Group dinner

Today we have attended a group dinner with our guest prof. Minoru Mizuhata. We spent a lot of time talking and enjoying delicious polish cuisine. We have taken a group picture to memorize that event!

Intern in our group

Our group becomes more and more international. For three months we will host Mr. Claudio Imparato from Italy. Claudio is a PhD student at University of Naples Federico II, where he works in the group of Prof. Antonio Aronne.

EEPM3 is close

The photocatalytic conference EEPM3 that will be organized by our group is getting closer and closer. See you in May in Kraków.

New group members

The Team of Photocatalysis has two new members: Dr. Taymaz Tabari from Iran joined us as a post-doc, while Mr. Kasidid Yaemsunthorn from Thailand will work on his PhD. Welcome to Kraków!

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

Marta Buchalska has got her PhD degree. Congratulation!

Processes of Photoinduced Charge and Energy Transfer in Presence of Nanocrystaline TiOPhotosensitized with TiIV Complexes

High photocatalytic activity upon irradiation with UV light is one of major advantage of TiO2. This material can also be easily modified and sensitized to be active in visible light range. Especially modification with organic compounds that contain O-donor bonding groups often leads to stable and colorful charge transfer complexes. The aim of this study was to determine the mechanisms of photoinduced charge and energy transfer processes, that occur in presence of colloidal, nanocrystalline TiOwith modified surface. An additional objective was to determine the influence of the structure of the modifier, crystalline form of TiO2 and the type of radiation (Uv, visible, NIR) on the relative efficiencies of these processes. Colloidal, nanocrystalline anatase and rutile (from NanoAmor) were used during this work. The surface of materials was modified with the derivatives of catechol, salicylic acid and phthalic acid. Absorption and emission spectra were measured for all the samples, as well as electrochemical and spectroelectrochemical studies. Photocatalytic activity of the materials was determined upon irradiation with various light ranges (UV, visible, UV-Vis, NIR) and with various substrates (p-chlorophenol, Azur B). Unexpectedly high photocatalytic activity of all materials was observed upon irradiation with UV-vis light. Degradation rates are higher than sums of the effects observed separately for UV and visible light. Upon excitation of both, the semiconductor (with UV light) and the surface complex (with visible light), the oxidized form of the ligand can be reduced back by electrons from the conduction band. Presumably, this process inhibits electron-hole recombination and leads to an increase of the lifetimes of valence band holes and TiIII-centre of the excited surface complex. Increased lifetimes improve efficiencies of interfacial electron transfer process. The possibility of singlet oxygen generation was confirmed in direct measurements of phosphorescence at = 1270 nm upon excitation at = 355 nm. In this conditions 1O2 was detected in presence of unmodified anatase and material modified with salicylic acid. The efficiency of this process is F = 1,2 ± 0,5 for modified material and is about 3 times lower for unmodified anatase. Presence of singlet oxygen was also determined by monitoring the process of photooxidation of SOSG. The oxidized form of this compound shows high emission in visible light range. Tests were performed upon irradiation with monochromatic (laser l = 405 nm) and bichromatic light (additional l = 355 nm or l = 785 nm laser). It was shown that upon irradiation with l = 405 nm, singlet oxygen is generated in so called modified Nosaka’s mechanism. In this process photogenerated superoxide radical is oxidized to 1Oby oxidized form of surface complex. Upon additional irradiation with l = 785 nm, singlet oxygen can be generated in the process of energy transfer from the high excited state of the electron in the conduction band. That contain TiO2 in anatase form show higher photocatalytic activity than materials that contain rutile. The highest efficiency of hydroxyl radical generation was determined for anatase modified with catechol. Salicylic acid modified anatase was the most active in the process of singlet oxygen generation.