Conference
Four members of our group have attended the 16th Czech – Polish Catalytic Symposium (CzePoCat), held in Ostrava, Czech Republic, on 2nd to 4th February 2017. We have presented 4 lectures.
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Award
On October 26, 2016, the President of the Republic of Poland, Andrzej Duda, nominated 99 academic teachers and employees of science and art at the Presidential Palace in Warsaw. Among the nominees there was Wojciech Macyk.
(photo by Krzysztof Sitkowski / KPRP)
Bez kategorii
Marcin Kobielusz has got his PhD degree. Congratulation!
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.
Group members
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.
Award
MSc. Marcin Surówka obtained a grant from National Science Centre within PRELUDIUM 8 programme. The project goal and title are “Charakterystyka spektroskopowa i fotokatalityczna materiałów opartych na tlenku tytanu(IV) modyfikowanych różnymi tlenkami metali”.
Congratulations!
Group members
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 InVO4 as 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 Cn substrates by utilizing carbon dioxide.
