Article

Research on Chemical Intermediates

, Volume 33, Issue 3, pp 251-268

First online:

Characterization of titanium dioxide photoactivity following the formation of radicals by EPR spectroscopy

  • V. BrezováAffiliated withDepartment of Physical Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava Email author 
  • , D. DvoranováAffiliated withDepartment of Physical Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava
  • , A. StaškoAffiliated withDepartment of Physical Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava

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Abstract

In order to find ways to characterize oxygen-saturated aqueous TiO2 suspensions, the formation of photo-induced free radicals was followed by EPR spectroscopy, using as indicators N-oxide and nitrone spin trapping agents, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3,3,5,5-tetramethyl-1-pyrroline N-oxide (TMPO), α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POB N), 4-(N-methylpyridyl)-N-tert-butylnitrone (MePyBN), as well as semi-stable free radicals, 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl (TEMPOL), cation radical of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), diammonium salt (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH). DMPO and TMPO are efficiently oxidized to the EPR-silent products via radical in termediates. Conversely, the nitrone spin traps (POBN and MePyBN) showed selective formation of hydroxyl radical spin adducts upon continuous irradiation of oxygenated TiO2 suspensions. Their concentrations increased proportionally with the amount of photocatalyst and irradiation time. The EPR spectrum of the semi-stable free radicals TEMPOL, ABTS·+ or DPPH is gradually eliminated during irradiation, and this system represents a simple technique for the evaluation of TiO2 activity.

Keywords

Titanium dioxide EPR spectroscopy free radicals hydroxyl radical spin-trapping technique TEMPOL DPPH ABTS·+