Unveiling the role of hematite crystal facets: {001}-facet enhances vanadium(V) reduction via optimizing biofilm electroactivity and extracellular electron transfer

Semiconducting mineral facets, when utilized as anodes, influence the electron transfer and redox processes within microbial fuel cells (MFCs). However, the mechanisms of V(V) reduction via semiconductor facet-modified MFCs, particularly the interfacial mineral-microbe interactions and electron transfer pathways, remain unclear. This study investigated the V(V) reduction performance of MFC anodes modified with {001}, {100}, and {214} facets of hematite. Concurrently, the electron transfer pathways and microbial metabolic routes involved in V(V) reduction were explored. The results indicated that V(V) reduction was effectively promoted by facet-hematite-modified anodes. Notably, the {001} facet exhibited optimal V(V) reduction performance, with a reduction rate reaching 87.16%. Electrochemical analysis confirmed that the {001} facet possessed the lowest charge transfer impedance and optimal electrocatalytic activity, significantly enhancing extracellular electron transfer, as evidenced by NADH and ETSA levels, which were 2.2 times and 1.54 times higher than the control group, respectively. Furthermore, the {001} facet facilitated robust biofilm formation and stimulated extracellular polymeric substance (EPS) secretion. Transcriptomic analysis further revealed that the {001} facet specifically upregulated the expression of key functional genes, including those encoding cytochrome c, riboflavin, NADH, and nitrate/nitrite reductases. This upregulation accelerated electron transfer and significantly improved the bioreduction efficiency of V(V).This research offered novel insights into electron transfer mechanisms at the mineral-microbe interface and advanced the understanding of vanadium bioremediation, holding significant importance for developing highly efficient bioelectrochemical technologies for heavy metal remediation.