Nanostructured surfaces and nanomaterials
Photoactivity of nanostructured TiO2/PTZ composites. Spectroscopic and electrophysical characterization
Shymanovska V.V.1, Kernazhitsky L.A.1, Naumov V.V.2, Fedorenko L.L.2, Smertenko P.S.2, Rudko G.Yu.2, Yukhymchuk V.O.2
1 Institute of Physics, National Academy of Sciences of Ukraine, Prospect Nauki, 46, Kyiv-03022, Ukraine. 
2 Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Prospect Nauki, 45, Kyiv-03022, Ukraine. 
E-mail: vadym.naumov@gmail.com

Hybrid organic dye-sensitized metal oxide composites are of great interest due to enhanced photoactivity for photocatalytic and photovoltaic applications [1]. We studied nanostructured titanium dioxide (TiO2) powder modified by phenothiazine (PTZ, C12H9NS). High-purity anatase and rutile TiO2 particles were synthesized by thermal hydrolysis followed by calcination, and then mixed and ground with a small (~5 wt.%) admixture of granular PTZ (98%, Fluka) at room temperature. At that, PTZ/TiO2 powder changes its color from white to dark blue. The structural, optical and electrical properties of the samples were characterized by XRD, FTIR, Raman, UV-Vis absorption and PL emission spectroscopy, and PV current-voltage measurements. XRD analysis showed that fine-dispersed PTZ/TiO2 has a nano- crystalline structure (crystallite size ~10-20 nm) without any phase changes compared to parent TiO2. FTIR spectra showed the existence of PTZ+• and Ti3+ ions and oxygen vacancies (VO) in the TiO2 matrix caused by PTZ. UV-Vis spectra demonstrated a shift in the absorption edge toward the visible region (> 400 nm) and a reduction in the band gap for direct and indirect electronic transitions in TiO2. These effects are due to the increased number of intrinsic defects associated with interstitial Ti3+ ions and [VO–Ti3+] vacancies. PL spectra of PTZ/TiO2 are almost similar to those of TiO2, while their intensities differ. Due to the high density of trap states and non-radiative recombination, the excitonic PL emission in PTZ/TiO2 is inhibited compared to TiO2. C-V curves measured under the loads in dark and under illumination showed essentially non-linear character of electron transport, caused by the drift-diffusion behavior of carriers and charge separation. Raman measurements carried out after electrical experiments revealed the nature of the secondary oxide phases in the form of thin films on ITO electrodes, resulting from the complex electrophotocatalytic effect. The distinctions between the PTZ/ TiO2 anatase and rutile properties are discussed. Research is in progress.

1.	Kernazhitsky L.A. et al. // E-MRS 2018 Fall Meeting, Warsaw.-P. D.P24.