Understanding the role of polydopamine and semiconductor nanostructure interlayer in the photocatalytic water splitting process

With the rapid development of nanotechnology and the design and synthesis of increasingly sophisticated nanomaterials, interest in their use in various fields such as catalysis and environmental protection has increased. At the interface between these two fields, nanomaterials are being used as photocatalysts, which allow the degradation of various types of organic pollutants using light in the UV-Vis range. Semiconducting nanomaterials, which include TiO2, are widely used as photocatalysts. As a result of light hitting the surface, electrons in the valence shell move to the conduction band. This creates electrons on the TiO2 surface that combine with oxygen from the air to form active oxygen species and electron holes. These, in turn, combine with water vapour and water to form hydroxyl radicals. Depending on the conditions, (h+) holes, OH, O2ˉ, H2O2 or O2 radicals play a major role in the photocatalytic reaction mechanism. However, a major obstacle to the use of TiO2 in photocatalysis is its ability to absorb only light in the ultraviolet range, which significantly limits its use. One material that has made a significant contribution to materials chemistry in the last decade is polydopamine (PDA). It is a biocompatible polymer with strong adhesion and absorption properties in the UV, Vis and NIR. The broad-spectrum light-absorbing ability of polydopamine has been exploited to enhance the absorption capabilities of TiO2. The resulting TiO2-PDA hybrid materials with a PDA shell of <3 nm exhibited relatively high solar energy conversion efficiencies for the photodegradation of organic dyes under visible light compared to conventional photocatalysts. Furthermore, studies have shown that the photostability of PDA-coated nanomaterials is higher than that of pure semiconductors. However, the mechanism of the phenomenon causing this improvement in properties is still unknown. Therefore, research is needed to understand the effects occurring at the nanoscale, which will allow the creation of advanced photocatalysts in the semiconductor-polydopamine system.In the OPUS competition project, we intend to investigate the electrical and optical changes of semiconductor nanocomposites (TiO2, Fe3O4, ZnO) coated with polydopamine and its analogues, using advanced microscopic and analytical spectroscopic techniques. To this end, I will use, among others, a state-of-the-art electron microscopy method with Electron Emission Spectroscopy (EELS) technology, which provides exceptional spectroscopic capabilities at the nanoscale to study: chemical composition, valence differentiation, 3D and 4D analysis of nanomaterials, and determination of the dielectric constant of the material in the optical frequency range.