Abstract book - Prof. Per Jensen, Ph.D. - Bergische Universität ...

Poster session, J20 183A450 TiO 2 Anatase nanoparticles: nanomotors converting CO 2Svatopluk Civiš, Martin FerusJ. Heyrovský Institute of Physical Chemistry, v.v.i., Academy of Sciences of the CzechRepublic, Dolejškova 3, 18223 Prague 8, Czech Republic.Civis S.Ferus M.Titanium dioxide is an attractive material for (photo)catalysis, solar cells, electrochromics andbatteries [1], while various fundamental studies would benefit from the accessibility of atotally 18 O exchanged material. The main motivation for synthesis of Ti 18 O 2 was theinvestigation of surface effects during titania/gas interaction [2]. Here we report, for the firsttime, the preparation of pure Ti 18 O 2 both in anatase and rutile forms. The interaction withcarbon dioxide was investigated with the aim to explore oxygen isotope exchange at theTi 18 O 2 /CO 2 interface. For this purpose, high-resolution Fourier transform infraredspectroscopy of the gas phase was adopted. In the present study, we have explored the oxygenisotope 16 O/ 18 O exchange between gaseous C 16 O 2 and solid Ti 18 O 2 . Although there have beenseveral earlier works aimed at isotope exchange reactions involving carbon dioxide, thereactions have been typically studied either on the C 18 O 2 /Ti 16 O 2 system or on a complicatedgaseous mixture containing, besides C 16 O 2 , also 18 O 2 or H 2 18 O and ordinary Ti 16 O 2 . To thebest of our knowledge, the isotope exchange reaction at the C 16 O 2 (g)/Ti 18 O 2 (s) interface isinvestigated here for the first time. Carbon dioxide offers several advantages as the targetmolecules for these studies: (i) The isotope exchange can be readily followed by highresolutionFTIR; (ii) It is the final product of the photocatalytic oxidation of organicmolecules; (iii) the adsorption mechanism of CO 2 is known in detail and moreover, it is ofprospective environmental impact for CO 2 removal from the atmosphere (for review ofisotope effects in atmospheric CO 2 and other gases). The present measurement in darkmixtures has, as its primary goal, the determination of the time-scale of the spontaneousisotope exchange between carbon dioxide and solid TiO 2 . The profiles of the individual linesof selected isotopologues (isolated lines in the spectrum) were fitted and quantified. Thequantification of the spectra was carried out on the basis of calibration measurements of theabsorption spectra of individual isotopologues (reference gases) of carbon dioxide at differentpressures. The concentrations of individual isotopologues determined from the intensityprofiles of the individual rotation-vibration lines are characterized by the exponential decreaseof the 16 O-C- 16 O isotopologue and the exponential increase of the 18 O-C- 18 O isotopologue.The 18 O-C- 16 O acts as an intermediate in the mixture and its concentration remains almostconstant.Vacuum-annealed Ti 18 O 2 (Sample T450) shows a very high spontaneous exchange activitywith gaseous C 16 O 2 . Based on the spectral intensity and the isotopic exchange measurement,we are in good agreement with the proposal of the formation of the bidentate bondedcarbonate as the major species for CO 3 on TiO 2 . The surface layer vacuum-annealed Ti 18 O 2 iscomposed of a nonstoichiometric mixture of Ti 4+ and Ti 3+ onto which the 18 O oxygen atomsare bonded. The calcination in vacuum creates vacancies. During the isotope exchange the 16 Ooxygen from the gaseous 16 O-C- 16 O bonds into the vacancy on the surface of the TiO 2 crystaland bidentate CO 3 from the CO 2 adsorption is formed. The 18 O oxygen from the surface layeris bonded to the carbon dioxide molecule and subsequently gaseous 16 O-C- 18 O and 18 O-C- 18 Oare released.References[1] Chen, X.; Mao, S.S. Chem. Rev. 2007, 107, 2891.[2] Kavan, L. Adv. Sci. Technol. 2006, 51, 20.