Rare [Cu4I2]2+ cationic cluster-based metal-organic framework and hierarchical porous composites design for effective detection and removal of roxarsone and antibiotics.

Fluorescence quenching induced by photoinduced electron transfer (PET) stands as an effective strategy for identifying water pollutants. Herein, a novel (4, 8)-connected three-dimensional framework Cu(I)-MOF ([Cu2I(tpt)]n) with unique 8-connected [Cu4I2]2+ cationic clusters is designed by employing the nitrogen-rich ligand (Htpt = 5-[4(1H-1,2,4-triazol-1-yl)]phenyl-2H-tetrazole). Water-stabilized Cu(I)-MOF exhibits outstanding fluorescence properties, facilitating its application in detecting organic pollutants in water. Benefiting from the fact that the Cu(I)-MOF possesses a higher lowest unoccupied molecular orbitals (LUMO) energy level than that of the analyte, the rapid d-PET can occur, entitling Cu(I)-MOF to a sensitive fluorescence quenching response to roxarsone (ROX), nitrofurazone (NFZ) and nitrofurantoin (NFT) (with detection limits as low as 0.13 µM, 0.15 µM, and 0.13 µM, respectively). The nitrogen-containing sites of melamine foam (MF) are utilized to facilitate the anchoring and growth of Cu-MOF crystals, which enables the preparation of hierarchical microporous - macroporous Cu(I)-MOF/MF composites. The ordered porous structure of Cu(I)-MOF/MF provides cavities and open sites for the efficient removal of ROX (qmax = 210.6 mg∙g-1), NFZ (qmax = 111.5 mg∙g-1) and NFT (qmax = 238.9 mg∙g-1) from water. This characteristic endows the Cu(I)-MOF/MF with rapid and recyclable adsorption capacity. Therefore, this work provides valuable insights to address the problem of detection and removal of pollutants in the aquatic environment.

Tetranuclear Cluster-Based Eu(III)-Metal-Organic Framework: Ratiometric Platform Design and Ultrasensitive Phenylglyoxylic Acid Detection.

Phenylglyoxalic acid (PGA) is a typical metabolite produced by the invasion of styrene into the human body. The detection of PGA can not only reflect the health status of the human body but also assess the level of styrene contamination in the environment. Herein, a novel Eu(III)-MOF (Eu-ttpd) with excellent fluorescence properties was designed by employing the tetrazole-based ligand of 5-((4'-(tetrazol-5'-yl)benzyl)oxy) isophthalic acid (H2ttpd), which successfully used a fluorescent sensor for PGA. The as-synthesized Eu-ttpd features the unique 10-connected tetranuclear cluster [Eu4(µ3-O)2(COO)8]4+ and exhibits a novel (3,10)-connected topological. Benefiting from the perfectly matched excited-state energy levels of the employed H2ttpd ligand with PGA, rapid photoinduced electron transfer (PET) and Dexter-ET can occur, which entitle Eu-ttpd a fast fluorescence quenching response to PGA with a remarkable LOD of 0.269 µM. More importantly, by integrating Eu-ttpd and Mg,N-CDs into the polyacrylamide hydrogel, we optimized Eu-ttpd into a hydrogel sensor which exhibited enhanced detection ability (LOD = 0.052 µM) accompanied by a distinguished color transformation (red-to-blue) and realized ultrasensitive and visual detection of PGA. This work offers an indication for the development of smart sensing materials for human health and environmental safety.

A Pitaya-Inspired Modular Cylindrical MOF-Based Capsule Design for Pesticide Signal Probes.

Excessive use of pesticides has brought about serious environmental risks worldwide that pose significant harm for human health. Herein, a series of metal-organic framework (MOF)-based gel capsules with a pitaya-like core-shell structure are constructed through a green polymerization strategy for pesticide detection and removal, namely ZIF-8/M-dbia/SA (M = Zn, Cd). Significantly, the ZIF-8/Zn-dbia/SA capsule exhibits sensitive detection of alachlor, a representative pre-emergence acetanilide pesticide, with a satisfactory detection limit of 0.23 µM. In addition, the MOF-based gel capsules can be extended to a universal visual platform for the noninvasive detection of pesticide residues with various MOFs, such as Eu-MOF, Tb-MOF, and Cu-MOF, and participating dye. Similar to pitaya, the ordered porous structure of MOF in ZIF-8/Zn-dbia/SA capsules offers cavity and open sites for removing pesticide from water with the maximum adsorption amount qmax of 61.1 mg·g-1 toward alachlor in a Langmuir model. Thereby, this work presents the universality of gel capsule self-assembly technologies, including the well-preserved visible fluorescence area and porosity of the different structurally diverse MOFs, offering an ideal strategy for water decontamination and food safety control fields.

Stimuli-Responsive Metal-Organic Framework on a Metal-Organic Framework Heterostructure for Efficient Antibiotic Detection and Anticounterfeiting.

Stimuli-responsiveness is an important characteristic that show promising potential in various applications. Herein, a novel ZIF-8-on-Tb-dpn (H3dpn = 5-(2',4'-dicarboxylphenyl)nicotic acid) heterostructure is constructed using a heteroepitaxial strategy combining the chemical-responsive (antibiotics) and light-responsive behaviors. The pyridine nitrogen of Tb-dpn acts as an anchor site for Zn2+, which helps to overcome the limit of lattice mismatch between two metal-organic frameworks (MOFs) and promotes the growth of ZIF-8 nanocrystals. Based on the synergy effect of two MOFs, ZIF-8-on-Tb-dpn exhibits an efficient turn-off response toward tetracycline and chloramphenicol via competitive absorption, Förster resonance energy transfer, and photoinduced electron transfer processes with limit of detection values of 5.6 and 37.6 nM, respectively, which are three- to -fivefold lower than those of Tb-dpn. Moreover, the nanocage of ZIF-8 is utilized to encapsulate photochromic spiropyran (SP) molecules and realize the reversible conversion between SP and merocyanine (MC) under visible light and ultraviolet light. The MC form is accompanied with strong adsorption at 555 nm, which can erase the emission of Tb3+. Therefore, a reversible invisible anticounterfeiting pattern is designed with SP ⊂ ZIF-8-on-Tb-dpn for information anticounterfeiting. The excellent stimuli-responsive ability makes the luminescent platform a potential candidate in luminescence applications.