ИСТИНА

Titania (TiO2) nanotubes is a promising material for use as photocatalyst or sensor [1]. In recent years, nanoheterostructures based on this material have been formed to improve absorption in the visible region of the spectrum and provide charge accumulation [2]. The purpose of this work was to obtain TiO2/BaTiO3 nanoheterostructures for sensor application. We have performed a study of defects (spin centers) in the structure of the samples in dark and under illumination. The formation of TiO2 nanotube arrays doped with carbon occurred by two-stage electrochemical oxidation of a previously prepared Ti-foil BT1-0 [2]. Nanoheterostructures TiO2/BaTiO3 were synthesized using a hydrothermal process with barium hydroxide. The EPR spectra at 300 K were recorded with a Bruker spectrometer ELEXSYSE500 (X-band). A xenon lamp with a total power of 500 W was used as a light source. A light flux of 100 mW/cm2 was created through an AM1.5 filter. The EPR spectrum of initial carbon doped TiO2 nanotubes consists of a single line with g = 2.0027, which can be attributed to carbon dangling bonds [3]. The EPR spectrum of the TiO2/BaTiO3 samples is a superposition of several EPR lines. First of all, it is carbon dangling bond. Barium (g = 1.974) and oxygen (g = 1.958) vacancies are also detected [4].When the samples are illuminated, the intensity of EPR signals from all spin centers increases. After turning off the illumination, after about 24 hours, the intensity of the EPR signals returns to its original state. We attribute this effect to defect recharging because of its reversibility. The long relaxation time of EPR intensity is probably due to charge separation: a hole remains in titania, while an electron is injected into barium titanate. The results obtained open up new possibilities for the development of gas sensors with improved selectivity based on nanocrystalline TiO2/ BaTiO3