UC Berkeley

The subject of this dissertation focuses on the development of reticular chemistry, where molecular building blocks are linked into extended frameworks using strong bonds, in the context of materials chemistry. Specifically, the work herein advances the frontier of reticular chemistry is three aspects: (a) bringing metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), the products of reticular chemistry, into nanometer size regime and integrating them into mesoscopic constructs; (b) developing reticular chemistry beyond crystalline materials and synthesizing glassy form of MOFs; (c) Designing woven frameworks where interlacing molecular threads form crystalline three-dimensional frameworks.

Chapter 1 introduces the principles and main discoveries of reticular chemistry under the scheme of covalent bond beyond molecules. By linking molecular building blocks into well-defined extended structures through strong covalent bonds, reticular chemistry has essentially brought covalent chemistry beyond discrete molecules and led to the discovery of numerous MOFs and COFs with diverse structures, different functional groups and vast surface areas. The chapters hereafter explore the synthesis and fabrication of MOFs and COFs as nanosized, glassy and woven materials.

Chapter 2 describes the fabrication of mesoscopic constructs of MOFs and inorganic nanocrystals, where thickness controlled and oriented Al2(OH)2TCPP MOF [TCPP = 4,4,4,4‴-(porphyrin-5,10,15,20-tetrayl)-tetrabenzoate] enclosures are uniformly grown on inorganic nanostructures with pristine interface. The fabrication process involves atomic layered deposition of alumina on inorganic substrates (i.e. silver nanocrystals) and reacting them with TCPP linkers to nucleate MOF. By growing Al2(OH)2TCPP MOF enclosure on silver nanocrystals, surface enhanced Raman spectroscopy can be employed to study the metalation process of the porphyrin units in the MOF.

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Chapter 3 generalizes the fabrication methodology of Al2(OH)2TCPP MOF enclosures to prepare thickness controlled cobalt metalated Al2(OH)2TCPP-Co MOF thin films and studied their performance as catalysts for electrochemical CO2 reduction. For Al2(OH)2TCPP-Co MOF of 50 nm thickness on carbon disk, 76% faradic efficiency for CO can be achieved at -0.7 V vs. RHE in aqueous media with a turn over frequency of 200 h-1 (per cobalt atom). The catalyst was found to be stable for at least seven hours. This study demonstrates that insulating MOFs can be active electrocatalyst when fabricated into thin films with thickness of tens of nanometers.

Chapter 4 expands reticular chemistry into glassy materials by developing the synthesis of porous MOF glasses, which consist of titanium-oxo clusters linked with bisphenol linkers. By employing m-cresol as a solvent-modulator, monolithic and transparent MOF glasses can be formed by evaporating viscous m-cresol solutions of the molecular building blocks. In this process, the glass transition temperature of this solution increases exponentially with decreasing amount of m-cresol until the vitrification of the glass. After removing m-cresol from the pores, the internal surface of MOF glasses can be accessible to gas molecules and display surface area of around 300 m2/g.

Chapter 5 turns to COFs and presents the synthesis of woven frameworks COF-505 and COF-112. In the synthetic design, aldehyde (amine) functionalized derivative of tetra-topic metal complexes [copper bis-phenanthroline for COF-505 and cobalt bis(diiminopyridine) for COF-112] are used as the tetrahedral building block, where the position of the aldehyde (amine) groups approximates a tetrahedral geometry. The tetrahedral building block is linked with a linear amine (aldehyde) to give a three-dimensional framework with diamond topology. The fact that the phenanthroline/diiminopyridine units are oriented in a mutually interlacing fashion ensures that the threads produced from linking them are entirely independent, with the metal ions serving as templates (points-of-registry) to bring those threads together in a precise manner at well-defined intervals. For COF-505, the copper(I) ions can be removed and inserted reversibly and tune the Young’s modulus of the material.

The dissertation concludes in chapter 6, which brings COFs into nanometer size regime and paves the way for the integration of COFs into mesoscopic constructs. In this chapter, a new synthetic approach employing Boc-protected amine building blocks is developed to homogenize the growth of imine COFs (LZU-1, TFPB-PDA COF and Por-COF) to produce monodisperse nanocrystals and oriented thin films. The synthetic approach avoids the formation of polyimine precipitate in the early stage of conventional imine COF crystallization process and allows crystalline COF particles to nucleate directly from clear solutions. This feature enables the imine COF growth to be tuned by modulators [i.e. poly(vinylpyrrolidone)] to give colloidally stable nanocrystals and manipulated by selective secondary nucleation to give uniform thin films.