Metal-Organic Frameworks: Defects, Spectroscopy and Catalysis

Abstract

In this PhD thesis we have studied the chemistry of defects within Metal-Organic Frameworks (MOFs) as well as the properties of the related Defect-Engineered Metal-Organic Frameworks (DEMOFs). We also have investigated the potential roles of MOF and DEMOF materials as new solid catalysts or porous hosts for functional guests, being it metal nanoparticles or electroactive organic molecules. Given the complexity of MOF materials, the wide variety of building blocks (i.e., linker and nodes), topologies, morphologies, dynamic nature and broad potential applications (with a special focus on catalysis) has to be rationalized in terms of general (physical) chemistry concepts. This is the topic of Chapter 1, which presents the core concepts behind MOF and DEMOF chemistry. A brief introduction on coordination chemistry, spectroscopy and an outline on what MOFs are and how they may be involved as solid catalysis is included. A literature survey of the various analytical methods used to study the relevant properties of MOF and DEMOF materials is presented in Chapter 2. In Chapter 3, we have compared two MOF materials with the same building blocks and different degrees or crystallinity, i.e. highly crystalline vs. amorphous. This also affects how Pd molecular precursors are deposited onto the surface of these MOF materials and subsequently agglomerate into metal nanoparticles by using different synthesis methods. Thus, we have shown that lattice order is an important feature for affecting the properties of MOF materials. The concept of disorder is also central to the theme covered in Chapter 4, where the effects of mixing MIL-100(Cr) and MIL-101(Cr) with a strong alkylating co-catalyst for the polymerization of ethylene have been studied. Different activities were observed and Scanning Electron Microscopy (SEM) imaging showed that although similar polyethylene is formed; morphology is optimal if MIL-101(Cr) is used as a catalyst. In Chapter 5, single-site defects in a HKUST-1 material, as created by the introduction of non-coordinating linkersare investigated. Following previous research, the aim was to better understand how defect linkers influence the properties of a MOF material. We have studied the following aspects of DEMOF materials: i) the location of defective linkers at the inter- and intra-crystal level, ii) the effect of the defective linkers on the crystal size (and size distribution) and morphology, iii) the effect of defective linkers on the formation of mesopore structures; and iv) the effect of defective linkers on the nature of the Cu sites on the paddlewheels. In Chapter 6, HKUST-1 is used as a host for the TCNQ electroactive molecule. We have studied the location of TNCQ within HKUST-1 and evaluated what is the effect of water in creating defects and conductivity. Finally, in Chapter 7, a critical discussion of the results and the potential avenues of research related to MOFs and DEMOFs for the coming years, including spectroscopy, microscopy of these materials and their applications in catalysis.