Detection of Superoxide Ions from Photoexcited Semiconductors in Non-Aqueous Solvents Using the ESR Spin-Trapping Technique

Abstract

The ESR spin-trapping technique using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and N-t-butylbenzylideneamine N-oxide (PBN) as spin-trap reagents has been applied to detect active oxygen radicals generated by the photoexcitation of powdery semiconductors (TiO2, WO3, CdS, and Fe2O3) in non-aqueous solvents such as dimethylsulfoxide (DMSO), benzene, ethanol, and acetonitrile. Appreciable amounts of superoxide ion (O2−) were detected from TiO2, WO3, Fe2O3, and CdS suspensions under photoexcitation. The hyperfine splitting constants (hfsc) of the superoxide ion and carbon(C)-centered radical spin adducts for DMPO and PBN could be determined in various non-aqueous solvents. Some characteristic features for the production of the superoxide ion and C-centered radicals are discussed in connection with the energy-level diagrams of the semiconductors and the redox potentials of the superoxide ion and non-aqueous solvents.

EPR study of photochemical transformations of triarylmethane dyes

“…Acid Red 87 (Eosin Y) and C.I. Basic Blue 9 (Methylene Blue) in DMSO/DMPO/Ar solutions caused the production of DMPO-SR adduct, originating from solvent, as was described previously [42]. Furthermore, photoexcitation of the latter dye in DMSO/ ND/Ar media resulted in the formation of threeline EPR signal (a N =0.730 mT; g=2.0045), assigned to MB cation-radical, MB + , produced by photoinduced electron transfer from the phenothiazine skeleton [50].…”

“…Basic Violet 3 (Crystal Violet) (Fig. 6a) was simulated using hyperfine splitting constants a N =1.278 mT, a H b =1.040 mT, a H g =0.142 mT and g=2.0059, in good accordance with the characteristics of DMPO-O 2 À adduct [27,42]. The equivalent EPR spectra were monitored and simulated for other dyes except for C.I.…”

“…À production upon irradiation of dyes, the photochemical experiments were performed in DMSO solvent, which is well known by its ability to stabilize super-oxide radical anions [27,[42][43][44]. The application of DMPO spin trapping agent in DMSO solvent clearly evidenced the substantial effect of oxygen on dye photodecomposition.…”

Heterogeneous Photocatalytic Reactions of Sulfur Aromatic Compounds

“…Reactive intermediates formed upon photoillumination of TiO 2 in CH 3 CN have been studied by ESR spin-trapping techniques, [100] and appreciable amounts of superoxide ion O 2 À were detected. The same reactive intermediate O 2…”

Decoration of titania nanofibres with anatase nanoparticles as efficient photocatalysts for decomposing pesticides and phenols

“…The anatase form of TiO 2 is the most photoactive and therefore is most suitable for environmental applications [5][6][7][8][9][10]. The rutile form is much less active towards most photocatalytic reactions [11][12][13][14][15][16]. Tanaka et al have presented the photocatalytic decomposition of a wide range of compounds over different TiO 2 polymorphs and have also presented the effect of calcination temperature on the TiO 2 prepared from different methods [17].…”