Studies in Framework Science Metal-organic Framework Composites BET Theory and Adsorption Reticular Chemistry and DNA Frameworks
Abstract Surfaces and self-assembly, two quintessential parts of modern nanotechnology, meet in the porous framework, a material formed by self-assembly and consisting only of surfaces, no bulk. This dissertation outlines the triangular relationship between frameworks, surfaces, and self-assembly. As such, it is organised in three distinct projects each corresponding to one of the three poles of this triangle. Frameworks | In this project, the chemistry of metal-organic framework (MOF) composites is explored. MOFs are porous coordination crystals made from the assembly of metal nodes and organic linkers. The Zr-MOF NU-901, which is known for its high thermal and chemical stability, is grown around plasmonic gold nanorods (AuNRs) in a core-shell bottlearound- ship encapsulation, and the synthesis is optimised to various morphology parameters. The resulting AuNR@NU-901 composites have multiple plasmonic applications. First, their use as drug delivery vehicles is explored: in this project, the photothermal energy conversion of AuNRs is used to trigger drug release from a MOF’s porosity under near-infrared light activation. In the second application, the composites were used as size-selective Raman sensors. Here, the MOFs porosity was used as a size-exclusion filter to gate the access of molecules to the plasmonic core where their characteristic Raman signal was amplified. In this proof-of-principle study, size-selective sensing from a mixed analyte solution was demonstrated, making AuNR@NU-901 a viable candidate for potential pollutant or pesticide sensing. Surfaces | The Brunauer-Emmett-Teller (BET) theory is one of the most widely used equations in physical chemistry. Developed in the 1930s, to this day it remains the most important figure of merit in porosimetry with far-reaching industrial and academic influences. Despite its widespread use, there remain significant issues with the manual calculation of BET surface areas. To probe this, 115 international collaborators with a strong track record in the study of nanoporous materials were brought together in a round-robin experiment: they were sent 18 anonymised isotherms and were asked to calculate their BET areas in the way they most saw fit. The results from this study show that reproducibility of BET area determination from identical isotherms is a largely ignored issue, raising critical concerns over the reliability of reported BET areas in the literature. To solve this major issue, a new algorithmic approach was developed to accurately and systematically determine the BET area of nanoporous materials. Self-assembly | Metal-organic frameworks and periodic DNA nanostructures are both assembled from constituent nodes and linkers. The similarities between these assemblies are herein described, and a common language for MOF chemistry and DNA crystals is developed: reticular colouring design (RCD). RCD not only represents a novel lens through which existing DNA crystals can be viewed, it can also lead to new and innovative designs by exploiting graph theoretical concepts of network topology that were developed for MOFs and related frameworks. As such, this project connects the dots and introduces two fields to one another that have traditionally little association. The triangular relationship frameworks – surfaces – self-assembly has appeared throughout this dissertation and my academic career at Cambridge. It has blessed me with an unconventionally multipolar PhD with interdisciplinary research and outside-the-box inspirations at the forefront. I hope that the dissertation standing at the end of this incredible journey will be of interest to the reader and contribute to some small extent to academic research and society.
Metal-organic frameworks, Nanotechnology, BET theory, MOF composites
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