title: Improved charge carrier separation in barium tantalate composites investigated by laser flash photolysis.
abstract: Charge carrier dynamics in phase pure Ba5Ta4O15 and in a Ba5Ta4O15-Ba3Ta5O15 composite have been studied by means of diffuse reflectance laser flash photolysis spectroscopy in the presence and absence of an electron donor, in order to reveal the reason for the improved photocatalytic performance of the latter. For the first time the transient absorption of trapped electrons with a maximum at around 650 nm and of trapped holes with a transient absorption maximum at around 310 nm is reported for tantalates. The decay kinetics of the photogenerated charge carriers could be fitted by second order reaction kinetics, and the direct recombination of the trapped electrons with the trapped holes was proven. In the absence of an electron donor, no difference in the decay behavior between the phase pure material and the composite material is found. In the presence of methanol, for the pure phase Ba5Ta4O15 the recombination of the charge carriers could not be prevented and the trapped electrons also recombine with the ˙CH2OH radical formed via the methanol oxidation by the trapped holes. However, in the composite, the electron can be stored in the system, the ˙CH2OH radical injects an electron into the conduction band of the second component of the composite, i.e., Ba3Ta5O15. Thus, the electrons are available for an extended period to induce reduction reactions.
authors.affiliation: Leibniz University Hannover, Institute of Technical Chemistry, 30167 Hannover, Germany. schneid@iftc.uni-hannover.de.
authors.forename: Jenny
authors.initials: J
authors.lastname: Schneider
authors.affiliation: Leibniz University Hannover, Institute of Technical Chemistry, 30167 Hannover, Germany. schneid@iftc.uni-hannover.de and Saint-Petersburg State University, Laboratory "Photoactive Nanocomposite Materials", Saint-Petersburg, 198504 Russia.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Nikitin
authors.affiliation: Carl von Ossietzky University Oldenburg, Institute of Chemistry, 26129 Oldenburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Wark
authors.affiliation: Leibniz University Hannover, Institute of Technical Chemistry, 30167 Hannover, Germany. schneid@iftc.uni-hannover.de and Saint-Petersburg State University, Laboratory "Photoactive Nanocomposite Materials", Saint-Petersburg, 198504 Russia.
authors.forename: Detlef W
authors.initials: DW
authors.lastname: Bahnemann
authors.affiliation: Justus-Liebig-University Giessen, Institute of Physical Chemistry, 35392 Giessen, Germany. roland.marschall@phys.chemie.uni-giessen.de.
authors.forename: Roland
authors.initials: R
authors.lastname: Marschall