Deciphering electron-shuttling characteristics of thionine-based textile dyes in microbial fuel cells

Prior studies indicated that OH and/or NH₂ substituent containing auxochrome compounds (e.g., 2-aminophenol and 1-amino-2-naphthol) could act as electron shuttles (ESs) to stimulate wastewater decolorization and bioelectricity generation in microbial fuel cells (MFCs). This study provided first-attempt to disclose how and why thionine-associated textile dyes (i.e., azure A and azure C) could also own such redox-mediating capabilities in MFCs. Due to the presence of iminium part as mediating group, N(CH₃)₂ or N(CH₃)H substituent could effectively mediate electron transport compared to NH₂ substituent for bioelectricity generation in MFCs. For dye-laden wastewater treatment, the presence of electron-mediating textile dyes (e.g., thionine, azure A and azure C) in MFCs is promising to stimulate biodegradation of organics and bioelectricity generation. With such ESs as stimulants, using MFC as operation strategy would be cost-effective for wastewater treatment as oxidation of organic pollutants could be automatically accelerated.