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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/125233
Modelling Nano-Oxide Materials with Technological and Environmental Relevance: Silica, Titania and Titanosilicates
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[eng] Properties of nanomaterials are known to be size dependent and generally are very different from those of the corresponding bulk. Such behaviour, which is strongly system and structure dependent, allows one to tune material’s properties by varying their dimensions. This tunability opens up many possibilities in nanotechnology for manufacturing materials with tailored properties for specific applications. Thus, understanding size-dependent properties of nanoparticles and mechanisms taking place at the nanoscale is fundamental for the improvement of existing materials and for the designing of more efficient and optimized ones. However, the synthesis of nanomaterials and their experimental characterization is difficult, especially for very small sizes. Here, theoretical modelling plays a fundamental role in the characterization of small nanoparticles for both helping experimental interpretation and predicting novel and potentially synthesizable materials with new properties.
In this thesis we focus on modelling of titania, silica and titanosilicate based materials because of their technological and environmental importance as they are employed in heterogeneous (photo-)catalysis, electronics and gas sensing to cite a few. For such systems, we firstly performed global optimization studies in gas-phase and water containing environments in order to identify the structures of nanoparticles. Secondly, we studied structural, energetic and electronic size-dependent properties of such nanoparticles as well as their reducibility, extrapolating up to the bulk macroscopic level in some cases. For such characterization we used accurate quantum mechanical methods based on Density Functional Theory (DFT).
Our results point to a series of important predictions, such as for instance: (i) the crystallinity of titania nanoparticles, which is the key property for the photoactivity of such material, is predicted to emerge when nanoparticles become larger than 2.0-2.5 nm; (ii) the mixing of titania and silica to form titanosilicates, which are an important class of materials used in industry as catalyst, is found be thermodynamically favorable at the nanoscale, contrary to the bulk; (iii) the hydration of silica and titania nanoclusters, which plays an important role in the aggregation and nucleation process during the synthesis of larger nanoparticles, is controlled by environmental factors such as temperature and water vapor pressure as predicted from calculated phase diagrams; iv) the oxygen vacancy formation energy, which is an indicator of the system reducibility, is found to be less energetically costly in small nanosilica clusters rather than in nanotitania which is the opposite of what happens at the corresponding bulk level. We hope to inspire experimental studies to address the synthesis of novel titanosilicates materials with potentially enhanced properties by using as building blocks the nanoparticles predicted here.
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CUKO, Andi. Modelling Nano-Oxide Materials with Technological and Environmental Relevance: Silica, Titania and Titanosilicates. [consulta: 10 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/125233]