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1. Unraveling the origin of the “Turn-On” effect of Al-MIL-53-NO ₂ during H ₂ S detection

   https://doi.org/10.1039/C9CE01595G  

   Zhu, Zan; He, Xiang; Wang, Wei-Ning (January 2020, CrystEngComm)

   Nitro-functionalized metal–organic frameworks (MOFs), such as Al-MIL-53-NO 2 , have been widely used in quantitative hydrogen sulfide (H 2 S) detection based on the “turn-on” effect, where fluorescence enhancements were observed upon contact with H 2 S. This was believed to be caused by the fact that the electron-withdrawing –NO 2 groups in the initial non-luminescent MOFs were reduced to electron-donating –NH 2 groups in the sensing process. However, since most H 2 S detection is conducted in a suspension system consisting of MOFs and solvents, it is still unclear whether these –NH 2 groups are on MOFs or in the liquid. Using Al-MIL-53-NO 2 as a model MOF, this work aims to answer this question. Specifically, the supernatant and undissolved particles separated from the Al-MIL-53-NO 2 suspensions after being exposed to H 2 S were analyzed systematically. The results showed that it is the free BDC-NH 2 (2-aminobenzene-1,4-dicarboxylic acid) in the solution rather than the formation of Al-MIL-53-NH 2 that really caused the fluorescence enhancement. In particular, the formed BDC-NH 2 was reduced from the shedded BDC-NO 2 (2-nitrobenzene-1,4-dicarboxylic acid) during the decomposition of Al-MIL-53-NO 2 , which was attacked by OH − in the NaHS solution. We anticipate that this work will offer new ways of tracing fluorophores for MOF-based sensing applications in aqueous systems. 

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2. Sodium-coupled electron transfer reactivity of metal–organic frameworks containing titanium clusters: the importance of cations in redox chemistry

   https://doi.org/10.1039/c8sc04138e  

   Saouma, Caroline T.; Tsou, Chih-Chin; Richard, Sarah; Ameloot, Rob; Vermoortele, Frederik; Smolders, Simon; Bueken, Bart; DiPasquale, Antonio G.; Kaminsky, Werner; Valdez, Carolyn N.; et al (January 2019, Chemical Science)

   Stoichiometric reduction reactions of two metal–organic frameworks (MOFs) by the solution reagents (M = Cr, Co) are described. The two MOFs contain clusters with Ti 8 O 8 rings: Ti 8 O 8 (OH) 4 (bdc) 6 ; bdc = terephthalate (MIL-125) and Ti 8 O 8 (OH) 4 (bdc-NH 2 ) 6 ; bdc-NH 2 = 2-aminoterephthalate (NH 2 -MIL-125). The stoichiometry of the redox reactions was probed using solution NMR methods. The extent of reduction is greatly enhanced by the presence of Na + , which is incorporated into the bulk of the material. The roughly 1 : 1 stoichiometry of electrons and cations indicates that the storage of e − in the MOF is tightly coupled to a cation within the architecture, for charge balance. 

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3. In situ formation of metal–organic framework derived CuO polyhedrons on carbon cloth for highly sensitive non-enzymatic glucose sensing

   https://doi.org/10.1039/c9tb01166h  

   Cheng, Siyi; Gao, Xiang; DelaCruz, Steven; Chen, Chen; Tang, Zirong; Shi, Tielin; Carraro, Carlo; Maboudian, Roya (August 2019, Journal of Materials Chemistry B)

   Metal–organic frameworks (MOFs) are considered promising templates for the fabrication of nanostructured materials with high porosities and high surface areas, which are important parameters for enhanced performance in sensing applications. Here, a facile in situ synthetic strategy to construct MOF-derived porous CuO polyhedrons on carbon cloth (CC) is reported. Uniform Cu(OH) 2 nanorods are first synthesized on carbon cloth, followed by the conversion of Cu(OH) 2 nanorods into porous CuO polyhedrons via a copper-based MOF, Cu–BTC, as the intermediate species. When evaluated as a glucose sensing electrode, the as-fabricated CuO polyhedrons/CC composite exhibits a high sensitivity of 13 575 μA mM −1 cm −2 with a fast response time ( t 90 ) of 2.3 s and a low detection limit of 0.46 μM. This work exemplifies the rational fabrication of porous nanostructures on conductive substrates for enhanced performance in glucose detection. 

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4. Cu(I/II) Metal–Organic Frameworks Incorporated Nanofiltration Membranes for Organic Solvent Separation

   https://doi.org/10.3390/membranes10110313  

   Upadhyaya, Lakshmeesha; Chiao, Yu-Hsuan; Wickramasinghe, S. Ranil; Qian, Xianghong (November 2020, Membranes)

   null (Ed.)

   Copper-based metal–organic frameworks (MOFs) with different oxidation states and near-uniform particle sizes have been successfully synthesized. Mixed-matrix polyimide membranes incorporating 0.1–7 wt% of Cu(II) benzene-1,2,5-tricarboxylic acid (Cu(II)BTC), Cu(I/II)BTC and Cu(I) 1,2-ethanedisulfonic acid (EDS) (Cu(I)EDS) MOFs were fabricated via non-solvent-induced phase inversion process. These membranes are found to be solvent resistant and mechanically stable. Liquid phase nanofiltration experiments were performed to separate toluene from n-heptane at room temperature. These membranes demonstrate preferential adsorption and permeation of the aromatic toluene over aliphatic n-heptane. The amount of MOF particles incorporated, the oxidation state of the Cu ion and membrane, and barrier layer thickness have a significant impact on the separation factor. Toluene/heptane separation factor at 1.47, 1.67 and 1.79 can be obtained for membranes incorporating 7 wt% Cu(II)BTC, Cu(I/II)BTC and Cu(I)EDS respectively at room temperature. 

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5. Identification of toxicity effects of Cu ₂ O materials on C. elegans as a function of environmental ionic composition

   https://doi.org/10.1039/c9en00686a  

   Munro, Catherine J.; Nguyen, Michelle A.; Falgons, Christian; Chaudhry, Sana; Olagunju, Mary O.; Bode, Addys; Bobé, Carla; Portela, Manuel E.; Knecht, Marc R.; Collins, Kevin M. (January 2020, Environmental Science: Nano)

   Previous work has shown that spherical CuO nanomaterials show negative effects on cell and animal physiology. The biological effects of Cu 2 O materials, which possess unique chemical features compared to CuO nanomaterials and can be synthesized in a similarly large variety of shapes and sizes, are comparatively less studied. Here, we synthesized truncated octahedral Cu 2 O particles and characterized their structure, stability, and physiological effects in the nematode worm animal model, Caenorhabditis elegans . Cu 2 O particles were found to be generally stable in aqueous media, although the particles did show signs of oxidation and leaching of Cu 2+ within hours in worm growth media. The particles were found to be especially sensitive to inorganic phosphate (PO 4 3− ) found in standard NGM nematode growth medium. Cu 2 O particles were observed being taken up into the nematode pharynx and detected in the lumen of the gut. Toxicity experiments revealed that treatment with Cu 2 O particles caused a significant reduction in animal size and lifespan. These toxic effects resembled treatment with Cu 2+ , but measurements of Cu leaching, worm size, and long-term behavior experiments show the particles are more toxic than expected from Cu ion leaching alone. These results suggest worm ingestion of intact Cu 2 O particles enhances their toxicity and behavior effects while particle exposure to environmental phosphate precipitates leached Cu 2+ into biounavailable phosphate salts. Interestingly, the worms showed an acute avoidance of bacterial food with Cu 2 O particles, suggesting that animals can detect chemical features of the particles and/or their breakdown products and actively avoid areas with them. These results will help to understand how specific, chemically-defined particles proposed for use in polluted soil and wastewater remediation affect animal toxicity and behaviors in their natural environment. 

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