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

Abstract

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.