Synthesis, Characterization, and Applications of Visible Light Active Metal-Organic Frameworks

Understanding how crystalline materials are assembled is important for the rational design of metal-organic frameworks (MOFs). Controlling their formation can allow researchers to streamline the synthesis of new materials as well as control their properties for targeted applications. In the first chapter of this thesis we report the construction of two 3-dimensional TbIII based MOFs (SION-1 and SION-2). Here, SION-2 acts as a metastable MOF and intermediate phase that partially dissolves and transforms into the thermodynamically stable MOF, SION-1. This chemical transformation occurs in a DMF/water solvent mixture, and is triggered when additional energy is provided to the reaction. In situ studies reveal the partial dissolution of the metastable phase after which the MOF components are reassembled into the thermodynamically stable phase. The marked difference in thermal and chemical stability between the kinetically and thermodynamically controlled phases is contrasted by their identical chemical building unit composition. Following the understanding of this transformation, an isostructural family of SION-1 and SION-2 had been constructed using lanthanide metal salts, where LnIII-SION-1 is comprised of Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu and LnIII-SION-2 is formed using Ce, Nd, Eu, Gd, Tb and Yb. The electronic properties of lanthanide based MOFs have not been extensively studied due to the general cognizance that LnIII ions behave as isolated free ions as their 4f orbitals do not contribute to bonding. Here, we systematically studied the electronic properties (UV-vis) of LnIII-SION-1 and LnIII-SION-2 and show that the higher the intensity of this absorption band in LnIII-SION-1 is due to the better overlap between Ln(5d) and ligand(pi*) orbitals and reveals that the lowest unoccupied crystalline orbitals are dispersed over an energy range and can be considered as a conduction band. We validated this observation by the non-linear I-V curves collected on CeIII- and YbIII-SION-1, both of which display dielectric properties. In the second chapter of this thesis, we rationally design a novel biologically derived MOF featuring unobstructed Watson-Crick faces of Ade pointing towards the MOF cavities. We show, through a combined experimental and computational approach, that Thy molecules diffuse through the pores of the MOF and become base-paired with Ade. The Ade-Thy pair binding at 40-45% loading reveals that Thy molecules are packed within the channels in a way that fulfill both the Woodward-Hoffmann and Schmidt rules, and upon UV irradiation, Thy molecules dimerize into ThyThy. This study highlights the utility of MOFs as nanoreactors for the synthesis of molecules that are otherwise difficult. Concluding this thesis, a biologically derived multimodal sensor MOF is synthesized and a formed into a device. The MOF, SION-9, is comprised of Ade and a porphyrin based ligand, and has tuneable conductive properties ranged from 2.69-4.20 x 10-8 - 7.43-7.34 x 10-6 S/cm. SION-9 is sensitive to both pressure and temperature simultaneously, and demonstrated both fast response times (< 60 ms) and a long shelf life (> 6 months).

Fluid-structure thermal coupling and ablation effects in atmospheric entry

Ojas Joshi

This thesis deals with the modelling of fundamental aspects of the mission engineering, the physics, and the constraints of atmospheric entry of space vehicles. The aim of this work is to formulate a coupled approach for the modelling and the simulation of thermal fluid-structure interaction in atmospheric entries, taking into account the thermochemical and physical response of the material composing the solid structure. Numerous missions that aim to explore planets, comets or regions outside our galaxy are planned for the next few years. During the phase of entry into the atmosphere of a planet or a moon, space vehicles encounter extreme heating conditions that can damage the structure and the on-board equipment. A Thermal Protection System (TPS) is hence installed to insulate the vehicle’s internal parts from high temperatures and heat fluxes. Ablative materials, which are composed of high-temperature resistant fibre porous structure filled with an organic matrix, are often used to manufacture heat shields of high speed entry vehicles. The hot gas around the spacecraft transfers energy fluxes to the vehicle through the fluid-structure interface. The solid then reacts, with part of the heat being conducted in the deeper layers of the material, and part being absorbed by physical and chemical transformations of the material itself. The organic phase of the ablative material evaporates – this process is called pyrolysis – and these gases are blown into the outer flow, creating thus a protective layer. Moreover, the surface of the TPS may react with the atmospheric gases, consuming in this way a fraction of the material. A model for these two phenomena and the thermal fluid-structure interaction is proposed in this thesis. Numerical simulations are one of the most widely used tools to design the TPS, and a detailed mathematical model allows to reduce margins in the sizing. Atmosphere gases and the spacecraft structure form two distinct systems that interact through the external surface of the TPS, and through which energy and mass exchanges occur. Many computational tools exist to simulate the physics of each of the two domains. A higher level of accuracy is however achieved if the problem is approached in a coupled fashion, where each system takes into account the thermophysical response of the other. An innovative coupling algorithm, which includes the direct evaluation of the surface chemistry, is presented in this thesis. Using this coupling procedure, numerical simulations of the TPS of a European Space Agency project are performed and key parameters for the sizing of the heat shield are evaluated and discussed.

EPFL2013

CO2 chemical transformations using metal-organic frameworks

Serhii Shyshkanov

During the last decades, intensive efforts have been applied to tackle the enormous emissions of CO2 into atmosphere. These efforts include not only developing efficient carbon capture techniques, but also the introduction of new ways to transform the captured CO2 into the valuable products. In this context, numerous catalytic systems have been developed for the reduction of CO2. Typically, homogeneous systems provide better selectivity, due to more precise control of the chemical properties of the catalytic moiety, and require milder reaction conditions, compared to the currently employed heterogeneous catalysts. However, the majority of industrial chemical processes deploy heterogeneous catalytic systems, as their comparative stability and facile separation of the products from the catalyst facilitates scale-up and continuous production. Therefore, the crucial vector of successful transfer of the newest achievements in chemical catalysis lies in merging the advantages provided by homogeneous catalysts with the benefits of heterogeneous systems. Metal-organic frameworks (MOFs) are crystalline materials formed by the self-assembly of metal ions or clusters with organic ligands and possess unique merits, such as extremely high surface area, uniform and tunable porous structure, wide opportunities for rational design. Amalgamation of the newly developed concepts, such as FLP chemistry, showing promising results in activation of CO2, as well as recent advances in conventional catalysis with MOFs should allow the advantages of MOFs as materials with directed assembly to converge with the versatile needs of a catalytic material an improve the potential for application of them both in industry and chemical synthesis. This thesis describes the implementation of the FLP concept into MOFs. A proof of a concept, demonstrating feasibility and potential applicability of this approach for CO2 fixation is followed by the development and evaluation of a recyclable and water tolerant heterogeneous MOF catalyst for FLP-mediated reduction of CO2. Additionally, MOF-based catalysts, employing incorporated functionalities and supported metal nanoparticles, were accessed for CO2 conversion.

EPFL2020

Exploration of zeroth-order Wavefunctions and Energies for Intramolecular Symmetry-Adapted Perturbation Theory

Jérôme Florian Gonthier

Non-covalent interactions occur between and within all molecules and have a profound impact on structural and electronic phenomena in chemistry, biology, and material science. Understanding the nature of inter-and intramolecular interactions is essential not only for establishing the relation between structure and properties, but also for facilitating the rational design of molecules with targeted properties. These objectives have motivated the development of theoretical schemes decomposing intermolecular interactions into physically meaningful terms. Among the various existing energy decomposition schemes, Symmetry-Adapted Perturbation Theory (SAPT) is one of the most successful as it naturally decomposes the interaction energy into physical and intuitive terms. Unfortunately, analogous approaches for intramolecular energies are theoretically highly challenging and virtually nonexistent. Here, we introduce a zeroth-order wavefunction and energy, which represent the first step toward the development of an intramolecular variant of the SAPT formalism. The proposed energy expression is based on the Chemical Hamiltonian Approach (CHA), which relies upon an asymmetric interpretation of the electronic integrals. The orbitals are optimized with a non-hermitian Fock matrix based on two variants: one using orbitals strictly localized on individual fragments and the other using canonical (delocalized) orbitals. The zeroth-order wavefunction and energy expression are validated on a series of prototypical systems. The computed intramolecular interaction energies demonstrate that our approach combining the CHA with strictly localized orbitals achieves reasonable interaction energies and basis set dependence in addition to producing intuitive energy trends. Our zeroth-order wavefunction is the primary step fundamental to the derivation of any perturbation theory correction, which has the potential to truly transform our understanding and quantification of non-bonded intramolecular interactions. (C) 2014 AIP Publishing LLC.

Amer Inst Physics2014