Fine Analysis of the Structure and Dynamics of Vanadyl Complexes Adsorbed on TiO 2 (Anatase) Surface: EPR Investigation
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Applied Magnetic Resonance
ORIGINAL PAPER
Fine Analysis of the Structure and Dynamics of Vanadyl Complexes Adsorbed on TiO2 (Anatase) Surface: EPR Investigation Anatoly I. Kulak1 · Sergey O. Travin2 · Alexander I. Kokorin2,3 Received: 1 June 2020 / Revised: 8 July 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract This work continues EPR investigation of photocatalytic systems based on vanadium modified titanium dioxide (anatase) surface containing various concentrations of VO2+ paramagnetic centers (PCs). Three different types of the isolated PCs are revealed on the surface of V–TiO2 nanoparticles and quantitatively characterized. Time-dependent transitions among these PCs were observed and kinetic behavior was described using new theoretical approach and the developed numerical calculation procedure. The slow-process kinetic rate constant has been calculated from EPR data.
1 Introduction Vanadium doping of titanium dioxide has been studied in detail in many works with the aim to increase photocatalytic activity and for enlarging the area of spectral sensitivity to the visible light region in processes of photodegradation of dyes [1–5], different organic compounds (ethanol, ethene, formic acid) [6–9], chlorinated hydrocarbons [10], NO2, NOx [11, 12]. Besides, an interest to V-doped TiO2 is connected with perspectives of its application as the heterogeneous catalyst [13–17], electrochromic [18, 19], photochromic [20], and ferromagnetic [21] materials, as an electrode material for electrocatalytic oxidative processes [22] and electrochemical nitrogen reduction [23], in lithium- and sodium-ionic batteries [24], photovoltaic cells [25], and in redox-sensors [26].
* Anatoly I. Kulak [email protected]‑net.by 1
Institute of General and Inorganic Chemistry, National Academy of Sciences of Belarus, Surganov Str. 9/1, 220072 Minsk, Belarus
2
N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russian Federation
3
Plekhanov Russian University of Economics, Moscow, Russian Federation
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The analysis of published data evidences about complex and in some cases noncertain dependence of functional properties of V-doped T iO2 on concentration of doped or adsorbed vanadium, on the method of modification and regimes of further treatment. As an example, studying photocatalytic activity of V-doped TiO2, some authors showed the maximum increase of the activity at vanadium content between 0.002 and 0.05 mol% [1–3] while others declared much higher concentrations [4, 6, 8, 10]. Also, strong influence on photocatalytic behavior causes a method of preparation: impregnation, sol–gel, implantation of vanadium ions, etc., and connected with them differences in either adsorbed forms (ions or complexes) or ions incorporated into crystalline lattice, or as V 2O5 nanoclusters forming micro- or nanoheterogeneous systems. In the previous paper we have demonstrated that using surface modification of TiO2 by adsorbing v
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