Reducible oxide chemistry,
structure and functions

 

COST Action CM1104 - WG2 (Synthesis and Characterisation)

 

The Core of the Research Team

 

Prof. Svatopluk Civiš (1955), the head of the Team  is the specialist in the field of the infrared diode laser and microwave spectroscopy of molecular ions and short lived species; laser chemistry and laser spectroscopy; Fourier transform spectroscopy and time resolved spectroscopy, Raman spectroscopy and electron microscopy. Prof. Civiš is the author or co−author of 129 scientific papers (WOS), and has received 657 citations (autocitations excluded, H−index:17).

 

 

 

Dr. Martin Ferus (1983) is a young researcher whose scientific work deals mainly with the high resolution molecular and atomic spectroscopy, GC−MS detection technique, kinetic models and their application for the study of molecular dynamics. His main interest is focused mainly on astrochemistry, fundamental spectroscopy and materials chemistry. Martin Ferus is an author of 27 scientific works cited in WOS, among them he is the first author of the spot-light paper published by us last year on the prebiotic synthesis of nucleobases in the prestigious Journal of the American Chemical Society.

 

 

 

Dr. Petr Kubelík (1984) is a young scientist specialized in the theoretical chemistry, molecular dynamics and fundamental spectroscopy. Petr Kubelík is the author of the Pkin chemical simulator which has been used in many studies dealing with the research on plasma chemistry using the time resolved FT spectroscopy of discharges or laser ablation technique. He is the author of 17 original research articles cited in WOS.

 

 

 

Mgr. Ekaterina Zanozina (1985) is a young researcher whose scientific career deals with the theroretical fundamental spectroscopy. Ekaterina Zanozina is the co-author of many studies specialized in the spectroscopy of high excited atoms in the Rydberg states. The spectra have been measured using unique method of laser ablation plasma emission time resolved spectroscopy and the data contributes to precise assignment of lines found in the spectra of the Sun and other stars. Moreover, the data are used for the characterization of plasma created during ablation process and the subsequent metal/metal-oxide nanoparticles formation.

 

 

Assoc. Prof. Zdeněk Zelinger (1956) is specialized in the laser high resolution spectroscopy. His main interest is the development of the new high sensitivity laser spectrometers using new, especially low cost lasers and detectors. Zdeněk Zelinger is a senior researcher, author of 77 scientific works cited WOS. He strongly cooperates with us providing the detection of selected reaction products of reducible oxides in the gas phase.

 

 

 

 

Assoc. Prof. Vladislav Chernov (1969) is specialized mainly in the theoretical spectroscopy. His contributes significantly in theoretical part of the project including spectroscopic calculations for the plasma characterization. Vladislav Chernov comes from the Voronezh State University and he is the fully employed scientist at our Institute.

 

Adam Pastorek, Kamila Riedlová and Petra Megová are students involved in the project during their bachelor and diploma course.

Introduction of the Research Topic

Our laboratory is engaged in the COST Action CM1104 as a member of Working Group 2 dealing with the Synthesis and Characterisation of reducible oxides. Reducible metal oxides are most versatile solid state compounds exhibiting a rich chemistry related to changes in the metal oxidation state. As complex materials such as porous networks, nanocrystals and functionalized surfaces, they play a paramount role in (photo)catalysis, microelectronics, energy conversion and storage, and sensor and fuel cell technologies. Our activity unites objective-driven experimental and theoretical research devoted to:
(1) exploring the origins and details of reducibility in oxides,
(2) creating novel routes for the growth and synthesis of nanostructured reducible oxide systems,
(3) exploiting and tailoring reducibility in oxide systems to yield specific functionalities and
(4) exploring novel applications and visionary concepts for the use of reducible oxide materials.
Among metal oxides, the most famous - titanium dioxide (titania, TiO2) – attracts considerable interest. Materials made of this compound have numerous applications in photocatalysis, solar cells, gas sensors, Li−ion batteries, electrochromics and catalysis. However, all the applications, their further development and the finding of new possible uses, also require a detailed understanding of the surface chemistry and physics of this material. Chemical processes on the titania surface, both thermally and photochemically activated, can be conveniently followed by oxygen isotope labeling which is the main experimental approach performed in our laboratory. The traditional method is based on the use of ‘ordinary’ Ti16O2 exposed to gaseous reactants, which comprise various 18O−isotope−labeled molecules, such as H218O or 18O2 and their corresponding 16O−isotope counterparts.  In particular, the reactions of H218O on photoexcited titania have led to fundamental questions that are relevant to photocatalysis. This approach is smoothly extendable to photo-assisted isotopic exchange reactions involving other molecules, such as gaseous oxygen, formic acid, alcohols, carbon monoxide, carbon dioxide and carbonates.

Our Recent Results: Room Temperature Spontaneous Conversion of OCS to CO2 on the Anatase TiO2 Surface

18O-isotope labelled titania (anatase, rutile) was synthesized using the TiCl4 hydrolysis and the the products were characterized by Raman spectra together with their quantum chemical modelling. (Phys. Chem. Chem. Phys., 2011, 13, 11583–11586). The main motivation for the synthesis of Ti18O2 was the investigation of surface effects during titania/gas interaction. The light–induced oxygen-isotope exchange between gaseous CO2 and solid Ti18O2 (anatase) and the spontaneous thermal isotope exchange that takes place between the vacuum-calcined solid Ti18O2 and CO2 were studied by gas-phase high-resolution Fourier transform infrared absorption spectroscopy over a period of several days. The absorption ro-vibrational spectra of all the measured carbon dioxide isotopologues were assigned and served as the quantification of the time-dependent isotope exchange between the oxygen atoms from the Ti18O2 solid and the oxygen related to the gaseous CO2. The C18O2 was formed as the dominating final product with a minor content of C16O18O. The rate of oxygen-isotope exchange is highly sensitive to the conditions of the titania pretreatment; vacuum-annealed Ti18O2 at 450 deg. C exhibited a very high spontaneous oxygen exchange activity with gaseous C16O2. A mechanism for the 18O/16O exchange process is discussed at the molecular level. The photocatalytic formation of methane, acetylene and C16O released from the Ti18O2 surface was observed after irradiation by an excimer laser (J. Phys. Chem. C 2011, 115, 11156–11162).

Subsequently, the interaction with carbon dioxide was investigated with the aim to explore also oxygen isotope exchange at the Ti18,17O2/CO2 interface. For this purpose, high−resolution Fourier transform infrared spectroscopy of the gas phase was again adopted. In the present study, we have explored the oxygen isotope exchange between gaseous C16O2 and solid Ti18O2 or Ti17O2. The present measurement in dark mixtures has, as its primary goal, the determination of the time−scale of the spontaneous isotope exchange between carbon dioxide and solid TiO2. The profiles of the individual lines of selected isotopologues (isolated lines in the spectrum) were fitted and quantified. The quantification of the spectra was carried out on the basis of calibration measurements of the absorption spectra of individual isotopologues (reference gases) of carbon dioxide at different pressures. The concentrations of individual isotopologues determined from the intensity profiles of the individual rotation−vibration lines are characterized by the exponential decrease of the 16O−C−16O isotopologue and the exponential increase of the 18O−C−18O isotopologue. The 18O−C−16O acts as an intermediate in the mixture and its concentration remains almost constant (in press, S. Civiš et al., Opt. Mater. (2013), http://dx.doi.org/10.1016/j.optmat.2013.04.009).

Our study also deals with the photoinduced isotope exchange between 18O atoms in the lattice of vacuum-calcinated solid Ti18O2 and 16O atoms of formic acid and its photoproducts. The rotation-vibration absorption spectra of all products from the photochemical reactions of formic acid were measured over a broad infrared spectral range and used to quantify the time-dependent isotope exchange between the oxygen atoms on solid Ti18O2 and the oxygen atoms in gaseous HC16O16OH and the isotopologues of CO2, CO and H2O. It was found that formic acid did not exchange oxygen with titania during adsorption and decomposition processes; strongly bonded formate species blocked active sites and thereby inhibited the exchange between CO2 and Ti18O2. Similar blocking was observed by adsorbed water. The isotopologues of C16O18O and C18O2 are the products of the spontaneous exchange of oxygen atoms in C16O2 and the active sites on Ti18O2 that are unblocked during the irradiation of the surface by UV photons. The C18O molecules are a product of the UV decomposition of C16O18O or C18O2 that is formed during the spontaneous exchange process (J. Phys. Chem. C 2012, 116, 11200−11205).

The recent results refer on the application of the high-resolution FT-IR spectroscopy combined with quantum chemical calculations to study of the chemistry of OCS-disproportionation over the reduced surface of isotopically labelled, nanocrystalline TiO2. Analysis of the isotopic composition of the product gases has revealed that the reaction involves solely OCS molecules from the gas-phase. Using quantum chemical calculations we propose a plausible mechanistic scenario, in which two reduced Ti3+ centres mediate the reaction of the adsorbed OCS molecules (will be published).

 

For formal and design remarks please contact martin.ferus@jh-inst.cas.cz All the rights for the figures, photos and text are reserved. Last upgrade: 11-04-2014