In situ single-crystal synchrotron X-ray diffraction studies of biologically active gases in metal-organic frameworks

In Situ Single-crystal X-ray Diffraction Studies of Physisorption and Chemisorption of SO2 within a Metal-Organic Framework and Its Competitive Adsorption with Water

Living on an increasingly polluted planet, the removal of toxic pollutants such as sulfur dioxide (SO2) from the troposphere and power station flue gas is becoming more and more important. The CPO-27/MOF-74 family of metal-organic frameworks (MOFs) with their high densities of open metal sites is well suited for the selective adsorption of gases that, like SO2, bind well to metals and have been extensively researched both practically and through computer simulations. However, until now, focus has centered upon the binding of SO2 to the open metal sites in this MOF (called chemisorption, where the adsorbent-adsorbate interaction is through a chemical bond). The possibility of physisorption (where the adsorbent-adsorbate interaction is only through weak intermolecular forces) has not been identified experimentally. This work presents an in situ single-crystal X-ray diffraction (scXRD) study that identifies discrete adsorption sites within Ni-MOF-74/Ni-CPO-27, where SO2 is both chemisorbed and physisorbed while also probing competitive adsorption of SO2 of these sites when water is present. Further features of this site have been confirmed by variable SO2 pressure scXRD studies, DFT calculations, and IR studies.

Mixed Metal-Organic Framework Mixed-Matrix Membranes: Insights into Simultaneous Moisture-Triggered and Catalytic Delivery of Nitric Oxide using Cryo-scanning Electron Microscopy

The fundamental chemical and structural diversity of metal-organic frameworks (MOFs) is vast, but there is a lack of industrial adoption of these extremely versatile compounds. To bridge the gap between basic research and industry, MOF powders must be formulated into more application-relevant shapes and/or composites. Successful incorporation of varying ratios of two different MOFs, CPO-27-Ni and CuBTTri, in a thin polymer film represents an important step toward the development of mixed MOF mixed-matrix membranes. To gain insight into the distribution of the two different MOFs in the polymer, we report their investigation by Cryo-scanning electron microscopy (Cryo-SEM) tomography, which minimizes surface charging and electron beam-induced damage. Because the MOFs are based on two different metal ions, Ni and Cu, the elemental maps of the MOF composite cross sections clearly identify the size and location of each MOF in the reconstructed 3D model. The tomography run was about six times faster than conventional focused ion beam (FIB)-SEM and the first insights to image segmentation combined with machine learning could be achieved. To verify that the MOF composites combined the benefits of rapid moisture-triggered release of nitric oxide (NO) from CPO-27-Ni with the continuous catalytic generation of NO from CuBTTri, we characterized their ability to deliver NO individually and simultaneously. These MOF composites show great promise to achieve optimal dual NO delivery in real-world medical applications.

Green Ultrasound-Assisted Synthesis of Rare-Earth-Based MOFs

Rare-earth (RE)-based metal organic frameworks (MOFs) are quickly gaining popularity as flexible functional materials in a variety of technological fields. These MOFs are useful for more than just conventional uses like gas sensors and catalyst materials; in fact, they also show significant promise in emerging technologies including photovoltaics, optical, and biomedical applications. Using yttrium and europium as ionic host centres and dopants, respectively, and 1,3,5-benzenetricarboxylic acid (H3-BTC) as an organic linker, we describe a simple and green approach for the fabrication of RE-MOFs. Specifically, Y-BTCs and Eu-doped Y-BTCs MOFs have been synthesised in a single step using an eco-friendly method that makes use of ultrasound technology. To establish a correlation between the morphological and structural properties and reaction conditions, a range of distinct reaction periods has been employed for the synthetic processes. Detailed analyses of the synthesised samples through powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared spectroscopy (FT-IR) have confirmed the phase formation. Furthermore, thermal analyses such as thermogravimetric analysis (TGA) have been employed to evaluate the thermal stability and structural modifications of the Y-BTC and Eu-doped Y-BTC samples. Finally, the luminescent properties of the synthesised samples doped with Eu3+ have been assessed, providing an evaluation of their characteristics. As a proof of concept, an Eu-doped Y-BTC sample has been applied for the sensing of nitrobenzene as a molecule test of nitro derivatives.