Validation of quenching effectiveness and pollutant degradation ability of singlet oxygen through model reaction system.

Quenching method is widely used to assess the contribution of specified reactive species through the probe inhibition efficiency (IE) caused by adding excessive quencher. However, for reactive species with weak ability such as singlet oxygen (O), the quenching results are prone to ambiguity. In this study, an O system using furfuryl alcohol (FFA) as a probe was successfully constructed by methylene-blue-N vis-photosensitization, to discuss the quenching, interference elimination and pollutant degradation ability of O. Inhibition of FFA transformation caused by both quenching and interrupting of O production was found. The quenching is affected by quencher dosage and ability, which depends on the second-order-rate constant (k). A high k means a strong ability, and less dosage is required to achieve the same IE. Comparison between the calculated ratio of reactive species consumed by quencher and experimental IE helps to judge the interruption of O production. None of the organic-solvents (methanol, ethanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, tetrahydrofuran, acetonitrile, acetone and chloroform) scavenged O, which would be used as screening-agent for other reactive species (e.g., hydroxyl radicals) that would interrupt O contribution assessment. Besides, O was powerless to degrade most selected pollutants. These results encourage proper use of quenchers and better experimental design.