Thesis defended

Kasidid Yaemsunthorn has got his PhD degree. Congratulations!

Phase-Dependent Photocatalytic Activity of TiO2 – the Role of Intrinsic and Extrinsic Factors

The doctoral thesis delves into the phase-dependent photoactivity of anatase and rutile TiO2, explored through various photocatalytic reactions involving oxidation and reduction processes. The investigation of the influential factors involved in this dependency has led to the identification of two primary categories: intrinsic factors, which relate to the physicochemical and characteristic properties of the materials themselves, and extrinsic factors, which are associated with the nature of the specific reactions and their corresponding reaction conditions. The study demonstrates that the photoactivity of TiO2 is relative to both intrinsic and extrinsic factors, and sheds light on the mechanisms underlying photocatalysis. By optimizing these factors, it is possible to enhance the photoactivity of TiO2 and develop more efficient and practical photocatalytic systems. These findings reveal the fundamental mechanisms underlying photocatalysis and pave the way for the development of more suitable photocatalysts for particular reactions, which are crucial for optimizing and realizing the practical use of photocatalysis for addressing the energy crisis and climate change.

Thesis defended

Paweł Mikrut has got his PhD degree. Congratulations!

Solar energy utilisation in shape- and redox-engineered photocatalytic systems

Thesis defended

Magdalena Mikrut has got her PhD degree. Congratulations!

Redox activity of particulate matter in the context of autoimmune diseases development.


Thesis defended

Michał Pacia has got his PhD degree. Congratulations!

Activation of O2, H2O and H2O2 in photoinduced electron transfer processes.

As part of the dissertation research was carried to recognize various aspects of activation of the O2, H2O and H2O2 presence of TiO2 materials. In the case of anatase and rutile the influence of O2 and H2O2 presence on ROS generation in the irradiated system was determined. It was proven that rutile, compared to anatase, performs better in both O2 and H2O2 reduction. The influence of the exposed crystal facets on redox properties of materials were also investigated. The facets were put in an order (101) > (100) > (001) according to their activity in the H2O2 activation via reduction. Monocrystalline rutile materials, with exposed(110), (101) or (001) facets were also tested. The next step involved tests on surface modified TiO2 materials. Proper approach to determining the EBG in the case of surface modified materials was established. Activity of materials modified with organic compounds coordinating to the surface of TiO2 was tested. Additionally, a series of other semiconductors were investigated in terms of H2O and H2O2 activation properties. One of the crucial parts of this work was to verify the suitability of available ROS detection and determination methods in the systems containing heterogeneous photocatalysts. Weaknesses of methods based on reduction of XTT and chemiluminescence of luminol have been shown. Both high selectivity and sensitivity of the method to analyze production of hydroxyl radicals based on the oxidation of TA was confirmed. By means of EPR spectroscopy, EDTA has been confirmed to have very good holes quenching properties.

Thesis defended

Mateusz Trochowski  has got his PhD degree. Congratulations!

Diversity of the photosensitization mechanisms of surface-functionalized oxide semiconductors.

The doctoral thesis is focused on verification of four hypotheses related to the photosensitization mechanisms of titanium(IV) oxide and zinc oxide. The first hypothesis concerned the possibility of protection of photosensitizers bound to the TiO2 surface by covering them with a thin layer of titanium(IV) oxide to improve the photostability. The strategy worked only for a minority of the tested samples. The second hypothesis was the higher stability of dihydroxy derivatives of anthraquinone comparised to catechol adsorbed at TiO2. Long-term photocatalytic tests have shown that all obtained materials are more photostable than the reference catechol/TiO2 system and some of them are also more active. The third problem concerned investigation how insignificant modifications of photocatalysts can significantly change their photocatalytic activity. A significant effect on photocatalytic activity, of the studied materials, in particular upon visible light irradiation, was observed, although changes in the phase composition, spectroscopic properties and morphology of the samples tested were negligible. The fourth hypothesis concerned determining of the mechanisms of localized surface plasmon resonance interaction with ZnO modified with Au nanoparticles. The analysis of emission spectra has shown that photosensitization of ZnO occurs most probably via the transfer of “hot” electrons.


Thesis defended

Marcin Surówka  has got his PhD degree. Congratulation!

Photocatalytic Degradation of Herbicides at Titanium(IV) Oxide Modified with Metal Salts and Oxides

The doctoral thesis was focused on environmental problems related to contamination of water with herbicides: 2,4-D and 2,4,5-T. One of the most promising methods for water purification is heterogeneous photocatalysis. In this work a wide library of photocatalysts based on titanium(IV) oxide was synthetized. They were modified with different amounts (0.01-0.50%mol metal:Ti) of salts and oxides of following metals: Fe, Co, Ga, Bi, W, Mo, V and Ni. The materials were calcined at three chosen temperatures and characterised structurally and spectroscopically with XRD, UV-vis/DRS and photocurrent measurements. Their photocatalytic activity was investigated in the processes of terephthalic acid oxidation and herbicides and azure B degradation. Based on these studies the most favourable synthesis parameters were proposed: small modifier content and middle chosen calcination temperature, which result in both anatase and rutile presence in the final material. The most significant conclusion stated in this work is confirmation of indirect influence of modifiers on the photocatalytic activity of the materials. The role of modifiers is mostly observed during the photocatalyst synthesis – they influence the anatase to rutile ratio, being the main factor determining the overall photocatalytic activity of TiO2. Therefore, such modifiers are regarded as TiO2-synthesis-steering factors.

Thesis defended

Marcin Kobielusz has got his PhD degree. Congratulation!

Activation of C1 molecules in photocatalytic systems. The influence of electronic structure on the processes

The aim of the work was to determine the influence of the electronic structure of a semiconductor on its photocatalytic activity. In this doctoral thesis a modified spectroelectrochemical method is proposed, as a new technique to characterize the electronic states localized close to the edge of the conduction band. Distribution of additional electronic states localized within the bandgap can be qualitatively and quantitatively characterized using this approach. The applicability of the method in determination of deep and shallow electron traps was confirmed for selected semiconductors, such as TiO2, ZnO and ZnS.The proposed method has been applied to determine the influence of the energy states localized within the bandgap on processes of carbon dioxide reduction and methane oxidation. The work was focused on the study of multi- and one-electron reduction of carbon dioxide, and on photocatalytic steam reforming of methane. The studied materials involved bare and modified semiconductors. The influence of applied modifications including metal deposition, thermal treatment, atomic layer deposition, etc. on the photoactivity in the processes of photocatalytic oxidation and reduction reactions, as well as on the electronic structures of materials, has been analysed and discussed. Results and conclusions described in the thesis extend knowledge not only on mechanism of C1 activation, but also can be very useful in elucidating other photocatalytic processes, such as water splitting, hydroxyl radicals photogeneration, organic synthesis and many others.

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.

Thesis defended

Rafał Sadowski has got his PhD degree. Congratulation!

Photocatalytic coatings for medicine and food industry

The main goal of the doctoral thesis was to obtain stable and photoactive upon visible light irradiation semiconductor coatings on various polymers. A further purpose of this study was to understand the nature of semiconductor particles binding to polymer surface and determination of physical and chemical properties of the photocatalytic coatings. Additionally, the most active coatings were subjected to microbiological tests based on a modified ISO standard. The goal has been achieved by three steps procedure: activation, immobilization and sensitization. The crucial step was activation of the polymer surface by a low temperature oxygen plasma. It was shown that plasma pre-treatment is essential for oxygen groups formation which contribute to titanium dioxide binding to the polymer surface. Unmodified TiO2 can only be used as a photocatalyst active under ultraviolet (UV) light, which limits future applications. For this reason coatings were photosensitized by titanium(IV) surface charge transfer complexes formed by impregnation with organic ligands (catechol, 2,3-napthalenediol, pyrogallol, salicylic acid, ascorbic acid and rutin). Moreover, the efficacy of such coatings against Escherichia coli and Staphylococcus aureus was demonstrated.

Thesis defended

Tomasz Baran has got his PhD degree. Congratulation!

Photocatalytic reduction of carbon dioxide in hybrid systems

Carbon dioxide utilization may contribute to controlling its atmosphere level, reducing the emission and recycling carbon. Various methods of CO2 reduction are under intensive study, including photocatalysis that is promising, environmentally friendly technique of solar to chemical energy conversion. Three strategies of CO2 reduction to useful chemicals and fuels were investigated: photocatalytic carboxylation of organic compounds with CO2 reducing coupling, photocatalytic CO2 reduction to C1 compounds and bioinspired systems for CO2 reduction to methanol by an enzymatic way with photocatalytic regeneration of coenzyme. Carboxylation of acetylacetone and 2,3-dihydrofuran with carbon dioxide has been performed by using ZnS-based photocatalysts. The formation of carboxylic acid, as proven by 13C NMR, GC-MS and IR, was observed. The reaction efficiency was enhanced after modification of ZnS with ruthenium nanoparticles. The reaction involves one-electron reduction of CO2 to CO2.-with photogenerated electrons from the conduction band of ZnS and one-hole oxidation of organic substrates to the relevant radical. Coupling of formed radicals leads to the formation of carboxylic acids through C-C bound formation. Multielectron CO2 reduction to C1 molecules has been studied using various neat and modified materials: ZnS, CuI, NiO, CuS. HCOOH and CO were found as the main reduction products. The amount and ratio of products were influenced by the type of materials, the presence of deposited ruthenium(0) nanoparticles at the surface of materials and solvent polarity. Last approach of CO2 utilization based on photochemical regeneration of NADH for the enzymatic CO2 to CH3OH reduction through the enzymes cascade: FateDH, FaldDH and ADH. A series of photocatalysts was employed as photocatalyst of reduction of NAD+ to NADH under visible light irradiation. TiO2 photosensitized with organic dye and inorganic chromium complexes, narrow band gap photocatalysts such as Cu2O and InVOas well as ZnS doped with iron or cobalt cations seems to be the most promising photocatalysts. Thorough investigations led to the development of a photocatalytic systems constructed of photocatalyst and electron mediator that yield in selective and efficient regeneration of 1,4-NADH isomer.studied processes can find applications for the solar-light-driven green synthesis of fuels or Cn+1 carboxylic compounds from Csubstrates by utilizing carbon dioxide.