Kinetics of Hydroxyl Radical Spin Trapping in Photoactivated Homogeneous (H2O2) and Heterogeneous (TiO2, O2) Aqueous Systems

Radical Intermediates in Photoinduced Reactions on TiO2 (An EPR Spin Trapping Study)

“…Despite the fact that the detection of hydroxyl radicals upon UVA irradiation of the aerated aqueous TiO 2 suspensions in the presence of 5,5-dimethyl-1-pyrroline N -oxide (DMPO) spin trap represents a frequently applied EPR technique [38,39,40,41,42,43,44,45,49], in order to bring the complete information on the radical species generated in the irradiated TiO 2 in different media we also report the results of EPR spin trapping experiments in aqueous TiO 2 suspensions using different spin trapping agents. As expected, immediately after the irradiation started, a typical four-line EPR signal attributed to • DMPO-OH spin-adduct with spin Hamiltonian parameters ( a N = 1.497 mT, a H = 1.477 mT; g = 2.0057 [50]) was generated in the system TiO 2 /DMPO/H 2 O/air, as is shown in Figure 2a.…”

“…EPR spectroscopy occupies an exclusive position in the investigation of titania photocatalysts, providing a characterization of paramagnetic centers produced via the trapped photogenerated electrons and holes [29,30,31,32,33,34,35,36], and of titanium dioxide materials with transition-metal ions doping [17,34]. A majority of the research exploiting EPR spectroscopy deals with the investigation of reactive radical intermediates produced in the irradiated TiO 2 particulate systems where the application of an indirect spin trapping technique is inevitable [37,38,39,40,41,42,43,44,45]. This method is based on the chemical reaction of a diamagnetic spin trap (ST) with a short-lived radical, producing a more stable nitroxide radical, i.e.…”

Reaction pathways of dimethyl phthalate degradation in TiO2–UV–O2 and TiO2–UV–Fe(VI) systems

“…The electron spin resonance (ESR) technique allows the monitoring of chemical reaction processes involving extremely small changes; thus, it provides a useful tool to disentangle the complex processes involved in photocatalytic experiments (Grela et al, 1996;Brezová et al, 1994a;Brezová et al, 1994b). The compound, 5, 5-dimethyl-1-pyrroline-1-oxide (DMPO), was used as a spin-trapping reagent in the reaction solution.…”

Fused-Ring Derivatives of Quinoxalines: Spectroscopic Characterization and Photoinduced Processes Investigated by EPR Spin Trapping Technique

“…Upon UVA irradiation hydrogen peroxide is decomposed generating reactive hydroxyl radicals identified as the corresponding spin adducts [47]. The EPR spectra monitored upon the photoexcitation of quinoxalines in DMSO/H 2 O/DMPO/O 2 solutions are fully compatible with this consideration, since the EPR signals measured correspond to the • DMPO-O 2 − /OOH, • DMPO-OH, • DMPO-CH 3 , • DMPO-OCH 3 spin adducts characterized with hfcc and g -values summarized in Table 2.…”