Computational Studies of Structure, Stability and Properties of Nanoporous Framework Materials

  • Framework materials are extended structures that are built into destined nanoscale architectures using molecular building units. Reticular synthesis methods allow stitching of a large variety of molecules into predicted networks. Porosity is an obvious outcome of the stitching process. These materials are classified and named according to the chemical composition of the building blocks. For instance, Metal-Organic Frameworks (MOFs) consists of metal-oxide centers that are linked together by organic entities. The stitching process is straight-forward, so that there are already thousands of them synthesized. Controlled growth of MOFs on substrates leads to what is known as surface-MOFs (SURMOFs). A low-weight, metal-free version of MOFs is known as Covalent Organic Frameworks (COFs). They consist of light elements such as boron, oxygen, silicon, nitrogen, carbon and hydrogen atoms. Diamond-like structures with a variety of linear organic linkers between tetrahedral nodes is called Porous Aromatic Frameworks (PAFs). The thesis is composed of computational studies of the above mentioned classes of materials. The significance of such studies lies in the insights that it gives about the structure-property relationships. Density Functional Theory (DFT) and its Tight-Binding approximate method (DFTB) were used in order to perform extensive calculations on finite and periodic structures of several frameworks. DFTB provides an ab-initio base on periodic structure calculations of very large crystals which are typically studied only using force-field methods. The accuracy of this approximate method is validated prior to reasoning. As the materials are energized from building units and coordination (or binding), stability vs. structure is discussed. Energy of formation and mechanical strength are particularly calculated. Using dispersion corrected (DC)-Self Consistent Charge (SCC) DFTB, we asserted that 2D COFs should have a layer arrangement different from experimental suggestions. Our arguments supported by simulated PXRDs were later verified using higher level theories in the literature. Another benchmark is giving an insightful view on the recently reported difference in symmetries of two-dimensional MOFs and SURMOFs. The result of it shows an extra-ordinary role of linkers in SURMOFs, providing metastability. Electronic properties of all the materials and hydrogen adsorption capacities of PAFs are discussed. COFs, PAFs and many of the MOFs are semiconductors. HOMO-LUMO gaps of molecular units have crucial influence in the band gaps of the solids. Density of states (DOS) of solids corresponds to that of cluster models. Designed PAFs give a large choice of adsorption capacities; one of them exceeds the DOE (US) 2005 target. Generally, the studies covered under the scheme of the thesis illustrate the structure, stability and properties of framework materials.

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Publishing Institution:IRC-Library, Information Resource Center der Jacobs University Bremen
Granting Institution:Jacobs Univ.
Author:Binit Lukose
Referee:Thomas Heine, Ulrich Kleinekathöfer, Christof Wöll, Petko Petkov
Advisor:Thomas Heine
Persistent Identifier (URN):urn:nbn:de:101:1-201305294754
Document Type:PhD Thesis
Date of Successful Oral Defense:2012/07/19
Date of First Publication:2012/09/06
PhD Degree:Physics
School:SES School of Engineering and Science
Other Countries Involved:Bulgaria
Library of Congress Classification:T Technology / TA Engineering (General). Civil engineering (General) / TA401-492 Materials of engineering and construction. Mechanics of materials
Call No:Thesis 2012/26

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