Engineering optoelectronics and smart sensors leveraging metal-organic framework materials

Thesis

Metal-organic frameworks (MOFs) have emerged as promising nanomaterials for the development of advanced sensing technologies. Indeed, their unparalleled features comprising structural diversity, tailorability, high porosity, large surface area, and adsorption affinities can offer superior sensing performance unattainable by the array of conventional materials for selective, fast, and sensitive detection of gases. However, for the integration of MOFs into sensor devices, a thorough understanding of the material’s underpinning properties and mechanisms is vital. In this integrated thesis, the key principles, which are used for functionalising MOFs with desired properties, are studied from the single-crystal level (Chapter 1). Herein, Chapter 2 introduces near-field infrared spectroscopy techniques for the chemical characterisation of individual MOF-type crystals at the nanoscale.

Based on this technique, Chapter 3 presents a new strategy to reveal the encapsulation of luminescent ‘guest’ molecules in the pores of the ‘host’ MOF framework. This so-called guest@MOF principle is a smart way to engineer novel material for sensors and optoelectronics, however, unambiguously proving the successful encapsulation in lieu of surface adsorption has been challenging thus far.

Turning to defect tuning - another strategy to tune MOF materials for sensing applications - Chapter 4 demonstrates how the combination of nanoscale analytics and density functional theory calculations can probe point defects in individual MOF crystals, further scrutinising their impact on mechanical properties.

Chapter 5 offers insights into the sensing mechanism itself by studying the exceptional response of a guest@MOF material towards volatile acetone. Herein, several spectroscopy techniques ranging from nanoscale analytics to in situ and operando techniques based on inelastic neutron scattering and synchrotron radiation, all corroborated by theoretical simulations, are used to explore the underlying principles of the unique sensing performance.

Building upon the findings of Chapter 3-5, Chapter 6 presents a detailed characterisation of a promising MOF material for sensing applications. Specifically, theoretical calculations and spectroscopy techniques can explain the interplay between the physical, chemical, and mechanical properties to provide a fundamental understanding of the material’s behaviour and structure-function relations.

Finally, Chapter 7 serves as a critical review of the presented findings, further highlighting their contribution to the future development of tailored MOF materials as next-generation sensors.

Authors: Möslein, AF

• DOI: 10.5287/ora-nbzdemna4
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: metal-organic frameworks; near-field infrared spectroscopy; nanoscale analytics; density functional theory
• Subjects: Engineering; Nanoscience