Quinone-mediated dissimilatory iron reduction of hematite: Interfacial reactions on exposed {001} and {100} facets

Although quinone-mediated bioreduction of iron oxides has been investigated extensively, little is known about the interfacial interactions between quinone and various exposed facets. In this study, the reduction of hematite {001} and {100} by Shewanella putrefaciens CN-32 with anthraquinone-2,6-disulfonate (AQDS) was investigated. The added AQDS can enhance the bioreduction of both hematite {001} and {100}, with hematite {001} showing a higher reduction degree than hematite {100}. No significant secondary iron oxides were found, but defects were observed in HR-TEM images. AQDS sorption was higher on hematite {001} (0.13 μM m^-2) than hematite {100} (0.1 μM m^-2). Electron transfer rate between hematite {001} and AQDS (19.6 s^-1) was higher than hematite {100} (18.2 s^-1). Tafel curves revealed that hematite {001} possesses lower resistance (3.5-2.4 Ω) than hematite {100} (4.1-2.9 Ω) with AQDS from 0 to 400 μM, indicating that hematite {001} is more favorable for electron transfer from cells or anthrahydroquinone-2,6,-disulfonate (AH₂QDS) to Fe oxide. In addition to the well-known electron shuttling role of AQDS, the higher adsorption sites and electrochemical activity of hematite {001} over {100} jointly contributed to the enhanced iron bioreduction. The findings provide a mechanistic understanding of the interactions between quinone and various facets of iron oxides.