Gas-phase approach to the studies of elementary steps of heterogeneous photocatalysis

The use of solar light in photocatalytic process of water splitting for hydrogen production is a key point for hydrogen energetics. Other fields of current and perspective applications of photocatalysis are water and air-purification from organic impurities, self-cleaning and sterilization of surfaces, "green chemistry" and others. All these applications dictate very big interest of the researches to the problems of photocatalysis. Titanium dioxide is the most effective known photocatalyst. But it has one disadvantage due to bad overlapping with the spectrum of solar radiation. For shifting of its absorption spectrum into the visible, the coverage by dyes is used as well as doping by different admixtures. On the way to creating the future efficient TiO2-based photocatalysits the main problem is the lack of knowledge about mechanism of photocatalytic process, including mechanism of reactive intermediates photogeneration responsible for photocatalytic behavior of titanium dioxide. Efficient catalytic activity and better fitting of absorption to solar radiation spectrum is provided by other superconductor tungsten trioxide WO3. For creation of task-oriented photocatalysts based on WO3 it is also necessary to know mechanism of oxygen-involved photocatalytic processes on its surface. It is known that the surface centers play a key role in heterogeneous catalysis. Moreover there is a perspective direction in photocatalysis where isolated centers of titanium oxide are used which are named single site catalysts. This approach allows one to provide many unusual photocatalytic processes where bulky photocatalysts are less effective. Mechanism of these sites action is not clear. Approach suggested in this project which is based on the use of small cluster (TiO2)nas the model should allow us to investigate the mechanism of reactive intermediates photogeneration on these centers. Suggested approach based on the use of small clusters (TiO2)n as a model of photocatalyst allows us to study mechanism of reactive intermediates photogeneration on these centers. According to the data of quantum-chemical calculations of structure and electronic properties of small clusters of tungsten trioxide even small clusters (WO3)n (n=2-4) can be considered as an adequate model for the study of photocatalytic processes in bulky photocatalyst. Generation of complexes of these clusters with oxygen in molecular beam allows us to use powerful technique of identification and investigation of elementary photoprocesses based on the velocity map imaging of photofragments appearing after photoexcitation of complexes. For investigation of these processes new approach is suggested. This approach is based on the use of complexes of small clusters of TiO2 and WO3 with oxygen as the model for the study of the processes proceeding on the surface of photocatalyst. This approach seems to be very promising because possibility to generate these complexes in molecular beam allows one to study elementary steps of heterogeneous photochemistry with the use of very powerful techniques like velocity map imaging which were elaborated for gas phase studies. Within our research, it is supposed to identify and investigate elementary photoprocesses, which govern photocatalytic activity of titanium dioxide and tungsten trioxide, to establish structure and energetic characteristics of photocatalyst-oxygen complexes, to study their photophysics and photochemistry, and to study supramolecular photoprocesses, analogous to those revealed by us in weakly bound complexes of oxygen. It is also supposed to study the effect of water molecules inclusion in the complex.

We have already discovered the process of formation of singlet oxygen from superoxide anion on the surface of TiO2 passing through the formation of superoxide anion as a result of electron photodetachment. We have shown that singlet oxygen reacts with titanium dioxide to form titanium peroxide without an activation barrier. We think that similar fast processes also take place on the surface of the photocatalyst particles. In connection with the important role of titanium and tungsten peroxides, their study is of great interest. But for this it is necessary to learn how to get them and we intend to investigate this question. Assessing the relevance of the planned research, it should also be noted that the importance of studying the mechanism of photogeneration of singlet oxygen and the implementation of a direct method for measuring the kinetics of processes involving superoxide anion is not limited to problems of photocatalysis. The fact is that singlet oxygen is an active agent in many biological systems, and is also a key agent in photodynamic therapy, widely used in the treatment of oncology. Therefore, new knowledge about the mechanisms of generation of singlet oxygen can be useful in many applications. The same applies to superoxide anion, which plays an important role in many biological processes. Reactions involving this particle are important from the point of view of such phenomena as oxygen toxicity, the formation and development of malignant tumors, the aging process. Superoxide anion plays a very important role in oxidative stress. Therefore, we believe that the results of the planned project aimed at studying the elementary physicochemical processes of photocatalysis will be of great importance in the application to the study of the above phenomena.


Tungsten Isotope-Specific UV-Photodecomposition of W(CO)6 at 266 nm

The Journal of Physical Chemistry A

Singlet Oxygen 1O2 in Photocatalysis on TiO2. Where Does It Come from?

The Journal of Physical Chemistry C

Reply to Comments on “Singlet Oxygen 1O2 in Photocatalysis on TiO2. Where Does It Come from?”

The Journal of Physical Chemistry C

An Automated Apparatus for Measuring Spectral Dependences of the Mass Spectra and Velocity Map Images of Photofragments

Instruments and Experimental Techniques

Decomposition Pathways of Titanium Isopropoxide Ti(OiPr)4: New Insights from UV-Photodissociation Experiments and Quantum Chemical Calculations

The Journal of Physical Chemistry A

Binding of oxygen with titanium dioxide on singlet potential energy surface: An ab initio investigation

Chemical Physics Letters