Thesis defended

Szymon Wojtyła has got his PhD degree. Congratulation!

Reactive molecular oxygen species (¹O₂ , O₃) in heterogenous catalysis

Numerous photocatalytic processes such as degradation of pollutants or organic synthesis occurs with reactive oxygen species, that are formed mainly as an effect of photoinduced charge transfer from excited semiconductor to O₂ and H₂O molecules. Photocatalytic activation of oxygen may lead to formation of two reactive oxygen species: superoxide radical anion and singlet oxygen. The former one is formed by one-electron reduction of oxygen while singlet oxygen can be generated on two pathways, involving either the electron transfer, generation of O₂^•- and its oxidation with a hole, or by a direct energy transfer to ³O₂ molecule. The goal of this thesis was to study the mechanism and efficiency of singlet oxygen formation from molecular oxygen O₂ and ozone O₃ in photocatalytic heterogeneous systems. It is more and more discerned that alongside novel photocatalysts developments, understanding of the mechanism of primary photocatalytic processes is crucial for the technological development of photocatalysis. In this context, this thesis focuses on understanding of the mechanisms governing oxygen activation based on photoinduced charge or energy transfer, resulting in singlet oxygen formation. Moreover, a new method of singlet oxygen detection was developed with this work. A series of heterogeneous semiconducting materials has been prepared: neat and silylated or doped TiO₂, silicon-based materials, wide band gap semiconductors, such as ZnS, ZnO, NiO, and semiconductors with a narrower band gap, e.g. CdS, Cu₂O, Fe₂O₃. All materials have been characterized using spectroscopic and crystallographic methods. They were tested as photocatalysts of singlet oxygen formation from O₂. Moreover, ozone was considered as an alternative substrate for singlet oxygen formation on a photocatalytic way. Obtained results prove that the prepared nanocrystalline materials are active photocatalysts and upon irradiation they are able to generate singlet oxygen based on one or both discussed mechanisms. Si, silylated TiO₂, Fe₂O₃, Cu₂O appeard particulary active oxygen photosensitizers. Formation of other reactive oxygen species, such as superoxide anion radical and hydroxyl radical from O₂ and O₃, has also been studied and discussed. Results and conclusions shine some new light on photocatalytic transformations involving ¹O₂ and O₃.