Chemical stability of a colorimetric indicator based on sodium alginate thin film and methylene blue dye upon active oxygen species exposure

Abstract

Active oxygen species (AOS) generated in the atmosphere can be applied in various industrial processes owing to their extremely strong oxidative ability. Methylene blue (MB) decolors upon exposure to AOS owing to dye degradation; this property can be used to detect the AOS. To detect AOS with higher oxidative ability, it is necessary to stabilize MB by mixing it with sodium alginate. In our previous work, we showed that the OH* concentration in the AOS increased under the high-humidity condition. Herein, the decolorization mechanism of MB-dyed sodium alginate thin films upon exposure to AOS was elucidated under low- and high-humidity conditions; decolorization was observed only under the latter. We analyzed an MB-dyed sodium alginate thin film indicator to elucidate the chemical reactions occurring as well as the decolorization mechanism generated under the high-humidity condition. We found that the decolorization of the film was caused by MB decomposition upon exposure to the AOS generated under the high-humidity condition.

Molecular Interactions between Methylene Blue and Sodium Alginate Studied by Molecular Orbital Calculations

“…The results demonstrated that both MB and SA share an ionic bond, as evidenced by a shift of UV absorbance corresponding to MB's benzene ring in complexation with SA and that SA strongly stabilizes MB-enough to prevent it from interacting with atmospheric AOSs other than highly reactive OH*. Moreover, previous studies have revealed that SA and MB interact between SA's carboxylates (-COO − ) and MB's nitrogen or sulfur atoms [1]. However, the details of the intermolecular interactions were unclear.…”

“…We reported a similar behavior of the MB complex with pullulan. In our previous study [1], we presented the development of a color indicator, which is composed of an SA or pullulan thin film embedding an MB reporter, for detecting AOSs with enhanced oxidative ability. We assumed that the SA or pullulan protects MB based on the fact that AOSs with a low oxidative ability cannot decolorize the MB.…”

“…Table 3 shows the comparison of the HOMO and LUMO energy levels of O 3 , MB, SA, pullulan, MB/SA, and MB-pullulan obtained at the same calculation level. The results can be used to analyze the thin film's decolorization mechanism [1]. As shown in Table 3, the LUMO level of O 3 is low (−4.90 eV).…”

“…Interactions between sodium alginate (SA) and methylene blue (MB) have been investigated for a long time. In particular, the chemical stability of the colorimetric indicator based on SA thin films and MB dyes upon exposure to active oxygen species (AOSs) has been examined [1]. Indeed, the MB/SA film indicators were discovered to be effective at detecting hydroxyl radicals (OH*) in the atmosphere.…”

“…In a previous result [1], an AOS indicator obtained from uniform thin films was developed using MB-dyed SA, which can be generated under atmospheric conditions. Previous studies selectively detect OH* among various AOSs and develop AOS technology for sterilization and surface modification of polymer substrates.…”