -NH₂/-COOH of NH₂-MIL-53(Al) reacted with the -CO-/-OH of TCs to form a complex. The electron of -NH₂/-COOH from the NH₂-BDC ligand transferred to the -CO-/-OH of TCs. -NH₂ of the NH₂-MIL-53(Al) interacted with the -CO-/-OH of TCs by hydrogen bonding. The quenching efficiency of the inner filter effect (IFE) was calculated to contribute 57-89%. The synergistic effect of photoinduced electron transfer (PET) and IFE account for fluorescence quenching. TCs were quantitatively detected in milk samples with recoveries of 85.15-112.13%; the results were in great accordance with high-performance liquid chromatography (HPLC) ( P > 0.05), confirming the NH₂-MIL-53(Al) nanosensor has potential applicability for the detection of TCs in food matrix.

Influence of the channel size of isostructural 3d–4f MOFs on the catalytic aerobic oxidation of cycloalkenes

The present work reports a new group of heterogeneous catalysts with a 3D structure, CuLnIDA, {[Cu₃Ln₂(IDA)₆]·8H₂O} (Ln: La^III, Gd^III or Yb^III), with an organic linker (H₂IDA: iminodiacetic acid).