Detection of superoxide ions in nonaqueous media. Generation by photolysis of pigment dispersions

Abstract

Irradiation of cadmium sulfide and metal-free phthalocyanine pigments dispersed in a wide variety of oxygen containing nonaqueous solvents has been shown to give rise to the formation of superoxide anions. These anions were identified by electron spin resonance with the use of a "spin trapping" technique. The 02~a dducts were identified by independently generating the superoxide ions using K02 and 18-crown-6 ether. Direct detection of 02" (as distinct from 02"/adduct) was accomplished by quickly freezing the systems to -160 °C. The hyperfine splitting constants for the 5,5-dimethyl-l-pyrroline 1-oxide (DMP0)/02" adduct were determined in various solvents and are shown to be a smooth function of solvent polarity parameters. The apparent efficiency of photoproduction decreases with decreasing polarity and surfactants appear to have little impact on the observed photochemistry. The results are discussed i:

Highly efficient photocatalytic oxidation of sulfur-containing organic compounds and dyes on TiO2 with dual cocatalysts Pt and RuO2

“…The signals can be assigned to two groups. The characteristic quartet peaks in the presence of photocatalysts TiO 2 , Pt/TiO 2 , RuO 2 /TiO 2 and Pt-RuO 2 /TiO 2 is assigned [23][24][25][26]. Photo-generated electron transfer to O 2 via photocatalyst, where superoxide species O 2 •− is formed when O 2 reacts with the photo-generated electrons [27].…”

The utilization of nitrone spin traps in a study of the photochemistry of pigment dispersions

“…The use of spin trapping techniques has since been extended to non-aqueous dispersions, particularly those of CdS and the organic pigment x-phthalocyanine (HzPc) (24). A variety of solvents were used and these demonstrated the general mechanism of photoinduced reduction of 0, to superoxide.…”

Electrochemical Biosensors in Nonaqueous Solutions and Their Applications

“…Most techniques for the detection of superoxide radical have used indirect spectroscopic methods, 52 such as spectrophotometric measurement, 53 chemiluminescence method, 54 and electron spin resonance spectroscopy. 55 However, these means are ex situ detection techniques with poor selectivity or sensitivity.…”