Chemical interaction between methylene blue dye and pullulan used for detection indicator of hydroxyl radicals

摘要

Active oxygen species (AOS) generated under atmosphere can be applied for a variously industrial process owing to extremely strong oxidative abilities. It is well known that excited singlet oxygen atom [O(1~D)], ozone (O3) and hydroxyl radicals (OH*), are of interest and value in surface modification. The AOS generated under ultraviolet (UV) lamps, whose wavelength are 185 and 254 nm was used in this experiment. We used the methylene blue (MB) dye that is decomposed by the ozone (O3) as a convenient indicator of detection of active oxygen species (AOS). In this case, the O3 is one of a low oxidation ability of active oxygen. Its colour turns to be transparent after the exposure of the AOS due to degradation of the dye. To detect higher oxidative active oxygen, we had to stabilize the MB due to mixing with water soluble polymers which has high affinity to methylene blue, and form the methylene blue composite film. pullulan is a natural and water soluble polysaccharide with excellent film-forming. Humidity condition affects generation species of the active oxygen. In the low humidity condition, O(1~D) and O3 are generated. In the high humidity condition, the most oxidative ability species OH*, is generated. By utilizing this property, decolourization mechanism of the composite film was investigated. As a result, decolourization of this composite thin film could be observed at only in a high humidity condition, which suggests that the decolorization in high humidity was caused by the OH*. However, this specific decolourization mechanism is unknown, and we elucidate the decolourization mechanism of methylene blue dye employed pullulan film due to the OH~*.