Exploring the Photoluminescence and Structural insights of MIL-53(Al) Metal-Organic Framework Under Multi-Stimulus Environment

Metal-organic frameworks (MOFs), known for their high porosity and crystalline nature, are composed of metal ions connected by organic linkers, making them a leading class of materials both in applications and in scientific exploration, blending diverse disciplines such as physics, chemistry and materials science.The main objective of this research is to explore the electronic and structural properties of a MOF sub-category, a prototype breathing MIL-53(Al) under various external stimuli, including mechanical pressure, temperature, and different solvents such as water and volatile organic compounds (VOCs). The experimental approach takes advantage of the combined use of different complementary techniques: structural properties are analysed using powder X-ray diffraction (PXRD) measurements, thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier-transform Raman (FT-Raman) spectroscopy; the photoluminescence (PL) properties are investigated through time-resolved photoluminescence (TRPL) spectroscopy, allowing us to discern the effects of different activation temperatures on the material's luminescence and structural integrity. The results deriving from this investigation have added new elements to the specialized literature in this field and can be grouped into the following points:- Response of MIL-53(Al) to various mechanical pressures and temperatures, as well as immersing it in solvents like water and VOCs, to study the PL changes and to understand the origins of the two distinct bands (UV and blue) observed in this MOF. - Fe³⁺ cation exchange experiments allow to explore the dynamics of such ions on the structural and luminescence properties of MIL-53(Al) and provide valuable insights into the relationship between the material's structural modifications and its photophysical behaviour. - MIL-53(Al) composites are synthesized with two different types of carbon dots (CDs) and their efficiency is evaluated in the photodegradation of organic dyes, specifically Rhodamine B (RhB). Overall, the comprehensive study presented in this PhD thesis enhances the understanding of the photophysical behaviour of MIL-53(Al) under various external stimuli, with important implications for sensing applications, and underscores the versatility of this material and its composites with carbon-based nanostructures, paving the way for future research in MOF-based materials for advanced photocatalysis applications.The present PhD thesis is organized in six chapters. Chapter 1 reports an overview on the general properties of MOFs and focuses on the state of the art of the works previously carried out on MIL-53(Al), that is the object of study of this PhD thesis. Chapter 2 deals with the background on the main microscopy and spectroscopy techniques suitable for the investigation of MOFs. Chapter 3 and 4 are devoted to the description of experimental methods and on the sample preparation procedures. The results are reported and discussed in Chapter 5. Finally, Chapter 6 summarizes the conclusions and the perspectives. Most of results obtained in this PhD work have been published on scientific journals and presented at international conferences, the references are available in a “List of related products” at the end of the Thesis.